Impacts of coastal and watershed changes on upper estuaries: causes and implications of wetland ecosystem transitions along the US Atlantic and Gulf Coasts Active
Estuaries and their surrounding wetlands are coastal transition zones where freshwater rivers meet tidal seawater. As sea levels rise, tidal forces move saltier water farther upstream, extending into freshwater wetland areas. Human changes to the surrounding landscape may amplify the effects of this tidal extension, impacting the resiliency and function of the upper estuarine wetlands. One visible indicator is the rapid conversion of some Southeast and mid-Atlantic tidal freshwater forested wetlands to ‘Ghost Forests’ in which trees die from increases in salinity. Because data on the complex causes and impacts of tidal extension are limited, this project takes an integrated, large-scale approach to research and monitoring to expand our ability to model these processes and apply them to other coastal areas along the Atlantic Coast, Gulf Coast, and internationally. Results of this effort will provide critical data to guide future decisions regarding the fate of carbon, water quality, coastal resilience, wildlife and fisheries, and effective allocation of taxpayer dollars for ecosystem restoration.
Statement of Problem: Throughout the southeastern United States, tidal freshwater forested wetlands (TFFW) found along the upper tidal estuary (where freshwater watersheds and estuaries meet), are converting to ‘Ghost Forests’ (dead trees) and then to oligohaline (low salinity) marsh. Nontidal floodplains are also converting into TFFW as tides extend farther upstream along rivers, and little scientific research has been directed toward describing or understanding the effects of this tidal extension.
Conversion is related to both changing sea level and associated salt-water intrusion and to human influences (e.g., land use change, coastal development, construction of dams, river dredging, etc). All these factors affect the resiliency and ecosystem services provided by wetlands of the upper estuary. Watershed inputs to the upper estuary (water, sediment, nutrients) also may determine the response of TFFW through complex interactions between the ecosystem, water, and landscape. Further, TFFW itself influences delivery of watershed sediment to lower tidal estuaries that are targets of restoration projects, making their function critical to ecosystem health.
Why this Research is Important: This project fills a large gap in integrative ecosystem research and monitoring of different coastal areas which vary in land use activity, tidal range, relative sea-level rise, watershed characteristics and changes, and delivery of ecosystem services for taxpayers. A primary outcome thus far has been the value assigned to TFFW in terms of carbon storage, sequestration, and conveyance; adding them to the list of important "blue carbon" wetlands globally.
“Blue Carbon” refers to carbon that is stored in coastal or marine ecosystems. In addition to the monetary value of the ecosystem services, these coastal wetland areas are crucial for protecting the coast from storm surge, mitigating downstream eutrophication (when a water body becomes overly enriched in nutrients), and providing wildlife and fishery habitat. By improving understanding of the processes and services provided by both healthy TFFW and those transitioned to marshes, managers and coastal inhabitants (and taxpayers) will be able to anticipate how past and current changes will affect the ecosystems in the future.
The TFFW transition/conversion phenomenon is not unique to the southeast and mid-Atlantic United States, and expansion of the project enhances our ability to (1) apply this research to other domestic and international coastal areas undergoing similar changes, and (2) add to critical information gaps on carbon sequestration to better understand the role of coastal ecosystems in the cycling of carbon and nutrients).
