Gregg Snedden, Ph.D.
Gregg Snedden is a research ecologist with the Wetland and Aquatic Research Center.
Gregg is broadly trained in aquatic ecology, fisheries, wetland plant ecology, and coastal physical oceanography. Gregg’s research interests include fluvial and physical oceanographic drivers of coastal wetland hydrology, impacts of hydrology to wetland plant performance and soil dynamics, effects of Mississippi River diversions on receiving basin wetlands, and most recently, teleconnections between coastal sea-level variability and global-scale climate dynamics and the implications these linkages may impart to coastal wetland landscape sustainability.
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
Nekton References and Targets: Assessing the Abundance and Density of Fish and Invertebrates Associated with Louisiana’s Marsh Habitat
Quantifying Changes in Wetland Area and Habitat Types in the Deepwater Horizon Louisiana Restoration Area 1985-Present with Remote Sensing
Delivery of Strategically Placed Sediment through Tidal Creeks to Adjacent Coastal Wetlands
Model Improvements for Louisiana’s 2023 Coastal Master Plan
Collecting Ecological Data and Models of Living Shoreline Restoration Projects
Dynamics and Fluxes of Nutrients along Environmental Gradients in the Florida Everglades, USA
Influence of Sea-Level Rise on Wetland Vegetation Community Structure, Primary Productivity, Organic Matter Decomposition and Carbon Storage
Soil Properties and Geochronology in Barataria Basin, Louisiana
Surface Water Hydrology and Nitrate Dynamics in Delta Islands of Prograding Wax Lake Delta, Louisiana
Sediment and Nutrient Retention by Wetlands Receiving Inflows from a Mississippi River Diversion: A Mass Balance Approach
Hydrodynamics and Sediment Transport in Deltas and Coastal Wetlands
Classifying Coastal Wetland Vegetation Communities with Unsupervised Artificial Neural Networks
Field observation of wind waves and current velocity (2020) along the Fog Point Living Shoreline, Maryland
Topo-bathymetric survey at Gandys Beach, New Jersey, 2018
Soil property and geochronology (137Cs and 210Pb) data (2014) in salt marsh soils of Jamaica Bay Estuary, New York City
Topographic and bathymetry survey (2019) along the Chincoteague Living Shoreline, Virginia
Field observation of current velocities (2019) along the Chincoteague Living Shoreline, Virginia
Field observation of wind waves (2019) along the Chincoteague Living Shoreline, Virginia
Field observation of current velocities (2018) in Gandy?s Beach, New Jersey with living shoreline structures
Soil properties and soil radioisotope activity across Breton Sound basin wetlands (2008-2013)
Field observations and spectral evolution of wind waves in Upper Delaware Bay with living shorelines
Mineral content, bulk density, and beryllium-7 activity of wetland soils of the Davis Pond Freshwater Diversion Outfall Area, Louisiana, in 2015
Soil properties, soil radioisotope activity, and end-of-season belowground biomass across Barataria basin wetlands (2016)
Primary production across a coastal wetland landscape in Louisiana, U.S.A. (2012-2014)
Patterns of marsh surface accretion rates along salinity and hydroperiod gradients between active and inactive coastal deltaic floodplains
Monitoring of wave, current, and sediment dynamics along the Fog Point Living Shoreline, Glenn Martin National Wildlife Refuge, Maryland
Field observations and long short-term memory modeling of spectral wave evolution at living shorelines in Chesapeake Bay, USA
ENSO and NAO linkages to interannual salinity variability in north central Gulf of Mexico estuaries through teleconnections with precipitation
Modeling surface wave dynamics in upper Delaware Bay with living shorelines
Spatial variability in vertical accretion and carbon sequestration in salt marsh soils of an urban estuary
Monitoring of wave, current, and sediment dynamics along the Chincoteague living shoreline, Virginia
Sources and chemical stability of soil organic carbon in natural and created coastal marshes of Louisiana
Estuarine Geomorphology, Circulation, and Mixing
Impacts of ocean-atmosphere teleconnection patterns on the south-central United States
Biomass allocation of tidal freshwater marsh species in response to natural and manipulated hydroperiod in coastal deltaic floodplains
Seasonal controls on sediment delivery and hydrodynamics in a vegetated tidally influenced interdistributary island
Science and Products
- Science
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Nekton References and Targets: Assessing the Abundance and Density of Fish and Invertebrates Associated with Louisiana’s Marsh Habitat
