High total phosphorus concentrations in organic flocculent sediments of shallow freshwater ecosystems

Kinsman, L.E., J. O'Brien, and S.K. Hamilton

Presented at the All Scientist and GLBRC Sustainability Meeting (2009-05-05 to 2009-05-07 )

Phosphorus (P) tends to be the ultimate limiting nutrient in aquatic ecosystems. The quantity of available P is often determined by sediment binding and release processes. We obtained 32 sediment samples from shallow freshwater ecosystems in Southwest Michigan. Sediment cores were separated into consolidated and flocculent strata for analysis of percent organic matter, total sediment phosphorus (TP), and HCl-extractable iron (HCl~Fe). Sediment TP ranged from 0.13-2095 µgP/gdw, with an average of 318 µgP/gdw. On average, flocculent sediment contained three times the TP (644 µgP/gdw) of consolidated strata below (217 µgP/gdw), and it was also higher in organic matter and HCl~Fe. Across all samples, total sediment P was unrelated to HCl~Fe, but was positively related to percent organic matter. Sequential phosphorus fractionation performed on a small subset of these samples suggests that the vast majority of P in these sediments is found in organic fractions. Many past studies have focused on the reactivity of inorganically-bound orthophosphate in sediments. Future studies should investigate the reactivity of the quantitatively dominant organic P fraction, with particular focus on the unique processes of flocculent sediments.

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