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Pistia stratiotes L. (water lettuce) is a floating tropical macrophyte long identified and managed as a non-native species within the State of Florida and other areas of the southern United States. Macrofossil seeds from Lake Annie, Florida, however, indicate abundant presence of P. stratiotes intermixed with other locally native macrophytes from ~13,500 to ~12,000 calibrated years before present (cal yr BP). This was soon after the lake depression first began filling with water as the piezometric groundwater surface of the Florida peninsula rose in response to rising seas during the transition (~18,000 to ~11,000 cal yr BP) from the Last Glacial Maximum (LGM) to the Holocene interglacial. These macrofossil records join several other lines of evidence supporting native status of P. stratiotes in the Florida peninsula. While recent cryptic invasion of non-native Pistia genotypes into some of Florida's freshwater ecosystems also appears likely, confirmed paleo-presence and contemporary persistence of native P. stratiotes subpopulations may have especially important management and conservation implications for Florida's spring-fed streams. Palaeobotanical evidence of this type may be useful in further resolving the global biogeography of P. stratiotes and other cryptic aquatic plant species. [ABSTRACT FROM AUTHOR]

For decades, diatoms have been recognized as powerful bio-indicators of modern water quality. They have also been utilized in the design of transfer functions, which can be applied to diatom assemblages in lake sediment cores to infer aspects of past lake hydrochemistry and estimate variables that can be incorporated into paleohydrology models. The Ounianga lakes, in the heart of the Chadian Sahara, possess unique and well-preserved sediment records that extend back beyond the middle Holocene. Today, the lakes display a range of hydrochemical conditions, from fresh to hypersaline. Mainly fed by fossil groundwater that originates in the Nubian Sandstone Aquifer System, measured conductivity across these lakes varies from 217 to 352,000 µS cm−1, values that are influenced by factors such as hydrology, local geomorphology (e.g., depth and area), and aquatic vegetation. Although these lakes have been on the UNESCO World Heritage List since 2012, they have never been studied in detail because they are located on the fringes of the Chadian Sahara. The distribution of diatom taxa in the lakes today is closely linked to water-column physical and chemical conditions, especially conductivity. Whereas each lake has particular features that influence its diatom flora, diatoms across a conductivity gradient enabled identification of three distinct waterbody types, freshwater lakes, meso-saline to hyper-saline lakes, and freshwater springs. Relationships between diatom species distributions and environmental variables were examined using multivariate analysis, which revealed that conductivity is the variable that explains most of the variance in the diatom flora. We used modern diatom assemblages from the lakes to develop a predictive model (transfer function) for conductivity, using the weighted averaging method. Our conductivity prediction model is strong, with a coefficient of determination (R2) of 0.89 between estimated and measured values, and a value of 0.78 using jackknife estimates of prediction. This study better constrained conductivity optima and tolerance values for diatom species found in the Ounianga lakes, thereby enabling development of a model that will yield better inferences for past conductivity, using diatoms from lake sediment records in the region. [ABSTRACT FROM AUTHOR]

The Houghton phase was a brief period of low water in the glacial Lake Minong (ancestral Lake Superior) basin during the early-mid Holocene. Previous lake-level reconstructions link the onset of the Houghton phase to the cessation of meltwater inflow and the formation of a stable lake level controlled by the St. Marys River bedrock sill. New stratigraphic evidence and radiocarbon dates from the Thunder Bay (Ontario, Canada) region point to a more complex paleohydrological history during this time. Specifically, we reconstruct a lowstand from > 9100 to 8900 cal yr BP that was followed by an increase in sedimentation and base level between ~ 8900 and 8700 cal yr BP, and a second low water period beginning ~ 8700 cal yr BP. Although in need of further testing, these rapid oscillations in the lake level likely reflect the varying contributions of meltwater inflow and high rates of evaporation to the water budget of glacial Lake Minong. Strandline evidence of the first lowstand may have been eroded or buried by the 8900 cal yr BP transgression, and the second lowstand was synchronous with closed basin conditions in the other Laurentian Great Lakes. Paleoecological (pollen, wood identification, plant macrofossil) analyses of organic deposits formed during the lowstands also yield exceptionally detailed 'snapshots' of the earliest biological communities that colonized the lake margin. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition (δ18O) of aquatic cellulose extracted from lake sediment cores has long been used to reconstruct past hydrological responses to climate variation and anthropogenic (e.g. mining, agriculture, forestry) disturbance. Application of this method depends upon a constant oxygen isotope fractionation factor between aquatic cellulose and lake water, often reported as α18Ocell-lw = 1.028. Prior field-based assessments of α18Ocell-lw, however, commonly relied on one-time measures of lake water δ18O, which introduces uncertainties because values may not represent lake water δ18O at the time of cellulose synthesis. We field-tested the use of α18Ocell-lw = 1.028 across a broad hydrological gradient of lakes within the Peace-Athabasca Delta (PAD), west-central Canada, where we constrained cellulose production by periphyton on artificial substrates to bracketed measurements of lake water δ18O collected in late May 2015 and late June 2015. Cellulose-inferred lake water δ18O, calculated using α18Ocell-lw of 1.028 ± 0.0015, corresponded with the range of measured lake water δ18O in 36 of 52 (75%) of our study lakes. Agreement improved to 86% for 'clean cellulose' samples that appeared to be of higher quality (i.e. those with minimal minerogenic material). Mean apparent α18Ocell-lw calculated for clean cellulose samples, using both May lake water δ18O (1.0286) and the May–June mean lake water δ18O (1.0275), did not differ significantly from 1.028, but was significantly, albeit slightly, below 1.028 using June lake water δ18O (1.0264). Closer correspondence of apparent α18Ocell-lw, calculated using May and May–June average lake water δ18O, suggested rapid and early colonization and cellulose production by periphyton. For samples that were a mixture of cellulose and minerogenic material, mean apparent α18Ocell-lw was significantly below 1.028 for these corresponding lake water δ18O measurements, but differences were small and would potentially lead to under-estimation of cellulose-inferred lake water δ18O by only 1–2‰ in sediment stratigraphic records. Overall, strong agreement observed between the cellulose-inferred and directly measured lake water δ18O supports application of α18Ocell-lw = 1.028 ± 0.0015 and lends confidence to paleohydrological reconstructions using this method in lakes of the PAD and elsewhere. [ABSTRACT FROM AUTHOR]

Peatland complexes in the humid highlands of Hawai'i are vital refuges of biodiversity and freshwater resources. Hawaiian peat deposits are also rare repositories of terrestrial ecosystem archives located in an otherwise vast expanse of ocean. We investigated the potential for researching the paleohydrological history of Hawaiian montane peatlands on Kohala, Hawai'i Island through analyses of testate amoebae and Cladocera. Surface peat was collected from a variety of ecohydrological habitats (from water pools to hummocks) and analyzed for modern testate amoeba and cladoceran species relative abundance. We identified 54 morphotype taxa from 21 genera of testate amoebae, 4 taxa and genera of littoral Cladocera, and the common peat rotifer Habrotrocha angusticollis. Testate amoeba diversity and morphotype occurrence mirrored observations from many high-latitude peatland studies. Constrained and unconstrained ordinations support the hypothesis that surface moisture, measured as water-table depth, is an important control on the distribution of testate amoebae and Cladocera in Hawaiian peatlands. Transfer functions relying on weighted-averaging and modern analogs were developed to predict water-table depths from species relative abundance data, and these perform well under leave-one-site-out cross-validation: RMSEP = 9.75–10.3 cm, R2 = 0.56–0.62. Including cladoceran abundance data in the calibration dataset produced modest model improvement: RMSEP = 1–8% and R2 = 2–13%. A weighted-average partial-least-squares transfer function was applied to microfossil assemblages from a 0.5 m-long peat core with a 210Pb decay chronology anchored by ten existing measurements of 210Pb activity and a Bayesian statistical framework. Microfossils were well-preserved in the peat core. The water-table depth optima of an abundant down-core taxa, Hyalosphenia subflava, is not precisely constrained in the calibration data set, but estimates match those of other tropical studies. A reconstruction of water-table depth indicates dry early nineteenth-century conditions, wet conditions in the late 19th to early twentieth centuries, followed by progressive drying for much of the twentieth-century. Testate amoeba composition appears to have been sensitive to severe drought in recent decades. The results signal that assemblages of testate amoebae and Cladocera are useful proxies of Hawaiian peatland paleohydrology and should be considered alongside other archives of Hawaiian environmental history. [ABSTRACT FROM AUTHOR]

Stoco Lake (Tweed, Ontario, Canada) has a history of industrial contamination and is heavily influenced by inflow from the Moira River. Stoco Lake is frequently affected by nuisance algal blooms (including cyanobacteria), which have largely been attributed to cultural eutrophication. To further our understanding of the environmental dynamics of Stoco Lake, we applied paleolimnological techniques to examine long-term trends in subfossil invertebrate assemblages, geochemistry, and inferred trends in whole-lake primary production from a sediment core representing ~ 70 years of environmental history. We examined past trends in Simuliidae abundance, geochemical variables, and historical river flow records to examine past hydrological conditions in Stoco Lake. Inferred whole-lake primary production and sediment core organic content increased between the late 1950s and early 1970s, likely reflecting increased eutrophication (e.g. from agricultural intensification and increased catchment activities), with some stabilization in the post-1970s sediments coinciding with the installation of a sewage treatment plant. The geochemical composition of the core highlighted the decrease in catchment-derived sediment inputs and an increase in percentage of organic content towards the top of the core. In addition, declines in the proportion of As and Ni coincided with the closure of the upstream Deloro Mine Site in the 1960s. Chironomidae and Chaoboridae (Diptera) assemblages indicate expansion of littoral habitat after the 1960s and a general stability of low-oxygen conditions in the hypolimnion over the past ~ 70 years. Several Simuliidae (Diptera: Nematocera) remains, indicators of fluvial conditions rarely discussed in paleolimnological studies, were present at their highest abundances in the pre- ~ 1975 sediments of the core, but disappeared after the early 1990s. Our findings suggest that changes in river flow (discharge, velocity, or seasonality) may have contributed to recent algal blooms. Overall, this study highlights the potential of Simuliidae in paleohydrological studies to help understand the role of river flow on lake conditions. [ABSTRACT FROM AUTHOR]

