Extreme rainstorms drive exceptional organic carbon export from forested humid-tropical rivers in Puerto Rico

Key Findings

Rivers that store, then export carbon to long-term storage in ocean sediments are particularly important. For rivers that flow directly into the ocean, more than 65% of particulate organic carbon (POC) – or suspended organic matter – can be buried in offshore sedimentary deposits.

In tropical rivers, extreme rainfall events can push more sediment into rivers; this is projected to occur more frequently as climate changes. Extreme rainfall events are believed responsible for more than half (52-60%) of POC exports by rivers each year.

About the Co-Author

A photo of Bill McDowell, COLSA researcher and recently published in Nature Communications journal

Bill McDowell, Professor, Natural Resources and the Environment

Contact information: Bill.McDowell@unh.edu, 603-862-2249, UNH Water Quality Analysis Lab website

This research first published in Nature Communications Journal.

Researchers: K. E. Clark, R. F. Stallard, S. F. Murphy, M. A. Scholl, G. Gonzalez, A. F. Plante, W. H. McDowell

Rivers in tropical climates are often associated with supporting diverse ecosystems and being great ecotourism destinations, but these tropical rivers may also play an important role in capturing, storing, and preventing organic carbon from converting to carbon dioxide. This prevention can reduce the greenhouse effect, which prevents heat from escaping the Earth's atmosphere and contributing to a changing climate that is responsible for extreme weather events around the world, including record-breaking storms, floods, and droughts.

For this study, professor Bill McDowell and his colleagues used 25 years (1991-2015) of water samples collected from within the Luquillo Experimental Forest at USGS stream gaging stations located on both rivers, as well as from the Lower Rio Mameyes Water Quality Project. The researchers were able to examine the amount of sediment in the rivers following major rainfall events, determining that upwards of 65 percent of particulate organic carbon (POC) runoff was buried in offshore sedimentary deposits in the ocean.

McDowell—who has been researching the biological, geological, and chemical cycles of the streams, forests, and watersheds in New Hampshire, Puerto Rico, and around the world for more than four decades—believes that findings from this study can add to a broader understanding of how river systems can help mitigate climate change. The Sierra De Luquillo Mountains are an island arc mountain chain, similar to tropical island arc mountain ecosystems around the globe that could also feed similar carbon sinks.

This material is based upon work supported by the NH Agricultural Experiment Station, through joint funding of the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 1019522, and the state of New Hampshire. Co-authors include K. E. Clark, R. F. Stallard, S. F. Murphy, M. A. Scholl, G. Gonzalez, and A. F. Plante.