Nutrients in New Zealand Rivers and Streams: An exploration and derivation of national nutrient criteria [article]

Adam Canning
2020 Figshare  
Executive SummaryMany of New Zealand's rivers are enriched with nutrients, primarily nitrogen and phosphorus,which can reduce ecosystem health via eutrophication. According to Environment Aotearoa(Ministry for the Environment and Statistics New Zealand, 2019), approximately 82% of rivers,by length, in pastoral land do not meet the ANZG (2018) default guideline values for nitrate-nitrogen and 77% for dissolved reactive phosphorus (DRP). Eutrophication is the increasedproduction of organic
more » ... n of organic matter. The most visible form of eutrophication is excessive algal growth,i.e., where rivers become covered in green slime. However, eutrophication does not alwaysinvolve excessive algal growth, nor is algal growth a requirement. Nutrient enrichment can alsoincrease and alter microbial activity, which can: alter invertebrate and fish growth (via changesin nutrient or macromolecule availability); increase hypoxia (which can suffocate invertebratesand fish); disrupt food web cycling and stability; reduce greenhouse gas storage and abatement;alter disease transmission; and alter the availability of nutrients and energy for downstreamsystems. Nitrogen and phosphorus are critical components of ecosystems and the species thatinhabit them. Anthropogenic nutrient enrichment should be minimised to maximise an aquaticecosystem's health.New Zealand's National Policy Statement for Freshwater Management (NPS-FM) containsgrades (or bands) for various measures (termed attributes) of aquatic ecosystem health. Whena measure receives a 'D' grade, or a grade lower than desired by the community (via a regionalplanning process), then the environment must be managed in a way that, over time (decided bythe community), improves that measure. This report outlines the approach adopted by theScience and Technical Advisory Group (STAG) to recommend dissolved inorganic nitrogen(DIN) and DRP criteria for consideration during the Government's Essential Freshwater reform.Usi [...]
doi:10.6084/m9.figshare.12116460.v1 fatcat:smphwg5fcve63lz6ntfg7hasd4