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Understanding Water Quality Variables in New Zealand Rivers

Explore the Waikato Regional Council's river water quality network, variables like major ions, contaminants, and trend analysis from 1993-2012 to comprehend sources of contaminants, conditions, and trends affecting water quality in New Zealand rivers.

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Understanding Water Quality Variables in New Zealand Rivers

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  1. Water quality, 1: Rivers Bill Vant, Waikato Regional Council

  2. Outline • Variables • Council’s river water quality network • Flow • Changes moving downstream • Sources of contaminants • Condition and trend

  3. Variables: “a huge number” • NZ Drinking Water 2005: standards for 140 contaminants • ANZECC 2000: guidelines for 250 ecological toxicants in water • USEPA (1998) identified “an estimated 87,000” potential endocrine disruptors

  4. Key types of variables • Major ions: Na, K, Ca, Mg, SO4, Cl, HCO3 • Plant nutrients: various forms of N and P • Inorganic suspensoids, e.g. silt particles • Microbes: viruses, bacteria, protozoans, plankton • Metals (e.g. As, Cd, Cu, Hg, Zn) • Pesticides & other synthetic organics

  5. Council’s river water quality network • Waikato River—10 sites, others—100 sites • monthly intervals • >20 variables (“general water quality”) • physical: temperature, conductivity, visibility • chemical: pH, oxygen, nutrients, geothermal • biochemical: BOD, chlorophyll a • microbiological: faecal coliforms, E. coli, enterococci • Waikato—since 1980; others—since 1990

  6. Conductivity @ Otamakokore, raw

  7. Flow @ Otamakokore

  8. Otamakokore, conductivity vs flow

  9. Conductivity @ Otamakokore, raw and flow-adjusted

  10. Piako Salinity (March 2012, high tide and low river flow)

  11. Piako Turbidity

  12. Nitrogen in rivers and land use

  13. Sources of N and P, 2000-09 (kg/ha/yr) Phosphorus Nitrogen

  14. Condition and trend

  15. A typical record

  16. Whangamarino: ecological health variables

  17. Trend analysis, using non-parametric statistics • slope (“seasonal Kendall slope estimator”) • = median (Ji - Ji-1, Ji - Ji-2, … , Fi - Fi-1, …) • p-value (“seasonal Kendall trend test”) • = +ve slopes cf. ve slopes

  18. Summary: current condition • excellent in places, poor in others—but not dire • conditions are often “at least satisfactory for desired uses” • differences between zones (e.g. Coromandel cf. Lowland Waikato) • these broadly reflect differing intensity of land use

  19. Summary: trends 1993-2012 • Waikato River: some improvement (ammonia, chlorophyll); some deterioration (turbidity, nitrogen) • Other rivers: some improvement (ammonia), some deterioration (nitrogen) • Pastoral agriculture likely to be the cause of much of the increase in nitrogen

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