A time-dynamic phosphorus model for the profundal sediments of Lake Erken, Sweden

Abstract

Phosphorus profiles in core samples from Lake Erken (Sweden) sediments are combined with a seasonal study of surficial sediments and pore water measurements to develop a model of the phosphorus dynamics in these sediments. Phosphorus is divided into four functional groups: inert phosphorus, organic phosphorus, phosphorus sorbed to iron and phosphorus dissolved in pore water. The model includes processes of sedimentation, burial, chemical equilibrium between dissolved phosphorus and phosphorus sorbed to iron, mineralization of organic phosphorus and vertical diffusion. The model is shown to produce reasonable profiles of concentrations of the four forms of phosphorus in the sediment compared with empirical data. About 50% of the settled phosphorus is eventually buried, and the rest is released to the overlying water column. The amount of phosphorus released is sensitive to temperature and oxygen concentration in the bottom water. Extrapolating the results to the whole area of sediment accumulation is not straightforward, but we suggest that around 3.0 tons of phosphorus is released annually from the profundal sediments of Lake Erken. Year to year variations in internal loading were related to the anoxic area, and we suggest that a shift in the sediment-water equilibrium of P due to an expected increase in temperature may result in increasing phosphorus concentration in the water column.