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Measuring and Assessing River Water Quality
Why We Measure River Water Quality
Monitoring of river water quality is carried out to determine whether the uses and values of the river are compromised by human resource use. If the state of the waterway is poor or degrading, then follow-up monitoring is carried to determine the cause(s).
Council has a legal responsibility to monitor the water quality in the district. There are many reasons for doing this:
- Establish baseline water quality: Understanding the condition and trend of water quality in areas unaffected by human land use, as well as those impacted by such land use, is critical to managing it. With over 9,000 kilometres of rivers in Tasman District, there are many situations where little is known about the water quality. To help get over this problem, sites in monitoring programmes have often been chosen because they represent typical situations and so information can be related to catchments where there is little information.
- Detect long-term trends: Often people become concerned that water quality at a particular place has deteriorated over time. Monitoring programmes often focus on identifying whether or not changes in water quality are occurring, because these may have the potential to affect the uses of that water.
- Determine suitability for uses: Water quality is frequently monitored to assess its suitability for specific purposes, such as swimming, source of drinking water, or as a habitat for fish and other aquatic animals. Measurements taken are usually compared against environmental guidelines. Such guidelines are generally expressed as numerical limits (such as concentrations of a contaminant) below which the water will be suitable for a particular purpose.
- Check compliance with standards: Sampling results from Council's groundwater quality monitoring programmes are often measured against the New Zealand Drinking Water Standards.
- Assess adequacy of controls on discharges: Discharges of contaminants to water require resource consent from Council. When authorisations are given (usually as discharge consents) account is taken of the likely impact of the discharge on the quality of the receiving waters, based on knowledge of the water body at that time. Restrictions are placed on the discharge to limit any unacceptable water quality impacts. Additional monitoring improves our understanding of the resource and helps us to determine if those restrictions are still appropriate.
Note: Definitions of all the water quality terms used on this page are in the Water Quality Glossary.
Important objectives for water quality and the broad indicators with which we measure community-derived objectives are listed in the table below:
| River Water Quality Objectives | River Water Quality Indicators |
|---|---|
| Acceptability for contact recreation eg swimming |
Water clarity Filamentous algae cover (slime) Disease-causing organisms (E.coli) |
| Acceptability for Food Gathering |
Water clarity Quality and Abundance of food resources Filamentous algae cover (slime) Disease-causing organisms (water and in shellfish) Mauri (life force) |
| Life supporting capacity (ecological condition) |
Biological condition (abundance and diversity of invertebrates, fish, birds) Quality and quantity of habitat including the water quality parameters: Dissolved oxygen and temperature, Physical habitat such as quality of spawning habitat (eg whitebait or trout) and extent of stream-side plants shading the stream. |
| Acceptability for stock drinking water | Disease-causing organisms (eg faecal coliforms) |
In addition to the above objectives there are other objectives that may influence our waterways such as:
- Flood capacity – maintenance of channel capacity to protect human life and property
- Non-contact recreation – includes quality of experience and public access
- Landscape character and aesthetics
How We Measure Water Quality
Water quality is measured by appropriately-qualified professionals either making various measurements on site or sending samples of water to the laboratory for analysis.
| Indicator | How Measured |
|---|---|
| Dissolved oxygen* | Water quality meter (eg YSI600QS or YSI6600) |
| Temperature* | Water quality meter (eg YSI600QS or YSI6600) or glass bulb thermometer |
| pH* | Water quality meter (eg YSI600QS or YSI6600) |
| Conductivity* | Water quality meter (eg YSI600QS or YSI6600) |
| Water Clarity* | Horizontal sighting of a black disc (usually 200m diameter) |
| Colour and appearance* | Qualitative measure based on colour chart |
| Faecal coliforms & E.coli* | Lab method: Membrane filtration |
| Filamentous algal growth on bed | Rapid Assessment Method #2, NZ Stream Periphyton Monitoring Manual |
| Macro-invertebrates | NZ Stream Macro-invertebrate Sampling Protocols #P1 |
| Fine sediment deposits, re-suspendable solids, imbeddedness | Semi-Quantitative method |
| Substrate size class distrubution | Quadrat method |
| Turbidity | Lab method: Light scattering |
| Nutrients | Lab method: various |
* Indicators (parameters) measured at every site
How water quality is assessed depends on the use of the water. Water suitable for some uses may be unacceptable for others. For example, water contaminated with treated sewage may be unsafe for swimming but still suitable for irrigation or industrial processes.
