Gregg Snedden, Ph.D.
Biography
EDUCATION
Ph.D., Oceanography and Coastal Sciences, Louisiana State University, 2006
M.S., Fisheries Science, Louisiana State University, 1997
B.S., Aquatic Ecology, University of Illinois, 1993
BACKGROUND
2007 - Present, Research Ecologist, USGS Wetland and Aquatic Research Center (formerly National Wetlands Research Center)
2005 - 2007, Post-Doctoral Research Fellow, UNC-Wilmington Center for Marine Science
2000 - 2005, Research Associate, Coastal Ecology Institute, Louisiana State University
1993 - 1997, Research Assistant, School of Forestry, Wildlife and Fisheries, Louisiana State University
Science and Products
Model Improvements for Louisiana’s 2023 Coastal Master Plan
The Louisiana Coastal Protection and Restoration Authority’s Coastal Master Plan is a blueprint for responding to environmental changes. As part of the agency’s continued engagement, USGS supports model developments and improvements for the 2023 Coastal Master Plan.
Collecting Ecological Data and Models of Living Shoreline Restoration Projects
Developing effective living shoreline restoration projects that can withstand hurricanes and storms requires a better understanding of how restoration structures reduce the impact of wave and current energy on marsh edges in estuaries and bays. Without this knowledge, existing living shoreline projects and adaptive management measures are more likely to fail, decreasing the possibility for...
Dynamics and Fluxes of Nutrients along Environmental Gradients in the Florida Everglades, USA
USGS research in the Florida Everglades will provide information on how environmental conditions and disturbances impact carbon storage in mangrove systems.
Influence of Sea-Level Rise on Wetland Vegetation Community Structure, Primary Productivity, Organic Matter Decomposition and Carbon Storage
This study will employ a space for time substitution to show long-term effects of rising sea-level and increasing salinity on vegetation community structure, primary production and decomposition. Productivity and decomposition rates will be estimated for four wetland plant community types defined by salinity zones and dominant plant species.
Soil Properties and Geochronology in Barataria Basin, Louisiana
Will wetland vertical accretion rates be enough to keep up with the predicted rates of sea level rise? USGS looks at soil properties and geochronology in Louisiana wetlands.
Surface Water Hydrology and Nitrate Dynamics in Delta Islands of Prograding Wax Lake Delta, Louisiana
The Wax Lake Delta is an ideal ecosystem to study the effects of a large-scale river diversion on the biogeochemistry of coastal wetlands, and the capacity of these wetlands to assimilate nutrients delivered by these diversions. USGS works to develop a better understanding of surface water hydrology and nitrate dynamics in this area.
Sediment and Nutrient Retention by Wetlands Receiving Inflows from a Mississippi River Diversion: A Mass Balance Approach
Diversions are currently used in the Mississippi River to stimulate delta growth via increased sediment supply. This technique may also help to reduce nutrient loads before its discharged into the ocean. Scientists at USGS assess how wetlands retain the sediment and nutrients that come from these diversions.
Hydrodynamics and Sediment Transport in Deltas and Coastal Wetlands
Diversions are being used to encourage Missippi River delta growth via increased sediment availability to coastal wetlands. USGS studies hydrodynamics and sediment transport in Louisiana to better understand how marshes and deltas respond to these sediment inputs.
Long-Term Carbon Burial in Marshes of the Mississippi River Delta
Wetlands along the Gulf of Mexico coast play an important role in the global carbon cycle, but as they rapidly convert to open water, their potential for carbon storage is declining. USGS is working to provide accurate, long-term marsh soil carbon sequestration rates.
Classifying Coastal Wetland Vegetation Communities with Unsupervised Artificial Neural Networks
Wetlands are often classified by their vegetation, which can help scientists track how these landscapes change over time. USGS turns to unsupervised artificial neural networks to help guide this classification process.
Drivers and impacts of water level fluctuations in the Mississippi River delta: Implications for delta restoration
This review synthesizes the knowledge regarding the environmental forces affecting water level variability in the coastal waters of the Mississippi River delta and relates these fluctuations to planned river diversions. Water level fluctuations vary significantly across temporal and spatial scales, and are subject to influences from river flow,...
Hiatt, Matthew R.; Snedden, Gregg; Day, John W.; Rohli, Robert V.; Nyman, John A.; Lane, Robert R.; Sharp, Leigh A. Mississippi river sediment diversions and coastal wetland sustainability: Synthesis of responses to freshwater, sediment, and nutrient inputs
Management and restoration of coastal wetlands require insight into how inundation, salinity, and the availability of mineral sediment and nutrients interact to influence ecosystem functions that control sustainability. The Mississippi River Delta, which ranks among the world's largest and most productive coastal wetland complexes, has experienced...
