Lake Perimeter Research Articles

Genetic diversity associated with N-cycle pathways in microbialites from Lake Alchichica, Mexico

Author(s): Alcantara-Hernandez, RJ; Valdespino-Castillo, PM; Centeno, CM; Alcocer, J; Merino-Ibarra, M; Falcon, LI | Abstract: Microbialites are an example of complex and diverse microbial assemblages where several metabolic pathways are interconnected for biomass formation coupled to mineral precipitation. Lake Alchichica (Mexico) is an oligotrophic environment where nitrogen (N) and phosphorus alternately limit productivity, and massive microbialite growths are found along the lake's perimeter. Previous studies have described the importance of N2 fixation in these microbialites, although other pathways associated with the N cycle, including denitrification, nitrification and anaerobic ammonium oxidation (anammox), had not been evaluated. This study identified the genetic diversity associated with N cycling in both metagenomic DNA and RNA expression by targeting key genes for nitrogenase (nifH), ammonia monooxygenase (amoA), nitrite oxidoreductase (nxrA, nxrB), hydrazine oxidoreductase (hzo) and nitrite (nirS and nirK) and nitrous oxide (nosZ) reductases. While the genetic potential for N2 fixation, ammonia oxidation, anammox and denitrification was present in the microbialites of Lake Alchichica, the most transcribed pathway was N2 fixation.

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

Abstract. Ponds smaller than 10 000 m2 likely account for about one-third of the global lake perimeter. The release of methane (CH4) and carbon dioxide (CO2) from these ponds is often high and significant on the landscape scale. We measured CO2 and CH4 fluxes in a temperate peatland in southern Ontario, Canada, in summer 2014 along a transect from the open water of a small pond (847 m2) towards the surrounding floating mat (5993 m2) and in a peatland reference area. We used a high-frequency closed chamber technique and distinguished between diffusive and ebullitive CH4 fluxes. CH4 fluxes and CH4 bubble frequency increased from a median of 0.14 (0.00 to 0.43) mmol m−2 h−1 and 4 events m−2 h−1 on the open water to a median of 0.80 (0.20 to 14.97) mmol m−2 h−1 and 168 events m−2 h−1 on the floating mat. The mat was a summer hot spot of CH4 emissions. Fluxes were 1 order of magnitude higher than at an adjacent peatland site. During daytime the pond was a net source of CO2 equivalents to the atmosphere amounting to 0.13 (−0.02 to 1.06) g CO2 equivalents m−2 h−1, whereas the adjacent peatland site acted as a sink of −0.78 (−1.54 to 0.29) g CO2 equivalents m−2 h−1. The photosynthetic CO2 uptake on the floating mat did not counterbalance the high CH4 emissions, which turned the floating mat into a strong net source of 0.21 (−0.11 to 2.12) g CO2 equivalents m−2 h−1. This study highlights the large small-scale variability of CH4 fluxes and CH4 bubble frequency at the peatland–pond interface and the importance of the often large ecotone areas surrounding small ponds as a source of greenhouse gases to the atmosphere.

The Role of Lake Expansion in Altering the Wetland Landscape of the Prairie Pothole Region, United States.

Interannual variation in lake extent is well documented in the Prairie Pothole Region, but the role of surface-water expansion, including lake expansion, in merging with and subsuming wetlands across the landscape has been minimally considered. We examined how the expansion of surface-water extent, in particular, the expansion of lakes across parts of the Prairie Pothole Region can alter landscape-level hydrologic connectivity among substantial numbers of previously surficially disconnected wetlands. Temporally static wetland, lake, and stream datasets were fused with temporally varying Landsat-derived surface-water extent maps (1990–2011) to quantify changes in surface-water connectivity. Under deluge conditions, lakes were found to create significantly larger complexes of surficially-connected wetlands relative to non-lake surface-water connections (e.g., only wetlands or wetlands and streams). Analysis of three specific lakes showed that lakes can merge with and subsume wetlands located kilometers to tens of kilometers from the National Wetland Inventory defined lake perimeter. As climate across the Prairie Pothole Region is highly variable, understanding historic patterns of surface-water expansion and contraction under drought-to-deluge conditions will be integral to predicting future effects of climate change on wetland function, loss and influence on other aquatic systems, including downstream waters.

