Carolina Bay Wetlands Research Articles

Phosphorus Fluxes in a Restored Carolina Bay Wetland Following Eight Years of Restoration

Phosphorus Fluxes in a Restored Carolina Bay Wetland Following Eight Years of Restoration

A rapid approach for ecological assessments in Carolina Bay wetlands that were previously converted to agriculture

Restoring wetlands is expensive, and methods for evaluating restoration condition are needed. This study developed chronosequences for use in ecological assessments (EAs) of restoration projects for Carolina Bay wetlands (CBWs) in the Southeastern US that were previously used for agriculture. An empirical method was also developed to estimate saturation levels to be used with the chronosequences. Data were collected from nine restored CBWs whose restoration ages ranged from 0 to 23 years. Plots were sorted into four Hydrologic Groups: 0–13 (Group 1), 14–50 (Group 2), 51–100 (Group 3), and 101+ (Group 4) consecutive days of saturation within 30 cm of the soil surface during the growing season. Litter thickness, tree basal area, and potential tree height were measured within a variable radius plot using a 10-factor prism across all Hydrologic Groups. Litter thickness and tree height reached an equilibrium at 15 years since restoration once crown closure occurred at the sites. In Groups 1 and 2, tree basal area reached an equilibrium at 15 years, and in Groups 3 and 4 it increased linearly to 23 and 21 years. Regression equations were developed (R2 = 0.57–0.73) to estimate saturation duration based on hydrology indicators, litter thickness, potential tree height, and soil type. These results showed that chronosequences and saturation duration would be useful for proposing performance standards in restored CBWs at time periods ranging from 5 to 23 years.

Soil organic carbon changes in a Carolina Bay wetland 15 years after restoration

AbstractEvaluating wetland restoration success is complicated. In this study, soil organic carbon (SOC) pools in a Carolina Bay wetland (CBW) were determined for pre‐ and post‐restoration periods and compared to values in reference wetlands to determine if SOC could be used to evaluate restoration success. The CBW was Juniper Bay in Robeson County, NC, USA, that had been restored for 15 years following its use for agriculture. Previously, we determined both pre‐restoration SOCs and post‐restoration hydrology. Saturation occurrence and anaerobic conditions (15 years following restoration) were confirmed with Indicator of Reduction in Soils (IRIS) tubes. Soil morphological features, litter thickness, and SOC to 75 cm were also determined. There were significant (p < 0.05) differences in numbers of hydric soil field indicators in the organic soils and no differences in the mineral soils (p > 0.10) between pre‐ and post‐restoration periods. Litter thickness post‐restoration increased linearly with saturation duration. SOC decreased following restoration by 49% in mineral soils and 24% in organic soils as compared to pre‐restoration values. SOC concentrations in the restored wetland were not significantly different than those in reference wetlands indicating that the Juniper Bay restoration was successfully sequestering C. Litter thickness may be a good indicator of restoration success. SOC levels may decrease compared to reference wetland values if pre‐restoration soils were in agriculture.

Hydrology and Vegetation Relationships in a Carolina Bay Wetland 15 Years after Restoration

Hydrology and Vegetation Relationships in a Carolina Bay Wetland 15 Years after Restoration

Assessing Carolina Bay Wetland Restoration Risks to Downstream Water Quality by Characterizing Land Use and Stream Proximity

Carolina Bay wetlands are distinct common components of the Southeastern US Coastal Plain. Many have a history of drainage for agriculture. Restoration of prior-drained Bays can increase P solubility and transport, with potential adverse impacts downstream. To assess risk of off-site P transport, we documented Bay land use, drained area, and proximity to streams and drainageways. We studied Bladen County, NC, where an exhaustive Bay inventory is available. Land-use was documented via classified Landsat decadal images from 1972 through 2010. We compared sequential image pairs to document land-use changes. Phosphorus risk to downstream waters was assessed based on stream proximity, agricultural land use, and arable area. At least 80% of Bays constituting 97% of total Bay area (51,704 ha) exhibited evidence of land-use change. Edges of Bays comprising 80% of Bay coverage were within 15 m of a stream; Bays comprising 13% were isolated. Twenty-one percent of Bay area remained drained in 2010. Prior, 28% of Bay area posed moderate to severe threats to downstream waters; as of 2010, 9%. Considering long-term effects of restoration-induced off-site transport of agrochemicals, land-use history, drained area, and stream/drainageaway proximity should be considered in choosing Bays for restoration.

