Human impacts on the Waikato River system, New Zealand

Abstract

The Waikato River drains 13% of the North Island. It rises in the Central Volcanic Plateau; the headwaters, including the Tongariro R., drain into oligotrophic Lake Taupo, important for fishing and holidaying. The river flows north from Taupo for 450 km to the sea near Auckland. Human impacts on the river system have been extensive, primarily dating from European colonisation begun in the 1800s. Most of the catchment below L. Taupo has been altered by agricultural development (mainly sheep and cattle rearing); the original forests and swamps have been lost leading to increased nutrient levels, erosion, light intensities, and water temperatures. There is also extensive use of the water for electricity generation. The Tongarino Power Scheme involves impoundment of water, and the diversion of additional water from the Whanganui River and other catchments with consequent effects on their biota. There are 8 hydro-electric dams on the Waikato River below Taupo causing barriers to migratory animals, downstream effects due to impoundments, and alterations to water flow regimes. Impacts of geothermal power stations, and the water-cooled Huntly Power Station in the lower Waikato are more localised. Eutrophication is enhanced by sewage and stormwater discharges, but all wastes now receive some form of treatment. There are only 340,000 people in the catchment and the major industrial pollution comes from meat and dairy processing and forestry. Some natural pollution results from geothermal inputs. Water abstraction and discharges into the river are now closely regulated. Extensive introductions of exotic biota have been made, notably trout, coarse fish, and macrophytes. The native biota has been little-studied and the biological processes operating in the river are poorly understood. It is not possible to assess the relative importance of eutrophication and habitat change, nor to predict the impacts of future changes.