2003: History of Nutrient Loading in Lake Matoaka

Daniel Thomas (Biology)

We examined one potential cause of the hyper-eutrophic state of Lake Matoaka, nutrient loading incurred through changing land use in the watershed over the last seventy-years. Empirical historical analysis by use of sediment cores or other means is difficult, so we used a mathematical model, Generalized Watershed Loading Functions (GWLF), to predict nutrient and sediment flow into the lake. Input into the model includes soil-type and land use ratios, and climate data. Changing land use was estimated by digitizing aerial photographs from approximately every ten years, from 1937 to 2000. GWLF predicted increasing loads of nitrogen and phosphorus as deforestation and development increased in the watershed, but decreased erosion/sediment. The nitrogen and phosphorus increases were expected, but heavy sedimentation has been observed for the lake in the past decades, contrary to the predictions of the model. This can be explained by the large intervals between aerial photographs; data from every ten years misses the vulnerable, transitional periods that soon-to-be-developed plots of land must undergo, when soils are exposed and disrupted, causing heavy erosion from rainfall. The results from GWLF point to development and deforestation of the College Woods as a likely cause of the eutrophication of Lake Matoaka.