We evaluated the feasibility of using testate amoebae to infer the quantitative paleohydrology of ombrotrophic mires during their early stages (fen and fen-bog transition) of development. Two transfer functions, one derived from ombrotrophic and the other from minerotrophic mires, were applied to a peat core from an ombrotrophic mire in a taiga region of west Siberia. An ombrotrophic transfer function was applied to the bog stage of mire development. In contrast, ombrotrophic and minerotrophic transfer functions were applied independently to infer water table depth in the fen and fen-bog transition stages. Results of the two approaches for calculating water table depth during the fen and fen-bog transition stages differed by as much as 38 cm for the same peat sample. The main reason for this discrepancy is presence of testate amoeba taxa (e.g. Centropyxis aculeata, Cyclopyxis eurystoma, Cyclopyxis eurystoma v. parvula) in the peat that inhabit both modern ombrotrophic and minerotrophic mires, but differ substantially, in cases by > 20 cm, in terms of their water table depth optima in the ombrotrophic and minerotrophic mire calibration data sets. This difference in inferred water table depth also stems, to a lesser degree, from the fact that the ombrotrophic mire model does not include taxa that inhabited exclusively minerotrophic mires in the fen and fen-bog transition stages. Given these findings, we propose that different models be used for different stages of development, to reconstruct past water table depth in ombrotrophic mires. We recommend use of a model based solely on the ombrotrophic mire data set for the bog stage, and application of a second model based on the minerotrophic mire data set, for the fen and fen-bog transition stages. Application of an ombrotrophic model to the early stages of bog development can yield erroneous paleohydrological reconstructions. [ABSTRACT FROM AUTHOR]

Sedimentological (dry density, micro-facies analysis on thin-slides, X-ray diffraction, layer counting) and elemental analyses (X-ray fluorescence) of a 3.5-m-long sediment core (MAH-B) from saline Lake Maharlou (SW Iran) were used to infer hydrological changes over the last ~ 3800 years. The sediment consists of thin, alternating beds of evaporites (halite, gypsum), carbonates (calcite, aragonite) and detrital minerals (quartz, muscovite, chlorite). We interpret the data with respect to three main hydrologic conditions: (1) nearly complete desiccation of the lake, marked by frequent halite layers, (2) hypersaline conditions marked by gypsum abundance, (3) wet conditions, characterized by high river-borne terrigenous sediment input with high potassium content. Distinct flood layers indicate fluvial activity. From about 3800-2000 cal year BP, terrigenous sediment supply was high, with peaks at 3700-3650, 3500-3450, and 3400-3250 cal year BP. Evaporative conditions were not common. From ca. 2000 cal year BP to present, detrital minerals are less abundant, and the increase in gypsum abundance suggests drier climate with enhanced evaporation. Frequent desiccation events occurred from 1100 to 700 cal year BP. The late Holocene hydrology of Lake Maharlou corresponds well with records of dune formation and phases of river alluviation in Iran and the Arabian Peninsula, and with regional speleothem records. In addition to the influence of climate change on the lake hydrology, ancient humans modified water drainage in the catchment. Periods of subterranean tunnel (qanats) use correspond to dramatic shrinkage of the water body. We propose that climate changes drove long-term water shortages that were enhanced by anthropogenic activities, leading to more frequent desiccation of the lake during the last millennium. [ABSTRACT FROM AUTHOR]

Pranhita-Godavari is one of the major rift basins of peninsular India that was actively filled when the Indian landmass was a part of Gondwanaland, the southern supercontinent. The basin-fill succession of this continental rift basin is characterized mainly by fluvial sandstones and mudstones. In the Early Jurassic this basin hosted a freshwater carbonate deposit characterized by a 20-30 m thick alternation of laminated and massive limestones. The remains and traces of land vertebrates, invertebrates and plants suggest that this limestone serves as one of the rare examples of freshwater carbonate depositing environment within a continental rift basin. The limestone interval is characterized by repeatedly stacked meter-thick laminated and massive carbonate-rich sediments. These sediments are classified into two facies associations representing two main depositional domains of a rift-bound, large, freshwater wetland system: a shallow lacustrine palaeoenvironment and a palustrine paleoenvironment. The former palaeoenvironment is characterized by laminated carbonate facies and the later one is by mottled, nodular and bioturbated limestone. Repeated influx of siliclastics by surface flow into ca-rich water bodies produced the laminated carbonates. Whereas, subaerial modifications and reworking of primary deposits resulted in palustrine carbonates. Vertebrate tracks, evidences of rooting, and the absence of deep basinal facies in this succession along with repetitive stacking of sediments formed in subaqueous and subaerial conditions indicates that the depositional environment was more akin to a modern wetland. This Jurassic carbonate wetland developed in the rift basin when the watershed on the adjacent rift shoulder exposed Proterozoic carbonate rocks that provided the ions necessary for carbonate accumulation. The repeated stacking of meter-scale lacustrine and palustrine carbonates in this limestone reflect long-periodicity fluctuations in water level possibly related to subsidence events of the rift valley. [ABSTRACT FROM AUTHOR]

Ancient lake sediments provide opportunities to reconstruct aquatic ecosystems during previous interglacials. In the summer of 2010, the ICDP project PALEOVAN drilled a complete succession of the lacustrine sedimentary sequence deposited during the last ~600,000 years in Lake Van, eastern Anatolia (Turkey). Previous palaeolimnological analysis of the Lake Van sediment record has shown diatoms to be absent over most of the sequence apart from a short interval during the Holocene. Here, we demonstrate the preservation of additional fragmentary diatom records during Marine Isotope Stage (MIS) 7 (243,000-191,000 years ago; Lisiecki and Raymo in Paleoceanography 20:PA1003, 2005; Jouzel et al. in Science 317:793-796, 2007) and MIS5e (130,000-116,000 years ago; Lisiecki and Raymo 2005; Jouzel et al. 2007), each spanning no more than a few thousand years. Although brief, the presence of contrasting diatom assemblages between these two interglacials provide a snapshot of varying water depth and, by inference, climate. Analysis of MIS7e samples suggests that lake water levels were low after a period when the lake was open (i.e., high lake levels with the presence of an outflow present), resulting in higher salinities and possibly less stable bottom waters, which switched between anoxic and oxic states more frequently. By contrast, the diatom assemblages during MIS5e are characteristic of fresh, relatively nutrient rich waters. This suggests that lake levels were high, that the lake was hydrologically open with an outlet, and that the bottom waters were anoxic for long periods of time. Furthermore, our palaeoconductivity estimates and modelling of the past lake volumes with respect to its salt content support the presence of an outflow. [ABSTRACT FROM AUTHOR]

We reconstructed the paleohydrologic and climatic history of the Lake Neor region, NW Iran, from the end of the late glacial to the middle Holocene (15,500-7500 cal yr BP). Subfossil chironomid and pollen assemblages in a sediment core from a peatland located south of Lake Neor enabled identification of four main hydrologic phases. The period 15,500-12,700 cal yr BP was characterized by a relatively dry climate with an open landscape, suggested by the abundance of Irano-Turanian steppe plants (e.g. Amaranthaceae, Artemisia and Cousinia). Dominance of several shallow-water and semi-terrestrial chironomid taxa (e.g. Pseudosmittia, Smittia/Parasmittia and Paraphaenocladius/Parametriocnemus) during this period is indicative of lower water tables in the wetland. Between 12,700 and 11,300 cal yr BP, chironomid taxa indicate higher wetland water tables, as suggested by the presence of Zavrelia, Chironomus anthracinus/plumosus-type and Micropsectra, which are inhabitants of open-water, lacustrine areas. The open-steppe vegetation remained dominant in the watershed during this time. Increasing wetland moisture could be explained by: (1) cool summers that reduced the evaporation rate; and/or (2) a decrease in duration of the summer dry season. The period 11,300-8700 cal yr BP was characterized by lower wetland moisture, contemporaneous with a delay in the expansion of deciduous forest, suggesting persistent dry climate conditions throughout the beginning of the Holocene, which may have been related to the intensified seasonality of precipitation. Around 8700 cal yr BP, higher wetland water levels, inferred from chironomids, occurred simultaneously with the onset of regional deciduous forest expansion, probably caused by a shortening of the summer dry period. We concluded that chironomids are appropriate paleoecological proxies to investigate global and local hydrologic variability in the Middle East. [ABSTRACT FROM AUTHOR]