Table 1 lists the different aspects of water quality we measure every quarter. It summarises why these are important and the guidelines used to assess them. The water quality measures in Table 1 are divided into two groups:
- those measuring whether water quality is suitable for plants and animals living in a river (ecological health)
- those that measure whether water quality is suitable for human uses such as swimming.
Biological Indicators of River Water Quality
A wide variety of fish, invertebrates, aquatic plants and algae are found in rivers and streams in Tasman District. The diversity and abundance of species found at each site provides an indication of stream health.
Invertebrates are particularly good indicators of water quality because they respond predictably in their tolerance to pollution, are not mobile enough to avoid the effects of pollution and the effects will be apparent for 2-3 weeks after a pollution event even if it is short-duration. The types of invertebrates that are present in a sample enable us to calculate biological indicators that reflect overall stream health. Over 157 different types of invertebrates have been identified from Council’s ecological monitoring of streams programme (this is estimated to be 95% of those known to occur in the District).
Analysing the tissue of plants and animals living in the stream can be useful, as they may accumulate contaminants over time. Even though present at a contaminated site, they may not be as healthy as the same species living in less stressful conditions. Council only does this analysis in response to specific incidents to determine the source of contamination
Where We Measure Water Quality
Water quality is measured at over 50 core sites throughout the district including Golden Bay, Buller, Waimea and Motueka areas. Sites in the programme were located to represent different river types (based on climate, source of flow, geology, land use/cover and size). In addition to monitoring at the core sites, impact monitoring (carried out to determine the source of contamination) is carried out many more sites but only for short periods (usually 1-2 years).
How We Assess Water Quality - Guidelines and Standards
In order to protect the uses and values identified for Tasman rivers certain mandatory and non-mandatory limits have been set. Mandatory limits are called standards, and non-mandatory limits are called guidelines. Council may develop more water quality standards in the future but for several water quality parameters standards would have to vary according to catchment or river section situations. More research is required to determine this. These situations include:
- stream types – spring-fed streams are often more vulnerable to deposition and in some cases need more stringent standards; soft-bottomed streams may produce more suspended solids
- geology – some areas naturally produce high levels of heavy metals or acidity or alkalinity
- particular uses and values – waterways that a used for swimming would generally need to have a more stringent standard than other waterways
The standards that apply generally to discharges in Tasman’s waterways are the following:
| Indicator | Guideline to which discharge can alter from the ambient (upstream) level* |
|---|---|
| Faecal coliforms (a disease-causing organism) | Less than 1000/100ml |
| Water clarity | Less than 40% |
| Water temperature | Less than 3oC |
| Oil and grease, films, scums, foams, floatable or suspended materials | Must not be "conspicuous" |
| Odour | Must not be "offensive or objectionable" |
Much of the Motueka and Buller Catchments are under the protection of Water Conservation Orders. These Orders are like national parks for waterways and provide more stringent water quality standards for those waterways.
