Mobile phosphorus in lake sediments, sludge and soil : A catchment perspective
Sammanfattning: Phosphorus (P), a key element in lake primary production and eutrophication, is accumulating in agricultural soil, urban landfills and lake sediments. This accumulation increases the risk for non-point losses of P to ground- and surface waters.Forms and amounts of potentially mobile P were determined in digested sewage sludge, soil, and lake sediment in order to predict maximum future non-point P-losses from these P-accumulating systems. To determine concentrations of potentially mobile P a new method was developed in which water differing in oxygen status is passed through samples enclosed in flow-through chambers. Released P was labeled potentially mobile P, and under oxic and anoxic conditions accounted for 20-30% and 95%, respectively, of the total P cement in digested sewage sludge after passage of water corresponding to 10 years of rain. P released from soil mixed with sludge accounted for 30-40% of the total P content.In the Lake Erken sediments, there was 4.8 g/m2 of potentially mobile P, which was made up of 3.7 g/m2 NaOH-nrP (organic-P) and 1.1 g/m2 BD-P (Fe-P). Organic-P mobilized under anoxic conditions in deeper sediment layers, probably representing bacterial-associated P, was adsorbed by iron (Fe) in the oxic surface sediments. Fe-P then acted as the main P-source to the water column during spring mixing. Analysis of sediments from six Washington lakes previously treated with aluminium (A1) showed that added A1 is buried in the sediment together with adsorbed P at a ratio of 11:1 (by weight).Sludge landfills and fertilized soils contains large amounts of potentially mobile P compared with lake sediments. Non-point P-losses from terrestrial systems thus have the potential to cause the eutrophication of lakes and coastal areas. Based on the results obtained in this work, its possible to estimate maximum future P losses from certain types of P-accumulating systems. This knowledge may be crucial in the development of cost effective measures for reducing P losses to surface waters. The recycling of P within terrestrial systems can help substantially to both reduce P-losses to aquatic systems and preserve P for generations to come.
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