Freshwater wetlands ‘at risk from hurricanes’
Freshwater coastal wetlands are more vulnerable to erosion during hurricanes than habitats with higher levels of salinity, a study suggests. US researchers say freshwater marshes have shallower root systems, leaving them at risk from wave erosion during storm surges. They added that the results could have implications for wetland restoration projects in hurricane-prone areas. The findings appear in the Proceedings of the National Academy of Sciences. “During the 2005 hurricane season, the storm surges and waves associated with Hurricanes Katrina and Rita eroded 527 square kilometres of wetlands within the Louisiana coastal plain,” the researchers wrote in their PNAS paper [pdf]. “Low salinity wetlands were preferentially eroded, while higher salinity wetlands remained robust and largely unchanged.” The team said that both freshwater and salt marshes within their study area were exposed to similar conditions during Hurricane Katrina, which struck the US Gulf coastline in August 2005. “We hypothesise that wave shear stresses generated during the hurricane exceeded the shear strength of the low salinity wetland soils, resulting in failure, whereas greater soil shear strength in the saline wetlands largely precluded erosion,” they suggested. “Soil shear strength and the resistance of the soil to erosion are determined by the properties of the vegetation. “We propose that resistance to erosion is primarily a function of rooting characteristics, which depend on the dominant species of vegetation – as controlled by salinity.” …
