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Assessing the ecological health of estuaries in southwest Australia

Deeley, D.M. and Paling, E.I. (1998) Assessing the ecological health of estuaries in southwest Australia. In: McComb, A.J. and Davis, J.A., (eds.) Wetlands for the future. Gleneagles Publishing, Glen Osmond, S.A. Australia, pp. 257-271.

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Southwestern Australia experiences a Mediterranean climate and its estuaries are at risk from eutrophication because of a limited oceanic tidal range, constricted or barred ocean entrances, shallow estuarine basins, extensive agricultural clearing and draining in catchments, fertilized sandy coastal plain soils with limited phosphorus sorption capacity, large inland catchments with little vegetative cover at the onset of winter rains and widespread erosion. Elevated nutrient and sediment loads to southwest estuaries have caused disruption of ecosystem processes in some estuaries including seagrass loss, macroalgal and phytoplankton nuisance, and anoxia. To investigate estuarine health in the southwest, five sites in each of eight estuaries and five sites at a marine reference location (45 sites), were investigated using a range of physical, chemical and biological indicators. Water and sediment nutrient concentrations were determined at each site, together with an assessment of the community structure of phytoplankton, and benthic macroinvertebrates. Historical water quality information was evaluated to provide perspective. Despite some past analytical uncertainty, there appears to have been a significant increase in median total phosphorus concentrations in both the upper Swan (12 to 90 µg L -1 ), and Peel-Harvey estuaries (15 to 70 µg L-1), from 1945 to 1995. Surface salinity transects in summer 1995 typified classical, lagoonal and reverse estuaries, depending on basin morphology, marine contact and runoff volumes. Summer N, P and chlorophyll a concentrations in estuarine waters were correlated and were consistent with the extent of agricultural development particularly for sandy coastal catchments. Phytoplankton species diversity (evenness) was inversely related to total cell densities and estuarine nutrient status. Macro-invertebrate diversity (evenness) was inversely related to abundance. The proportion of cyanophyte and dinoflagellate cells in phytoplankton communities was high for some diverse pristine sites with low levels of chlorophyll a, low for all sites with moderate levels of chlorophyll a, and high for some sites with high levels of chlorophyll a. The suite of environmental indicators evaluated here collectively provided a useful indicator of estuarine health.

Item Type: Book Chapter
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Publisher: Gleneagles Publishing
Copyright: © McComb and Davis
Notes: Papers from an international conference on wetland ecology held in Perth, November
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