Phosphorus Fractionation in relation to algal growth (Scenedesmus Obliquus) in western river Sediment of Urmia Lake basin

Background and Objectives: Phosphorus is a finite resource and an essential nutrient for sustaining all forms of life in aquatic environment. It was also found in various chemical forms which might be gradually released into water column and exacerbate eutrophic condition in rivers and lakes. Thus, P fractionation provide useful insight into risk posed by P-associated sediments to aquatic environment. There is little information available regarding P chemical forms and its bioavailability in aquatic ecosystems in Iran and there was limited number of publications regarding the evaluation of P forms release from river sediments. The published reports and field observations clearly insist on the phytoplankton growth and some dense algal blooms occurring during years with low water in river sediments. Thus, evaluation of P in aquatic environments by algal bioassay and threats of losing biodiversity could be essential.
Material and Methods: Thirty four river sediments from seven main rivers of the Urmia Lake basin were taken from depth of 0-10 cm for algae (Senedesmus Obliquus) bioavailable P evaluation by sequential chemical extraction. Phosphorous pools in these sediments extracted using operationally defined method that includes as exchangeable (EXCH-P), iron and aluminum oxide-bound (Fe/Al-P), calcium bound (Ca-P), and residual P (RES-P). Principle component analysis was conducted to determine the important properties and chemical forms of P in sediment samples. Algal bioassay was carried out to distinguish the bioavailable P fractions. Hierarchical cluster analysis and Pearson simple correlation were applied for selection of the samples of algal assay and determining bioavailable P fraction, respectively.
Results: Generally, sediments had coarse texture with high amount of silt and very fine sand. Principle component analysis indicates that particle and carbonate-related properties have significant role in determination of sediments properties. The average rank order of P extraction by sequential extraction were, Ca-P > RES-P > Fe/Al-P > EXCH-P for all rivers except the Simineh Chai. Simineh Chai sediments had higher concentration of Fe/Al-P than RES-P, indicating possible pollution in the river. There was significant correlation between Fe/Al-P (r = 0.947, P< 0.0001), EXCH-P (r = 0.668, P < 0.01), and RES-P (R=0.563, P Conclusion: Analysis of P fractions in sediments by sequential chemical extraction shows that Fe/Al-P fraction provided higher potential bioavailability, and due to significant correlation with algal growth is proper indicator to evaluate river health and eutrophication of Urmia Lake. River sediment of Urmia Lake had high ability to retain P in Ca-P fraction which could be recalcitrant P pool for algal growth.