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Fresh water River water quality
Macroinvertebrates
Freshwater macroinvertebrates are aquatic animals such as insects, worms and snails. Sampling both the types of macroinvertebrate taxa (that is, groups of similar individuals) present in a waterway, as well as the number of each of these taxa provides an indication of overall river health and water quality.
Two common measures of macroinvertebrates are the:
- Macroinvertebrate Community Index (MCI)
- percentage of the total abundance comprising Ephemeroptera, Plecoptera, and Trichoptera taxa (%EPT).
The MCI looks at the whole macroinvertebrate population structure and provides a score that indicates general water quality. Generally, an MCI score of less than 80 indicates poor water quality and a score of greater than 119 indicates excellent water quality.
Some macroinvertebrates are particularly sensitive to pollution, so are good indicators of water quality degradation that has been caused by human activity. In particular, the contribution to the total abundance of macroinvertebrates belonging to the sensitive Ephemeroptera, Plecoptera and Trichoptera groups (mayflies, stoneflies and caddisflies) forms a measurement called ‘%EPT’. Low %EPT indicates a river is under pollution stress, while high %EPT indicates good water quality.
Current situation
Between 2005 and 2007, the average MCI score across 66 sites of the National River Water Quality Network was 109. The MCI scores show that 51 sites (77 per cent) had good to excellent water quality.
Water quality category of national monitoring network sites based on average MCI scores, 2005-2007
MCI |
Number of sites in each category |
|
|---|---|---|
MCI score |
Water quality category |
|
>119 |
Excellent |
15 |
100-119 |
Good |
36 |
80-99 |
Fair |
12 |
<80 |
Poor |
3 |
Note: data is derived from 66 sites of the 77 that make up the national monitoring network.
Data source: compiled by the Ministry for the Environment using data collected by the National Institute of Water and Atmospheric Research (NIWA).
Data source: compiled by the Ministry for the Environment using data collected by the National Institute of Water and Atmospheric Research (NIWA).
Three sites had MCI scores below 80, indicating poor water quality:
- Waikato River in Hamilton
- Manawatu River near Palmerston North
- Rangitaiki River in Bay of Plenty.
All of these sites are downstream of developed land (eg, hydro dams, urban areas or farming).
Fifteen sites had MCI scores above 119 indicating excellent water quality. Thirteen of these 15 sites are ‘baseline’ or ‘pseudo-baseline’ sites, which are typically in the headwaters with upstream catchments dominated by native forest. ‘Baseline’ sites are likely to have little or no diffuse or point source pollution and should therefore be near-natural, while ‘pseudo-baseline sites’ can be lightly impacted by surrounding land-use. Two of the sites with MCI scores above 119 were ‘impact’ sites:
- Motu River in eastern Bay of Plenty
- Buller River near Greymouth.
The sites in the national network have been ranked based on nutrient levels, water clarity, bacterial levels, macroinvertebrates and periphyton. The results are presented in river water quality league tables.
Long-term trends
MCI
MCI has gradually increased (improved) in national network rivers with low MCI scores over 1990–2007. Formal trend analysis will be carried out on this data later this year.
Trends in MCI in rivers in the national monitoring network, 1990-2007
Notes:
(1) Data is derived from 66 sites of the 77 that make up the national monitoring network.
(2) Higher MCI indicates better water quality.
(3) Hazen method used to calculate 5th and 95th percentiles.
(4) The break in the graph between 1995 and 1996 is where there was a change in preservative used, which appears to have altered the proportion of low scoring taxa found in samples. Results prior to 1996 should be compared with caution to results from 1996 onwards.
Data source: compiled by the Ministry for the Environment using data collected by NIWA.
(1) Data is derived from 66 sites of the 77 that make up the national monitoring network.
(2) Higher MCI indicates better water quality.
(3) Hazen method used to calculate 5th and 95th percentiles.
(4) The break in the graph between 1995 and 1996 is where there was a change in preservative used, which appears to have altered the proportion of low scoring taxa found in samples. Results prior to 1996 should be compared with caution to results from 1996 onwards.
Data source: compiled by the Ministry for the Environment using data collected by NIWA.
Read table of data of these graphs (above and below)
%EPT
Monitoring of rivers in the national network over 1989–2007 showed that the relative abundance of macroinvertebrates sensitive to pollution (as measured by %EPT) has increased for rivers with median %EPT, but has remained relatively stable for rivers with the highest and lowest percentage of EPT individuals. Formal trend analysis will be carried out on this data later this year.
Trends in %EPT in rivers in the national monitoring network, 1989-2007
Notes:
(1) Data is derived from 66 sites of the 77 that make up the national monitoring network.
(2) Higher %EPT indicates better water quality.
(3) Hazen method used to calculate 5th and 95th percentiles.
(4) Oxyethira sp. and Paroxyethira sp., which are from the Trichoptera order, have been excluded from the %EPT calculation, as they are typically not sensitive to pollution.
(5) The break in the graph between 1995 and 1996 is where there was a change in preservative used, which appears to have altered the proportion of low scoring taxa found in samples. Results prior to 1996 should be compared with caution to results from 1996 onwards.
Data source: compiled by the Ministry for the Environment using data collected by NIWA.
(1) Data is derived from 66 sites of the 77 that make up the national monitoring network.
(2) Higher %EPT indicates better water quality.
(3) Hazen method used to calculate 5th and 95th percentiles.
(4) Oxyethira sp. and Paroxyethira sp., which are from the Trichoptera order, have been excluded from the %EPT calculation, as they are typically not sensitive to pollution.
(5) The break in the graph between 1995 and 1996 is where there was a change in preservative used, which appears to have altered the proportion of low scoring taxa found in samples. Results prior to 1996 should be compared with caution to results from 1996 onwards.
Data source: compiled by the Ministry for the Environment using data collected by NIWA.
This information has come from the latest state of the environment report Environment New Zealand 2007.
This data comes from the National River Water Quality Network which is operated by NIWA with funding from the Foundation for Research, Science and Technology.
You can access the national network data for 2007, as well as more site information, in this spreadsheet.
What can you do?
- Fence off rivers, lakes and wetlands to help protect our waterways. Planting native vegetation or other plants enhances water quality and biodiversity.
- Planting trees also prevents soil erosion. Minimise water use by using plants that are suitable for local conditions and use mulch around them to retain moisture.
- For more advice on stream and wetland protection contact your local or regional council or the New Zealand Landcare Trust.
- Follow urban design and industry best practice guidelines to reduce contaminants getting into waterways.
- Boat owner? Before entering a lake or river, remove all weeds, flush out jet units and wash your boat down to avoid introducing new aquatic pests into the waterway. Visit www.biosecurity.govt.nz for more information on stopping the spread of pests species.
Return to the main river water quality page.
Last updated: March 2009
