Benthos associated with two New Zealand coastal outfalls

Abstract

The benthic ecological impacts of 2 New Zealand ocean outfalls were studied. They are the country's largest (discharging 0.8 m 3 s -1) at Hastings, and longest-established (operating since 1965 and with a present discharge of 0.28 m 3 s -1 ) at Gisbome. Both discharge essentially biodegradable domestic and food-processing-industry wastes. Samples were collected about each outfall and analysed for particle size, oil and grease, readily oxidisable carbon (ROC), total Kjeldahl nitrogen (TKN), volatile solids, and macrofauna. Changes in the sediments indicated that the effluents contained inorganic paniculate material in the mud/very fine sand size range. Peaks in concentrations of oil and grease, ROC, TKN, and volatile solids occurred at the diffusers. Numbers of taxa were low near the outfalls, but increased with distance away. Numbers of individuals were also low at the outfalls, increasing within 100 m, before dropping to normal levels. No grossly polluted zone, devoid of macrofauna, was found; however, it appeared that a "polluted" zone occurred within 200 m of the diffusers and a "transitional" zone extended to between 800 and 1600 m from the Gisborne outfall, and 400 and 1600 m at Hastings. Multivariate classification and ordination indicated that over the area sampled, the discharges were the main factor shaping the patterns of community structure.

Benthos associated with an estuarine outfall, Tauranga Harbour, New Zealand

“…With increasing distance, species numbers increase and high individual abundances decline. Although such changes in species and abundance have been observed around other local outfalls (Knox & Fenwick 1981;Roper et al 1989) the benthos near Tauranga outfall was not affected in this way. This was presumably because in this situation physical sediment characteristics (i.e., PS and sorting), rather than the discharge, were more important in determining abundances of taxa and individuals.…”

“…The higher mud levels up to 400 m to the west of the outfall are consistent with the net flow in this direction. Roper et al (1989) found a similar change in the sediments near the Gisborne outfall, where inorganic material settling out of the effluent increased sediment muddiness. It is possible, however, that mud deposits about the Tauranga outfall are natural, and unrelated to the discharge.…”

“…Therefore it is likely mat the true extent of chemical contamination of the sediments about the outfall is more accurately reflected in the concentrations of OG. Roper et al (1989) showed that "oil and grease" concentrations act as a good marker of the extent of chemical contamination of sediments about sewage outfalls. Elevated OG levels were restricted to within 50 m of the Tauranga outfall.…”

“…Previous studies of benthic ecological effects associated with New Zealand outfalls have dealt with ocean outfalls discharging into open coastal waters (Knox & Fenwick 1981;Roper et al 1989). Physicochemical sediment properties are altered and benthic invertebrate community structure is profoundly affected in response to such discharges.…”

Effects of trace metals on infaunal species composition in polluted intertidal and subtidal marine sediments near a lead smelter, Spencer Gulf, South Australia

“…However, the presence of the highly abundant T d ulongii is likely to increase, not decrease, the availability of metals to higher trophic level consumers such as fish, which may prove to be another significant impact of species that are introduced by ships' ballast waters. The polychaetes Capjtella 'capitata' and Heterornastus filiformis are opportunistic species capable of exploiting sewage-contaminated conditions (Grassle & Grassle 1976, Roper et al 1989. Both are widely distributed in many marine and estuarine habitats in Australia.…”