Impact of sewage discharging on environmental geochemical processes of nutrients in the Yangtze estuarine and tidal flats

Influences of sewage discharge on environmental geochemical processes of nutrients were investigated in the Yangtze estuarine and tidal flats. The result indicated that the environmental elements obviously responded to sewage discharging. There was obvious enrichment of NH4+-N, TIN, TDP, Ads-P, Fe-P and CFAP+ Ca-P in overlying water, surface sediments and its pore waters adjacent to sewage outlets in the Yangtze estuary. The enrichment of nutrients N and P was considered to be related not only to the inputs of nutrients from sewage outlets, but also to the changes of environmental factors induced by sewage discharge. On the contrary, there was no significant enrichment of NOx--N in the tidal water, pore waters and surface sediments from the Yangtze estuary, which showed that external inputs of nutrients was not the primary factor controlling the distributions of NOx--N. It was also shown that the diffusive fluxes of nutrients N and P across sediment-water interface was markedly higher at sewage outlets than the control sampling sites in tidal flats, indicating that sewage discharge not only increased the accumulation of nutrients N and P in the tidal flats, but also strengthened the exchange processed of nutrients across tidal sediment-water interface.