Quaternary Science Reviews 116 (2015) 72e94
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Quaternary Science Reviews
journal homepage: www.elsevier.com/locate/quascirev
2700 years of Mediterranean environmental change in central Italy:
a synthesis of sedimentary and cultural records to interpret past
impacts of climate on society
Scott A. Mensing a, *, Irene Tunno b, Leonardo Sagnotti c, Fabio Florindo c, Paula Noble d,
n-Carrasco c, Gabriele Cifani f,
Claire Archer d, Susan Zimmerman e, Francisco Javier Pavo
f
b
Susanna Passigli , Gianluca Piovesan
a
Department of Geography, University of Nevada, Reno, NV, USA
degli Studi della Tuscia, Viterbo, Italy
Dendrology Lab, DAFNE Universita
c
Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
d
Department of Geosciences, University of Nevada, Reno, NV, USA
e
Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, CA, USA
f
degli Studi di Roma Tor Vergata, Rome, Italy
Universita
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 October 2014
Received in revised form
21 March 2015
Accepted 23 March 2015
Available online
Abrupt climate change in the past is thought to have disrupted societies by accelerating environmental
degradation, potentially leading to cultural collapse. Linking climate change directly to societal disruption is challenging because socioeconomic factors also play a large role, with climate being secondary or
sometimes inconsequential. Combining paleolimnologic, historical, and archaeological methods provides
for a more secure basis for interpreting the past impacts of climate on society. We present pollen, nonpollen palynomorph, geochemical, paleomagnetic and sedimentary data from a high-resolution 2700 yr
lake sediment core from central Italy and compare these data with local historical documents and
archeological surveys to reconstruct a record of environmental change in relation to socioeconomic
history and climatic fluctuations. Here we document cases in which environmental change is strongly
linked to changes in local land management practices in the absence of clear climatic change, as well as
examples when climate change appears to have been a strong catalyst that resulted in significant
environmental change that impacted local communities. During the Imperial Roman period, despite a
long period of stable, mild climate, and a large urban population in nearby Rome, our site shows only
limited evidence for environmental degradation. Warm and mild climate during the Medieval Warm
period, on the other hand, led to widespread deforestation and erosion. The ability of the Romans to
utilize imported resources through an extensive trade network may have allowed for preservation of the
environment near the Roman capital, whereas during medieval time, the need to rely on local resources
led to environmental degradation. Cool wet climate during the Little Ice Age led to a breakdown in local
land use practices, widespread land abandonment and rapid reforestation. Our results present a highresolution regional case study that explores the effect of climate change on society for an underdocumented region of Europe.
© 2015 Elsevier Ltd. All rights reserved.
Keywords:
Central Italy
Mediterranean environments
Society and climate
Paleoenvironmental change
Pollen
Paleomagnetism
Geochemistry
Historical documents
Late Holocene
Roman Empire
1. Introduction
The extent to which past abrupt climate change has directly
resulted in societal disruption or cultural collapse, and the ability of
* Corresponding author.
E-mail address: smensing@unr.edu (S.A. Mensing).
http://dx.doi.org/10.1016/j.quascirev.2015.03.022
0277-3791/© 2015 Elsevier Ltd. All rights reserved.
societies to adapt to these changes is strongly debated (Berglund,
2003; Diamond, 2005; Munoz et al., 2010), but is potentially significant for modern communities facing future climate change
(Büntgen et al., 2011). Studies concerned with the link between
climate and human affairs have increasingly recognized the need to
examine societal change in parallel with climate change (Dearing
et al., 2008; Coombes et al., 2009; Munoz et al., 2010; McCormick
et al., 2012), although the tendency persists among physical
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
scientists to link cultural shifts directly to climate change
(O'Sullivan, 2008; Aimers, 2011). Detailed historical analyses based
on precisely dated documents have identified instances when
climate has led to significant societal disruption or ‘collapse’, but
these analyses also detail multiple examples in which socioeconomic factors played the larger role in environmental change, with
climate being secondary or inconsequential (Ladurie, 1971). For this
reason, it is critical that studies attempting to elucidate the impact
of climate on society closely couple paleoecologic methods with
historical and archaeological methods (Dearing et al., 2008;
O'Sullivan, 2008; Coombes et al., 2009; Harris, 2013).
The relationship between climate change and cultural response
can be addressed in areas where multi-proxy studies of cores from
lakes with very high sediment accumulation rates can be examined
within the context of a well-documented written history (Berglund,
2003). Such a history may provide insights into human adaptive
strategies that allowed societies to cope with past climate change
(Fraser, 2011). Several recent high-resolution syntheses have drawn
a link between climate stability and the expansion, and eventual
contraction, of the Roman Empire (Büntgen et al., 2011; McCormick
et al., 2012). These studies note that focused regional case studies
with highly resolved datasets are still needed to test the potential
effect of rapid climate change on human societies. Such datasets are
particularly needed in under-documented regions of the Roman
Empire, including southern Europe, and the regions near Rome.
In central Italy, archival materials are nearly continuously
available from ~700 CE (common era) in the records of the Farfa
Abbey (Leggio, 1995a) in northern Lazio, Central Italy, with some
written records extending back to the Roman period (De Santis and
Coarelli, 2009). These documents provide a written environmental
history that can be compared with physical paleoecologic reconstructions. Paleoecologic reconstructions for the last 3000 years
are still underrepresented in Italy (Roberts et al., 2004; Magri,
2007) with studies from the southern Alps and North Italy
(Kaltenrieder et al., 2010; Joannin et al., 2014), the northern and
central Apennines (e.g. Mercuri et al., 2002; Brown et al., 2013;
Branch and Marini, 2014), the Tiber Delta (Di Rita et al., 2010),
and southern Italy, Sicily and Sardinia (e.g. Russo Ermolli and di
Pasquale, 2002; Di Rita and Magri, 2009; Tinner et al., 2009; Di
Rita and Melis, 2013; Sadori et al., 2013). These studies record the
major changes in vegetation in relation to human activity during
this time period but present very different impacts depending on
sites and historical periods. In addition, the sampling resolution is
generally at the centennial or millennial scale and cannot be easily
compared with historical records. The last 3000 years are of
particular interest because they encompass several important climatic changes often associated with cultural change, including the
Roman Optimum (100 BCE e 200 CE; BCE e before common era),
the Medieval Warm Period (MWP), ~950 to 1250 CE, and the Little
Ice Age (LIA) ~1250 to 1850 CE, (Büntgen et al., 2011; Christiansen
and Ljungqvist, 2012; McCormick et al., 2012).
In this paper, we present multiple physical proxies (pollen, nonpollen palynomorphs, paleomagnetism, sedimentology, geochemistry and charcoal) from a small lake in the Rieti Basin, Central Italy,
to reconstruct a high-resolution record of environmental history
from the present through the pre-Roman period. The basin, located
approximately 80 km north of Rome, has a well-documented
archeological record from pre-Roman times (Coccia et al., 1992)
and historical documents from early Roman times (Coccia et al.,
1992; Leggio, 1995a). We compare our physical proxies with the
well-documented historical record of human activity and cultural
change, and with independent climate records to explore the link
between the timing of climate change, environmental change, and
historical events. This study complements previous high-resolution
regional syntheses from central and northern Europe (Ladurie,
73
1971; Büntgen et al., 2011; McCormick et al., 2012) by providing a
new site in southern Europe at the center of the Roman Empire. The
results contribute to our understanding of Mediterranean forest
dynamics and can be used to verify recent efforts to model the
history of deforestation in Europe (Kaplan et al., 2009).
2. Study area
Lago Lungo (369 m above mean sea level) is one of four remnant
lakes of ancient Lacus Velinus in the Rieti Basin (Fig. 1), an intermontane depression in the Central Apennines that locally reach an
elevation of 2217 m at Monti Reatini (Calderoni et al., 1994). The
Velino, Salto and Turano Rivers flow into the basin, which is then
drained by the Velino River, which plummets over a travertine sill
at Marmore Falls. Other sources of inflow into the basin are
numerous artesian springs that lie along the eastern edge of the
basin. Water level in the basin is controlled by the elevation of the
travertine sill (Calderoni et al., 1994). During prehistoric time,
travertine built up during warm periods, raising the sill and
expanding wetlands, and alternatively eroded during cold periods
draining the valley (Calderini et al., 1998; Soligo et al., 2002). Between ~6000 and 3000 yr BP a large shallow lake (Lacus Velinus)
filled the basin (Calderoni et al., 1994). Written documents suggest
that the Romans cut a channel through the travertine sill to drain
the land in ~270 BCE (Coccia et al., 1992). Since that time, water
level in the basin has been controlled periodically by maintaining
existing channels and cutting new channels (Lorenzetti, 1989).
Historical maps suggest that the size and shape of lakes, their
proximity to the Velino River, and the extent of wetlands in the
basin has changed through time. Today, Lago Lungo has a maximum
depth of up to 7 m with a surface area of 0.78 km2 and surface level
maintained at 369 m above sea level (Riccardi, 2006). Inflow is from
a network of ditches that drain surrounding wetlands, springs, and
farmland. Lago Lungo is protected within Riserva Naturale dei Laghi
Lungo e Ripasottile (Riccardi, 2006).
The geology of the region is characterized by recently uplifted
marine sediments. The Central Apennines are primarily composed
of Upper Triassic to Middle Miocene carbonates (Parotto and
Praturlon, 1975; Cosentino et al., 2010). Rieti is a seismically
active extensional basin within the Apennine thrust system and is
partially filled with Upper Pliocene and Holocene continental and
marine sediments (Cavinato and De Celles, 1999; Soligo et al.,
2002). Travertine outcrops are present across the basin, associated with past periods of warm wet climate. Seismic activity has
influenced the location and discharge of springs responsible for
depositing the travertines (Soligo et al., 2002). The largest spring in
the basin, Santa Susanna Spring, has a discharge of 4.1 m3 s 1 and is
located ~3 km northeast of Lago Lungo (Spadoni et al., 2010).
Modern vegetation is dominated by agriculture in the basin and
heavily managed forest on the surrounding slopes. Phragmites and
Salix species grow in a narrow (~15 m) band of protected land
within the reserve, while beyond the reserve border the basin floor
is nearly entirely devoted to agriculture (Casella et al., 2009). Forest
vegetation at lower elevations within the basin is characterized by
temperate deciduous forest (e.g. Carpinus betulus L., Fraxinus spp.,
Ulmus campestris Auct.) with an important submediterranean
component (Quercus pubescens Willd., Quercus cerris L.; Carpinus
orientalis Miller; Ostrya carpinifolia Scop.); in the foothills on steep/
shallow soils some patches of Mediterranean trees and shrubs
(Quercus ilex L., Phyllirea variabilis L., Pinus halepensis Miller) are
present while in the mountain belt (above 800e900 m) beech
(Fagus sylvatica L.) forests are common. Climatically the area is
within a transition zone between warm and cool temperate climates with a Mediterranean precipitation pattern characterized by
low precipitation during summer. Mean annual temperature varies
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S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Fig. 1. Rieti Basin study site map.
between 4 C in January and 21 C in July with annual precipitation
of 1117 mm (Fig. 4.29 in Leone, 2004). The general temperature and
precipitation regime is strongly controlled by the North Atlantic
Oscillation (NAO) with warm dry climate predominating during
positive phases of the NAO, and cool wet climate during negative
pez-Moreno
phases (Hurrell, 1995; Piovesan and Schirone, 2000; Lo
et al., 2011).
