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River water quality report – Expert Reaction

A river quality report and interactive from Land, Air, Water Aotearoa (LAWA) has measured the health of our rivers through data on 10-year trends from sites around the country.

The report assesses river water based on nine quality indicators and looks at the health of macroinvertebrates (snails, worms and insects) for the first time, concluding they may be struggling to thrive at some sites.

The SMC asked experts to comment on the report Please feel free to use these comments in your reporting.

Professor Jenny Webster-Brown, Waterways Centre for Freshwater Management, University of Canterbury/Lincoln University, comments:

“This 10 year water quality trend analysis won’t come as a surprise to any who maintain an interest in the health of New Zealand’s rivers and streams. We are getting a consistent story from almost all water monitoring – around a third of our (routinely monitored) rivers and streams, lakes and groundwaters have reduced quality, attributable to human activities.

“This new trend analysis indicates that a similar proportion of our rivers and streams appear to be actively degrading with respect to one or more of the parameters commonly used to assess water quality and, more critically, that this is indeed significantly affecting their ecosystems.The addition of MCI to this trend analysis means that we are not just looking at the physical and chemical parameters which have the potential to affect ecosystems, but also the direct response of those ecosystems to changing water quality.

“The fact that more than 50 per cent of the sites appear to have improved with respect to some parameters (e.g, clarity, ammonia and total phosphate concentrations), indicates that change for the better is possible when the source of contamination is correctly identified and effectively reduced. However, it only takes a single contaminant to disrupt an ecosystem.

“Trend analyses such as this can show us where greater effort is needed to protect our water resources. They also demonstrate one of the huge benefits of now having a central repository (LAWA) for almost all of NZ’s water monitoring data!”

No conflict of interest.

Professor Troy Baisden, Professor in Lake and Freshwater Science, University of Waikato, comments:

“The LAWA 10-year trends release represents a significant step forward for New Zealand’s environmental monitoring of rivers and streams. This is now a large, consistent dataset with a routine assessment. The improving quality of the data and careful analysis is a testament to all those involved in collection and analysis.

The dataset shines light into how we’re doing on freshwater. Importantly, it shows improvements are genuinely possible and are happening. Almost, equally it shows declines that need attention.

“Many Kiwis are likely to be most concerned about declines in faecal pathogens, indicated by E. coli, meaning people are more likely to get sick from swimming.

“Reporting on MCI (macroinvertebrates) is an important step. This index measures the health of the little critters that are the food for iconic fish and taonga species. It has the greatest coverage of sites of all the parameters reported. It also shows the worst trends. That’s concerning because this index is an integrated measure of ecological health.

“Now that we have this dataset, what can we do to make it better? A first step would be to ensure reporting better informs decisions. The LAWA release doesn’t tell us where the problems are, or how bad they are.

“The analysis could help us focus more on what matters. Trends are reported for nine parameters, yet only two or three tend to provide useful focus at each site. Until we see LAWA take these steps, the results don’t point to what farmers or communities can do to create improvements. Many really want to take action, and directions are needed.

“And, what’s missing? It is common internationally to report an indicator of oxygen. This is important because excess nutrients lead to algal growth, and the dead and decomposing algae consume oxygen. Fish, as well as their food measured by MCI, can’t live long with oxygen. To make better sense of declines in MCI, I’d like to see an indicator of deadly low oxygen events.

“Overall, the LAWA 10-year trends analysis should be lauded as a big step for environmental data in New Zealand. Yet, it also reminds us we have a lot of work for scientists and society as a whole if we want our children to be proud of how we managed the freshwater they’ll inherit.”

Conflict of interest statement: Funded as the Bay of Plenty Regional Council Chair in Lake and Freshwater Science.

Professor Angus McIntosh, Professor of Freshwater Ecology, University of Canterbury, comments:

“That Macroinvertebrate Community Index (MCI) data are now available in the LAWA National River Water Quality 10-year Trend Summary is very helpful because they present one of the best available measures of the life-supporting capacity of our rivers.

“The insects and other small animals that the MCI is based on must actually live in the river during the aquatic phase of their life cycle, so they represent the cumulative effects of conditions over time. Moreover, many sensitive insects have relatively long life cycles, so will only be present if conditions are good over a longer period of time.

“Thus, the declining trends in MCI, whereby two out of five monitored sites are likely or very likely degrading is a real worry. It’s encouraging that other water quality measures are improving at many sites, but the MCI trends indicate that much more needs to be done to reverse negative trends in freshwater ecosystem health.

“River life-supporting capacity, as represented by the MCI, could still be declining even though water quality itself might have stabilised, if legacy effects of past poor conditions still remain. For example, accumulated fine sediment due to past poor riparian management can clog stream habitats even though the sources of sediment may have been stopped. In those cases, active river restoration would be needed to bring about recovery.”

Conflict of interest statement: I am a leader of the Canterbury Waterway Rehabilitation Experiment (CAREX; carex.org.nz) which has developed and implemented restoration solutions for lowland agricultural waterways, funded primarily by the Mackenzie Charitable Foundation.

Dr Mike Joy, Senior Researcher, Institute for Governance and Policy Studies, Victoria University of Wellington, comments:

“The results in this LAWA trend analysis report show MCI deteriorating at most sites where trends were found. The MCI is what is known as biological assessment or ‘bioassessment’ and is considered by most freshwater scientists to be a superior and more holistic and robust measure of freshwaters than the monthly snap-shot physico-chemical ‘water quality parameters’.

