THERE ARE SO MANY LAKES AND MY CORER IS SO SMALL: PROVIDING REGIONAL CONTEXT FOR SEDIMENT-CORE STUDIES OF ANTHROPOGENIC CHANGE

Within the last several decades, the paleolimnological analysis of lake-sediment cores has developed into an extremely powerful tool for assessing the magnitude and timing of anthropogenic impacts on aquatic and terrestrial systems. During this period a variety of techniques have been refined to the point that quantitative assessment of eutrophication, erosion, and toxic pollution are now possible. Such methods have usually been applied at individual sites on an experimental basis to refine methodologies or to answer management problems unique to that lake. Few studies have utilized paleolimnological tools to survey historic changes in water quality for a large number of lakes, largely because of the effort required for the analysis of a single sediment core.

For the lake-rich state of Minnesota, where the study of sediment records has a long history, we have been able to compile a database of several hundred ²¹⁰Pb-dated cores spanning a range of human impacts from land-use conversion to long-range atmospheric pollution. The lakes themselves range from those in near-pristine wilderness areas to lakes totally embedded in urbanized or row-cropped catchments. This compilation provides a large-scale picture of the magnitude of change that Minnesota’s lakes have undergone in the last two centuries, how that change varies by region, how it is modulated by local geographic factors (e.g. watershed size, topography), and what the most important drivers are. This information represents an important baseline for management efforts aimed at reversing these negative consequences, and at the same time helps improve our understanding of the biogeochemical processes involved.

This large core database also provides valuable context for individual core studies involving single lakes, such as those aimed at local management concerns or developed for student research projects and other educational purposes. The changes manifest in individual lakes can be compared to those represented in a larger population to answer questions such as, are the changes represented in the study lake large/small relative to other regional lakes, is the timing of change similar or different, and what does this tell us about likely drivers and the effect of local factors such as topography, hydrology, and geology?