The National Oceanic and Atmospheric Administration (NOAA) is leading a Monitoring and Adaptive Management (MAM) activity with USGS collaborators to establish reference ranges and restoration targets, assess data gaps for focal nekton species and/or guilds associated with Louisiana’s estuarine and coastal habitats, implement the fixed-area sampling strategy to quantify fishes and invertebrates...Quantifying Changes in Wetland Area and Habitat Types in the Deepwater Horizon Louisiana Restoration Area 1985-Present with Remote Sensing
USGS researchers will quantify wetland change and wetland vegetation community type change through the analyses of aerial vegetation survey data and investigate potential relationships between Normalized Difference Vegetation Index (NDVI) and marsh elevation change.Delivery of Strategically Placed Sediment through Tidal Creeks to Adjacent Coastal Wetlands
In the summer of 2021, instrumented platforms were deployed at Seven Mile Island Living Laboratory, New Jersey to conduct time series measurements of tidal velocity, turbidity, surface elevation, sediment concentration, and suspended sediment characteristics. The collected data will be used to provide decision support to the U.S. Army Corps of Engineers as they plan dredging activities in the Gulf...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 long...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.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. - Data
Field observation of wind waves and current velocity (2020) along the Fog Point Living Shoreline, Maryland
This dataset contains measurements of wave height, peak wave period, and water depth taken every 0.5 hours from February 13 to June 12, 2020, at three wave gauge locations along the Fog Point shoreline in Martin National Wildlife Refuge, Maryland. These wave gauges were continuously sampled at 10 Hz, capturing 20-minute bursts every 30 minutes (peak wave periods longer than 7s were removed). AdditTopo-bathymetric survey at Gandys Beach, New Jersey, 2018
This Data Release contains field topo-bathymetric survey data in a selected saltmarsh shoreline along Gandys Beach, New Jersey, where constructed oyster reefs (CORs, aka oyster castles) were installed to protect the shoreline and enhance habitat for oyster and other species. Oyster castles were constructed as a part of a living shoreline project along Gandys Beach in 2016 in response to the damagSoil property and geochronology (137Cs and 210Pb) data (2014) in salt marsh soils of Jamaica Bay Estuary, New York City
This dataset contains soil property and geochronology (Cesium-137 and lead-210 dating) data from soil cores collected in August 2014 in salt marshes of Jamaica Bay Estuary, New York City.Topographic and bathymetry survey (2019) along the Chincoteague Living Shoreline, Virginia
This dataset contains field topographic and bathymetric data measured during February to April 2019 across oyster castles and mud flats along the Chincoteague Living Shoreline, Virginia, where constructed oyster reefs (CORs, aka oyster castles) were installed to protect the shoreline and enhance habitat for oyster and other species.Field observation of current velocities (2019) along the Chincoteague Living Shoreline, Virginia
This dataset contains measured current velocity during March 1 to May 2, 2019, at eleven locations along the Chincoteague Living Shoreline, Virginia.Field observation of wind waves (2019) along the Chincoteague Living Shoreline, Virginia
This dataset contains measured (interval = 0.5 hour) wave height, peak wave period, water level, and water depth during March 1 to May 1, 2019, at five wave gage locations along the Chincoteague Living Shoreline, Virginia. These wave gages were sampled continuously at 10 Hz to take 20-min bursts every 30 min. These data were used for the analysis of wave attenuation along the oyster-reef-based livField observation of current velocities (2018) in Gandy?s Beach, New Jersey with living shoreline structures
This dataset contains measured (interval=20 minutes) current velocity during February 1 to April 4, 2018 at seven locations along the Gandy's Beach, New Jersey in upper Delaware Bay. These data were used for the analysis of current pattern dynamics along the coast in upper Delaware Bay with oyster-reef based living shoreline structure for shoreline protection.Soil properties and soil radioisotope activity across Breton Sound basin wetlands (2008-2013)
