Grantee Research Project Results
Intra- and Interspecific Response of Tidal Wetland Plants to Increases in Salinity and Inundation as Predicted by Changes in Sea LevelEPA Grant Number: FP917369
Title: Intra- and Interspecific Response of Tidal Wetland Plants to Increases in Salinity and Inundation as Predicted by Changes in Sea Level
Investigators: Sutter, Lori A
Institution: Virginia Institute of Marine Science
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Global Change
Authorities are confident that the sea level is rising as a result of global climate change. Those marshes currently upstream of the salt front but still under tidal influence, tidal freshwater marshes (TFM), may experience the greatest shifts in ecosystem structure and function as a result of sea level rise. The overall objective of this work is to identify community level responses of tidal freshwater marsh plant communities to sublethal levels of salinity.
This project is taking a multi-pronged approach to investigate macrophyte response to both top down and bottom-up controls. This study will use observational field data along a salinity gradient to determine the spatial and temporal dynamics of vegetation communities (biomass, nutrient accumulation and net photosynthesis) as well as the community’s relationship to soil nutrients and porewater chemistry. Using mesocosms, this study will measure the vegetative stress response to sub-lethal levels of salinity and what role inter-specific competition plays in observed community changes. Finally, through a manipulative field experiment, this study will determine the role of invertebrate herbivores in plant community structure and resource allocation.
Plants are anticipated to assimilate nutrients proportionally to what is bio-available in their respective environment. Generally, plants grown under higher salinity are expected to have lower biomass, net photosynthesis and tissue nutrient ratios (C:N and C:P) relative to those grown in lower salinity. For those that do not demonstrate a decline in net photosynthesis, biomass is expected to diminish under higher salt conditions, suggesting that individual plants are stressed to the point that they cannot make productive use of the carbon they are fixing. Perennial plants are expected to fix more carbon than annuals and store a meaningful amount below ground. Inter-specific competition also is expected to decline in the presence of higher salt. With an increase in salinity, C:N is expected to be driven down, thereby increasing the palatability of the vegetation and potentially exacerbating herbivory stress.
Potential to Further Environmental/ Human Health Protection
Since 1987, formal efforts to reduce nutrient and sediment pollution in the Chesapeake Bay have been underway through the establishment of total maximum daily loads (TMDLs) of nitrogen, phosphorus (P) and sediment. With increasing salinity, P is released from TFM sediment and made biologically available in the open waters of the estuary. As the salt front moves upriver in the face of sea level rise resulting from global climate change, P will be released from TFM where it was previously retained. Preliminary results of this work indicate that a salt tolerant species retains less P than the native TFM species. If P is released with increased salinity and the vegetation utilizes less, the additional nutrient inputs into the estuary may lead to unexpected issues with excess P that are not being considered in the current Bay P “diet.”