There’s mixed news in Land, Air Water, Aotearoa (LAWA)’s 10-year trends report which was released yesterday:
. . .LAWA River Water Quality Lead Dr Tim Davie said the 10-year trends released today show the complexity of freshwater ecosystems.
“Looking at the trends, we see a mixed bag of improving and degrading sites across all water quality parameters. At the national level, for every parameter there are more sites showing signs of getting better than getting worse, except for the MCI trend which shows 2 out of 5 monitored sites are likely or very likely degrading,” said Dr Davie.
The MCI is used by scientists to monitor changes in macroinvertebrate populations because macroinvertebrates are responsive to multiple environmental changes such as flow, habitat, temperature, water quality and sediment. Macroinvertebrates are small animals (e.g. insects, worms, and snails) that live on or just below the stream-bed and are an important food source for fish.
“Macroinvertebrates are a good indicator of the wider health of waterways and have a high ecological value, so it’s disappointing to see they’re under pressure.
“On the other hand, it’s positive to see improving trends for the eight chemical-physical water quality indicators as we know these are quicker to respond to change. It is particularly encouraging to see ammoniacal nitrogen improving at many sites given the work of councils in reducing point source discharge and farmers keeping stock out of waterways,” said Dr Davie. . .
Dr Davie said that populations of freshwater insects, worms and snails were “likely or very likely degrading” at two out of five sites being monitored which was disappointing he doesn’t think the overall picture is bleak:
“They respond to different things like climate, the amount of sediment and a lot of different things,” Dr Davie said.
“So they’re a better overall indicator [of the state of the ecosystem] but they do take longer to respond.
“We know that our river systems can take a long time for the macroinvertebrates to improve when you start doing things to improve them.”
It was positive to see improving trends for the eight other water quality indicators, including clarity, turbidity, E. coli, nitrogen and phosphorus, Dr Davie said.
It is positive to see improvements in these indicators but of course not everyone thinks that:
However, Victoria University water scientist Mike Joy said snapshot samples of chemicals from sites selected by councils were giving skewed results.
“You can have what look like improvements because the amount of nitrate is going down in the water,” Dr Joy said.
“But what you haven’t accounted for is the amount of algae going up in the water.
“And that’s why the invertebrates are showing virtually the opposite [to the other results] because they have been wiped out – they can’t survive because of oxygen depletion and their habitat being smothered by algae. That’s the invertebrates showing the true story that the nitrates aren’t showing.” . .
Meanwhile, farming and irrigation and population pressure continued to degrade waterways, he said.
“I’d love to know how anyone would expect it could be getting better when we haven’t done anything to make it better.” . .
His bias is trumping the science here.
Rivers in areas with irrigation are generally cleaner than those in areas without irrigation.
It is also wrong to say farming continues to degrade waterways and “we haven’t done anything to make it better.”
Dr Davie said there was a lot of work going on trying to keep stock out of rivers and planting alongside rivers – but the flow-on effects for macroinvertebrates took longer. . .
Farmers have spent, and are continuing to spend, considerable money and time creating and protecting wetlands, fencing off waterways and doing riparian planting.
Water quality didn’t degrade suddenly and it won’t magically improve overnight.
But the report shows more sites are improving than degrading which indicates changing practices and protective measures are having a positive impact.