This proposal addresses the problem of determining the hydrochemical response of a groundwater-fed lake to climate change over Holocene time. We intend to determine the relative importance of ground water and surface water input to Elk Lake, Grant Co., Minnesota. We will examine and compare information obtained from ostracode (Crustacea) species distributions, ostracode shell chemistry, and models that describe hydrochemical reactions and groundwater flow. The proposed research will provide an independent means of determining how a lake interacted with groundwater during specific times of past climate change, as well as insight into how lake-groundwater systems can react to future climate change. Our approach will be 1) define the ground water source(s) flowing into Elk Lake at present; 2) recover a complete Holocene core from the lake; 3) reconstruct the solute history using ostracode species distributions, trace-elements, and stable isotope analyses; and 4) test two hypotheses concerning the groundwater input and resultant lake chemistry through Holocene time. This study will provide a new way of reconstructing regional changes in surface hydrology as it responds to climate change and has wide application to the field of hydrology and climatology. The results should be of practical value to hydrologists concerned with surface water-groundwater interactions, and to climatologists interested in climate model validation and forecasting of climate- induced hydrologic changes.