3. Materials and methods
3.1. Core recovery
Previous studies of Lago Lungo recovered cores on land near the
lakeshore using geologic drilling equipment and subsequently did
not recover the upper sediments containing the last few thousand
years (Calderoni et al., 1994). For this study, we worked on a floating
platform anchored near the center of the lake. Cores were collected
in 2009 and in 2012. Water depth at the core site was 4.2 m in 2009
and 4.4 m in 2012. Surface sediments were obtained using a clear
plastic tube fitted with a piston to recover the sedimentewater
interface (core LUN12-2C). The unconsolidated surface sediments
were stabilized with Zorbitrol (sodium polyacrylate absorbent
powder) while the core was still in an upright position. Overlapping
cores (LUN09 in 2009 and LUN12-1A, 1B, 2A, and 2B in 2012) were
recovered with a modified square-rod Livingstone hand operated
corer, extruded directly into rigid ABS (Acrylonitrile Butadiene
Styrene) plastic tubing, and capped for transport.
LUN09 spanned sediment depths from 54 to 605 cm and was
recovered in six sections. We used GPS to relocate the LUN09 core
site in 2012 for taking the next set of cores. Cores LUN12-1A and 1B
were taken within 2 m of each other and spanned from 10 to
870 cm depth (ten sections) and 60e1028 cm depth (twelve sections) respectively. Cores LUN12-2A, 2B and 2C were taken ~10 m
from the other set and within 2 m of each other. LUN12-2A spanned
from 60 to 1300 cm depth (fifteen sections) and LUN12-2B, the
longest core, from 20 to 1438 cm depth (nineteen sections). LUN122C, the surface core, contains the sedimentewater interface to
123 cm depth.
LUN-09 was described, analyzed and stored at the Tuscia University Paleoecology Laboratory in Viterbo, Italy. Cores LUN12-1A
and 1B were transported to the Tuscia University Paleoecology
Laboratory for storage and subsequent u-channel sampling for
paleomagnetic analyses. Cores LUN12-2A, 2B- and 1C were shipped
to the United States National Lacustrine Core Facility (LacCore) in
Minneapolis, Minnesota for initial core description, sampling for
pollen, charcoal, smear slide and LOI analysis, and permanent
storage.
3.2. Initial core description and analysis
Core LUN09 was split, photographed and the sediments
described in July, 2009. This core was used for pollen analysis of the
upper 5 m of core. Cores LUN12-2A, 2B and 2C were first logged
whole using a Geoteck Multisensor Core Logger to measure density,
acoustic wave velocity, electrical resistivity and loop-sensor magnetic susceptibility at 1-cm resolution. Cores were then split, the
surface cleaned, imaged with a digital line scanner at ~300 dpi, then
placed on a Geotek MSCL-XYZ core scanner and measured at 0.5cm resolution for magnetic susceptibility and color. Magnetic susceptibility data and core images were input into an electronic
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
standard core description sheet and the sheets annotated for
stratigraphy, sedimentology and correlation points between cores
using both the images and the freshly split cores. Smear slides,
taken every 20 cm and from selected strata, were used to aid in core
description and to identify the major sedimentologic components.
The observed sedimentologic features and magnetic susceptibility data were used to correlate cores LUN12 2A, 2B, and 2C, often
allowing for a visual match of individual suites of bands and layers
between cores (Figs. 2 and 3). Areas of core distortion, caused by
coring artifacts, and sections with no core recovery were identified,
and a continuous ‘master core,’ hereafter referred to as LUN12-2,
was constructed from the three cores, that spans a total sedimentary thickness of 14.4 m. Magnetic susceptibility was further used
to correlate between core LUN12-2 and LUN12-1A and 1B, and
LUN09, which were neither photographed nor logged in detail.
Samples (1.25 cm3) were taken every 10 cm (3e5 cm in sediment transition zones) from LUN12-2 for measuring percent total
organic matter (%organic) and percent carbonate (%CaCO3) using
the loss on ignition method protocols at LacCore based on Dean
(1974) and Heiri et al. (2001). Samples were weighed, dried at
100 C for 24 h, then combusted at 550 C for four hours followed
by combustion at 1000 C for two hours.
Core LUN12-2 was transported to the Large Lakes Laboratory in
Duluth, Minnesota for analysis using the ITRAX x-ray fluorescence
Fig. 2. Correlation of cores 2A, 2B, and 2C based distinctive sedimentologic features.
Livingston core sections are denoted for cores 2A and 2B. Shaded areas denote sections
used in composite core, pictured in Fig. 3. 1 ¼ oxidized band; 2 ¼ discontinuously
laminated dark silty marl; 3 ¼ varicolored banded clay, silt, and carbonate; 4 ¼ gray
clay; 5 ¼ organic-rich marl with calcite stringers.
75
(XRF) scanner (Cox Analytical Instruments) to provide elemental
geochemistry data. The LUN12-2 core was scanned at a resolution
of 0.5 cm throughout, except for the middle 7 sections (2B-5L
through 11L), which were scanned at a resolution of 0.2 cm to pick
up observed variations in sedimentary banding. The top section
(LUN12-2C) was also scanned at a 0.2 cm resolution. The scanner
was operated using a molybdenum source, 30 s dwell-time, a
voltage of 30 kV and an x-ray current of 30 mA to obtain peak areas
for elements SiePb. A principal component analysis using the rda
function in the vegan 2.0-6 package in R, version 2.1.5.2 (R
Development Core Team, 2012) was performed on the raw XRF
data output, on both the whole core and on individual sections as
an initial data analysis step to determine gross distribution patterns
and co-variance of elements. Time series plots for core LUN12-2
were then generated for a subset of elements determined to be of
interest as sedimentologic and lake chemistry proxies (Ti, Fe, Mn,
Ca, and Sr). Raw counts of the element subset were normalized by
centering and standardizing the data (raw data-mean of data/
standard deviation), allowing for the comparison of the minima,
maxima, and trends of major elements with very different ranges of
counts within the core.
3.3. Rock magnetism and paleomagnetism
Natural and artificial magnetizations were measured at room
temperature at the paleomagnetic laboratory of the Istituto
Nazionale di Geofisica e Vulcanologia (INGV) in Rome, on a narrowaccess (45 mm diameter) automated pass through ‘2G Enterprises’
DC 755 superconducting rock magnetometer (SRM), housed in a
Lodestar Magnetics shielded room. The cryogenic magnetometer is
equipped with in-line orthogonal alternating field (AF) demagnetization coils, with optional application of a single-axis direct current (DC) field for production of an anhysteretic remanent
magnetization (ARM). Rock magnetic and paleomagnetic properties were measured at 1-cm spacing on u-channel samples
collected from 4 distinct and partly overlapping cores (LUN09,
LUN12-1A, LUN12-1B and the lower 5.4 m of LUN12-2B).
To minimize sample dehydration and alteration, u-channel
samples were stored in a refrigerated room until they were processed. For each u-channel, we first measured both the low-field
magnetic susceptibility (k), using a Bartington magnetic susceptibility probe MS2C in-line with the rock magnetometer, and the
natural remanent magnetization (NRM). Then, all u-channels were
AF demagnetized in 10 steps (using peak fields of 5, 10, 15, 20, 30,
40, 50, 60, 80 and 100 milliTesla (mT), with remanence vectors
measured after each demagnetization step, in order to investigate
the stability of the NRM and to reveal possible secondary
overprints.
Finally, an ARM was imparted using a 0.05 mT direct current
(DC) bias field and an axial 100 mT peak AF, and translating the uchannel through the AF and dc coil system at a speed of 10 cm/s, the
lowest speed allowed by the software running the measurements.
The adopted procedure equals an AF decay rate of ca 67 mT/halfcycle and results in the highest ARM intensity achievable with the
employed instrumental setting and management software
(Sagnotti et al., 2003; Sagnotti, 2013). The ARM was then measured
and stepwise AF demagnetized using the procedure applied to the
NRM.
From the AF demagnetization data of both the NRM and the
ARM we computed the median destructive field (MDF), which is
defined as the value of the peak AF necessary to reduce the
remanence intensity to half of its initial value.
The raw magnetic moment data measured by the three
orthogonal SQUID sensors of the SRM system were automatically
corrected by compensating for the different shape and widths of
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S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Fig. 3. High resolution images of the Lago Lungo Master core (LUN 12-2). Individual cores sections used in the master are labelled. White boxes represent core sections with no
recovery. Running depth is a continuous measure (m) of the total core length.
the response function curves of the three SQUID pick-up coils
(Roberts, 2006). Moreover, we took particular care in avoiding
eventual disturbance effects that may be introduced during the
coring, cutting and sampling procedures and could result in
remanence deflections due to plastic deformation of the soft sediments. We also disregarded the paleomagnetic data for ~5 cm at
both ends of each u-channel to avoid disturbances linked to edge
effects.
3.4.
210
PB, 137CS, and
14
C AMS analysis
Continuous 1-cm3 samples were taken from the full length of
the surface core (LUN12-2C), freeze dried and sent to Flett Research
Ltd. for 210Pb and 137CS analysis. Plant macrofossils for 14C AMS
dating were not found during the initial core description, therefore
extensive efforts were made to obtain datable materials. To find
plant macrofossils and macroscopic charcoal, we sieved a total of
525 cm of core (90 samples, 5 from LUN09 and 85 from LUN12). For
LUN09 we subsampled 20-cm long sections of half the core
(~200 cm3 per sample), soaked the sediments in a 5% solution of
sodium metaphosphate for 12 h, and then sieved at 250 mm. We
followed the same process for LUN12 but decreased the sample size
to 5-cm long sections (~50 cm3). Two microscopic charcoal samples
were picked by hand from samples that appeared to be richer in
charcoal. We concentrated pollen from a 20 cm section of core for
14
C AMS dating, following Newnham et al. (2007) then purified the
concentrate using flow cytometry (Tennant et al., 2013).
One macrofossil (LTL 4680A) was submitted for AMS analysis at
CEDAD at the University of Salento, Brindisi, Italy; all others were
submitted to the Center for Accelerator Mass Spectrometry (CAMS)
at Lawrence Livermore National Laboratory, USA. All macrofossils
were chemically pretreated with the standard acid-base-acid (ABA)
treatment before being combusted under vacuum and graphitized
according to standard procedures (Vogel et al., 1984).
To test for the magnitude of a potential aquatic reservoir effect, a
Phragmites plant growing in the lake was uprooted and pieces of
the roots, stem, and leaves were rinsed in deionized water before
transport to LLNL for radiocarbon analysis. All samples were pretreated, graphitized, and measured according to the same protocols
as the fossil samples; dates on the roots and leaves were replicated.
3.5. Tephra analysis
Italy has a history of active volcanic eruptions, although most
are well to the south of our site and no tephras from the last three
millennia have been confirmed for our region (Giaccio et al., 2009;
Sulpizio et al., 2014). Nevertheless, to test the potential for tephrochronology, twelve 10e40 cm thick samples were collected from
LUN12-1B at age intervals, based on the paleomagnetic secular
variation age model, discussed below, corresponding to periods of
eruptions from Vesuvius, Phlegrean Fields, Ischia Island, Vulcano
and the Lipari Islands. Eight samples were prepared on alloy stubs
for morphological and textural observations and qualitative
chemical analysis of components using a Zeiss EVO MA 10 scanning
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
electron microscope (SEM) equipped with an Oxford ISIS microanalysis system at INGV in Pisa. No tephra were recovered and this
line of investigation was not pursued further.
