Environmental report calls attention to the need for more research on water quality

An opinion editorial by NIWA Chief Scientist of Freshwater and Estuaries, Scott Larned.  

The quality of New Zealand’s waterways features prominently in a newly released report on the state of our environment.

The report, Environment Aotearoa 2019 (EA2019), was prepared by the Ministry for the Environment and Statistics New Zealand as required by the Environmental Reporting Act. EA2019 uses investigations from five environmental domains (land, freshwater, marine, climate and air) to report on priority issues.

Water quality is one of those issues, but the summaries in EA2019 cannot convey the real-world complexity of water quality, which is a collective term for the multitude of physical, chemical and biological variables that are measured in rivers, urban streams, lakes, aquifers and coastal waters.

This complexity dominates water management and policy-making and should be part of our public debate. For example, phosphorus concentrations in most of the lakes in EA2019 have decreased over the last 10 years, which seems like good news. However, the average rate of decrease is about 0.01% per year, so substantial improvements could take decades – not such good news. Despite the complexities, some broad water-quality patterns are evident. EA2019 reports that rivers, lakes and groundwater in agricultural areas have greatly elevated levels of nitrogen, phosphorus, and faecal bacteria, compared to levels in native-forest areas. The same national-scale pattern has been reported for more than 20 years, which indicates that recent mitigation efforts like stock exclusion have had moderate effects at best. Many urban rivers are degraded in terms of all water-quality variables measured, including heavy metals. This is also a persistent pattern.

Coastal water quality monitoring is a recent initiative for most councils and data are scarce, but early results indicate that nitrogen, phosphorus and faecal bacteria concentrations are elevated in coastal waters near river mouths and in river-dominated estuaries.

It is important to note that the water-quality states and trends reported in EA2019 are only patterns. Maps in the report show spatial patterns in water quality across New Zealand, and water-quality trend analyses show patterns of degradation and improvement over time. But there is little information in the report about the causes of water-quality degradation and improvement. The shortage of cause-and-effect information is not by design, it is because that information is critically lacking. Ironically, environmental reporting in New Zealand is required by law to use an evidence-based ‘pressure-state-impact’ approach, where pressures are the human activities that cause water-quality degradation. Water-quality patterns alone provide minimal evidence about the activities that cause them.

There is no question that large-scale intensification of agriculture and urban expansion has had adverse effects on water quality in New Zealand. However, improving water quality is not simply a matter of ‘reducing agriculture’ or ‘reducing urban areas’. The specific activities that are causing degradation in specific locations need to be identified, then mitigated.

Most water-quality monitoring programmes are operated by regional councils. For decades council monitoring has been narrowly focused on detecting water-quality patterns. This focus now needs to be expanded to include human activities. The resulting data can be used to link activities directly to water quality, which will enable mitigation. In agricultural and forestry areas, the activities that need to be monitored include fertiliser use, irrigation, soil tillage, clear-felling, and cattle stocking and feeding. In urban areas, those activities include wastewater drainage and treatment, earthworks, building construction and road runoff.

Reporting water quality-patterns without evidence of the causes of degradation or improvement invites speculation. Recent reports about water-quality improvements have been followed by claims from the primary sector that fencing stock out of waterways led to the improvements. Similarly, recent reports about water-quality degradation have been followed by claims from environmentalists that dairy farming is primarily to blame. In both cases, no cause-and-effect evidence was presented. Instead, these claims are based on general principles: stock exclusion may lead to improvements in some variables and dairy farming is likely to contribute to some adverse effects. Advocates on both sides claim to know both the pressures that cause ecological and water quality degradation, and the management actions required to reverse degradation. But they have not acknowledged the risks of being wrong. If costly management actions are not effective, the agencies responsible lose credibility, more effective solutions are delayed, and the collateral economic and social costs remain.

An instructive example of the need for strong evidence comes from Lake Rotorua. Phosphorus enrichment from sewage discharge was long assumed to cause algae blooms in the lake. Starting in the 1970s, upgrades to remove phosphorus were added to the Rotorua sewage treatment plant at great cost. These upgrades removed most of the sewage-derived phosphorus, but algae blooms continued into the 2000s. Subsequent research indicated that the algae were stimulated by nitrogen as well as phosphorus, and that agricultural land and the lake bed were sources of both nutrients, in addition to sewage.

To make a complicated situation even more complicated, there is growing evidence that natural climate cycles like El Nino are closely linked to trends in water quality in New Zealand. The specific causes by which climate variation affects water quality are not yet clear but could include changes in soil erosion and nutrient leaching. What is clear is that water quality is controlled by multiple pressures, some of which are under our immediate control (like fertiliser use), while others are not (like climate). This situation makes identifying the controllable human activities that degrade water quality a matter of great urgency.

Finally, we should acknowledge that most activities on land that are presumed to cause water-quality degradation in New Zealand are legal. Un-consented discharges and other prohibited or non-complying activities are unlikely to account for the large-scale water quality degradation that has occurred in the last century. Instead, the large-scale degradation is primarily the result of the cumulative effects of numerous consented or permitted activities such as treated effluent discharge, fertiliser use and grazing. What is needed is legislation to tighten up the legal activities, including wastewater treatment and agriculture and forestry practices. The freshwater reforms that are currently underway (www.mfe.govt.nz/fresh-water), the recent National Environmental Standards for Plantation Forestry (www.mfe.govt.nz/land) and the new review on stormwater, wastewater and drinking water (www.dia.govt.nz/Three-waters-review) are addressing these needs.