B13B-0438 INVITED
Using Peat Archives to Quantify Relative Sea-Level Change and Coastal Subsidence
Building on a long tradition, peat records continue to play a critical role in reconstructions of Holocene relative sea-level change along the Earth's low-energy shorelines. In many cases, rates of coastal subsidence can be extracted from such relative sea-level data. Recent years have seen considerable attention being focused on refining the paleoenvironmental significance of coastal peat beds by means of a variety of biological and geochemical proxies. The principal goal is to reduce the vertical indicative range of peat samples with respect to tide levels. Geochronolology constitutes the other key element in studies of peat records. The advent of accelerator mass spectrometry in radiocarbon dating has significantly improved age models. The use of plant macrofossils, combined with dating uncertainties now as little as 2 to 3 per mil, makes it possible to develop chronologies with 100-year resolution and sometimes better (calibration uncertainties are typically the limiting factor). Examples are provided of sea-level studies from the US Gulf Coast where the indicative range of brackish to saline marsh peat is on the order of a few decimeters only. This effectively sets the limit of the vertical resolution that can currently be attained. However, this level of resolution does allow differential crustal movements over millennial timescales to be reconstructed with a precision of fractions of millimeters per year. In addition, peat-based relative sea-level records play a crucial role in quantifying compaction rates, as illustrated by a case study from the Mississippi Delta.
B13B-0439 INVITED
Mineral or Vegetable? The Importance of Organic and Inorganic Contributions to the Sustainability of Deltaic Marsh Landscapes
In the face of sea-level rise deltaic soils must build vertically. Once riverine sediments accumulate to interidal elevations or sea-level rise inundates previously dry land, vegetative growth contributes to soil building both through enhanced trapping of sediments in suspension and through direct contributions of below ground production. In sheltered or microtidal environments the contributions of marine, estuarine and riverine processes to mineral sedimentation is largely event driven and at the landscape scale the extent of the resulting deposits depend upon the type and scale of event. For example, unconstrained riverine flooding can provide material to large areas while the influence of coastal storms is dependent upon their size and angle of approach. In many contemporary systems, however, the distribution of sediments from these natural pulses is constrained by management activities. Processes influencing soil development in these areas may mimic those prevalent in deltas abandoned by channel avulsion. The role of organic accumulation becomes more important in these systems but in areas subject to storm surge and wave energy, peat dominated soil substrates can be especially vulnerable to damage. The multi-year return interval of the events most effective in delivering mineral sediments to delta soils, the cyclic nature of the some of the climatic controls, and climate change influences on storm and flood frequency and intensity, means that for long periods or over large areas delta soil development is dependent upon organic contributions. In addition, the volumetric and structural contributions of below ground plant material to soil development can be important in abandoned deltas or managed systems with regular but limited sediment inputs. Examples from Mississippi Delta Plain and the Sacramento-San Joaquin Delta provide examples of the range of process conditions driving soil development and provide opportunities for understanding how organic and inorganic accumulation at seasonal and annual time scales ultimately contribute to the sustainability of delta landscapes.
B13B-0440
Peat Formation Processes During the Past 7000 Years in the Sacramento San Joaquin Delta, California, USA
The 1,400 km2 tidal marsh that formed during the Holocene in the Sacramento--San Joaquin Delta was largely drained for agriculture during the past 150 years. The remaining peat constitutes an archive of marsh formation processes and environmental conditions through the millennia. The goals of the REPEAT (Rates and Evolution of Peat Accretion through Time) project are to determine past rates and processes of peat accretion to benefit future wetland restoration efforts. Peat cores were collected across the Delta during 2005 from drained, farmed islands and from remnant, marsh islands in the Delta. Radiocarbon analyses of plant macrofossils were used to construct age models for vertical peat profiles. Peat began forming approximately 6,600 calibrated years before present (cal yr BP). Over the last 150 years, approximately 2/3 of the original peat thickness on the farmed islands has been lost because of land-surface subsidence. On the marsh islands, estimated rates of vertical accretion range from 0.06 to 0.53 cm yr-1. Mean rates of vertical accretion at the marshes suggest that three out of the four marsh sites are capable of keeping pace with current rates of sea-level rise. Bulk density, % OM (organic matter), % contribution of OM vs. inorganic matter (IM) to soil volume, and vertical accretion rates show considerable variability through the millennia. Some variability is associated with a period of high precipitation and freshwater discharge between approximately 4,000 to 2,000 yr BP. The hydrogeomorphic setting of marshes appears to largely control the amount of IM incorporated into peat through time. Sediment supply will likely determine whether remnant and restored tidal marshes can keep pace with future sea-level rise in the Delta.
