Conventional biological measures for monitoring aquatic ecosystem health, such as macroinvertebrates, can be difficult to apply in large rivers. These difficulties include obtaining representative samples, and limited understanding of factors affecting macroinvertebrate distribution and abundance in large rivers. Alternative measures such as the rate of organic matter decomposition and river metabolism offer potential for monitoring the ecological condition of large rivers.
Changes in dissolved oxygen saturation over a 24-hour period in the Waikato River at Hamilton Gardens (April 2008) used as the basis for calculating river metabolism.
In association with Waikato Regional Council, LERNZ researchers have investigated the utility of macroinvertebrates as monitoring tools to assess the health of non-wadeable rivers. Some metrics that reflect human pressure were identified in a survey of New Zealand boatable rivers, and an approach using ecological response differentials with wadeable streams was used to develop quality classes for Waikato non-wadeable rivers.
LERNZ researchers have also worked with collaborators at the Cawthron Institute, Nelson, to test the application of organic matter breakdown rates and measures of ecosystem metabolism, such as gross primary production and ecosystem respiration, as indicators of large river health. We have tested the use of tensile strength loss of standard cotton strips and loss in mass of wooden sticks across various pressure gradients, and found that cotton strips but not sticks showed promise as ecological indicators. Gross primary production was also found to reflect land use pressures and based on this work we were able to develop extent estimates for non-wadeable river condition using a probability monitoring network design.