Freshwater

New Zealand’s freshwater and estuarine resources provide significant cultural, economic, social, and environmental benefits. Competition for the use of these resources is intensifying, and many rivers, lakes and estuaries are now degraded.

This research project investigated whether the mechanisms for periphyton removal in rivers relate more directly to hydraulic and geomorphic conditions than flow metrics.

This research project aimed to understand the causes behind differences in mercury in trout and other organisms in the Bay of Plenty/Te Arawa lakes—in particular what features of each lake explain why mercury in trout is higher in some lakes than in other lakes.

Many of our iconic native fish species, such as whitebait and eels, rely on river flows to cue key life-cycle stages, including migration and reproduction. As pressures on water resources increase, the risk of disrupting these flow cues, and therefore impacting fish populations, becomes greater.

Three plants of an endemic submerged quillwort (Isoëtes) were recovered from Lake Ōmāpere by NIWA in 1998, prior to the lake weed (Egeria densa) dying off and the lake switching into an algal dominated turbid state. No further isoëtes plants have been observed in the lake since that time.

NIWA and Meridian are developing a management strategy on LINZ crown owned lakes for pest aquatic plants – weeds, the alga Didymosphenia geminata (Didymo) and filamentous green algae (both native and introduced) - in the Waitaki Catchment.

The River Environment Classification (REC) is a database of catchment spatial attributes, summarised for New Zealand's river network. The attributes were compiled for the purposes of river classification, while the river network description has been used to underpin models. 

NIWA are contributing to and testing the open source Delft3D model so that it can be used to simulate the response of braided rivers and their ecosystems to the changes in river flow associated with water use schemes, such as dams.

The ability to properly manage our freshwater resources requires a solid understanding of the flora and fauna which live in and interact with them.

Aquatic systems are under threat due to the introduction of invasive exotic species such as water weeds. Modelling work by NIWA has provided new information on which water bodies may be at greatest risk.

NIWA has developed a rapid, desktop model which assesses the potential impact of introducing new fish species to New Zealand. The model is customised to New Zealand's unique environment and endemic fish.