Download Healthy Rivers: Plan for Change

Healthy Rivers: Plan for Change
Water quality
What are the water quality contaminants the plan change looks at and where do they
come from?
Four main types of contaminants affect the rivers: nutrients (Nitrogen [N] and Phosphorus [P]), sediment and E-coli
bacteria. They can come from:
• point source discharges such as municipal and factory discharges
• diffuse discharges e.g. run-off from land use.
Other natural sources e.g. native forest, geothermal activity.
What impact do hydro dams have on water quality attributes especially clarity?
A multitude of factors impact on water quality along the Waikato River.
The dams change the upper section of the Waikato River from a fast moving river into a series of lakes. This slows down
water flow and affects the riparian areas surrounding the lakes.
The reduced flow rate allows time for:
• sediment to settle, making the water clearer
• UV light from the sun to kill off harmful bacteria
• algae to grow, which reduces clarity.
Although the dams significantly affect the Waikato River, they also provide a renewable energy source for New Zealand,
which contributes to the regional and national economy.
What happens to nutrients not taken up by plants before they reach the water?
We have a good understanding of what happens to nutrients in the farm system and what happens to them within the
soil root zone. Beyond the root zone water and dissolved nutrients move through what is called the vadose zone. Our
understanding of what happens in this zone is limited, more nutrients are taken up within the soil profile. How this
happens is not yet well understood.
Groundwater and surface water are also connected and may interact.
• Surface water can reach groundwater when it filters through soils to recharge groundwater.
• Groundwater can reach surface water when solid rock layers prevent water infiltrating downwards. This creates
shallow groundwater flows which can reach the surface as a sleep or spring. This means that nutrients in groundwater
are likely to enter surface water and can then become available for aquatic plants and algae to grow. Generally, the
more nutrients supplied to streams from groundwater, the greater the growth of plants/algae.
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How does Waikato Regional Council assess the health of waterways?
The council measures a waterway’s health by monitoring water chemistry and aquatic life.
Water chemistry monitoring
Water samples are taken each month at 68 river and stream sites monitored by Waikato Regional Council and NIWA.
There are 12 sites on the Waikato River, five on the Waipa River, and 51 on tributary streams throughout the catchment.
Aquatic life monitoring
Water chemistry sampling onnly tells us about the state of the water at a specific time (i.e the day of sampling). However,
waterways are continually affected by the surrounding environment.
Monitoring the ecology of streams gives a broader picture of the health of the waterway because the life in the water way
integrates conditions over time. Invertebrates (insects, snails etc) are a very good indicator of local conditions (e.g water
chemistry, habitat, temperature, flow).
Fish can be a good indicator of the health of the entire network, as many need to swim up and down the river to breed.
No fish in a certain area of the river could be due to poor water quality, or due to restrictions in access.
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