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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]

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]

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]

Abstract: Phosphorus release to ground or surface waters is commonly observed in wetlands that were restored on previously drained and farmed land, but the precise location of where the P is dissolved within the soil is unknown. This study compared the concentration of dissolved P in both the rhizospheres and soil matrix under saturated conditions. Experiments were conducted in rhizotrons (glass-walled boxes) which were filled with Ap horizon material from an Aeric Alaquod in a restored wetland. Phosphorus release was monitored from the rhizospheres of bald cypress roots (Taxodium distichum, L.), and an unplanted control representing the soil matrix. The rhizotrons were saturated for 120days, and soil water was collected twice monthly at three depths. Numbers of live and dead roots were determined monthly. Following saturation, vigorous root growth was observed near the surface (0 to 22cm depth) throughout the 120days saturation period, while up to 30% of the roots in the lower layer (41 to 59cm depth) died after 20days of saturation. Rhizosphere processes did not increase P concentrations in the soil solution compared to the matrix controls. In the top layer of the planted treatment dissolved total P concentrations were 3.5 times lower than matrix concentrations (peak DTP of 700–900μg P L−1””) due to oxygen loss by root aerenchyma. Significantly larger amounts of dissolved organic C and Fe2+ were found in the rhizospheres than the matrix. Dissolved total P concentrations in the rhizosphere were equal to DTP concentrations in the matrix during the first 54days of saturation, but lower than those of the matrix thereafter, most likely due to plant uptake. These findings indicate that under saturated conditions plant rhizospheres do not cause more P to be released to the soil water over that of the matrix, and may contain lower amounts of P than the soil matrix due to plant uptake. These results pertain to soils having an organic C concentration of at least 26gkg−1 or higher. [Copyright &y& Elsevier]

Abstract: Understanding dissolution and transport of phosphorus (P) from organic soils in agricultural fields and restored wetlands is critical for devising management strategies to mitigate P losses. The objective of this study was to evaluate the dissolution of P in water flowing through the vadose zone-shallow ground water continuum of an organic soil. Three 90cm×50cm×8cm flow cells were uniformly packed with organic soil material from a Ponzer muck (Terric Haplosaprists) collected from an area that had been in agricultural production for at least 30years. The packed flow cells were instrumented with soil solution samplers and platinum-tipped redox electrodes at approximately 5cm below a simulated water table (WT), and in the capillary fringe (CF) at approximately 5 and 20cm above the WT to collect soil solution and monitor the reduction potential (Eh), respectively. Distilled water was continuously supplied at constant rates of 1.2, 2.4, and 3.6Ld−1 to one end, and drained at the other end of the flow cells while maintaining a WT at 12cm above the bottom of the midpoint of each flow cell. Phosphorus concentration in the outflow solution was consistently above the USEPA water quality criteria of 0.1mgL−1. Changes in pore-water velocity did not alter the amounts of P leached within the time frame of the experiment. Dissolved phosphorus concentrations at both 5cm below and 5cm above the WT were significantly higher than at 20cm above the WT. This observation indicated that P that leached out of the flow cells was not only from the saturated zone but also from the lower part of the CF. These results suggest that controlling the height of the WT to limit saturation of P enriched surficial soils, while considering the contribution of the CF, may be an effective management tool for limiting P export from restored wetland sited on former agricultural fields. [Copyright &y& Elsevier]

Reduction and oxidation measurements create important data for analysis of wet soils. These measurements are actually recordings of voltage (EH) over time between a reference electrode and a sensor electrode inserted into a soil. The sensor electrodes are usually made of platinum wire (Pt electrode). Hydric soils require a period of reduction, and these measures can provide the length of time that the reduction process is occurring. The voltage results from an exchange of electrons between a redox couple such as ferrous and ferric iron during the process of reduction and oxidation. In soils that have fluctuating wet and dry conditions, wide fluctuations in Eh occur. Micro site differences complicate these measurements in that anaerobes may be active and at 1-cm away they are completely inactive. The ferrous-ferric iron couple usually dominates these measurements but other couple often contributes complicating the measurements and interpretations of the data. Reference electrodes are often fine for laboratory work but are not rugged enough for the field. In this chapter, suggestions for improvement are discussed. Field-measuring equipment and the Pt electrode are also sensitive and subject to problems that often lead to spurious results in the field. These problems are discussed at length. Iron-coated tulles and other methods of establishing redox conditions are relatively recent and are discussed, also. [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]

Abstract: Substantial horizontal solute transport has been demonstrated to occur in the capillary fringe (CF) above a flowing ground water, yet the importance of the CF for solute movement has generally been ignored. This study was conducted to evaluate the fate and horizontal transport of surface-applied nitrate (NO3 −) in the CF under simulated hydrologic conditions that varied flow rates. Two soils of different organic carbon content were packed in separate 240-cm long, 60-cm high and 25-cm thick flow cells. A simulated water table (WT) was established at 20cm above the bottom of each flow cell and different pore-water velocities across the flow cell were simulated while a solution containing NO3 − and bromide (Br−) was continuously applied over a small area on the surface of the soil in the flow cell. Soil solution samples were collected from two depths below the WT and two depths within the CF above the WT at four locations along the flow cell. Subsurface horizontal transport of surface-applied NO3 − tended to occur exclusively in the CF as the pore-water velocity was increased. In the flow cell with soil having a small amount of organic carbon (0.3gkg−1), normalized concentration of NO3 − and Br− remained very comparable at all monitoring locations above and below the WT. Nitrate loss via denitrification in this case was not observed as conditions were oxidizing. In flow cells with soils having an organic carbon content of 35gkg−1, some Br− was detected below the WT while NO3 − was essentially absent. Conditions below the WT favored NO3 − loss via denitrification as reflected by very low redox potentials (<250mV). These results suggest that collection of samples from the CF should be considered when monitoring subsurface fate and transport of surface-applied NO3 − in locations with laterally moving shallow ground water. [Copyright &y& Elsevier]

