28
Aug
Synthetic Fertilizers Disrupt Carbon-Capturing Ability of Salt Marshes
(Beyond Pesticides, August 28, 2019) Salt marshes, areas of coastal grassland regularly flooded by saltwater, provide a major global service by sequestering and storing carbon in the form of organic matter. However, research finds that nitrate from synthetic fertilizers found in agricultural runoff could change the microbial composition of the salt marshes to encourage organic matter decomposition and, therefore, carbon release versus capture. The study, “Nitrate addition stimulates microbial decomposition of organic matter in salt marsh sediments,” was published in Global Change Biology.
Researchers from Massachusetts conducted their study on salt marsh sediments located in Plum Island Sound, MA. They took three core samples from the site, sectioning each one into shallow, mid, and deep sediments. The researchers set out to determine “the role of nitrate as an electron acceptor, and its effect on organic matter decomposition and the associated microbial community in salt marsh sediments.” In sum, they tested soil samples to see how a large amount of available nitrate would impact microbes, and therefore the carbon-sequestering constitution of the soil, versus a plain saltwater control.
The results indicate that nitrates stimulate the production of dissolved inorganic carbon, leading to decomposition of organic matter that would otherwise remain stable in salt marsh sediments. By changing the available resources and altering the function of metabolic pathways, nitrates shift the composition of the microbial community to taxa that drive breakdown of organic matter via denitrification. Even samples from the “deep” section of the core, generally noted as resistant to microbial degradation, showed organic decomposition when exposed to nitrate.
First author Ashley Bulseco, PhD, wrote, “Traditionally, we have viewed salt marshes as resilient to nitrogen pollution, because the microbes there remove much of the nitrogen as gas through a process called denitrification. But this research suggests that when nitrate is abundant, a change occurs in the microbial community in salt marsh sediments that increases the microbes’ capacity to degrade organic matter. This potentially reduces the ability of the marsh to store carbon.”
According to Project Drawdown, a research organization that analyzes potential solutions to global warming, “While limited in area, coastal wetlands contain large carbon sinks; protecting them would secure an estimated 15 gigatons of carbon, equivalent to over 53 gigatons of carbon dioxide (CO2) if released into the atmosphere.”
The global climate crisis requires that all mitigations to climate change garner attention and action. Nitrates from agriculture runoff are perpetrators of not only disrupting these carbon-capturing salt marshes, but also creating algal blooms and subsequent dead zones, destroying soil health, and threatening human safety. Further, the researchers of this study warn that by stimulating the nitrogen cycling process can lead to nitrous oxide (N2O) production – a green house gas with 263 times the heat trapping potential of CO2.
To reduce the use of synthetic fertilizers that threaten the environment, Beyond Pesticides recommends advocating for organic agriculture, purchasing organics to leverage demand in the marketplace, and encouraging organic land management at the local level (city, town, and/or county). For assistance with such advocacy in your community, contact Beyond Pesticides at [email protected] or 202-543-5450.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Marine Biological Laboratory
