Soil and water

Learn how salt marsh plants can signal carbon sequestration capacity

Coastal wetlands such as seagrass beds, mangroves and salt marshes play a vital role along the coastline, from protecting against storm surges to providing essential habitat for animals to capturing carbon atmospheric.

We are still only just beginning to understand the complex workings of these highly productive ecosystems and their role in mitigating the climate crisis, but UConn researchers are taking a further step towards understanding how marsh vegetation salt, their bacterial communities and vegetation can help predict the potential of a marsh. be a blue carbon pool. The research was recently published in the journal Estuaries and coasts.

“Coastal marshes are increasingly recognized as important ecosystems because they sequester and store a lot of carbon. There is a growing interest in understanding these blue carbon ecosystems due to our current climate crisis, ”says Beth Lawrence, co-author and College of Agriculture, Health and Natural Resources Assistant Professor of Wetland and Plant Ecology in the Department of Natural Resources and the Environment and the Center for Environmental Science and Engineering.

Lawrence explains how salt marshes serve as focal ecosystems in conservation and restoration. They are the habitat of a wide range of species, including endangered species like the salt marsh sparrow. Located at the interface between land and sea, these ecosystems buffer the energy of storms and perform other important functions, such as removing excess nitrogen from the water that flows to estuaries where it can otherwise lead to algae blooms and oxygen-deprived “dead zones”.

Development brings about changes in water movement (see sidebar) and Lawrence says that often tidal-restricted salt marshes become less salty and moist, resulting in changes in the plants growing there. Plants that thrive in these brackish conditions can be invasive, such as Phragmites australis, which has become the bane of coastal managers, says Lawrence.

Tidal restoration aims to reconnect cut marshes to the ocean to improve habitat. Increasing the size of culverts under roads, railways or bridges or removing tidal gates can restore tidal flow and the organisms that depend on it.

To observe how tidal restoration can alter the carbon cycle and soil microbes, the researchers sampled several Connecticut marsh sites, including less disturbed “reference” marshes and formerly restricted marshes that have since suffered a restoration.

“Restored by the tide and unrestored references differed in terms of carbon density and amount of carbon in the soil. Very small sites had likely dried up to some extent and lost carbon, ”says Lawrence.

This makes sense, Lawrence says, because in wetter soils microbes don’t break down carbon-rich plant material as efficiently as in dry soils, therefore the material and carbon in it remains. When microbes can feast on plant material under drier, more oxygenated conditions, the carbon is lost to the atmosphere as carbon dioxide, in a process called mineralization.

Other measurements between tidal restored and undisturbed marshes were the same for all parameters used in the researchers’ measurements, including soil chemistry, plant biomass, and microbial communities. However, there were big differences between the vegetation zones.

“The main difference we saw was in the plant communities,” says Lawrence. “We found differences in microbial respiration as well as in microbial communities living in the soils of different vegetation zones. These results suggest that plants and microbes respond to differences in environmental conditions. “

Aiden Barry ’19 (CAHNR) sampling soil for microbial analysis in the field (contributing photo).

By knowing which plants are thriving where, researchers can gain insight into the biological processes at play in the swamp by noting which plants are present.

“I think one of the main lessons from our study is that these vegetation bands are good indicators of what’s going on hydrologically and biogeochemically,” says Lawrence. “For example, if we see natives Alterniflora spartine growing, we know the environment is saltier than where Phragmites grows. These soils are likely to have a different bacterial community composition and process carbon and nitrogen differently than in a higher, drier community.

Given the importance of the salt marshes and the need to continue restoration work, Lawrence says managers could use satellite imagery or drones to observe vegetation on a larger spatial scale to get an indication of conditions. growth as well as the carbon capture capacity of a system. This could help focus restoration efforts and follow-up.

“Managers are really interested in scaling,” says Lawrence. “The quantification of the carbon and nutrient cycle is very long and detailed, so an important implication of this work is that the dominant vegetation in salt marshes can be used as an indicator of certain biogeochemical processes. We need to carefully consider how we spend our limited conservation dollars. “

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