3.6. Pollen and charcoal analysis
A total of one hundred samples (0.625 cc volume) were processed for pollen analysis using acid digestion procedures (Faegri
and Iversen, 1985); two samples from the surface core (LUN122C), forty from LUN09 (40e605 cm depth), and fifty-eight from
LUN12-2B (460e1438 cm depth). A known quantity of an exotic
tracer (Lycopodium) was added to each sample during processing
(Stockmarr, 1971) and counted along with pollen for calculating
pollen concentration. Pollen counts for LUN09 (6 m in length) were
completed before recovering LUN12-2B (14.4 m in length), therefore we counted duplicate samples from each core for the overlapping section from 460 to 605 cm depth. Duplicate counts were
similar, and in the overlapping section we used only the counts
from LUN12-2B, which were done at a later date, for a total of
ninety-one samples in the final pollen diagram. A minimum of 400
terrestrial pollen grains were counted per sample (mean ¼ 441)
except for samples with very low concentration rates (n ¼ 23), in
which case a sum of 200e300 grains were counted (mean ¼ 222).
Pollen count totals excluded aquatic pollen types, such as Typha,
Nuphar and Potamogeton, algae, and non-pollen palynomorphs.
Pollen and non-pollen palynomorphs were identified using
reference material in the Tuscia University Paleoecology Lab, published keys and manuscripts (Punt and Malotaux, 1984; Punt et al.,
1991; Chester and Raine, 2001; Blackmore et al., 2003; Beug, 2004;
van Geel and Aptroot, 2006; Cugny et al., 2010; van Geel et al.,
2011). TC pollen (Taxaceae and Cupressaceae) was assumed to be
Juniperus, a native taxa. Species of Quercus were identified as either
Q. pubescens e robur L. type, or Q. cerris L. (deciduous) or Q. ilex L.
(evergreen) following Van Benthem et al. (1984). For plotting purposes Quercus is represented as deciduous or evergreen (Q. ilex
type). Members of the family Poaceae were identified as cereals if
grains were >37 mm, pore diameter was >2.7 mm and annulus
€hler and Lange (1979). Pollen
thickness was >2.0 mm, following Ko
percentages were calculated from the sum of terrestrial pollen,
excluding indeterminate grains and Cannabis type (which was
retted in the lake at certain periods). Accumulation rates
(grains cm 2 yr 1) were calculated by dividing concentration
(grains cm 3) by the number of years per sample (yr cm 1) and
normalizing by number of Lycopodium counted. Aquatic taxa, algae,
and non-pollen palynomorphs are presented as accumulation rates,
since they appear intermittently in the record and total quantity
represents actual abundance better than does percentage. Zonation
was interpreted from a constrained single-link dendrogram created
using CONISS in the PolPal plotting program (Nalepka and Walanus,
2003). Data input included the fifty-three terrestrial taxa with at
least one strata of >1% of the pollen sum, excluding Cannabis type
and indeterminate grains.
Charcoal particles were counted on pollen slides in two size
fractions, 50e125 um and >125 um elongest dimension (Sadori
and Guardini, 2007). All fragments that met the criteria of being
black and having a visible cellular structure were counted.
3.7. Archaeological, historical and archival documents
The bulk of the archaeological documentation is represented by
two surveys carried out in the area in the 1980s by the University of
Perugia and in the 1990s by the British School at Rome (Coccia et al.,
1992, 1995).
The early medieval phase is well documented by one of the most
important collections of Europe: the archive of the Farfa Abbey,
77
which contains a body of documents concerning the history of the
territory between the 8th and the 12th century AD. The late medieval phase (13the15th century) is well documented through the
archive of the Comune of Rieti and that of Rieti cathedral
(Caciorgna, 1998, 2000; Leggio, 1998). The history from 16th century onward has been analyzed in detail by means of additional
, 1939; Lorenzetti, 1989) and map collections in the
archive (Dupre
Archivio di Stato in Rome and Rieti (Lorenzetti, 1990, 1994, 2009). In
correlating the sedimentary evidence with historical evidence we
have provided names and time periods following the system
developed by Coccia et al. (1995) based on changes in archeologic
ceramics in the Rieti Basin.
4. Results and discussion
4.1. Chronology
Developing a core chronology based largely on 14C dating
proved challenging given that the carbonate bedrock introduces
the potential for significant old-carbon effects and plant macrofossils were hard to find and not well-distributed throughout the
core. We therefore developed two independent age models, one
Fig. 4. Plot of all 14C AMS radiocarbon and 210Pb dates (Table 2) and PSV age model and
cultigen dates (Table 1) used in this study. Black line represents the age model derived
from PSV tie points including rock magnetic variables (RPI, inclination and declination)
and cultigens (Cannabis, Zea mays and forest transition) described in Table 1. Green line
represents the age model derived from 14C on leaf fragments from LUN12 and 210Pb
basal date (Table 2). PSV uncertainties represent the 65% and 95% of confidence levels
n-Carrasco et al., 2009). 14C
according to the SCHA.DIF.3k model predictions (Pavo
uncertainties represent the 2 sigma range of the mean probability using Calib 7.1
(Reimer et al., 2013). (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
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S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Table 1
Tie points used in the PSV age model, including rock magnetic variables (RPI, inclination and declination) and cultigens (Cannabis, Zea mays, and forest transitions). Text in bold
n-Carrasco et al.,
represent PSV features indicated with arrows in Fig. 7. Error on PSV ages is the 95% confidence interval according to the SCHA.DIF.3k model predictions (Pavo
2009).
Run depth (cm)
Age BP (present ¼ 2000)
Age CE/BCE
0
110
134
160
236
335
366
531
838
913
986
1074
1260
1323
1458
0
170
250
340
450
610
680
910
1180
1280
1400
1700
2300
2500
2700
2000
1830
1750
1660
1550
1390
1320
1190
820
720
600
300
300
500
700
based on historical documentation of biostratigraphic markers
along with the information provided by the paleomagnetic secular
variation (PSV), and another based on radiometric analyses (Fig. 4).
4.1.1. Biostratigraphic markers
Historical documentation of specific biotic changes within the
basin (biostratigraphic markers we refer to as cultigens) were
compared with the pollen reconstruction to provide estimated
dates in the upper section of the core. Zea mays (corn) was introduced into Europe only after the first voyage of Columbus in 1492
CE. The first historical documents noting cultivation of Z. mays in
Italy are from 1605 CE and most documents indicate that cultivation was initially sparse, introduced into central Italy after 1700
(Messedaglia, 1927). The first documented planting of Z. mays in the
Rieti Basin is given as between 1740 and 1760 CE (De Felice, 1965;
Covino, 1995) and we attribute a date of 1750 CE to the core
depth (134 cm) with the first appearance of Zea pollen (Table 1).
Cannabis cultivation in the Rieti Basin for rope production
expanded in the mid-17th century, peaked in the late 18th century,
and eventually declined by the mid-19th century (Galli, 1840;
Zuccagni-Orlandini, 1843; Nigrisoli, 1857; Celetti, 2007). The peak
in Cannabis-type pollen (see Results Fig. 12) is coincident with the
first appearance of Zea pollen. We designated a date of 1660 CE to
the beginning of the rise in Cannabis-type pollen (160 cm), and a
date of 1830 CE to the end (110 cm), a time when alternative fibers
such as linen and cotton began replacing Cannabis across Europe
(Lavrieux et al, 2013; see also Rull and Vegas-Vilarrúbia, 2014 for
the rapid decline of hemp).
Reforestation associated with land abandonment following the
Black Plague in 1349 CE depth has been documented repeatedly
throughout Europe (van Hoof et al., 2006; Yeloff and van Geel,
€ ld et al., 2010; Fraser, 2011). Written documents from
2007; Sko
Rieti described a similar pattern of land abandonment and reforestation towards the end of the 14th century (Leggio, 1995b; Naspi,
2010) and we gave a date of 1390 CE to the major transition from a
deforested to forested landscape evident in the pollen record about
335 cm depth.
4.1.2. Paleomagnetic analysis
The measured rock magnetic properties (k, NRM, ARM, MDF)
were used to correlate cores LUN12 1A, 1B, 2A, 2B, 2C and LUN09
between overlapping sections and enabled us to build a composite
magnetic section for the lake (Fig. 5). We constructed an age model
based on the rock magnetic data and biostratigraphic cultigens
described above.
Error PSV data 95% (ca 2s)
61
49
71.5
78
119
144.5
145.5
203.5
105.5
137.5
Notes
Extrapolated
Cultigen (end Cannabis peak)
Cultigen (Zea mays first appearance)
Cultigen (beginning Cannabis peak)
Inclination, Declination
Cultigen (transition from deforested to forested)
RPI (weak evidence)
RPI (weak evidence)
Inclination, RPI
RPI
Inclination, RPI
RPI (weak evidence)
RPI
RPI (weak evidence)
Inclination, Declination
The NRM demagnetization data allowed the unambiguous
identification of a Characteristic Remanent Magnetization (ChRM)
throughout all the sequence. The data indicate that the whole
sequence is characterized by an almost single-component NRM,
unambiguously isolated after removal of a weak viscous overprint
in AF steps of 5e10 mT (Fig. 6). The orientation of the ChRM was
defined by principal component analysis (Kirschvink, 1980) by
fitting a line between the 10 and 50 mT AF demagnetization steps.
The maximum angular deviation for each determined ChRM direction is 1 on average, with a full range of variation between 0.1
and 5 . The MDF of the NRM typically ranges between 15 and 40 mT
indicating that magnetite is the main magnetic carrier in the
sequence.
The ChRM declination of individual u-channels was arbitrarily
rotated to align trends between adjacent sections. The stratigraphic
trends in the ChRM declination and inclination are characterized by
large amplitudes and high-frequency oscillations around the expected values for a geocentric axial dipole (GAD) field at the site.
These wide oscillations and amplitudes are however unexpected,
considering the recent models of paleosecular variation (PSV) of the
ngeomagnetic field over the last millennia (Gallet et al., 2002; Pavo
Carrasco et al., 2009; Korte et al., 2011). In any case, these variations
are consistent between the analyzed cores and the reconstructed
ChRM directional trends are replicated in the overlapping sections
of the distinct cores (Fig. 7).
To estimate relative paleointensity (RPI) variation, we normalized the NRM by k and by the ARM intensity. The NRM/ARM ratio
was computed also from the values measured after the 20 mT and
40 mT AF steps. All the normalization methods resulted in a similar
pattern and therefore support a general coherency between the
different normalization procedures and indicate a reliable reconstruction of the RPI trend. After removal of data affected by edge
effects at the u-channel breaks, lithological boundaries and magnetic susceptibility spikes, the broadly smoothed paleomagnetic
trends can be correlated to the available PSV curves and models for
Europe: the directional (declination and inclination) archeomagnetic PSV curve (Gallet et al., 2002) built with a high quality
archeomagnetic dataset from France, and the full geomagnetic field
vector (declination, inclination and intensity) provided by the
n-Carrasco et al. (2009)
archeomagnetic SCHA.DIF.3k model of Pavo
(Fig. 7). This correlation enabled us to point out various depth-age
tie-points from prominent PSV features.
In order to estimate the temporal error of the paleomagnetic tiepoints we have calculated the temporal resolution of the regional
model SCHA.DIF.3k at the geographic coordinates of Lago Lungo.
For each tie-point, the three geomagnetic field elements, i.e.
