We tested the hypothesis that there would be measurable losses of phosphorus (P) from surficial sediments of Upper Klamath Lake (UKL), Oregon, if sediments were a source of P during an algal bloom.
We compared concentrations of total and forms of P at various depths in cores collected before and after
the onset of a large Aphanizomenon flos-aquae bloom. Concentrations of inorganic P were determined
in extraction solutions of MgCl2 (1 M, pH 8), citrate-dithionite-bicarbonate, and 1 M HCl. Sediments
below 2 cm were dominated by residual P which is defined as total P minus inorganic P. During the study period, data from the top 2-cm of sediment indicated (a) significant decrease in total P concentration,
primarily associated with iron oxyhydroxides at one site, and (b) significant increase in total P concentration associated with residual P at a second site. Data from two other sites indicated no net changes in concentrations of total P.