Interstitial water chemistry and nutrients fluxes from tropical intertidal sediment
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Depth profiles of chlorinity, nutrients, pH and alkalinity in interstitial waters from high porosity, carbon rich sediment cores of Gorai creek (near Bombay) were studied in different seasons to evaluate temporal changes in relation to their concentrations in the overlying creek water. The high chlorinity creek water infiltrating in the bed after September, progressively pushed down the monsoonal low chlorinity water trapped in the sediment resulting in a well-defined chlorinity minimum at the intermediate depth which progressively migrated downwards as the dry season advanced. In the presence of high concentrations of NO3-N throughout the core lengths, the occurrence of high Talk was attributed to the enhanced rate of surface microbial activity and its subsequent downward transport with chlorinity. The inorganic products (NO3-N, NO2-N, NH4 +-N, PO4 3--P) of aerobic oxidation of organic matter accumulated in the 0-4 cm sediment section before their transport. The nature of NO3-N profile suggested its generation in the surficial sediment followed by utilization in the intermediate level with the consumption rate decreasing in the bottom sections. An intermediate maxima of NH4 +-N and PO4 3- -P prevailed in most cores which gradually shifted downwards with chlorinity. A continuous build-up of NH4 +-N in the interstitial waters unlike other nutrients was evident. Markedly high N:P molar ratios in surficial sections suggested the removal of PO4 3--P from interstitial water. The fluxes of all nutrients were oriented towards the water column. Hence, the nutrients released in the surficial interstitial water were partly transported to the overlying water with a significant portion migrating into the sediment with chlorinity.
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