Surface water quality in Tasman District
A technical report has been prepared (Tasman District Council Ref: R05007 and Cawthron Report No. 933, June 2005) by Roger Young (Cawthron Institute), Trevor James (TDC) and Joe Hay (Cawthron Institute) presenting results of the Tasman District Council’s “State of the Environment” Surface Water Quality Monitoring Programme from 1999 to April 2004.
The report incorporates monitoring data collected by National Water Quality Network (NIWA) from 1989 to 2003 and other data including data collected as part of the ICM Motueka programme.
Along with physical and chemical indicators, results from macroinvertebrate and periphyton indicators are presented.
The report highlights freshwater quality issues and outlines what Tasman District Council is doing to help improve water quality where it is found to be poor.
The report can be obtained from Trevor James at Tasman District Council or downloaded below (Note: very large file size)
Tasman District Council
189 Queen Street
Private Bag 4
RICHMOND
State of surface water quality
in Tasman District 
(22 756 KB) Note: Big file
EXECUTIVE SUMMARY
As part of its obligations under the Resource Management Act, Tasman District Council monitors the state of surface water quality and river health at selected sites throughout the Tasman District. Data from this monitoring programme and selected information collected as part of scientific studies carried out by other agencies in the District are reviewed in this report.
A range of water quality parameters have been measured at most sites on a
quarterly basis at base flow since 1999. Samples of aquatic macroinvertebrates
have been collected annually since 1999 at most of the water quality sampling
sites. Some types of macroinvertebrates are tolerant to pollution while others
are not. Therefore, the presence or absence of particular macroinvertebrate
species can indicate the ecological health of a site. The amount and types of
periphyton (or algae) growing on the river bed is also indicative of river
health and has been measured quarterly at most of the water quality sampling
sites since 2001.
A cluster analysis of the water quality results identified three groups of
sites. One group consistingof eight small streams had poor water quality. These
sites (subsequently labelled as the “red” sites) have poor water clarity and
high concentrations of nutrients and faecal indicator bacteria compared with
other sites in the District and often exceed water quality guidelines. Dissolved
oxygen concentrations were low at times at some of these sites. All of these
sites are on small streams draining land that has been intensively developed for
agriculture, horticulture, or urban usage. Sites in this group include:
Motupipi, Watercress and Winter Creeks (near Takaka), Little Sydney and Waiwhero
Creeks (near Motueka), Kikiwa (upper Motueka) and Reservoir Creek in Richmond. A
second group of 11 sites (subsequently labelled as the “yellow” sites) have
better water quality than the red sites, but tend to have lower water clarity
and higher concentrations of nutrients and faecal bacteria than that in the high
quality (“green”) sites. The yellow sites include small streams and the
downstream end of moderate sized rivers that drain intensively developed areas.
Sites in this group include: lower Riwaka, lower Sherry (near Tapawera), Mangles
(near Murchison), lower Onekaka (Golden Bay), lower Wai-iti (near Brightwater),
Motupiko (upper Motueka catchment), Black Valley (in St Arnaud), and Kaituna
(near Collingwood).
The remaining “green” sites had the highest water quality and included
forested headwaters and also the downstream reaches of the District’s large
rivers. Sites in this group include: Motueka, Takaka, Aorere, Buller,
Matakitaki, Waimea, Wairoa, Wangapeka.
Sites draining low elevation land had higher concentrations of TN, NO3-N, NH4-N,
DRP, TP, E. coli, and suspended sediments than sites draining hill country,
mountains or flowing from a lake. Oxygen saturation was lowest in first order
streams. Concentrations of nutrients also tended to be highest in the smaller
streams. Concentrations of nutrients, E. coli and suspended sediment at sites
classified as having pastoral land cover were higher than at sites with
indigenous forest or exotic forest land cover. Similarly, water clarity was
lower at pastoral sites than in forested sites. The effects of land use on water
quality are widely recognised and the results of this analysis are consistent
with earlier nationwide studies of water quality patterns.
Continuous water temperature records were available for 23 sites, mostly within
the Motueka River catchment. Data from well-shaded headwater streams never
exceeded the temperature criteria for protecting ecosystem health during the
summer. However, the water temperature criterion was regularly exceeded during
summer at sites on small unshaded streams draining developed land (e.g.
Waiwhero, Little Sydney, Kikiwa). The temperature criterion was also regularly
exceeded in the lower reaches of the Tadmor and Motueka rivers.
Trends in water quality were determined at the three National River Water Quality Network sites (Motueka at Gorge, Motueka at Woodstock, Buller at Longford) where sampling has been conducted monthly since 1989. Concentrations of ammonium nitrogen declined at all three sites over the course of the data record, whereas concentrations of total nitrogen increased at all three sites. Water clarity also tended to increase at all three sites, including the Gorge site, which is upstream of any human land use, over the course of the data record. The fact that these changes were consistent among all three sites suggests that this trend is related to climatic changes, rather than changes in land management. However, nitrate nitrogen concentrations and conductivity increased significantly at the Motueka at Woodstock site over the course of the data record, but not at the other sites, suggesting that these changes may be related to changes in land use within the Motueka Catchment over the last 16 years.
Macroinvertebrate communities indicated good ecosystem health at the majority of
the sites that were sampled. However, ecosystem health appears to be poor in
many of the small lowland streams that drain the intensively developed parts of
the District (e.g. Motupipi River, Watercress Creek, lower Reservoir Creek,
Waiwhero, Little Sydney). These sites were also identified as having poor water
quality.
Periphyton communities were also indicative of good ecosystem health at the
majority of sites. However, again the small lowland streams draining intensively
developed land often had excessive accumulations of nuisance algae.
In terms of water quality, the Tasman District is lucky because all of the
District’s large rivers have a significant proportion of native forest in
their catchments. Therefore, any inputs of pollutants from developed land in the
middle and lower reaches are substantially diluted by the large volume of high
quality water from upstream. The main threats to water quality and stream health
in the Tasman District relate to the intensification of agriculture in the
District, and to a lesser extent the expansion of residential development in the
District. The main problems with water quality in the Tasman District are
currently found in small streams which drain intensively developed land.
Restoration efforts should focus on reducing nutrient and faecal bacteria inputs
to these systems. Efforts should also be made to increase the amount of
bank-side vegetation along these streams to provide shading and keep water
temperatures below the critical levels required for protecting ecosystem health.
If improvements can be made to the water quality of many small streams, this
will also lead to cumulative improvements in the quality of water in the main
rivers.
Water quality monitoring sites throughout the Tasman District NRWQN = National River Water Quality Network sites ICM = Integrated Catchment Management programme sites.