Spatio-temporal variability of surface sediment phosphorus fractions and water phosphorus concentration in Lake Peipsi (Estonia/Russia)

Abstract

Spatial and temporal variations in the contents of total phosphorus and five P-fractions were investigated in the surface sediments of large and shallow Lake Peipsi (area 3555 km 2 , mean depth 7.1 m) and compared with total phosphorus (TP), dissolved inorganic P (PO 4 -P) and dissolved oxygen (O 2 ) concentration in the overlying water column. The aim of the study was to determine the relationships between the sediment P and water P concentration dynamics. Samples from the uppermost 10-cm layer of the sediment and water samples from surface and near-bottom layers were collected simultaneously at six monitoring stations twice a year (in March and August) from 2004 to 2009. The results indicated that the concentrations of different P-fractions in the studied sediments varied greatly. Total P in sediment ranged from 470 to 1400 mg kg -1 dry mass (DM), while the loosely bound (labile) P (NH 4 Cl-P) was the smallest and the most variable fraction (range from 3.6 to 43 mg kg -1 DM). The metal oxide-bound P (NaOH-P) was also highly variable (range from 48 to 660 mg kg -1 DM), whereas the concentration of calcium-bound P (HCl-P) was relatively even (range from 300 to 550 mg kg -1 DM) in all the studied sediments. Redundancy analysis results revealed that different phosphorus fractions in sediment had statistically significant relationships with bottom-water variables like TP (in winter) and O 2 (in summer). Our results show that the oxygen conditions have deteriorated in the lake during the last decades, which may have enhanced the release of P from the sediments.