B13B-0441
Peat Deposits of the Sacramento-San Joaquin Delta, California: An Archive for Anthropogenic Contamination of Mercury, Lead, and Other Trace Metals
A marsh originally 1,400 km2 in area, prior to anthropogenic modification, started forming approximately 7,000 years ago at the confluence of the Sacramento and San Joaquin rivers (the Delta). A vertical profile of peat from Browns Island (BRI), an island not affected by farming, contains higher concentrations of various inorganic anthropogenic contaminants including mercury (Hg) and lead (Pb) in the shallow, most-recently deposited peat compared to concentrations in pre-anthropogenic peat deposited at depth. In the top 55 cm of the BRI profile, where peat is less than ~100 years old based on 137Cs and 210Pb data, Hg concentrations averaged 0.34 parts per million (ppm, dry basis), with a standard deviation (sd) of 0.22 ppm. This compares with an average Hg concentration of 0.042 ppm (sd 0.002 ppm) in deeper material deposited between about 6,300 and 2,350 calibrated years before present (cal yr BP), based on radiocarbon dating of plant fossils. Average concentrations of Pb were 45 ppm (sd 14 ppm) in the top 55 cm compared with 9 ppm (sd 2 ppm) in the lower, older part of the BRI profile. Normalizing Pb concentrations by Ti to account for variable amounts of inorganic material results in a depth profile with near-constant values of Pb/Ti between about 6,300 and 2,350 cal yr BP and an increase in Pb/Ti values with decreasing age beginning about 2000 cal yr BP. Lead isotope ratios 206Pb/207Pb and 208Pb/207Pb determined from bulk-sediment digestions indicate the strong influence of lead from gasoline in the top 55 cm of the peat profile. A decline in Pb/Ti values with increasing elevation in the top 10 cm of the profile along with a return of more radiogenic Pb isotopic compositions reflect the phasing out of leaded gasoline in automobiles during the late 1970s and 1980s. An increase in the variability of 208Pb/207Pb values beginning about 2000 cal yr BP may represent the earliest detectable anthropogenic influences corresponding to Roman mining and metallurgical activity. A systematic shift towards less radiogenic Pb isotope ratios starting at about 830 cal yr BP may reflect the time of maximum mining and metallurgical activity in China during the Sung Dynasty. Although the various hydrogeomorphic settings within the Delta have led to variable inorganic inputs over time and space, peat deposits in the Sacramento-San Joaquin Delta still may represent useful archives of local and global environmental changes during the Holocene and Anthropocene.
B13B-0442
Elevated CO2, nitrogen availability and marsh tolerance for sea-level rise
Tidal wetlands experiencing increased rates of sea-level rise must increase rates of soil elevation gain to
avoid permanent conversion to open water. The maximal rate of sea-level rise that these ecosystems can
tolerate depends partly on mineral sediment deposition, but the accumulation of organic matter is equally
important for many wetlands. Plant productivity drives organic matter dynamics and is sensitive to global
change factors such as elevated atmospheric CO2 and nitrogen eutrophication. It remains unknown how
global change will influence organic mechanisms that determine future tidal wetland viability. We manipulated
atmospheric CO2 concentration and nitrogen availability (2 x 2 factorial) in a highly organic tidal marsh.
Elevated CO2 (ambient + 340 ppm) accelerated soil elevation gain by 3.9 mm yr-1, an effect caused primarily
by stimulating belowground plant productivity. Nitrogen additions, despite increasing aboveground
productivity, tended to reverse elevation gains, perhaps by reducing root productivity and stimulating soil
decomposition. Therefore, increases in the greenhouse gas, CO2, may paradoxically aid some coastal
wetlands in counterbalancing rising seas, but nitrogen pollution may negate this effect regionally. These
effects on the organic mechanisms of marsh elevation gain may help explain patterns marsh formation and
disappearance worldwide.
http://www37.homepage.villanova.edu/jonathan.langley/projects.htm
B13B-0443
Peat Archives: The Key To Unravel The Influence Of Peat Compaction On Delta Evolution
Peat is most compressible of all natural soils. Therefore, compaction of peat layers leads to substantial
amounts of land subsidence. In Holocene deltas, which are often densely populated, subsidence due to peat
compaction is caused by anthropogenic processes such as loading by construction works and groundwater
level lowering, but also, a significant amount of compaction is caused by natural processes. However, there is
a lack of knowledge concerning effects of peat compaction on the evolution of deltas, which is mainly due to
a lack of field data and suitable methods to quantify peat compaction in fluvial-deltaic settings on Holocene
time scales (100-103 years).
