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William Conner, Ph.D. - Research & Projects

Ecology and Management of Forested Wetland Ecosystems of the Southern United States

Summary

Forested wetlands have been an influential component of the economy and culture of the southern United States since the earliest settlements. These ecosystems have been used for transportation, food and fiber, flood control, wildlife habitat, recreation, and all too often, a fertile site for conversion to agriculture. The importance of wetlands to the southern economy and concern over their decreasing extent has lead to a surge of research activity as well as litigation and discord over competing wetland uses. Hydrology is one of the most important driving forces in forested wetlands, and the length, depth, and timing of flooding determines the diversity and productivity of these systems. Changes in normal hydrology patterns due to stream channelization or construction of roads, canals, levees, or dams affect the establishment and growth of forest species. Another aspect of hydrology that needs consideration, especially in coastal areas, is eustatic sea level rise and subsidence. The long-term impacts of disturbance is a major area of research in Dr. Conner’s program.  Only long-term research can consider both the short- and long-term fluctuations of key driving forces. In addition, Dr. Conner is examining processes across the entire southern United States to determine if all wetlands function similarly.

Projects

Retreat of Tidally Influenced Freshwater Forested Wetlands in the Southeast: Biogeochemical Investigations and Field Support (2014-2019), USGS – GCC funding, William Conner and Alex Chow (Clemson University)

Photograph of a tidal forest

Tidal freshwater forested wetlands are unique ecosystems that provide an opportunity for understanding the unique structuring of freshwater forests along hydroperiod, salinity, and microtopographical gradients. The goal of this project is to take a regional approach in studying community dynamics of tidal freshwater forested wetlands to understand the ecology and potential effects of sea-level rise on this ecosystem. Study plots were established in a previous GCC project (Dieback and Restoration of Coastal Forests of the Southeast Under Changing Climate; Interactive Effects of Drought Severity, Hurricanes, Sea-Level Rise and Coastal Management) in tidal freshwater swamps with varying tidal influence in riverine and non-riverine watersheds in coastal South Carolina. Plots extended from healthy to stressed cypress-tupelo communities and consisted of cypress stands located along a transect gradient from fresh to brackish environments. Monthly field trips are made to the sites to collect tree growth, litterfall, water level, and soil salinity data. Further, additional data regarding microhabitat use and availability will be collected, and distinct strategies of species preference for microsite will be elucidated through dedicated whole-tree eco-physiological studies. This study will increase our understanding of tidal freshwater forested wetlands at the regional level, thereby providing a better base of knowledge from which future management goals can draw. A broad understanding of community composition, their associations with soil and hydrology, and usage of microtopography will help direct future restoration and mitigation efforts. Learning the physiology associated with water transport in trees under differing environmental conditions will allow us to understand the specific physiological requirements of trees at different microtopographic and landscape positions. This knowledge, in turn, will help balance municipal river-water use with environmental responses to flow management. These advancements will increase our ability to sustain ecosystem health, conserve and preserve wildlife, and minimize relative sea-level rise by enhancing long-term carbon sequestration.

Identifying and Evaluating Impacts to Wetlands from the Savannah River Estuary (2013-2017), U.S. Army Corps of Engineers funding, Jamie Duberstein and William Conner (Clemson University)

Photograph of William Conner at Congaree National Park

The Savannah Harbor Expansion Project will result in conversion of some freshwater marsh to brackish marsh and some saltwater marsh into brackish marsh. The specific objective of the proposed work effort is to identify environmental changes to native flora within these tidal wetlands of the Savannah estuary marsh areas during the monitoring period. This project is monitoring 12 marsh sites in the Savannah River estuary in Georgia and South Carolina. The fieldwork generally replicates the procedures used by the USGS Florida Fish and Wildlife Cooperative Research Unit (FL Coop Unit) when they monitored these wetlands in the past.

Ecological Stress in Coastal Ecosystems: Exploring the Influences of Sea Level Rise and Urban Development (2014-2017), Earthwatch funding, Alex Chow and William Conner (Clemson University)

Coastal forested wetlands are important in protecting upland areas from storm damage and saltwater intrusion.  They are important habitats for many important game and endangered wildlife species as well as being important to our culture and history. Developing an understanding how these systems respond to natural and manmade environmental changes will help us guide sustainable use for future generations.  Citizen scientists are being used to increase our understanding of the overall biological, chemical, and hydrologic processes occurring in this ecosystem and how rising sea level and saltwater intrusion affects these processes.  Specifically, they are being used to collect data in coastal wetlands to determine how water quality, nutrients, forest resources, and overall habitat quality has been affected by past saltwater intrusions into these freshwater forested systems.  This research will help scientists, water managers, and habitat and wildlife conservation managers to understand the changes occurring as freshwater forests transition to marsh and hopefully secure its long-term conservation and availability.

Collaborative Research: Halocarbon Biogeochemistry in Coastal Wetland Ecosystems – Exploring the Transition from Forested Wetland to Salt Marsh (2015-201), Alex Chow and William Conner

The relatively flat southeastern US coastal plain, from Texas to North Carolina, is particularly susceptible to sea level rise. As sea level rises, the boundary between the low-lying coastal freshwater forest and high marsh moves up slope. Forest vegetation is replaced successively by coastal salt marsh. Not only does saltwater intrusion change vegetation composition, high chloride and bromide levels can enhance halogenation processes of terrestrial organic matter, producing halocarbon through incorporating chlorine and bromine into natural organic matter.  Importantly, halocarbons are considered as ozone depleting compounds within the atmosphere. This highly interdisciplinary research will dramatically improve our understanding of chlorine and bromine biogeochemistry and demonstrate the importance of halogens in carbon cycles. This collaborative research represents a new and unique collaboration between four investigators with different specialties from universities in the northeast, southeast and western United States.  Undergraduate students from the three universities will participate in field and laboratory studies and will share their experiences through web conferences. Graduate and undergraduate students will have opportunities to interact with citizen scientists and learn how to disseminate the scientific knowledge to the general public.

Halogens have historically been treated as inert elements in natural humification processes.  However, recent studies have demonstrated that chlorine and bromine are active components in C cycles. The overall goal of this research is to assess novel decomposition process routes of terrestrial organic matter in forested wetlands with high levels of chloride and bromide. The research project includes both field investigations and controlled experiments, to determine the impacts of sea level rise on C and halogen biogeochemical cycles along salinity gradients in Winyah Bay, South Carolina.  Fluxes of halogenated ozone depleting compounds and greenhouse gases, as well as concentrations of organochlorine and organobromine in soil and litter and water will be measured along salinity transects and within controlled plots. Determining the seasonal variation of halocarbon in air, soil, and water from freshwater forested wetland, salt-degraded wetland, and salt marsh sites, representing the transition of coastal wetland under sea level rise, will be useful in developing a mechanistic and landscape understanding of how sea level rise affects decomposition, humification, and halogenation processes of terrestrial organic matter in coastal wetlands. The controlled field experiments using different concentrations of chloride and bromide waters would illustrate their roles in humification and decomposition processes.