Shorelines that formed in closed watershed-lake systems record past climate conditions. A simple monthly water balance model was used to explore the link between past climates, paleoclimate proxies, and the hydrologic system response of a closed watershed-lake system in the Great Basin, USA. The model was applied at a high spatial resolution and calibrated with available modern hydroclimate and watershed data and then used with existing paleolake shoreline estimates to investigate how climate and hydrologic conditions in the late Pleistocene differed from modern conditions. A range of climate conditions, ∆T (0 to −8 °C) and ∆P (1.9-2.4) from the modern climate, resulted in steady model simulations of the late Pleistocene lake highstand. Modeling results also indicate the watershed-lake system response is much more sensitive to changes in precipitation than to changes in temperature, and that the range of possible combinations of these variables can be reduced significantly when the results are compared with an independent modeling study that inferred paleoclimate conditions from glacial moraines in the Wind River Range near the eastern portion of the Great Basin. The modeling effort also revealed that physiographic heterogeneities and seasonality play a significant role in how the watershed-lake system responds to changes in precipitation and temperature, highlighting the importance of simulating the system behavior with an appropriate degree of spatial resolution. The significance of model calibration and performance evaluation over the modern period was demonstrated through a comparison of the calibrated model results with those obtained using default parameter values with the original model. [ABSTRACT FROM AUTHOR]

In this study, compound-specific hydrogen isotope values of n-alkanes ( n-alkane δD) in a sediment core that dates to 18.5 cal ka BP were used to reconstruct the paleohydrological processes that couple glacial meltwater and precipitation at Lake Pumoyum Co, on the southern Tibetan Plateau. The lowest lake level, from 18.5 to 15.0 cal ka BP, may reflect both less glacial meltwater and less precipitation entering the lake. Glacial meltwater generally increased from 15.0 to 7.2 cal ka BP and decreased after 7.2 cal ka BP, whereas precipitation generally increased from 15.0 to 10.2 cal ka BP, decreased from 10.2 to 7.2 cal ka BP, then remained stable and moderate to the present. Comparisons of our results with records in adjacent areas and beyond suggest that the glacial meltwater supply during the past 15 cal ka corresponds well with changes in the Indian Summer Monsoon (ISM), which are driven by summer insolation at millennial time scales, whereas the precipitation does not match well with ISM changes during the Holocene. Therefore, paleohydrological processes at Lake Pumoyum Co have shown complex responses to climate change. Overall, our results emphasize that reconstruction of paleohydrological processes of lakes on the Tibetan Plateau should be carried out with caution because of glacial meltwater input. [ABSTRACT FROM AUTHOR]

The Sahara desert oasis of Ounianga Serir in northern Chad comprises seven shallow but perennial lakes, which are maintained against an extremely negative local moisture balance by continuous inflow of fossil groundwater from the Nubian Sandstone Aquifer. Here we analyze the lithostratigraphy, charcoal, and fossil mollusks in short, dated sediment cores from three of these lakes (Edem, Hogou, and Agouta) to assess the hydrological and environmental stability of these unique aquatic ecosystems over the last few centuries. Our results indicate that the studied lakes remained relatively stable and fresh over the past 200-600 years, confirming the dominant and constant nature of groundwater input, preventing desiccation. Modest lake-level fluctuations did occur but were not synchronous between the lakes, arguing against climate variability being their primary cause. Likely, their site-specific history was determined by variations in groundwater through-flow, influenced by migration of sand dunes separating the lakes. The desert setting is responsible for characteristic lacustrine sediments comprised of carbonate mud with silt and sand. The associated fossil assemblages of freshwater mollusks suggest that the present-day mollusk fauna of Ounianga Serir may be more species-rich than previously thought. Our data expand the known distribution of the Palaearctic snail Valvata nilotica markedly south and westward into the central Sahara. [ABSTRACT FROM AUTHOR]

This study aimed to: (1) investigate intra-sample variability in the stable isotope composition (δC and δO values) measured in several individual mollusc shells; and (2) determine the optimum number of individual mollusc shells required to obtain stable isotope values representative of the mean climate signal for a sediment sample. Seven hundred and six gastropod shells were analysed, representing eight species. These eight species were most abundant and consistently present in the sediment sequence of the Paddenluch outcrop, Brandenburg, northeast Germany. Significant differences between minimum and maximum δC and δO values of the shells were recorded within all sediment samples and for all analysed species. Within the sediment samples, the greatest mean variability in both δC and δO values was found for Hippeutis complanatus, 5.84 and 5.23 ‰, respectively. The greatest intra-specific variability in C and O isotope values within individual sediment samples, however, was 10.2 and 6.8 ‰, respectively. Significant differences between minimum and maximum δC and δO values of individual mollusc shells within the same sediment sample are probably the result of population isotope variability, variations in species life span, thickness of the sediment sample, sediment accumulation rate, and environmental fluctuations during the time span when the sediment was deposited. Shells were randomly selected to determine the optimum number of shells necessary to obtain stable isotope values that are representative of the mean climate signal, from a 1-cm sample of sediment. For each layer of the Paddenluch sediment sequence, 15 or more shells (N ≥ 15) was the required sample size to provide representative isotope values and yield a reliable mean isotope value. Sample sizes with fewer shells displayed more variable mean δC and δO values. Stable isotope composition of the analyzed molluscs was species-specific, with differences in mean δC and δO values of 2.5 and 3 ‰, respectively. This illustrates the need to use mono-specific samples throughout a sediment sequence to generate reliable data. [ABSTRACT FROM AUTHOR]

We present a testate amoebae training set for building a paleohydrology transfer function. Ninety-one samples were collected from three Sphagnum peatlands in the Lesser Khingan Mountains, NE China. Redundancy analysis revealed that depth to the water table (DWT) and moisture content (% water) are the primary factors that control testate amoebae assemblages. Transfer functions for prediction of these two environmental variables were developed. The root mean square error (RMSEP) for DWT and moisture content were 6.74 cm and 1.49 %, respectively, assessed with 'leave-one-out' cross validation. We applied a more robust cross validation method for clustered structure data, 'leave-one-site-out,' and the RMSEP of the best performance model increased to 6.90 cm and 1.67 %, but all models still had predictive power. The effect of uneven sampling was tested using new statistical approaches. Greater numbers of samples in the middle range of the gradient yielded smaller RMSEP values than did samples from the extreme wet and dry ends of the spectrum, where there were fewer samples. Our results indicate this training set is a potentially important tool for paleoenvironmental reconstruction in the Lesser Khingan Mountains, NE China. It will contribute to understanding climate change, particularly past monsoon activity, in this region. [ABSTRACT FROM AUTHOR]

Seismic, pollen, stable isotope and lithologic stratigraphies of Sluice Pond, northeastern Massachusetts, were investigated to reconstruct local climate conditions from the latest Pleistocene to present. We present a new lake-level curve, constrained largely by acoustic reflectors and well-dated sediment cores from the deep basin and margin of the lake. Bulk δS data from the basin core provide valuable information regarding anoxia and water-column stratification. The lake-level history is corroborated with pollen-based, transfer-function-derived reconstructions of temperature and precipitation from the basin core. The lower stratigraphy reveals a time of cold/dry climate from ca. 11.7-8.2 ka BP (1 ka = 1,000 cal yr), with a minor lake-level increase centered at ca. 11.0 ka BP. An increase in regional temperature/moisture is apparent in sediments younger than 8.2 ka BP. A warm/dry climate is reconstructed from ca. 5.1-3.5 ka BP, concomitant with the well-established regional Tsuga (eastern hemlock) minimum. Sediments deposited since 3.5 ka BP reveal a general deepening of the pond and organic-rich conditions, with another minor dry episode from ca. 2.0-1.3 ka BP. Uppermost sediments record anthropogenic disturbance. The hydroclimate variability inferred from the Sluice Pond sediment record is consistent with previous reconstructions of lake level and vegetation in the southern portion of the northeastern US. It is not, however, consistent with reconstructions from locations farther north, many of which possess evidence of a dry period ca. 9.0-5.0 ka BP. The likely explanation for this discrepancy lies in air mass distribution associated with the position and amplitude of the circumpolar vortex throughout the Holocene. This new record of Holocene regional hydroclimate variability adds to the spatial coverage of existing reconstructions, and helps constrain forcings associated with such variability. [ABSTRACT FROM AUTHOR]

Unlike other aquatic continental ecosystems such as lakes, small coastal brooks have not been used as indicators of anthropogenic or climatic impacts. Our study addresses reconstructing the evolution of coastal brooks in the southwest of Spain from the early seventeenth century to the end of the twentieth century using fieldwork, remote sensing, historical sources and microrelief. These brooks have had a continuous regression, losing 84.7 % of their length since 1630 AD. From the seventeenth century to the beginning of the twentieth century, climatic factors were responsible for the filling and siltation of the thalweg of brooks with sandy sediments of eolian origin. The alternation of dry and humid periods during the Little Ice Age in southern Spain favoured the mobilisation of sandy sediments in a process of secondary dunification, which was initiated during the eighteenth century and prominent at the end of the Little Ice Age. This process has coincided with a loss of water availability or an increase of aridity in some lakes and lagoons of southwestern Europe at the end of the nineteenth century. However, during the second half of the twentieth century, the average annual rate of thalweg regression almost quadrupled to 432.2 m year mainly due to anthropogenic impacts associated with logging. These changes coincide with the mobilisation of sandy sediment and the erosion of coastal brooks in southwestern Portugal and other continental aquatic ecosystems in southwestern Spain. Therefore, we believe that changes in small coastal brooks can be used as indicators of anthropogenic and climatic impacts and, in the future, as sentinels to study the effects of climatic change just as lakes, reservoirs and rivers are considered. [ABSTRACT FROM AUTHOR]

