Storm Deposition and 137Cs Accumulation in Fine-grained Marsh Sediments of the Mississippi Delta Plain

Response to Comment on "Wetland Sedimentation from Hurricanes Katrina and Rita"

“…We agree that some sediments will be eroded over time, and we also think that some of these eroded sediments will be stored in local waters and even remobilized to be transported back into the marsh by local storms. However, it has been shown several times that hurricane deposition results in a net sediment gain, not a net loss (7)(8)(9), and that a hurricane depositional signal appears in the sediments (10).…”

Numerical modeling of the effects of Hurricane Sandy and potential future hurricanes on spatial patterns of salt marsh morphology in Jamaica Bay, New York City

“…The end result can be conversion of marshes into mudflats or even into open water, or increased vegetation mortality can be caused by increased salinity exceeding the vegetation's threshold of salt tolerance as a result of saltwater intrusion (Cahoon, 2006). On the contrary, storms can also deliver enough sediment to raise soil surface elevation and stimulate organic matter production, thus helping coastal wetlands to survive rising sea level and subsidence (Chmura and Kosters, 1994;Cahoon, 2006;Turner and others, 2006;Tweel and Turner, 2012). The effect of major hurricanes on sediment accumulation can be detected by identifying the coincidence of cesium-137 ( 137 Cs) and lead-210 ( 210 Pb) activity peaks with mineral peaks, indicating that although storm-induced sediment may become reworked by physical or biological processes, some of the storm-induced sediment is indeed retained and incorporated into the long-term sediment accumulation for maintaining surface elevation (Chmura and Kosters, 1994).…”

“…On the contrary, storms can also deliver enough sediment to raise soil surface elevation and stimulate organic matter production, thus helping coastal wetlands to survive rising sea level and subsidence (Chmura and Kosters, 1994;Cahoon, 2006;Turner and others, 2006;Tweel and Turner, 2012). The effect of major hurricanes on sediment accumulation can be detected by identifying the coincidence of cesium-137 ( 137 Cs) and lead-210 ( 210 Pb) activity peaks with mineral peaks, indicating that although storm-induced sediment may become reworked by physical or biological processes, some of the storm-induced sediment is indeed retained and incorporated into the long-term sediment accumulation for maintaining surface elevation (Chmura and Kosters, 1994). The thickness of newly deposited mud on Louisiana's coastal wetlands during Hurricane Katrina was 5.18 ± 7.7 centimeters (cm; range: 0-68 cm) (Turner and others, 2006;McKee and Cherry, 2009).…”

“…This influence of large storms on subsurface processes appears to be the single most important difference between high frequency, low magnitude cold fronts or winter storms and low frequency, high magnitude hurricanes (Cahoon and others, 1995). The greatest impact on erosion and deposition in coastal wetlands could be caused by hurricane-force winds (greater than or equal to 74 miles per hour [mph]), not by the passage of winter fronts (Chmura and Kosters, 1994).…”

“…Sediment from hurricanes varies spatially (uneven thickness or spatial discontinuity) depending on the characteristics of the hurricanes (for example, storm track, wind speed, areal extent, and forward speed), location relative to hurricane path, and local bathymetry and channel morphology (Chmura and Kosters, 1994;Turner and others, 2006;Williams and Flanagan, 2009;Tweel and Turner, 2012). Normally, more stormgenerated sediment deposition was found at areas closer to the storm track and with a higher bulk density in the top surface layer, a higher mineral content, and coarser grain size compared to pre-storm condition or sites far away from the storm track (Cahoon and others, 1995;Turner and others, 2006;McKee and Cherry, 2009;Tweel and Turner, 2012).…”