Phosphorus Release from Sediments in Aquatic Ecosystems: A Cross-System Study

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Lake sediments, by their ability to retain or release dissolved phosphorus, play a critical role in controlling p- lading to the water column. In the ocean P release can be predicted relatively accurately simply from a knowledge of how much decomposition occurred. Thus, in marine systems post- decompositional factors (sorption, mineral formation, microbial immobilization) are of minor importance in comparison to decomposition. In freshwaters, on the other hand, these post- decompositional factors are of major importance making sediment P release much more difficult to predict. Despite decades of research on sediment P release in freshwaters, and lists of factors that might influence this release in the laboratory, there is essentially no knowledge as to which of these factors are actually important in natural systems; consequently there is limited ability to predict P release. Cole, Caraco, and Likens propose to investigate the controls of P release in both hard and soft-water lakes over a very broad geographic range. They will use a straightforward, in situ, geochemical approach modified from oceanography, to investigate P release both empirically across a large number and range of lake types, and mechanistically in a of suite six lakes that differ dramatically in their P release responses. Preliminary results suggest that: 1) Contrary to standard limnological dogma, oxic versus anoxic conditions explains very little of the enormous natural variation in sediment P release among systems; 2) this variation is best explained by the sulfur content of the system. Cole, Caraco and Likens are very productive and innovative researchers who have provided a unique way to investigate nutrient fluxes. The Institutional support for this research is excellent. The investigators propose a feasible mechanism to explain phosphorus fluxes in freshwater systems. The tests proposed in this research should lead to important information that will impact water management policies.