ASSESSING TWO CENTURIES OF ANTHROPOGENIC IMPACTS TO REX LAKE, SUMMIT COUNTY, OH

The sediment in Rex Lake, a kettle lake in Northeast Ohio, preserves a record of past anthropogenic impacts to the lake and its watershed. Rex Lake is connected to a series of kettle lakes and human-made reservoirs that forms the Portage Lakes System, a popular recreational area. The upper 4 m of sediment, from the middle of the lake, was cored and measured for physical properties, sedimentology and trace metal content. Four intervals having distinct sediment characteristics were identified and related to changing anthropogenic activities. Below 133 cm core depth, an organic-rich mud having low sediment density, magnetic, and trace metal content is present. This sediment is inferred to have accumulated while the watershed was forested prior to Euro-American settlement of the area in 1800. Between 133 and 70 cm depth, organic content decreases, magnetic content and sediment density increase slightly, and trace metal content remains low. This sediment is interpreted to reflect land clearance and increasing soil erosion to the lake as the watershed was settled. A similar decline in organic content, attributed to land clearance occurs in nearby kettle lake cores, for which independent age control exists. Between 70 and 20 cm depth, organic content decreases to its minimum value whereas the magnetic content and sediment density increase greatly. Trace metal concentration increases greatly, with Pb nearly reaching the Probable Effect Concentration value of 128 mg/kg. Boating and other human activities in the Portage Lakes greatly increased during the 20^th century and resulted in the elevated trace metal concentrations. The upper 20 cm of sediment has low organic content and declining magnetic and trace metal content. The reduction in trace metal concentration reflects the effectiveness of the Clean Air and Water Acts, although Pb concentrations have not yet reached natural background level. This study shows that lake sediment cores can be used to assess anthropogenic impacts on lakes and thereby place potential future trends in historical context.