Modeling wetland transitions and loss in coastal Louisiana under scenarios of future relative sea-level rise

This study uses modeling results for coastal Louisiana to examine spatial and temporal variation in future wetland loss, and how this variation is influenced by different causes of land loss represented in the modeled processes. Fifty-year model predictions illustrate specific vulnerabilities of the wetlands and the conditions under which they occur, e.g., long-term changes vs. specific events. Environmental scenarios were used to examine model sensitivity to changes in future patterns of precipitation, evapotranspiration, subsidence, and eustatic sea level rise. Based on the model results, the magnitude of wetland loss increases more than three-fold from low to high scenario. The model allows vegetation types to change over time as environmental conditions change. Each type is sensitive to different land-loss causing factors. Across all scenarios, the largest contributor to wetland loss is inundation loss of saline marsh ->40% of loss. Inundation loss of brackish marsh increases from low to high scenarios. Salinity induced loss of fresh wetlands increases from low to high scenario and coastwide contributes <10% of the total wetland loss. Marsh edge erosion is relatively consistent in magnitude across scenarios but its relative contribution decreases from low to high. Model outputs show two contrasting responses to environmental change over a 50-year simulation: a relatively linear response of land area over time, and a non-linear response where a large collapse event is triggered in a single year. Land loss varied dramatically over time within the 50-year simulations with little loss in the first two decades and high rates of loss 25-40 years into the future. Across most of the coast, and for all scenarios, the majority of land loss is caused by excessive inundation. Understanding the threshold conditions for inundation for different species and species mixtures is crucial to predictions of vegetation change, and subsequent wetland loss. (C) 2019 Elsevier B.V. All rights reserved.