Effect of catchment disturbance on seston quality and quantity in Brisbane Water, NSW

Abstract

The direct effect of catchment disturbance on water parameters and the quality and quantity of seston were investigated in Brisbane Water, NSW Australia. Nutrient concentrations, faecal coliform levels and seston quality and quantity varied among catchments in Brisbane Water. Three of the four major catchment creeks entering Brisbane Water are sourced from disturbed catchments (Erina, Narara and Kincumber Creeks), including both industrial and residential areas, while one is sourced from a relatively undisturbed catchment (Woy Woy Creek). Monitoring occurred during wet and dry weather. After rainfall, elevated levels of nitrite/nitrate (NO x ) were recorded at the developed location at EC although the differences were not significant. Particulate nitrogen (PN) increased significantly at the developed locations at NC and EC after rainfall. The increases in these two forms of nitrogen after rainfall suggest non-point sources within the catchment. Ammonia (NH 3) concentrations were consistently higher at Erina Creek, even during dry weather suggesting a point source of NH 3 pollution. Variations in phosphate (PO 4) concentration among locations sampled were significant on only one occasion but no trends in the variation were apparent. Although not always significant, trends in total particulate matter (TPM), particulate inorganic matter (PIM) and particulate organic matter (POM) concentrations showed higher levels at developed locations, particularly after rainfall. The %POM was lower at developed locations than at Woy Woy Creek due to relatively greater increases in PIM. On some dates sampled, trends in seston quality measures indicated poorer quality seston associated with developed catchments (i.e. %PC, %PN, PC:Chl a, Chl a:TPM and PN:Chl a) but these were significant for only some tests. The PC:PN ratio, however, did not follow the same patterns as other seston quality indicators. By altering the quantity and quality of the seston, overdevelopment can potentially lead to changes in estuarine food webs. The significance of these changes depends on factors such as the ability of primary consumers to adapt their feeding strategies in order to accommodate for shifts in the quality and quantity of food available to them.