COOCCURRENCE AND POTENTIAL CHEMICAL COMPETITION OF PHOSPHORUS AND SILICON IN LAKE SEDIMENT

Various chemical approaches were used to characterize P and Si in the surface sediment of Lake Vesijarvi, Southern Finland. The dynamic equi librium between solid and solution P in aerobic and anaerobic sediment was investigated by means of desorption-sorption isotherms. The sedim ent material was rich in hydrated Al and Fe oxides and, accordingly, h ad a high P sorption capacity and a very low P concentration (5 mu g l (-1)) in the interstitial water under aerobic conditions. Approximatel y 25-30% of total P and almost 90% of total Si were bound in mineral l attices, i.e. in a stable form not participating in biological and che mical transformations. Organic P comprised about 20-25% of total P and was mainly in practically insoluble form not extractable by dilute ba se or acid. Phosphorus participating in sorption-desorption reactions was considered to originate from reserves bound on oxide surfaces. Whe n the oxide bound P reserves were determined by fractionation analysis , a large amount of Si (corresponding to about 30% of biogenic reserve s) was also dissolved. Anaerobiosis increased distinctly the occurrenc e of both elements in the interstitial water. These dissolution patter ns suggest that P and Si are bound to the same components and, therefo re, compete with each other for the sorption sites. This chemical comp etition, in turn, may be of importance in the nutrient exchange betwee n solid and solution phase in sediment. Copyright (C) 1996 Elsevier Sc ience Ltd