Phosphorus Dynamics Near Bald Cypress Roots in a Restored Wetland

Core Ideas Previous tree exposure to saturated conditions limited root death after ponding. Root growth and death had no apparent effect on concentrations of Fe2+, DOC, or DTP. Concentrations of Fe2+ were related to water table levels and redox status. Phosphorus concentrations were controlled by iron reduction and oxidation. Phosphorus (P) dissolution occurs commonly in wetland soils restored from agricultural land. Associated with P release are high concentrations of dissolved organic carbon (DOC) and Fe2+. This field study evaluated the effect of a fluctuating water table on the root dynamics of bald cypress (Taxodium distichum L. Rich.) to determine whether root death created soil reduction microsites, potentially contributing to P dissolution. The study site is a restored Carolina bay wetland with organic soils. Root growth and death were monitored on 16 6‐yr‐old bald cypress using minirhizotrons. Root dynamics, water table levels, and soil porewater chemistry and redox potential in the root zone were monitored for 2 yr. Soil solution samples were analyzed for Fe2+, pH, DOC, and P. High rates of root growth occurred during dry conditions, whereas root death occurred during sustained periods of saturation, particularly within 20 cm of the surface. Cyclic changes in concentrations of Fe2+, DOC, and dissolved total P (DTP) were related to water table position but not to changes in root numbers. After sustained periods of saturated conditions, redox potential decreased to 0 mV, Fe2+ increased to 1.75 mg Fe2+ L–1, and DOC increased to 350 mg L–1, resulting in peak DTP concentrations of 750 μg L–1, compared with 100 μg L–1 during dry periods. This study showed that in these high‐C soils (∼20% organic C) rooting dynamics had minimal impact on changes in P concentrations and that P dissolution was largely controlled by Fe reduction processes occurring within the C‐rich soil matrix.

How important are aquatic predators to mosquito larval populations in natural wetlands? A case study from Carolina bays in Georgia

Predation is believed to be an important natural control on larval mosquito populations. However, empirical evidence for predator impacts is lacking, especially from natural wetlands (swamps and marshes). Over a 2-year period, we sampled larval mosquito populations and naturally co-occurring predator assemblages (aquatic invertebrates, fishes) from ten depressional wetlands (Carolina bays) located on a wildlife management area in east central Georgia. We collected a diversity of mosquito larvae and predators (odonates, bugs, beetles, flies, and fishes) from the wetlands, with predator numbers substantially exceeding mosquito larval numbers. However, using a community ecology approach with multivariate ordination and correlation techniques, we found no compelling evidence that these predators were controlling mosquito larval distributions (i.e. significant negative statistical associations were not detected). Those mosquitoes that successfully breed in Carolina bay wetlands (Culiseta melanura, Coquillettidia perturbans, Anopheles crucians) appear well adapted to co-exist with a plethora of naturally occurring predators.

Using Land-Use Change, Soil Characteristics, and a Semi-Automated On-Line GIS Database to Inventory Carolina Bays

Carolina Bay wetlands are common in the southeastern US Coastal Plain and important to water quality, carbon sequestration, and habitat. Only South Carolina and Georgia have statewide inventories. We developed and evaluated a novel way to identify and delineate Bays using Bay-dense Bladen County, NC as a testbed. We posited that Bay land use had changed in the past 40 years and that Bays comprise a small subset of their surrounding soils. We classified decadal Landsat images as forest, agriculture, urban, and water. We used 812 previously delineated Bays to identify common Bay soils. From areas with common Bay soils and land-use change, we identified 548 new Bays and delineated them using a semi-automated on-line digitization tool. We saved new Bays to a Google Fusion Table for download and integration within a GIS. To gauge accuracy, Bays were scored on soils, land-use change, wetland delineation, and landscape position. Potential errors included omission of some small Bays (3.3–14.6 % of total Bay area) and commission of misclassified Bays (11 % of 1360 Bays), an estimated overall accuracy of 74 to 86 %. With 1360 delineated Bays, we estimated that as many as 478 have not yet been identified. These are most likely <5.76 ha.

