Subtask 4.3: Spatial Prediction of Northern Gulf Coast Landscape Structure

Subtask Leaders: Don Cahoon - USGS Patuxten Wildlife Research Center, Beltsville Laboratory
Glen Guntenspergen - USGS Natural Resources Research Institute, University of Minnesota

Subtask 4.3 Aim:

There is considerable interest in the response of coastal wetlands to rising sea-level and the impact of changes in the intensity and frequency of tropical cyclones predicted from recent global change assessments. Subsidence, erosion, sea-level rise, and anthropogenic changes to sediment delivery rates are affecting coastal wetlands world wide. In some regions, these influences are converting significant portions of coastal wetland to open water.

As a consequence of predicted changes in the rate of sea-level rise and other stressors, integrated assessments of coastal wetland vulnerability and wetland loss are being developed. Early broad-scale assessments of wetland vulnerability were developed to improve estimates for coastal flooding due to storm surges and wetland losses due to accelerated sea-level rise. Because of the lack of site-specific information for the variables contributing to the persistence of wetland elevation in optimal locations of the tidal zone, more generalized threshold responses have been used. These approaches used simple assumptions concerning rates of sea-level rise, subsidence, and response of wetlands to sea-level forcing to identify specific regions around the world where wetland losses may exceed 65 percent by the 2080s. However the method used in these earlier assessments is difficult to validate and emphasizes the need for continuing research on wetland response to sea-level rise.

Plot-based mass balance models have focused on vertical adjustment of wetlands to accelerated sea-level rise and have identified a number of important controls on wetland response. In addition, the need for additional information includes: sedimentation, organic soil formation, vertical accretion, and surface elevation change as well as the interaction among these processes and their temporal and spatial variability as being important in being able to predict coastal wetland vulnerability. However, the use of these models present significant upscaling problems when applied to regional spatial scale and/or longer time periods. To some extent, these problems are being addressed by the development of landscape scale simulation models. Landscape models are one of the few tools that can be used to predict the effects of complex interactions and the long-term effects of global change both spatially and temporally. Most existing coastal wetland landscape models are computationally intensive and present significant challenges as a tool for predicting the response of coastal wetlands to sea-level change, anthropogenic stressors, and storminess. Newer assessments of coastal wetland response to sea-level rise emphasize a more quantitative mechanistic understanding of the variables which control the behavior of wetland systems and modeling wetland behavior at the landscape scale. Unfortunately, these models present significant challenges when downscaling to specific regions where local effects may over-ride broad-scale controls.

There is a need to develop new landscape scale models which combine the attributes of numerical but computationally intensive models and process intensive plot based models which would include better input data and improved spatial and temporal output predictions. Landscape models ultimately are one of the few tools that can be used to predict the effects of complex spatial interactions and the cumulative long-term effects of changes in sea-level and changes in the pattern of storminess associated with cyclonic activity.

Subtask 4.3 Activities:

The goal of Subtask 4.3 is to improve the research capacity to model coastal wetland vulnerability and predict the spatial structure of the Northern Gulf of Mexico coast in the Year 2100.

The specific objectives of this subtask include:

• Evaluate existing coastal wetland models and their use as a research and predictive tool;
• Modify a newly developed landscape scale coastal wetland model which incorporates key features of existing coastal wetland models, all the primary drivers of wetland behavior, and new research on coastal wetland stability;
• Use temporal change data collected in the Northern Gulf Coast Ecosystem Change and Hazard Susceptibility Project and surface and subsurface environmental and biotic data collected in the USGS BRD Global Change Research Project “Predicting the persistence of coastal wetlands to global change effects ” to construct an integrated perspective on the potential for changes in wetland structure and vulnerability along the Northern Gulf Coast; and
• Initiate a long-term coastal monitoring program for the Northern Gulf Coast which will monitor key process variables including accretion, shallow subsidence, and coastal wetland elevation and will be used to parameterize the newly modified landscape model.