Environment Canterbury has released two reports by the National Institute of Water and Atmospheric Research (NIWA).
The first report models nutrient loading into Lake Benmore and its associated lakes, the second is a literature review of nitrate toxicity to freshwater species.
Environment Canterbury acting Chief Executive Ken Taylor, says the organisation commissioned the NIWA reports to make sure the best and latest available science was applied to environmental management issues facing Canterbury.
“The reports will help us work with communities and resource users to ensure sound environmental practices and regulation,” says Mr Taylor.
“They give us the information we need to help us develop and implement plans to set limits for key contaminants as part of our role to safeguard the region’s ground and surface water,” he says.
Lake Benmore water quality report
The first report will help Environment Canterbury better understand and manage water quality in the Waitaki lakes in response to land use changes.
“In the case of the Lake Benmore water quality report, we’re interested in maintaining the environmental values of Lake Benmore and its downstream lakes”, says Mr Taylor. ‘”Water quality is a key concern as land use intensification occurs.”
“The lakes of the Upper Waitaki Basin are a local, regional and national asset for their ecological, recreational, commercial and tourism values.”
“What’s helpful for us is that the report makes predictions about the relationship between different nutrient loads into the lakes, in-lake processes, lake water quality and its associated values,” he says. “This gives us a framework to help us set acceptable nutrient loads which enable us to meet our environmental objectives.”
NIWA scientist Ned Norton says “Water quality is a key concern when land use is intensified because there is a need to manage increased loads of contaminants such as nutrients, sediment and microorganisms entering waterways. We modelled several future scenarios that involved increasing nutrient loads to Lake Benmore. The model strongly indicated that the Ahuriri Arm of the lake is more sensitive to nutrient increases than the Haldon Arm. Consequently, nutrient loads from the Ahuriri catchment would need to be managed at a lower level than those from the Haldon Arm catchment.”
“Our report provided a set of options for environmental objectives for Lake Benmore and recommended catchment nutrient load limits (in tonnes of nitrogen and phosphorus per year). Setting objectives and nutrient load limits for Lake Benmore could establish the ‘line in the sand’ for managing cumulative effects of multiple nutrient inputs in the upper Waitaki catchment“, Mr Norton says.
A review of nitrate toxicity to freshwater species
The second report is a review of nitrate toxicity to freshwater species. This report, commissioned by Environment Canterbury and part funded by the Ministry for the Environment, is a literature review to help Environment Canterbury maintain suitable guidelines to manage and protect aquatic ecosystems, particularly lowland streams.
“We’re interested in the impact nitrate has on the health of our lowland streams and what limits we need to set to achieve our environmental objectives”, says Mr Taylor.
“The report, which was internationally peer reviewed, highlights that freshwater ecosystems are much more sensitive to nitrate than previously thought.”
This report will be of interest to regional councils managing water quality issues throughout the country. The Ministry for the Environment is currently reviewing the guideline values.
Report author and NIWA scientist Dr Chris Hickey says “this guideline review was undertaken to incorporate recently published international data on the sensitivity of freshwater fish and macroinvertebrate species to nitrate. Relevance to species resident in Canterbury’s aquatic ecosystems was a key component of the review.”
“The review included data on three highly sensitive fish species found in Canterbury’s rivers and lakes (rainbow trout, lake trout and Chinook salmon). The updated guideline covering chronic (long-term) effects of nitrate was almost 10 times lower than the human health drinking water guideline for nitrate, and markedly lower than the previous aquatic ecosystem guideline,” Dr Hickey says.
NIWA’s report noted that there was no nitrate toxicity data for New Zealand native species such as mayflies and some native fish that are known to be highly sensitive to other common toxic contaminants. “The updated chronic guideline values are not exceeded in most New Zealand rivers at present, but numerous small lowland streams do have higher nitrate concentrations.”
“Decreasing water quality trends in New Zealand rivers point to the need to better manage cumulative inputs of nutrients into ground and surface waters. We need some debate at local, regional and national levels on both the adequacy and the implementation of water quality guidelines for aquatic species protection, and this report provides a good catalyst for that to happen. Given the current trajectory in water quality, particularly for many groundwaters, there are serious implications for aquatic species in many of our lowland streams,” Dr Hickey says.
Both reports are available on Environment Canterbury’s and NIWA’s websites at www.ecan.govt.nz/publications/ and www.niwa.co.nz.
ENDS
For more information:
Lake Benmore Water Quality report – a modelling method to assist with assessments of nutrient loadings.
NIWA Scientist Ned Norton
Phone 03 3438054
Mobile 027 2439546
A review of nitrate toxicity to freshwater aquatic species
NIWA Principal Scientist Dr Chris Hickey
Phone 07 856 1713
Mobile 027 486 7429
Environment Canterbury acting Chief Executive Ken Taylor
Phone: 03 371 7109
Mobile: 027 295 4359
Additional notes:
1. ANZECC background. The ANZECC water quality guidelines form the basis for aquatic species protection in New Zealand. The guidelines were last derived in 1998 and published in 2000. A revision process is currently being initiated.
Reference: ANZECC (2000). Australian and New Zealand guidelines for fresh and marine water quality. National Water Quality Management Strategy Paper No. 4, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra, Australia.
Web link:
http://www.mfe.govt.nz/publications/water/anzecc-water-quality-guide-02/
2. Ministry of Health
The New Zealand drinking water guideline for nitrate is 50 mg/L as NO3 (equivalent to 11.3 mg/L as nitrate-nitrogen (NO3-N)
MoH (2005). Drinking water standards for New Zealand 2005. Ministry of Health, Wellington, New Zealand.
Web link:
http://www.moh.govt.nz/moh.nsf/pagesmh/4423?Open
3. WQ trends report
MfE (2007). Environment New Zealand 2007. No. ME847. Ministry for the Environment, Wellington.
Web link:
http://www.mfe.govt.nz/publications/ser/enz07-dec07/html/chapter10-freshwater/index.html
4. Nitrate units of measurement
Care must be taken in comparing reported nitrate measurements and guidelines. They may be reported as either nitrate (NO3) or as nitrate-nitrogen (NO3-N).