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Restoring wetlands on agricultural land can release soil phosphorus (P) to surface waters. Phosphorus is a limiting nutrient in many freshwater systems, thus restricting its release will improve surface water quality by preventing algal blooms. A P balance was used to examine how P was cycling in a Carolina Bay wetland eight years after restoration from prior-drained agricultural land. The change in soil P was evaluated between archived samples taken at restoration (2005), and eight years after restoration (2013). Measured P fluxes included atmospheric deposition, plant uptake, and loss to surface water outflow. The soil total P pool at the time of restoration was 810 kg P ha−1. No significant (α = 0.05) decrease in the soil P pool was observed over the eight years. Atmospheric deposition contributed 1.0 kg P ha−1 yr−1, plants incorporated 3.3 P ha−1 yr−1 into woody biomass and 0.4 kg P ha−1 yr−1 as forest floor litter, and 0.2 kg P ha−1 yr−1 was lost to surface waters draining the wetland. Because the loss of P to surface waters was small, and because runoff water concentrations of P declined through this period of study to concentrations below those likely to cause eutrophication (< 0.1 mg L−1), we concluded that the wetland was not contributing to the degradation of surface water quality of nearby streams following restoration. Further, isolated wetlands such as that studied may be promising sites for future wetland mitigation projects due to limited impacts on surface water quality. [ABSTRACT FROM AUTHOR]

Restoring wetlands is expensive, and hydrology criteria are needed to determine if restored sites are saturated long enough to support the planted vegetation. This study determined relationships among hydrology, soils, and vegetation in a restored Carolina Bay wetland (CBW) to identify field indicators of saturation duration. The study site was in Robeson County, NC in a CBW that had been restored for 15 years. Water-table data for the five-year period following restoration were used to establish saturation periods of: ≤13, 14-50, 51-100, and 101-225 consecutive days occurring during the growing season and within 30 cm of the surface. Sampling plots were established 15 years after restoration along a hydrologic gradient to identify vegetation type, tree basal area, tree height, wetland hydrology field indicators, and inundation. The number of hydrology field indicators increased 50%, going from ≤13 to 101-225 days of saturation. Dominant tree species at the restored site were similar to those found in three reference CBWs. Where saturation occurred for 101+ days, tree basal area and height decreased 40-69% compared to where saturation periods were shorter. Areas that experienced saturation for <51 days contained trees that were 10 cm larger in diameter, had more shrubs and vines, and contained less areal cover of graminoids compared to areas that had saturation for 101- 225 days. Regression equations predicted average saturation duration during the growing season using number of hydrologic field indicators and tree height with R2 values between 0.62 and 0.73. Such relationships would be useful to evaluate restoration success. [ABSTRACT FROM AUTHOR]

Wetlands are often located in landscape positions where they receive runoff or floodwaters, which may contain toxic trace metals and other pollutants from anthropogenic sources. Over time, this can lead to the accumulation of potentially harmful levels of metals in wetlands soils. To assess the potential risk of Cu and Zn buildup in wetland soils in North Carolina, soil data from 88 wetlands were analyzed. In a subset of 16 wetlands, more intensive sampling was conducted. Samples were analyzed for Mehlich 3 Cu and Zn, and a subset of the samples was analyzed for total Cu and Zn. Overall, Mehlich 3 Cu and Zn were low, with mean values of 0.9 mg/kg for Cu and 3.2 mg/kg for Zn. Warning levels for Mehlich 3 Zn were only exceeded in three of the 88 sites; elevated Mehlich Cu was not observed. Total Cu and Zn were also low, with only a few sites having elevated levels; however, there was not a strong linear relationship between Mehlich 3 and total metals. Mean levels of Mehlich 3 Cu and Zn in wetlands were much lower than for human-impacted upland soils and background threshold concentrations that might be indicative of disturbance were much lower than warning levels for agricultural soils. The very low mobile Zn and Cu in most of these wetlands indicated that these metals do not pose a risk to the biota in most North Carolina wetlands, but wetlands with a direct and significant anthropogenic source of metal contamination could be exceptions. [ABSTRACT FROM AUTHOR]

