River water quality in New Zealand: an introduction and overview.

摘要: Robert J. Davies-Colley National Institute of Water and Atmospheric Research (NIWA), PO Box 11-115, Hillcrest, Hamilton, New Zealand. ABSTRACT: River water quality is important to uses values within rivers also in bodies downstream. here encompasses: the physico-chemical attributes aquatic life that vary diurnally (e.g. dissolved oxygen, temperature); optical related transmission light through visual clarity); major nutrient elements, nitrogen phosphorus, promote plant growth including nuisance algae (nitrate-N ammonia-N are toxic life); faecal microbial contaminants can cause illness people consuming or recreating downstream waters. affected by both point-source pollution (wastewater discharge) diffuse from land use. In Zealand, improved wastewater treatment over several decades has resulted being dominated sources. The three categories (1) fi ne sediment, causing reduced clarity sedimentation river beds bodies, (2) nutrients (N, P), promoting (particularly algae) growth, (3) microbes, representing a hazard human users consumers contaminated shellfi sh. Toxic metals may contaminate waters draining relatively small areas, nationally, urban mining-affected land. compared with Europe, North America Asia, be described as ‘fairly good’, very good (i.e. supports most habitat for life) conservation estate – lands reserved ecological recreation purposes. However, this must qualifi ed recognition widespread developed land, particularly pastoral agriculture, sediment clarity, contamination, enrichment. Furthermore, depends strongly on fl ow state, even such Motueka (Tasman District, northern South Island), which generally ‘good’ quality, typically turbid faecally polluted stormfl ows. Grazing livestock (on 40% Zealand’s area) mobilises all pollutant, result catchments moderately degraded. Intensifi cation use increases severity pollution. While worst found (a few) urbanor mine-affected other elevated, soiland vegetation-disturbing adversely affect quality. For example, cropping 1.5% sediment. plantation forests (7% appreciably better than pasture, approaches native vegetation cover except periodic ‘disturbance’ associated harvest tree crop removal canopy cover. Fine mobilisation remains an issue forestry. Unfortunately Zealand been declining last 25 years, despite large expenditure (or diversion rivers) city factory wastewaters clean-up tracked long-term monitoring showing reduction certain pollutants ammoniacal-N biochemical oxygen demand. gains point control have negated steadily increasing pollution, phosphorus enrichment intensifi agriculture. Fortunately, there recent encouraging signs decline health arrested, reversed, stabilisation improvement few (polluted) regions where effort management riparian fencing planting) controls. Diffuse much more diffi cult manage It seen whether freshwater reforms, national ‘bottom lines’ protecting secondary contact habitat, provide desired outcome terms Enduring challenges include improving continuing pressures towards agricultural expansion, additional pressure global warming driving temperatures ows some areas. Some work done internationally valuing rivers, but less their little research Valuing seems likely remain formidable challenge because multiple convolved dimensions by) those values.