Modeling circulation and seasonal fluctuations in perennially ice‐covered and ice‐walledLakeUntersee,Antarctica

Lake Untersee, Antarctica, is a freshwater perennially ice covered lake bounded along its north by the Anuchin glacier. The Massachusetts Institute of Technology general circulation model, used on a representative wedge‐shaped lake and actual bathymetry for Lake Untersee, produces estimates for circulation and long‐term temperature and mixing trends. Modeled circulation is dominated by an anticyclonic gyre in front of the glacier, with slowerflow exhibited around the lake's perimeter, allowing effective mixing throughout most of the lake with time scales of one month. Estimated velocities bound maximal glacial flour particle size atfor effective transport throughout the lake, consistent with the sediment's mostly fine composition observed in field studies, and mixing time scales mean nonuniformities in measuredconcentration likely require recent or ongoing sources. Areas in which large temperature gradients prevent exchange of fluid demonstrate minimal mixing, such as the lake's upper water layers and the anoxic basin in the south, and circulation is consistently slowed in the northern sheltered bay area. Mean flow velocities fluctuate by about one fifth of their magnitude between summer and winter, and the lake's almost homothermal body temperature varies by about one tenth of a degree over the same period. While calculated temperature profiles qualitatively agree with field data, the model's long‐term equilibrium temperature differs substantially, likely due to poor description of heat transfer with the glacier. Model robustness tests show results differ by ∼ 10% when either grid scale or water temperature are halved.

The Tienchi Pond on Lanyu Island (Western Pacific): Lake formation and potential as environmental archive

The formation, evolution, and potential as a climate archive of Tienchi Pond was evaluated using geomorphology, sedimentology, geochemistry, and AMS radiocarbon measurements of tree ring cores. Tienchi Pond is a small ephemeral lake situated on the subtropical Lanyu Island in the Western Pacific Ocean about 90km east of southern Taiwan. The lake is situated on a mountain ridge and is today characterized by numerous dead trees and stumps. The position at the boundary between the two main components of the SE Asian monsoon system, the Asian landmass and the Western Pacific, makes this lake particularly interesting as a potential natural climate archive.Since previous studies have shown that the bedrock underlying the lake formed over 2my ago, a volcanic crater origin was ruled out. Rather, element ratios of K/Ti and Ca/Fe together with 210Pb dating suggest a recent origin for the lake, probably as the result of a natural damming event in the southern, narrower, part of the lake basin, or as a result of increased precipitation at the end of the Little Ice Age (or a combination of both). Radiocarbon measurements on a dead tree near the lake perimeter show 14C levels of more than 1.7% modern radiocarbon near the bark, suggesting that the tree died in the early 1970s. In contrast, by correlating a large number of radiocarbon measurements to a northern hemisphere reference curve, it was shown that trees closer to the center of the lake died in the early 20th century. This agrees with a scenario where a small lake formed by initial damming, and gradually grew larger through erosion of the surrounding shore lines caused by rapid lake level oscillations.

Early warnings of regime shifts: evaluation of spatial indicators from a whole‐ecosystem experiment

Critical transitions between alternate ecosystem states are often preceded by increased variance and autocorrelation in time series of ecosystem properties. Analogous changes may occur in spatial statistics as ecosystems approach thresholds for critical transitions. Changes in spatial statistics near thresholds have been described using models, laboratory experiments, and remotely sensed data, but there have been no tests using deliberate manipulations of whole ecosystems in the field. We previously documented a whole‐lake manipulation resulting in a transition to predator dominance, a type of critical transition. The food web of an experimental lake was forced via cascading trophic interactions from a stable state characterized by abundant prey fish, small zooplankton, and high chlorophyll concentrations to an alternative state dominated by predatory fish, large zooplankton and low chlorophyll concentrations. Time series of zooplankton and chlorophyll concentrations provided early warning of the regime shift. Here we test if similar early warning signals were present in space by applying spatial variance and the discrete Fourier transform to spatially distributed prey fish catch data from this regime shift. Prey fish spatial distributions were monitored daily using minnow traps deployed around the lake perimeter. Added predators reduced prey fish populations and altered their spatial distributions. Increases in spatial variance and shifts to low frequency spatial variance were observed up to a year in advance of the shift. There was no response in an adjacent reference lake. Our results demonstrate that spatial signals of approaching thresholds can be detected at the ecosystem scale.