This study focuses on Holocene monsoon dynamics on the central Tibetan Plateau (TP) inferred using a sediment record from Lake Nam Co. A high-resolution (decadal) multi-proxy approach, using geochemical, micropaleontological, and sedimentological methods was applied. Fifteen AMS-C ages were used to establish the chronology, assuming a reservoir effect of 1,420 years. Our results point to a first strong monsoonal pulse at Lake Nam Co ~11.3 cal ka BP, followed by colder and drier conditions until ~10.8 cal ka BP. A warm and humid climate from ~10.8 to ~9.5 cal ka BP is related to a strong summer monsoon on the central TP, triggering a lake-level highstand at ~9.5 cal ka BP. Declining minerogenic input after ~9.5 cal ka BP indicates less moisture availability until ~7.7 cal ka BP. Following stable conditions between ~7.7 and ~6.6 cal ka BP, a warm and wet climate is inferred for the time span from ~6.6 to ~4.8 cal ka BP. A change towards drier conditions after ~4.8 cal ka BP points to a weakening of the Indian Ocean Summer Monsoon on the central TP, further diminished after ~2.0 cal ka BP. A short-term wet spell occurred from ~1.5 to ~1.3 cal ka BP. By comparing the results derived from Lake Nam Co with several lacustrine records from the central, northern, and eastern TP, a similar but not synchronous pattern of monsoon-driven paleoenvironmental change is observed. Although the general trend of lake and catchment evolution on the TP during the Holocene is also reproduced in this record, pronounced spatial and temporal offsets with respect to distinct climate events were detected, suggesting periods of non-uniform moisture and temperature evolution. [ABSTRACT FROM AUTHOR]

A significant relationship between the distribution and abundance of chironomids and water depth has long been recognized. Few studies on this topic, however, have been carried out in arid regions where the chironomid community is usually controlled by water salinity. Bosten Lake, northwest China, the largest inland freshwater lake (~1,260 km) in the country, provides a unique opportunity to investigate this relationship in an arid region. A total of 42 surface sediment samples from water depths of 0.9-17.0 m, and 12 chironomid taxa, were used in the analysis. The first principal component analysis (PCA) axis explained 59.3 % of the variance in the chironomid assemblage and there was a significant correlation between PCA axis 1 scores and water depth (R = 0.84, P < 0.001). The chironomid assemblages change significantly at 8.0 m water depth. This threshold corresponds to an abrupt change in the basin slope and the spatial distribution of aquatic vascular plants. Redundancy analysis showed that abundances of Chironomus plumosus-type, Microchironomus and Cryptochironomus are positively correlated with water depth, whereas abundances of Tanytarsus, Polypedilum nubifer-type, Cricotopus and Psectrocladius sordidellus-type are negatively correlated with water depth. These ecological relationships are supported by published data. Qualitative chironomid-inferred changes in lake level and diatom-inferred changes in salinity from sediment core BSTC001 were compared. Close agreement in trends for these two variables validates the use of chironomid assemblages to study palaeo-hydrological variability in this westerlies-dominated, arid region of central Asia. [ABSTRACT FROM AUTHOR]

Sediment layers of uniform age within lakes (isochrones) and their patterns reflect accumulation processes which can be correlated with hydrologic conditions in lake basins. The sedimentary archives in three small dystrophic lakes in northeastern Poland are described based on the correlation of local pollen assemblage zones in cores that were collected from the centers and margins of each lake. Past regional groundwater levels could be discerned from the shape of the isochrones, whether plane parallel or concave in configuration in relation to the lake basin shape. The concave configuration of the isochrones in the studied lakes shows that regional groundwater levels remained mostly high and stable throughout their history. The water levels in each lake during the Late Glacial and throughout the Holocene were different and no single, common water-level fluctuation pattern was identified in the three water bodies. The lack of such a finding suggests that the lakes are influenced dominantly by local hydrological factors. [ABSTRACT FROM AUTHOR]

The stratigraphic, geochemical, and organic matter study of the late Holocene San Nicolás succession of the Cauca paleolake (Santa Fé-Sopetrán pull-apart basin) in the middle Cauca Valley, northern Colombia, suggests that it was deposited in a ria lake environment, at sedimentary accumulation rates in excess of 600 cm ky between ~3500 and ~500 yr BP. Laminated deposition occurred, first under igapo (black-water), and then under varzea (white-water) conditions. The transition occurred ca. 3000 yr BP, a time of major change in El Niño/Southern Oscillation (ENSO) behavior in the Cariaco Basin, thus reflecting the southern migration of the intertropical convergence zone and intensified rain upstream the Cauca Valley. A second, but less conspicuous change occurred ca. 2000 yr BP, which apparently corresponds to the intensified and/or more frequent ENSO activity in the Galapagos Islands. Our contribution describes, for the first time, a ria lake sedimentary succession from the northern Andes and demonstrates the high potential of these hitherto undervalued deposits for the reconstruction of the paleohydrological history of the northern Andes. [ABSTRACT FROM AUTHOR]

Water depth is an important environmental variable that explains a significant portion of the variation in the chironomid fauna of shallow lakes. We developed site-specific and local chironomid water-depth inference models using 26 and 104 surface-sediment samples, respectively, from seven kettlehole lakes in the Plymouth Aquifer, southeast Massachusetts, USA. Our site-specific model spans a depth gradient of 5.6 m, has an $$ {\text{r}}_{\text{jack}}^{2} $$ of 0.90, root mean square error of prediction (RMSEP) of 0.5 m and maximum bias of 0.7 m. Our local model has a depth gradient of 11.7 m, an $$ {\text{r}}_{\text{jack}}^{2} $$ of 0.71, RMSEP of 1.6 m and maximum bias of 2.9 m. Principal coordinates of neighbourhood matrices (PCNM) analysis showed that there is no influence of spatial autocorrelation on the site-specific model, but PCNM variables explained a significant amount of variance (4.8%) in the local model. This variance, however, is unique from the variance explained by water depth. We applied the inference models to a Holocene chironomid record from Crooked Pond, a site for which multiple, independent palaeohydrological reconstructions are available. The chironomid-based reconstructions are remarkably similar and show stable water depths of ~5 m, interrupted by a 2-m decrease between 4,200 and 3,200 cal a BP. Sedimentological evidence of water level fluctuations at Crooked Pond, obtained using the so-called Digerfeldt approach, also shows a drop in water depths around that time. The period of reconstructed lower water levels coincides with the abrupt decline in moisture-dependent hemlock in this region, providing further evidence for this major palaeohydrological event. The site-specific model has the best performance statistics, but the high percent abundance of fossil taxa from the long core that are absent or rare in the training set makes the site-specific reconstruction unreliable for the period before 4,400 cal a BP. The fossil taxa are well represented in the local model, making it the preferred inference model. The strong similarity between the chironomid-based reconstructions and the independent palaeohydrological records highlights the potential for using chironomid-based inference models to determine past lake depths at sites where temperature was not an influencing factor. [ABSTRACT FROM AUTHOR]

Hala Lake is located in the Qilian Mountains, Qinghai Province, China, at 4,078 m a.s.l. Its sediments contain an archive of climate and hydrologic changes during the Late Quaternary, as it is located close to the area influenced by the East-Asian summer monsoon and westerly-driven air masses. Sedimentation patterns and depositional conditions within the lake were investigated using eight sediment cores from different water depths, and this information was used to evaluate the feasibility of using a single core to reconstruct past climate and hydrological conditions. Long core H7, from the center of the lake (65 m water depth) and core H8 from a western, near-shore location (20 m water depth), were compared in detail using sediment composition and geochemical data (X-ray fluorescence, loss-on-ignition and CNS analysis). Age models were constructed using 17 AMS radiocarbon dates and indicate negligible reservoir error for sediments from the lake center and ~1,000 year errors for the near-shore sediment core. Cores H1-H5 and HHLS21-1 revealed a sediment succession from sand and silty clay to laminated clay on the southern side of the lake. Undisturbed, finely laminated sediments were found at water depths ≥15 m. Core H5 (2.5 m long), from 31 m water depth, yielded abundant green algal mats mixed with clayey lake deposits and was difficult to interpret. Algae occurred between 25 and 32 m water depth and influenced the dissolved oxygen content of the stratified lake. Comparison of cores H7 and H8 yielded prominent mismatches for different time periods, which may, in part, be attributed to internal lacustrine processes, independent of climate influence. We thus conclude that data from a single sediment core may lead to different climate inferences. Common shifts among proxy data, however, showed that major climate shifts, of regional to global significance, can be tracked and allow reconstruction of lake level changes over the last 24,000 years. Results indicate advance of glaciers into the lake basin during the LGM, at which time the lake experienced lowest levels, 25-50 m below present stage. Stepwise refilling began at ca. 16 kyr BP and reached the −25 m level during the Bølling/Allerød warm phase, ca. 13.5 kyr BP. A desiccation episode falls within the Younger Dryas, followed by a substantial lake level rise during the first millennium of the Holocene, a result of climate warming, which promoted glacier melt. By ca. 7.6 kyr BP, the lake reached a stable high stand similar to the present level, which persisted until ca. 6 kyr BP. Disturbed sediments in core H7 indicate a single mass flow that was most likely triggered by a major seismic event ~8.5 kyr BP. Subsequent lake development remains unclear as a consequence of data mismatches, but may indicate a general trend to deteriorating conditions and lake level lowstands at ca. 5.0-4.2, 2.0 and 0.5 kyr BP. [ABSTRACT FROM AUTHOR]

