Marsh Elevation Response to Hurricanes Katrina and Rita and the Effect of Altered Nutrient Regimes

Our scientific understanding of the marshes along the north shore of Lake Pontchartrain, Louisiana, is limited in terms of the processes required to sustain them and how to best manage them in the face of predicted rising sea levels. Subject to localized subsidence and urban development, these marshes may also be affected by increased nutrient loading in the future from proposed Mississippi River diversions and continued urbanization. This study presents data on marsh surface elevation change across a series of experimental plots located in Big Branch Marsh National Wildlife Refuge, Louisiana, that were subject to varying additions of phosphorus and nitrogen as well as a lethal herbicide treatment. These plots were also affected by Hurricanes Katrina and Rita in 2005. The rate of marsh elevation change prior to the storm suggests these marshes were maintaining elevation in the face of sea-level rise. A dramatic increase in elevation occurred following the storms but was followed by a proportional decrease in elevation. Soil data indicate the increase was caused by an influx of highly organic material at all plots. The results show how both storm and nonstorm processes contribute to elevation change and the maintenance of these marshes in the face of sea-level rise.