Therefore, new field methods to measure the amount of peat compaction in fens and swamps are developed.
These methods are based on 1) dry bulk density and organic matter content measurements in vertical peat
profiles, 2) 14C dating and 3) detailed analysis of sediment sequence stratigraphy based on logged
boreholes. A new coring device has been developed to collect sufficiently large samples of uncompacted
(modern) peat, without disturbing the internal structure. We present data obtained with these methods from
the Rhine-Meuse delta (The Netherlands), the Cumberland Marshes (Canada) and the Biebrza National Park
(Poland).
Values of up to about 50 % of compaction (percentage of the initial thickness) are observed at sites where
the peat layer is relatively thick, has a high organic matter content and is overlain by a meters thick sediment
overburden. It is hypothesized that accommodation space created by peat compaction is an important
mechanism controlling the development of natural levees of low gradient rivers. Peat compaction underneath
natural levees, and crevasse splay deposits, fixes river channels and prevents renewed avulsion, arguable
the most important process controlling sediment distribution in deltas. Herewith, we contradict the hypothesis
stating that subsidence due to peat compaction creates changes in cross-valley gradient which possibly
drives avulsion. Avulsions in peatlands are controlled by other mechanisms than peat compaction.
Results of this ongoing study are of high value for predicting sites of severe subsidence due to peat
compaction and to determine its influence of delta evolution.
http://www.geo.uu.nl/fg/palaeogeography/
B13B-0444
Multiproxy Analysis of Droughts, Landscape Changes, Sediment Dynamics, and Human Disturbances in Hudson River Marsh Peat, using Pollen, Spores, Macrofossils, LOI, and X- Ray Fluorescence Spectroscopy
Marsh peat is an excellent archive for local and regional paleoecological and paleoclimate studies because of high preservation and low disturbance. Under climatic and anthropogenic changes, sediment composition and sedimentation patterns can be altered. Using this principle, we have implemented the use of field portable X-Ray Fluoresecence Spectroscopy (Innov-X, USA) to rapidly quantify stratigraphic sediment elemental composition changes. We will discuss findings from two marshes of the lower Hudson Estuary, NY. More than 250 cm depth of Piermont Marsh sediment (41.00N, 73.91W) and 100 cm depth of Iona Island Marsh sediment (41.30N, 73.97W) were analyzed. Dry and homogenized samples were used to minimize errors from water absorption and heterogeneity. In combination with our pollen, spores, macrofossil, organic/inorganic content profiles, and radiometric dating (C-14, Cs-137, and Pb-210) at Piermont (Pederson et al., 2005) and Iona (Peteet et al., 2006), we found many emerging XRF proxies for droughts, landscape changes, inorganic matter content, sedimentation rate, pollution history, and human impacts. Both cores captured human disturbances after the European Settlement, when there are pronounced changes in plants composition, invasive species expansion, organic/inorganic content, and sediment dynamics. At the longer time scale, where Pederson et al.(2005) identify Medieval Warming mega-droughts at Piermont, we found zinc, titanium, and potassium to be useful. The results suggest, 1) Many metal pollutants, such as lead, copper, and zinc, can be quantified quickly with these methods, 2) The profiles of these pollutants agree with the Ambrosia rise and radiometric dating, so the peaks can be rapidly identified and used as an additional time marker, 3) Zinc concentrations prior to the Industrial Revolution vary to a greater degree than the anthropogenic signal. The trend is closely related to the trend of charcoal and moisture-sensitive vegetation, which is linked to droughts/fires, 4) Titanium and potassium concentrations correlate with the changes in inorganic content, which is linked to changes in erosion/sediment supply to the site and organic carbon accumulation. We are in the process of analyzing the Piermont core at greater depths to identify other major droughts/fires and landscape changes using Zn, Ti, and K. So far we have observed major shifts prior to the Medieval Warm Period, suggesting other major droughts that need further investigation. We will also discuss the accuracy of using this method in samples from various Hudson River marshes versus one performed by an independent lab.
