Hydric Soil Field Indicators Research Articles

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.

Development and application of the Hydric Soil Technical Standard

AbstractThe 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.

A Comparative Review of Methods of Using Soil Colors and their Patterns for Wetland Ecology and Management

ABSTRACTSoil color patterns are essential to understand hydrologic regime and biogeochemical processes in wetland ecosystems. Munsell Soil Color Chart (MSCC) has been traditionally and predominantly used to identify and quantify hydric soil field indicators, but several simple, low-cost alternatives have become recently available to compare their efficacy in complementing the MSCC in soil color assessment. We conducted an intensive literature review on studies utilizing different methods to identify and quantify hydric soil colors and associated patterns; these include 1) the MSCC, 2) the Nix Color Sensor, 3) mobile phone camera (MPC) and medium-end digital camera photography, and 4) colorimetry and spectrometry. A review of these methods elucidates their respective strengths and weaknesses and highlights the importance of considering study-specific attributes in determining which method to choose for field studies of hydric soil colors. Redoximorphic features (RMFs) require methods capable of capturing small and heterogeneous soil surfaces and features such that the MSCC and digital photography are the most appropriate methods; on the other hand, the Nix Color Sensor provides rapid assessment of soil color that does not necessitate rigorous training to overcome biases that might come about in more subjective methods such as the MSCC. Overall, all alternative methods reviewed have their own merits and capacity to complement measurements made by the MSCC.

Improving Hydric Soil Identification in Areas Containing Problematic Red Parent Materials: a Nationwide Collaborative Mapping Approach

Hydric soil identification utilizes diagnostic morphologic features, including iron transformations, resulting from anaerobic conditions. However, soils derived from some red parent materials (RPM) fail to develop characteristic hydric soils morphologies, confounding hydric soil and wetland delineation. Laboratory and field methods addressing resistant RPM soils exist, but application remains limited by uncertainty regarding problematic RPM distribution. In response, a collaborative effort (>50 participants) documented problematic RPM distribution across the contiguous United States. Specifically, >1100 samples from >450 locations underwent laboratory analysis using the Color Change Propensity Index to identify problematic RPM soils. Geospatial analysis linked verified problematic soils with associated geologic units and soil series, generating maps of RPM distribution. Potential problematic RPM was identified in the Northeast and Mid-Atlantic, Great Lakes, South-central, and Desert Southwest-Western Mountains (problematic RPM regions herein), encompassing diverse groups of soils and parent materials. Despite the observed variability in soil characteristics, results suggest that problematic RPM was consistently derived from sedimentary, hematite-rich red bed formations developed where deposition of terrestrial sediments occurred in near-shore, marginal-marine environments. Understanding problematic RPM soils distribution promotes the appropriate application of existing hydric soil field indicators, including F21 – Red Parent Material, thus improving approaches to hydric soil identification and wetland management.

Development of New Hydric Soil Field Indicators: Guidelines for Data Collection and Submission

Development of New Hydric Soil Field Indicators: Guidelines for Data Collection and Submission

Hydric Soil Field Indicators for Use in Mid-Atlantic Barrier Island Landscapes

Hydric soils in Holocene-aged barrier island landscapes in the Mid-Atlantic region of North America lack morphologies typically associated with saturated and reducing conditions. Furthermore, many better drained (nonhydric) soils have low chroma colors due to parent material effects, making identification and delineation of wetlands problematic. Our objective was to develop field indicators that could be used to effectively recognize hydric soils in these environments. Soils along 10 topographic transects were evaluated at Assateague Island National Seashore, Maryland. Transects spanned a gradient of topographic positions from dune crests to interdunal swales. Water tables and reducing conditions were monitored to determine hydric status. Soil descriptions along each transect were used to identify morphological features indicative of soil wetness. Of 16 monitored and documented hydric soils, only five met recognized field indicators. Hydric soils were best identified by the presence of matrix colors with chromas less than 2 in mineral soils or the presence of at least 1 cm of muck (Oa horizon). On the basis these characteristics, we propose two new indicators restricted for use in Holocene-aged barrier island landscapes in the Mid-Atlantic region. These indicators will allow identification of hydric soils, improving the accuracy and ease of delineation of wetlands.

