Studies assist in restoring Lake Ellesmere
The ecosystem of Te Waihora (Lake Ellesmere) is threatened by past human activity on the Canterbury plains, which has resulted in a high accumulation of nutrients in the water, and, combined with low lake levels, problems with algal blooms. Two NIWA research projects are helping Ngai Tahu and Environment Canterbury (ECan) to improve the lake’s water quality and biodiversity.
How does lake level affect salinity?
The level of the lake is managed by ECan, who regularly open a channel through the coastal gravel bar connecting the lake to the sea, allowing the lake water to be refreshed. In one study, we are measuring seawater flows into the lake during the open channel period to assess the effect on the long-term salinity regime of the lake.
In challenging, and sometimes extreme, weather conditions, NIWA and ECan field teams collected spot measurements of flow, and using lake height, wind, tides, and sea conditions, constructed a time-series record of seawater inflows. We will use the data to develop models of water salinity in relation to lake level. This research is funded by ECan.
Lake openings and biodiversity
The second study measures how lake openings impact on fish populations. The aim: to determine the optimum times when the lake should be opened to the sea to restock and maintain fish populations.
While more than 50 species of fish are known to live in the lake the most important species for the fisheries are patiki(flounders) and tuna (eels).
By monitoring the levels of these species over the next three years, we will discover how the timing and duration of natural and artificial lake openings affect the number ofjuvenile fish being recruited to the lake, and the escape of pre-spawning adults on their migration to the sea.
The three-year research programme, funded by Ngai Tahu, will help develop and sustain both customary and commercial fishing in the lake.