Coastal Terrestrial Interface Carbon Cycling in a Warmer Climate

Coastal wetlands

wetland

An area of land that is periodically saturated with water, which influences the types of plants and animals that can live there. Wetlands include swamps, marshes, bogs, and other similar areas.

Source: A student's guide to Global Climate Change Source

are global hotspots of carbon storage, and locations where carbon and nitrogen

nitrogen

Nitrogen, represented by the symbol N and atomic number 7, is a colorless, odorless, and tasteless gas that constitutes approximately 78% of Earth's atmosphere. It is vital for all life forms, as it is a fundamental part of amino acids, proteins, and DNA.

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cycles have a far larger impact on land, water, and air than expected from the area they occupy. In many ways the mechanisms by which coastal wetlands respond to elevated CO2

carbon dioxide (CO2)

An important heat-trapping gas, also known as a greenhouse gas, that comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions.

Source: NASA Source

and warming are similar to other terrestrial

terrestrial

The geographical and biological features that are associated with the Earth's solid, rocky surface, residing on or resembling the land or terrain found on our planet.

Source: NASA Source

ecosystems, but coastal wetlands are also unique because biological and physical responses to disturbance are strongly controlled by rates of sea level rise. High rates of soil carbon

soil carbon

The measurable amount carbon dioxide stored in soil. It is the primary indicator of soil health, and it impacts the chemical, physical, and biological characteristics of the soil.

Source: Science Direct Source

sequestration in these systems are the result of complex feedbacks between vegetation and the physical environment. Plants are “ecosystem engineers” because they build soil elevation, and control aerobic and anaerobic microbial decomposition of organic matter. Such complex feedbacks are largely absent in present-day global-scale forecast models. We will investigate the complex interactions between plants, soils, and climate that influence carbon cycling using an existing experiment that began in 2016, the Salt Marsh Accretion Response to Temperature eXperiment (SMARTX). SMARTX is a field experiment located at the Global Change Research Wetland, a 22-hectare brackish tidal marsh on the western shore of Chesapeake Bay in Maryland. The site is operated by the Smithsonian Environmental Research Center with support from the Department of Energy (the site’s original sponsor), National Science Foundation, United States Geologic Survey, and National Oceanic and Atmospheric Administration for over three decades. Several other experiments located at the site will be leveraged to extend the data provided by SMARTX.

SMARTX is a whole-system experiment deployed in two plant communities, with warming from the plant canopy to 1.5 m depth. Warming treatments are applied as a gradient from ambient to +5.1°C. Elevated carbon dioxide is crossed at the temperature extremes in one of the plant communities. To date, we observed that warming and elevated carbon dioxide change shoot and root growth in ways that are most easily explained by a warming-induced increase in microbial decomposition leading to higher soil nitrogen availability. Warming also increased emissions of the greenhouse gas methane

methane

A hydrocarbon that is a primary component of natural gas. Methane is also a greenhouse gas (GHG), so its presence in the atmosphere affects the earth’s temperature and climate system

Source: EPA Source

in SMARTX.

We will install a new system of soil sensors that continuously measure soil water content and salinity,

salinity

Salinity is the dissolved salt content of a body of water. It is a strong contributor to conductivity and helps determine many aspects of the chemistry of natural waters and the biological processes within them.

Source: EPA Source

which we hypothesize are controlling the plant growth response to warming. A new technique will be used to quantify soil organic matter decomposition rates and nitrogen availability to test hypotheses that explain changes in root versus shoot growth across the treatments. A new system of soil oxygen sensors will be installed to test hypotheses about the influence of root growth on methane production and emissions. Finally, stable isotope techniques will be used to gain insights on the mechanisms by which methane is produced, consumed, and emitted, and their response to our treatments. Data from SMARTX will be used to refine our ecosystem-scale marsh carbon model, and to modify an Earth system model

earth system model (ESM)

A model that simulates how chemistry, biology, and physical forces work together. These models are similar to, but much more comprehensive than, global climate models.

Source: U.S. Department of Energy Source

to enable the first-ever representation of tidal wetland dynamics at a global scale. The result will be an improved ability to forecast the stability of coastal wetlands and the carbon they contain in the 21st century.