Our research investigates the influence of historical clearcut logging practices on percent organic matter, sediment accumulation rate, and phytoplankton communities in two northern Wisconsin lakes. Extensive networks of inland lakes and rivers, in addition to railroads, facilitated timber harvesting in northern Wisconsin in the late 1800s and early 1900s. By the early 1920s, the northern forests were predominantly cutover. In streams, elevated runoff, sedimentation, and nutrients appear to drive ecological changes following deforestation. However, responses of lakes to deforestation are less consistent and it appears as though landscape characteristics play a strong role in shaping lake response to landscape disturbance. Our research investigates the responses of lakes occupying different landscape positions to deforestation driven by logging and fire.
Results/Conclusions
Sediment cores from Allequash and Sparkling lakes in the Northern Highlands Lake District indicate changes in organic carbon content, sediment accumulation rate, and phytoplankton communities over the time period analyzed, ca. 1885-1950 CE. Exact dates of clearcut logging in our lake catchments are uncertain, however we believe harvesting occurred in this region around 1900-1909 CE based upon historical accounts. In both lakes, the highest values of percent organic matter occurred in 1890 (Allequash, 50.8%; Sparkling, 54.48%), but these levels tend to decrease over the following 40 years. Sediment accumulation rate in Sparkling Lake shows a sharp increase between 1886-1902 CE, potentially signaling logging-induced erosion. Phytoplankton communities, as indicated by sedimentary fossil pigments, also show shifts prior to and following the logging era. Allequash shows an increase in cyanobacterial concentrations, a trend substantiated by negative δ15N isotope signatures over the same period. Similar changes in cyanobacteria are not evident in Sparkling Lake, potentially indicating the effect of landscape position in shaping lake response to watershed disturbance.
