Climate and Anthropogenic Influences on Aquatic Ecosystems in the Valley of the Great Lakes, Mongolia
The semi-arid plateaus of western Mongolia have a wide range of lake and other aquatic ecosystems, ranging from large, saline basins to small freshwater mountain lakes and wetlands. Thousands of years of human habitation and a highly variable climate combine to create a complex series of stressors on these ecosystems. After participating in a large hydrobiological survey which sampled sediment, water chemistry, ostracode, chironomid, and diatom communities from lakes, rivers and wetlands across western Mongolia, I used the collected diatom and water chemistry samples to develop a diatom-based calibration for lake salinity that was then applied to sediment core samples. By applying this calibration to diatom records in sediment cores, in conjunction with other geochemical proxies, I was able to reconstruct salinity variation over the past several thousand years and use the reconstruction to infer changes in moisture availability to the lakes. This history of drought could then be compared with regional temperature reconstructions, and inferences of drought from neighboring regions in Central Asia to better understand possible impacts of current and future warming on moisture availability. The examination of past variability in the lakes also allowed me to recognize that modern conditions in the lakes were far different than at any time in the past, including during previous warm intervals. This conclusion led me to an investigation of modern human impacts and a hypothesis that recent changes in the traditional nomadic grazing practices, due to changing political and economic conditions after the end of Soviet policies, have combined with recent drought to increase the input of sediment and nutrients to the lakes, leading to deleterious conditions. Future research in this area will focus on determining the mechanism for increased erosion, working to determine the relative impact of human land-use versus climate change on the deteriorating condition of many lakes, measuring the effects of increased nutrients on the lakes with in-lake experiments, and continuing to document the interactions of environmental and cultural changes on the watersheds. See http://www.smm.org/mongolia/
Landscape-level controls on terrestrial, aquatic, and wetland responses to climate change in the southern Canadian Arctic
Climate is changing rapidly in the Arctic as evidenced by a 0.4°C per decade rise in temperature over the past 40 years. Ecological responses to this warming include increases in lake productivity, permafrost thaw, shrub expansion, and northward shifts in the subarctic tree line. Paleoecological studies have played an important role in understanding modern and historic climate change in the Arctic, but relatively little is known about how landscape, in particular peat development and exposed till, constrains terrestrial, aquatic, and wetland responses to climate. In this project we study six lakes across the forest-tundra ecotone of northern Manitoba. In lake sediment, peat, and soil cores we will variously analyze pollen/spores and charcoal, diatoms and silica, phosphorus, carbon and nitrogen (including isotopes), magnetic remanence, pollen/spores, and grain size. Our objectives are to (1) understand the role of landscape in mediating lake and terrestrial ecosystem responses to climate, and (2) investigate the impacts of changes in terrestrial and wetland ecosystems on adjacent lakes. Results will be broadly applicable to on-going efforts that model the impacts of warming on carbon dynamics in the arctic tundra and peatlands. See www.smm.org/scwrs
Evaluating Past Drought Conditions in the Nebraska Sand Hills Using Paleolimnologic Records
Working with an established data set of diatom samples and water chemistry collected from lakes across Nebraska, I helped to investigate how diatom assemblages could be used to infer changing water levels in the inter-dune lakes of the Nebraska Sand Hills. The lakes are surface expressions of the regional water table and fluctuate rapidly with large changes in available moisture. Diatom responses to these lake level changes appears to be complex, but a model to infer large and persistent changes in water level was developed. Research into the past movement of the sand dunes had established a Holocene history of major drought episodes, however, using lake records allows for a more temporally refined history of drought and provides the means to investigate regional differences in the timing and magnitude of drought episodes.