We used 39 surface samples from Marcella Lake, Yukon Territory, to examine the distribution of chironomid head capsules in relation to depth and to develop a site-specific (intralake) inference model for reconstructing past lake levels. Ten of the 34 most-frequently occurring taxa encountered in the surface-sediment samples are significantly related to depth. We then applied the site-specific inference model and a previously developed regional model to samples from deep- and shallow-water cores from Marcella Lake. The inferences were compared to an independent Digerfeldt-type reconstruction of lake level history and to moisture inferences drawn from pollen data. Although the site-specific model was good in having better performance statistics than the regional model, it was bad at producing depth reconstructions because most samples from the long cores lacked suitable analogues in the site-specific training set. None of the chironomid-based reconstructions was a good match to the Digerfeldt-type reconstruction. Inconsistencies remain between the paleohydrological inferences derived from the chironomid depth models, the Digerfeldt-type reconstruction and pollen-inferred reconstructions of past moisture regimes. [ABSTRACT FROM AUTHOR]

Stratigraphic variations in diatom composition and phytolith abundance in a sediment core from a small, hydrologically isolated waterbody, Lake Nhauhache, Mozambique, provide evidence of water-level fluctuations over the past ~2,300 years. Ten AMS radiocarbon dates on bulk sediment samples show that the lake came into existence about 2,300 years ago and that it has dried out since then, but only for brief time periods. Changes in the diatom assemblage composition indicate that lake level fluctuated in response to shifting humidity conditions. The changes reflect wetter conditions ca. 300 BC-AD 800, more variable conditions between AD 800 and 1150, a distinct dry phase within the time span AD 1150-1700 and a return thereafter to more humid conditions until present. There is general agreement between the Lake Nhauhache record and other records from the Southern Hemisphere summer rainfall region. This suggests that sediments from small interdunal lakes, which are abundant along the coast of southern Africa, provide reliable, regional paleoenvironmental information about an area from which more such data are needed. [ABSTRACT FROM AUTHOR]

Holocene environments have been reconstructed by sedimentological, mineralogical and organic geochemical analysis of a 270-cm core from Santa Ninha Lake, a floodplain lake in lower Amazonia. Dated by fourteen AMS-radiocarbon dates, the sediment core has a basal age of 5,600 cal years BP and different sedimentary units were identified. These units document various hydrologic phases in the evolution of this lake. Reduced Amazon River influence, with reduced high-water levels of the river, characterized the period between 5,600 and 5,100 cal years BP. Comparison with other Amazonian and Andean paleoclimate studies point to a dryer climate during this phase. After 5,100 cal years BP coarse sediments and quartz increase which suggest a higher inflow of the Amazon River. Between 5,000 and 2,300 cal years BP the coarse sediments and quartz remain high but the organic carbon showed the lowest values. The riverine inflow caused dilution of the organic material produced in the lake and consequently low rates of carbon flux in these phases were recorded. These results show that the hydrodynamics of the Amazon River strongly influence the behavior, productivity and consequently the sedimentation process in the floodplain lakes. [ABSTRACT FROM AUTHOR]

Opal, organic C and N contents, and organic δC and δN stable isotopes were analyzed on a sedimentary sequence spanning the past ~12,000 years from Dune Lake, a shallow groundwater-fed lake in the boreal forest region of central interior Alaska. The chronology, based on Pb and 15 AMS radiocarbon dates on terrestrial materials, indicates that 5 m of biogenic sediment accumulated following dune stabilization at ~10,000 cal yr BP. Previous studies on lake level and pollen were synthesized with these data to assess Holocene changes in hydrogeology and climate. Variability in groundwater level and flux has a strong control on lake level and are negatively correlated with the δC of organic matter produced within the lake. This relationship results from the input of groundwater with high pCO and with dissolved inorganic carbon depleted in C, which subsequently affects lake phytoplankton δC signatures. A rapid rise in lake level between ca. 11,000 and 9,500 cal yr BP coincided with stabilization of the dune field adjacent to the lake and expansion of vegetation around the lake, including white spruce. Organic δC values are relatively low and constant between about 10,000 and 6,000 cal yr BP, and then steadily increase until about 2,000 cal yr BP, suggesting a pattern of high followed by dropping lake levels generally consistent with results from core-transect studies. Higher-frequency fluctuations of 2-3 ‰ in δC are common, and suggest variability in aspects of the lake-carbon cycle over multi-decadal timescales. Recent trends in groundwater and lake level, river discharge, and precipitation suggest an important role for wintertime precipitation in the regional groundwater system. The unusual hydrology of this system relative to most other lakes studied for paleoclimate in this region provides a novel insight into different seasonal aspects of Alaskan paleoclimatology. The record is consistent with a general long-term decrease in wintertime precipitation, possibly accompanied by an increase in permafrost extent, over the Holocene. [ABSTRACT FROM AUTHOR]

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800-7,200 (9,900-8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world's largest freshwater resources. [ABSTRACT FROM AUTHOR]

Multiple proxies record aridity in the northern Great Lakes basin ~8,800-8,000 cal (8,000-7,200) BP when water levels fell below outlets in the Michigan, Huron and Georgian Bay basins. Pollen-climate transfer function calculations on radiocarbon-dated pollen profiles from small lakes from Minnesota to eastern Ontario show that a drier climate was sufficient to lower the Great Lakes, in particular Georgian Bay, to closed basins. The best modern climate analog for the early Holocene late Lake Hough stage in the Georgian Bay basin is Black Bass Lake near Brainerd MN. Modern annual precipitation at Brainerd is ~35% lower than at Huntsville ON, in the Georgian Bay catchment; warmer summers and colder, less snowy winters make Brainerd drier than the Georgian Bay snow belt. These values parallel transfer function reconstructions for the early Holocene from pollen records at five small lakes in the Georgian Bay drainage basin. Higher evaporation and evapotranspiration due to greater seasonality during the early Holocene produced a deficit in effective moisture in Georgian Bay that is recorded by the jack/red pine pollen zone that spanned ~8,800-8,200 cal (8,000-7,500) BP. This deficit drove late Lake Hough ~5 m below Lake Stanley in the Huron basin, following diversion of Laurentide Ice sheet meltwater from the Great Lakes basin. The level of Georgian Bay largely depends not on fluvial input from its own drainage basin, but rather from Lake Superior, where the early Holocene moisture deficit was greater. Reconstruction of paleoclimates in Minnesota, northwestern Ontario and Wisconsin produced a closed lake in the Superior basin, which removed the main water input to Georgian Bay. Once the inflow through the St. Marys River was reduced and inflow from other tributary streams was adjusted for isostatic and climatic differences, input was <5% of modern values. Consequent high evaporation rates produced a significant fall in lake level in the Georgian Bay basin and a negative water budget. This reduction in basin supply, together with the high conductivity of stagnant water in late Lake Hough inferred from microfossils in lowstand sediments, peaked at the end of the jack/red pine zone, ~8,300-8,200 (7,450 ± 90) BP. These major hydrologic changes resulting from climate change in the recent geologic past draw attention to possible declines of the Great Lakes under future climates. [ABSTRACT FROM AUTHOR]

The evolution of the early Great Lakes was driven by changing ice sheet geometry, meltwater influx, variable climate, and isostatic rebound. Unfortunately none of these factors are fully understood. Sediment cores from Fenton Lake and other sites in the Lake Superior basin have been used to document constantly falling water levels in glacial Lake Minong between 9,000 and 10,600 cal (8.1-9.5 ka) BP. Over three meters of previously unrecovered sediment from Fenton Lake detail a more complex lake level history than formerly realized, and consists of an early regression, transgression, and final regression. The initial regression is documented by a transition from gray, clayey silt to black sapropelic silt. The transgression is recorded by an abrupt return to gray sand and silt, and dates between 9,000 and 9,500 cal (8.1-8.6 ka) BP. The transgression could be the result of increased discharge from Lake Agassiz overflow or the Laurentide Ice Sheet, and hydraulic damming at the Lake Minong outlet. Alternatively ice advance in northern Ontario may have blocked an unrecognized low level northern outlet to glacial Lake Ojibway, which switched Lake Minong overflow back to the Lake Huron basin and raised lake levels. Multiple sites in the Lake Huron and Michigan basins suggest increased meltwater discharges occurred around the time of the transgression in Lake Minong, suggesting a possible linkage. The final regression in Fenton Lake is documented by a return to black sapropelic silt, which coincides with varve cessation in the Superior basin when Lake Agassiz overflow and glacial meltwater was diverted to glacial Lake Ojibway in northern Ontario. [ABSTRACT FROM AUTHOR]

