Drainage Influences Coastal Salt Marsh Productivity and Soil Biogeochemistry

Coastal wetlands display ecohydrological zonation such that horizontal differences in plant zones are driven by soil aeration and varying groundwater levels. However, it is less clear how variable levels of drainage directly impact biotic and abiotic factors in coastal wetland ecosystems. To determine the impacts of drainage levels, simulated tides in mesocosms with varying degrees of drainage were created with Spartina alterniflora and Salicornia pacifica, the dominant coastal salt marsh plant species on the United States' Atlantic and Pacific coasts respectively. We measured biomass production and photosynthesis as indicators of plant health, and we also measured soil and porewater characteristics to help interpret patterns of productivity. These measures included above and belowground biomass, porewater pH, salinity, ammonium concentration, sulfide concentration, soil redox potential, net ecosystem exchange, photosynthesis rate, respiration rate, and methane flux. We found the greatest plant production in soils with intermediate drainage levels, with production values that were 13.7% higher for S. alterniflora and 57.7% higher for S. pacifica. Understanding how drainage impacts plant species is important for predicting wetland resilience to sea level rise, as increasing water levels alter ecohydrological zonation.