Zafer Defne, PhD
My research finds its form in providing answers to questions related to coasts and ocean, based on my knowledge of physical oceanography and experience in data sciences.
Biography
Dr. Zafer Defne received his PhD in Coastal and Ocean Engineering from Georgia Institute of Technology, with a minor in Information Technology Applications in Oceanography. His expertise includes computational fluid dynamics and data analysis. His work on numerical modeling of coastal ocean has been used to assess storm surge, residual circulation, sediment transport and water quality, as well as marine renewable energy. His recent research is on assessment of the physical state of coastal wetlands using geospatial data.
Science and Products
Estuarine Processes, Hazards, and Ecosystems
Estuarine processes, hazards, and ecosystems describes several interdisciplinary projects that aim to quantify and understand estuarine processes through observations and numerical modeling. Both the spatial and temporal scales of these mechanisms are important, and therefore require modern instrumentation and state-of-the-art hydrodynamic models. These projects are led from the U.S....
Coastal Model Applications and Field Measurements- Field Measurements and Model Applications
Several components of this project are applications to evaluate the model against critical field measurements or to test new model components. Data from field measurements is described in our publications and available in our databases.
Estuarine Processes Eutrophication
Increased loadings of nutrients to estuaries have altered ecosystem function by encouraging growth of phytoplankton and macroalgae while inducing large swings in dissolved oxygen and threatening the sustainability of seagrass meadows. We are measuring and modeling these processes to understand the future trajectory of estuarine ecosystems.
Estuarine Processes Tidal Wetlands
Tidal wetlands are an important geomorphic and ecological feature of the coastal zone. Our projects deal with the physical forcings that affect wetland stability over event-to-annual timescales, including wave attack, sediment supply, and sea-level rise.
Estuarine Processes Model Development
We are developing new routines within the COAWST model framework to represent coupled bio-physical processes in estuarine and coastal regions. These include routines for marsh vulnerability to waves, estuarine biogeochemistry, and feedbacks between aquatic vegetation and hydrodynamics.
National UVVR Map
This map shows the unvegetated and vegetated area of coastal wetlands and adjacent land (inland and shorelines) for the Conterminous United States computed from 2014-2018 Landsat imagery at ~30 meter horizontal resolution.
Coastal Wetlands: The State and Future of a Precious Resource
Coastal wetlands, and salt marshes specifically, are simultaneously geomorphic and biologic systems. They proliferate across a narrow range of elevation, water level, and salinity conditions. Salt marshes rely on their own growth and sediment input to maintain or increase their extent, whereas physical forces such as waves and sea-level rise tend to reduce it.
COAWST model of Barnegat Bay creeks to demonstrate marsh dynamics
The COAWST modeling framework was extended to add two key processes that affect marshes, erosion due to lateral wave thrust (LWT) and vertical accretion due to biomass productivity. The testing of the combined effects of integrating these two processes was done by modeling marsh complexes within Forsythe National Wildlife Refuge and the Barnegat Bay estuary, New Jersey.
Geospatial Characterization of Salt Marshes for Massachusetts
This data release contains coastal wetland synthesis products for Massachusetts. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and tidal range are calculated for smaller units delineated from a digital elevation model, providing the spatial variability of physical factors that influence wetland health.
Wave thrust values at point locations along the shorelines of Massachusetts and Rhode Island
This product provides spatial variations in wave thrust along shorelines in Massachusetts and Rhode Island. Natural features of relevance along the State coast are salt marshes. In recent times, marshes have been eroding primarily through lateral erosion. Wave thrust represents a metric of wave attack acting on marsh edges.
Wave thrust values at point locations along the shorelines of Chesapeake Bay, Maryland and Virginia
This product provides spatial variations in wave thrust along shorelines in the Chesapeake Bay. Natural features of relevance along the Bay coast are salt marshes. In recent times, marshes have been eroding primarily through lateral erosion. Wave thrust represents a metric of wave attack acting on marsh edges. The wave thrust is calculated as the vertical integral of the dynamic pressure of...
Coastal Wetlands of Blackwater salt marsh complex, Chesapeake Bay, Maryland
This data release contains coastal wetland synthesis products for the geographic region of Blackwater, Chesapeake Bay, Maryland. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and others, are calculated for smaller units delineated from a digital elevation model, providing the spatial variability of physical factors that influence wetland health.
