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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]

Evaluating 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. Core Ideas: Wetland soils had less organic C after 15 years of restoration than the pre‐restoration, agricultural soils.Organic litter accumulated on the post‐restoration surface and its thickness increased with saturation.Organic C levels in restored soils were similar to those found in reference wetlands of the same type. [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]

The concept of hydric soils evolved over time with advances in soil science and wetland resource management. Hydric soils are identified in the field by examining morphological characteristics, including organic matter accumulation and redoximorphic features that form in response to prolonged periods of saturation and anaerobic conditions. The Hydric Soil Technical Standard (HSTS) was developed to provide a quantitative procedure for evaluating the hydric status of a soil based upon direct measurements of saturation, anaerobic conditions, and precipitation normality. In practice, the HSTS is used for (a) identifying hydric soils when a field indicator of hydric soils may not be present (e.g., naturally problematic or disturbed soils); (b) evaluating the current functional hydric status of a soil; (c) developing new field indicators of hydric soils; and (d) proposing changes to existing field indicators of hydric soils. The HSTS procedures have progressed over several decades with new approaches to soil analysis, including novel methods to document anaerobic conditions. The following review describes the development of the hydric soils concept and provides guidance for measuring each HSTS component. Practical approaches for collection and submission of HSTS data to the National Technical Committee for Hydric Soils, the group responsible for approving approaches to hydric soil identification in the United States, are also discussed. Expanding the understanding and application of the HSTS promotes technical accuracy, transparency, and efficient decision making in support of hydric soil and wetland resource management. [ABSTRACT FROM AUTHOR]

Featured Application: Results of this study can be used by health authorities to set limits on the thickness of saprolite material needed below on-site septic system drainfields in order to remove E. coli from home sewage. Results will also be of interest to field personnel evaluating sites for on-site wastewater disposal. Saprolite, weathered bedrock, is being used to dispose of domestic sewage through septic system drainfields, but the thickness of saprolite needed to remove biological contaminants is unknown for most saprolites. This study developed and tested a simple method for estimating the thickness of saprolite needed below septic drainlines to filter E. coli from wastewater using estimates of the volume of pores that are smaller than the length of the coliform (≤10 μm). Particle size distribution (texture) and water retention data were obtained for 12 different saprolites from the Piedmont and Mountain regions of North Carolina (N.C.). Saprolite textures ranged from clay loam to coarse sand. The volume of pores with diameters ≤10 μm were determined by water retention measurements for each saprolite. The data were used in an equation to estimate the saprolite thickness needed to filter E. coli. The estimated saprolite thicknesses ranged from 36 cm in the clay loam to 113 cm for the coarse sand. The average thickness across all samples was 58 cm. Saprolite thickness estimates increased as silt percentage decreased and as sand percentage and in situ saturated hydraulic conductivity increased. Silt percentage may be most useful for estimating appropriate saprolite thicknesses in the field. [ABSTRACT FROM AUTHOR]

Water table data collected for hydric soil and wetland identification studies require supporting analysis of rainfall normality. Water table measurements made after periods when precipitation is within a normal range are believed to represent long-term trends, whereas data collected following periods of abnormally high precipitation represent rare events, potentially resulting in erroneous hydric soil determinations. The USDA-NRCS currently uses two different methods to assess normal precipitation ranges; both have been used to assess hydric soils. This study compared methodologies that identify normal precipitation periods by using: (i) the range defined by the 30th and 70th percentiles observed within a 30-yr period [i.e., the Climate Analysis for Wetlands Tables (WETS) method] and (ii) long-term monthly mean precipitation ± one SD (i.e., the U.S. Soil Taxonomy method). Comparisons were made for 30 geographically diverse locations and soil moisture regimes. The results demonstrated that the U.S. Soil Taxonomy method yielded normal precipitation ranges approximately twice as large as those from the WETS method. As a result, the U.S. Soil Taxonomy method precluded the occurrence of drier than normal conditions in many instances and displayed increased sensitivity to infrequent high rainfall events. Three case studies evaluated the implications of method selection on hydric soil identification, demonstrating that the U.S. Soil Taxonomy method identified normal conditions more frequently than the WETS method. As a result, the adoption of the WETS method, which accounts for the non-normal distribution of precipitation data, as the sole method to determine normal precipitation periods for hydric soil assessment is recommended. [ABSTRACT FROM AUTHOR]

