Researchers have discovered that the effects of wildfires extend beyond terrestrial ecosystems. Aquatic ecosystems are also changing rapidly. The study discovered that fire debris alters lakes and other aquatic ecosystems, potentially affecting fisheries and water quality.
Climate change has increased the number and severity of destructive wildfires in recent years, causing devastation all over the world. According to climate change projections, the environmental and economic damage caused by wildfires will spread and worsen in the coming years.
While previous research has focused on the effects on land, new research from the University of California, San Diego, and other institutions indicates that wildfires are also causing rapid changes in aquatic ecosystems.
The researchers, led by School of Biological Sciences Professor Jonathan Shurin’s laboratory, compared how aquatic systems change with the addition of burnt plant matter, including the effects on food webs. Their findings were published in two research studies in the journal Global Change Biology.
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.
Professor Jonathan Shurin
Among the research findings are that fire chemically transforms plant debris and alters the role of aquatic ecosystems as key players in the carbon cycle. The changes indicate a fundamental shift in how these aquatic systems store, process, and emit carbon. The findings are also significant because aquatic ecosystems act as sinks, capturing water flows and storing carbon in their sediments.
“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.”
The findings emerged from a series of experiments conducted at UC San Diego, 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.
Because carbon enters their system from neighboring sources, many normally functioning lake and pond ecosystems tend to emit more carbon dioxide than they absorb. According to the new research, this relationship may change as the amount of burned wildfire materials increases. The study discovered that ponds receiving burned materials had lower overall carbon dioxide emissions than 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,” said Shurin. “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.”
“More frequent and intense wildfire may alter the capacity of aquatic systems to store, transform and exchange carbon with the atmosphere,” the researchers conclude in the paper. They note that in the future, forecasts of climate change should include integrative models that account for feedbacks between aquatic and terrestrial ecosystems in order to fully understand changes to the global carbon cycle.
The research was carried out on experimental pond systems over a 90-day period. At 10, 31, 59, and 89 days, the researchers tested different amounts of burned and unburned plant matter. The researchers fertilized sage plants with nitrogen as part of their research to track the chemical’s movement from plant leaves into the food web and into hosts such as plankton. This labeling enabled them to follow the path of dead plants through plankton and other aquatic species and determine how nitrogen transfer differed in response to burning.
“By using the nitrogen tracer in plant materials, we found less burned plant-derived nitrogen was being incorporated by zooplankton, indicating that burning reduced the transfer of nitrogen to higher organisms,” said Wall. “This agreed with other findings, which showed burned treatments had lower carbon dioxide concentrations, greater oxygenation and higher rates of photosynthesis relative to unburned treatments.”
“Burning changes the chemistry of leaves and that affects their cycling through freshwater ecosystems,” according to Shurin. The experimental ponds’ inhabitants changed as the influence of burnt matter increased. Unburned test ponds contained aquatic system-specific species such as zooplankton. Ponds with high concentrations of burned material, on the other hand, became havens for insects such as mosquitoes.
“These impacts were shifted by fire treatment,” the researchers reported. “Burning increased the elemental and organic composition of detritus, with cascading effects on ecosystem function.”