Elsey-Quirk, Tracy; Graham, Sean A.; Mendelssohn, Irving A.; Snedden, Gregg; Day, John W.; Shaffer, Gary P.; Sharp, Leigh Anne; Twilley, Robert R.; Pahl, James; Lane, R.R. Hydrodynamic controls on sediment retention in an emerging diversion-fed delta
The morphodynamics of river-dominated deltas are largely controlled by the supply and retention of sediment within deltaic wetlands and the rate of relative sea-level rise. Yet, sediment budgets for deltas are often poorly constrained. In the Mississippi River Delta, a system rapidly losing land due to natural...
Keogh, Molly E.; Kolker, Alexander S.; Snedden, Gregg A.; Renfro, Alisha A. Patterning emergent marsh vegetation assemblages in coastal Louisiana, USA, with unsupervised artificial neural networks
QuestionAre self‐organizing maps (SOMs) useful for patterning coastal wetland vegetation communities? Do SOMs provide robust alternatives to traditional classification methods, particularly when underlying species response functions are unknown or difficult to approximate, or when a need exists to continuously classify new samples obtained under...
Snedden, Gregg A.
Numerical modeling of the effects of Hurricane Sandy and potential future hurricanes on spatial patterns of salt marsh morphology in Jamaica Bay, New York City
The salt marshes of Jamaica Bay, managed by the New York City Department of Parks & Recreation and the Gateway National Recreation Area of the National Park Service, serve as a recreational outlet for New York City residents, mitigate flooding, and provide habitat for critical wildlife species. Hurricanes and extra-tropical storms have been...
Wang, Hongqing; Chen, Qin; Hu, Kelin; Snedden, Gregg A.; Hartig, Ellen K.; Couvillion, Brady R.; Johnson, Cody L.; Orton, Philip M. A landscape-scale assessment of above- and belowground primary production in coastal wetlands: Implications for climate change-induced community shifts
Above- and belowground production in coastal wetlands are important contributors to carbon accumulation and ecosystem sustainability. As sea level rises, we can expect shifts to more salt-tolerant communities, which may alter these ecosystem functions and services. Although the direct influence of salinity on species-level primary production has...
Stagg, Camille L.; Schoolmaster, Donald R.; Piazza, Sarai C.; Snedden, Gregg; Steyer, Gregory D.; Fischenich, Craig J; McComas, Robert W. Drivers of barotropic and baroclinic exchange through an estuarine navigation channel in the Mississippi River Delta Plain
Estuarine navigation channels have long been recognized as conduits for saltwater intrusion into coastal wetlands. Salt flux decomposition and time series measurements of velocity and salinity were used to examine salt flux components and drivers of baroclinic and barotropic exchange in the Houma Navigation Channel, an estuarine channel located in...
Snedden, Gregg What role do hurricanes play in sediment delivery to subsiding river deltas?
The Mississippi River Delta (MRD) has undergone tremendous land loss over the past century due to natural and anthropogenic influences, a fate shared by many river deltas globally. A globally unprecedented effort to restore and sustain the remaining subaerial portions of the delta is now underway, an endeavor that is expected to cost $50–...
Smith, James E.; Bentley, Samuel J.; Snedden, Gregg; White, Crawford Inundation and salinity impacts to above- and belowground productivity in Spartina patens and Spartina alterniflora in the Mississippi River Deltaic Plain: implications for using river diversions as restoration tools
Inundation and salinity directly affect plant productivity and processes that regulate vertical accretion in coastal wetlands, and are expected to increase as sea level continues to rise. In the Mississippi River deltaic plain, river diversions, which are being implemented as ecosystem restoration tools, can also strongly increase inundation in...
Snedden, Gregg A.; Cretini, Kari Foster; Patton, Brett Forcing functions governing salt transport processes in coastal navigation canals and connectivity to surrounding marshes in South Louisiana using Houma Navigation Canal as a surrogate
Understanding how circulation and mixing processes in coastal navigation canals influence the exchange of salt between marshes and coastal ocean, and how those processes are modulated by external physical processes, is critical to anticipating effects of future actions and circumstance. Examples of such circumstances include deepening the channel...
Snedden, Gregg
Submergence Vulnerability Index development and application to Coastwide Reference Monitoring System Sites and Coastal Wetlands Planning, Protection and Restoration Act projects
Since its implementation in 2003, the Coastwide Reference Monitoring System (CRMS) in Louisiana has facilitated the creation of a comprehensive dataset that includes, but is not limited to, vegetation, hydrologic, and soil metrics on a coastwide scale. The primary impetus for this data collection is to assess land management activities, including...
Stagg, Camille L.; Sharp, Leigh A.; McGinnis, Thomas E.; Snedden, Gregg A. Predictive occurrence models for coastal wetland plant communities: delineating hydrologic response surfaces with multinomial logistic regression
Understanding plant community zonation along estuarine stress gradients is critical for effective conservation and restoration of coastal wetland ecosystems. We related the presence of plant community types to estuarine hydrology at 173 sites across coastal Louisiana. Percent relative cover by species was assessed at each site near the end of the...
Snedden, Gregg A.; Steyer, Gregory D.