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
79
Fig. 5. Stratigraphic trends of k, NRM and ARM of the various cores, correlated to a common depth.
declination, inclination, and intensity, are defined by a temporal
Probability Density Function (PDF). The PDF depends on the value
of the geomagnetic field element at the corresponding time and its
uncertainty (the a95 in the case of the directional elements and the
intensity standard deviation, sF, for the intensities). The combination of the three PDFs for each geomagnetic element provides a
final PDF which area allows us to calculate the minimum and
maximum time for each tie-point. Then, the temporal resolution of
the regional model is given by the difference of this maximum and
minimum. Table 1 contains the paleomagnetic tie-points used in
this study with the geomagnetic field elements and their uncertainties, at 95% confidence levels, according to the SCHA.DIF.3k
n-Carrasco et al., 2009).
model predictions (Pavo
4.1.3. 210PB, 137CS, and 14C AMS analysis
CS-137 activity was significantly above background for the core
interval 24e41 cm with maximum activity at 28e29 cm depth,
assumed to be 1963 CE. The CRS model of 210Pb activity indicated an
age of 1954 CE at 33.5 cm depth, and it was concluded that the CRS
model provided a reasonable estimates of age in this core. The 210Pb
chronology produced a date of 1905 CE at 50.5 cm depth.
Fifteen radiocarbon dates were obtained from twelve depths in
the LUN09 and LUN12-1B cores (Table 2 and Fig. 4). Sieving yielded
six plant macrofossils and two macroscopic charcoal samples; all
remaining plant macrofossils and microscopic charcoal were found
during the sub-sampling process. Sorting of pollen by flow
cytometry yielded 1.5 million pollen grains which were divided
into two samples (of 900,000 and 600,000 pollen grain) to obtain
replicate dates for the interval 172e202 cm in LUN09. The same
interval yielded a sample of leaf fragments large enough to produce
replicate radiocarbon dates. The leaf replicates produced essentially
identical radiocarbon ages, but were significantly younger than the
pollen replicates, by ~400 years. The pollen replicates are likely
older because they integrate grains from the whole 30 cm sediment
sample, whereas the leaves may represent a single depth of
younger age.
The radiocarbon samples generally fit into two categories, based
on their age and depth in the core. Between 1000 and 260 cm four
samples have calibrated radiocarbon ages of ~2800 years cal yr BP,
with a fifth (343 cm) dating to 3500 cal yr BP. Because of the similarity in age, despite a wide stratigraphic range, and the variety of
materials (Table 2), it seems likely that these samples represent the
occasional tapping of some remnant deposit formed at or before
2800 yr BP.
The second group of samples (n ¼ 10) cluster between 266 and
159 cm, and produce radiocarbon ages ranging from 1800 to
780 cal yr BP. This second group also represents a wide range of
sample types, and may be the result of a period of widespread and
active erosion, caused by wetter overall climate or more intensive
human disturbance of the landscape, or both. The two groups of
dates overlap at ~260 cm depth.
We considered the relatively fragile uncharred leaf macrofossil
14
C dates (Table 2) the most reliable upon which to develop a
et al., 2001). Although we were
radiometric chronology (Hatte
unable to identify leaf fragments to species, all appeared to be
terrestrial. Macrofossils from core LUN-12 were considered more
reliable than those from LUN-09 because they were recovered from
5-cm thick sections rather than 20 cm-thick sections. Since the
sections from each core overlapped stratigraphically, we used the
14
C dates from leaf macrofossils in LUN-12 (Table 2, samples with
80
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Fig. 6. Representative demagnetization diagrams analyzed with the DAIE workbook (Sagnotti, 2013). For the vector component diagrams, black (white) circles indicate projection
on the horizontal (vertical) plane. When demagnetization steps are selected for PCA, the corresponding symbols turn to red (for horizontal projection) and to light blue (for vertical
projections). The stereoplots are equal-area projections, with solid symbols representing points on the lower hemisphere. The plots showing the decay of the NRM intensity as a
function of the demagnetization steps are shown on the right side of each equal-area projection.
center depths of 166, 193.5, 213.5, 238.5, 268.5, and 998.5 cm) in
addition to the 210Pb date (from 50.5 cm) to build an alternative age
model.
4.1.4. Age model selection
To directly compare the two age models, we replotted the
LUN-12 PSV data using the radiometric dates as tie points (Fig. 8),
and compared this fit with the available PSV curves and models
n-Carrasco et al., 2009).
for Europe (Gallet et al., 2002; Pavo
Comparison of the two age models shows that the 14C-based age
model (Fig. 8) produces a poor fit between the LUN-12 PSV data
and the PSV curves and models for Europe, especially when
compared with the age model based on biostratigraphic markers
and PSV tie points (Fig. 7). Note that each age model spans 3000
years, however in the 14C-based model 3000 yr BP is at 10 m
depth and in the PSV model this is at 14.4 m depth. The 14C-based
age model also produces ageedepth relationships that are
inconsistent with the written history. For example, the 14C based
age model gives a date of 1380 CE for the depth of 134 cm, the
first occurrence of Z. mays pollen, a physical impossibility given
the introduction history of that crop. The 14C-based age model
also results in dramatic changes in sedimentation rates at 268 cm
depth from 6.92 to 0.96 mm yr 1. Although this is physically
possible, there is no indication in the appearance of the sediments
(Fig. 3), or the geochemistry (Fig. 10) to support such a change at
this depth. An organic rich interval occurs between 180 and
250 cm depth. The nature of the sediments, the magnetic properties and the geochemistry of this interval strongly indicate that
it was deposited during a period of dramatically reduced
terrigenous input in the basin. In the PSV based age model (Fig. 7)
this interval would span about one century around 1530e1650 CE,
a period of intense cold when historical maps indicate a very wide
lake covering most of the basin. Conversely, in the 14C based
model (Fig. 8) this stratigraphic interval would correspond to
about three centuries in the early medieval time (600e900 CE), a
warm period for which historical sources indicate widespread
forest cutting and therefore a greatly increased terrigenous input
in the basin. Down core, further issues in interpreting the data
emerge, including deforestation and draining of the basin by 400
BCE, more than a century before archaeological and written records suggest any Roman impacts.
Given the problems associated with the 14C-based age model,
we conclude that the PSV age model produces the most accurate
chronology. In the PSV model, all three paleomagnetic measurements (inclination, declination and intensity) can be tied to the
European PSV model through the full length of the core (Fig. 7),
sedimentation rates do not change abruptly (Fig. 4), and the pollen
record is consistent with known history. In addition, the 210Pb date,
although not used to create the model, was consistent with the
model. In contrast, most of the 14C ages fall within only one meter of
the core. The clustering of macrofossils argues for the potential that
macrofossils were transported to the lake irregularly, perhaps
during a wet phase through flooding, erosion and redeposition of
old materials. We do not have a complete explanation for the unusual 14C dates, but radiocarbon dating of the different parts of the
modern Phragmites shows that unidentified plant material that is
from an aquatic plant might be 500 years too old (or more)
(Table 2). Terrestrial plants that can grow in standing water (e.g.
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
81
Fig. 7. PSV trends for the measured cores, plotted as a function of the common depth and age. Age was estimated by correlation with PSV reference curves and models (Arche n-Carrasco et al., 2009). Prominent PSV features (inclination, declination and RPI shown in bold in Table 1) used
omagnetic data from France, Gallet et al., 2002; scha.dif.3k of Pavo
for depth vs age correlation and cultigens (significant changes in forest phase, and appearance of Zea mays and Cannabis type) from the pollen data are marked by arrows.
et al., 2001), and
Salix) generally produce reliable 14C dates (Hatte
several of the dated samples were identifiably terrestrial, suggesting this is only a partial explanation. We intend to further explore
the complexities of 14C production and uptake within the study
area.
4.2. Geochemical proxies
Several elements (Ca, Sr, Ti, Fe, Mn, and S) serve as proxies for
siliclastic input, and authigenic or endogenic mineral fractions. The
relationship of these elements can be seen in biplots of Principal
Components 1 and 2 (Fig. 9), where the eigenvectors (red arrows) of
the elements are superimposed over the data points, and 3 eigenvector trajectories (numbered 1, 2, and 3) are interpreted to have
sedimentologic significance. The Medieval Period (MP) and Little
Ice Age (LIA) intervals are plotted separately to show changes in
elemental behavior between these two intervals (Fig. 9a, b). Ca is
representative of the calcium carbonate (CaCO3) component of the
sediments, indicated by the good correlation between the Ca XRF
and percent CaCO3 derived from LOI (Fig. 10), and shows a distinct
separate trajectory on the PCA plots (Fig. 9). Sr can co-precipitate
with Ca as SrCO3 when the lake waters are saturated with CO3
(Haenssler et al., 2013), seen in the profile when Sr and Ca track
together. Sr can also behave conservatively as a detrital element,
tracking closely with Ti (Kylander et al., 2011). Ti is used in this
study as a proxy for siliclastic detrital input into the lake (Haberzettl
et al., 2008), controlled by erosion, weathering, and runoff within
the catchment. Ti is representative of other conservative clastic
elements such as K, Rb, and Zr that have near-identical profiles
throughout the core, and are seen to have near identical eigenvectors with Ti (Fig. 9). Fe, while at times also behaving as a detrital
element (Fig. 9b), is also influenced by redox processes and subject
to remobilization at the sedimentewater interface (Croudace et al.,
2006). Mn is also influenced by redox processes, forming highly
insoluble oxides in oxygenated conditions (Kylander et al., 2011)
and is used here as an indication of changes in redox behavior of the
upper few cm of the sediment. Mn shows a distinct trajectory in the
PCA biplots, where Fe follows the behavior of Mn most closely in
the MP (Fig. 9a). Sulfur shows an interesting profile and has been
used as an indicator of evaporative balance and lake level changes,
as it precipitates in chemically concentrated lake waters (Haenssler
et al., 2013).
4.3. Core stratigraphy
Core stratigraphy is delineated by gross sedimentologic characteristics that are supplemented with petrographic observations,
and time series curves of k and geochemistry. The sequence is
subdivided into four stratigraphic intervals that are assigned names
based on their chronostratigraphic significance. The sedimentology
of these intervals is described below.
4.3.1. Archaic through Early Medieval interval: 1438e800 cm, Age:
700 BCEe870 CE
This interval represents a number of historical periods (Coccia
et al., 1995); including the Archaic (700e500 BCE), pre-Roman
(500e300 BCE), Roman (300 BCEe400 CE), Late Antique
(400e600 CE), and Early Medieval (600e800 CE) periods.
82
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Fig. 8. PSV trends for core LUN-12-1A and 1B, plotted as a function of the 210PB and 14C AMS dates. In relation to the PSV reference curves and models (Archeomagnetic data from
n-Carrasco et al., 2009).
France, Gallet et al., 2002; scha.dif.3k of Pavo
Table 2
Macrofossil 14C dates for cores LUN09 and LUN12 and modern Phragmites plant. MAP is the median age probability. Min and max represent the 2 sigma error. Difference is the
age difference between the PSV age model and 14C age model graphed in Fig. 4. Dates marked with* are those used in the 14C age model and indicated with arrows in Fig. 8.
Core
Depth (cm)
Lab ID
Material
14
LUN12-1C
LUN-09-1
LUN-09-1
LUN12-1C
LUN12-1C
LUN-09-1
LUN-09-1
LUN-09-1
LUN12-1C
LUN12-1B
LUN-09-1
LUN12-1B
LUN-09-1
LUN12-1B
LUN-09-1
161e171
172e202
172e202
191e196
211e216
172e202
172e202
158.5e159.5
236e241
266e271
260e261
996e1001
586e587
512e517
343e344
162752
152975
152973
162753
162754
155264
155263
LTL 4680A
162755
162767
152974
162757
152103
162756
152102
Modern phragmites
Leaf fragment
Leaf fragments
Leaf fragments
Leaf fragments
Leaf fragments
Sorted pollen
Sorted pollen
Plant macro
Bark
Leaf fragments
Seed
Leaf fragments
Charcoal
Seed
Charcoal
840
930
960
1145
1300
1255
1445
1343
1600
1845
2680
2745
2730
2790
3290
14
C age (yr BP)
162760
162758
163123
162759
Leaf
Root
Root
Stem
>Modern
>Modern
>Modern
540
163124
Stem
270
NH atmosphere
in 2013, >40 deg N
C age
All measured at CAMS-LLNL, except LTL 4680A, measured at CEDAD.
