Success story

Supporting Taranaki Regional Council with Ecosystem Metabolism Application 

Dissolved oxygen – how much oxygen is in the water – is a key aspect for determining waterway health. Like us, aquatic life needs oxygen, and a lack of DO means an unhealthy river.

DO is measured to determine whether there is enough oxygen in the water to support aquatic life. We can associate low DO levels with inputs of organic pollution, or the excessive growth of aquatic plants and algae.

Daily changes in DO levels are an important part of ecosystem metabolism calculations. Levels vary depending on the time of day, peaking mid-afternoon when all aquatic plants are photosynthesising and releasing oxygen into the water. Levels are typically at their lowest at dawn, due to an uptake of oxygen by aquatic life throughout the night.

These daily changes are used to establish how fast plants are growing (gross primary production) and their rate of oxygen take (ecosystem respiration). We know that abnormally high or low rates of ecosystem metabolism are signs of an unhealthy river.

TRC wanted support as they began to audit their DO data, which involves data checks and cleaning, alongside preparations for ecosystem metabolism calculations. TRC also wanted guidance on how to calculate ecosystem metabolism, and support with site selection and equipment for DO monitoring.

Through A2E, Roger Young and Paula Casanovas (Cawthron Institute) provided their expert support. This involved a series of recommendations around sampling sites for DO monitoring, with practical suggestions on:

· how often to undertake DO sampling and the minimum amount of monitoring time required at each site.

· the best ‘spots’ for a regional DO monitoring network, including locations for below point source discharges.

· using equipment like sensors with wipers, and methods for metabolism calculation.

Roger and Paula also provided advice around quality control of data for use in metabolism calculations, along with some help on the code used for metabolism calculations and interpreting this data.

Roger and Paula’s expert guidance means TRC’s capability has lifted in determining the health of their river systems. TRC now have a greater understanding on appropriate targets to set, what is involved with measuring DO and ecosystem metabolism, and a selection of potential monitoring sites.