Gregg Snedden, Ph.D.
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
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
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...
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.
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.
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.
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.
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.
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.
Hydrologic index development and application to selected Coastwide Reference Monitoring System sites and Coastal Wetlands Planning, Protection and Restoration Act projects
Hourly time-series salinity and water-level data are collected at all stations within the Coastwide Reference Monitoring System (CRMS) network across coastal Louisiana. These data, in addition to vegetation and soils data collected as part of CRMS, are used to develop a suite of metrics and indices to assess wetland condition in coastal Louisiana...Snedden, Gregg A.; Swenson, Erick M.
Hurricane Influences on Vegetation Community Change in Coastal Louisiana
The impacts of Hurricanes Katrina and Rita in 2005 on wetland vegetation were investigated in Louisiana coastal marshes. Vegetation cover, pore-water salinity, and nutrients data from 100 marsh sites covering the entire Louisiana coast were sampled for two consecutive growing seasons after the storms. A mixed-model nested ANOVA with Tukey's HSD...Steyer, Gregory D.; Cretini, Kari Foster; Piazza, Sarai C.; Sharp, Leigh A.; Snedden, Gregg A.; Sapkota, Sijan
Hydrography and bottom boundary layer dynamics: Influence on inner shelf sediment mobility, Long Bay, North Carolina
This study examined the hydrography and bottom boundary-layer dynamics of two typical storm events affecting coastal North Carolina (NC); a hurricane and the passages of two small consecutive extratropical storms during November 2005. Two upward-looking 1200-kHz Acoustic Doppler Current Profilers (ADCP) were deployed on the inner shelf in northern...Davis, L.A.; Leonard, L.A.; Snedden, G.A.
Sediment discharge into a subsiding Louisiana deltaic estuary through a Mississippi River diversion
Wetlands of the Mississippi River deltaic plain in southeast Louisiana have been hydrologically isolated from the Mississippi River by containment levees for nearly a century. The ensuing lack of fluvial sediment inputs, combined with natural submergence processes, has contributed to high coastal land loss rates. Controlled river diversions have...Snedden, G.A.; Cable, J.E.; Swarzenski, C.; Swenson, E.