Investigations into the effects of desalination effluents upon the physiology and ecology of diatoms

Holdway, Patricia Ann (1976) Investigations into the effects of desalination effluents upon the physiology and ecology of diatoms. University of Southampton, Doctoral Thesis.

Abstract

When potable water is obtained through the desallnation of brackish or sea water an effluent stream at an elevated salinity is produced- The temperature and metallic ion levels of the effluent water are also increased by most of the desalination processes which are currently in widespread use. Organisms inhabiting the outfall area of a desalination plant may thus be subjected not only to osmotic and thermal stress but also to the influences of elevated concentrations of potentially toxic metallic ions, such as copper and zinc. The reactions of diatoms, the dominant primary producers in many marine and estuarine environments, to the conditions found in a desalination effluent were examined by means of laboratory studies together with in situ investigations undertaken at the desalination plant located in Jersey, C.I. Since the composition of a desalination effluent can vary greatly between individual plants it was necessary to expose diatoms to a wide range of salinity, temperature and metallic ion levels before the possible effects of a desalination discharge could be fully ascertained. Therefore, the physiological reactions of selected diatom species were examined whilst the cells were subjected to desalination, effluent analogues prepared to many different salinity, (temperature and copper levels. Analyses of the intracellular productivity, population growth and copper uptake rates demonstrated that the experimental parameters did not influence the diatoms in a purely additive fashion; elevated salinities acted antagonistically upon copper toxicity, whereas the toxic action of the metal was increased at elevated temperatures. Despite the inhibitory effects which high levels of the desalination effluent analogues exerted upon physiological processes, no morphological influences were noted when the cells were examined with an electron scanning microscope. Although the results obtained from electron probe microanalysis of diatom cells showed no indication of any site regulating copper entry into the cell, the rate of extracellular production increased in the presence of copper, and it was suggested that the extracellular products may act in a protective fashion by binding and transporting the potentially toxic ions out of the cells. Additional investigations were conducted in an in situ situation, the distribution and frequency of diatom species being related to the physico-chemical levels of the effluent water from the Jersey desalination plant. Contact with the, undiluted effluent proved fatal to all diatom species, and it is probable that conditions in the littoral zone would prove unfavourable for recolonization for a period after the plant had ceased to function, due to the leaching ofLiIadsorbed metallic ions from the rocks and sediments.

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