% all d13C values assumed to be 25 per mil, as per Stuiver and Polach (1977).
±
mg C
min
(cal yr BP)
MAP
(cal yr BP)
Max
(cal yr BP)
MAP year CE
Difference
cal 14C-PSV
100
90
60
40
100
30
40
50
35
30
35
35
130
100
100
±
0.036
0.275
0.03
0.065
0.04
mg C
777*
844
859
1054*
1208*
1211
1340
1271
1476
1780*
2785
2833*
2861
2920
3530
±
543
573
588
771
889
940
1069
1050
1113
1363
2382
1108
1874
2062
2979
30
30
1.031
0.9668
1.057
0.0034
939
1048
965
1171
1381
1277
1400
1345
1557
1865
2849
2925
3215
3207
3826
Cal yr BP
(2-sig range)
5
5
5
515e560
598e632
283e433
0.0039
1175
1105
1090
895
740
740
610
680
475
170
835
885
910
970
1580
year CE
0.647
0.610
0.945
0.836
567
680
737
967
981
1085
1294
1174
1406
1712
2748
2763
2471
2744
3274
Fraction
modern
1.0158
1.0209
1.0238
0.9350
0.138
0.039
0.31
0.19
0.187
0.616
0.0038
0.0039
0.0039
0.0033
1955
1955
1955
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
83
Fig. 9. Principal components analysis biplots for core 12LUN-2 showing variations in elemental composition from XRF data: a) Medieval interval and b) Little Ice Age interval.
Samples are plotted as open circles and eigenvectors for elements in red. Axis 1 is largely related to carbonate ( values) versus siliciclastic (þvalues) component. 1) carbonate rich
eigenvectors; 2) siliciclastic-rich eigenvectors; 3) redox eigenvectors. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of
this article.)
Sedimentologically, the interval consists of a dark, discontinuously
laminated, silty to clayey marl. The color is dark gray to black and
fades to an olive color within hours of being exposed to air, indicating the presence of unstable monosulfides, or other redoxsensitive minerals in a reduced state. Small (<1 mm) black
streaks in the core are aggregates of sub-micron-sized opaque black
minerals within a clay matrix. Microscopic examination shows that
the carbonate phase is significant (50%) in the form of calcite
rhombohedrons (ranging from 2 to 20 mm), detrital carbonate
allochems (<5 mm), Phacotus algal grains (5e10 mm), and rare
fragments of Charophyte algae (>10 mm). The silt fraction is largely
quartzofeldspathic, subangular, and occurs throughout, becoming
an increasingly larger component towards the top of this interval.
There is a diatom component (estimated at <10%) consisting predominantly of cyclotelloid phytoplankton with smaller amounts of
araphid periphyton.
Some trends are observed in the lower and upper portions of
this interval. At the base, the carbonate component is highest in the
core and shows a gradual decline until 1250 cm (~300 BCE). This is
indicated in both a decrease in Ca counts and %CaCO3 determined
Fig. 10. Geochemical and sedimentological parameters, including Loss on Ignition data (LOI), magnetic susceptibility, selected elemental data from XRF (reported in kilacounts per
second). Sediment accumulation rate was calculated from the age model. Stratigraphic intervals discussed in text are abbreviated on the left; Modern Interval (MI), Little Ice Age
(LIA), Medieval Period (MP), Transitional Zone (TR) between MP and RE, and Roman Era and Migration Period (RE). Boundaries of pollen zones (dashed lines) listed on right are also
discussed in the text.
84
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Fig. 11. Selected pollen taxa of trees, vines and shrubs, and total pollen accumulation rate. Unfilled lines represent 5X exaggeration.
by LOI, with a proportional increase in siliclastic components, as
seen in the counts of Ti and Fe (Fig. 10). The k has a baseline of
~10 E 5 SI, at the bottom of the core, then increases to ~20 5 sl, at
1150 cm reciprocating the decreased carbonate fraction. Sediment
accumulation rates decrease with the drop in carbonate from
~7 mm yr 1 to the lowest rate in the core (~3 mm yr 1). The top
~1 m of this interval, during the Early Medieval Period
(875e800 cm; ~800e900 CE), shows some interesting sedimentological and geochemical features, although the distinction from
the sediment below is not readily seen macroscopically in the core
photos (Fig. 3). The k signal shows large, frequent peaks above
100 5 Sl (Fig. 10), sediment accumulation rate rapidly increases to
~12 mm yr 1 and there is a brief increase in carbonate content
relative to siliciclastics. The uppermost ~45 cm, above 815 cm (870
CE), shows a large elemental shift commensurate with a decrease in
organic matter and carbonate content. Diatoms are absent above
815 cm.
4.3.2. Medieval interval: 800e335 cm, Age: 870e1390 CE
This interval consists of gray thin bedded clay and siltyeclay
bands 1e30 mm thick, intercalated with varicolored reddishbrown, black, and buff-colored bands 2e10 mm thick. The
reddish-brown to black layers appear to be rich in Fe and Mn, based
on alignment of the core photos to the scanning XRF signal (Figs. 3
and 10). Fe and Mn show a close correspondence in the MP and
have a similar eigenvector trajectory (Fig. 9a). The buff layers are
2e12 mm thick carbonate-rich bands that locally are hard and
concretionary. Fine silty sand bands, 5e20 mm thick are
interspersed throughout this interval, and contain as much as 80%
quartzo-feldspathic grains. The carbonate fraction consists of small
rhombohedrons, (2e5 mm), small detrital allochems (2e5 mm),
Phacodus fragments (5e10 mm), and Charophyte fragments
(10e80 mm). Sediment accumulation rates are high, a result of
increased siliciclastic input, with correspondingly lower organic
matter and carbonate fractions than the preceding interval. Diatoms are absent from this entire interval, with the exception of
very rare fragmented or corroded frustules. The trends of the major
elements, which shift dramatically at a core depth of 815 cm, persist
throughout this interval. The top of this interval is marked by a very
large k peak not seen in the elemental data and a drop in sediment
accumulation rate (Fig. 10).
4.3.3. Early Modern e Modern: 335e140 cm, Age: 1390e1740 CE
At a depth of 335 cm, the sedimentology of the shifts markedly.
Siliciclastic content declines rapidly and then becomes variable,
dominated by organic-rich calcareous material containing
gastropod fragments and diatoms. Much of the organic matter
appears to be aquatic in origin. Within this interval are two light
yellowish zones rich in thin carbonate stringers and lenticular
concretions. Petrographically, the carbonate is largely dendritic and
ascicular, and of unknown genesis. A subordinate fraction of the
carbonate is definitively algal, composed of Charophyte and Phacodus grains. Chemically, counts of siliciclastic elements (i.e. Ti) in
this interval are the lowest in the core, and Ca and Sr have several
maxima (Fig. 10). Mn and Fe are decoupled throughout this interval,
and large peaks in S are observed for the first time, concurrent with
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
85
Fig. 12. Selected pollen taxa of herbs, crop plants and indeterminate pollen. Unfilled lines represent 5X exaggeration.
none of the other elements. The organic matter content is the
highest throughout the core, following trends in both Ca and Sr.
4.3.4. Late modern to Contemporary interval 0e140 cm, Age:
1740e2000
This interval is composed of mottled and homogeneous to
discontinuously laminated grayeblack marl. The gray color appears
to be related to carbonate content, with the lighter bands showing a
higher percentage of carbonate grains. Diatoms are common as is
aquatic organic matter. The carbonate fraction is more heterogeneous than lower intervals, and is composed of a mix of calcite
rhombohedra, detrital allochems, Phacodus, and subordinate
amounts of dendritic grains. There is a clay-sized siliclastic
component, containing small amounts of fine (2e5 mm) silt grains.
4.4. Pollen, non-pollen palynomorphs and charcoal
We identified ninety different pollen types, nine non-pollen
palynomorphs and eleven algae types. Pollen taxa with percentages consistently >1% are presented for trees (Fig. 11) and herbs
(Fig. 12) and for the most abundant aquatic pollen, algae, and nonpollen palynomorphs (Fig. 13). Dominant taxa and percentages are
summarized in Table 3.
Five pollen zones were interpreted from the dendrogram. Zone
1 (1438e1145 cm; 700 BCE to 1 CE) includes the Archaic, preRoman and Roman republican periods (Coccia et al., 1992). Zone 2
has been divided into two subzones; Zone 2A (2A, 1145e970 cm; 1
CE to 600 CE) corresponds to the Roman Imperial period through
Late Antique period, and Zone 2B (970e800 cm; 600 to 870 CE)
corresponds to the Early Medieval period. Zone 3 (800e335 cm;
870 to 1390 CE), corresponds to Medieval through Late Medieval
time, Zone 4 (335e140 cm 1390 to 1730 CE) corresponds to the
Early Modern and Modern periods, and Zone 5 (140e0 cm; 1730 CE
to present) corresponds to the late Modern through Contemporary
periods.
4.5. Interpretation of major phases of environmental change
There is a strong coupling between sedimentological and palynological shifts indicating that the factors affecting the lake's
depositional environment were also at work affecting the plant
cover in the surrounding landscape. The resolution of our age
model is centennial to sub-centennial and allows us to identify the
major shifts in environmental change to compare with the rich
collection of archeological and archival evidence and independent
climatic reconstructions. The record allows for recognition of
distinct periods or phases within the last 2700 years. Here we
discuss the seven most important environmental phases in a historical context and the potential climatic and human causes that
may have caused those changes.
4.5.1. Pre-Roman: a climate driven system (700e300 BCE)
Environmental change during the pre-Roman period appears to
be largely a response to climate rather than human activity. The
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Fig. 13. Selected aquatic pollen, algae, non-pollen palynomorphs and charcoal. Units for charcoal are accumulation rate of number of pieces. Unfilled lines represent 5X
exaggeration.
climate was cool and wet at the beginning of our record. The Calderone glacier, 50 km to the east in the Gran Sasso d'Italia mountain
group, advanced between 900 and 750 BCE and periglacial soils are
found in the Apennines during the same period (Giraudi, 2005;
Giraudi et al., 2011). Archaeological excavations and surveys from
near Lago Lungo reveal small settlements along the 375 m contour,
suggesting habitation in a generally marshy environment around
small lakes (Coccia et al., 1995). The Sabini, who inhabited the region, were an advanced culture and primarily exploited the land for
pastoralism with little evidence of forest modification (Cifani,
2003). The literary tradition reports that in the Rieti Basin the
cults of Vacuna and Hercules played an important role, the first as
the deity of water and woods and the latter the god of springs and
cattle (Alvino and Leggio, 2006; Camerieri, 2011).
There was a well-developed floodplain forest (Alnus glutinosa
and Fraxinus excelsior) probably covering much of the basin floor
and lakeshore and a rich mesophyllous forest (Fagus, deciduous and
evergreen Quercus, Ulmus, C. betulus, Acer, and Corylus) on the uplands (Fig. 14). The abundance of Fagus pollen, and the presence of
Asterosporium, a spore associated with Fagus, suggests that beech
forests grew on the lower mountain slopes well below 1000 m,
while today they are restricted above 900e1000 m (Piovesan et al.,
2005).The mix of tree species as well as monolete and trilete ferns
(e.g. Osmundo-Alnion and Alno-Ulmion alliances; Cutini et al., 2010)
supports an interpretation of a minimally impacted forest (Russo
Ermolli et al., 2014). This widespread mixed floodplain mesophyllous forest confirms that the landscape ecology of Central Italy was
less affected by the Mid Holocene ‘mediterraneanization’ than
other southern regions of the Mediterranean basin (Sadori et al.,
2011).