Standards that apply for Buller and Motueka waterways are provided in the table below:
| Indicator | Standard to which a discharge can alter from the ambient (upstream) levels) |
|---|---|
| Suspended solids or turbidity (a measure of dirtiness) | Less than 1 mg/l or 1 NTU when the ambient concentration is less or equal to 10mg/l or 10 NTU respectively |
| Water clarity | Less than 20% |
| Water temperature | Less than 3oC alteration or increase to no more than 20oC |
| pH | 0.5 pH units when ambient pH lies outside the range of 6-9 pH units |
|
Undesirable biological growths - Filamentous growth (eg algae) more than 20mm long - Weight of growth (biomass) |
Buller - Less than 40% cover of bed Motueka - Less than 30% cover of bed Buller - Less than 100mg chlorophyll a/m2 , less than 40g Ash-free dry weight/m2 Motueka - less than 120mg chlorophyll a/m2, less than 35g Ash-free dry weight/m2 |
| Disease-causing organisms - E.coli | Median less than 126 E.coli/100ml (over more than 5 samples taken over a 30-day period) |
| Dissolved oxygen | Greater than 80% saturation |
| Food - birds, fish, invertebrates | Must not be rendered unsuitable for human consumption |
Note: These standards only apply to waterways identified in Schedule 3 of the Water Conservation Order from May to October and apply all the time to waterways identified in Schedule 2.
Buller Water Conservation Order (TRMP Part V Annex 1)
Motueka Water Conservation Order (TRMP Part V Annex 2)
Condition Class Criteria for Water Quality Indicators
| Indicator (units) | Relevance | Categories | |||
|---|---|---|---|---|---|
| Excellent | Satisfactory | Unsatisfactory | Totally Unsatifactory | ||
| Dissolved Oxygen1 (% saturation) | Certain level of oxygen required for aquatic animals to 'breathe' | >90 | 80-90 | 60-80 | <60 |
| pH 2 (pH units) | Can affect plants and animals eg eroding membranes | 7-8 | 6.5-7 or 8-8.5 | 6.0-6.5 or 8.5-9 | <6 or >9 |
| Turbidity 2 (NTU) | Can restrict algae and other plant growth, gill damage on invertebrates and fish or reduced feeding | <2 | 2-5 | 5-10 | >10 |
| Temperature 2 (oC) |
High temperatures can reduce trout spawning success Fish health |
<10 <16 |
10-12 16-18.5 |
12-14 18.5-20 |
>14 >20 |
| Total Phosphorus2 (mg/l) | Causes nuisance plant growth | <0.01 | 0.01-0.034 | 0.034-0.2 | >0.2 |
| Dissolved reactive phosphorus 2 (mg/l) | Causes nuisance plant growth | <0.005 | 0.005-0.01 | 0.01-0.5 | >0.5 |
| Total Nitrogen 2 (mg/l) | Causes nuisance plant growth | <0.1 | 0.1-0.6 | 0.6-2.0 | >2.0 |
| Total Ammonia-N 1 (mg/l) | Toxic to fish and invertebrates | <0.1 | 0.1-0.88 | 0.88-1.5 | >1.5 |
| Nitrate2 (mg/l) | Causes nuisance plant growth, toxic to fish and invertebrates | <0.5 | 0.5-4.9 | 4.9-7.2 | >7.2 |
| Water clarity 2 (meters) | Visibility - recreation | >4 | 2.5-4 | 1.6-2.5 | <1.6 |
| E.coli - single 4sample (no./100ml) | Human health - contact recreation | <55 | 55-260 | 260-550 | >550 |
| E.coli - median 2(no./100ml) | Human health - contact recreation | <25 | 25-150 | 150-200 | >200 |
| Filamentous green algae 5 (% cover of bed) | Amenity (slippery bed), natural character - recreation | <5 | 5-30 | 30-50 | >50 |
| Nitrate 2 (mg/l) | Animal health | <0.5 | 0.5-0.4 | 0.4-150 | >150 |
1 ANZECC 1992; Australian and New Zealand Guidelines for fresh and marine water quality. Australia and New Zealand Environment and Conservation Council.
2 ANZECC & ARMCANZ 2000; Australian and New Zealand Guidelines for fresh and marine water quality. Australia and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand. Download ANZECC Guidelines
3 ANZECC 2000 (Amendment recommend by Chris Hickey NIWA 30/09/2002)
4 Ministry for the Environment and Ministry of Health 2003; Microbiological Water Quality Guidelines
5 New Zealand Periphyton Guideline 2000: Detecting, Monitoring and managing Enrichment of Streams. Biggs,BFJ