Relationships of Marsh Soil Strength to Belowground Vegetation Biomass in Louisiana Coastal Marshes

Wetland plants are subject to a range of physical stresses (e.g. inundation, salinity) that affect their productivity or health, which in turn may translate into wetland soils that vary in resistance to physical perturbations in the coastal setting. A primary goal of this study was to test a newly developed instrument designed to measure in-situ resistance to shear failure (soil strength) of marsh soils. The Wetland Soil Strength Tester (WSST) was used at 11 marsh types in coastal Louisiana, where soil bulk density ranged from organic to mineral (0.02-1.24 g cm(-3)). Based on analyses of live and dead components of both above and belowground biomass, live belowground biomass explained the most variation in marsh soil strength among the vegetation types. The WSST was capable of detecting in-situ live root biomass differences for 8 of 11 marsh types, where only the young deltaic marsh types were not significant. For all the sample plots (n = 227), an increase of 10-Nm soil strength corresponded to an increase of 200 g m(-2) of live belowground biomass (R-2 = 0.35, p < 0.0001). WSST measurements, combined with other monitoring data, may help in the assessment of wetland condition.