Plant colonization and soil properties on newly exposed shoreline during drawdown of Lake Mead, Mojave Desert

Drawdown of Lake Mead from 1998 to 2011 reduced the lake's perimeter by more than 400 km while exposing more than 25,000 ha of formerly submerged land. To evaluate primary plant succession and soil properties in this new shoreline habitat, we sampled surfaces last submerged 3, 6, 9, or 13 years before sampling (including a never-submerged control) using 150, 100 m2 plots at 3 sites varying in topography and soil parent material. Consistent with previous research, abundance of the exotic saltcedar (Tamarix ramosissima) declined with increasing surface age. Conversely, cover of native species was greatest overall on older surfaces across sites. Early successional native perennial species colonized the 13-year-old surface. Unexpectedly, multivariate soil properties did not differ between never-submerged and formerly submerged surfaces. Based on the first 13 years of plant colonization along the Lake Mead shoreline and previous research on longer term Mojave Desert vegetation succession, managers can likely anticipate (1) continued development of an early colonizing native shrubland persistent for several decades, and (2) eventual colonization by species of the mature vegetation inhabiting never-submerged surfaces. Moreover, we observed colonization of formerly submerged land by a rare plant of special conservation designation, California bearpoppy (Arctomecon californica), suggesting that even after many years of submersion, rare plant habitat along the Lake Mead shoreline may be reclaimed. While Lake Mead's drawdown might be viewed negatively from a perspective of maintaining full-pool water storage, it has re-exposed a vast area of new terrestrial habitat increasingly colonized by native species as invasive species abundance declines through time.

Does lake size matter? Combining morphology and process modeling to examine the contribution of lake classes to population-scale processes

With lake abundances in the thousands to millions, creating an intuitive understanding of the global distribution of morphology and processes in lakes is challenging. To improve researchers' understanding of large-scale lake processes, we developed a parsimonious mathematical model based on the Pareto distribution to describe the distribution of lake morphology (area, perimeter, and volume). While debate continues over which mathematical representation best fits any one distribution of lake morphometric characteristics, we recognize the need for a simple, flexible model to advance understanding of how the interaction between morphometry and function dictates scaling across large populations of lakes. These models make clear the relative contribution of individual lakes to the total amount of lake surface area, volume, and perimeter. They also highlight the critical thresholds at which total perimeter, area, and volume would be evenly distributed across lake-size classes having Pareto slopes of 0.63, 1.00, and 1.12, respectively. These morphological models can be used in combination with process models to create overarching “lake population” level models of process. To illustrate this potential, we combined the model of surface area distribution with a model of carbon mass accumulation rate. We found that even if smaller lakes contribute relatively less to total surface area than larger lakes, the increasing carbon accumulation rate with decreasing lake size is strong enough to bias the distribution of carbon mass accumulation toward smaller lakes. This analytical framework provides a relatively simple approach to upscaling morphology and process that can be easily generalized to other ecosystem processes.

Lake shoreline in the contiguous United States: quantity, distribution and sensitivity to observation resolution

Summary Quantifying lake biogeochemical processing at broad spatial scales requires that we scale processes along with physical metrics. Past work has primarily scaled lentic processes using estimates of lake surface area. However, many processes important to lakes, such as material, energy and biological fluxes and biogeochemical cycling, scale with lake perimeter. We estimate the total lake perimeter for the contiguous United States (U.S.) and examine the sensitivity of this estimate to measurement resolution. At the original mapping resolution, lakes in the contiguous U.S. have a total perimeter of over 1.8 million km. The change in measured perimeter versus measurement resolution for the contiguous U.S. had a log‐log slope (also known as the fractal dimension) of −0.21, generally less than previously reported estimates. With changing observation resolution, total measured perimeter was most sensitive to the inclusion or exclusion of small lakes, not shoreline complexity. The total aquatic–terrestrial interface in lakes is less than one‐tenth that of streams and rivers, which collectively account for over 21 million km of shoreline in the contiguous U.S. This study further describes the distribution of lake perimeter and proposes a technique that can contribute to understanding continental‐scale processes.

Adaptation and constraint in a stickleback radiation

The evolution of threespine sticklebacks in freshwater lakes constitutes a well-studied example of a phenotypic radiation that has produced numerous instances of parallel evolution, but the exact selective agents that drive these changes are not yet fully understood. We present a comparative study across 74 freshwater populations of threespine stickleback in Norway to test whether evolutionary changes in stickleback morphology are consistent with adaptations to physical parameters such as lake depth, lake area, lake perimeter and shoreline complexity, variables thought to reflect different habitats and feeding niches. Only weak indications of adaptation were found. Instead, populations seem to have diversified in phenotypic directions consistent with allometric scaling relationships. This indicates that evolutionary constraints may have played a role in structuring phenotypic variation across freshwater populations of stickleback. We also tested whether the number of lateral plates evolved in response to lake calcium levels, but found no evidence for this hypothesis.