B13B-0445
Carbon and Nitrogen Isotope Variation in Peat Bogs in the Midwestern US: Implications for Holocene Climate Reconstruction
A peat core, from near the center of Minden Bog in Michigan, representing about 3500 years of accumulation was previously analyzed for plant macrofossils, colorimetric humification, and testate amoebae to yield three independent climate proxies (Booth and Jackson, 2003). The plant macrofossil data show the site to be sensitive to bog water table fluctuations. The data suggest that this may be related to regional climatic changes. We analyzed the carbon and nitrogen isotopes, as well as the carbon-nitrogen ratios in the bulk peat samples to determine if fluctuations of these records correspond to climate events as seen in the plant microfossil and amoebae records. The degree to which peat-based carbon and nitrogen isotope records reflect changes in the relative distribution of vegetation and, in turn, reflect temperature changes in effective precipitation (precipitation minus evapotranspiration) will be assessed. Peat carbon and nitrogen isotope records will be compared with existing proxy climate records and with a temperature reconstruction based on testate amoebae in bogs. We expect that climate-related changes, in the relative abundance of vegetation remains accumulating in the peat bogs, will be recorded in the organic matter in forms of carbon and nitrogen isotopes.
B13B-0446
A fen Peat Nearby Regensburg (Bavaria, Germany) as an Archive for the Reconstruction of Past Environmental Conditions in a Prehistoric Settlement Area
Within the frame of the DFG-funded project "Peat, colluvisols and soils as archives for the reconstruction of the palaeoenvironment in the Regensburger Altsiedelland (Burgweinting, City of Regensburg)" multi- disciplinary studies are carried out to reveal past environmental conditions and effects of humans on local and regional ecosystem. The study site Regensburg-Burgweinting lies at the outskirts south-east of the City of Regensburg (Bavaria, Germany). The climate is continental with an annual mean air temperature of 8 - 9°C and a mean annual precipitation of 600 - 700 mm. The study site is situated on the loess covered high terrace of the Danube river. In the south of the high terrace the Lower Bavarian Tertiary Hills border. Due to the good climatic and edaphic conditions, this area is settled since the Palaeolithic Period. Since 1994, an archaeological excavation takes place in advance of municipal building activities. Meanwhile an area of c. 40 ha is excavated. The main geoarchive is a fen (c. 5.4 ha large), situated along the Islinger Muehlbach, c. 500 - 1000 m south-west of the excavation site. The fen developed in a topographic depression at the border from the high terrace to the Lower Bavarian Tertiary Hills. It is mainly fed by ground water from the underlying jurassic limestone as aquifer. Stratigraphic prospection of the fen by hand drillings shows, that the peat is up to 5.50 m thick. Based on the stratigraphic information, three long peat cores from the centre of the fen were recovered with a Russian peat corer and three peat/colluvial sequences were gained from the margin of the fen by percussion drilling. As a main core, profile 7038-302 was selected, since the peat sequence is complete and undisturbed with exception of the uppermost c. 50 cm section. The profile was subsampled in 1 cm increments and herefrom 1 cm3 peat was sampled for palynological investigation. Analyses of the sediment samples include bulk analyses of total contents of CNS, sequential determination of LOI (550°C and 950°C) and colorimetric humification to characterize major variations in peat stratigraphy. To obtain information about vegetation and land-use history pollen analyses are carried out. Microscopic charcoal analyses are performed to reconstruct the fire history. In addition, five AMS 14C ages are available. The peat profile 7038-302 from the centre of the fen is in total 455 cm long. The loess basis in 455 – 341 cm depth is overlain by 341 cm thick fen peat, which is in parts strongly decomposed. According to the 14C ages peat formation started during the Late Glacial Period and lasted during the Holocene. The uppermost peat layer is disturbed because of former drainage measures. Microscopic charcoal analyses were carried out for the section from c. 60 to 170 cm sediment depth, covering the Bronze Age Period to the Neolithic Period. The analyses show, that charcoal particles are almost continuously present. Four fire activity phases can be distinguished. With the exception of the youngest phase, there are no strictly defined episodes. Furthermore, low charcoal counts in the Early to Middle Bronze Age peat might correspond with a lack of archaeological findings in the archaeological excavation. Future work includes above all microscopic charcoal and pollen analyses on this profile. Further analyses are carried out on another peat profile from the centre of the fen to assure the results and on two selected peat/colluvisol sequences from the margin of the fen.
