Phosphorus fluctuation in water and deposition into sediment within an emergent macrophyte stand

Seasonal fluctuation of phosphorus in water, and total phosphorus and different inorganic P fractions (extracted by NH₄Cl, NH₄F, NaOH and H₂SO₄) and organic P fraction (residual P) in surface sediment, were measured in the littoral of oligotrophic Lake Pääjärvi (southern Finland). After the emergence of Equisetum fluviatile L. shoots in mid June, water exchange between the littoral and pelagial area diminished and phosphorus concentrations in water and in surface sediment increased in the inner and mid littoral zones. Phosphorus pool in flocculent, easily resuspensible sediment composed on average 62% of inorganic phosphorus and 38% of organic phosphorus. 63% of the inorganic phosphorus, on the average, was extracted from apatite-P fraction 29% from iron-P fraction 7% from aluminum-P fraction and less than 1% from loosely-bound P fraction. During the growing season, net accumulation of sediment and phosphorus was measured only in the inner littoral zone whereas the outer littoral zones acted rather as a source of phosphorus for the pelagic area. The results of this study indicated that nutrient dynamics in littoral environment was through changes in flow environment greatly governed by the macrophytes.