Abstract
The eutrophication of freshwater is a concern across the world and often occurs in areas that are in close proximity to human development. Early indicators of nutrient enrichment are generally evidenced in the littoral zones of lakes due to their proximity to incoming sources of sediment and associated nutrients. Previous studies in local lakes of northern Idaho indicated that the rapid growth of periphyton and its high biomass were directly related to human density in the sub-watersheds, making periphyton monitoring a possible tool to identify bays at risk of eutrophication. I tested the hypothesis that monitoring the growth of periphyton on artificial substrates was a tool capable to distinguish variation in watershed anthropogenic activity across bays. Seasonal nutrient loads delivered to two of the study bays were quantified to make preliminary comparisons between watersheds. The loads of total phosphorus and total residue differed between watersheds disproportionally to watershed area, indicating that some factor(s) other than watershed size, such as differences in land use, interact to cause differential nutrient loading between the bays. Despite evidence that the watersheds differed in nutrient loading indicators, periphyton response did not differ to a high degree of confidence between bays. Differential nutrient loading to bays of Coeur d’Alene Lake may be masked by different bay-specific retention regimes or other in-bay processes that lead to internal loading. These findings indicated that the approach used in this study to monitor periphyton was not a satisfactory method to detect nutrient enrichment in bays of Coeur d’Alene Lake.