Prey Capture Success by Established and Introduced Populations of the Venus Flytrap (Dionaea muscipula)

We examined whether the ecological function (i.e., prey capture) of a rare, endemic carnivorous plant, Venus flytrap ( Dionaea muscipula ), was maintained in managed habitats along the sand rims of Carolina bay wetlands at a preserve in the coastal plain of South Carolina, U.S.A. We hypothesized that prey capture would be similar between established and introduced plants because environmental conditions were similar. Number of traps, trap length, trap width, and prey length did not significantly differ between introduced and established populations, and most indicators of prey capture success significantly favored plants growing in introduced sites. Plants in introduced sites had almost 10% more closed traps, had significantly more traps with prey, had more traps with multiple prey items, and had a greater proportion of closed and total traps containing prey. When combined across sampling dates, ants and spiders composed the majority of captured invertebrates; spiders predominated in established sites while ants predominated in introduced sites. Prey availability on one date at a subset of sites was significantly greater in introduced sites. Our data supported the effectiveness of the clearing and transplanting restoration activity for Venus flytraps by showing that individual plants growing in introduced sites have similar structure and function as those in established sites. Consistently greater prey capture success by introduced plants likely contributed to their growth, although underlying reasons for differences in prey capture between introduced and established plants remain uncertain. Evaluating prey capture of carnivorous plant populations provides insight into mechanisms underlying restoration success.

Phosphorus Dissolution in the Rhizosphere of Bald Cypress Trees in Restored Wetland Soils

Phosphorus release to ground or surface waters has been observed in wetlands restored from farmland. This study examined whether rhizospheres of bald cypress (Taxodium distichum L.) are a source of increased P dissolution compared with the soil matrix. The study was conducted in root-box rhizotrons filled with mineral and organic soil materials (Aeric Alaquods and Terric Haplosaprists, respectively) from a Carolina bay wetland restored from row crop agriculture. Rhizotrons were planted with bald cypress saplings or left unplanted to simulate rhizosphere and matrix conditions, respectively. Ponding was imposed for 128 d. Soil pore water was sampled in three layers (0–22, 22–41, and 41–59 cm) in each rhizotron twice monthly for dissolved total and reactive P, dissolved organic C (DOC), Fe2+, and redox potential (Eh). Manual root counts monitored growth and death monthly. Root death was most prevalent at 41 to 59 cm, while vigorous root growth was observed near the surface. The rhizosphere treatments exhibited increased Fe2+ dissolution and increased concentrations of DOC relative to matrix conditions; however, no corresponding P increase occurred. Near the surface, rhizosphere P concentrations declined below matrix concentrations after 60 d of ponding. Our results show that the rhizosphere of bald cypress did not cause higher P concentrations than matrix values for mineral and organic soils with 3.5 and 19.5% C, respectively. In addition, root growth near the surface resulted in more oxidizing conditions and/or plant uptake of P, which decreased P concentrations below matrix values.

Ecology of Chicken Turtles (Deirochelys reticularia) in a Seasonal Wetland Ecosystem: Exploiting Resource and Refuge Environments

Abstract Chicken turtles (Deirochelys reticularia) were studied at Dry Bay, a Carolina bay wetland in South Carolina, USA, between 1994 and 2005. A total of 461 individual turtles was marked from 1993–1998. Minimum ages at maturity for males and females were 2 and 5 yr, respectively. All females reproduced each year, and 60% of reproductive females produced two clutches per season. Clutch size averaged 9.8 eggs, and both clutch and egg size increased with body size. Hatchlings averaged 29.2 mm PL, and body sizes were similar among years. Yearling survivorship varied from 7.0–43.0% (mean = 20.4%) among years. The highest survivorship of a hatchling cohort to age 5 was 0.21. Survivorships of juveniles and adults while in terrestrial refugia were higher than survivorships while in aquatic habitats. No adult females survived a 2-yr drought (2001–2003), and the bay was repopulated by mature males and juvenile females (most from the 1998 hatchling cohort) that had survived the extended drought in terrestrial re...