Objective(s): We hypothesize that ecosystem functions, sediment and nutrient processes, and carbon sequestration vary in predictable ways in different coastal environments as nontidal floodplains convert to TFFW and TFFW convert to marshes. Through extensive data collection over 15 years, we have quantified several processes and changes to sedimentation, nutrient uptake and release, forest condition, and balance of habitat. From analyses of these data we developed an understanding of emergent processes at multiple scales that are critical to future investigation, culminating in predictive models and advancements to ecological theory of coastal wetland change. In order to further expand our focus from TFFW stresses and degradation, our focus moves to the larger scale of the entire upper estuary landscape, guiding a series of new goals and objectives:
- Maintain repeated measurements at existing field sites in order to reach a full 20-year-record of change, while also incorporating new site locations farther inland, upriver, and into non-tidal zones
- Incorporate new studies to determine where sediment is coming from and what potential land use and management practices may influence sedimentation
- Continue documenting how biogeochemical cycles are affected by changes in the watershed and estuary
- Perform comparative carbon studies between regions to determine generality
- Map and describe tidal extension and landward habitat conversion to develop accurate land cover maps of tidal wetland habitat distribution
- Advance dynamic models to predict upper estuarine habitat change, coupled with elevated CO2 experiments simulating environmental stress to support future modeling
- Begin proactive efforts to compare upper estuarine wetlands of the US Atlantic and Gulf Coasts to similarly positioned habitat conditions globally (e.g., Pacific Northwest, Australia, New Zealand)
Methods: We use a combination of complementary field, laboratory, modeling, and remote sensing techniques to achieve our objectives. Changes in vegetation, tidal extent, surface elevation, and microtopography are measured using field data collection. For example, plots of trees and herbaceous vegetation are surveyed over time to document a record of habitat change, while direct measurements of growth records inform contemporary and historic productivity.
Water level and salinity are measured continuously with logging devices. Surfaces of hummocks and hollows are measured annually to assess changes in elevation, accretion, subsidence and general resilience to sea-level rise. More complex methods that involve both field collection and laboratory analyses are required to measure soil biogeochemistry, nutrients, and carbon (C) storage and flux.
We collect and analyze shallow soil cores (up to 1-meter in depth), for total organic carbon and nitrogen, and date them using Pb-210 activity to determine rates of soil C burial. In analyses of deeper cores (up to 6-7 meters depth), macrofossils, pollen, C-14, and carbon and nutrient sequestration are used to develop historic baselines prior to rising sea-level conditions. Further soil and vegetation analyses assess ground carbon stocks, belowground net ecosystem productivity, greenhouse gas production (CO2, CH4, N2O) in soils of hummocks and hollows, and transpirational demand on soils in forests vs. newly converted marsh.
Finally, river channel bathymetry, longitudinal sampling of suspended and bed sediment, and analysis of sediment stable isotopes and metals to determine changes in mineral and organic sediment sources (“sediment fingerprinting”) are used together to determine how channels and floodplains have changed and have impacted sediment transport. We will use remote sensing techniques to gather information on the extent of tidal flooding along upper estuarine reaches in our study areas. Using our data, we will validate remote sensing results and apply it to regional and national mapping efforts, as well as model development. Synthesizing the various data streams is accomplished through development and application of both statistical and dynamic process models to generate new understanding and tools to predict ecosystem change in new coastal areas.
Below are other science projects associated with this project.
Below are data or web applications associated with this project.
Below are publications associated with this project.
Hydrology of flooded and wetland forests
Processes contributing to resilience of coastal wetlands to sea-level rise
Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance
Hydrologic exchanges and baldcypress water use on deltaic hummocks, Louisiana, USA
Ecosystem level methane fluxes from tidal freshwater and brackish marshes of the Mississippi River Delta: Implications for coastal wetland carbon projects
Wetland tree transpiration modified by river-floodplain connectivity
Head-of-tide bottleneck of particulate material transport from watersheds to estuaries
The vulnerability of Indo-Pacific mangrove forests to sea-level rise
Forested wetland habitat
Sediment and nutrient trapping as a result of a temporary Mississippi River floodplain restoration: The Morganza Spillway during the 2011 Mississippi River Flood
Annual growth patterns of baldcypress (Taxodium distichum) along salinity gradients
Coastal and wetland ecosystems of the Chesapeake Bay watershed: Applying palynology to understand impacts of changing climate, sea level, and land use
Below are partners associated with this project.
- Overview
Estuaries and their surrounding wetlands are coastal transition zones where freshwater rivers meet tidal seawater. As sea levels rise, tidal forces move saltier water farther upstream, extending into freshwater wetland areas. Human changes to the surrounding landscape may amplify the effects of this tidal extension, impacting the resiliency and function of the upper estuarine wetlands. One visible indicator is the rapid conversion of some Southeast and mid-Atlantic tidal freshwater forested wetlands to ‘Ghost Forests’ in which trees die from increases in salinity. Because data on the complex causes and impacts of tidal extension are limited, this project takes an integrated, large-scale approach to research and monitoring to expand our ability to model these processes and apply them to other coastal areas along the Atlantic Coast, Gulf Coast, and internationally. Results of this effort will provide critical data to guide future decisions regarding the fate of carbon, water quality, coastal resilience, wildlife and fisheries, and effective allocation of taxpayer dollars for ecosystem restoration.
