Joseph Donovan - US grants

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.

This study will utilize high-resolution analysis of cores from closed-basin lakes in the northern Great Plains to determine the frequency, intensity, duration, periodicity, and synchrony of droughts during the Holocene and to examine how vegetation and fire responded to drought. Since vegetation and lakes in the Northern Great Plains are highly sensitive to drought, this region offers an extraordinary opportunity to document decadal- to-century scale climate cycles in the mid-continental United States.

The working hypothesis is that the signal of drought from a single site is regional and that droughts were synchronous across the region. To test this hypothesis, the study will utilize lake-sediment mineralogy, fossil pollen, carbon isotopes of charcoal, and charcoal abundance to develop detailed reconstruction of drought cycles from the Northern Great Plains at a decadal scale. This will facilitate evaluation of the teleconnections between mid-continental climate and the North Atlantic region, where recent investigations have linked century to millennial scale climate oscillations to variations in solar irradiance.

This research has the potential for broad impact in range of physical and social sciences. Assessment of drought impacts forecast by atmospheric models for the Northern Great Plains requires understanding of natural drought variability. Evidence from paleoscience suggests that 20th century droughts (e.g., the Dust Bowl) do not provide perspective on the range of severe droughts that have occurred in even the recent past. Historical evidence is incomplete and paleoscience data have not yet been assembled at appropriate temporal and spatial scales to assess the intensity, periodicity, and impacts of past droughts.