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The wetlands of the southern Louisiana coast are disappearing due to a host of environmental stressors. Thus, it is imperative to analyze the spatial and temporal variability of wetland vertical accretion rates. A key question in accretion concerns the role of landfalling hurricanes as a land-building agent, due to their propensity to deposit significant volumes of inorganic sediments. Since 1996, thousands of accretion measurements have been made at 390 sites across coastal Louisiana as a result of a regional monitoring network, called the Coastal Reference Monitoring System (CRMS). We utilized this dataset to analyze the spatial and temporal patterns of accretion by mapping rates during time periods before, around, and after the landfall of Hurricane Isaac (2012). This analysis is vital for quantifying the role of hurricanes as a land-building agent and for understanding the main mechanism causing heightened wetland accretion. The results show that accretion rates averaged about 2.89 cm/year from stations sampled before Isaac, 4.04 cm/year during the period encompassing Isaac, and 2.38 cm/year from sites established and sampled after Isaac. Accretion rates attributable to Isaac's effects were therefore 40% and 70% greater than before and after the event, respectively, indicating the event's importance toward coastal land-building. Accretion associated with Isaac was highest at sites located 70 kilometers from the storm track, particularly those near the Mississippi River and its adjacent distributaries and lakes. This spatial pattern of elevated accretion rates indicates that freshwater flooding from fluvial channels, rather than storm surge from the sea per se, is the main mechanism responsible for increased wetland accretion. This significance of riverine flooding has implications toward future coastal restoration policies and practices. [ABSTRACT FROM AUTHOR]

Hurricanes play an important role in shaping the coast of Louisiana. Although the sedimentary signatures of hurricane deposits have been documented in several different coastal environments along the northern Gulf coast, no studies have as yet documented the signatures in wetlands adjacent to large, inland brackish water bodies. In this paper we present results of a case study documenting the distribution and characteristics of storm surge deposits related to Hurricane Isaac (2012) in a wetland on the western shore of Lake Pontchartrain, Louisiana. Hurricane Isaac, a category1 storm, made landfall near the mouth of the Mississippi River on August 28, 2012. Due to its large size and slow movement, Isaac generated strong easterly winds across Lake Pontchartrain, producing a large storm surge along the west shore of the lake and unprecedented flooding in the surrounding lowlands. Loss-on-ignition, XRF, radioisotopic, and grain-size analyses conducted on sediment cores and surface samples from the area identify two distinct sedimentary signatures for the Hurricane Isaac deposits. Near the lake shore the signature is characterized by a laminated silty sand with a geochemical profile closely resembling that of lake bed material. Storm deposits located in a brackish swamp ~ 1km inland consist of a dark, low-organic mud with low concentrations of terrestrial metals and elevated concentrations of Br, S, and Cl. Differences in the storm signal are explained by the differing effect of topographical features on the depositional and transportation processes occurring at the two sites. Utilizing the geochemical/compositional signatures as a hurricane-generated storm surge proxy indicates the possible occurrence of a similar event predating the historical record. [ABSTRACT FROM AUTHOR]