CORRELATION OF HISTORICAL AND SEDIMENTOLOGICAL RECORDS FROM GOSHORN LAKE, A SMALL LAKE IN A COASTAL DUNE COMPLEX OF LAKE MICHIGAN

Sand in small lakes associated with coastal dune complexes has been used as a proxy for aeolian activity. To do this, it is important to use a sampling strategy that maximizes the probability of encountering aeolian sand and minimizes the probability of encountering sand transported by fluvial processes or washed or slumped into the lake from the shores. To test possible sampling strategies, lake sediments were collected from Goshorn Lake in Allegan County, Michigan. This lake abuts a Lake Michigan coastal dune complex at one end, has a stream entering it from the opposite end, and is subject to anthropogenic disturbances along its banks. Aerial photographs, township building records, and a published oral history of the lake were used to reconstruct aeolian activity and anthropogenic disturbance over the last 76 years. This history was compared to sand concentration as a function of depth obtained by textural analysis of 12 Glew cores collected across the lake basin. ¹³⁷Cs analyses were used to identify the 1963 bomb peak as a temporal reference point. The least amount of sand occurs in the cores furthest from the dunes and closest to the stream. A few small sand peaks, <20%, are present. Cores collected closer to the dunes are characterized by multiple sand peaks, between 20–80% sand in the lower to middle portion of the core. In the upper portions of the cores, the upward decrease in sand begins before 1963, consistent with aerial photographs showing a decrease in dune activity after 1938. One Glew core recorded a spike in sand after 1963. Historical records suggest this can be attributed to major construction activity along the shore at that location during this time period. The small sand peaks near the stream inlet may reflect increases in fluvial flux while sand peaks near the lake margins can reflect increases in sand washed into the lake after shoreline disturbances. Therefore, the majority of the sand in the lake sediments appears to be aeolian. By collecting cores at the end of a lake closest to the dunes and avoiding stream inlets and lake margins, it is possible to maximize the probability of encountering aeolian sand. Combining this strategy with an age model based on ²¹⁰Pb dating (currently in progress) will extend the history of aeolian activity around Goshorn Lake back beyond the 1938 starting date of aerial photography.