Sea-level and Storm Impacts on Estuarine Environments and Shorelines (SSIEES)

Science Center Objects

This project assesses the physical controls of sediment and material exchange between wetlands and estuarine environments along the northern Gulf of Mexico (Grand Bay Alabama/Mississippi and Vermilion Bay, Louisiana) and the Atlantic coast (Chincoteague Bay, Virginia/Maryland).

four photos showing wetlands

Estuary photos from Vermillion Bay, Louisiana. (Credit: Chris G. Smith, USGS. Public domain.)

A coastal system is an integrated and complex set of environments inter-related and inter-connected through physical and ecological processes and associated feedbacks. The Sea-level and Storms Impacts on Estuarine Environments and Shorelines (SSIEES) Project investigates the role extreme events (hurricanes, floods, and strong frontal systems) and sea-level change have on material exchange between marshes and adjacent estuarine water bodies along the northern Gulf of Mexico and the Atlantic coast including Grand Bay Alabama/Mississippi, Vermilion Bay, Louisiana, and Chincoteague Bay, Virginia/Maryland.

Project Goals

  • Advance the understanding of sediment exchange and transport within the estuary and the adjacent estuarine shoreline environments.
  • Address the short-term and long-term implications of storm- and sea level-related processes on the evolution of the estuarine system.

Project Objectives

  • Quantify sedimentation rates and sediment source to the estuary proper as well as the adjacent shoreline environments.
  • Use sediment texture and bathymetric change to evaluate areas of the estuary that act as sinks (short-term vs long-term) or sources of sediment to the coastal ocean.
  • Quantify decadal to centennial scale change in shoreline position and interior vegetative coverage.

Approach

  • Extend and analyze spatial and temporal datasets to identify and quantify physical processes affecting all estuarine environments.
  • Integrate field measurement of accretion and subsidence with a multi-decadal scale remote sensing analysis to extend discrete physical process interpretations over a broader spatial domain.

The SSIEES Project will evaluate wetland-estuarine material exchange using the following project structure, which can be readily linked back to the prior stated objectives:

Research Tasks

Evaluate the sediment storage and mobility in the estuary/bay/lagoon environment

subbottom profiling survey and targeted coring

Example of the activities utilized to evaluate sediment storage in the open water estuarine system, initially bathymetry and subbottom profiling surveys are conducted to evaluate sediment sinks within the estuary that are then followed by targeted coring and subsequent analyses of core material. (Public domain.)

The focus of this task is to examine the role that marsh and shoreline erosion contribute to the sediment budgets of the adjacent open-water estuarine system. Sediments derived from marsh shoreline erosion generally have higher organic matter content than sediments derived from the erosion of barrier islands or delivered by rivers. Understanding the sediment budget in these estuarine environments provides a comprehensive perspective of what factors drive the estuary health and integrity.

Objectives

  • Map bathymetry and sub-bottom characteristics for coastal embayments and compare with historical data to understand bay-scale infilling.
  • Quantify sediment characteristics and identify bulk sediment provenance to quantify the contribution of marsh sediments to the estuary proper.
  • Quantify sedimentation rates derived from shallow cores distributed throughout the bay.

Methodology

  • Conduct single-beam and/or swath bathymetry surveys of the bay.
  • Collect grab samples to characterize the modern surficial sediments.
  • Collect shallow cores (~50 cm) to determine recent environmental change.
  • Assess bay sedimentation rates using a combination of radionuclides and bathymetric data.

Assess and quantify dominant physical depositional and erosive processes in estuarine-shoreline environments

The goal of this task is to quantify physical and biogeochemical controls on sediment accretion and erosion in estuarine marsh-wetlands around the northern Gulf of Mexico and the Atlantic coast. Achievement of this goal will provide ground-truth data to compare with estimates of areal changes assessed through remote sensing techniques as well as establish a model of wetland response to episodic events such as hurricanes or persistent drivers like sea-level. While current statewide coastal monitoring networks provide critical information, especially with respect to recent (last 5 years) marsh accretion in restoration areas, these investigations have not addressed long-term, historical accretion rates for much of the northern Gulf of Mexico.

Wetland sediment sampling using a peat auger

Example of wetland sediment sampling using a peat auger. (Public domain.)

Objectives

  • Identify the dominate modes of sedimentation and erosion within a particular estuarine marsh-wetland type and evaluate significance relative to proximity to sediment source.
  • Develop multi-proxy technique (microfossils, geochemical markers, and chronology) to understand how natural and anthropogenic activities in estuarine marsh-wetlands have altered dominate modes of sedimentation, and
  • Develop a quantitative model to evaluate how certain estuarine marsh-wetlands respond (deposition or erosion) to episodic events (storms, brown marsh episodes).

Methodology

  • Marsh coring proximal to monitoring sites where infrastructure includes meteorological (MET) stations, sediment elevation tables (SETs), and water level gauges.
  • Use lead-210 and cesium-137 to quantify historic marsh accretion rates.
  • Use basic sediment properties and grain size to sediment provenance.
  • Use foraminiferal assemblages and geochemical tracers to evaluate environmental change.
  • Link core based chronologic events with remote sensing datasets to aid in scaling point measurements (cores) from local- to regional-scale.

Conduct a chronological geospatial assessment and quantification of episodic impacts in wetland environments

comparison between 1848 and 2006 map

A simple comparison between the 1848 U.S. Coastal and Geodetic Survey T-Sheet #243 map (left) and the 2006 U.S. Department of Agriculture (USDA) National Agriculture Imagery Product (right) for the Grand Bay region located at the border of Mississippi and Alabama. A digitized surface/shoreline from the 1848 survey is presented in red and overlain onto the National Agriculture Imagery Program (NAIP) image to highlight the extensive estuarine marsh-wetland area loss. (Public domain.)

The goal of this task is to map, characterize, and quantify cumulative episodic event-driven loss in northern Gulf of Mexico coastal wetlands over the past century using available remotely sensed data. Achievement of this goal will provide spatially explicit estimates of wetland loss/gain caused by episodic large-scale drivers versus changes from persistent drivers such as sea-level rise and cumulative cold-front passages (Barras, 2003; Barras, 2006; Barras, 2009).

Objectives

  • Compile historical imagery and remote sensing datasets to quantify hurricane-induced wetland losses in northern Gulf of Mexico (Grand Bay Alabama/Mississippi; Vermilion Bay, Louisiana) and Atlantic coast (Chincoteague Bay, Virginia/Maryland).
  • Relate observed features to storm characteristics, morphological type (Morton and Barras, 2011), and potential cumulative event effects to understand how landscape setting influences feature evolution.
  • Evaluate episodic impacts on wetlands with contrasting long-term trajectories (e.g. accreting, stable, and degrading).
  • Integrate 2-dimensional episodic wetland change information with core data to assist in the development of a quantitative wetland response model.

Methodology

  • Digitize areal extent of wetland losses caused by both historical and recent hurricanes as bracketed by areal imagery.
  • Identify episodic wetland loss data using the storm-impact feature classification scheme developed by Morton and Barras (2011).
  • Compile and analyze cumulative event history to quantify episodic event driven wetland loss over time within the study area.