Visual Assessment and Interpolation of Low Chroma Soil Colors

Color is one of the most obvious properties of soils and is utilized in many soil evaluation strategies. Color data are usually documented using Munsell notation of hue, value, and chroma, with the latter two parameters normally documented to the nearest whole unit. Soil colors with chroma less than or equal to 2 are particularly important in soil classification and soil interpretation, especially with regard to the identification of field indicators of hydric soils. During a field study of dune soils on late Holocene barrier island landscapes, the investigators sought to improve the quality of color data by noting color value and chroma to the nearest half unit by interpolating between chips in the Munsell book. To evaluate whether interpolating color to half units of value and chroma was justifiable, a study was initiated using 23 homogenized and randomized soil samples collected from dune profiles in the study area. Moist color values were generally 6 or less and moist chromas were 3 or less, while hue mostly ranged between 10YR and 5Y. As experienced soil morphologists, we estimated moist and dry colors to the nearest half unit of value and chroma, using the same reference color book and under fixed lighting conditions. A digital colorimeter was used to measure the color of the soil samples to the nearest 0.1 unit of hue, value, and chroma. This study demonstrates that when individuals are forced to select a whole chip rather than interpolating between chips, there is a significantly greater error in the estimation of both the Munsell value and chroma. Therefore, experienced soil morphologists appear to be justified in interpolating Munsell value and chroma to the nearest half unit.

Interpreting morphological features in wetland soils with a hydrologic model

Abstract Wetlands in the United States are protected by law and are identified by their hydric soils, wetland hydrology, and vegetation. Hydric soils are easily identified by color characteristics termed hydric soil field indicators, that form under saturated and anaerobic conditions, but wetland hydrology is difficult to assess. This study determines how often seven hydric soil field indicators met wetland hydrology requirements which require a water table be within 30 cm of the surface for 14 days or more during the growing season in over half the years. Studies were conducted at five sites in North Carolina in both wetland and upland plots. Soils ranged from Aquic Paleudults to Typic Haplosaprists across all sites. The water-table simulation model DRAINMOD was calibrated to soil conditions in individual plots. Long-term rainfall data were used with the calibrated models to compute 40 years of daily water table data to represent both wet and dry years. It was found that the hydric soils with field indicators composed of organic materials in layers over 20 cm thick (Histosol and Histic epipedon field indicators) met wetland hydrology requirements each year, and in addition were ponded with water for periods between 67 to 139 days on average each year during the growing season. Plots in mineral soils having the Dark Surface (S7) indicator as well as the Sandy Mucky Mineral (S1) indicator also met the saturation requirements for wetland hydrology every year, and were ponded for only 3 days per year on average. Other mineral soils with an Umbric Surface (F13) or a Depleted Matrix (F3) field indicator met wetland hydrology requirements in approximately 95% of the years, and had water tables within 30 cm of the surface for 40 days per year on average. The Redox Depressions (F8) field indicator occurred in a small depression that was saturated for 87% of the year for periods averaging approximately 30 days. These results showed that hydric soil field indicators can be calibrated to long-term water table data that will allow precise assessments of wetland hydrology on-site.

Using Magnetic Susceptibility to Delineate Hydric Soils in Southeastern Coastal Plain Soils

Identifying hydric soil boundaries is one component in delineating jurisdictional wetlands. Evaluating hydric soil field indicators using borings along transects is an invasive and arduous task. Magnetic susceptibility (MS) has been used successfully as a geophysical method for determining hydric soil boundaries by detecting a drop in soil magnetism when iron minerals mobilize or are recrystallized in alternating reducing and nonreducing conditions. Magnetic suseptibility has not, however, been fully evaluated in the soils of the southeastern coastal plain, where iron minerals are uncommon and a substantial amount of wetland delineation work is performed. Five relatively pristine and two disturbed wetland sites in northern Florida were rapidly evaluated by recording uncorrected volumetric MS measurements (n = 12 hydric; n = 12 nonhydric) on 1 by 7 yd transect grids centered on the hydric soil boundary as determined by field indicators. At the more sensitive “×0.1” instrument setting, instrument drift obscured any true differences in the populations of hydric and nonhydric MS values. Two additional sites in southeastern Georgia and two of the original sites were selected for a more intensive survey (n = 30 random hydric; n = 30 random nonhydric) volumetric MS measurements recorded inside a 3 by 20 yd transect block centered on the hydric soil boundary. Values were air-corrected for temperature drift, and the hydric and nonhydric populations were compared. All four sites showed significant (P < 0.004) differences in both population means and medians. However, the necessity for air correction, statistical analysis, and the lack of a unique MS value separating hydric and nonhydric populations make the use of this technique for delineating the precise hydric soil boundary impractical in this region. Mass specific MS measurements of the surface soils at two sites had a marginal correlation (R2 = 0.78) with total and ammonium oxalate extractable iron, and trace amounts of iron minerals—most likely maghemite and goethite—were magnetically separated from filter residue and unaccounted for in the total iron analysis. This sporadic occurrence of ferrimagnetics has an overriding but difficult-to-quantify influence on the effectiveness of this method in the southeastern coastal plain.

