By Daniel Collins
The Government recently released a new round of freshwater reform proposals. A significant part of them included additions to the National Policy Statement for Freshwater Management with regards to water quality.
The NPSFM currently directs Councils to undergo a process of setting limits for water quality degradation, but neither the process nor consistent numerical targets had been outlined. Until now.
Targets that have now been proposed within the National Objectives Framework (NOF) include “national bottom lines” – thresholds of water quality attributes that good management should prevent our waterways from crossing. For Version 1 of the NOF, the proposed attributes, their limits, and implications are summarised in the table below.
It is important to understand, though, that Councils are obliged to maintain or improve water quality within their regions. They cannot simply let conditions degrade down to the bottom line. And so the NOF also includes other water quality bands, much like a report card, where the bottom lines separate a C grade from a failing D.
|Attribute||Water body||Bottom line||Description||Chlorophyll a||Lakes||12 mg/m3 (ann. median), 60 mg/m3 (ann. max.)||Lake ecological communities are moderately impacted by additional algal and plant growth arising from nutrients levels that are elevated well above natural reference conditions.|
|Total Nitrogen||Lakes||750 mg/m3 (ann. median, seasonally stratified/brackish*), 800 mg/m3 (ann. median, polymictic)||(same as above)|
|Total Phosphorus||Lakes||50 mg/m3 (ann. median)||(same as above)|
|Nitrate toxicity||Lakes and Rivers||6.9 mg NO3-N/L (ann. median), 9.8 (ann. max.)||80% species protection level: Starts impacting regularly on the 20% most sensitive species (12% reduction in growth)|
|Ammonia Toxicity**||Lakes and Rivers||1.3 mg NH4-N/L (ann. median), 2.2 (ann. 95%ile)||80% species protection level: Starts impacting regularly on the 20% most sensitive species (reduced survival of most sensitive species)|
|Dissolved Oxygen||Rivers (below point sources)||5 mg/L (7-day mean minimum), 4 (1-day minimum)||Moderate stress on a number of aquatic organisms caused by dissolved oxygen levels exceeding preference levels for periods of several hours each day. Risk of sensitive fish and macroinvertebrate species being lost.|
|Periphyton***||Rivers||200 mg chl-a/m2||Periodic short-duration nuisance blooms reflecting moderate nutrient enrichment and/or alteration of the natural flow regime or habitat.|
|E. coli (Escherichia coli)||Lakes and Rivers||1000 E. coli/100 mL||People are exposed to a moderate risk of infection (between 1 and 5% risk) from exposure to water used for wading or boating (except boating where there is high likelihood of immersion).|
|Cyanobacteria – Planktonic||Lakes and Rivers||Biovolume equivalent of < 1.8 mm3/L of potentially toxic cyanobacteria OR < 10 mm3/L total biovolume of all cyanobacteria||Low risk of health effects from exposure to cyanobacteria|
|Suitability for Recreation Grade (SFRG)||Lakes and Rivers||Fair||Water-quality tests and assessment of potential contamination sources indicate recreational beaches within this category have a moderate risk of infection. The beach is generally satisfactory for contact recreation, though there are potential contamination sources. Caution should be taken during periods of high rainfall, and contact recreation avoided if water is discoloured.|
* Intermittently closing and opening lagoons (ICOLs) are not included in brackish lakes.
** Based on pH 8 and temperature of 20⁰C.
*** Exceeded on no more than 2 occasions, with no exceedances in successive months (based on a monthly monitoring regime).
This covers many of the water quality attributes already discussed in the current Waiology series, or will be discussed in future articles, but what’s missing?
The Government’s proposal also lists attributes that will come under consideration during 2016-2019. These cover wetlands, groundwater, mahinga kai, and further attributes for rivers and lakes. Massey University’s Russell Death argues that there should have been no need to delay inclusion of some of these limits.
No limits have been proposed for estuaries, as of yet, but there is progress in that direction.
No limits have been proposed with regards to invertebrates as bioindicators, which Massey University’s Mike Joy points out should be included, however the bioindicators periphyton, chlorophyll-a, and cyanobacteria are there.
And there is some debate about the utility of the SFRG, and of lumping all sources of E. coli together (see pending Waiology article).
We can now expect continued progress on community-based limit-setting as well as expansion of the list of attributes within the national bottom lines. This is a very significant opportunity for prioritising science directions: How do we fill the gaps in the water quality limits?
Dr Daniel Collins is a hydrologist and water resources scientist at NIWA.