Bioavailability of sediment phosphorus in geochemically contrasting aquatic systems

Excess amounts of bioavailable inorganic phosphorus (BAPi) can lead to a host of deleterious effects including eutrophication of water bodies. As phosphorus (P) often limits primary production in freshwater ecosystems, I examined the changes in bioavailability of sediment bound P as it was stored, transformed, transported, and released in various aquatic systems including an agricultural stream system, a wetland complex, and four geochemically distinct lakes.;Large stores of BAPi were present in stream sediments, but amounts varied with depositional environment, total P concentrations, and iron (Fe) concentrations. BAPi was stable in streambed sediments while post-depositional mineralization of organic P resulted in an increase in the BAPi fraction. The most important factors that influenced dissolved and particulate BAPi transport through the wetland complex during runoff events were extent of wetland inundation (r2 = 0.87), rainfall amount (r2 = 0.42), and rainfall maximum intensity (r2 = 0.37). The wetland was an overall sink for dissolved BAP i and source of particulate BAPi, but BAPi storage varied widely among individual events, ranging from 5% to -64%.;Interactions between P and Fe appeared to influence internal loading in the four lakes. The lake with the highest P loading (Lake Mendota) had the smallest Fe loading, while the lake with the lowest P loading (Sparkling Lake) had the largest Fe loading. Low P retention appeared to be associated with low Fe:P ratios in sediments and pore waters, while high P retention appeared to be associated with high Fe:P ratios. Fe(II) binding by carbonate and sulfide decreased pore water concentrations of Fe and availability of Fe for P scavenging during turnover.;Both geochemical and hydrodynamic controls on BAPi accumulation and transport should be considered when attempting to decrease loadings of P from streams to downstream waters or internal loadings of P in lakes. BAP i is conserved during storage in sediments, thus reduction of non-point loads to the streams and lakes may be masked by release of BAPi from sediments to overlaying water.