Human activities continue to degrade freshwater ecosystems in New Zealand. In an attempt to halt this, central government policies such as the National Policy Statement for Freshwater Management (NPSFM) have been developed. A fundamental concept of the NPSFM is that Regional Councils must monitor representative samples of waterbodies at the spatial scale of Freshwater Management Units (FMUs), and not at the larger regional-scale as previously done. Another fundamental requirement is for councils to “maintain or improve” ecosystem health in streams. One measure of ecosystem health are biotic indices that summarise invertebrate communities. The NPSFM contains tables of numeric values of selected indices that have been set to condition bands; A (excellent) to D (below the national bottom line).
These new requirements will impose significantly increased demands for sampling programmes within individual FMUs, particularity when operating under new nationally standardized sample collection and processing protocols. Invertebrate sample processing is a time-consuming and expensive component of monitoring programmes that requires highly skilled staff, yet still has constraints on the accuracy and resolution of identification. These deficiencies undermine our ability to describe biodiversity with confidence at sites.
Environmental DNA (eDNA) in contrast offers a potentially unparalleled way for councils to obtain high resolution data to species level, and collect more samples than are currently logistically possible at a cost that is, at worse, no greater than traditional techniques. During December 2020-May 2021, Regional Councils throughout New Zealand undertook an eDNA sampling trial of 53 sites. We compared ecosystem health assessments made by traditional assessments to those made using eDNA, and contrasted the ability for these two datasets to distinguish differences in ecosystem health in streams draining catchments dominated by different land use. We discuss the results and their implications for councils as they begin to implement the monitoring programmes required under the NPSFM.