Exposures along the lower Kaministiquia River (near Thunder Bay, Ontario, Canada) provide insight into early Holocene lake level fluctuations and paleoenvironmental conditions in the northwestern Lake Superior basin. These exposures show at least two large paleochannels which were downcut into offshore sediments, and were later filled with >2 m of sand, ~3 m of rhythmically laminated silt and clay, and ~6 m of interbedded silt and sand. Buried by the rhythmically laminated silty clay unit is a well-preserved organic deposit with abundant plant macrofossils from terrestrial and emergent taxa, including several upright tree trunks. Three AMS radiocarbon ages were obtained on wood and conifer cones from this deposit: 8,135 ± 25 (9,130-9,010 cal), 8,010 ± 25 (9,010-8,780 cal), and 7,990 ± 20 (8,990-8,770 cal) BP. This sequence records an early postglacial high-water phase, followed by the Houghton lowstand, and reflooding of the lower Kaministiquia River Valley. The drop in lake level associated with the Houghton phase forced the ancestral Kaministiquia River to downcut. By ~9,100 cal (~8,100) BP, older channels eroded into subaqueous underflow fan deposits in the Thunder Bay area near Fort William Historical Park (FWHP) were abandoned and colonized by a Picea- Abies- Larix forest. Based on stratigraphic data corrected for differential isostatic rebound, the lake was below the Sault Ste. Marie bedrock sill between at least 9,100 cal (8,100) and 8,900 cal (8,000) BP. Shortly after 8,900 cal BP, the lake quickly rose and buried in situ lowland vegetation at FWHP with varved sediments. We argue that this transgression was due to overflow from glacial Lakes Agassiz or Ojibway associated with the retreat of the Laurentide Ice Sheet from the Nakina moraine and/or the Cochrane surge margins in the Hudson Bay Lowlands. A continued rise in lake level after 6,420 ± 20 (7,400 cal) BP at FWHP may record uplift of the North Bay outlet above the Sault Ste. Marie bedrock sill and the onset of the Nipissing transgression in the Lake Superior basin. [ABSTRACT FROM AUTHOR]

Variations in the location and strength of convection in the Western Pacific Warm Pool (WPWP) have a profound impact on the distribution and amount of global rainfall. Much of the variability in WPWP convection is attributed to variations in the El Niño-Southern Oscillation, for which the long-term trends and forcing mechanisms remain poorly understood. Despite the importance of WPWP convection to global climate change, we have very few paleohydrological reconstructions from the region. Here we present a new paleolimnologic and paleohydrologic record spanning the past 1,400 years using a multi-proxy dataset from Lake Logung, located in East Java, Indonesia that provides insights into centennial-scale trends in warm pool hydrology. Organic matter δC data indicate that East Java became wetter over the last millennium until ca. 1800 Common Era (CE), consistent with evidence for the southward migration of the Intertropical Convergence Zone (ITCZ) during this time. Superimposed on this long-term trend are four decade- to century-scale droughts, inferred from organic matter δC and calcite abundance data. They are centered at 1030, 1550, 1830, and 1996 CE. The three more recent droughts correlate with hydrologic anomalies documented in other proxy records from the WPWP region on both sides of the equator, and the two most recent droughts correlate in time with historically documented periods of multiple, intense El Niño events. Thus, our record provides strong evidence that century-scale hydrologic variability in this region relates to changes in the Walker Circulation. Human activity within the lake catchment is apparent since 1860 CE. [ABSTRACT FROM AUTHOR]

The frequency of nuisance algal blooms has been increasing during the last two decades in the shallow, headwater East Pond (Smithfield, Maine, USA). Meanwhile, the hydrologically linked North Pond has not experienced an increase in algal blooms, despite similar morphometry and higher external nutrient loads. Possible explanations for this difference include stronger trophic cascade effects from planktivorous white perch ( Morone americana) in East Pond as well as differences in phosphorus (P) release from the sediments of these two lakes. We conducted a paleolimnological investigation of these two lakes to assess whether sedimentary evidence supported trophic cascade effects based on cladoceran ephippia size, diatom fossils, and fossil pigments or biogeochemical controls based on potential sedimentary P release as the primary driver of these increased algal blooms in East Pond. At the time of white perch introduction (~1930-1950), ephippia size increases in East Pond, although no changes are observed in either diatom abundance or trends in the algal pigments. Instead, algal pigments increase in recent decades (~1980 to present) along with an increase in diatom taxa with higher TP optima These results suggest that predation by white perch is not resulting in top-down effects on algal abundance in East Pond, as predicted by the trophic cascade hypothesis. While the P content of sediments from both lakes is relatively equal, the releasable P in the top 10 cm of sediment in East Pond constitutes a greater percentage of the P extracted. Also, North Pond sediments exhibit a greater capacity to permanently bury P via the mechanisms of sorption to Al(OH) and a slower mineralization of organic P compounds. The results of this investigation suggest that the ultimate driver of the recent algal blooms in East Pond is internal P release from the sediments instead of trophic cascade effects. [ABSTRACT FROM AUTHOR]

The Mytilinii Basin, eastern Samos Island, Greece, is one of many basins that developed in southeastern Europe during the Upper Neogene. The oldest lacustrine portion is of Late Miocene age, and besides tuffs, includes bituminous limestones, marlstones, dolostones and porcelanites of the Pythagorion Formation, and the limestones and diatomites of the overlying Hora Beds. Younger sedimentary rocks of Turolian through Pliocene age partially covered the Pythagorion Formation and Hora Beds (PFHB). Diatom floras range from well preserved to highly corroded and from sparse to abundant. The main taxa include Cyclotella aegaea, C. aegaea var. pythagoria, an unidentified Cyclotella and Nitzschia frustulum, and less common Epithemia turgida, E. reichelti, Synedra ulna, Tryblionella granulata, Encyonema silesiaca, Diploneis ovalis and Cocconeis placentula. Chrysophyte cysts, Hydrobia molluscs and trace fossils occur sporadically. The environmental evolution of the PFHB can be divided into three major stages. Fluctuating shallow to deeper waters in a saline lake characterized Stage A. Saline lake and playa environments with evidence for frequent earthquake events in the form of convolute bedding, drape folds and brecciated sediments characterized Stage B. During Stage C, the lake may have partially or completely split into two separate lakes. In the southeast, a saline playa passed laterally into a deeper-water lake. Locally, fresher-water ponds occurred. Subsequently, a deeper, possibly oligotrophic lake developed. In contrast, a saline lake with abundant diatoms formed in the northwest of the basin, in which diatom blooms led to whiting events and deposition of carbonate laminae. Cyclotella dominated the early floras in this water body, with later assemblages being co-dominated by Cyclotella and Nitzschia frustulum, possibly reflecting seasonal changes. Sedimentation was terminated by uplift and (or) increasing aridity associated with the Messinian Salinity Crisis. [ABSTRACT FROM AUTHOR]

Elemental and isotopic compositions of organic matter in surficial sediments from five transects across Lagoa do Caçó (Brazil) were analyzed to identify the depth-related processes that affect the production and deposition of sedimentary organic matter in this shallow tropical lake. Each of four transverse transects began at a margin dominated by aquatic macrophytes ( Eleocharis), crossed the central deep part of the lake, and terminated in the opposite, macrophyte-dominated margin. In each transect, TOC concentrations, C/N ratios, and δC values decreased between 0 and 4 m, whereas δN values increased. The variables remained stable in sediment from 4 m water depth to the center of the lake at 10 m. The depth-related patterns reflect differences in both the delivery and the deposition of organic matter in the lake. Organic matter is produced in abundance in the marginal area by emersed and submerged macrophyte vegetation that diminishes with depth and disappears at 4 meters. After the disappearance of macrophytes, organic matter is produced at low rates principally by open-lake phytoplankton. Drawdown of dissolved oxygen is high in the lake margins, but it is low in the oligotrophic open waters of the lake. Preservation of organic matter is consequently better in sediments of the lake margins than in deep waters. The depth-related pattern of organic matter delivery and deposition in the sediments of Lagoa do Caçó, in which water levels are sensitive to groundwater fluctuations, shows that the elemental and isotopic compositions of sediment organic matter can provide a record of changes in the paleohydrology of this and other similar shallow lake systems. [ABSTRACT FROM AUTHOR]

Sequences of paleo-shorelines and the deposits of rift lakes are used to reconstruct past climate changes in East Africa. These recorders of hydrological changes in the Rift Valley indicate extreme lake-level variations on the order of tens to hundreds of meters during the last 20,000 years. Lake-balance and climate modeling results, on the other hand, suggest relatively moderate changes in the precipitation-evaporation balance during that time interval. What could cause such a disparity? We investigated the physical characteristics and hydrology of lake basins to resolve this difference. Nine closed-basin lakes, Ziway-Shalla, Awassa, Turkana, Suguta, Baringo-Bogoria, Nakuru-Elmenteita, Naivasha, Magadi-Natron, Manyara, and open-basin Lake Victoria in the eastern branch of the East African Rift System (EARS) were used for this study. We created a classification scheme of lake response to climate based on empirical measures of topography (hypsometric integral) and climate (aridity index). With reference to early Holocene lake levels, we found that lakes in the crest of the Ethiopian and Kenyan domes were most sensitive to recording regional climatic shifts. Their hypsometric values fall between 0.23–0.29, in a graben-shaped basin, and their aridity index is above unity (humid). Of the ten lakes, three lakes in the EARS are sensitive lakes: Naivasha (HI = 0.23, AI = 1.20) in the Kenya Rift, Awassa (HI = 0.23, AI = 1.03) and Ziway-Shalla (HI = 0.23, AI = 1.33) in the Main Ethiopian Rift (Main Ethiopian Rift). Two lakes have the graben shape, but lower aridity indices, and thus Lakes Suguta (HI = 0.29, AI = 0.43) and Nakuru-Elmenteita (HI = 0.30, AI = 0.85) are most sensitive to local climate changes. Though relatively shallow and slightly alkaline today, they fluctuated by four to ten times the modern water depth during the last 20,000 years. Five of the study lakes are pan-shaped and experienced lower magnitudes of lake level change during the same time period. Understanding the sensitivity of these lakes is critical in establishing the timing or synchronicity of regional-scale events or trends and predicting future hydrological variations in the wake of global climate changes. [ABSTRACT FROM AUTHOR]