The maximum highstand of Lacus Velinus, determined by
geomorphic and archeological evidence (Ferreli et al., 1992), is reported to have occurred in the Iron Age (beginning ~850 BCE). The
lake environment was a hydrologically open hard-water system
(Ferreli et al., 1990) deep enough to support aquatic phytoplankton
(i.e. cyclotelloid diatoms). Carbonate content and Ca relative
abundance show a gradual decline in Lago Lungo from 700 to 400
BCE. The sediment accumulation rate during this period remains
low, indicating that the decrease in carbonate is not due to dilution
by clastic input. Instead, the carbonate trend reflects a change in
lake chemistry affecting carbonate saturation and precipitation.
The Lacus Velinus highstand reached an elevation of 375 m a.s.l.,
then dropped to ~372 m a.s.l. during pre-Roman time (pre 270 BCE),
prior to any human modifications to the basin (Ferreli et al., 1990).
The coincidence of a larger deeper lake in ~850 BCE, receding
during pre-Roman times from its highstand supports the role of the
water balance in affecting the observed carbonate trend. The
gradual decline in carbonate content may reflect climaticallydriven changes in lake hydrochemistry, although the specific
drivers affecting carbonate deposition in this system need more
investigation.
4.5.2. Roman Republican: initial manipulation of the drainage
system (300e1 BCE)
About 270 BCE, the Romans are purported to have created Cava
Curiana, a drainage canal cut through the travertine sill at the
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87
Table 3
Description of key pollen taxa, non-pollen palynomorphs, algae, and charcoal results, summarized by pollen zonation. Percentages and accumulation rates are averages for the
zone unless indicated otherwise.
Zone
Key taxa
Description of pollen, non-pollen palynomorphs, algae, and charcoal
Zone 5
140e0 cm
1740e2000 CE
Late Modern &
Contemporary
Poaceae
Quercus (decid.)
TC (Juniperus)
Ostrya
Olea
Modern landscape established. Poaceae (22% is the most common single pollen type and herbs (10.3%) have
increased. Tree pollen (60.2%) is dominated by deciduous Quercus (19.7%), Juniperus (13.3%) and Ostrya (9.2%)
with minor amounts of Fagus, Fraxiunus ornus and Corylus (each <1.5%). Alnus (1.5%) is nearly absent. Olea
(3.8%) is important and shrubs (Phillyrea 2.9%) are now more abundant. Total pollen accumulation rate is
54,800 grains cm 2 yr 1.
Zone 4
335e140 cm
1390e1740 CE
Modern
Quercus (decid.)
Poaceae
Alnus
Ostrya
Fagus
Juglans
Olea
TC (Juniperus)
Abrupt return to a forest phase. Percentage of tree pollen (73.0%) nearly as high as pre-Roman, although
Quercus (30.2%) now much more common than other taxa; Alnus 10.8%), Ostrya (9.4%), Fagus 3.9%, Ulmus,
Fraxinus ornus, Corylus and Carpinus betulus (each <1.6%). Tree crops emerge; Olea (1.4%) and Juglans (1.8%).
Poaceae (11.9% and herbs (7.2%) decrease, ferns (2.1%) nearly disappear. TC (Juniperus) increases to 10.0%
at 134 cm and Cannabis type peaks at 31.4%. Highest pollen accumulation rate (137,500 grains cm 2 yr 1).
Zone 3
800e335 cm
870e1390 CE
Medieval
Trilete/Monolete
Poaceae
Quercus (decid.)
Cichorioideae
Cereals
Sporormiella
Glomus
Abrupt transition to a deforested phase. Pollen of Poaceae (19.1%), herbs (21.0%) and fern (24.2%) more
abundant than trees (31.7%). Trilete ferns average 17.7% and reach 55.7%. Cereals increase (1.6%) and
associated weeds of cultivated land increase; Cichorioideae (6.2%), Plantago, Amaranthaceae, Asteraceae,
Caryophyllaceae and Apiaceae (all >1%). Sporormiella (1130 grains cm 2 yr 1) and Glomus
(780 grains cm 2 yr 1) increase. Charcoal (1380 grains cm 2 yr 1) remains high. Quercus (13.6%)
and Alnus (4.1%) decrease dramatically. Total pollen accumulation rate at lowest level
(9800 grains cm 2 yr 1).
Zone 2B
970e800 cm
870e600 CE
Early Medieval
Quercus (decid.)
Alnus
Ostrya
Fagus
Poaceae
Trilete/Monolete
Glomus
Total forest pollen remains stable (60.5%) but diversity decreases. Poaceae (11.6%), herbs (15.6%) and total
ferns (10.4%) also change little, but trilete ferns increase. Deciduous Quercus (20.9%), Alnus (13.4%) and
Salix (2.0%) increase but all other tree taxa decline; Ostrya (7.3%), Fagus 4.5%), Corylus (2.6%), Carpinus
betulus (<1%). Glomus (500 grains cm 2 yr 1) and charcoal (1325 grains cm 2 yr 1) both increase. Total
pollen accumulation rate decreases (14,800 grains cm 2 yr 1).
Zone 2A
1145e970 cm
1e600 CE
Roman imperial
and Late Antique
Ostrya
Alnus
Quercus (decid.)
Fagus
Corylus
Carpinus betulus
Poaceae
Trilete/Monolete
Glomus
Forest taxa, particularly Alnus, decrease but remain dominant (63.1%) and grasses (12.9%), herbs (12.7%) %)
and ferns (9.1%) increase. Main tree pollen types are Ostrya (12.3%), Alnus (12.0%), deciduous
Quercus (11.5%), Fagus (11.3%), Corylus (3.6%) and Carpinus betulus (2.1%). Herbs typical of disturbance
begin to increase, including Cichorioideae (1.8%), Brassicaceae (1.5%), Ranunculaceae (1.4%) and
Plantago (1.0%). Cereals (0.6%) increase and are consistently present. Glomus, an indicator of erosion,
increases (380 grains cm 2 yr 1) and charcoal reaches a peak (900 grains cm 2 yr 1) in the 1st to
2nd centuries.
Zone 1
1438e1145 cm
700 BCEe1 CE
Archaic,
Pre-Roman &
Roman Republic
Alnus
Quercus (decid.)
Ostrya
Fagus
Carpinus betulus
Asterosporium
Forest phase dominated by tree pollen (81.3%). Herbs (5.9%), Poaceae (6.2%) and ferns (4.4%) are a small
component of the pollen. Tree pollen is diverse composed of Alnus (21.2%), deciduous Quercus (18%),
Ostrya (15.3%) and Fagus (8.6%) with small quantities of Corylus (3.3%), Carpinus betulus (3.2%),
Ulmus (1.6%) and Fraxinus excelsior (1.3%). Asterosporium is at a maximum (260 grains cm 2 yr 1).
Total pollen accumulation rate is high (55,000 grains cm 2 yr 1)
location of the Marmore Falls to facilitate drainage and reclamation
of the basin (Leggio and Serva, 1991). There is a magnetic susceptibility spike at ~300 BCE as well as an inflection point in many of
the geochemical curves, including carbonate, TI and S, which may
be associated with the channel cutting. The sediment remains dark
gray to black with anoxic sulfides similar to the Pre-Roman core
interval, and no discernible sedimentological change accompanies
the magnetic susceptibility spike. However, if channel cutting
served to lower Lago Lungo and temporarily isolate it from the
larger lake system, then the subtle increases in the S signal seen
above the magnetic susceptibility spike may reflect a more isolated
stagnant lake with slightly more sulfidic mineralization. The steady
decline in Alnus pollen beginning ~200 BCE (Fig. 14) supports an
interpretation of a lowered water table; however, large areas of the
valley must have remained wet given the continued persistence of
Alnus. The decline in Alnus was permanent, indicating that after this
change the basin never again reached the same extent of flooded
forest. Pliny the Elder (Naturalis historia 3, 109) described the Rieti
basin as covered by dense forest and beyond the change in Alnus,
there is no evidence for forest degradation (Fig. 14).
Alnus requires standing water, and a reduction in Alnus suggests
a reduction in wetland area in the valley. This interpretation supports the argument that the Romans first drained the Rieti Basin in
the first quarter of the 3rd century BCE, as recorded by historians
(Sisani, 2009). This reclamation work appears to have been sufficiently successful to have lowered the water table enough to reduce
the flooded forests. The Roman water works do not appear to have
changed land use practices. Archeological surveys indicate that
local settlements were consolidated (Coccia et al., 1995) but in the
1st century BCE Varro emphasized the importance of sheep
pasturing (Varr. 2.2.9) and the geographer Strabo described the
Rieti valley as a place of domestic livestock, mules particularly
(Strab. 5.3.1). The increase in disturbance taxa during this period
supports an interpretation of increased pasturage.
4.5.3. Imperial Roman through Late Antique: intensification of land
use (1e600 CE)
Climatically, the period from 1 to 200 CE is considered part of
the Roman Optimum, with exceptional climate stability and
favorable conditions that coincide with the rise of Imperial Rome
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Fig. 14. Summary diagram with selected data. Arboreal pollen includes all tree taxa presented in Fig. 11 except Alnus. Disturbance taxa include all herbs plus trilete ferns shown in
Fig. 12. Diatoms were identified from smear slide analysis. Stratigraphic intervals follow Fig. 10.
(McCormick et al., 2012). Reconstructed temperatures during this
period were mild (Fig. 14), similar to the first half of the 20th
century (Christiansen and Ljungqvist, 2012; northern hemisphere
extratropical 2000 temperature reconstruction e ftp://ftp.ncdc.
noaa.gov/pub/data/paleo/contributions_by_author/
christiansen2012/christiansen2012.txt URL and data accessed).
What is particularly striking is that while the population of Rome
expanded to more than one million (Lo Cascio and Malanima, 2005)
there is no evidence for intensive exploitation of the Rieti Basin
through land clearance or deforestation. Forests declined during
the Imperial period in relation to the Republican period (66% vs.
81% total AP respectively; Table 3, Fig. 14), though the extent of
degradation appears limited. The impact on the forest shows
alternating phases of more pressure (1stand 4th century) or less 3rd
century (see also Russo Ermolli et al., 2014) consistent with the
demographic and socio-economic trends of Rome (Leggio, 2000;
Costambeys, 2009).
Around 1 CE there is an abrupt increase in disturbance species
(e.g. Rumex, Brassicaceae, Cichorioideae, Apiaceae, and trilete
spores) although a diverse flooded forest assemblage persisted.
Pollen of cereals are present, but not abundant (Fig. 12) and Sporormiella, an indicator of domesticated livestock, is consistently
present. Archeological evidence of settlement is restricted to the
alluvial fans and low hill-slopes above the valley floor, concentrated
between 380 and 480 m with no evidence of large settlements
above 600 m (Coccia et al., 1995). The main nucleated settlement
was Reate (Cifani, 2003) and the economy was probably oriented
towards pastoralism and trade with the nearby Apennine
communities. We infer that the basin was partially cleared for
pasture but remained marshy and that livestock grazing was more
important than agriculture, although even pasturage may not have
been intensive.