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 condi-tions, 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study provides quantitative ecological targets for restoring degraded peat-based Carolina Bays in the Carolina Flatwoods Ecoregion. Cluster analysis of vegetation data from three Carolina Bay reference sites in Bladen County, North Carolina, indicated four plant communities present: pond pine (Pinus serotina) woodland, non-riverine swamp forest dominated by swamp gum (Nyssa biflora), high pocosin dominated by evergreen shrubs with scattered pond pine, and bay forest dominated by loblolly bay (Gordonia lasianthus). We classified bay soils according to surface organic layer thickness (OLT) into mineral, histic, shallow organic, and deep organic types. We monitored the water table of each soil type in one bay throughout one growing season. The soil types with corresponding water table regimes were: mineral (9.4 cm mean OLT with a rooting zone water table [RZWT] 39% of the monitoring period), histic (27.5 cm OLT and 76% RZWT), shallow organic (63.9 cm OLT and 84% RZWT), and deep organic (102.5 cm OLT and 57% RZWT). Pearson residual analysis and correspondence analysis revealed that pond pine woodland was positively associated with mineral and histic soils, non-riverine swamp forest with shallow organic soil, bay forest with deep organic soil, and high pocosin with deep organic soil. We concluded that peat-based Carolina Bay restoration in the Carolina Flatwoods Ecoregion should be gauged against reference data which suggests: 1) pond pine woodland be established on mineral and histic soils; 2) non-riverine swamp forest be established on shallow organic soils; and 3) high pocosin and bay forest be established on deep organic soils. [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]

Successful wetland mitigation is determined by goals and performance standards of a U.S. Army Corp of Engineers approved mitigation plan. This study collected and reviewed historical data for a mitigation site prior to construction to reduce the cost and risk of mitigation failure. Historical records were reviewed to evaluate the hydrology, vegetation, and soils of a drained Carolina bay wetland. Historical data were obtained from courthouse records, aerial photographs, personal interviews, the local Natural Resources Conservation Service, and the National Railroad Historical Society. Photographs and interviews indicated there was open water before drainage, suggesting a potential source of consistent hydrology. Organic soils subside when influenced by land clearance, drainage, and agricultural activities and could result in a water table above the soil surface once hydrology is restored. Aerial photographs show that several drainage systems have existed over the last 90 yr. Soils along the lines of the earlier drainage ditches and a former railroad line still show disturbance to depths of 1 m. These areas of disturbance could affect vegetation establishment. Records of agricultural practices suggest higher nutrient levels than those of undisturbed Carolina bays, indicating that undesired vegetation could compete with desired vegetation. Historical information verified that Juniper Bay is a viable restoration site and identified areas where design change could help improve chances for success. Similar historical reviews with other mitigation sites can help reduce cost and risk through evaluation of hydrology, soils, and vegetation. [ABSTRACT FROM AUTHOR]

Lateral transport of waterborne contaminants is generally assumed to occur below the water table (WT), but recent laboratory studies have suggested that subsurface lateral solute transport could occur above the WT through the capillary fringe (CF). The objective of this study was to evaluate the horizontal transport of solutes in the CF and shallow groundwater (SGW). Two consecutive field experiments were conducted in a Leon sand (Aeric Alaquod) at a site with a shallow WT. In both experiments, a bromide (Br-) solution was applied to the bottom of an auger hole dug to within 10 cm above the projected CF. Movement of Br- in the subsurface was monitored by collecting CF and SGW samples using nests of tension samplers installed at radial distances of 60, 120, 220, and 320 cm from the application spot. Each nest of samplers contained a tension sampler at 45, 60, 75, 90, and 105 cm depth. Bromide transport was monitored for 58 d in the first experiment while the more detailed second experiment was conducted for 84 d. Peak Br- concentration generally occurred in the upper 60 cm of the soil where the CF was located for most of the experiment. The Br- plume that entered the CF moved horizontally in it until Br- was partially moved into the SGW by the fluctuating WT. In the second experiment, approximately 48% of the Br- detected in the CF at a distance of 320 cm from the application spot was still in the CF after 15 cm of rain through 59 d. [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]