Sources of dissolved inorganic nutrient fluxes in the Gazi Bay and implications for coastal ecosystems

Abstract

Nutrient fluxes of dissolved N H /, N 02, N 0 3\ P 0 43' and Si(OH)4 in the water column and nearshore sediments were measured in situ in the Mangrove, Seagrass and Coral reef biotopes of the Gazi Bay. The measurements were made using benthic flux bell-jar chambers each of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, external sources (fluvial discharge) and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on the nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay. Measured benthic flux rates varied between -270 and +148; -60 and +63; -79 and +41; -79 and +75; and +30 and +350 micromoles/m2/h for N H /-N ; N 0 2'-N; NCV-N; P 0 43'-P and Si(OH)4-Si respectively. Assessment of these values showed that they were comparable to those theoretically calculated from interstitial sediment-water nutrient concentrations. However, differences in flux direction (+ve or -ve) and magnitude were attributed to external sources as well as interactive effects of the three biotopes.