Coastal wetlands of Hudson Valley and New York City, New York
This data release contains coastal wetland synthesis products for the geographic region of Hudson Valley and New York City, New York. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence...
Coastal wetlands of north shore Long Island, New York
This data release contains coastal wetland synthesis products for the geographic region of north shore Long Island, New York. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence wetland...
Slope Values Across Marsh-Forest Boundary in Chesapeake Bay Region, USA
The marsh-forest boundary in the Chesapeake Bay was determined by geoprocessing high-resolution (1 square meter) land use and land cover data sets. Perpendicular transects were cast at standard intervals (30 meters) along the boundary within a GIS by repurposing the...
Coastal wetlands of eastern Long Island, New York
This data release contains coastal wetland synthesis products for the geographic region of eastern Long Island, New York, including the north and south forks, Gardiners Island, and Fishers Island. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model.
U.S. Geological Survey hydrodynamic model simulations for Barnegat Bay, New Jersey, during Hurricane Sandy, 2012
We used the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST; Warner and others, 2010) model to simulate ocean circulation, waves, and sediment transport in Barnegat Bay, New Jersey, during Hurricane Sandy. The simulation period was from October 27 to November 4, 2012. We used a 2012 digital terrain model (Andrews and others, 2015) to prescribe the prestorm bathymetry.
Coastal wetlands from Jamaica Bay to western Great South Bay, New York
This data release contains coastal wetland synthesis products for the geographic region from Jamaica Bay to western Great South Bay, located in southeastern New York State. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model.
Conceptual marsh units for Cape Cod National Seashore salt marsh complex, Massachusetts
The salt marsh complex of Cape Cod National Seashore (CACO), Massachusetts, USA and approximal wetlands were delineated to smaller, conceptual marsh units by geoprocessing of surface elevation data. Flow accumulation based on the relative elevation of each location is used to determine the ridge lines that separate each marsh unit
Quantifying slopes as a driver of forest to marsh conversion using geospatial techniques: Application to Chesapeake Bay coastal-plain, USA
Coastal salt marshes, which provide valuable ecosystem services such as flood mitigation and carbon sequestration, are threatened by rising sea level. In response, these ecosystems migrate landward, converting available upland into salt marsh. In the coastal-plain surrounding Chesapeake Bay, United States, conversion of coastal forest to salt...
Molino, Grace Damore; Defne, Zafer; Aretxabaleta, Alfredo; Ganju, Neil Kamal; Carr, Joel A. A geospatially resolved wetland vulnerability index: Synthesis of physical drivers
Assessing wetland vulnerability to chronic and episodic physical drivers is fundamental for establishing restoration priorities. We synthesized multiple data sets from E.B Forsythe National Wildlife Refuge, New Jersey, to establish a wetland vulnerability metric that integrates a range of physical processes, regulatory information and physical/...
Defne, Zafer; Aretxabaleta, Alfredo; Ganju, Neil Kamal; Kalra, Tarandeep S.; Jones, Daniel K.; Smith, Kathryn Are elevation and open-water conversion of salt marshes connected?
Salt marsh assessments focus on vertical metrics such as accretion or lateral metrics such as open-water conversion, without exploration of how the dimensions are related. We exploited a novel geospatial dataset to explore how elevation is related to the unvegetated-vegetated marsh ratio (UVVR), a lateral metric, across individual marsh “units”...
Ganju, Neil Kamal; Defne, Zafer; Fagherazzi, Sergio Understanding tidal marsh trajectories: Evaluation of multiple indicators of marsh persistence
Robust assessments of ecosystem stability are critical for informing conservation and management decisions. Tidal marsh ecosystems provide vital services, yet are globally threatened by anthropogenic alterations to physical and biological processes. A variety of monitoring and modeling approaches have been undertaken to determine which tidal...
Wasson, Kerstin; Ganju, Neil Kamal; Defne, Zafer; Endris, Charlie; Elsey-Quirk, Tracy; Thorne, Karen M.; Freeman, Chase M.; Guntenspergen, Glenn R.; Nowacki, Daniel J. ; Raposa, Kenneth B. Hydrodynamic and morphologic response of a back-barrier estuary to an extratropical storm
We investigated the hydrodynamic and morphologic response of Barnegat Bay-Little Egg Harbor, New Jersey, USA to Hurricane Sandy. We implemented a three-dimensional, coupled ocean-wave-sediment transport model of the estuary and explored the role of offshore water levels, offshore waves, local winds and waves by systematically removing forcings...