The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine are identified using 14C and high-resolution (cm-by-cm) particle size analysis of sediment cores taken from six post-glacial lakes (~0.1–1.4 km2). A total of nine sediment cores (4.5–6 m long) were taken near the base of stream delta foreslopes. End-member modeling of the particle-size frequency distributions from each core produces 3–5 representative end member distributions, or end members (EMs). Concurrent increases in mean and median particle size, and in the relative abundance of the coarsest EM(s), indicate increased transport capacity of inflowing tributaries, resulting from rainstorms. In all 9 cores, particle size data show clear signs of episodic, high-energy sediment transport events where proxy measurements such as loss-on-ignition and magnetic susceptibility do not, demonstrating the sensitivity of particle size analysis in paleostorm investigations made using lake sediment cores. Floods caused by storms in this region peaked around 1.4, 2.1, 3.0, 3.9, 6.8, 8.2, and 11.5 ka cal BP, and presently appear to be increasing in frequency. Periods of storminess in New Hampshire and Maine correlate well with other records of precipitation and climate in the northeastern United States during the Holocene, further supporting modern records which show tropical air masses as a primary driver of extreme precipitation events in New England (Ludlum ; Konrad ; Sisson and Gyakum ). [ABSTRACT FROM AUTHOR]

Sub-fossil insect remains have the potential to characterise changing environmental conditions in both lentic and lotic water systems, however, relatively few studies have been undertaken in riverine environments. This paper uses sub-fossil caddisfly larvae (Trichoptera) and aquatic beetles (Coleoptera) to reconstruct river flow conditions for a large paleochannel (from multiple monoliths) using the Lotic invertebrate Index for Flow Evaluation (LIFE). Examination of the larval Trichoptera and Coleoptera remains indicated a marked change in the community and flow environment, as suggested by paleoLIFE scores within the profile of three of the monoliths examined. At the base of the channel the community was characterised by taxa indicative of high energy lotic habitats with predominantly mineral substrates (e.g. Trichoptera: Hydropsyche contubernalis and Brachycentrus subnubilis, Coleoptera: Elmis aenea and Esolus parallelepipedus). Within three of the monoliths there was a change in community composition to one indicative of a low energy backwater/lentic environment with abundant submerged and emergent vegetation (e.g. Trichoptera: Phryganea bipunctata and Limnephilus flavicornis, Coleoptera: Colymbetes fuscus and Hydrobius fuscipes). Detrended Correspondence Analysis (DCA) and loss of mass on ignition (LOI) indicated the presence of a strong environmental gradient within the data, associated with river flow. The utilisation of two aquatic insect orders provides clear evidence of temporal changes within the instream community and when combined with knowledge of ecological and habitat associations, allows differences between the two groups to be interpreted more clearly. [ABSTRACT FROM AUTHOR]

Since the end of the Last Glacial Maximum, hydrology in Europe has been influenced by both climate changes, and since Neolithic times, an increase in human activity. Paleohydrological reconstructions, especially from lake studies, can help identify the respective impact of these two factors. The present work focuses on a lacustrine geosystem, the Sarliève paleolake in the Massif Central (France), in an unusually dry, temperate area. The lake sediment geometry (core drillings, geotechnical methods), and the geochemical and mineralogical characterization of the catchment rocks and soils, and of the lacustrine deposits, indicate major variations in paleohydrology during the last 12,000 years as dated by C, palynology and tephrochronology. In addition, a model quantifying detrital versus biochemical lacustrine components was developed to identify hydrological trends. The data show that the Sarliève area was characterized mainly by remarkably dry conditions, hence sharpening the climatic trends at middle latitudes in Western Europe. Three main hydrological phases are distinguished since the Late Glacial: (1) 13.7-7.5 ka cal BP, a dominant dry climate, with a peak at ca. 8 ka cal BP, leading to a lowstand in water level and unusual mineral authigenesis, zeolite then dolomite, constituting up to 60% of the lacustrine sediments; (2) 7.5 to ca. 5.3 ka cal BP, repeated short-duration hydrological alternations that could have been climate-driven: lowstands in water level with up to 60% biochemical minerals versus higher water levels with <10% biochemical minerals; (3) 5.3 ka cal BP to the Middle Ages (i.e. beginning in the 5th century AD), a hydrological trend towards perennial high water level, with mainly detrital sediments, probably linked to climate evolution, except periods of obvious human-driven drying during the last two millennia. [ABSTRACT FROM AUTHOR]

The multidisciplinary study of sediment cores from Laguna Zoñar (37°29′00′′ N, 4°41′22′′ W, 300 m a.s.l., Andalucía, Spain) provides a detailed record of environmental, climatic and anthropogenic changes in a Mediterranean watershed since Medieval times, and an opportunity to evaluate the lake restoration policies during the last decades. The paleohydrological reconstructions show fluctuating lake levels since the end of the Medieval Warm Period (ca. AD 1300) till the late 19th century and a more acute dry period during the late 19th century – early 20th century, after the end of the Little Ice Age. Human activities have played a significant role in Laguna Zoñar hydrological changes since the late 19th century, when the outlet was drained, and particularly in the mid-20th century (till 1982) when the spring waters feeding the lake were diverted for human use. Two main periods of increased human activities in the watershed are recorded in the sediments. The first started with the Christian conquest and colonization of the Guadalquivir River Valley (13th century) particularly after the fall of the Granada Kingdom (15th century). The second one corresponds to the late 19th century when more land was dedicated to olive cultivation. Intensification of soil erosion occurred in the mid-20th century, after the introduction of farm machinery. The lake was declared a protected area in the early 1980s, when some agricultural practices were restricted, and conservation measures implemented. As a consequence, the lake level increased, and some littoral zones were submerged. Pollen indicators reflect this limnological change during the last few decades. Geochemical indicators show a relative decrease in soil erosion, but not changes in the amount of chemical fertilizers reaching the lake. This study provides an opportunity to evaluate the relative significance of human vs. climatic factors in lake hydrology and watershed changes during historical times. Paleolimnological reconstructions should be taken into account by natural resources agencies to better define lake management policies, and to assess the results of restoration policies. [ABSTRACT FROM AUTHOR]

Paleohydrology studies at Mathews Pond and Whitehead Lake in northern Maine revealed synchronous changes in lake levels from about 12,000 14C yrs BP to the present. We analyzed gross sediment structure, organic and carbonate content, mineral grain size, and macrofossils of six cores from each of the two lakes, and obtained 72 radiocarbon dates. Interpretation of this paleo-environmental data suggests that the late-glacial and Younger Dryas climate was dry, and lake levels were low. Early Holocene lake levels were considerably higher but declined for an interval from about 8000 to 7200 14C yrs BP. Sediment of both lakes contains evidence of a dry period at ∼7400 14C yrs BP (8200 cal yr). Lake levels of both sites declined abruptly about 4800 14C yrs BP and remained low until 3000 14C yrs BP. Modern lake levels were achieved only within the past 600 years. The west-to-east, time-transgressive nature of lake-level changes from several sites across northeastern North America suggests periodic changes in atmospheric circulation patterns as a driving force behind observed moisture balance changes. [ABSTRACT FROM AUTHOR]

Recent advances in paleolimnology have enabled reconstructions of past sockeye salmon ( Oncorhynchus nerka) dynamics using a number of proxy-indicators, including diatoms and stable isotopes. Thus far, studies have focused on nursery lakes with high escapement densities and low flushing rates, ensuring that levels of salmon-derived nutrients (SDN) are high and are incorporated into the food chain. This study examines three oligotrophic sockeye salmon nursery lakes in Alaska (Afognak and Saltery lakes) and British Columbia (Hobiton Lake) to determine if sockeye salmon populations can be tracked in nursery systems with lower salmon escapement densities, higher flushing rates and/or higher terrestrial input. We adopted a multi-proxy approach using diatoms, stable isotopes (δ15N), organic carbon to nitrogen (C/N) ratios and pollen to draw inferences from 210Pb-dated sediment cores. δ15N showed little response to historic variation in sockeye salmon populations, even in Saltery Lake, which has a very high escapement density, and in Afognak Lake, in which average escapement is known to have increased. Dilution effects due to high flushing rates were likely partly responsible for the low δ15N and minimal variation throughout the cores, although very high terrestrial input in Hobiton Lake also dampened the salmon signal. Small changes in diatom species assemblages, however, were evident in all three lakes and may be in response to fluctuating loads of salmon-derived nutrients. Most notably, increases of mesotrophic diatom taxa, such as Asterionella formosa and Aulacoseira subarctica, corresponded to increased salmon production in Alaskan lakes as a result of enhancement (fertilization) activities and climatic changes. Changes in the relative abundance of Cyclotella pseudostelligera in Hobiton Lake may also be in response to a significant decline in sockeye salmon populations off the west coast of Vancouver Island in the 1970s. Other factors, however, such as logging and lake fertilization may also have influenced diatom species composition. These results confirm that, while salmon-derived nutrients may be of key importance in juvenile salmonid development in some lakes, this may not be the case in all systems, especially those in which flushing rates are high. Further, in these systems, diatom communities appear to respond more sensitively to fluctuations in salmon populations (and therefore nutrients) than stable isotope methods, provided that other changes in trophic status are minor. [ABSTRACT FROM AUTHOR]