Statement of Problem: Throughout the southeastern United States, tidal freshwater forested wetlands (TFFW) found along the upper tidal estuary (where freshwater watersheds and estuaries meet), are converting to ‘Ghost Forests’ (dead trees) and then to oligohaline (low salinity) marsh. Nontidal floodplains are also converting into TFFW as tides extend farther upstream along rivers, and little scientific research has been directed toward describing or understanding the effects of this tidal extension.
Conversion is related to both changing sea level and associated salt-water intrusion and to human influences (e.g., land use change, coastal development, construction of dams, river dredging, etc). All these factors affect the resiliency and ecosystem services provided by wetlands of the upper estuary. Watershed inputs to the upper estuary (water, sediment, nutrients) also may determine the response of TFFW through complex interactions between the ecosystem, water, and landscape. Further, TFFW itself influences delivery of watershed sediment to lower tidal estuaries that are targets of restoration projects, making their function critical to ecosystem health.
Why this Research is Important: This project fills a large gap in integrative ecosystem research and monitoring of different coastal areas which vary in land use activity, tidal range, relative sea-level rise, watershed characteristics and changes, and delivery of ecosystem services for taxpayers. A primary outcome thus far has been the value assigned to TFFW in terms of carbon storage, sequestration, and conveyance; adding them to the list of important "blue carbon" wetlands globally.
“Blue Carbon” refers to carbon that is stored in coastal or marine ecosystems. In addition to the monetary value of the ecosystem services, these coastal wetland areas are crucial for protecting the coast from storm surge, mitigating downstream eutrophication (when a water body becomes overly enriched in nutrients), and providing wildlife and fishery habitat. By improving understanding of the processes and services provided by both healthy TFFW and those transitioned to marshes, managers and coastal inhabitants (and taxpayers) will be able to anticipate how past and current changes will affect the ecosystems in the future.
The TFFW transition/conversion phenomenon is not unique to the southeast and mid-Atlantic United States, and expansion of the project enhances our ability to (1) apply this research to other domestic and international coastal areas undergoing similar changes, and (2) add to critical information gaps on carbon sequestration to better understand the role of coastal ecosystems in the cycling of carbon and nutrients).
Objective(s): We hypothesize that ecosystem functions, sediment and nutrient processes, and carbon sequestration vary in predictable ways in different coastal environments as nontidal floodplains convert to TFFW and TFFW convert to marshes. Through extensive data collection over 15 years, we have quantified several processes and changes to sedimentation, nutrient uptake and release, forest condition, and balance of habitat. From analyses of these data we developed an understanding of emergent processes at multiple scales that are critical to future investigation, culminating in predictive models and advancements to ecological theory of coastal wetland change. In order to further expand our focus from TFFW stresses and degradation, our focus moves to the larger scale of the entire upper estuary landscape, guiding a series of new goals and objectives:
- Maintain repeated measurements at existing field sites in order to reach a full 20-year-record of change, while also incorporating new site locations farther inland, upriver, and into non-tidal zones
- Incorporate new studies to determine where sediment is coming from and what potential land use and management practices may influence sedimentation
- Continue documenting how biogeochemical cycles are affected by changes in the watershed and estuary
- Perform comparative carbon studies between regions to determine generality
- Map and describe tidal extension and landward habitat conversion to develop accurate land cover maps of tidal wetland habitat distribution
- Advance dynamic models to predict upper estuarine habitat change, coupled with elevated CO2 experiments simulating environmental stress to support future modeling
- Begin proactive efforts to compare upper estuarine wetlands of the US Atlantic and Gulf Coasts to similarly positioned habitat conditions globally (e.g., Pacific Northwest, Australia, New Zealand)
Methods: We use a combination of complementary field, laboratory, modeling, and remote sensing techniques to achieve our objectives. Changes in vegetation, tidal extent, surface elevation, and microtopography are measured using field data collection. For example, plots of trees and herbaceous vegetation are surveyed over time to document a record of habitat change, while direct measurements of growth records inform contemporary and historic productivity.
