Written by: Amy Gault, Master of Science (Environmental Science) student
Our freshwater environments support our way of life – water sustains our agriculture, industries, tourism, energy, ecosystems, and the health and well-being of people and communities (1). In New Zealand, we are fortunate to have plenty of freshwater, but like the rest of the world, lots of our uses have been steadily degrading them, something we have been able to better understand by using various monitoring strategies.
Traditionally, water monitoring has mainly focused on the physical attributes and chemistry of water, all which were commonly used to assess the ‘health’ of the systems (1, 2). This has been heavily criticised by ecologists for being misleading as the value of chemical water quality data is a very limited indicator of biodiversity health. This wasn’t properly addressed until around the 1980’s and the application of biological monitoring began to gain traction. This is around when New Zealand developed an index to measure the biological variables using aquatic macroinvertebrates (3).
The macroinvertebrate community index (MCI) was initially designed to provide measures of organic pollution and how that could impact living things (3). As most macroinvertebrate species tend to stay in one place, are long lived, easy to collect and count, abundant, and diverse, their use as an indicator of freshwater health has grown to be the most commonly measured biological variable in New Zealand (1, 3). This technique has been used to represent ‘biological health’ which has thought to be inclusive of human health and safety (4, 5).
This term ‘biological health’ began to be used synonymously with wider ‘ecosystem health’ when considered in combination with other water quality measures. Ecologists had major issues with this term as well, as it casts a massive generalisation and over-simplification of underlying ecological function (5).
The National Policy Statement for Freshwater Management (6), the key piece of legislation for freshwater under the RMA, holds two mandatory values for regional councils to adopt; human health and ecosystem health (6). The original document held little to no guidance on how this would be achieved however, leaving managers to design independent monitoring programs for each individual region. This was somewhat recognised and rectified in the 2017 amendments and further developed in the 2019 draft, making the MCI a compulsory monitoring tool for all regional councils (7).
Although this is a good start, there is a growing body of evidence suggesting that although the MCI is responsive to multiple human induced stressors, it isn’t to all stressors (5, 9, 10). Because of this, the MCI provides a good indicator of the macroinvertebrate component of ecosystem health, but not ecosystem health as a whole (5). This is thought to have led our monitors astray, reducing our ability to effectively track key environmental changes and baseline conditions.
We are now facing the million-dollar question: how can we monitor our freshwater environments in a holistic way given the many logistical limitations? A new proposed framework is tackling this question head on.
The framework focuses on ‘biophysical ecosystem health’, a concept built from the definition of ecosystem health outlined in the NPS-FM (6), reflecting the importance of physical, chemical, and biological components of ecosystems. It combines the monitoring of aquatic life, water quality, water quantity, physical habitat, and ecological processes, integrating them to gain a far more accurate picture of the total ecosystem function (10). This more intricate combination of variables has a clearer focus on the systems resilience under our many influences at various levels of physical organisation.
With increasing pressures being forced on our freshwater systems, we need to have comprehensive monitoring to set appropriate limits and mitigation efforts to ensure the protection of this incredibly valuable resource. This new framework will still not be perfect, that is just the reality of trying to force a humanised construct on an ever-complex system. It does, however, demonstrate that the best chance we have is to integrate inputs from all kinds of specialists to make sure we are getting the clearest understanding of these amazing systems and how we can ensure it’s quality into the future.
- Ministry for the Environment & Stats NZ (2017). New Zealand’s Environmental Reporting Series: Our Freshwater 2017. Retrieved from www.mfe.govt.nz and www.stats.govt.nz.
- Davies, P. E., Harris, J. H., Hillman, T. J.& Walker, K. F. (2010). The Sustainable Rivers Audit: assessing river ecosystem health in the Murray-Darling Basin, Australia. Marine and Freshwater Research. 61(7), 764-777.
- Stark, J. D. (1993). Performance of the Macroinvertebrate Community Index: Effects of sampling method, sample replication, water depth, current velocity, and substratum on index values. New Zealand Journal of Marine and Freshwater Research. 27(4), 463-478
- Armitage, P. D., Moss, D., Wright, J. F. & Furse, M. T. (1983). The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running water sites. Water research. 17, 333–347.
- Clapcott, J., Wagenhoff, A., Neale, M., Storey, R., Smith, B., Death, R… (2017). Macroinvertebrate Metrics for the National Policy Statement for Freshwater Management. Cawthron Institute report no. 3073. Retrieved from: www.cawthron.org.nz and www.mfe.govt.nz .
- National Policy Statement for Freshwater Management (NPS-FM), 2017. Retrieved from: Retrieved from: www.cawthron.org.nz and www.mfe.govt.nz.
- Draft National Policy Statement for Freshwater Management (NPS – FM), 2019. Retrieved from: Retrieved from: www.cawthron.org.nz and www.mfe.govt.nz.
- Lepori, F., Palm, D., Brannas, E. & Malmqvist, B. (2005). Does restoration of structural heterogeneity in streams enhance fish and macroinvertebrate diversity?. Ecological Applications. 15(6), 2060-2071.
- Jahnig, S. C. & Lorenz, A. W. (2007). Substrate-specific macroinvertebrate diversity patterns following stream restoration. Aquatic Sciences. 70, 292-303.
- Clappcott, J., Young, R., Sinner, J., Wilcox, M., Storey, R., Quinn, J., Daughney, C. & Canning, A. (2018). Freshwater Biophysical Ecosystem Health Framework. Cawthron Institute report no. 3194. Retrieved from: www.cawthron.org.nz and www.mfe.govt.nz.