Distribution of the Amphipod Diporeia in Lake Superior: The Ring of Fire

Diporeia, formerly the dominant benthic macroinvertebrate in the Great Lakes, remains a keystone species in Lake Superior. Little is known, however, about fine scale amphipod distributions, especially as influenced by the production, transport and transformation of energy resources. Here, we document the distribution and abundance of Diporeia along 19 transects around the lake's perimeter. Regions of elevated density, averaging 958±408Diporeia/m2 (mean±S.D.) were observed along all transects, typically within slope habitat (depth of 30–125m). Waters shoreward (shelf habitat, <30m) and lakeward (profundal habitat, >125m) of these regions supported significantly lower densities, averaging 239±178/m2 and 106±59/m2, respectively. Amphipods within regions of elevated density, termed here the Ring of Fire, account for two-thirds of the lakewide population while occupying only one-quarter of the benthic habitat. The Ring of Fire, observed lakewide as a band averaging 14.2±9.4km in width, is characterized as a region of transitional sediment deposition with gentle slope, proximate to nearshore locations of elevated primary production. Within the Ring of Fire exceptionally high densities are found in the south central region, where the Keweenaw Current and slope bathymetries serve to funnel production from adjoining regions of high production. Density measurements for the 173 stations sampled here are used to estimate lakewide Diporeia standing stock (22.5–37.7trillion individuals, 4.4–7.4Gg dry weight, 2.1–3.5Gg C), individual and biomass density (274–460/m2, 0.05–0.09gDW/m2, 0.03–0.04gC/m2) and areal (0.02–0.03gC/m2/yr) and total (1.6–2.6GgC/yr) production.

Automated Lake Shoreline Mapping at Subpixel Accuracy

Accurate assessment of lake extent and variation is essential for understanding the global hydrological cycle and necessitates the use of satellite data. The intrinsic scale of lake dynamics is finer than the spatial resolution of available images. Lake change detection requires mapping lake shorelines with high positional accuracy as they are employed for calculating changes in area and volume. There exist many techniques for mapping lake shorelines from multispectral images, and their accuracy decreases as the image spatial resolution degrades. In addition, lake shorelines obtained from images have a zagged appearance, which not only provides an unrealistic representation but also overestimates the lake perimeter. This letter presents a method for subpixel lake shoreline mapping. The approach is used to map subpixel shorelines from Landsat Enhanced Thematic Mapper Plus images acquired in the lake-rich Arctic Coastal Plain of northern Alaska, where lakes dominate the landscape and change significantly over time. High performance of the proposed approach is demonstrated by the agreement of subpixel shorelines with high-resolution QuickBird panchromatic images. The subpixel shorelines estimated by the proposed approach are smooth and lead to precise area estimation and displacement error reduction when compared with the shorelines obtained using image segmentation. The proposed approach has great potential in regional-scale shoreline mapping.

Importance of groundwater and macrophytes for the nutrient balance at oligotrophic Lake Hampen, Denmark

ABSTRACTAn ecohydrological study was carried out at an oligotrophic seepage lake, Lake Hampen, Denmark, to determine the seepage in and out of the lake and determine the mass budgets for nutrients. The lake is primarily surrounded by forest, although there are agricultural fields bordering a small portion of the lake perimeter. The water and mass balances indicate that there is a groundwater input of 1643 × 103 m3 year−1 into the lake (∼70% of total input) and a groundwater output of 1997 × 103 m3 year−1. The groundwater input carries with it 2253 kg N year−1 (∼67% of total input) and 40 kg P year−1 (∼85% of total input). The majority of the nitrogen is leached from the agricultural fields bordering the lake. Concentrations as high as 1750 µM nitrate were measured in the rhizosphere of the littoral zone at this location. It is estimated that the macrophytes are able to take up 1695 kg N year−1 (∼50% of the input). The phosphorus uptake by plants was 310% of the input, indicating that plants are highly dependent on accumulated and remineralized phosphorus in the lake. The nutrients lost through recharge was much lower than input through groundwater discharge entailing a high retention of nutrients in the lake (92–96%). A significant part of the retained nitrogen may be lost through denitrification. Although the plant uptake may have slowed the eutrophication of the lake, the excess nutrients may over time give rise to eutrophication and a shift towards pelagic production. Copyright © 2011 John Wiley &amp; Sons, Ltd.

