A MULTI-CENTURY BIOGEOCHEMICAL RECORD FROM A SMALL SHALLOW LAKE: EVIDENCE OF A SUCCESSFUL CONSERVATION EFFORT

As part of a larger study of shallow lakes in West-Central MN, we used a ²¹⁰Pb age- dated core from Blakesley Lake and analyzed sediment accumulation rates, loss on ignition (LOI), C:N ratios, fossil diatom communities, and elemental data as proxies to understand the past ecology of the lake. Our data suggests that there were two important changes in land use impacting this lake. A significant increase in inorganic sediment (> than 15 % increase), sediment accumulation rates and elemental concentrations (e.g. Al) indicative of catchment erosion (3-4 times pre-settlement values) and an increase in C:N values of organic matter indicate a sharp increase in erosion and input of terrestrial materials near the settlement horizon in 1890. Following the establishment as a protected Waterfowl Production Area (WPA) during the 1970s a desired shift towards pre-settlement values was recorded. This research has implications for the protection and restoration of shallow lake ecosystems. Shallow lakes are known to exist in two distinct stable regimes; either a clear-water regime which is dominated by macrophytes or a turbid regime which is dominated by algae. Despite the land use changes, diatom assemblages suggest that Blakesley Lake has been biologically stable over the last 160 years. A number of other study lakes from this region show no such stability and a tendency towards the turbid regime in recent decades. A better understanding of the controls that are keeping this system stable might provide useful clues to the management of biologically stable systems.