Dynamics of redoximorphic feature formation under controlled ponding in a created riverine wetland

Abstract 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 ...

Disturbance and the three parameters of wetland delineation

Under current U.s. wetland delineation procedures, an area must have hydric soils, wetland hydrology, and hydrophytic vegetation to be considered a wetland. This study investigated the level of correlation between these three parameters on sites disturbed by humans versus relatively undisturbed sites. Based on our data set of nearly 1,800 data points from 188 sites in northeastern Illinois and northwestern Indiana, USA, relatively “disturbed” locations are significantly less likely to meet all three wetland criteria than “undisturbed” locations. Disturbance also affects an area’s likelihood to meet or fail particular wetland parameters, depending on the type of disturbance. Also, areas dominated by common hydrophytic species are significantly less likely to meet all three wetland criteria in disturbed areas versus undisturbed areas. This study suggests the need for quantitative studies of the three wetland criteria on both disturbed and undisturbed sites to refine further the USFWS wetness ratings and hydric soil field indicators relative to the effects of disturbance.

Calibrating Hydric Soil Field Indicators to Long‐Term Wetland Hydrology

Jurisdictional wetlands are required to be saturated to the surface for 5% or more of the growing season in 5 out of 10 yr, but practical field methods for confirming this are lacking. This study determined whether hydric soil field indicators were related to wetland hydrology requirements. Water table levels were monitored daily for 2.5 yr in a toposequence of nine soil plots that included well to poorly drained members (Oxyaquic Paleudults and Typic Albaqualfs). Monitoring data were used to calibrate a hydrologic model that simulated water table levels from inputs of hourly rainfall data. Forty years of rainfall data were then used with the model to compute long‐term daily water‐table levels in each plot. These data were summarized as “saturation events”, which are the frequency that water tables were at or above preselected depths for at least 21 d. Twenty‐one days was the average period needed for Fe reduction to begin in these saturated soils. This condition must occur for hydric soil field indicators to form. Regression equations were developed to relate saturation events to percentages of redoximorphic features. The r2 values for relationships between percentages of redoximorphic features and saturation events were &gt;0.80 for depths of 15 cm, and &gt;0.90 for depths between 30 and 90 cm. Results showed that the depleted matrix field indicator, in which redox depletions occupy &gt;60% of the horizon, occurred in soils that were saturated for 21 d or longer at least 9 yr out of 10. This indicated the depleted matrix indicator occurred in soils that were saturated nearly twice as long, and more frequently, than the minimum requirements needed to meet wetland hydrology requirements.

Using magnetic susceptibility to facilitate more rapid, reproducible and precise delineation of hydric soils in the midwestern USA

