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Ripple effects: Wildfires reshape aquatic ecosystems

A study from the University of California San Diego has revealed a concerning trend: not only are wildfires wreaking havoc on land, but they’re also transforming aquatic ecosystems in ways that could have far-reaching implications for water quality and fisheries. 

The research, led by Professor Jonathan Shurin of the School of Biological Sciences and his team, is featured in two papers published in the journal Global Change Biology.

Growing crisis

Climate warming has led to more frequent and severe wildfires globally, and this surge is not just a terrestrial issue. 

“The effects of wildfires are not limited to terrestrial systems,” said study co-author Chris Wall. “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.”

Altered aquatic ecosystems 

The research shows that fire chemically alters plant debris, changing the fundamental role of lakes, ponds, and streams in the carbon cycle. This alteration is crucial because aquatic ecosystems are significant carbon sinks, capturing water flows and storing carbon in their sediments. 

The findings indicate a shift in how these systems process and store carbon, with potential consequences for atmospheric CO2 levels.

How the research was conducted 

The study was conducted over 90 days using experimental pond systems. The researchers explored the effects of burned and unburned plant matter. 

“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.

The team used a novel approach by fertilizing sage plants with nitrogen to track its movement from plants to aquatic species, like plankton. 

Key insights

“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.”

Carbon dynamics 

One striking revelation was that ponds with burned plant matter emitted less carbon dioxide compared to those with unburned material, suggesting a potential increase in carbon storage. 

On the other hand, this capacity diminished with higher amounts of burned material, leading to greater CO2 emissions.

“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.”

Species composition 

The researchers also observed a transformation in the species composition within these aquatic ecosystems. 

Ponds with heavy loads of burned material became breeding grounds for insects like mosquitoes, diverging from the typical aquatic inhabitants like zooplankton.

“These impacts were shifted by fire treatment,” said the researchers. “Burning increased the elemental and organic composition of detritus, with cascading effects on ecosystem function.”

Study implications 

This research underscores the need for climate change models to incorporate interactions between terrestrial and aquatic ecosystems. 

As climate change projections forewarn of escalating environmental and economic damages due to wildfires, understanding these aquatic transformations becomes vital for future conservation and management strategies.

“More frequent and intense wildfire may alter the capacity of aquatic systems to store, transform and exchange carbon with the atmosphere,” wrote the researchers.

They noted 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.

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