Gaps in understanding
The gap widens when assessing impacts of changing water quality on "things we value", including te ao Māori, ecological health and human health. Despite having more than 500 sites evaluated for contamination trends, only 41 have data for a cultural health index assessing Māori interactions with water.
This is concerning because the dual goals for this synthesis report were to assess pressures on the environment as well as the resulting impacts.
In many cases, the data can't help detect recent change. Data and maps for land cover and erosion date to 2012. In other cases, the data presented is very coarse, but tells a compelling story that pollution has been significant.
Compared to native land cover, agriculture yields 2.2 to 9.7 times higher concentrations of contaminants. Urban concentrations are 3.3 to 30 times higher.
What's changing
Changes for animal numbers (separated into dairy cattle, beef cattle, and sheep) show meaningful trends that differ on the North and South islands.
Modelled estimates show the dairy sector contributed 39 per cent of nitrate leaching in 1990, rising to 65 per cent in 2017.
But water-quality data is presented in a format where the main story is nearly equal numbers of increasing and declining trends in water quality. The use of modelled water-quality data obscures useful detail.
The report's model results suggest streams and rivers don't exceed toxic nitrate concentrations. But the dataset underpinning the analysis has sites that clearly exceed this limit.
Only by looking at sites that exceed limits, or will do so soon, can we better understand how to use environmental reporting to help us live sustainably.
Sharpening focus
One danger of repeating rather than updating information in environmental reports is that it reinforces excuses for not taking action. The report correctly points out that slow passage of contaminants through groundwater can delay the impacts of land use by years or decades.
It quotes average lags calculated for water entering Lake Rotorua of 50 years or more. These estimates make recovery seem impossible, but recent updates suggest otherwise by using models that more accurately represent how water moves.
This shows improvements in nitrate concentration trends in streams with very old water and suggests that restoration work has halted algal blooms in the lake.
Overall, the report gives a sense that change has occurred over decades, and faster change is possible only if we can overcome knowledge gaps to sharpen our focus.
• Troy Baisden is professor and chair in lake and freshwater sciences, University of Waikato.