Water level and salinity are measured continuously with logging devices. Surfaces of hummocks and hollows are measured annually to assess changes in elevation, accretion, subsidence and general resilience to sea-level rise. More complex methods that involve both field collection and laboratory analyses are required to measure soil biogeochemistry, nutrients, and carbon (C) storage and flux.
We collect and analyze shallow soil cores (up to 1-meter in depth), for total organic carbon and nitrogen, and date them using Pb-210 activity to determine rates of soil C burial. In analyses of deeper cores (up to 6-7 meters depth), macrofossils, pollen, C-14, and carbon and nutrient sequestration are used to develop historic baselines prior to rising sea-level conditions. Further soil and vegetation analyses assess ground carbon stocks, belowground net ecosystem productivity, greenhouse gas production (CO2, CH4, N2O) in soils of hummocks and hollows, and transpirational demand on soils in forests vs. newly converted marsh.
Finally, river channel bathymetry, longitudinal sampling of suspended and bed sediment, and analysis of sediment stable isotopes and metals to determine changes in mineral and organic sediment sources (“sediment fingerprinting”) are used together to determine how channels and floodplains have changed and have impacted sediment transport. We will use remote sensing techniques to gather information on the extent of tidal flooding along upper estuarine reaches in our study areas. Using our data, we will validate remote sensing results and apply it to regional and national mapping efforts, as well as model development. Synthesizing the various data streams is accomplished through development and application of both statistical and dynamic process models to generate new understanding and tools to predict ecosystem change in new coastal areas.
- Science
Below are other science projects associated with this project.
- Data
Below are data or web applications associated with this project.
- Publications
Below are publications associated with this project.
Filter Total Items: 56Hydrology of flooded and wetland forests
In this chapter we will examine the hydrology of forested areas that are subject to soil saturation by rain, groundwater, or surface flooding. They include mangroves and other tidal forests, the forested portions of peatlands, and tree dominated wetlands defined by the Ramsar Convention (Mathews 1993). They also include estuarine tidal forests, palustrine forested wetlands, and the portionAuthorsT. M. Williams, Ken W. Krauss, T. OkruszkoProcesses contributing to resilience of coastal wetlands to sea-level rise
The objectives of this study were to identify processes that contribute to resilience of coastal wetlands subject to rising sea levels and to determine whether the relative contribution of these processes varies across different wetland community types. We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to marsh by mAuthorsCamille L. Stagg, Ken W. Krauss, Donald R. Cahoon, Nicole Cormier, William H. Conner, Christopher M. SwarzenskiComponent greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance
Coastal marshes take up atmospheric CO2 while emitting CO2, CH4, and N2O. This ability to sequester carbon (C) is much greater for wetlands on a per-area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecAuthorsKen W. Krauss, Guerry O. Holm, Brian C. Perez, David E. McWhorter, Nicole Cormier, Rebecca Moss, Darren Johnson, Scott C Neubauer, Richard C RaynieHydrologic exchanges and baldcypress water use on deltaic hummocks, Louisiana, USA
Coastal forested hummocks support clusters of trees in the saltwater–freshwater transition zone. To examine how hummocks support trees in mesohaline sites that are beyond physiological limits of the trees, we used salinity and stable isotopes (2H and 18O) of water as tracers to understand water fluxes in hummocks and uptake by baldcypress (Taxodium distichum (L.) Rich.), which is the most abundantAuthorsYu-Hsin Hsueh, Jim L. Chambers, Ken W. Krauss, Scott T. Allen, Richard F. KeimEcosystem level methane fluxes from tidal freshwater and brackish marshes of the Mississippi River Delta: Implications for coastal wetland carbon projects