The influence of Wisconsinan glaciation and contemporary stream hydrology on microsatellite DNA variation in rainbow trout (Oncorhynchus mykiss)

Microsatellite DNA variation was examined in rainbow trout ( Oncorhynchus mykiss ) populations from throughout British Columbia, Canada, to address the roles of historical isolation, postglacial dispersal, and contemporary geomorphology in structuring genetic variation and differentiation. We detected signatures of historical isolation and postglacial recolonization in the form of “interior” and “coastal” population groupings, a decline in genetic variation as distance increased from putative glacial refugia, and different extents of isolation-by-distance in different regions. Rainbow trout populations were structured genetically into major regions and into smaller watersheds and then into drainages. Within drainages, high levels of dispersal and gene flow were inferred between geographically proximate and contiguous lakes. Elevation, stream branching points (nodes), fluvial distance, migration barriers, and stream and lake order influenced genetic diversity within, and differentiation among, populations. Habitat characteristics, particularly lake surface area and perimeter, were poor predictors of genetic variation. Although founder events and postglacial dispersal influenced broadscale patterns of genetic diversity in rainbow trout, our results suggest that contemporary factors can strongly modulate historical patterns.

Variation in local weather explains differences in fire regimes within a Québec south-eastern boreal forest landscape

Variation in natural disturbance regime within a landscape is important for species population dynamics, because it controls spatial arrangement of sites providing regeneration and survival opportunities. In this study, we examine the differences in fire regime and evaluate possible sources of its variation between the surrounding mainland and the islands of Lake Duparquet (44.5 km2), a typical boreal lake in north-western Quebec, Canada. Dendrochronological reconstructions suggest that fires were frequent and of variable intensity on the islands, whereas fires were less frequent on the adjacent mainland, but were usually large and intense. Islands were significantly drier and warmer than the mainland, and maximum values of Fire Weather Index were significantly higher on the islands during both the early part of the fire season (May–June) and the whole fire season (May–September). The lightning density within the lake perimeter was significantly higher than in the surrounding mainland (0.63 v. 0.48 year–1 km–2 respectively). This pattern was a result of the differences in lightning density during the first half of the lightning season. The study suggests that more fire-prone local weather and higher frequency of lightning strikes could cause a higher frequency of low-intensity fires on the islands, compared with the mainland.

Anisotropic elastocreep in glacial ice: A mechanism for intergranular melt and recrystallization

[1] Bonded ice crystals under pressure are in a heterogeneous stress state because of the mechanical anisotropy of constituent grains. This condition plays a role in intergranular melt and recrystallization, which in turn influence properties such as permeability and biologic habitability. To examine this, we develop an anisotropic elastocreep model simulating subgrain-scale stresses in polycrystalline ice, choosing in particular the thermal and deformational regime of the Lake Vostok accretion ice. A critical assumption with regard to localized melting is the macroscopic deviatoric stress. Our calculations indicate that for a macroscopic deviatoric stress of 50 kPa, ice at 0.04°C below the bulk melting temperature would contain regions, at scales ∼1% the grain size, where the liquid phase is thermodynamically favored. This translates to scales of ∼5 mm in the lower few meters of the Vostok accretion under a deviatoric stress that is plausible near the lake perimeter. Less internal melting is indicated in analyses of ice relatively far from the lake margins due to the assumed presence of lower macroscopic deviatoric stress. Simulated strain energy jumps of 1–2% across grain boundaries of accretion ice near the lake boundaries are large relative to free surface energy, indicating the importance of the former in boundary migration recrystallization. Collectively, these findings are consistent with measured dislocation densities (>107–1010 m−2) and irregular grain morphologies found in core samples. The calculated melting point depressions associated with anisotropy fall short of experimental values by a factor of ∼2, while the calculated strain rates deviate by ∼20%.

