Biomonitoring of organic pollution using periphyton, South Branch, Canterbury, New Zealand

Abstract

Abstract The use of periphyton to monitor the effects of organic pollution in shallow, swift New Zealand rivers was tested using a slaughterhouse effluent discharge to the South Branch, Canterbury. Eight 1 ‐week long artificial substrate accrual periods were used. A range of taxonomic and biomass determinands were analysed for during the first 2 periods. However, only chlorophyll a, ash‐free dry weight (AFDW) and their derivative the Autotrophic Index (AI), were used for subsequent monitoring as they provided the most efficient means of discriminating the effluent impacts. Intensive chemical monitoring during these first 2 sampling periods identified a highly concentrated organic waste with high daily variability (x total Kjeldahl nitrogen = 5.04 and 1.90 mg 1‐1, %CV = 74 and 79). Effluent volumes were slowly reduced over a 4‐month period. This resulted in reductions in the AI (maximum of 4377 down to 191) of downstream communities and demonstrated the benefit of effluent diversion. The community also responded to low‐level organic contamination at the control site as shown by the AI. There was a highly significant correlation (r=0.926) between biochemical oxygen demand and the AI. There were no significant differences in the AI between control and impact sites for 2 sampling periods after the effluent had been diverted from the river. It is concluded that periphyton have the potential to provide good data on the biological effects of organic discharges to shallow, swift New Zealand rivers to complement water quality monitoring data.