Effect of environmental forcing on the fate of nutrients,dissolved organic matter and heavy metals released by a coastal wastewater pipeline

摘要

Discharges of nutrients,urea,dissolved organic matter and heavy metals by a sewage underwater pipeline are analysed in comparison to environmental conditions in a shallow coastal zone.Variable thermo-haline stratifications of the water column and currents in upper (2.62-34.97 cm s~(-1)) and deeper (0.83-10.91 cms~(-1)) layers drive vertical diffusion and lateral transport of wastewaters.Loads of reactive phosphorus (0.13 tons d~(-1)) and ammonium (1.62 tons d~(-1)) by the pipeline are not negligible compared to the major river loads in the gulf.High concentrations of urea (< 11.51 mu mol N dm~(-3)) were found in the area of wastewater release.Ammonium uptake (6.14-534 nmol Nd m~(-3) h~(-1)) strongly exceeded nitrate uptake (0.19-138 nmol N dm~(-3) h~(-1)),indicating that discharges of ammonium by the pipeline are actively assimilated by plankton community even at low levels of light.Distribution of Zn (<27.7 ppb),Cu (<25.6 ppb),Cd (<0.80 ppb) and Pb (< 13.5 ppb) in the water column and the measurement of their complex-forming capacity in seawater did not indicate a persistent perturbation of the pelagic environment due to heavy metals.