Timing and patterns of basin infilling as documented in Lake Powell during a drought

Between 1999 and 2005, drought in the western United States led to a >44 m fall in the level of Lake Powell (Arizona-Utah), the nation's second-largest reservoir. River discharges to the reservoir were halved, yet the rivers still incised the tops of deltas left exposed along the rim of the reservoir by the lake-level fall. Erosion of the deltas enriched the rivers in sediment such that upon entering the reservoir they discharged plunging subaqueous gravity fl ows, one of which was imaged acoustically. Repeat bathymetric surveys of the reservoir show that the gravity fl ows overtopped rockfalls and formed small subaqueous fans, locally raising sedi- ment accumulation rates 10-100-fold. The timing of deep-basin deposition differed regionally across the reservoir with respect to lake-level change. Total mass of sediment transferred from the lake perimeter to its bottom equates to ~22 yr of river input.

Effect of wind variability on topographic waves: Lake Kinneret case

We studied the winter wind driven circulation in Lake Kinneret (northern Israel) using state of the art atmospheric (Regional Atmosphere Modeling System (RAMS)) and oceanic (Regional Ocean Modeling System (ROMS)) general circulation models. During winter the lake is completely mixed and mainly forced by the passage of synoptic weather systems. The lake's dynamic response was identified using various wind regimes. The response of the lake to a uniform wind stress resulted in the formation of a double‐gyre circulation pattern. After removal of the wind stress, the double‐gyre pattern slowly rotated cyclonically (with a time period of several days) around the lake perimeter, consistent with the pattern of the lowest‐mode basin‐scale topographic (vorticity) wave. The use of RAMS‐simulated wind fields resulted in a less symmetric structure of the double‐gyre pattern due to the presence of a curl in the wind field. Using various wind regimes to force the lake indicated that the presence of a positive or negative curl in the wind field might result in a shift in the topographic wave frequency to a higher or lower value, respectively. This result may be easily applied to motions on the geophysical scale. The currents predicted by RAMS‐ROMS agree well with measured data near the center of the lake. Forcing the model with a spatially uniform wind field constructed from a single station resulted in poor agreement with the observed currents, indicating the importance of the wind field spatial pattern.

Assessing pelagic and benthic metabolism using free water measurements

Automated in situ sensors for measuring changes in dissolved oxygen (DO) at high frequency have facilitated estimates of gross primary production (GPP) and respiration (R) in aquatic systems. Lake researchers usually rely on a single sensor for these estimates, but such point measurements may miss important spatial heterogeneity in within‐lake processes and may not accurately represent systemwide values of metabolism. Here we combine simultaneous measurements of metabolism using DO sensors along transects from the shore to the center of a lake with a spatial model to better understand the underlying heterogeneity in processes contributing to whole‐lake epilimnetic metabolism. We use this model to achieve better estimates of epilimnetic GPP and R and to determine the relative contributions of benthic‐littoral vs. pelagic processes to these estimates. We compared the spatially explicit process‐based model to estimates of metabolism from both a single sensor at the lake's center and a spatially explicit averaging of multiple sensor sites. Estimates of both GPP and R varied on average 2.5‐ to 3.2‐fold from site to site within the same lake, whereas variations were sometimes as high as 6‐ to 7‐fold. Estimates of GPP and R near the perimeter of lakes were on average greater than measurements in the middle of the lake. Our model estimates that benthic‐littoral processes accounted for ~40% of epilimnetic GPP and R. A single, centrally located sensor often misses a significant component of this benthic metabolism and accounts for only ~81% of lakewide GPP and R.

Holocene temperature variability in western Ireland: Evidence from limnic ostracode assemblages and stable isotope values

Western Ireland is ideally situated to receive maritime precipitation that has uncomplicated trajectory histories. Biota in Irish lakes therefore have the potential to divulge temperature and precipitation records for the Holocene. Blanket bog cores adjacent to Lough Corrib contain abundant ostracoda whose calcite shells were analyzed for stable oxygen and carbon isotope values. The earliest Holocene sediments are characterized by the cool water, oligotrophic ostracode Limnocytherina sanctipatricii that displays relatively high δ18O and δ13C values, indicative of cool, arid conditions. Middle Holocene sediments are characterized by cool, humid conditions differentiated by abundant Metacypris cordata that thrived on productive carbonate benches surrounding the lake perimeter. Relatively low oxygen isotope values suggest cool, wet conditions. Carbon isotope values are relatively low as DIC was dominated by terrestrial organic matter. Late Holocene warm, humid conditions are differentiated by decreased Metacypris cordata abundance and relatively high δ18O values in response to increased atmospheric warmth and increased rates of vegetative production. Possible climate excursions include the 8.2 kyr cold event and the Middle Holocene Thermal Maximum.