Abstract
Anthropogenic activities alter the delivery of nutrients, particularly nitrogen-N and phosphorus-P, to water bodies resulting in increased aquatic primary productivity. This process is referred to as cultural eutrophication and often results in blooms of toxic cyanobacteria which produce some of the most potent toxins known to humans, making management strategies imperative. Fernan Lake, a small lake in northern Idaho has experienced harmful algal blooms since the 1990’s. It is hypothesized that these blooms result from the presence of excess phosphorus, however, few data were previously available to test this hypothesis. Before any management action can be implemented at Fernan Lake, a detailed analysis of the loading relationships of nutrients and sediment to the lake is required. I performed a detailed mass balance of Fernan Lake using high resolution data to calculate a water and nutrient budget for the lake to quantify the amount of P and sediment retained during one calendar year. Fernan Lake retained 81% of the P and 68% of the sediment that entered it. The majority of the loads came in during the short (January-May) runoff period. I used two methods to quantify internal loading in Fernan Lake and tested if sampling only one site was adequate to describe whole-lake concentrations. Sources of the internal loading that Fernan experiences can be attributed to either wind-induced sediment resuspension or phosphorus excretion by the large fish community. Further research is needed to identify the source of internal loading. This study gives insight into the loading relationships in Fernan Lake, and provides directions for future research.