Ministry for the Environment and Statistics New Zealand provide a national picture of the environment in regular reports produced under the Environmental Reporting Act 2015. Below is the overview of the freshwater domain from the Environment Aotearoa 2015 report.
Freshwater domain at a glance
The condition of our lakes, rivers, streams, wetlands, and groundwater is important for a number of reasons. For Māori, fresh water is a taonga and essential to life and identity. Our economy depends on having plentiful water – agriculture, tourism, and hydroelectricity generation particularly rely on water. New Zealanders and tourists enjoy many forms of recreation that use our lakes and rivers, such as swimming, kayaking, and fishing. Our waterways also support many indigenous animals, plants, and ecosystems. Fresh water is primarily taken for hydroelectricity generation and irrigation for farms, and our fresh water quality depends mainly on the dominant land use in a catchment.
- Water quality is very good in areas with indigenous vegetation and less intensive use of land. Rivers in agricultural and urban areas have reduced water clarity and aquatic insect life, and higher levels of nutrients and Escherichia coli (E.coli) bacteria.
- The greatest impact of excessive nutrients in New Zealand rivers is nuisance slime and algae (periphyton) growth. This growth can impede river flows, block irrigation and water supply intakes, and smother riverbed habitats. Poor water clarity and elevated E.coli levels also affect our ability to use fresh water for recreation.
- Between 1990 and 2012, the estimated amount of nitrogen that leached into soil from agriculture increased 29 percent. This increase was mainly due to increases in dairy cattle numbers and nitrogen fertiliser. Once in the soil, excess nitrogen travels through soil and rock layers, ending up in groundwater, rivers, and lakes.
- Between 1989 and 2013, total nitrogen levels in rivers increased 12 percent, with 60 percent of monitored sites showing statistically significant increases. About 49 percent of monitored river sites have enough nitrogen to trigger nuisance periphyton growth, as long as there is enough sunlight, phosphorus, and a lack of flood events for periphyton to bloom. Phosphorus also triggers nuisance periphyton growth. About 32 percent of monitored sites have enough phosphorus to trigger this growth.
- High levels of nitrogen can also be harmful to fish; however, less than 1 percent of monitored river sites have nitrogen levels high enough to affect the growth of multiple fish species.
- Water clarity improved at two-thirds of monitored sites between 1989 and 2013. E.coli levels are higher in urban and pastoral areas, but meet acceptable standards for wading and boating at 98 percent of monitored sites.
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