A number of other pollen reconstructions from the Italian
peninsula have also found only limited evidence of deforestation
during the Roman Imperial period, including sites near Naples
(Russo Ermolli and di Pasquale, 2002), Colli Euganei west of Venice
(Kaltenrieder et al., 2010), Calabria (Joannin et al., 2012), Abruzzo
(Branch and Marini, 2014) and near Ostia, the ancient port for Rome
(Di Rita et al., 2010; Sadori et al., 2011). Our findings contrast with
arguments for extensive forest clearing and burning in the vicinity
of Rome (e.g. McNeil, 1992; Hughes, 2011) and support the argument that deforestation was localized and degradation limited
(Grove and Rackham, 2001).
The Roman Empire supported a complex trade network and one
possible reason for the lack of exploitation of the Rieti Basin may
have been the ‘globalization’ of production of Imperial Rome. Rieti
was interconnected with Rome and likely benefited from external
resources, potentially reducing pressure on local resources
(Champion, 1995). Local sites, such as Rieti, would not have been
sufficient to support the large urban population of Rome and may
have been spared from environmental degradation while distant
regions were exploited. Egypt appears to have enjoyed exceptionally favorable conditions between 1 and 200 CE (McCormick et al.,
2012) and food production and transport may have been more
efficient from such distant locations as opposed to local sites with
limited agricultural capacity and barriers to transport. Rieti was on
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the Via Salaria, one of the most important trans-Apennine roads
between Rome and the Adriatic Sea (Coccia et al., 1992), but the
Marmore Falls prevent easy access by water to the Tiber River
making it difficult to ship bulky resources (e.g. wheat, charcoal) to
Rome. Another possibility is that, in order to prevent deforestation
and soil erosion and to mitigate Tiber flooding in the area of Lacus
Velinus, the forests were provided some level of protection as sacred woods, following the Sabini cult of Vacuna, identified as Vittoria or Diana by the Romans (Coccia et al., 1992; Alvino and Leggio,
2006).
Between 400 and 600 CE, during the Late Antique period,
sometimes referred to as the Migration Period, we see a further
degradation of the forest with a decline in Ostrya and increase in
grassland (Poaceae), indicating more intensive coppicing of forests
and possibly an intensification of local resource extraction. The Late
Antique or Migration Period (400e600 CE), a time with cooler than
average temperatures and general disruption following the Roman
Empire (Büntgen et al., 2011; Christiansen and Ljungqvist, 2012), is
sometimes identified as a period of climatic instability which may
have contributed to cultural upheaval (McCormick et al., 2012). In
Rieti, there are few indications of upheaval, however trade networks appear to have been disrupted requiring greater reliance on
local products. With the fall of Rome, the Ostrogoths ruled Rieti
between 400 and 570 CE and maintained the Roman system of
governance (Leggio, 1989). Archaeological data support the presence of a thriving community (Coccia et al., 1995) though limited
ceramics from this period indicate a potential breakdown in the
trade system (Coccia et al., 1992). A decline in Ostrya and increase in
disturbance taxa suggest possibly more intensive coppicing of forests and an intensification of local resource extraction, with less
reliance on traded goods.
4.5.4. Early medieval: intensification of forest disturbance and
sedimentation (600e900 CE)
This phase represents a transition period with a complex series
of changes in the vegetation, sedimentary, magnetic and
geochemical proxies. Between 600 and 735 CE temperatures in the
northern hemisphere remained cooler than average (Christiansen
and Ljungqvist, 2012) though in central Europe, climate became
milder, with warming temperatures and an increase in precipitation (Büntgen et al., 2011). At our site, loss of forest biodiversity
began ~600 CE, particularly the softer hardwoods (Fagus, Tilia,
Ulmus, Acer, and F. excelsior) (Zone 2B, Fig. 11) and there was an
increase in disturbance taxa (Fig. 12) and erosion (Glomus, Fig. 13).
High percentages of Alnus indicate that the valley floor remained
marshy, suggesting that human impacts were concentrated on the
hill slopes.
A cool to mild climate should not have resulted in loss of forest
biodiversity and we suggest that this environmental shift resulted
from a change in the governing authority and associated changes in
land use. The Lombards gained control of Rieti around 590 CE
(Naspi, 2010). There are few written documents for this period, but
Rieti has been described as changing from a city of stone to a city of
wood (Leggio, 2000) and between ~600 and 800 CE, the softer
desirable hardwoods appear to have been selectively removed
initiating the decline in forest biodiversity (Fig. 11). In addition, the
Farfa Monastery of the Benedictine order, established in the end of
the 6th century in the Sabini Mountains (Fig. 1), became increasingly important in the 8th century. The monks were responsible for
managing large areas of the landscape, including the Rieti Basin
(Leggio, 1994) and forest cutting was widespread (Leggio and Serva,
1991).
From ~735 CE (900 cm depth) until ~870 CE (800 cm depth) the
forest recovers somewhat, with an increase in Quercus and Ostrya,
although there is no increase in the soft hardwoods. Disturbance
89
indicators decrease, Ti decreases, carbonate and Ca increase, and
MS is high and variable. Written sources describe an increase in
flooded area, expansion of Lago Lungo (lacus Totoni) and Lago di
Ripasottile (lago Maggiore) and the formation of many lamae (little
lakes) (Leggio, 1994, 1998). This would appear to be a climatic
impact, rather than a human induced change, though dominance of
Quercus and Ostrya in the overstory suggests an actively coppiced
forest.
4.5.5. Medieval through Late Medieval: peak deforestation and
sedimentation (900e1390 CE)
The most extensive degradation of the environment occurred
during the Medieval Period (~870e1390 CE) when forest cover was
greatly reduced and herbs and ferns increased (Fig. 14). Temperatures in the northern hemisphere began warming after 900 CE with
a well-defined peak between 950 and 1050 CE (Fig. 14) and a
maximum temperature anomaly of 0.6 C (Christiansen and
Ljungqvist, 2012). Climate reconstructions from the central
eastern Alps (Büntgen et al., 2011) and central Italy (Guiot and
Corona, 2010) show elevated temperature from 700 to 1250 CE
with a thermal maximum of 0.3 C between 1053 and 1171 CE
(Trachsel et al., 2012). A precipitation reconstruction (Palmer
Drought Severity Index e PDSI) using Cedrus atlantica (Endl.
re) from Morocco (Esper et al., 2007; Trouet et al., 2009)
Carrie
shows that the period from 1050 to 1400 CE was anomalously dry
across the western Mediterranean (Fig. 14). The initiation of forest
cutting throughout the Rieti Basin coincides with the period of
warmest temperatures, and climate change appears to have been a
strong catalyst leading to environmental degradation; however
socioeconomic changes are also important during this period.
Sediment accumulation rates reach their highest levels by 900
CE. The high percentages of indeterminate pollen (Fig. 12) as well as
Cichorioideae, a taxon commonly found on disturbed sites with
pollen particularly resistant to degradation (Bottema, 1975), support an interpretation of high erosion and increased bare soil.
Cichorioideae have been demonstrated to be good indicators of
open landscapes dominated by pastures and cultivated fields
(Florenzano et al., 2015). Some of the indeterminate pollen are
likely degraded tree taxa, could suggest that the level of deforestation may not have been as high as the pollen diagram indicates;
however there is no reason to believe that the percentage of
indeterminate pollen are skewed towards tree types since many
herbaceous taxa are equally subject to degradation. Fern spores
(trilete) are very high between 925 and 1075 CE. Ferns require
mineral soil for regeneration, further supporting an interpretation
that large areas with thin soils must have been present and loss of
tree cover must have been widespread. The elemental proxy for
erosion, the detrital element Ti, remains high throughout the MP,
supporting the claim that deforestation and agricultural land use
peaked during this time. Sediments throughout this phase are
varicolored silty and clayey bands (Fig. 3) indicative of episodic
sedimentation and potentially greater fluvial influence. The very
high sediment accumulation rates begin to decline after 1100 CE.
Written and archeological evidence support the hypothesis for a
large increase in population, leading to saturation of the lower
elevation sites for agriculture, and a push to exploit higher elevations. During the Medieval period, settlements were constructed at
elevations above 1000 m (Coccia et al., 1992). Terraced walls related
to farming were found between 700 and 1000 m (Coccia et al.,
1995) and active deforestation and a series of ‘hospitals’ for tending to farm workers have been documented at 1400 m (Naspi,
2010). It also seems reasonable to conclude that warmer temperatures allowed farming and grazing to be successful at higher elevations. As population grew and settlement expanded upslope,
farmers likely pushed the limits of what local resources were
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capable of supporting. Introduction of the heavy plough, horse
collar and harrow were technological innovations that may have
partially offset the limits of local production by permitting a more
intensive agriculture (Sereni, 1973).
Documents record an increase in deaths due to malaria (BruceChwatt and de Zulueta, 1980; Sabbatani, 2005) which may have
also contributed to building settlements at higher elevation
(Leggio, 1994). Settlement was not dispersed, but largely concentrated in fortified settlements or castles (incastellamento) for security. More than forty settlements in the Rieti Basin are first
mentioned in the Farfa monastery documents in the period between 1050 and 1200 CE, of which fifteen of these hill towns are
still occupied (Coccia et al., 1992). Dispersed settlements did not
completely disappear, but the broad pattern was one of the population concentrated into fortified settlements in defensible locations governed by powerful and wealthy lords (Leggio, personal
communication). A sharp decline and intermittent absence of Alnus
from the record indicates that the valley must have also been
heavily managed and utilized for cereal production. Only through
constant maintenance of the drainage system was it possible to
prevent the basin from becoming marshland (Coccia et al., 1992).
This maintenance was probably aided by a drier than normal
climate (Fig. 14) and large available labor force. A possible explanation for the new phase of exploitation of the valley is that the
slopes were not sufficient to maintain the needs of the increasing
population (Naspi, 2010).
Following the MWP thermal maximum, the initial cooling of the
LIA began, reaching a temperature anomaly of 0.8 C about 1310
CE (Fig. 14; Büntgen et al., 2011; Christiansen and Ljungqvist, 2012;
Trachsel et al., 2012). The black plague of 1347 CE, and subsequent
famines and plagues resulted in a local population decline of >50%
by 1400 CE (Leggio, 1989). Cooler than average temperatures between 1350 and 1390 CE appear to have been a catalyst leading to
collapse of the local land management system. As high elevation
settlements were abandoned (Leggio, 1995b; Naspi, 2010) disturbance species decreased, and forest taxa and Alnus begin to steadily
increase (Fig. 14).
4.5.6. Little Ice Age: rapid reforestation and reduced sedimentation
(1390e1700 CE)
A combination of climatic change, plague, earthquakes and
political instability led to a collapse of the local system by the early
15th century. Precipitation increased and temperatures remained
cool (Büntgen et al., 2011; Christiansen and Ljungqvist, 2012). By
~1390 CE, the PDSI reconstruction from Morocco records anomalously wet conditions (Fig. 14), with peak wetness in the 15th and
16th centuries (Esper et al., 2007). Records of major floods on the
Tiber River through Rome began an upswing in the 14th century
and reached a maximum in the 15th century with a total of
seventeen major floods, an average of one every 6 years (Bersani
and Bencivenga, 2001; Giraudi, 2012). In contrast, only three major floods were recorded in the 13th century. San Matteo church
documents and the 1445 CE Rieti cadastral survey indicate that
lakes in the basin reached their maximum extent during this period
(Leggio, 2007).
The rock magnetic parameters (Fig. 5) indicate a significant
event at the very end of the Medieval interval (337 cm depth, ~1380
CE) followed immediately by changes in the geochemical data
(Fig. 10) and representing a permanent change in the sedimentary
dynamics in the lake. All clastic proxies (k, Ti, and smear-slide
petrography) dropped to zero at 335 cm depth. Such a change
required an abrupt adjustment to the sedimentary environment,
cutting off all access of siliciclastic input. This shift coincided with a
series of physical influences on the environment (strong earthquakes in central Italy (Galli and Nasso, 2009) and increased
precipitation) as well as socioeconomic influences (depopulation
following the Black Plague, local political instability). Historical
documents of the second half of the 14th century report difficulties
in managing the drainage system of the basin and consequent
famine (Leggio and Serva, 1991). The geochemistry is very distinct
with large peaks in Sr, S and Ca (Fig. 10) that are indicative of
changes in water chemistry and potentially a rearrangement of
source waters to include a more SO4-rich source.
