Document Type

Report

Publication Date

January 1983

Abstract

Introduction: Phosphorus inputs to lakes and reservoirs from tributary streams and non-point sources are well-known contributors to nuisance algal growths that degrade water quality for potable and recreational uses in lakes and reservoirs. However, phosphours inputs to the euphotic zone may also occur from within the lake itself, as a result of releases from both oxic and anoxid sediments. Such releases may originate from phosphorus inputs to a lake or reservoir during high runoff periods in the previous winder or spring, or they may represent phosphorus trapped in the sediment many years earlier, when phosphorus contributions from natural or anthropogenic sources were higher that at present. Whatever their origin, phophours loading from sediments may exacerbate the eutrophication process or delay the recovery of a eutrophic lake or reservoir following reductions in external phosphous loading aimed at water quality restoration (Begtsson 1978, Larsen et al, 1975, 1981). This phenomenon has been graphically linkened to the "memory" of a lake for its previous trophic state: oligotrophic, lakes tend to trap phophorus in their sediments, thus remaining oligotrophic, while eutrophic lakes mine their sediments for phosphorus during summer stratification and further contribute to the production of late summer and fall phytoplankton blooms (Imboden 1974). Virtually no information is availabe on the extent to which internal phosphorus loading is important in reservoirs in the Intermountain West, or on the factors controlling phosphous uptake or release in these sediments. in fact, there reaims considerable debate over the accuracy of the simple paradigm outlined above for all lakes and reservoirs. Under certain circumstances, oxic release rates of phosphorus from some sediments can be substantial, while anoxic release rates may be relatively low (Holdren and Armstrong 1980). A series of studies on sediments in several reservoirs in the Intermountain West is being conducted at the Utah Water Research Laboratory, Utah State University, in order to further our understanding of important sediment-water interactsion in the phosphorus cycles of such reservoirs. The data reported here represent preliminary results from the first field season of these studies. They relate to the phosphorus chemistry of the sediments themselves, and to P release simulations carried out on intact sediment cores incubated in the laboratory. The aim of the discussion that follows is to compare the chemistry and release rates of cores from several reservoirs, and to suggest some implications of these results regarding the potential for further eutrophication or the potential for recovery of the reservoirs under study. Because the inferences are drawn from preliminary data, the conclusions should be regarded as tentative. Messer et al. (1983) has presented a rationale for related such sediment release data to the impact on the overlying water column.

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