This dataset contains vertical profiles of soil bulk density, percent organic matter, percent total carbon and cesium-137 activity from the surface down to 50-60 cm deep at 25 marsh locations across Breton Sound basin, Louisiana. These data will provide information related to rates of vertical accretion, organic and mineral accumulation and carbon burial in wetland soils across a large portion ofField observations and spectral evolution of wind waves in Upper Delaware Bay with living shorelines
This dataset contains measured (interval=0.5 hour) water depth, wave height, and peak wave period during February 2 to April 4, 2018 at six wave gage locations along the Gandy's Beach, New Jersey in upper Delaware Bay. These data were used for the analysis of spectral evolution of wind waves along the coast in upper Delaware Bay with oyster-reef based living shoreline.Mineral content, bulk density, and beryllium-7 activity of wetland soils of the Davis Pond Freshwater Diversion Outfall Area, Louisiana, in 2015
These data provide information regarding beryllium-7 radioisotope activity, bulk density, and percent organic matter for wetland soils in the immediate outfall region of an operational Mississippi River diversion. From them, information relating to short-term mineral sediment mass accumulation rates and sediment retention rates in the receiving basin can be inferred.Soil properties, soil radioisotope activity, and end-of-season belowground biomass across Barataria basin wetlands (2016)
The sustainability of coastal wetlands largely hinges on their ability to accrue elevation capital at a rate that equals or exceeds relative sea-level rise. A better understanding of these processes is needed to accurately assess the sustainability of these landscapes, and to predict their response to restoration measures such as sediment delivery through river diversions.Primary production across a coastal wetland landscape in Louisiana, U.S.A. (2012-2014)
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 been documented, we lack an understanding of the lan - Publications
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Patterns of marsh surface accretion rates along salinity and hydroperiod gradients between active and inactive coastal deltaic floodplains
High subsidence rates are inherent to coastal deltas worldwide, contributing to rapid rates of relative sea-level rise and compromising the sustainability of coastal wetlands. Different parts of river deltas, however, experience accretion or erosion, depending on the coupling between ecological and morphological processes. Wetland expansion occurs in active deltaic coastal basins that are connecteAuthorsAndy F. Cassaway, Robert R. Twilley, Andre S. Rovai, G.A. SneddenMonitoring of wave, current, and sediment dynamics along the Fog Point Living Shoreline, Glenn Martin National Wildlife Refuge, Maryland
Living shorelines with salt marsh species, rock breakwaters, and sand nourishment were built along the coastal areas in the Glenn Martin National Wildlife Refuge, Maryland, in 2016 in response to Hurricane Sandy (2012). The Fog Point living shoreline at Glenn Martin National Wildlife Refuge was designed with the “headland - breakwater - embayment” pattern. Scientists from the U.S. Geological SurveAuthorsH. Wang, Q. Chen, W.D. Capurso, N. Wang, L.M. Niemoczynski, M. Whitbeck, L. Zhu, G.A. Snedden, C.A. Wilson, M.S. BrownleyField observations and long short-term memory modeling of spectral wave evolution at living shorelines in Chesapeake Bay, USA
Living shorelines as a nature-based solution for climate change adaptation were constructed in many places around the world. The success of this type of projects requires long-term monitoring for adaptive management. The paper presents a novel framework leveraging scientific machine learning methods for accurate and rapid prediction of long-term hydrodynamic forcing impacting living shorelines usiAuthorsNan Wang, Q. Chen, Hongqing Wang, William D. Capurso, L.M. Niemoczynski, Ling Zhu, Gregg SneddenENSO and NAO linkages to interannual salinity variability in north central Gulf of Mexico estuaries through teleconnections with precipitation
Though the importance of Earth's internal climate modes such as the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) to regional-scale climate variability is well recognized, the degree to which these oscillations are reflected by spatio-temporal salinity variability over interannual timescales in estuaries is less understood. Here an 11-year continuous salinity monitorAuthorsGregg SneddenModeling surface wave dynamics in upper Delaware Bay with living shorelines