Identifying sites meeting wetland hydrology requirements is simple when long-term (>10 years) records are available. Because such data are rare, we hypothesized that a single-year of hydrology data could be used to reach the same conclusion as with long-term data, if the data were obtained during a period of normal or below normal rainfall. Long-term (40-45 years) water-table and rainfall data were obtained for two sites in North Carolina (with modeling), and one site in Minnesota (direct measurements). Single-year wetland hydrology assessments were made using two-rainfall assessment procedures recommended by the U.S. Army Corps of Engineers for their Wetland Hydrology Technical Standard, and two other rainfall assessment methods that were modifications of those procedures. Percentages of years meeting wetland-hydrology conditions during normal or drier than normal periods were identified for each plot with each rainfall assessment method. Although the wetland hydrology criterion was met in over 90% of the years across all plots using the long-term records, the four assessment techniques predicted the criterion was met in 41-81% of the years. Based on our results, we recommend that either the Direct Antecedent Rainfall Evaluation Method, or its modified version, be used for wetland hydrology assessment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hydric soils are identified on-site using morphological features called "field indicators". It is not known how long it takes for these indicators to form, nor whether they occur in created wetlands inundated for approximately 5% of the growing season, which is the minimum duration needed to meet wetland hydrology requirements. This study evaluated formation of redoximorphic features and hydric soil field indicators under field conditions following controlled, short-term floods that produced ponding events. A flood plain was constructed along an artificial stream channel (100-m long) where flooding was controlled by dams at each end of the channel. Floodwaters inundated soils on the flood plain nine times over a 3-year period. Ponded water was kept on the soils for periods ranging from 4 to 44 days. During ponding events, Fe2+ concentrations were approximately 1 to 4 mg/L, which indicated that the soils were anaerobic and undergoing Fe reduction. Redox depletions formed in A horizons following a single 7-day ponding event. Abundance of depletions increased from 2% to an average of 15% after nine ponding events. Most depletions were approximately 1 cm in diameter and had Munsell hues of 2.5Y and 5Y, values of 4, and chromas of 2 or less. The depletions appeared to form in place by loss of both Fe and C. Hydric soil field indicators developed in all plots after nine ponding events over a 3-year period and included the depleted matrix, redox dark surface, and a variant of the depleted dark surface. All indicators formed by a reduction and/or oxidation of Fe. [ABSTRACT FROM AUTHOR]

Clayey subsurface strata in precipitation-driven wetlands act as aquitards that retain water and can affect wetland hydrology. If the aquitard layers have been cut through by drainage ditches, then restoring wetland hydrology to such sites may be more difficult because of the need to fill ditches completely with low hydraulic conductivity material. Ground penetrating radar (GPR) surveys were conducted to determine the depth and continuity of shallow clay layers and identify those that have been pierced by drainage ditches at Juniper Bay, a 300-ha drained Carolina bay in North Carolina, USA that will be restored. Carolina bays are a wetland type that occur as numerous, shallow, oval-shaped depressions along the Atlantic Coastal Plain. The GPR interpretations found that moderately fine-textured (clay loam, sandy clay loam, silty clay loam) and fine-textured (sandy clay, silty clay, clay) aquitards underlay coarser-textured horizons in most of the bay at an average depth of 1.6 m. Extensive ground truthing showed that, on average, GPR predicted the depth to these aquitards to within 16% of their actual depth. An atypical GPR reflection in the southeast sector of the bay was interpreted as a fluvial deposit without aquitards until a depth of 3 to 5 m. This area may require different restoration strategies than the rest of the bay. By comparing the depths of aquitards and drainage ditches, several areas were identified as likely locations of ditch-induced aquitard discontinuity that may require filling or lining of suspect ditches to prevent potential water losses if there are downward hydraulic gradients. Cost estimates by two professional firms indicated that GPR could provide large volumes of data with cost and time efficiency. GPR surveys are proposed as a useful tool for characterizing potential wetland restoration sites on the Atlantic Coastal Plain and other regions with similar soils. [ABSTRACT FROM AUTHOR]

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, his 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 stages, 15, 20, and 30 years ago. Meart total subsidence was not significantly different (0.10 level) over time and averaged 121 cm for the three drainage periods. The mean rate of primary subsidence across the three drainage periods was 4 cm yr-1, while secondary subsidence was approximately 2 cm yr-1. Subsidence values were variable across Juniper Bay and were not related to distance from a field ditch. Restoration of the hydrology in Juniper Bay to predrainage water-table elevations could result in a water table that is >1 m above the existing soil surface. [ABSTRACT FROM AUTHOR]

Hydric soils are identified on-site using visible features called 'field indicators.' It is not known how long it takes for these indicators to form nor whether they occur in created wetlands less than 5-years old. This study evaluated chemical and morphological changes in acreated wetland to monitor the development of hydric soil field indicators over time. A deep marsh, created in 1989, was studied from 1992 through 1994 at the Des Plaines River Wetlands Demonstration Project near Chicago, Illinois, USA. Soil and water samples were collected twice a year from two transects having plots in the following landscape positions: in the marsh, along the marsh edge, in a transition zone to the upland, and in the upland. Detailed profile descriptions were also completed twice per year. In 1994, the soils were classified from the marsh to upland as Typic Endoaquoll, Mollic Endoaquept, AquicHapludalf, and Ochreptic Hapludalf. Soil pH values ranged from 7.3 to 7.8 in the upper 15 cm. Carbonates were closest to the surface in the marsh and edge positions. Organic C levels were similar among soils throughout the study at approximately 20 g C/kg soil. Redox potentials and water-table measurements indicated that soil in the marsh andedge positions met the definition of hydric soils throughout the study, while upland positions did not, and soil in the transition positions met the definition in some years. Hydric soil field indicators formed by Fe reduction developed over time in the marsh and edge plots and in some plots of the transition to the upland. The depleted matrix indicator, which formed by the reduction and removal of Fe from thesoil matrix, gave the most consistent results for identifying hydricsoils. Full development of the indicator in all edge plots was complete 5 years after the marsh was constructed. Indicators formed by organic matter accumulation (organic bodies) also developed in the marshwithin this period. [ABSTRACT FROM AUTHOR]