Nutrient Concentrations and Distributions within the Lower Elwha River during Dam Removal

Abstract

The objective of this research was to characterize nutrient concentrations and distributions throughout the Elwha River watershed, focusing on dissolved inorganic nitrogen (DIN), phosphorus and silicic acid. Previous research has indicated that the Elwha River is oligotrophic, however with the removal of the dams comes the subsequent discharge of a large fraction of the 1.9x106 m3 of sediment trapped behind the dams. Understanding the nutrient composition and distribution relative to grain size and suspended sediments will provide scientists with perspective as to how the ecosystem is going to react to dam removal. Sediments and their pore water were collected in the field and analyzed. Additional data was included from U.S. Geological Survey and the Department of Ecology. The culmination of this data demonstrates that the upper stretches of the Elwha River are nutrient poor but the recent removal of the two dams has led to an increase of nutrients within the nearshore environment, which is hypothesized to be related to the discharge of sediment based on this research. Implications for future studies can be made that refer to primary productivity, riparian health and the return of salmon.