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Wildfires changing aquatic ecosystems

REGION — Increasingly severe and numerous wildfires are changing the face of land across the globe, but new research by UC San Diego and others reveals that aquatic ecosystems are also being transformed, the school recently announced.

Led by Professor Jonathan Shurin’s laboratory at UCSD‘s School of Biological Sciences, the researchers compared how aquatic systems change with the input of burnt plant matter, including effects on food webs. Their results are featured in two studies published in the journal Global Change Biology.

“The effects of wildfires are not limited to terrestrial systems,” said postdoctoral scholar Chris Wall, a member of Shurin’s group and first author of one of the studies. “When we think about wildfires increasing, especially in the West, it’s important to remember that burned materials flow directly into waterways that are vital for people and wildlife. We’re now recognizing that wildfires can greatly influence ecosystem health, with implications for water resources, like aquifers and recreational fishing.”

Fire chemically transforms plant debris and changes the role of aquatic ecosystems in the carbon cycle, the research found. The shifts point to a fundamental change in the way these aquatic systems store, process and emit carbon.

The findings emerged from a series of experiments conducted at UCSD, and carry implications for aquatic ecosystems in areas such as the Sierra Nevada mountains – where Shurin’s group conducts research – and other regions.

“We’ve seen the impact that these huge fires have had on watersheds, so we’re working in these natural systems to understand how different components of climate change are altering the ecosystems,” said Shurin, a faculty member in the Department of Ecology, Behavior and Evolution.

Many normally functioning lake and pond ecosystems tend to emit more carbon dioxide than they absorb since they receive carbon into their system from neighboring sources, researchers said. The new study showed that this relationship could change with the increased input of burned wildfire materials, finding that ponds receiving burned materials had less carbon dioxide emissions relative to unburned material, indicating a shift toward greater carbon storage.

“Burned plant matter fuels the biological carbon pump of lakes, allowing them to soak up more CO2 from the atmosphere,” Shurin said. “However, this capacity for increased carbon storage was lost as the amount of burned material increased, with treatments receiving the greatest amounts of burned plant material exhibiting highest CO2 export to the atmosphere.”

Unburned test ponds displayed species characteristic of aquatic systems such as zooplankton. Ponds with heavy loads of burned material, on the other hand, transformed into havens for insects such as mosquitoes, the researchers found.

“These impacts were shifted by fire treatment,” they noted in their report. “Burning increased the elemental and organic composition of detritus, with cascading effects on ecosystem function.”

According to the authors of the studies, in the future, forecasts of climate change should include models that account for feedbacks between aquatic and terrestrial ecosystems in order to fully understand changes to the global carbon cycle.

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