Living shorelines gain increasing attention because they stabilize shorelines and reduce erosion. This study leverages physics-based models and bagged regression tree (BRT) machine learning algorithm to simulate wave dynamics at a living shoreline composed of constructed oyster reefs (CORs) in upper Delaware Bay. The physics-based models consist of coupled Delft3D-FLOW and SWAN in four-level nesteAuthorsLing Zhu, Q. Chen, Hongqing Wang, Nan Wang, Kelin Hu, William D. Capurso, L.M. Niemoczynski, Gregg SneddenSpatial variability in vertical accretion and carbon sequestration in salt marsh soils of an urban estuary
Salt marshes in New York City’s Jamaica Bay have been disappearing and deteriorating since early 1900s, resulting in the loss of long-term accumulated carbon storage. However, the spatial variations and mechanisms in vertical accretion and soil organic carbon (SOC) sequestration across this highly urbanized estuary remains unclear. In this study, we collected soil cores to a depth of ~ 50 cm acrosAuthorsHongqing Wang, Gregg Snedden, Ellen K. Hartig, Q. ChenMonitoring of wave, current, and sediment dynamics along the Chincoteague living shoreline, Virginia
Nature-based features, also called living shorelines, are increasingly applied in coastal protection and restoration. However, the processes and mechanisms (feedbacks and interactions) of wave attenuation, current velocity change, and sediment deposition and erosion along the living shoreline remain unclear, thus limiting the adaptive management of living shoreline restoration projects for coastalAuthorsHongqing Wang, Q. Chen, Nan Wang, William D. Capurso, L.M. Niemoczynski, Ling Zhu, G.A. Snedden, Kevin S. Holcomb, Bowdoin W. Lusk, Carol W. Wilson, Sean R. CornellSources and chemical stability of soil organic carbon in natural and created coastal marshes of Louisiana
Coastal marshes are globally important for sequestering carbon, yet sea-level rise and anthropogenic stressors can reduce their capacity as carbon sinks. Marsh restoration can offset a portion of carbon loss through the degradation of natural marshes, but potential differences in the sources and stability of soil organic carbon (SOC) between created and natural marshes may affect their function asAuthorsMegan Kelsall, Tracy Quirk, Carol Wilson, Gregg SneddenEstuarine Geomorphology, Circulation, and Mixing
To understand the processes affecting the distribution and cycles of particulates, pollutants, nutrients, and organisms in estuaries, it is insufficient to focus solely on the biological and chemical aspects of the processes. Water sources and movements (e.g. evaporation, precipitation, riverine discharge, submarine ground water discharge, wetland hydrology, and tidal exchange) as well as other hyAuthorsGregg Snedden, Jaye E. Cable, Björn KjerfveImpacts of ocean-atmosphere teleconnection patterns on the south-central United States
Recent research has linked the climate variability associated with ocean-atmosphere teleconnections to impacts rippling throughout environmental, economic, and social systems. This research reviews recent literature through 2021 in which we identify linkages among the major modes of climate variability, in the form of ocean-atmosphere teleconnections, and the impacts to temperature and precipitatiAuthorsRobert V. Rohli, Gregg Snedden, Elinor R. Martin, Kristine L. DeLongBiomass allocation of tidal freshwater marsh species in response to natural and manipulated hydroperiod in coastal deltaic floodplains
Deltaic floodplains are highly vulnerable to relative sea level rise (RSLR) depending on the sediment supply from river channels that provides elevation capital as adaptation mechanism. In river channels where levees have restricted sediment supply to coastal deltaic floodplains, river sediment diversions have been proposed as a restoration strategy to increase elevation allowing for marshes to esAuthorsAndre S. Rovai, Robert R. Twilley, Alexandra Christiensen, Annabeth McCall, Daniel J. Jensen, Gregg Snedden, James T. Morris, John A. CavellSeasonal controls on sediment delivery and hydrodynamics in a vegetated tidally influenced interdistributary island
River deltas are maintained by a continuous supply of terrestrial sediments that provide critical land building material to help sustain and protect vulnerable ecological communities and serve as natural storm protection barriers. Local hydrodynamics are important in determining the degree to which fluvial sediments are removed from the water column and retained on the delta complex. During 2014,AuthorsRichard Styles, Gregg Snedden, S. Jarrell Smith, Duncan B. Bryant, Brandon M. Boyd, Joseph Z. Gailani, Brady Couvillion, Edward Race