Geochemical distribution and forms of phosphorus in the surface sediment of Netravathi-Gurupur estuary, southwestern coast of India.

Estuaries are the most productive transition ecosystem and phosphorus (P) plays an important role in these ecosystems. Therefore, in the present study, sequential extraction method was used to determine the abundance of five sediment P fractions (calcium (Ca- P), Iron (Fe P), aluminum (Al P), exchangeable (Ex-P) and organic (Org P) bound P) in Netravathi-Gurupur estuary, India. Total phosphorus (TP) content varied from 435-810 mg/kg (non-monsoon) and 258–699 mg/kg (monsoon). Inorganic P was dominant part. Different P fractions followed similar order (Fe-P > Ca-P > Al-P > Org-P > Ex-P) with respect to seasons. Fe P was dominant fraction, indicating probable anthropogenic stress. Sediment may act as source of P as bioavailable P constituted 40–69.2 % of TP. Molar ratio of OC to Org-P in sediment indicated terrestrial sources of organic matter. However, the estimated phosphorus pollution index were lower than one except a few cases indicating less ecological risk with respect to sedimentary TP load. [Display omitted] • Sediment P speciation in the Netravathi-Gurupur estuary was studied firstly. • Sedimentary total P is dominated by inorganic pool. • Fe-bound P was dominant chemical forms of P indicating probable anthropogenic stress. • A significant proportion of the sedimentary P pool can be potentially bioavailable. • Average phosphorus pollution index was lower than one indicating less ecological risk. [ABSTRACT FROM AUTHOR]