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Source: NIWA – National Institute of Water and Atmospheric Research

Scientists know so little about how storms affect the delicate balance of lake ecosystems that we may be unable to protect them from the effects of climate change, says a NIWA scientist.

Lake scientist Piet Verburg was part of an international team of 39 researchers from 20 countries who carried out a recent review of current knowledge on how lake ecosystems respond to extreme storm events.

They discovered a huge worldwide gap in knowledge. And that, says Dr Verburg, is scary because as extreme weather events increase with climate change, lakes may change dramatically, threatening ecosystem health and water quality.

The team’s findings have been published today in the journal Global Change Biology.

The scientists reported they cannot confidently predict how lakes will respond to the more frequent and intense storms that are expected in a warming world.

“If extreme weather events significantly change carbon, nutrient, or energy cycling in lakes, we better figure it out quickly,” says Jason Stockwell, an aquatic ecologist at the University of Vermont who led  the new  research, “because lakes can flip, like a lightbulb, from one healthy state to an unhealthy one—and it can be hard or impossible to flip them back again.”

The new study focused on phytoplankton—microscopic plants commonly known as algae. Phytoplankton are of particular concern because they are the base of the food web and a critical driver of water quality.

In a search of thousands of scientific articles from around the world, the scientists found just 31 studies on 18 lakes that connected storms to freshwater lake conditions, and then to phytoplankton. Not only was the information sparse, but the few available findings were inconsistent.

It became clear that the scientific community has a poor understanding of how phytoplankton respond to storms, or how their responses may differ by storm types, across different lakes, or even at different times of year.

Dr Verburg said none of the 31 papers were about New Zealand lakes and the only related research involved a 1970s paper looking at how macrophytes were uprooted by an intense stormcausing a lake to become more turbid and stopping plants becoming reestablished.

“Research in this area has become urgent – lakes are definitely changing because of climate change and we need to know more about the role of storms in changing them.”

Dr Verburg said it was known that lakes were becoming warmer in New Zealand which for deep lakes meant that typically the shallow warmer water mixed less with the deeper colder water which had flow on effects to the entire ecosystem.

“Again that is something that needs a lot closer investigation. My fears are that the nutrient reductions being planned will not be sufficient and many lakes will become more eutrophic because of climate change effects.”

Dr Verburg has applied for funding to study aspects of climate change effects on Lake Taupo. He and the other scientists involved in the review are calling for a collaborative, multi-disciplinary effort.

They suggest several research directions including integrating watershed and lake physical models with biological models to better predict phytoplankton responses to storm-induced changes to lake conditions. The scientists also recommend continued and expanded long-term lake monitoring programs, coupled with networks of electronic high-frequency sensors, to evaluate short-term changes, emergent patterns, and long-term responses of lakes and water quality to storm events.

MIL OSI