Spatial and historical variation in sediment phosphorus fractions and mobility in a large shallow lake

Temporal and spatial variation in sediment P composition and mobility were investigated in Loch Leven. Little change was observed in total sediment P (surface sediment at 4m depth), in comparison to a previous study (1990), despite significant reduction of external point sources of P. Labile P and residual P have both increased (0.007-0.039 mg PO4-P and 0.121-0.420 mg PO4-P per gram dry weight of sediment, respectively) since 1990. An analysis of P fractions, along a depth transect, indicated elevated labile P concentrations in shallow water sediment (< 12 m overlying water depth). Regression analysis showed that spatial variability in reductant-adsorbed P was significantly related to sediment chlorophyll a concentration (R-2 = 0.733, p < 0.05). This may be linked to the production of oxygen, by benthic algae, resulting in the maintenance of an oxygenated layer at the sediment surface. Variation in labile P was best explained by overlying water temperature and equilibrium phosphate concentration (EPCO). (c) 2005 Elsevier Ltd. All rights reserved.