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Executive Summary

Background and purpose

This report draws together monitoring data from 14 dairy farming catchments in New Zealand to provide a baseline of water quality (and land use) in these catchments to assist with future water-quality trend assessments.

The Dairying and Clean Streams Accord is the main driver for assembling the information provided in this report. However, Accord actions are not the only factors that influence the water-quality results presented.

The 14 monitored catchments lie in 12 of the 16 jurisdictional regions in New Zealand. They range in size from 6 km2 to 211 km2, generally occupy flat to rolling lowlands that are dominated by dairying, and span a range of latitudes and climatic conditions. Five of the catchments are termed Tier 1 catchments in this report in recognition of their inclusion in a Best Management Practice catchment monitoring programme that began in 2001. The remaining catchments are termed Tier 2 catchments; some are part of ongoing regional council state-of-environment monitoring programmes, while monitoring was instigated in others more recently, specifically to establish a baseline.

Baseline information is presented for a period of monitoring between 2001 and 2007, with a focus on data collected in 2006/07. Various guidelines are used to provide a context for the baseline results. However, this report does not focus on particular catchment values, nor on whether these values are being preserved or compromised.

Main results

  • The majority (10) of the monitored catchments had median Escherichia coli concentrations that indicate higher levels of faecal contamination than the ‘average’ lowland pastoral farming catchment in New Zealand. One catchment, Taharua in Hawke’s Bay, had relatively low Escherichia coli concentrations, similar to those found in catchments with predominantly natural land use (ie, relatively undisturbed).

  • Soluble inorganic nitrogen (nitrate–nitrite nitrogen + ammoniacal nitrogen) exceeded the guideline for the prevention of nuisance periphyton growth in all catchments except for one. In all but two of the dairy catchments, nitrate–nitrite nitrogen concentrations exceeded the medians reported for lowland pastoral catchments in New Zealand.

  • Dissolved reactive phosphorus exceeded the guideline for prevention of nuisance periphyton growth in half of the catchments (seven).

  • Excessive weed (macrophyte) and/or algal growth was measured or observed on occasion in seven out of nine catchments for which information was available. However, there are subjective elements to this assessment and results should be interpreted with caution. There is a need to improve the way quantitative periphyton and macrophyte data is gathered and assembled for future reports.

  • Median ammoniacal nitrogen concentrations were below the concentrations at which detrimental effects on aquatic life begin to be observed in all catchments. However, two catchments had peak (spot daytime) measurements that exceeded the Australia and New Zealand Environment and Conservation Council (ANZECC) toxicant guideline, and a further two exceeded a more conservative guideline.

  • Four out of 13 catchments had median turbidity levels that were at, or in excess of, ANZECC guidelines for ecosystem protection (5.6 nephelometric turbidity units (NTU)). One of the likely consequences of this is reduced visual foraging areas for native fish (with a detrimental effect on their condition). However, no fish data was available to conclude whether such sediment effects were occurring.

  • Spot measurements of dissolved oxygen concentrations indicate that the requirements for supporting aquatic life were generally met in all catchments during daylight. However, continuous recorder data available for five catchments indicates that night-time excursions well below recommended guidelines occurred in four of these. Furthermore, measured daytime peaks and sags indicate large fluctuations in several other catchments, which may indicate serious depletions are occurring but are not being captured by spot measurements.

  • Macroinvertebrate (aquatic insects, snails and worms) scores varied widely. Five catchments had average metric scores indicating relatively clean water or mild degradation, while five had average scores indicating moderate to severe pollution. No data was available for four catchments.

  • Deterioration from upstream to downstream was found within most of the catchments for nitrate–nitrite nitrogen (eight out of 12 catchments), dissolved reactive phosphorus (six out of 10) and suspended solids (seven out of 10). E. coli increased in the downstream direction in half of the catchments, but decreased in the downstream direction in the other half.

Commentary

Monitoring results indicate that water quality is generally degraded in the selected dairy catchments, particularly with respect to faecal and nutrient contamination. However, the extent and pattern of degradation are variable, both within and between catchments, as is the evidence of ecological consequences (bearing in mind that many of the guidelines such as ANZECC that have been used as reference points indicate the risk of adverse consequences rather than describing actual effects). This highlights the complex and scale-dependent nature of the relationships between land use and water quality in modified catchments, and also reflects the differing underlying geology and natural stream bed conditions.

The ability to characterise some aspects of land use and water quality (including ecosystem health) for this report has been limited. For example, verified farm-scale information on the extent and effectiveness of waterway protection (both Accord waterways and smaller feeder streams) is not available for most catchments. With respect to water quality, more detailed analysis of the magnitude and frequency of extreme results using continuous recorder data
(eg, the bottom of the dissolved oxygen profile, water temperature spikes), in addition to average conditions, is needed.

Recommended next steps

  • It is recommended that the Ministry for the Environment coordinate a review of the catchment monitoring programmes to determine their value for ongoing inclusion in nationally focused reporting.

  • The review should include consideration of capturing new or additional land-use and water-quality data and the requirements for trend detection.

  • Concurrent with the above review, funding and resourcing arrangements for ongoing monitoring will need to be agreed between the relevant parties, recognising the substantial costs associated with collecting robust environmental data. This should include consideration of the interaction between the monitoring objectives of local and central government, science and research providers, and industry for each of the catchments.

  • Notwithstanding the outcome of a monitoring programme review, the Ministry for the Environment expects to produce further reports on the catchments in 2012 and 2017 using this baseline report as a reference point.

 

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