PHOSPHORUS FRACTIONS IN SEDIMENT PROFILES OF THE EUTROPHIC LAKE MOGAN, TURKEY

摘要

This study was conducted between July 2004 and June 2005 to determine the seasonal and spatial patterns of phosphorus in the littoral sediment of Lake Mogan, and its potential release into the lake water. Total phosphorus and phosphorus fractions in the sediment and overlying water samples were taken mainly from a selected station in the lake, and additionally, some chemical and physical parameters were measured. The amount of released phosphorus was estimated using the total filterable orthophosphate concentrations related to the sediment pore as well as overlying waters with the water content of the sediment, and the diffusion coefficient depending on the temperature. During the research period, sediment phosphorus release fluctuated between 0.002-0.062 μg.m~(-2)d~(-1) reaching a minimum in November and a maximum in June. The estimated values of phosphorus release into the lake quantitatively suggest that the effect of sediment over the trophic level of the lake was minimal. During the research period, total phosphorus (TP) concentrations of the sediment samples varied between 286.00 μg g~(-1) DW and 892.25 μg g~(-1) DW, and the trophic level of the lake was found to be eu-trophic. The greater proportion of phosphorus fractions preventing phosphorus release into the lake was estimated to be organically-bound (Org≈P; 36%), and this fraction was followed by the calcium-bound (Ca≈P; 35%), iron+alumi-nium-bound (Fe+Al≈P; 16%) and carbonate-bound (CO_3≈P; 13%) phosphorus fractions, respectively. With regard to low-sediment phosphorus release into the lake, the iron+ aluminium-bound fraction (Fe+Al≈P) was effective because of the high iron content of the sediment (13450-44450 μg g~(-1) DW). During the research, another effectual component in the low-release of phosphorus was a high TFe/TP ratio (mean 45.33). High sediment clay content and macro-phyte presence at the station were the other effective factors of low-sediment phosphorus release.