Evaluating Hydroperiod Response in Restored Carolina Bay Wetlands Using Soil Physicochemical Properties

Abstract Carolina bays are shallow depression wetlands found in the southeastern United States that have been severely altered by human activity. The need to restore these complex and diverse systems is well established, but our limited understanding of wetland hydrologic processes in these systems hinders our ability to assess the effectiveness of bay restoration efforts. Carolina bays exhibit a wide range of moisture regimes from seasonally saturated to semipermanently inundated. Differing physicochemical properties of soils within bay interiors may control bay hydrology. However, previous efforts to establish relationships between soil characteristics and bay hydrology have been inconclusive. An assessment of soil and hydroperiod was initiated in 16 bays designated to be restored and 6 bays that were not restored (reference). Soil morphology was described, and permanent monitoring wells were installed at each site. Multiple regression analysis was used to determine relationships between the soil physicochemical characteristics and the bay hydroperiod for restored and reference bays in both pre‐ and postrestoration periods. A significant relationship (r2= 0.75, p= 0.02) between prerestoration hydroperiod and clay content in the argillic horizon (Bt) of the reference bays was observed. This relationship was then used to evaluate hydroperiod change in the restored bays from the postrestoration period. The relationship accurately identified sites that exhibited high prerestoration hydroperiods and did not need hydrologic restoration (n= 4) and effectively showed sites that exhibited substantial increases in hydroperiod due to the restoration activities (n= 7).

Effect of climate fluctuations on long-term vegetation dynamics in Carolina bay wetlands

Carolina bays and similar depression wetlands of the U.S. Southeastern Coastal Plain have hydrologic regimes that are driven primarily by rainfall. Therefore, climate fluctuations such as drought cycles have the potential to shape long-term vegetation dynamics. Models suggest two potential long-term responses to hydrologic fluctuations, either cyclic change maintaining open emergent vegetation, or directional succession toward forest vegetation. In seven Carolina bay wetlands on the Savannah River Site, South Carolina, we assessed hydrologic variation and vegetation response over a 15-year period spanning two drought and reinundation cycles. Changes in pond stage (water depth) were monitored bi-weekly to monthly each year from 1989–2003. Vegetation composition was sampled in three years (1989, 1993, and 2003) and analyzed in relation to changes in hydrologic conditions. Multi-year droughts occurred prior to the 1989 and 2003 sampling years, whereas 1993 coincided with a wet period. Wetland plant species generally maintained dominance after both wet and dry conditions, but the abundances of different plant growth forms and species indicator categories shifted over the 15-year period. Decreased hydroperiods and water depths during droughts led to increased cover of grass, upland, and woody species, particularly at the shallower wetland margins. Conversely, reinundation and longer hydroperiods resulted in expansion of aquatic and emergent species and reduced the cover of flood-intolerant woody and upland species. These semi-permanent Upper Coastal Plain bays generally exhibited cyclic vegetation dynamics in response to climate fluctuation, with wet periods favoring dominance by herbaceous species. Large basin morphology and deep ponding, paired with surrounding upland forest dominated by flood-intolerant pines, were features contributing to persistence of herbaceous vegetation. Drought cycles may promote directional succession to forest in bays that are smaller, shallower, or colonized by flood-tolerant hardwoods.

The ecological boundaries of six Carolina bays: Community composition and ecotone distribution

Community and environmental gradients within the ecological boundaries of Carolina bay wetlands may provide important information on the interaction between Carolina bays and associated uplands, and may also provide guidance for improved management. We established twelve 30-m transects on the sloping rims of each of six Carolina bays in northeastern South Carolina to characterize the community gradient, as well as important environmental factors producing this gradient. Mid-points of the transects were placed on jurisdictional wetland boundaries. Hydrology, soil properties, and plant species composition were measured within these transects. On average, transects included an elevation change of 0.6 m that corresponded with gradients of hydrology, soil properties, and community characteristics. Decreasing surface soil moisture (i.e., fewer flood events) and decreasing soil nutrients were associated with a shift from shrub-bog vegetation with relatively low alpha diversity and prominence of evergreens to a relatively diverse and heterogeneous community characterized by grasses, herbs, low shrubs, and vines. Ecotones, identified by abrupt changes in community composition, were more frequently found outside jurisdictional wetland boundaries. Likewise, five near-endemic and endemic plant species were found outside the wetland boundaries. Our data reinforce the need for better understanding of how Carolina bays interact with adjacent landscape elements, and specifically how ecological boundaries are influenced by this interaction.

