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Appendix 2: Water quality in New Zealand: The current situation

[See www.mfe.govt.nz for full report.]

For rural lowland water bodies in New Zealand, agriculture is considered to be the primary source of diffuse (non-point) source discharges. Materials used in agricultural production - such as fertilisers and pesticides - as well as discharges from the soil and animals move into both surface and groundwater systems at higher rates than would be the case under natural systems, leading to problems of nutrient and microbial contamination, and sediment accumulation.

Rivers

In addition to regular regional council monitoring at designated sites on particular rivers, the River Environment Classification (REC) system enables assumptions about the overall health of rivers to be drawn. The system uses the physical characteristics [The six factors are climate, topography (source of flow of the river), geology and land cover of each section'supstreamcatchment, the last two includelocalattributes of the section of the river itself. These 6 factors are used to classify river sections in to a class, eg, a river might be in a "cool dry climate class in a lowland area with a soft sedimentary geology and a pastoral surrounding land use".] of rivers to group them, and also groups them at a range of scales. Findings are:

  • In terms of climate:
    • rivers in wet climates, which are regularly flushed, generally have higher water quality compared to rivers in drier climate areas.
  • In terms of land use:
    • rivers surrounded by natural land use (eg, native bush and tussock) or exotic forestry have good water quality
    • there is also good water quality in areas of low intensity agriculture such as sheep farming
    • poor water quality is found in catchments dominated by intensive agriculture, or in urban land use. Urban and agricultural land use is predominantly found in lowland areas.
  • In geographical terms:
    • mountain, lake-fed and many hill-sourced rivers generally have good water quality
    • rivers in hill areas have variable quality
    • lowland rivers suffer the most from poor water quality - the effect is magnified in lowland water with a drier climate.

In summary, urban and intensive agricultural land use is predominantly found in lowland areas and it is lowland areas that are suffering the most from poor water quality. The effect is magnified in lowland water with a drier climate. Approximately 44 percent of New Zealand's rivers lengths are low elevation water courses and half of these consistently fail guidelines for:

  • E. Coli
  • nutrients (nitrogen, phosphorus, ammonia)
  • clarity (except in extremely wet areas).

Over the past 20 years, improvements in water quality have resulted from effective management and the reduction of point-source discharges to rivers, though only small changes in quality are apparent over the last six to seven years. However a national and regional trend is shifting from direct discharges being the major contributors of contaminants to diffuse sources such as overland runoff and leaching to groundwater.

For example, E. Coli levels in the Waikato River have reduced considerably since the 1970s, which coincides with the time of major improvements to urban wastewater treatment. Since then most of the deteriorating trends have occurred in the lower reaches of the Waikato River where there has been an increase in levels of faecal coliform bacteria. Taupo township stopped discharging sewage waste water to the Waikato River at the end of 1995. Since then the levels of enterrococci bacteria in the Waikato River downstream of Lake Taupo have fallen by about 70 percent.

The effect of non-point source contamination on water quality is becoming clear through studies and case studies, for example:

For nutrients, Environment Southland has detected increases in concentrations in major catchments over the last two decades, most noticeably in the last decade. It has found that phosphorus levels generally meet guidelines but levels are increasing in the lower reaches of catchments.

Clarity measurements by Environment Southland show variability in local rivers. While clarity has improved in the lower Waiau, upper Oreti and Mataura Rivers over the last two decades, it is deteriorating in the lower Mararoa. Clarity remains constant and generally meets guideline levels in the Aparima and Matarua Rivers. This suggests an increased contribution from lower catchment sources, because soil conservation efforts have reduced inputs in upper reaches of the catchment. Run-off and stocking rates may be significant factors in the lower catchment. This contrasts with a time when point-source discharges were considered more significant.

Lakes

Generally, there is a range in lake water quality. It is poor in some of the smaller and shallower lakes, while the large, deep lakes have apparently high quality and visible water quality problems seem rare. The larger deeper lakes are, however, difficult and expensive to monitor and details of their water quality are relatively unknown.

Quality problems in some lakes are becoming more significant. In Lake Taupo and the Rotorua Lakes there is an observed increased growth in certain weeds and nuisance slimes. Lake Brunner is showing evidence of increasing nutrient levels and Lake Hayes is affected by phosphorus enrichment. Lowland lakes such as Lake Waipori and Lake Ellesmere Te Waihora have nutrient problems. Nuisance weeds are apparent in Lake Dunstan and Lake Wanaka. Less is known about the larger lakes in the South Island than those in the North Island.

Groundwater

Around 50 percent of community water supplies use groundwater either as a sole or partial source, as well as the many domestic wells in the rural community. Interconnections between surface and groundwater mean that contaminated groundwater can recharge surface water and spread the contaminant.

There is no national record of incidents or levels of microbiological contamination of aquifers in New Zealand. Regional councils gather information according to the importance of groundwater to the region and the aquifers susceptibility to microbial contamination. Currently drinking water appears to be free of microbial contamination. This is significant because 80% of the groundwater bores used for community water supplies are not chlorinated before entering the reticulation system, [Sinton LW. 2001. Microbial contamination of New Zealand's aquifers. Chapter 9 inGroundwaters of New Zealand. The Caxton Press, Christchurch, New Zealand.] and this includes bores serving the cities of Napier and Hastings, Lower Hutt and Christchurch.

While bore contamination can be a regular occurrence, (and this could be due to the construction of the well heads), shallow unconfined aquifer contamination seems to be largely still a risk than a reality. Otago has recorded microbial contamination in two shallow unconfined aquifers and high faecal coliform counts have been recorded throughout the lower Waitaki Alluvium groundwater system. This is an area in which there are many dairy farms, which are irrigated by both spray and flood irrigation of fresh water, and spray irrigation of dairy-shed effluent. Septic tanks can also contribute to coliform counts.

Nutrient contamination of groundwater from agricultural land use appears to be pronounced in some regions, particularly around areas of processing, intensive horticultural and cropping activity. Trends in groundwater nitrate are difficult to evaluate because data is patchy for some areas and regular sampling over a long periods has not yet occurred. However, the data that is available indicates that nitrate contamination is becoming a problem in all regions of the country, and that nitrate "hotspots" will increase in the future. [Close ME, Rosen MR, Smith VR. 2001. Fate and transport of nitrates and pesticides in New Zealand's aquifers. Chapter 8 inGroundwaters of New Zealand. The Caxton Press, Christchurch, New Zealand.]

Nitrate-nitrogen concentrations in shallow groundwaters also frequently exceed Ministry of Health guidelines in areas where stock densities are high and upper soils permeable. Individual cases are receiving media attention; such as Environment Canterbury's recent report on high nitrate concentrations in groundwater south-east of Ashburton District's three meat processing plants and in the coastal region around Dorie/Pendarves, an irrigated arable crop area. In some places, nitrate concentrations have risen over the last 10 years in some wells. Testing shows that none of the groundwater samples from 114 recently tested wells in the Ashburton-Rakaia Plains have exceeded the Ministry of Health's drinking water standard for nitrates.

Nutrient leaching via groundwater has also been identified as a significant source of nutrient contamination of lakes.


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