New Insights Into Legacy Phosphorus From Fractionation of Streambed Sediment
Emma Lannergård, Oskar Agstam‐Norlin, Brian Huser, Sara Sandström, Jelena Raković, Martyn N. Futter
Abstract
Abstract Streambed and lake sediment was studied in Sävjaån, a eutrophic mesoscale catchment (722 km 2 ) in central Sweden. Triplicate sediment cores from five lakes and nine streams, ranging from headwater to fourth order, were sampled. The sediment was analyzed with a sequential extraction method, where six different phosphorus (P) fractions were measured. The results showed that streambed sediments store considerable amounts of P and in some cases have comparable P contents (g/kg DW) to lake sediment. Land use, soil type, and drainage area (location in the catchment) had a significant effect on the different P fractions found in surficial sediments. Sediment from lakes and forested headwater streams generally had high proportions of organic P and iron bound P. In larger streams located in agricultural areas on clay soils closer to the catchment outlet, with dense sediment and a relatively low proportion of organic matter, P was to a larger extent bound to calcium. Streambed sediment may be an important catchment scale P store and should be considered when modeling catchment P dynamics. The large stores of streambed legacy P should also be considered when performing ditch maintenance to avoid unnecessary mobilization of bioavailable P.