Carbon dioxide exchange between the atmosphere and a temperate salt marsh
Open Access
- Author:
- Ruiz-Plancarte, Jesus
- Graduate Program:
- Meteorology and Atmospheric Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 06, 2020
- Committee Members:
- Jose Dolores Fuentes, Dissertation Advisor/Co-Advisor
Jose Dolores Fuentes, Committee Chair/Co-Chair
Raymond Gabriel Najjar, Jr., Committee Member
Kenneth James Davis, Committee Member
Robert P. Brooks, Outside Member
David Jonathan Stensrud, Program Head/Chair - Keywords:
- Carbon
salt marsh
coastal
inundation
tides
Virginia
Salt marsh
Coastal
Inundation
Gross Primary Productivity
Wetland
Remote sensing
Light use efficiency - Abstract:
- Wetlands along the Atlantic Coast are constantly threatened by human impact, as seen after the devastating losses in the 1970s. The remaining wetlands are sinking and shrinking, as rivers with replenishing sediments become redirected and rising sea level rates strain this ecosystem. Ironically, wetland loss carries an increased threat to human safety as they protect from coastal hazards such as erosion and flooding from storms. As more wetlands disappear, their stored carbon is released into the atmosphere, directly impacting global temperatures. The overall effectiveness in mitigating wetland loss depends upon two matters: First, stakeholders must identify and assess the current state of the wetland to characterize the stressors to the ecosystem; Second, stakeholders need to evaluate the areas where the wetland is most vulnerable to develop mitigation strategies. The research described in this dissertation directly addresses these matters. The first part of this dissertation focuses on understanding the carbon ex- change with the atmosphere in a Virginia salt marsh ecosystem. We show how this ecosystem is affected by tidal inundation to limit carbon dioxide exchange from the atmosphere. Using continuous measurements on a 7-m tower, properties of the surface layer (e.g., air temperature, soil temperature, photosynthetically active radiation) above the marsh are resolved to determine their influence on the this carbon dioxide exchange. We utilize the eddy-covariance methodology to identify how tidal influence and environmental drivers modified the carbon dioxide exchange by the marsh. During the most productive period time of the year, a tidal inundation of 0.8 m reduces daytime uptake of atmospheric CO 2 and night- time release of CO2 to the atmosphere by 5 ± 1.2 µmol CO2 m−2 s−1 and 3 ± 0.7 µmol CO2 m−2 s−1 , respectively. The marsh was found to be a sink of atmospheric CO2 equal to 269 ± 9.1 gC m −2 over the course of the full year by integrating the CO2 exchange. These results help clarify the processes affecting carbon dioxide exchange in salt marshes which can be extrapolated to studies with global envi- ronmental changes (e.g., increasing sea level rates) and regional modification (e.g, coastal engineering). The second part of this dissertation utilizes information on how climate and environmental drivers affect the marsh’s light-use efficiency to estimate regional gross primary productivity. The model employs various satellite observations along with the tower measures to calculate the gross primary productivity of the marshes within the Virginia Coast Reserve. The analysis showed that between 2001 to 2017 the average daily GPP per m2 across the VCR was 2.8 ± 1.8 gC m−2 day−1 . In addition we report that the total average GPP for the VCR during 2001 to 2017 was 0.16 ± 0.01 TgC year−1 . Results identified how the primary productivity of this region is being reduced 0.04 TgC over the past 15 years. With the use of an enhanced vegetation index (EVI2) we identified that the creek edges, the boundary of upland and marsh, and areas behind eroded barrier islands are showing the most reduction in EVI2 value during the 15 year comparison. If the downward trend of primary productivity continues, it would be of interest to policymakers to take action in order to salvage the valuable ecosystem services that the Virginia Coast Reserve provides.