Simulating the water budgets of natural Carolina bay wetlands

Wetland restoration projects attempt to recreate the hydrology found in natural wetlands, but little is known of the water budgets associated with wetlands in their natural state. The objective of this study was to compute the water budgets of three natural Carolina bay wetlands in Bladen County, North Carolina, USA. DRAINMOD models of various locations in the bays were calibrated with measured water table depths over a 2-yr period using inputs of rainfall, air temperature, and soil physical properties. The models were successful in simulating water table depths at all well locations during the calibration period with average absolute deviations between simulated and measured water table depths of approximately 4 cm. Measured and simulated data revealed very shallow (< 0.1 m) water table depths at all of the bays. Groundwater inflow was a significant component of the water balance at locations near the perimeters of the bays, ranging from 3%–26% of the total water input for these sites during the study period. A semi-confined aquifer below one of the bays was likely the source of groundwater inflow for that bay. Meanwhile, locations near the centers of the bays did not have groundwater inflow as an input to their water budgets. Groundwater outflow for the centers of the bays ranged from 2%–21% of rainfall. Areas near the perimeters of the bays were recharge, discharge, or flow-through wetlands depending on hydrologic conditions at the sites. Areas near the centers of the bays exhibited characteristics of recharge wetlands only. These results were consistent across the three Carolina bays studied, and can be used to better understand the hydrology of natural Carolina bays, improving the success of restoration projects of similar sites.

Physical Properties of Natural Organic Soils in Carolina Bays of the Southeastern United States

Hydrologic models are useful tools for designing wetland restoration projects, but they are difficult to use for sites with natural organic soils because few soil property data are available for these soils. The objective of this study was to measure the physical properties of organic soils needed to calibrate hydrologic models of three natural Carolina Bay wetlands in the southeastern USA. Undisturbed soil cores were collected at each site for laboratory measurement of saturated hydraulic conductivity, soil water characteristic curves, bulk density, particle density, and total porosity. Field measurements of saturated hydraulic conductivity were also made. The Oi, Oe, and Oa horizons in the natural organic soils had similar bulk densities (0.16 g cm -3 ), total porosities (0.90 cm 3 cm -3 ), and particle densities (1.50 g cm -3 ). However, field-measured saturated hydraulic conductivities decreased as the level of decomposition increased, going from 45 to 7.1 to 1.5 cm h -1 for the Oi, Oe, and Oa horizons, respectively. Soil water characteristic data revealed an abundance of large pores (>0.3 mm) in the Oi horizons, which likely explains their high saturated hydraulic conductivity relative to the Oe and Oa horizons, which had fewer large pores. Using the data collected in this study, mathematical relationships were developed to predict the total porosity and the saturated hydraulic conductivity of these organic soils based on more easily obtainable data, such as bulk density and the organic horizon type.

Presence and Absence of Bats Across Habitat Scales in the Upper Coastal Plain of South Carolina

During 2001, we used active acoustical sampling (Anabat II) to survey foraging habitat relationships of bats on the Savannah River Site (SRS) in the upper Coastal Plain of South Carolina. Using an a priori information-theoretic approach, we conducted logistic regression analysis to examine presence of individual bat species relative to a suite of microhabitat, stand, and landscape-level features such as forest structural metrics, forest type, proximity to riparian zones and Carolina bay wetlands, insect abundance, and weather. There was considerable empirical support to suggest that the majority of the activity of bats across most of the 6 species occurred at smaller, stand-level habitat scales that combine measures of habitat clutter (e.g., declining forest canopy cover and basal area), proximity to riparian zones, and insect abundance. Accordingly, we hypothesized that most foraging habitat relationships were more local than landscape across this relatively large area for generalist species of bats. The southeastern myotis (Myotis austroriparius) was the partial exception, as its presence was linked to proximity of Carolina bays (best-approximating model) and bottomland hardwood communities (other models with empirical support). Efforts at SRS to promote open longleaf pine (Pinus palustris) and loblolly pine (P. taeda) savanna conditions and to actively restore degraded Carolina bay wetlands will be beneficial to bats. Accordingly, our results should provide managers better insight for crafting guidelines for bat habitat conservation that could be linked to widely accepted land management and environmental restoration practices for the region.

Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland

AbstractFew studies have examined the spatial and temporal migration patterns of snakes to and from active‐season habitats. We conducted a year‐long population‐level analysis of cottonmouth Agkistrodon piscivorus migration patterns by monitoring snakes entering and leaving a Carolina bay wetland that was encircled by a continuous terrestrial drift fence. Cottonmouths used the wetland during the active season and left the bay in the fall to overwinter in other habitats. Adults and juveniles did not differ in time of arrival at the bay but juveniles left the bay earlier than adults. Spatially, captures of adult cottonmouths entering and leaving the bay were distributed non‐randomly, with capture peaks corresponding to the directions to the nearest permanent aquatic habitats. Juveniles' immigration patterns in the spring were biased in the same directions as those of the adults, but they left non‐directionally in the fall. This suggests that neonates do not rely on adult scent trailing to locate hibernacula, and that in a region with moderate winter temperatures, suitable overwintering sites may not be a limited resource. Additionally, our study demonstrates that cottonmouths make extensive use of upland habitats and underscores the importance of both critical upland habitat and forested corridors between wetlands and hibernacula for the conservation of wetlands herpetofauna.

Modeling the climatic and subsurface stratigraphy controls on the hydrology of a Carolina bay wetland in South Carolina, USA

Restoring depressional wetlands or geographically isolated wetlands such as cypress swamps and Carolina bays on the Atlantic Coastal Plains requires a clear understanding of the hydrologic processes and water balances. The objectives of this paper are to (1) test a distributed forest hydrology model, FLATWOODS, for a Carolina bay wetland system using seven years of water-table data and (2) to use the model to understand how the landscape position and the site stratigraphy affect ground-water flow direction. The research site is located in Bamberg County, South Carolina on the Middle Coastal Plain of the southeastern U.S. (32.88° N, 81.12° W). Model calibration (1998) and validation (1997, 1999–2003) data span a wet period and a long drought period, which allowed us to test the model for a wide range of weather conditions. The major water input to the wetland is rainfall, and output from the wetland is dominated by evapotranspiration. However, the Carolina bay is a flow-through wetland, receiving ground water from the adjacent upland, but recharging the ground-water to lower topographic areas, especially during wet periods in winter months. Hypothetical simulations suggest that ground-water flow direction is controlled by the gradient of the underlying hydrologic restricting layer beneath the wetland-upland continuum, not solely by the topographic gradient of the land surface. Ground-water flow may change directions during transition periods of wetland hydroperiod that is controlled by the balance of precipitation and evapotranspiration, and such changes depend on the underlying soil stratigraphy of the wetland-upland continuum.

Estimating primary and secondary subsidence in an organic soil 15, 20, and 30 years after drainage

Abstract Wetland hydrology can be restored to soils that have been drained by plugging ditches to return the water table to its original elevation. Organic soils subside after drainage, and when ditches are plugged the restored water table may rise above the soil surface, killing newly planted vegetation. This study developed a method to estimate amounts of primary (settling) and secondary (oxidation) subsidence that could be applied to any organic soil. Primary subsidence was estimated from differences in bulk density between the drained and representative undrained sites. Secondary subsidence was estimated from accumulation of sand in the surface (Oap) horizons and changes in bulk density between oxidized and unoxidized organic horizons. Total subsidence was the sum of primary and secondary subsidence. Bulk density, particle size, and organic carbon data were gathered from one drained (Juniper Bay) and three undrained Carolina bay wetlands. Juniper Bay was drained with a network of ditches in three stag...