Increasingly cooler temperatures pushed people out of the
highest elevation settlements, resulting in widespread land abandonment (Leggio, 1995b; Naspi, 2010) and rapid recovery of forests.
Recurring plagues through the first half of the 16th century
(Barbiera and Dalla-Zuanna, 2009; Tozzi, 2009; Alfani, 2010)
reduced the Italian population to its lowest level in Medieval time
(Fig. 14) by the mid-15th century (Capasso and Malanima, 2007).
The peak in percent arboreal pollen and pollen accumulation rate
~1600 CE coincides with the coolest temperatures during the LIA
(Ladurie, 1971). This pattern of land abandonment and reforestation following demographic decline from the black plague, and
deterioration of the climate has been documented repeatedly
throughout Europe (van Hoof et al., 2006; Yeloff and van Geel,
2007; Fraser, 2011). While the reforested phase in many northern
European sites lasted about a century, it lasted for two centuries in
Italy. Political instability and the persistent presence of mercenary
bands made it increasingly unsafe to pasture livestock far from
settlements and hunting and fishing became increasingly important (Lorenzetti, 1989). By the mid-15th century, the meat of deer
and wild boar was less expensive than that of domesticated animals
and predators such as bears and wolves were present (Leggio,
1995a) providing evidence for return of a functioning forest
ecosystem. This pattern of the increased importance of game over
domesticated animals has been documented in France as well
(Vecchio, 1974).
Despite extensive land clearing and erosion during the Medieval
Period, forests quickly recovered during the Little Ice Age (Fig. 14),
although forest biodiversity did not return to the level of the Roman
and pre-Roman periods. One possible reason for the quick recovery
may have been associated with the practice of coppicing, in which,
although dramatically thinned, stems remain in the landscape and
stem sprouts grow rapidly in the absence of repeated cutting. High
percentages of Alnus indicate that the basin must have been flooded
through much of this period. The lake expansion in the 15th century was so widespread in the basin that the 1445 CE cadaster reported thirty-eight small lakes (Leggio and Serva, 1991); moreover
in the historical maps of 1500e1600 CE the flooded area is
expanded, often reported as a single lake.
Tree crops, particularly Olea (olive) and Juglans (walnut),
became more important after 1390 CE (Fig. 11). Around 1350 CE, a
set of local regulations were codified governing the pruning and
maintenance of tree crops (Caprioli, 2008). During Medieval time,
olives as well as walnut were not important food crops in this
interior area of the Sabina (Leggio, 1995b; Naspi, 2010) but after
1390 CE they increased in abundance and became a larger proportion of the diet. Following an initial increase in Olea pollen, there
is a distinct decrease in abundance between ~1550 and 1650 CE,
coincident with an intense cold period documented throughout
central and southern Europe, with the coldest temperatures
occurring in the late 16th and early 17th centuries (Ladurie, 1971;
Trachsel et al., 2012; Moriondo et al., 2013). At least seven
different years with olive-killing frosts were recorded in Provence,
France between 1565 and 1600 CE (Ladurie, 1971). The Rieti basin is
a marginal environment for olives and the decline in pollen is likely
attributable to repeated killing frosts.
After 1600 CE Alnus pollen shows a continuous and permanent
decline providing evidence for a lowering water table (Fig. 14)
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
despite steady or increased precipitation (Esper et al., 2007). Since
the 13th century, many efforts had been made to construct new
channels to remove water from the basin, including an unnamed
channel in 1325 CE, Cava Reatina (1422 CE), Cava Paolina (1547 CE)
and Cava Gregoriana (1575 CE). These efforts were largely unsuccessful until construction of Cava Clementina in 1601 CE (Lorenzetti,
1989; Leggio and Serva, 1991). Decline in Alnus after 1600 CE appears to be a response to human activity rather than climate.
4.5.7. Late Modern and Contemporary: modern forest with lake
eutrophication (1700 CE to present)
By the 18th century, the vegetation structure was essentially
modern. Drainage of the basin removed all flooded forest and
agriculture included introduced crops such as Z. mays (Fig. 11).
Cannabis type production peaked in the late 18th and early 19th
centuries, with the very high pollen percentages likely associated
with retting in pools adjacent to the lake (Celetti, 2007). The slopes
remained forested but contained much less biodiversity than the
original landscape, even though pollen percentages suggest that
total forest cover is not significantly less now than during the preRoman period. The successional species Juniperus communis and
J. oxycedrus are now an important forest constituent whereas for
most of the record they were a minor component of the vegetation.
The lakes appear to have become increasingly eutrophic with
dramatic increases in diatoms, soft-bodied algae and calcareous
algae towards the present (Fig. 13). The intensity of human impacts
increased such that the human signal of environmental change is
much stronger than the climate signal.
5. Conclusions
Our 2700 year paleoenvironmental reconstruction on the
fringes of Rome records a complex interaction between climate and
socioeconomic conditions as drivers of environmental change. The
influence of Rome on the Rieti Basin during the Roman Republican
Period seems to be modest. Despite the channel excavations that
formed the falls at Marmore and drained the basin, our multi-proxy
record indicates that the effects on both the aquatic ecosystem and
landscape were minimal. During the Imperial Roman Period, a time
of generally mild climate referred to as the Roman Optimum, there
is no evidence for deforestation in the Rieti Basin and only limited
impact on the environment, although Rome reached one million
inhabitants. The Roman Empire supported a complex trade
network that allowed importing resources from distant regions,
similar to modern globalization. Rieti was interconnected with
Rome and likely benefited from external resources, which reduced
pressure on its local resources, resulting in preservation of the
environment. With the fall of Rome, despite a cooler climatic period
associated with an interval of general disruption in central Europe
referred to as the Migration Period, the Ostrogoths filled the power
vacuum in Rieti and generally maintained an environment similar
to that which existed during the Roman period. Only with the
arrival of the Lombards and establishment of local monasteries at
the start of the Medieval Period (~600 CE) does deforestation
become apparent, with clearing for agriculture and selective
removal of desirable tree species for housing and manufacture. This
period is manifested in a strong signal in the Lago Lungo record that
transgresses all of the biological, geochemical, and sedimentological proxies.
The climatically optimal Medieval Warm Period appears to have
been a catalyst for expanded land use and widespread environmental degradation. Local population was higher than during Roman time, placing greater pressure on local resources, but another
possibly crucial difference was the lack of an interconnected trade
network capable of supplementing local resources. As population
91
grew and settlements expanded upslope, they likely pushed the
limits of what local resources were capable of supporting. When a
cooling trend began in the 13th century, the highest elevations
began to be abandoned and the forests began to recover somewhat.
By the late 14th century, plague devastated the local population.
Persistent cooler and wetter climate led to wide scale land abandonment and rapid reestablishment of the forest and wetlands.
Climate change, coinciding with earthquakes produced marked
changes in the local sedimentological regime of Lago Lungo,
including diversion of siliclastic input and altered lake hydrochemistry. The Medieval period in Rieti has a complex socioeconomic history, but the evidence supports the argument that the
shift from warm and mild climate to cool and wet climate was an
important catalyst in disrupting the community. This disruption
lasted for nearly two centuries. By the 1600s, despite being one of
the coldest periods of the LIA, improved methods in hydrologic
works led to the eventual permanent draining of the basin and
renewed agricultural expansion which has continued to today.
The detailed reconstruction of climatic and environmental
changes from sedimentary records is dependent upon reliable
dating of the sedimentary sequences. In the case of Lago Lungo
interpretation of the 14C dates is challenging; however the sediments are characterized by good paleomagnetic properties, with an
almost single-component ChRM that can be easily isolated with
stepwise AF demagnetization. The ChRM inclination and declination values oscillate around the mean values expected for the GAD
field at the site, but the amplitude and the frequency of the variation are too high for geomagnetic secular variation. The paleomagnetic trends (ChRM inclination, declination and relative
paleointensity) can be replicated at high-resolution between four
distinct cores, ruling out disturbance as a cause for this variation.
Regardless of the high-amplitude and high-frequency variation,
when broadly smoothed the reconstructed paleomagnetic trends
can be correlated to the reference curves from models of paleosecular variation (PSV) during the last 3000 years, as reconstructed
from archeomagnetic data collected across Europe. Together with
constraints coming from pollen and sediment analysis, the paleomagnetic trends allow the construction of a high-resolution age
model and indicate that some changes observed in the pollen
assemblage and in sedimentation in the Rieti basin can be associated to societal factors and others to climatic change. Paleomagnetism is a powerful tool for providing alternative age models for
study sites with 14C records that are difficult to interpret. The rich
documentary record for the region provides an opportunity to
further explore questions of environmental change in relation to
societal versus climatic causes. Addressing some of these questions
will require further refinement of our age model to reduce temporal
uncertainty.
Contributions by authors
Mensing co-led the field coring, analyzed pollen, contributed to
development of the age model and climate proxy framework, and
oversaw the project; Tunno assisted in field coring and analyzed
pollen and charcoal; Sagnotti and Florindo conducted all rock
magnetism and paleomagnetism analyses and developed the PSV
age model; Noble created the core description, conducted smear
slide analysis and analyzed elemental chemistry; Archer analyzed
elemental chemistry; Zimmerman conducted all radiocarbon ana n-Carrasco helped
lyses and helped develop the age model; Pavo
develop the age model and associated error analysis; Cifani and
Passigli conducted historical archival research (Section 3.7),
contributed interpretation of historical documents, and specifically
authored historical sections in paragraphs 4.5.1, 4.5.2; 4.5.3 by G.
Cifani and paragraphs 4.5.4, 4.5.5, 4.5.6, 4.5.7 by S. Passigli;
92
S.A. Mensing et al. / Quaternary Science Reviews 116 (2015) 72e94
Piovesan coordinated all Italian research components, co-led the
field coring, interpreted pollen results in relation to local forest
ecology, contributed to development of the age model and climate
proxy framework and contributed to historical research. All coauthors contributed to writing the manuscript.
Acknowledgements
We are grateful to the many people who helped make this study
possible, Microtephra analysis was performed by Paola Del Carlo,
Antonella Bertagnini, Alessio di Roberto of INGV, Pisa, Italy. Cores
were processed at LACORE, Minneapolis with assistance from
Anders Noren, Christina Brady, Amy Mybro and Jessica Heck. Fig. 1
was created by Emanuele Ziaco. Funding was provided by the National Science Foundation (GSS-1228126) to Mensing and Noble,
international travel awards and sabbatical leave from the University
of Nevada, Reno to Mensing, the Sabina Universitas and Province of
Rieti. We are grateful to Luigi Sandoletti for technical support,
Giulia Sandoletti for laboratory assistance, Emanuele Presutti Saba,
Emanuele Ziaco, and Gianluca Bonavigo for field and coring assistance, and DAFNE Universit
a degli Studi della Tuscia for field
transportation. Paolo Bellezza, Maurizio Sterpi at the Riserva Naturale dei Laghi Lungo e Ripasottile provided housing at the field site
and boat access to Lago Lungo. Stefano Pizetti helped arrange
housing in Viterbo for U.S. participants. Comments from an anonymous reviewer significantly improved the manuscript. This is
LLNL-JRNL-665781.
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