Defne, Zafer; Ganju, Neil Kamal; Moriarty, Julia M. Identifying salt marsh shorelines from remotely sensed elevation data and imagery
Salt marshes are valuable ecosystems that are vulnerable to lateral erosion, submergence, and internal disintegration due to sea-level rise, storms, and sediment deficits. Because many salt marshes are losing area in response to these factors, it is important to monitor their lateral extent at high resolution over multiple timescales. In this...
Farris, Amy S.; Defne, Zafer; Ganju, Neil Kamal Spatial distribution of water level impact to back-barrier bays
Water level in semi-enclosed bays, landward of barrier islands, is mainly driven by offshore sea level fluctuations that are modulated by bay geometry and bathymetry, causing spatial variability in the ensuing response (transfer). Local wind setup can have a secondary role that depends on wind speed, fetch, and relative orientation of the wind...
Aretxabaleta, Alfredo; Ganju, Neil Kamal; Defne, Zafer; Signell, Richard P. Estimating connectivity of hard clam (Mercenaria mercenaria) and eastern oyster (Crassostrea virginica) larvae in Barnegat Bay
Many marine organisms have a well-known adult sessile stage. Unfortunately, our lack of knowledge regarding their larval transient stage hinders our understanding of their basic ecology and connectivity. Larvae can have swimming behavior that influences their transport within the marine environment. Understanding the larval stage provides insight...
Goodwin, J.D.; Munroe, D.M.; Defne, Zafer; Ganju, Neil Kamal; Vasslides, James Role of tidal wetland stability in lateral fluxes of particulate organic matter and carbon
Tidal wetland fluxes of particulate organic matter and carbon (POM, POC) are important terms in global budgets but remain poorly constrained. Given the link between sediment fluxes and wetland stability, POM and POC fluxes should also be related to stability. We measured POM and POC fluxes in eight microtidal salt marsh channels, with net POM...
Ganju, Neil Kamal; Defne, Zafer; Elsey Quirk, Tracy; Moriarty, Julia M. Physical response of a back-barrier estuary to a post-tropical cyclone
This paper presents a modeling investigation of the hydrodynamic and sediment transport response of Chincoteague Bay (VA/MD, USA) to Hurricane Sandy using the Coupled Ocean-Atmosphere-Wave-Sediment-Transport (COAWST) modeling system. Several simulation scenarios with different combinations of remote and local forces were conducted to identify the...
Beudin, Alexis; Ganju, Neil Kamal; Defne, Zafer; Aretxabaleta, Alfredo Exposure potential of salt marsh units in Edwin B. Forsythe National Wildlife Refuge to environmental health stressors
Natural and anthropogenic contaminants, pathogens, and viruses are found in soils and sediments throughout the United States. Enhanced dispersion and concentration of these environmental health stressors in coastal regions can result from sea level rise and storm-derived disturbances. The combination of existing environmental health stressors and...
Defne, Zafer; Ganju, Neil K.; Jones, Daniel K.; Reilly, Timothy J.; Aquino, Kimberly C.; Carbo, Chelsea L.; Kaufhold, Erika E.; Benzel, William M.; Fisher, Shawn C.; Griffin, Dale W.; Iwanowicz, Luke R.; Loftin, Keith A. Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes
Salt marshes are valued for their ecosystem services, and their vulnerability is typically assessed through biotic and abiotic measurements at individual points on the landscape. However, lateral erosion can lead to rapid marsh loss as marshes build vertically. Marsh sediment budgets represent a spatially integrated measure of competing...
Ganju, Neil K.; Defne, Zafer; Kirwan, Matthew L.; Fagherazzi, Sergio; D'Alpaos, Andrea; Carniello, Luca
Assessing Salt Marsh Vulnerability Nationwide
Salt marshes are among the most productive and valuable ecosystems in the world. The vegetation in these coastal systems acts as a buffer between land and sea. This natural buffer helps reduce flooding, erosion, and subsequent damage to property and infrastructure by slowing down the flow of water and dissipating waves during storms.