Abstract: Histosols are a huge reservoir for C, covering <1% of the world''s land surface but storing up to 12% of total soil C. Thorough comprehension of factors controlling the rate of soil C loss from Histosols is critical for proper management of these C sinks. Two experiments evaluated how formerly cultivated, warm-climate Histosols undergoing wetland restoration respond to decreases in soil temperatures via vegetative shading, under different water table conditions. We compared temperature and soil CO2 efflux differences from intact soil cores under three levels of light reduction in a greenhouse: 0%, 70%, and 90%. Soil in full sun was consistently warmer and showed higher efflux rates than 70% and 90% shade treatments: 4.132, 3.438, and 2.054μmol CO2 m−2 s−1, respectively. Shade treatments reached peak efflux rates at similar water potential, −2 to −4kPa. A field experiment subjected in-situ soil to full sun, 70% light reduction, and light reduction from naturally occurring herbaceous vegetation. Shade treatment effects on soil temperature and C mineralization were evident throughout the growing season. Vegetative shade effects on soil temperature were greatest in August and September when soil under vegetation was 5–11°C cooler than unshaded soil. Soil CO2 efflux was correlated strongly with soil temperature; daily efflux rates were consistently highest from unshaded soil. Efflux across treatments showed a strong seasonal correlation to soil moisture, increasing as soil dried in response to water table decline. Soil water potential was unaffected by shade treatment, suggesting temperature effects were solely responsible for efflux differences between treatments. All results confirm that surface shading has a strong influence on soil temperatures and C mineralization rates. Management to enhance vegetative shading in wetland restoration projects may be an effective strategy for slowing soil C losses and promoting soil C sequestration when O2 is not limiting. [Copyright &y& Elsevier]

Abstract: It is commonly assumed that nitrate (NO3 −) and other anions entering the soil move downward through the vadose zone, and then move horizontally in the groundwater. Recent laboratory studies, however, indicate that water movement and transport of pollutants can also take place in the capillary fringe (CF) above the water table (WT). This field study evaluated the fate of NO3 − in the CF and shallow groundwater (SGW) for a sandy soil (Aeric Alaquod) with shallow water table. Ten L of a solution containing approximately 18 mmol L−1 nitrate [2.66 g L−1 Mg(NO3)2] and 77 mmol L−1 bromide (9.12 g L−1 KBr) were applied to the soil above the CF. The movement of both NO3 − and Br− was monitored for 84 days by using tension lysimeters installed at depths between 45 and 105 cm at radial distances of 20, 60, 120, 220 and 320 cm from the application point. Nitrate and Br− plumes that entered the CF from the unsaturated zone moved horizontally in the CF until both species were partially carried into the groundwater by the fluctuating WT following rain events. Normalized concentrations of NO3 −N and Br− remained comparable as they moved horizontally in the CF up to 320 cm from the tracer application spot. However, below the WT the detected normalized concentration of Br− was higher than that for NO3 − indicating nitrate loss, perhaps due to denitrification. When monitoring subsurface NO3 −, solely relying on collection of groundwater samples may lead to an underestimation of the extent of NO3 − contamination and transport in the subsurface. [Copyright &y& Elsevier]

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]

Abstract: Groundwater flow in sedimentary rock saprolite, and in soils derived from this material, is strongly influenced by sedimentary layering and fractures inherited from the parent bedrock. The main objectives of this study were to determine whether parent bedrock lithology and infilling of fractures and other macropores with pedogenically derived clays and Fe/Mn oxides also play major roles in controlling hydraulic conductivity and groundwater flow. The study was carried out by measuring profiles of saturated and unsaturated hydraulic conductivity, K sat and K(ψ), and comparing them to soil and saprolite pedology and lithology in a 3.4 m deep pit excavated in interbedded limestone and shale saprolite. In the depth interval of 50 to 100 cm, there was an abrupt decline in K sat and K(0) by a factor of up to 250. This corresponds to the occurrence of a zone where almost all of the fractures and other macropores are occluded with pedogenic clays and Fe/Mn oxides. Below a depth of 100 cm, both degree of pore infilling and hydraulic conductivity tend to vary, with a spatial regularity that is similar to the thickness of sedimentary layering in the saprolite. However, variations in hydraulic conductivity do not always correspond to changes in lithology, suggesting that hydraulic conductivity is a result of the complex interaction of several factors, including parent bedrock lithology and the degree of infilling of the macropores. Similarities between hydrogeologic conditions at this site and at research sites in weathered sedimentary shale/siltstone and carbonate rock settings at the Oak Ridge Reservation in Tennessee and in weathered crystalline rock in North Carolina indicate that macropore infilling plays an important role in controlling hydraulic conductivity and groundwater flow for a variety of different types of parent bedrock. [Copyright &y& Elsevier]