Sedimentological Effects of Aeration-Induced Lake Circulation

Abstract

ABSTRACT Multiple sediment cores were collected from each of ten Minnesota lakes (five aerated and five non-aerated) to evaluate the long-term effects of aeration-induced circulation on sediment accumulation and composition. Coring sites for each basin were widely spaced at different depths to encompass a range of depositional environments, and sediments were dated by 210Pb methods. All lakes, aerated and non-aerated, show an increase in sediment accumulation commencing around the time of European settlement in the region (c. 1880). At the same time, sedimentary organic content decreases by 5–40% in all but three lakes due to increased inputs of silts and clays from erosion of catchment soils. Sediment accumulation rates do not decline with the onset of aeration in any of the aerated lakes, but in most cases remain near maximum values to the present day. A recent decrease in sediment flux, evident in one non-aerated lake, was driven by land-use changes in the catchment that decreased nutrient and sediment loading. Sedimentary organic content does not decline in any of the lakes, aerated or non-aerated, during the last two decades. Historic patterns of sediment accumulation and composition in the aerated lakes are no different from that shown by non-aerated lakes. Results from this study do not support claims that aeration-induced circulation will enhance the removal of organic sediments from lake basins either by mineralization or offshore transport.