Recent Sedimentary History of a Eutrophic Reservoir: Long Lake, Washington

Abstract

Through abatement of present high nutrient loadings to the reservoir and preservation of sediment integrity, we predict that eutrophic Long Lake will experience a rapid recovery after the City of Spokane, Washington, establishes an advanced wastewater treatment plant with phosphorus removal. Two sediment cores were zoned into annual layers according to profile concentrations of organic matter, nitrogen, phosphorus, and diatom frustules. Sedimentation rate was 26 mm∙yr−1 between 1958 and 1973. Below the 25 mm-depth, phosphorus and diatom profiles were most obvious because clay particles, entering the reservoir during spring runoff, covered the biological material precipitated the previous year. This mechanism effectively prevents internal recycling of nutrients, particularly phosphorus, from the bottom sediments. Key words: reservoir, sediment cores, phosphorus, nitrogen, organic matter, diatom frustules, clays, internal nutrient recycling, recovery