RWQE monitoring data are assessed against attribute tables in the National Objectives Framework of the National Policy Statement for Freshwater Management.
Copper and zinc concentrations are compared against Australian and New Zealand Guidelines for fresh and marine water quality chronic toxicity default guideline values (95% level of protection) for freshwater.
Because water hardness affects the toxicity of some metals, where metal concentrations exceed trigger values, site-specific, hardness-modified trigger values are calculated based on recommendations in the Australian and New Zealand Guidelines. Since the availability of water hardness data varies across sites, the calculation of hardness-modified default guidelines values and their application is undertaken in the following two ways:
Macroinvertebrate Community Index (MCI) scores are assessed against quality classes recommended for the Greater Wellington Region and Greater Wellington Natural Resources Plan (NRP) plan outcomes. Soft bottomed MCI scores (MCI-sb) have also been calculated for the seven sites that were sampled which have soft substrates.
River Class | Poor | Fair | Good | Excellent | All rivers | Significant rivers | |
---|---|---|---|---|---|---|---|
1 | Steep, hard sedimentary | < 110 | 110-120 | 120-130 | ≥ 130 | ≥ 120 | ≥ 130 |
2 | Mid-gradient, coastal and hard sedimentary | < 80 | 80-105 | 105-130 | ≥ 130 | ≥ 105 | ≥ 130 |
3 | Mid-gradient, soft sedimentary | < 80 | 80-105 | 105-130 | ≥ 130 | ≥ 105 | ≥ 130 |
4 | Lowland, large, draining ranges | < 90 | 90-110 | 110-130 | ≥ 130 | ≥ 110 | ≥ 130 |
5 | Lowland, large, draining plains and eastern Wairarapa | <80 | 80-100 | 100-120 | ≥ 120 | ≥ 100 | ≥ 120 |
6 | Lowland, small | < 80 | 80-100 | 100-120 | ≥ 120 | ≥ 100 | ≥ 120 |
Monthly observations of percent streambed periphyton cover (filamentous and mat-forming periphyton) are compared against the periphyton composite cover guidelines (Matheson et al. 2012). The threshold for nuisance mat cover is twice that for filamentous periphyton cover, so the periphyton weighted composite cover (PeriWCC) can be defined as filamentous periphyton cover + (mat periphyton cover / 2) with a nuisance guideline of ≥ 30%.