Sulfate from seawater inhibits methane production in tidal wetlands, and by extension, salinity has been used as a general predictor of methane emissions. With the need to reduce methane flux uncertainties from tidal wetlands, eddy covariance (EC) techniques provide an integrated methane budget. The goals of this study were to: 1) establish methane emissions from natural, freshwater and brackish wAuthorsGuerry O. Holm, Brian C. Perez, David E. McWhorter, Ken W. Krauss, Darren J. Johnson, Richard C. Raynie, Charles J. KillebrewWetland tree transpiration modified by river-floodplain connectivity
Hydrologic connectivity provisions water and nutrient subsidies to floodplain wetlands and may be particularly important in floodplains with seasonal water deficits through its effects on soil moisture. In this study, we measured sapflow in 26 trees of two dominant floodplain forest species (Celtis laevigata and Quercus lyrata) at two hydrologically distinct sites in the lower White River floodplaAuthorsScott T. Allen, Ken W. Krauss, J. Wesley Cochran, Sammy L. King, Richard F. KeimHead-of-tide bottleneck of particulate material transport from watersheds to estuaries
We measured rates of sediment, C, N, and P accumulation at four floodplain sites spanning the nontidal through oligohaline Choptank and Pocomoke Rivers, Maryland, USA. Ceramic tiles were used to collect sediment for a year and sediment cores were collected to derive decadal sedimentation rates using 137Cs. The results showed highest rates of short- and long-term sediment, C, N, and P accumulationAuthorsScott H. Ensign, Gregory B. Noe, Cliff R. Hupp, Katherine SkalakThe vulnerability of Indo-Pacific mangrove forests to sea-level rise
Sea-level rise can threaten the long-term sustainability of coastal communities and valuable ecosystems such as coral reefs, salt marshes and mangroves. Mangrove forests have the capacity to keep pace with sea-level rise and to avoid inundation through vertical accretion of sediments, which allows them to maintain wetland soil elevations suitable for plant growth. The Indo-Pacific region holds mosAuthorsCatherine E. Lovelock, Donald R. Cahoon, Daniel A. Friess, Glenn R. Guntenspergen, Ken W. Krauss, Ruth Reef, Kerrylee Rogers, Megan L. Saunders, Frida Sidik, Andrew Swales, Neil Saintilan, Le Xuan Thuyen, Tran TrietForested wetland habitat
A forested wetland (swamp) is a forest where soils are saturated or flooded for at least a portion of the growing season, and vegetation, dominated by trees, is adapted to tolerate flooded conditions. A tidal freshwater forested wetland is a forested wetland that experiences frequent but short-term surface flooding via tidal action, with average salinity of soil porewater less than 0.5 g/l. It isAuthorsJamie A. Duberstein, Ken W. KraussSediment and nutrient trapping as a result of a temporary Mississippi River floodplain restoration: The Morganza Spillway during the 2011 Mississippi River Flood
The 2011 Mississippi River Flood resulted in the opening of the Morganza Spillway for the second time since its construction in 1954 releasing 7.6 km3 of water through agricultural and forested lands in the Morganza Floodway and into the Atchafalaya River Basin. This volume, released over 54 days, represented 5.5% of the Mississippi River (M.R.) discharge and 14% of the total discharge through theAuthorsDaniel Kroes, Edward R. Schenk, Gregory B. Noe, Adam J. BenthemAnnual growth patterns of baldcypress (Taxodium distichum) along salinity gradients
The effects of salinity on Taxodium distichum seedlings have been well documented, but few studies have examined mature trees in situ. We investigated the environmental drivers of T. distichum growth along a salinity gradient on the Waccamaw (South Carolina) and Savannah (Georgia) Rivers. On each river, T. distichum increment cores were collected from a healthy upstream site (Upper), a moderatelyAuthorsBrenda L. Thomas, Thomas W. Doyle, Ken W. KraussCoastal and wetland ecosystems of the Chesapeake Bay watershed: Applying palynology to understand impacts of changing climate, sea level, and land use
The mid-Atlantic region and Chesapeake Bay watershed have been influenced by fluctuations in climate and sea level since the Cretaceous, and human alteration of the landscape began ~12,000 years ago, with greatest impacts since colonial times. Efforts to devise sustainable management strategies that maximize ecosystem services are integrating data from a range of scientific disciplines to understaAuthorsDebra A. Willard, Christopher E. Bernhardt, Cliff R. Hupp, Wayne L. Newell - Partners
Below are partners associated with this project.