Estuarine and MaRsh Geology Research Project

Science Center Objects

The goal of the Estuarine and MaRsh Geology (EMRG) Research Project is to study how and where short- and long-term marsh and estuarine coastal processes interact, how they influence coastal accretion or erosion, and how they pre-condition a marsh’s resiliency to storms, sea-level change, and human alterations along the northern Gulf of Mexico (Grand Bay and Point aux Chenes, Mississippi and St. Marks, Florida).

A scientist stands in a grassy marsh with a long tube-shaped piece of equipment designed to pull cores of earth from the ground

A short marsh push core, exhibiting a sandy event layer on top, collected from Point aux Chênes, Mississippi marsh during sample collection in October 2018 for sediment and radiochemical analyses. (Credit: Alisha Ellis, USGS. Public domain.)

Interactions between coastal estuaries, marshes, and upland environments are a complex web of inter-related and inter-connected physical and ecological processes. The Estuarine and MaRsh Geology (EMRG) project focuses on how specific geologic and geomorphic variables such as sediment properties and shoreface slope, respectively, impact the erosion and accretion rates of marsh environments in both the short- and long-term. To do this we use field observations, oceanographic sensors, and field collected sediment samples paired with marsh-estuarine system models run for various scenarios such as with a modified geomorphology or sea-level change.

Project Objectives: 

1) Define the key geologic and geomorphic variables that influence marsh width and elevation for each study area, 

2) Quantify elevation and geomorphic gradients along natural boundaries (upland-marsh, marsh-estuary, estuary-ocean), and 

3) Evaluate the importance of geo-variables and gradients on marsh resiliency through modeling marsh-estuary systems. 

Approach: 

Photo looking down on 3 scientists kneeling in the marsh to retrieve their sediments tiles

Sediment tiles, used for short-term sedimentation rates, are collected in November 2019 from Point aux Chênes, Mississippi marsh following a 3-month deployment; the sediment accumulated on the tile will be measured and analyzed for diatoms and sediment properties. (Public domain.)

1) Assess key metrics through field collection, laboratory analyses, and data mining that link geologic variables with physical forces (such as hydrodynamics and storm events) and ecological responses that can be mapped and assessed over space and time:

A.   Organic matter accumulation, inorganic sedimentation, elevation change   

  • Determine sediment provenance and properties 
  • Calculate short-term (tile) sedimentation rates (Be-7, Th-234) 
  • Calculate long-term (core) sedimentation rates (Pb-210, Cs-137) 
  • Identify foraminifera microfossils as proxies of paleo-marsh type  

B. Bathymetric  changes  

  • Collect multi-beam bathymetry to compare with past bathymetric maps 

C.    Shoreface  slope  and  curvature  

  • Derive metrics from multi-beam surveys and satellite imagery 
  • Conduct shoreline survey using GPS during field work in Grand Bay and Pointe aux Chenes. 

D.   Geology of the marsh shoreline type and/or shallow stratigraphy 

  • Characterize environments, sediment properties, and marsh shoreline types at the surface and, where possible, downcore   

E.    Short and long-term shoreline change and measurements of lateral sediment flux  

  • Digitize historical topographic-sheets for comparison with modern shorelines to determine change in lateral extent of marsh platform 
  • Collect field and sensor measurements of marsh edge erosion and sediment delivery  

F.    Marsh-upland boundary change rates  

  • Identify foraminifera and diatom microfossils as proxies of paleo-marsh type, geomorphology, and environmental change 
  • Map depth to peat to determine modern and past lateral and vertical marsh extent

2) Incorporate results from field derived bathymetry, sediment, shoreface, shoreline, and oceanographic data analyses into numerical models to define marsh-estuarine system processes including coastal hydrodynamics (tides, waves) and sediment transport. These models improve our understanding of the interactions and feedbacks between oceanographic processes, geology, geomorphology, and marsh ecology under scenarios of past, present, and future conditions (for example, storms, sea-level change and modified geomorphology) and identify where more information may be required to advance our knowledge of marsh resiliency.

 

Extent of Model Domain shown relative to coastal Alabama and Mississippi

Map of coastal Alabama and Mississippi, showing the Gulf of Mexico, Mobile Bay, Mississippi Sound, and the Grand Bay estuary. The extent of a Delft3D flow, wave, and sediment transport model is shown by the red dashed line. An area of special interest surrounding Grand Bay is outlined by a dot-dashed blue line. (Public domain.)