Phosphorus dynamics in water and sediments in urbanized and non-urbanized rivers in Southern Brazil

Phosphorus flux models show that the removal tends to be a common feature in polluted estuarine systems whereas the release of P to the adjacent coastal area occurs in pristine environments. This study analyzes the distribution of P in water and sediments along six rivers in the south coast of Brazil. Three rivers located inside protected areas were considered non-polluted and used as a control of urbanization. The other three, situated within urbanized areas, were considered as having highly elevated concentrations of P. Results showed a different behavior of P in water and sediments located in urbanized and non-urbanized areas. The concentrations of dissolved organic (P-org) and inorganic (P-inorg) phosphorus in water, and the total phosphorus (P-tot) and polyphosphate (P-poly) in sediments where higher in the urbanized rivers compared to the non-urbanized ones. Both P of punctual origin and of diffuse origin contributed to the maintenance of elevated concentrations and disturbed the natural fluxes along the polluted rivers. The minimum and maximum concentrations in urbanized areas varied from 0.39 to 12.45 (μM) for P-org and 0.00 to 5.92 (μM) for P-inorg in water, and in sediments from 89.90 to 808.16 (μM g−1) for P-tot and 0.00 to 76.51 (μM g−1) for P-poly. In non-urbanized areas concentrations in water varied from 0.22 to 1.20 (μM) for P-inorg and 4.43 to 5.56 (μM) for P-org, and in sediments from 45.91 to 652.26 (μM g−1) for P-tot and 0.00 to 8.61 (μM g−1) for P-poly. Using a hierarchical sampling design and a simple model of variation of P (Kd model) it was possible to demonstrate that urbanized and non-urbanized estuaries may act as sinks or sources of P. The variation of P analysis in different points along each of the six rivers showed that release and removal areas may occur within a same river independently of its urbanization.