Water Resources Research Act Program

Details for Project ID 2007MD143B

Responses of Species-Rich Low-Salinity Tidal Marshes to Sea Level Rise: a Mesocosm Study

Institute: Maryland
Year Established: 2007 Start Date: 2007-03-01 End Date: 2009-03-01
Total Federal Funds: $53,772 Total Non-Federal Funds: $123,056

Principal Investigators: Andrew Baldwin, Peter Sharpe

Project Summary: Problem: Coastal wetlands in the Chesapeake Bay and elsewhere are at risk of loss or alteration due to increases in water level and salinity from sea level rise. For example, extensive brackish wetlands at Blackwater National Wildlife Refuge on Marylands eastern shore have converted to open water during the last century due to the combined effects of background water level rise and land subsidence. To date the majority of research on effects of sea level rise on coastal wetlands has focused on salt and brackish marshes; little research exists on effects of sea level rise on tidal freshwater and intermediate marshes in the upper reaches of Atlantic coast estuaries (collectively referred to here as low-salinity tidal marshes). The lack of research on these systems is surprising given that they have considerably higher plant diversity than brackish and salt marshes, support myriad wildlife species, and are critical nursery habitat for commercially important species such as rockfish. Sea level rise is likely to result in increases in salinity and soil waterlogging in low-salinity marshes, causing stress or mortality of salt-intolerant species and altering vegetation diversity and species composition. While this broad prediction is possible based on current knowledge, little is known about the responses of plant diversity to specific changes in salinity and waterlogging regimes. Information allowing prediction of how low-salinity marsh vegetation will respond to increases in salinity, water level, or both is critical to developing mitigation strategies and designing wetland restoration or enhancement projects in the face of sea level rise. Objectives: The broad goal of this proposed research is to understand how increases in salinity and water level will influence plant diversity and ecosystem function of tidal low-salinity marshes. Specific objectives are to: 1) Create experimental wetland mesocosms containing species from tidal oligohaline and freshwater marshes 2) Expose mesocosm plant communities to a factorial arrangement of salinity and inundation treatments 3) Relate changes in plant communities and indices of ecosystem function to potential changes in water level and salinity predicted under various sea level rise scenarios Methodology: Experimental plant communities will be created in greenhouse mesocosms using plants of low-salinity and brackish marshes and an inoculation of marsh soil containing buried seeds of annuals and other marsh species (i.e., the seed bank). In the mesocosms we will expose the plant communities to three levels of soil waterlogging (water level 10 cm above, level with, and 10 cm below the soil surface) and five levels of salinity (0, 1.5, 3, 6, and 12 parts per thousand or ppt) in a 3 x 5 factorial treatment arrangement in a randomized block design (n = 3 blocks). Vegetation will be monitored non-destructively as Leaf Area Index from May until September, when the aboveground and belowground plant biomass will be harvested, weighed, and analyzed for nutrients. Environmental variables such as soil redox potential and salinity will be measured and related to vegetation and ecosystem parameters. This approach will allow us to detect changes in plant composition, diversity, and indices of ecosystem function (biomass and nutrient pools). Based on experimental results from this study, regression models will be developed to predict changes in diversity, composition, and ecosystem function for a range of sea level rise scenarios.