Lamination thickness measurements in sediments from Lake Tuborg, northern Ellesmere Island, Canada document an increase in high-energy hydrologic discharge events from ∼1865 to 1962. The timing of these events corresponds with evidence for an increase in the amount of melt on the adjacent Agassiz Ice Cap, as recorded in ice cores. There appears to have been a non-linear change in depositional energy resulting from a dramatic increase in Agassiz meltwater discharge, particularly after ∼1908. A strong correlation between the Lake Tuborg varve thickness record, the amount of melting on the Agassiz Ice Cap and Eureka 900 mb air temperature records suggests that changes in the height of the freezing level in the atmosphere have affected the extent of summer melting on the Agassiz Ice Cap, leading to high volume discharge events and associated sediment flux to Lake Tuborg. [ABSTRACT FROM AUTHOR]

Mid-Holocene changes in vegetation, palaeohydrology and climate were investigated from the sediments of Lake Vankavad in the northern taiga of the Usa Basin, NE European Russia, through the analysis of pollen, plant macrofossils, Cladocera and diatoms. Lake Vankavad was probably formed at ca. 5000 BP (ca. 5600 cal. BP) and initially it was shallow with a littoral cladoceran fauna. Macrofossil and pollen results suggest that dense Betula-Picea forests grew in the vicinity and the shore was close to the sampling point. At ca. 4600 BP (ca. 5400 cal. BP) the water level rose coincident with the decrease in the density and area of forests, probably caused by cooling climate and accelerated spread of mires. There was also a further rise in the water level at ca. 3500 BP (ca. 3800 cal. BP). The initiation of the lake, followed by two periods of rising water-level, as well as the increase in mire formation, was a consequence of a rise in groundwater level. This probably reflects lower evapotranspiration in a cooling mid-Holocene climate and/or higher precipitation in the lowland area. Also the decreased forest density and area may have contributed to the lower evapotranspiration. It is also possible that permafrost aggradation or changes in peat ecosystems might have affected the hydrological conditions in the area. [ABSTRACT FROM AUTHOR]

Changes in the diatom assemblages preserved in a sediment core taken from a small lake located north of arctic treeline on the western Taimyr Peninsula, Russia, were examined in order to investigate late Holocene (i.e., ca 5000 cal yr BP to present) climatic and environmental changes within the region. Early diatom assemblages were dominated by benthic Fragilaria taxa and indicate a transitional phase in the lake history, most likely reflecting lake development and environmental change associated with treeline retreat to the south of the study site. Concurrent with pollen and macrofossil evidence of a vegetation shift to shrub tundra in the catchment basin at ca 4200 cal yr BP, an increase in cold-water taxa, followed by little change in diatom assemblages until ca 2800 cal yr BP, suggests that conditions were relatively cool and stable at this time. The last ∼2000 years of the Middendorf Lake record have been marked by fluctuating limnological conditions, characterized by striking successional shifts between Fragilaria pinnata and Aulacoseira distans var. humilis. Recent conditions in Middendorf Lake indicate an increase in diatom taxa previously rare in the record, possibly associated with twentieth-century climatic warming. The Middendorf Lake record indicates that significant limnological change may occur in the absence of catchment vegetation shifts, suggesting late-Holocene decoupling of aquatic and terrestrial responses to climatic and hydrological change. Our study results represent one of the few paleoecological records currently available from northern Russia, and highlight the need for further development of calibration data sets from this region. [ABSTRACT FROM AUTHOR]

The water chemistry of a groundwater-fed sinkhole-pond near St. Louis, Missouri, and its associated climate during the last glaciation are reconstructed by comparison with autecological data of modern ostracodes from about 5,500 sites in Canada. A 4.8-m succession of fossiliferous sediment yielded ostracode assemblages that collectively are generally found today in ponds in North America including the species Cyclocypris ampla, C. laevis, Cypridopsis vidua, Candona crogmaniana, C. distincta, and C. ohioensis. Fossils of Picea needles and the ostracode Cyclocypris sharpei imply that best analog sites for the succession are in central to south-central Canada. The pond formed 23,300 ± 400 cal yr BP when a sinkhole became plugged by a clay bed about 1 m thick. By about 20,250 cal yr BP, the pond had desiccated and was buried by loess. The sediment accumulation rate was about 0.18 cm/yr, and each sample interval (6 cm) represents a time slice of ≈33 years. Data from this record provides the first fairly high resolution proxy record of the glacial paleoclimate of the mid-latitude of North America. The analog data indicate the water in the hydrologically-open spring-fed pond was less than 1 m deep. The paleoclimatic reconstructions imply gradually drier conditions and uniform, cool temperatures. The shallow water depth indicates that the temperature reconstruction is robust with mean annual temperatures (MATs) that ranged between 0.8 and 3.9°C, and mean July temperatures that ranged from 16.8 and 18.1°C. Other estimated climatic parameters include mean annual precipitation (MAP; 430 to 840 mm/yr), and moisture balance (P-E; −111 to 298 mm/yr). Compared to values measured today at St. Louis, the MAP was about 400 mm less, MAT about 10°C cooler, and P-E, about the same. These values are consistent with other published reconstructions based on modern analog analysis of fossil beetles and pollen, and paleothermometry based on amino acid racemization. The total dissolved solids (TDS) progressively increased from about 87 to 431 mg/L. Changes in TDS reflect either the balance between the relative inputs of karst groundwater and overland flow, or changes in the duration of water-rock interaction associated with the groundwater. The postulated long-term 900 ± 200 year cyclicity of growing-season moisture and temperature, attributed to El Niño-Southern Oscillation cycles, is not expressed in the reconstructed hydrologic or climatic data. This is attributed, in part, to the mediating effect on temperature by monothermic groundwater input to this flow-through system. [ABSTRACT FROM AUTHOR]

Peatland testate amoebae are sensitive indicators of local hydrology and have been used as proxies for surface moisture conditions in fossil studies. However, few regional calibration datasets exist in North America, and knowledge of testate amoeba ecology and distribution patterns are limited. The objectives of this study were to (1) investigate the relationship between testate amoebae, environment, and Sphagnum species in Michigan peatlands; (2) generate transfer functions from this dataset that can be applied to fossil data; and (3) describe vertical variation of testate amoebae inhabiting Sphagnum moss. Testate amoeba assemblages from 139 microsites within 11 peatlands in Michigan were compared to assess variability between and within peatlands. Most peatlands contained similar testate amoeba assemblages, although within individual peatlands the amount of assemblage variability is correlated to the amount of environmental heterogeneity. Of the measured environmental variables, depth to water table showed the strongest relationship with testate amoebae. Depth to water table can be reconstructed from fossil data with a mean error of ±7.5 cm, although predictive ability deteriorates in extremely dry environments (>30 cm water table depth). Vertical variation in testate amoeba assemblages was investigated at 89 Sphagnum-dominated microsites by directly comparing amoeba assemblages and the abundance and frequency of common taxa in upper and lower portions of the Sphagnum stem. Except for extremely dry microsites, considerable vertical variation in assemblage composition exists. Many agglutinate taxa are more abundant on lower portions of the Sphagnum stem, and taxa containing symbiotic zoochlorellae are more abundant on upper portions. Refinements in sampling procedures and analysis may improve the predictive ability of transfer functions. [ABSTRACT FROM AUTHOR]

A 450 cm sediment core spanning the last 3,500 years was collected from 4.6 m of water in Lake Infernão, located in the floodplain of the Moji-Guaçu River in SE Brazil, to reconstruct the wetland system (river and lake) paleohydrology. A multidisciplinary approach using isotopic (13C and 15N), chemical (C/N ratio and lignin derived phenols) and physical analyses (% water content and density) were used in this study. A coarse sand unit in the lower part of the core (450–417 cm) corresponds to the paleoriver. The rest of the sediment core (dark clay) shows a gradual change from a fluvial to a lacustrine environment. 14C dates from the lower part of the core (417–200 cm), demonstrate an inversion and narrow span in age (3,000–3,500 yrs B.P.) corresponding to a period of rapid fluvial sedimentation and reworking. The lake seems to have been well established only after 3,000 yrs B.P. The change from a fluvial to a lacustrine environment is inferred from the isotopic and chemical data. Sediment of the fluvial phase is characterized by higher δ13C values, lower C and N content and a lignin content representative of woody-tissues. Sediment of the lacustrine phase show a gradual decrease in δ13C values toward the top of the core reflecting the influence of organic carbon derived by phytoplankton and aquatic macrophytes (C3 plants). The trend to higher C and N content and low C/N ratios also support this interpretation. The lower lignin content indicates increase contributions of non-vascular plants (phytoplankton). Similarly, the slight increase of non-woody tissues (higher C/V ratios) and the predominance of angiosperm plants (high S/V ratios) as organic matter source indicate an increase contribution of aquatic plants during the lacustrine phase. Our data presented here in addition to the geomorphological information and the available paleoclimatic scenario of pollen-inferred analyses for aquatic systems from the southeastern Brazil point to a climatic origin for this fluvial-lacustrine transition at about 3,000 yrs B.P. and to a climatic evolution leading to the present conditions and to a consequently gradual isolation of Lake Infernão from the influence of the Moji-Guaçu River. [ABSTRACT FROM AUTHOR]