Development of management bands for ecosystem metabolism in non-wadeable rivers

Waikato Regional Council is developing appropriate monitoring and reporting tools for assessing ecosystem health in non-wadeable rivers.  This report was commissioned to explore the use of ecosystem metabolism and inform management bands for ecosystem metabolism in non-wadeable rivers.

Ecosystem metabolism is a measure of how much organic carbon is produced and consumed in river ecosystems. Ecosystem metabolism responds to a wide variety of factors including light intensity, water temperature, nutrient concentrations, organic pollution, chemical contaminants, flow fluctuations and loss of riparian vegetation. This sensitivity to factors that can be affected by human impacts makes ecosystem metabolism a good functional indicator of river ecosystem health. However, some of these factors also vary naturally with river size and therefore it is necessary to determine relevant benchmarks, for wadeable versus non-wadeable rivers for example.

In this study metabolism data from national and international studies were used to determine whether stream size was a significant predictor of ecosystem metabolism. Additional data on catchment and riparian condition was also gathered where possible.

While not accounting for all factors that can influence ecosystem metabolism, this review provided a large data set to determine suitable benchmarks for using rates of ecosystem metabolism as functional indicators of river health.  In this report, new management bands are proposed for non-wadeable rivers.

Application of recommended ecosystem metabolism bands to data from 28 non-wadeable Waikato rivers indicated that the majority of sites had ‘Satisfactory’ ecosystem health when measurements were taken.

Report: TR 2016/02

Author: Joanne Clapcott (Cawthron Institute)