“The MCI is a much more holistic measure because it gets around many of the problems highlighted below of snap-shot samples because the invertebrates must survive at a site over long time periods and thus they integrate the overall status not just a single point in time.

“The MCI results do not support LAWA’s previously claimed improvements in water-quality. The MCI trends do however support my earlier criticism of claims of improvements using flawed measures (details below).

“My criticism of physico-chemical analyses as used in New Zealand are detailed below:

“My first criticism is around site selection, the sites that are used are chosen by the agencies collecting the data (Regional Councils) are used for reporting on their own achievements (or lack of) around protecting water quality. Thus, there is an obvious driver for a bias in site selection towards sites that give a positive picture.

“Clarity and turbidity – these are both measures of sediment suspended in the water sample. However, from an ecosystem and human health perspective, what is suspended in water is far less important than the sediment that ends up on the riverbed smothering habitat and life (known as deposited sediment). But note deposited sediment is not included.

“E. coli – this is just one of a suite of indicators that could be used to indicate faecal contamination potentially threatening to human health. Problematically, E. coli levels in freshwater are extremely variable depending on rainfall, so monthly sampling will miss almost all this variability. Additionally, faecal contamination does not cover the many other potential human health issues like toxic cyanobacteria, cryptosporidium and many more.

“NH 4 (ammonium) – this can be toxic to aquatic life but is generally only high enough to be an issue in waterways immediately downstream of out of pipe discharges (point sources). This means the results are very dependent on where the sample is taken in relation to such discharges.

“The rest of the nutrient measures Total Nitrogen (TN), Total Organic Nitrogen (TON), Dissolved Reactive Phosphorus (DRP) and Total Phosphorus (TP) are just different forms of nitrogen and phosphorus. The reason they are measured is because when there are high levels of them in water they can lead to excess algal growth which leads to other ecosystem health issues, which are described below. These nutrient measures vary by orders of magnitude daily in degraded rivers in response uptake by algal mats. Thus, monthly sampling naturally misses most if not all of this crucial variance. More worrying is the fact that the nitrogen in the water reduces as algal mats form and bloom.

“Therefore, much of what is claimed as improving water quality can in fact be excess algal growth taking up the nitrogen (removing it from the water to grow and thus not picked up in water samples). Thus, the way they are measured are flawed, and can give a completely opposite result than the one they were measured to indicate.

“Phosphorus is required by algal mats too, but mats grow on the riverbed thus they sit in and on and grow in sediments that are high in phosphate (phosphate binds preferentially to sediment). This means it is of little or no consequence how much phosphorus is in the monthly grab water sample because the alga can get all the phosphorus they need for growth from the deposited sediment they are growing on. There can be almost no detectable phosphorus in grab samples but algae growth still become excessive, negating the point of measuring phosphorus in rivers (note it is an important measure for
lakes).”

No conflict of interest.

Dr Scott Larned, NIWA Manager – Freshwater Research, comments:

“Identifying the directions of temporal trends in water quality variables is an important step in river management; those trend directions are provided by the LAWA results. Two additional pieces of information are needed to put these trends into context: the magnitude (or rate) of trends, and the average (or median) water-quality state at each site. Trend magnitude is needed to judge whether improvement or degradation is progressing at very slow but detectable rates, or at rapid rates so that changes are evident to people and are likely to affect river organisms. Information about water-quality state is also needed to evaluate trends. For example, very slow improvements that are starting from a highly degraded state may indicate that substantial improvement will take decades, while very gradual degradation at pristine sites may be less concerning.

“Readers need to recognise that water-quality trends only describe temporal patterns, and provide no information about the causes of those patterns. The trends in the LAWA results may have been caused by land use change, mitigation actions such as stream fencing, changes in wastewater treatment, climate variation, and many other factors. The evidence base that links water quality trends to causes is very limited in New Zealand; this was the conclusion of a new NIWA-led review of land-use effects on aquatic environments. What is needed is a shift in the focus of monitoring and reporting programmes from identifying water-quality patterns alone to identifying cause-and-effect relationships. This shift is needed to guide land use decisions and management actions.

“MCI and other macroinvertebrate indicators can provide information about the ecological health of rivers, based on what we know about their sensitivities to stressors such as fine sediment. NIWA and international researchers have reported lags between improvements in stream habitat and water quality and responses in macroinvertebrate indicators, particularly where the improved sites are far from sources of sensitive invertebrate species to colonise the sites. These lags may have contributed to the patterns in MCI trends compared with trends in water quality variables in the LAWA results.

“The MCI scores used in the LAWA report are potentially useful but have limitations. They are based on the presence/absence of species, not their abundances or proportions. Quantitative and semi-quantitative indicators can provide more information. Further, MCI scores change in response to multiple variables, including river flow and physical habitat conditions. To ensure that management actions are effective, macroinvertebrate indicators need to be linked to changes in specific stressors.

Conflict of interest statement: NIWA and subcontractors are currently carrying out national water quality state and trend analyses under contract to the Ministry for the Environment, and we have assisted LAWA and Cawthron with data provision and analyses.


ends

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