Clamshells on the beach

Trillions of empty clam shells in the Colorado River delta are the only evidence of a once prosperous community. Freshwater no longer reaches the delta in most years, thanks to extensive damming 

What Can Dead Clams Tell Us about Carbon Emissions?

December 9, 2016

Clamshells on the beach

Trillions of empty clam shells in the Colorado River delta are the only evidence of a once prosperous community. Freshwater no longer reaches the delta in most years, thanks to extensive damming and water diversions along the Colorado River. The downstream ecosystem has paid the price.

Jansen SmithJansen Smith, PhD '17

In April 2015, after seeing some of my work on the ecology of the delta, Dan Auerbach sent me an email framed around a simple question: “What about the carbon cycle?” Cornell’s first NatureNet fellow, Dan is now at the EPA’s Office of Water. Having interacted only briefly through the Atkinson Center’s research fellows group, we decided to get together to brainstorm.

Clam shells are made out of calcium carbonate, so clams should be net carbon sinks—or so we thought. After consulting a handful of experimental studies on shell formation, we quickly realized that clams do store carbon in their shells, but they also produce carbon dioxide when they make their shells. And clams release carbon dioxide through respiration. Clams are a carbon source!

To our surprise, the decline in clam populations in the Colorado River delta—from up to 125 clams per square meter 100 years ago to three clams per square meter today—resulted in a net reduction in carbon emissions.

Our story was starting to take shape, but needed to be tested. We decided to pitch the idea to two Atkinson Center faculty fellows, Alex Flecker and Greg Dietl. With our team assembled, we started to place the results in context across the entire Colorado River system.

The reduction in carbon emissions from the clams was roughly equivalent to eliminating emissions from 15,000 cars each year. In light of climate change, it’s tempting to view these reduced emissions as good news. Unfortunately, in comparison to carbon emissions from upstream Colorado River water management, the reduction in clam emissions was small. Pumping water to Las Vegas or Phoenix, for example, emits more carbon dioxide by at least an order of magnitude—with effects far more detrimental to the atmosphere.

In fact, over the past 50 years, water management decisions along the Colorado River have resulted in a net increase in carbon emissions. Our team published an article this fall based on our findings.

In the estuary itself, the reduction in emissions—which may have once accounted for as much as 70 percent of carbon in the delta ecosystem—has been ecologically important. Clams move carbon between the water column and seafloor when they feed, influencing nutrient availability for the entire ecosystem. With clams in the Colorado River delta no longer filling this carbon-cycling role, the estuary’s ecology has changed—perhaps dramatically. We hope to learn more in future research. Next spring, Greg Dietl and I will return to the Colorado River delta to study the living snail and clam community.

 

Jansen Smith is a PhD candidate in Cornell’s Department of Earth and Atmospheric Sciences. The Atkinson Center’s Sustainable Biodiversity Fund has supported his research in the Colorado River delta.

 

Read more about the project in the Cornell Chronicle.

 

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