Biotic and abiotic factors mediating coastal elevation
Humans impact Southern Louisiana marshes through pollution and global change that causes severe weather events and sea level rise. In addition to habitat destruction, these factors put marshes at risk of erosion. Increased nutrients, such as from pollution, can alter plant biomass allocation above- or belowground. Marsh grasses can also mitigate erosion and promote buildup of sediments through accretion. This study aims to determine whether changes in nutrient levels in marshes alter biomass allocation to a degree that impacts land elevation by limiting erosion and/or promoting accretion. This study includes analyses of: impacts of nutrient levels on the biomass allocation of marsh grasses, the correlation between biomass allocation and land elevation/inundation risk, and models of indirect correlations between nutrient levels and marsh elevation, mediated by plant biomass. Marshes with higher N tended to have both lower above- and belowground biomass (AGB and BGB, respectively); higher P was correlated to lower AGB. It is likely that nutrient levels are so high that they no longer benefit the grasses, causing lower biomass. Higher BGB in marshes correlated to lower submergence risk; higher AGB in marshes generally correlated to lower land elevation. These results are likely varied because of geographic location and other confounding variables. Higher nutrients indirectly correlated to lower elevation and lower elevation change, while high nutrients also correlated to decreased submergence risk and increased projected elevation. Further field and/or greenhouse experiments are necessary to understand how increased nutrients in marshes can impact land elevation through biotic means.