B13B-0447
Novel proxies for reconstructing paleohydrology from ombrotrophic peatlands: biomarker and compound-specific H and C stable isotope ratios
Ombrotrophic peatlands are excellent archives for paleohydrologic information because they are hydrologically isolated from their surroundings. However, quantitative proxies for deciphering peatland archives are lacking. Here, we present development and application of novel organic geochemical methods for quantitative reconstruction of paleohydrology from the ombrotrophic sediments, and comparison of organic geochemical data with conventional paleoecological proxies. Application of these methods to the sediments of several North American and European peatlands has revealed significant changes in the hydroclimate throughout the Holocene. The plant assemblage living at the surface of the peatland is tightly controlled by surface moisture. Under wet conditions, Sphagnum mosses, with no active mechanism for drawing water from below the surface of the peatland, are dominant. During dry conditions, vascular plants are more productive relative to Sphagnum. A ratio of the abundance of two biomarkers representing Sphagnum and vascular plants sensitively records changes in hydrologic balance (Nichols et al., 2006, Org. Geochem. 37, 1505-1513). We have further developed stable isotope models to compute climate parameters from compound-specific H and C isotope ratios of biomarkers to create a more comprehensive climate reconstruction. Vascular plant leaf waxes carry the D/H ratio signature of precipitation that is little affected by evaporation, whereas the Sphagnum biomarker records isotopic ratios of the water at the peatland surface, which is strongly enriched by evaporation. Evaporation amount can be calculated using the differences between D/H ratios of the two types of biomarkers. C isotope ratios of Sphagnum biomarkers can also be used to quantify surface wetness. Methanotrophic bacteria live symbiotically with Sphagnum, providing isotopically light carbon for photosynthesis. These bacteria are more active when the Sphagnum is wet, thus providing more 13C-depleted CO2. Using a mass balance model we can use the carbon isotope ratios of Sphagnum biomarkers to assess the contribution of methane-derived CO2, and hence, the wetness of the peatland surface.
B13B-0448
Repeated aggradation and degradation of Holocene permafrost peatland: controlled by climate or autogenic processes?
Boreal and subarctic peatlands are important reservoirs of organic carbon, but significant uncertainty remains on the carbon dynamics of these high-latitude ecosystems, particularly in permafrost peatlands. While numerous studies on Holocene permafrost peatlands exist from Canada and northern Europe, a data gap exists for similar studies in Alaska. Here we present plant macrofossil analysis, carbon content analysis, and AMS radiocarbon dating results and investigate long-term vegetation change and permafrost dynamics from a subarctic thermokarst peatland near the Tanana River to the west of Fairbanks, Alaska. The peatland likely initiated from an old floodplain of the Tanana River in the early Holocene as indicated by fine silty/ clayey sediment at the base of the peat cores. Organic matter content remained below 80%, with large fluctuations (10-40%), until the latest thermokarst development horizon. Aggradation and degradation of permafrost appears to have occurred multiple times throughout the Holocene, as indicated by several replicated sequences showing a typical succession beginning with sedge-dominated peat, followed by Sphagnum peat, and finally highly decomposed sylvic peat, with spruce needles and charcoal in some of these intervals. Subsequent permafrost degradation returned the site to a wet fen, and this pattern repeats itself over the course of the Holocene. Charcoal is present throughout the core, beginning in the basal mineral sediment, but it appears that only large fires might have played a role in triggering permafrost decay. The most recent thermokarst development has resulted in high Sphagnum peat accumulation, a pattern observed at several permafrost collapse scar peatland sites, which may have important implications for carbon dynamics of the discontinuous permafrost zone in the face of climate warming. The repetition of permafrost aggradation and degradation indicates that a combination of both climatic and autogenic processes have played an important role in controlling permafrost peatland dynamics in the Alaskan interior throughout the Holocene.
B13B-0449
Can Phytolith Concentrations Indicate That Wind Erodes Drained Peatlands?
