LAND USE IMPACTS ON WATER QUALITY IN THE VALLEY OF THE GREAT LAKES MONGOLIA

The Valley of the Great Lakes (Western Mongolia) is a hydrologically closed basin in an ecologically significant region of Central Asia. The region includes several areas designated “Strictly Protected” by the Mongolian government and is registered on the UNESCO Biosphere Reserve and World Heritage List. Understanding the development of the modern landscape and fluctuations in climate and land-use over the geologically recent past is important to understanding present impacts on the landscape and future conservation of these sensitive eco-regions. Since the end of Soviet authority in 1991, traditional nomadic herders have seen large incentives to increase the number of livestock in their household, particularly numbers of cashmere goat. Mongolians in this region, as well as domestic and wild animals, are dependent on scarce and diminishing freshwater resources. The increasing demand and transitional regulation of these resources may be increasing the nutrient load in these systems and creating a deleterious situation for both wildlife and local herders. In order to more fully evaluate recent eutrophication of water bodies and provide a background for future conservation efforts, a paleolimnological study of past water quality is being undertaken using a diatom-based transfer function, alongside other proxies, from numerous lake cores in the region. Presented here is a diatom-based calibration set, linking modern diatom assemblages with their present preferred environment. Surface assemblages and a suite of water chemistry variables were collected from 64 lakes in the region, ranging from fresh to hyper-saline, and across a variety of ecological gradients. Total phosphorous (TP) and Secchi depth, traditional indicators of water quality and lake trophic status, are strongly correlated with changing diatom assemblages and reconstructions are based on this inference model. Analysis of historical diatom communities from multiple lakes indicates increasing TP and decreasing Secchi depth in the most recent several decades.