Infection risk from our waterways
The health of our lakes and rivers is one of many reasons to shift away from the fossil fuels driving climate change. Olivia Wannan reports.
By dragging our feet on climate action, we increasingly condemn our beloved lakes and rivers to a future of salmonella contamination, algal blooms, species extinctions and drying out, a new report warns.
Our Freshwater 2020, produced by the Ministry for the Environment and Statistics NZ, is a stark reminder that the alreadythreatened health of our waterways rests on our ability to urgently shift away from fossil fuels.
Even if emissions stay at historically low levels, temperatures will continue to rise in the coming decades, due to the lag between releasing greenhouse gas and the effects on our atmosphere, seas and waterways.
As the climate warms, rain storms will intensify, snowfall will decrease, glaciers will melt, soils will dry out and the sea level will rise – each affecting our lakes and rivers.
In the east, regions such as Hawke’s Bay will see increasingly low waterways by the end of the century, says Ministry for the Environment departmental science adviser Dr Alison Collins.
In the west – particularly in the South Island – rivers and lake levels are expected to rise, potentially leading to flooding.
After extreme downpours, drinking water and swimming spots are at high risk of being contaminated with infectious stomach bugs such as salmonella and harmful strains of E.coli, she says. Northern and remote eastern communities with less-developed water supply systems are particularly vulnerable.
Toxic algal blooms will become more common, as warmer temperatures reduce the mixing between upper and lower levels of deep lakes, boosting nutrient levels at the surface and algal growth. Without the waters mixing, the lake bottom is also deprived of oxygen, which drives out animals such as crayfish (ko¯ura) and mussels (ka¯ kahi).
Combined with pollution and habitat loss, climate change is likely to push some freshwater species – both native and introduced – to extinction, the report says.
More-frequent
droughts
and floods will affect species’ ability to breed and migrate, Collins says.
‘‘We’ll see changes to habitats that species are really dependent on,’’ she says. ‘‘Our rivers in urban areas, in farming areas and in forestry areas are highly polluted. With extreme weather, there’s likely to be an increased possibility of erosion and transfer of pollutants.’’
As the oceans rise, species living in freshwater estuaries will be inundated with seawater, while also being susceptible to wash-outs after storms.
Of the survivors, many are expected to shift inland and south to escape the salinity and warmer temperatures.
That’s if there’s suitable freshwater left. Farms and orchards in drought-struck regions are likely to demand water be diverted to irrigation. ‘‘That’s really going affect what we can grow where,’’ Collins says.
Our cities and towns will see direct effects, such as low-lying areas flooding more often, as well as indirect effects – if lakes dry up, hydro power stations won’t be able to reliably provide renewable electricity.
There’s robust data supporting these impacts, but timeframes are harder to predict, Collins says. ‘‘Because climate change is based on what we do globally in terms of our emissions … we can’t say with any certainty when something’s going to change.’’
Forest & Bird freshwater advocate Tom Kay says boosting the health of waterways today will give them, and us, a better chance to cope with the projected impacts.
Kay says central and local government can help by passing, implementing and enforcing the draft National Policy Statement for Freshwater Management as part of the Government’s wider action plan. ‘‘It will do a much better job of protecting our ecosystems but also protecting public health.’’
Individuals and communities can, and are, getting together to measure and boost the health of the rivers, lakes and streams in their areas, Kay says. ‘‘That’s probably one of the most obvious things we can do is, reconnect with our local stream, understand what its issues are. That’s what is leading to people doing riparian planting.’’
Kay says the alert level four lockdown hasn’t affected waterways much – ‘‘the farming’s still happening, we’re still flushing our toilets’’ – but a post-lockdown spend-up could. ‘‘Our concern lies with where all this investment goes.’’
In theory, storing water in dams could protect rivers, lakes and regions during dry spells, Kay says. ‘‘But instead what happens is we build big water storage schemes and big lakes and then we use the water every year to intensify our operations … Then you get a drought year and we’ve used all the water already.’’