Christopher M. Swarzenski

Hydrology of Tidal Freshwater Forested Wetlands of the Southeastern United States

Preface. 1. Tidal freshwater swamps of the southeastern United States: effects of land use, hurricanes, sea-level rise, and climate change T.W. Doyle et al.- 2. Hydrology of tidal freshwater forested wetlands of the southeastern United States R.H. Day et al.- 3. Soils and biogeochemistry of tidal freshwater forested wetlands C.J. Anderson, B.G. Lockaby.- 4. Plant community composition of a tidally influenced, remnant atlantic white cedar stand in Mississippi B.D. Keeland, J.W. McCoy.- 5. Sediment, nutrient, and vegetation trends along the tidal, forested Pocomoke River, Maryland D.E. Kroes et al.- 6. Vegetation and seed bank studies of salt-pulsed swamps of the Nanticoke River, Chesapeake Bay A.H. Baldwin.- 7. Tidal freshwater swamps of a lower Chesapeake Bay subestuary R.D. Rheinhardt.- 8. Biological, chemical, and physical characteristics of tidal freshwater swamp forests of the lower Cape Fear River/Estuary, North Carolina C.T. Hackney et al.- 9. Ecology of tidal freshwater forests in coastal deltaic Louisiana and northeastern South Carolina W.H. Conner et al.- 10. Ecology of the coastal edge of hydric hammocks on the Gulf Coast of Florida K. Williams et al.- 11. Ecological characteristics of tidal freshwater forests along the lower Suwannee River, Florida H.M. Light et al.- 12. Community composition of select areas of tidal freshwater forest along the Savannah River J. Duberstein, W. Kitchens.- 13. Ecology of the Maurepas Swamp: effects of salinity, nutrients, and insect defoliation R.S. Effler et al.- 14. Selection for salt tolerance in tidal freshwater swamp species: advances using baldcypress as a model for restoration K.W. KRAUSS et al.- 15. Assessing the impact of tidal flooding and salinity on long-term growth of baldcypress under changing climate and riverflow T.W. Doyle et al.- 16. Conservation and use of coastal wetland forests in Louisiana S.P. Faulkner et al.- 17. Tidal freshwater forested wetlands: future research needs and an overview of restoration W.H. Conner et al.- Appendix 1.- Index.-

Water level observations in mangrove swamps during two hurricanes in Florida

Little is known about the effectiveness of mangroves in suppressing water level heights during landfall of tropical storms and hurricanes. Recent hurricane strikes along the Gulf Coast of the United States have impacted wetland integrity in some areas and hastened the need to understand how and to what degree coastal forested wetlands confer protection by reducing the height of peak water level. In recent years, U.S. Geological Survey Gulf Coast research projects in Florida have instrumented mangrove sites with continuous water level recorders. Our ad hoc network of water level recorders documented the rise, peak, and fall of water levels (± 0.5 hr) from two hurricane events in 2004 and 2005. Reduction of peak water level heights from relatively in-line gages associated with one storm surge event indicated that mangrove wetlands can reduce water level height by as much as 9.4 cm/km inland over intact, relatively unchannelized expanses. During the other event, reductions were slightly less for mangroves along a river corridor. Estimates of water level attenuation were within the range reported in the literature but erred on the conservative side. These synoptic data from single storm events indicate that intact mangroves may support a protective role in reducing maximum water level height associated with surge.

Marsh mat flotation in the Louisiana delta plain

Vertical mat movement in relation to surface-water fluctuations was measured for 1 year at three marshes differing in dominant emergent vegetation and location in the Mississippi River delta plain of coastal Louisiana, U.S.A.. The freshwater marsh, dominated by Panicum hemitomon, floated directly with ambient water levels, provided they were high enough to float the mat. Water levels varied by c. 70 cm and mat movement by 55 cm. An intermediate-salinity marsh closer to the Gulf of Mexico and dominated by Sagittaria falcata moved 35 cm vertically during the study period, and water levels moved 70 cm. A brackish marsh, dominated by Spartina patens, moved only 3 cm in response to c. 40 cm of vertical water movement (...)

Processes 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 measuring processes controlling wetland elevation. We found that, over 5 years of measurement, TFFWs were resilient, although some marginally, and oligohaline marshes exhibited robust resilience to sea-level rise. We identified fundamental differences in how resilience is maintained across wetland community types, which have important implications for management activities that aim to restore or conserve resilient systems. We showed that the relative importance of surface and subsurface processes in controlling wetland surface elevation change differed between TFFWs and oligohaline marshes. The marshes had significantly higher rates of surface accretion than the TFFWs, and in the marshes, surface accretion was the primary contributor to elevation change. In contrast, elevation change in TFFWs was more heavily influenced by subsurface processes, such as root zone expansion or compaction, which played an important role in determining resilience of TFFWs to rising sea level. When root zone contributions were removed statistically from comparisons between relative sea-level rise and surface elevation change, sites that previously had elevation rate deficits showed a surplus. Therefore, assessments of wetland resilience that do not include subsurface processes will likely misjudge vulnerability to sea-level rise.

Assessing coastal wetland vulnerability to sea-level rise along the northern Gulf of Mexico coast: Gaps and opportunities for developing a coordinated regional sampling network

Coastal wetland responses to sea-level rise are greatly influenced by biogeomorphic processes that affect wetland surface elevation. Small changes in elevation relative to sea level can lead to comparatively large changes in ecosystem structure, function, and stability. The surface elevation table-marker horizon (SET-MH) approach is being used globally to quantify the relative contributions of processes affecting wetland elevation change. Historically, SET-MH measurements have been obtained at local scales to address site-specific research questions. However, in the face of accelerated sea-level rise, there is an increasing need for elevation change network data that can be incorporated into regional ecological models and vulnerability assessments. In particular, there is a need for long-term, high-temporal resolution data that are strategically distributed across ecologically-relevant abiotic gradients. Here, we quantify the distribution of SET-MH stations along the northern Gulf of Mexico coast (USA) across political boundaries (states), wetland habitats, and ecologically-relevant abiotic gradients (i.e., gradients in temperature, precipitation, elevation, and relative sea-level rise). Our analyses identify areas with high SET-MH station densities as well as areas with notable gaps. Salt marshes, intermediate elevations, and colder areas with high rainfall have a high number of stations, while salt flat ecosystems, certain elevation zones, the mangrove-marsh ecotone, and hypersaline coastal areas with low rainfall have fewer stations. Due to rapid rates of wetland loss and relative sea-level rise, the state of Louisiana has the most extensive SET-MH station network in the region, and we provide several recent examples where data from Louisiana’s network have been used to assess and compare wetland vulnerability to sea-level rise. Our findings represent the first attempt to examine spatial gaps in SET-MH coverage across abiotic gradients. Our analyses can be used to transform a broadly disseminated and unplanned collection of SET-MH stations into a coordinated and strategic regional network. This regional network would provide data for predicting and preparing for the responses of coastal wetlands to accelerated sea-level rise and other aspects of global change.