An ecological survey on the effect of the dump ground on benthos in Poverty Bay

Abstract

An investigation of the sediments and ecology of the dump ground was conducted in March 1995. The primary purpose of the investigation was to analyse factors which may be affecting the benthic biota on the dump ground. These include heavy metal content of the sediments, grain size characteristics of the sediments, and population distribution of the benthic biota on and surrounding the dump ground. It was intended that information obtained could be utilised in future investigations on the ecology of the dump ground, noting changes that have occurred over time. Heavy metal analysis of Cadmium, Chromium, Copper, Mercury, Lead, and Zinc from the dump ground, turning basin, and inner harbour area indicate that concentrations of all heavy metals were all very low and well within resource consent limits. Sediment and ecological samples from 25 sites on and surrounding the dump ground were taken. Two other sites were also surveyed, one from the turning basin, another from the inner harbour area (dredged material). Examination of the sediments has shown that although the dredged material consists solely of mud sized particles the sediments of the dump ground are mainly sand sized sediments. This suggests that during the dumping process dispersion of mud occurs. Mud is transported off the dump ground in a southeasterly direction. Ecological evaluation indicates benthic species diversity and abundance of macrofauna is high, with no species in particular dominating the species assemblage. Comparison between this study and a 1993 survey shows increased diversity over the dump ground. Increased population abundance was evident and larger sized bivalves are indicative of an ageing population. Field experiments examining the kelp beds indicate a decline in the population of Ecklonia radiata from 1993 to 1996. It is thought that this decline may be due to suspended sediment load from the Turanganui River, as the kelp beds are situated in the direction of discharge from the River.