The effects of human activities on stream water quality: case studies in New Zealand and Germany
Doyle, Paul Norman
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Three case studies explore the effects of human activities on coastal streams and review measures to control the negative consequences of human activities. The first case study, an urban and a rural/forested stream in New Zealand, measured descriptors of water quality, including nutrients, dissolved oxygen and bacterial indicators of faecal contamination. The urban and rural catchments have stream-water qualities that fail to meet standards for fish life or bathing. Of the five sites studied, only one catchment, which had a substantial forest component (50%), had bacterial counts which meet the Australian Recreational Water-quality Guidelines for Secondary Contact (Faecal coliforms and enterococci, ANZECC, 2000) and the New Zealand Interim Guidelines for Freshwater Bathing (Escherichia coli, MofE, 2000). Only one site (which was downstream of a sediment-detention dam) had water clarity which met the Ministry of the Environment's (MofE, 1994) guideline for contact recreation.The results from this New Zealand case study indicate that the absence of riparian vegetation altered the temperature, pH and dissolved oxygen regime, that livestock increased levels of nitrate, turbidity and bacteria indicators of faecal contamination and that urban land use increased peak flows, peak-flow turbidity and bacterial indicators of faecal contamination and decreased base flows.The second case study, of a stream in the former Deutsche Demokratische Republik (East Germany), measured a similar suite of parameters and compared the German stream's 2001 water quality with records from 1991 (directly after the reunification of Germany). Measured levels of total nitrogen, nitrate, ammonium, phosphate and dissolved oxygen all showed significant improvements between 1991 and 2001. Stricter controls and regulations are thought to be the cause.The final case study reviews plans for an urban residential development in the catchment of the New Zealand rural/forested stream. Degraded sections of the stream could actually be improved if the development is sensibly managed. However, the sensitive nature of the receiving environment (a marine reserve) requires that measures be taken to avoid or mitigate any deleterious effects. Plans by the relevant authority, the North Shore City Council, are a major step forward from the unsustainable development of the neighbouring catchment. Still, more needs to be done. Ten recommendations have been made to ameliorate the potential negative impacts of the development.