Examination of reactive phosphate fluxes in an eutrophicated coastal area

Abstract

Reactive phosphate (RP) fluxes over sediment in an eutrophic bay were obtained under different conditions. The results were assessed together with water column, sediment solid, and liquid-phase parameters. The RP fluxes ranged from 0 to 1,300 μgatP × m(-2)d(-1) day depending on the sediment site and other variables. At stations with relatively high net RP fluxes, the clay fraction was >3% and disproportionate with salinity, which explained why the RP effluxes decreased by inhibition of the organic coating on particulate matter with increased SO(4) (-2) ions and good competition of RP anions with SO(4) (-2). The RP flux in Fe/RP ratios >2 in surface water decreased to approach a minimum asymptotically, which was thus defined with a hyperbolic curve to determine the maximum rate of the RP flux (J(RP)). The [RP(porewater)](initial)/[RP(ambient)] (initial) ratios were suggested to govern the net RP flux regionally, so the critical value where the RP flux turns positive could indicate eutrophication with Chl-a values <500 μg/g. So, this study investigated the phosphate fluxes between sediment and water column and determined the factors influencing the RP fluxes in the inner bay of Izmir.