March 25, / AMLA Science News Examiner / SA Kyle
The current restoration of the Huntington Beach wetlands could hold a more significant ecological recovery than previously imagined—beyond giving habitat to endangered species like the California Least Tern, the saltwater marsh could help fight global warming by acting as a natural carbon sink. But the very quality that endows this wetland with its unique ability to fight global warming—its connection to the ocean—may be its undoing. Global warming, in the end, may win.
According to the first State of the Carbon Cycle Report, wetlands in North America are estimated to sink, or store in their soils, 49 million tons of carbon from the atmosphere each year.
“Wetlands tend to store organic carbon in their soils because they’re wet,” said Dr. Jason Keller, professor of biology at Chapman University, “When there isn’t oxygen available, they store carbon in their soils.”
Salt marshes or brackish marshes that have some connectivity to the ocean are likely to be net sinks of carbon from the atmosphere.
Wetlands are also a natural source of greenhouse gases like carbon dioxide, methane, and nitrous oxide, however. Microbes that live in the soil of these ecosystems break down plant matter, and in the process release gas. This is why some marshes smell like rotten eggs: gas is released by microbes that use sulfate found in saltwater. It is the smelly sulfate microbes at Huntington Beach that make it such a good candidate to sink carbon from the atmosphere.
“Salt marshes or brackish marshes that have some connectivity to the ocean are likely to be net sinks of carbon from the atmosphere,” said Keller.
The sulfate found in ocean water drives a microbial process called sulfate reduction, which replaces the microbes that produce methane in freshwater marshes. Because saltwater marshes absorb CO2 from the atmosphere and don’t make methane, they are natural carbon sinks. They can even absorb enough CO2 from the atmosphere to be important on a regional scale.
If companies ever have to pay to reduce the amount of carbon they produce, wetland restoration that could pay for itself by taking enough carbon out of the air to pay for its construction.
In fact, some wetland restorations are being proposed as carbon sinks, according to Keller. State governments are interested in how salt marshes can be used as a carbon trading tool because they are well suited to storing large amounts of carbon, while not releasing the more potent greenhouse gas, methane.
Keller imagines that if companies ever have to pay to reduce the amount of carbon they produce, wetland restoration that could pay for itself by taking enough carbon out of the air to pay for its construction.
“If we can restore a large number of these [eco]systems, we have the potential to take some carbon out of the atmosphere,” said Keller. “And you also get all of the other benefits that you get with a marsh: you’re creating habitat, which is always a good thing, you’re creating flood control, which is always a good thing.”
Although wetlands could be a powerful tool in combating greenhouse gases, climate change itself could threaten wetland ecosystems. The drying of Southern California and a rising sea level could destroy saltwater marshes like the ones at Huntington Beach.
The global concern for Mediterranean regions, according to climate simulation models, is that there will be a significant drying by mid-century.
“The global concern for Mediterranean regions, according to climate simulation models, is that there will be a significant drying by mid-century,” said Dr. Dan Cayan, a climate researcher at University of California in San Diego. The California Climate Change Center predicts that Southern California’s rainfall will decrease by 10 to 20 percent over the next 50 years.
When wetlands dry out, organic carbon stored in the soil suddenly has access to oxygen. Microbes that feed on this kind of aerobic respiration cause the drying wetland to vent carbon dioxide, rather than storing it.
“[This] would mean a long term chronic release of carbon dioxide,” said Keller.
When combined with the 4.7 to 10.5 degree temperature rise predicted by the California Climate Change Center by the end of the century, the drying trend is expected to significantly accelerate.
“As it gets warmer, you increase evapo-transpiration which could be a cause of wetlands drying out even faster than they would if just precipitation changed,” said Keller, “There are feedbacks as well. It gets warmer and drier, which causes wetlands to release carbon dioxide, which causes it to get warmer and even drier.”
Rising sea level is the other significant threat to the survival of coastal wetlands like the marshes at Huntington Beach. Though projections vary, the rise in sea level we see today is higher than any point in history, according to Keller.
Our coast could march dramatically inward in the next hundred years, and that places coastal wetlands in a real challenge.
“Our coast could march dramatically inward in the next hundred years, and that places coastal wetlands in a real challenge,” said Keller, “Wetlands can only exist if they can add soil at the same rate or faster than the sea level is rising. If the sea level rises an inch, the wetland gets flooded unless it can add an inch of soil. It’s not clear that all wetlands are going to be able to do that.”
Today, biologists around the world are playing a catch-up game as the natural world as shows its beginning signs of global warming. They are trying to understand how ecosystems will function and, in turn, affect a warmer world.
“All of these interactions make it really, really difficult,” said Keller.
Say you take a specific ecosystem and warm it two degrees, Keller explains. Scientists think they can predict a certain result from this. But if it warms two degrees and gets wetter, that will change the prediction. And if it warms two degrees and gets drier, then a different prediction is made.
But the natural systems Keller and his colleagues work with are much more complex. He explains that often they are dealing with ecosystems that are warming, changing in precipitation levels, and experiencing higher nitrogen and CO2 levels from anthropogenic activities.
“So these interactions of multiple climate change factors are an area where people are still trying to figure out how all these things come together,” said Keller.