Biogenic silica, eutrophication risk and different forms of phosphorus in surface sediments of Anzali wetland, Caspian Sea.

This investigation aimed to determine the contents of biogenic SiO ₂ and different phosphorus forms (P) and to evaluate phosphorus ecological risk in surface sediment of Anzali wetland. According to the results, biogenic SiO ₂ ranged from 0.29 to 3.04%. Also, the average biogenic SiO ₂ at all studied stations was 1.36 ± 0.83%. Results indicated that total P (TP) was between 493 and 771 ppm, averaged 637.20 ± 79.41 ppm. Moreover, inorganic P (INTP) ranged from 256.63 to 376.89 ppm and composed 51.46 ± 4.68% of total P. The percentage of P-forms was in descending order: residual-P > Fe-P > Ca-P > Al-P > labile-P. Phosphorus pollution index (PPI) ranged from 0.82 to 1.29, with an average of 1.06 in the sediment of the Anzali wetland. The Sediment P saturation (SPS) values varied considerably from 40.96 to 83.57, with an average SPS value of 49.1. Based on the eutrophication risk index, all stations except one had a low eutrophication risk index.
(Copyright © 2021 Elsevier Ltd. All rights reserved.)