Surface elevations of organic soils in peatlands in the Sacramento-San Joaquin Delta, California, have dropped by as much as fifteen meters since they were drained for agricultural use in the late 19th and early 20th centuries. In this and analogous areas, peat loss is commonly attributed to microbial oxidation of the organic material; while wind erosion is generally considered to be a minor factor. However, in the soil science literature it is widely accepted that organic soils are highly susceptible to wind erosion. The goal of this study is to investigate the competing roles of wind erosion and oxidation in the loss of peat in the Sacramento-San Joaquin Delta by using natural phytoliths found in these peat soils. Phytoliths are biogenic opal; unlike organic matter they are not removed by oxidation. Because of their size, mostly between 2-50 microns, phytoliths are very susceptible to aeolian removal and hence are potentially a good proxy for wind erosion. In this study we sampled peat from drained farmlands and nearby undrained wetlands of the Sacramento-San Joaquin Delta. Samples were treated using conventional phytolith extraction methods. Phytolith concentrations were determined by adding a known quantity (lycopodium spore tablet) of tracer to the phytolith extract (coarse silt fraction >20 microns) and counting the tracer along with the phytoliths. Compared to the phytolith concentrations in undrained peat, the phytolith concentrations should substantially increase in the drained soils as the organic matter oxidizes, unless wind is also eroding the peat. Preliminary results demonstrate an increase in phytolith concentrations for the portion of soil profile (top 45 cm) that has been mixed by agricultural equipment of the drained peat (mean=3.6x104 phytoliths/cm3) compared to the undrained wetland peat (mean=2.3x104 phytoliths/cm3.) However, this higher phytolith concentration in the drained peat is well below the expected phytolith concentration (3.4x105 phytoliths/cm3) if there had been no removal of phytoliths, suggesting that wind erosion is a contributor to the degradation of peat drained for farming.
B13B-0450
Environmental Magnetism of Cores from Peat Deposits of the Sacramento-San Joaquin Delta, California
We have conducted an environmental magnetic study of cores from 12 sites in the Sacramento-San Joaquin Delta of California. Eight of the sites are on tracts and islands that were created in the late 19th and 20th centuries when marshes were leveed and drained to create agricultural land. The other four sites are march islands that have never been drained. Most of the cores penetrate underlying clay deposits that predate the formation of the peat. Over 50 meters of core was studied from the 12 sites. Measurements were made of the acquisition and demagnetization of anhysteretic remanence and isothermal remanence, two laboratory- induced magnetizations that provide information about the concentration and mineralogy of the magnetic fraction. In all of the cores, the peat-rich intervals have fairly low magnetic intensities, indicating significant dilution of the clastic material by the organic material of the peat. Some variations in intensity can be discerned, which appear to be due to changes in climate and/or landscape. Material from the top of the cores from the farmed islands has much higher magnetic intensities, indicative of the concentration of clastic material that occurs as organic material is lost by oxidation and/or wind erosion. The most interesting results come from the bases of the cores where the transition from non-organic clays and silts to organic-rich peat is marked by a 100-fold decrease in the concentration of magnetic material. Detailed analysis of this transition indicates that it was usually very abrupt although in several cases the sudden decrease in concentration is followed by a short interval of moderate concentration before the final, lowest concentrations are attained. This intermediate state provides insights into the nature of the transition from an estuarine to a paludal environment.
B13B-0451
Environmental Conditions for the Formation of Peat in the Sacramento-San Joaquin Delta of California as Recorded by Palynological Data
We report on a palynological study undertaken in the framework of Project REPEAT for the purpose of identifying the role of vegetation and plants communities in the formation of the peat deposits of Sacramento- San Joaquin Delta in California. The principal goal of this study was to determine if general climatic conditions had a strong effect on the process of the peat formation, or if local environmental and/or hydrological conditions played a dominant and perhaps singular role. An additional goal was to better understand the interrelationship of local plant communities with the dynamics of peat development. Three cores, situated in different locations at different elevations and characterized by different modern plant communities, were selected for a comparison: Webb Track Levee (WTL), Brown Island (BRI) and Frank's Wetland (FW). Three- hundred and twenty samples were analyzed using standard palynological procedures. Since about 6500 years BP, when peat first started to form, the pollen suggests that general climatic conditions in the area did not change dramatically. However recognizable shifts in forest vegetation occurred at least twice: once between about 5000 and 4500 years BP and again between 3000 and 2500 years BP. In both cases, there are higher percentages of conifera pollen at all three locations. Another important signal in the cores is the proportion of the pollen from sedge and grasses species, which can be used to track wet/dry variations at the different locations. Pollen data from the BRI and FW sites have similar ratios of arboreal/non-arboreal pollen, but there are significant differences in pollen percentages of species within both groups, which can be related to differences in local settings. The pollen data correlate well with environmental magnetic results and with sedimentary records.