Biogeomorphodynamics of Coastal Ecosystems under Conditions of Climate Change and Nutrient Enrichment

Abstract

At a given time, tidal landforms inhabit one of three alternate elevation-determined stable states: salt marsh, sub-tidal platform, or tidal flat. The balance between soil production and sea level rise controls transitions between states. Due to increasing anthropogenic inputs to the carbon and nitrogen cycles, CO2 and nutrient enrichment rates are rising. What effect will this have on the evolution of the tidal landform? The present thesis recognizes that (1) soil production depends on halophyte biomass, (2) nutrient enrichment promotes a shift in biomass production from below- to aboveground thus increasing potential for sediment trapping, and (3) elevated CO2 causes an increase in total biomass production. Through use of point- and one-dimensional models, the present thesis finds that under constant suspended sediment levels equal to 20 kg/m3, (1) nutrient enrichment decreases accretion and increases suspended sediment requirements necessary to maintain accessibility of the salt marsh state, (2) elevated CO2 increases accretion decreases suspended sediment requirements necessary to maintain accessibility of the salt marsh state, and (3) the increase in accretion affected by CO2 addition is greater in magnitude than the decrease affected by nutrient enrichment. Thus we can infer that in a future scenario including increasing CO2, nutrient enrichment, and decreasing suspended sediment concentration, the enhancement effect of CO2 will dominate and a net increase in accretion will occur.