Relationship between coastal vegetation biomass with elevation and salinity gradients

Surges and waves generated by hurricanes and other severe storms can cause devastating damage to property and loss of life in coastal areas. Vegetation in wetlands and coastal fringes can reduce storm surges and waves while complementing traditional coastal defense approaches such as permanent levees, seawalls and gates. The effectiveness of marsh vegetation in attenuating storm surge energy and reducing soil erosion depends on the level of primary production at the time of the storm surge and the ability of marsh vegetation to recover rapidly from damage caused by the storm surge. Marsh production depends on a variety of abiotic factors, including salinity, flooding stress, and nutrient availability. Recovery of marsh vegetation from damage caused by storm surges depends in large part on characteristics of the dominant plants (e.g., biomass allocation to belowground parts). In this study, I quantified differences in abiotic and vegetation characteristics between high and low marshes at coastal and inland sites. I hypothesized that total primary production would be lower in low marshes and at coastal sites than in high marshes and at inland sites due to increased stress associated with tidal flooding and/or salinity. I also hypothesized, however, that belowground biomass allocation during the hurricane season would be greater in coastal marshes and in low marshes than in inland marshes or in high marshes, which in turn could allow more rapid recovery from damage caused by storm surges. Soil and plant samples were collected from December 2009 to November 2010 in both low and high marsh zones directly along a coastal edge as well as further inland on eight transects at Graveline Bayou and at the Grand Bay National Estuarine Research Reserve (GNDNERR) on the Mississippi Gulf Coast. Hydrologic and chemical data for these eight transects, including salinity, pH, and water depth, were obtained from the monitoring stations at GNDNERR. Field measurements included collection of soil cores and plant samples within a 0.25 m2 quadrat, plant heights, percent cover, and elevation. Laboratory analyses of the soil samples included moisture, bulk density, organic matter content, mean grain size, and sand, silt, and clay percentages. Laboratory analyses of the plant samples included measurements of above- and belowground biomass, stem diameter and rhizome thickness. The results shothat plant aboveground production was higher in inland and high marshes than in coastal and low marshes but plant rhizomes were thicker in coastal and low marshes with all sampling seasons combined, which indicated that native vegetation at lower elevation in close proximity to storm surges within coastal marshes tended to have lower aboveground production and higher belowground production. In inland marshes, vegetation tended to produce high aboveground biomass in summer and then moved carbohydrates to belowground in fall. The results that coastal vegetation produced higher aboveground biomass with lower sand percentage and higher silt percentage in high marshes suggested that vegetation production tended to be higher with higher clay and peat properties. The finding that coastal vegetation tended to produce higher belowground biomass in summer than was found in inland marshes was consistent with the hypothesis that plants in coastal marshes are better able to withstand storm waves and survive hurricane events