The ecological effects of stormwater on the Macro-ZooBenthos of Wellington Harbour

Abstract

This study attempted to test the hypotheses that: 1. Stormwater is a significant source of pollution affecting the shallow water marine ecology of Wellington Harbour. 2. The Abundance Biomass Comparison (ABC) method is an effective method for detecting pollution in areas which may be disturbed by freshwater outflow. 3. There are taxa which are indicative of pollution levels at sites influenced by freshwater outflow in Wellington Harbour. The ABC method was used for this purpose, and the Shannon-Weiner Diversity and Evenness Proportion indices were used to corroborate ABC method results. Results were compared with known pollution incident histories and with the ABC method study by Aitken (1993) of similar sites within Wellington Harbour. Three sites were sampled: Petone, Kaiwharawhara and Waiwhetu. Each site targeted a predominantly residential, commercial or industrial stormwater catchment. Based upon the results, the Petone site was found to be unstressed or unpolluted. The Kaiwharawhara site was found to be moderately stressed or moderately polluted. Both these results were consistent with results from the Shannon-Weiner indices, the known pollution incident histories, the ABC method study by Aitken (1993), and expectations based on species diversity theory. The Waiwhetu site was found to be unstressed or unpolluted, from the ABC analysis. This was consistent with results from the Shannon-Weiner indices, and the ABC method study by Aitken (1993). However these results were inconsistent with the known pollution incident history, and expectations based on species diversity theory. Possible explanations include that: 1. Local physical conditions convey the pollutants away from the site; 2. The biomass is dominated by bivalve molluscs which can avoid pollution incidents and which feed from the water column rather than near the substrate where contaminants accumulate and persist; and 3. The ABC method is limited in its ability to detect non-organic disturbance or pollution, or that the method's viability is affected by certain community compositions, giving a false result. Two taxa which could be indicative of pollution levels at sites affected by freshwater outflow in Wellington Harbour were identified as the polychaete family Glyceriidae and a family of Nemertia (proboscis worm). This study demonstrated that freshwater outflow does not preclude the use of the ABC method for detecting disturbance or pollution. This study confirmed the hypothesis that stormwater is a significant source of pollution affecting the shallow water marine ecology at the mouths of the Kaiwharawhara and Waiwhetu Streams, in Wellington Harbour.