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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. 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. 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.

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.

Core IdeasNormal rainfall ranges are best defined by the 30th and 70th percentiles of historic data.Mean ± SD produces a normal rainfall range twice as large as that of percentiles.Mean ± SD normal rainfall will cause some upland soils to be classified as hydric soils. 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.

Core IdeasPrevious 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 distichumL. 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–1during 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.

Phosphorus release to ground or surface waters has been observed in wetlands restored from farmland. This study examined whether rhizospheres of bald cypress (Taxodium distichumL.) 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.

Soils provide long‐term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid‐phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk‐sample and spatially resolved synchrotron X‐ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace‐element reactivity in different soil microsites. Spatially resolved X‐ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro‐ (or nano‐)reactors of unique composition. An example of this microreactor concept is shown for micro‐X‐ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field‐scale behavior of soil contaminants.

Ground-penetrating radar (GPR) can be used to determine the depth to a subsurface layer if the user can identify where the ground surface is on the GPR trace. This study demonstrates a simple field procedure for unequivocally determining the ground surface in a GPR trace. A “lift test” was performed simply by raising the transceiving antenna unit off the ground and setting it back down while the GPR unit was recording. This procedure produced a distinct wave pattern on the GPR profile that clearly showed the soil surface. The lift test improved accuracy of depth estimates by approximately 10% in a GPR study to determine depths to moderately fine and fine textured horizons at a drained Carolina bay wetland restoration site. Though easy to perform, this procedure has apparently not been used in many GPR studies. The lift test provides an efficient means of determining the soil surface in GPR surveys, a necessity if accurate depth measurements are to be made.

Review: 66 refs.