Distribution and speciation of phosphorus in sediments of Dongping Lake, North China

Dongping Lake is an important regulator for the Eastern Route of South-to-North Water Diversion Project in China, and the water quality assurance of it is of great importance. To investigate the distribution characteristics and burial process of phosphorus (P) in Dongping Lake as well as their relationship with regional economic development and human activities, 33 spatially distributed surface sediment samples and one lake sediment core were extracted from Dongping Lake. A harmonized procedure for the P forms in freshwater sediments developed by the European Programme, Standards, Measurements, and Testing was used in this paper. The results show that NaOH–P (P bound to Al, Fe, Mn oxides or hydroxides), HCl–P (Ca-bound P), inorganic phosphorus (IP), organic phosphorus (OP), and total phosphorus (TP) in the surface sediments show a strong spatial variability. The highest NaOH–P and OP concentrations were observed in the eastern and south-eastern region of the lake and decreased gradually away from the mouth area of Dawen River. We deduced that anthropogenic input via the Dawen River is the main contributor. The higher concentration of HCl–P occurred in the north-west region of the lake and increased in a gradient away from the mouth area of Dawen River, and this pattern of distribution could be related to grain-size effects and higher transport energies close to riverine inlets. Pollution reflected by phosphorus in the core sediments of Dongping Lake is well consistent with the economic development history of Dongping County. From the beginning of the 20th century to the middle 1970s, the concentrations of each P speciation did not vary largely and runoff of the Yellow River mainly contributed to the P accumulation in the sediment, which might reflect the background values of them in the lake in pre-industrial period. The stable Mz (mean grain size), low loss-on-ignition (LOI), and high sedimentary flux also support this. The rapid increase of NaOH–P and OP at 10–0 cm (especially 5–0 cm) indicates the enhancing anthropogenic eutrophication since the middle 1970s. The LOI peak period and a coarsening of particle size also support this interpretation. However, the decreasing of TP and HCl–P was attributed to the change in sediment supply. As due to construction of dams around the lake, runoff of the Dawen River mainly contributed to the P accumulation in the sediment during this period.