Standard field indicators, currently used for hydric soil delineations [USDA-NRCS, 1998. Field indicators of hydric soils in the United States, Version 4.0. In: G.W. Hurt et al. (Ed.), United States Department of Agriculture-NRCS, Fort Worth, TX], are useful, but in some cases, they can be subjective, difficult to recognize, or time consuming to assess. Magnetic susceptibility (MS) measurements, acquired rapidly in the field with a portable meter, have great potential to help soil scientists delineate and map areas of hydric soils more precisely and objectively. At five sites in Illinois (from 5 to 15 ha in area) with contrasting soil types and glacial histories, the MS values of surface soils were measured along transects, and afterwards mapped and contoured. The MS values were found to be consistently higher in well-drained soils and lower in hydric soils, reflecting anaerobic deterioration of both detrital magnetite and soil-formed ferrimagnetics. At each site, volumetric MS values were statistically compared to field indicators to determine a critical MS value for hydric soil delineation. Such critical values range between 22×10 −5 and 33×10 −5 SI in silty loessal or alluvial soils in Illinois, but are as high as 61×10 −5 SI at a site with fine sandy soil. A higher magnetite content and slower dissolution rate in sandy soils may explain the difference. Among sites with silty parent material, the lowest critical value (22×10 −5 SI) occurs in soil with low pH (4.5–5.5) since acidic conditions are less favorable to ferrimagnetic mineral neoformation and enhance magnetite dissolution. Because of their sensitivity to parent material properties and soil pH, critical MS values must be determined on a site specific basis. The MS of studied soil samples (0–5 cm depth) is mainly controlled by neoformed ultrafine ferrimagnetics and detrital magnetite concentrations, with a minor contribution from anthropogenic fly ash. Neoformed ferrimagnetics are present in all samples but, based on high χ FD% (∼5% to 10%), are most prevalent in high pH Mollisols of northeastern Illinois. Scanning electron microscope images display significantly more detrital magnetite alteration in hydric soils, substantiating that reductive dissolution of magnetite (aided by microorganisms) is a primary cause for lower MS. Fly ash comprises 8–50% of the >5 μm strongly magnetic particles and typically accounts for 5–15% of the total MS signal. The proportion of fly ash in >5 μm strongly magnetic fractions is greater in hydric soils because of lower natural magnetite contents, possibly combined with historical topsoil accumulation in lower landscapes. Magnetic fly ash particles are also more altered in low MS soils, implying that significant magnetite dissolution can occur in less than 150 years.

Hydric Soils in a Southeastern Oregon Vernal Pool

Vernal pools on the High Lava Plain of the northern Great Basin become ponded in most years, but their soils exhibit weak redoximorphic features indicative of hydric conditions. We studied the hydrology, temperature, redox potentials, soil chemistry, and soil morphology of a vernal pool to determine if the soils are hydric, and to evaluate hydric soil field indicators. We collected data for 3 yr from piezometers, Pt electrodes, and thermocouples. Soil and water samples were analyzed for pH, organic C, and extractable Fe and Mn. Soils were ponded from January through April or May, but subsurface saturation was never detected. Soil temperatures 50 cm below the surface rose above 5°C by March. Clayey Bt horizons perched water and limited saturation to the upper 10 cm. Redox potentials at a 5-cm depth were often between 200 and 300 mV, indicating anaerobic conditions, but producing soluble Fe 2+ concentrations <1 mg L 1 . Extractable soil Fe contents indicated Fe depletion from pool surface horizons and accumulation at or near the upper Btl horizon. Depletions and concentrations did not satisfy the criteria of any current hydric soil indicators. We recommend development of new indicators based on acceptance of fewer, less distinct redox concentrations for recognition of a depleted A horizon, and on presence of a thin zone containing redox concentrations located in the upper part of the near-surface perching horizon.

A field method for determing percentage of coated sand grains

Several USDA‐NRCS hydric soil field indicators require estimation of the percentage of organic‐coated sand grains (black grains). For example, to meet the Dark Surface field indicator the soil layer must contain at least 70% coated (black) grains. Field experience has shown that the estimation of the percentage of coated sand grains is often subjective and highly variable from one soil scientist to another. In order to overcome this variability a set of standards was created using a mixture of black and light gray (representing uncoated grains) sand grains. Weighing out each component for the desired ratio and mixing them in a 47‐mm‐diam. petri dish we made a set of three standards consisting of 50, 70, and 90% black grains. To test the effectiveness of these standards, soil scientists estimated the percentage of coated grains from similarly prepared samples first without the use of the standards and then with the use of the standards for comparison. Individuals improved the accuracy of their estimates by 10 to 60% and their hydric soil identification by 16%. The standards are easily prepared, easy to use, and portable.

Propensity of Soils to Develop Redoximorphic Color Changes

Most soils with seasonally high water tables exhibit redoximorphic features, such as Fe depletions and concentrations. Some soils formed from red parent materials apparently are less typical in their behavior and have in this sense been described as problematic. Regulatory guidelines have mentioned such problematic red soils, and the Field Indicators of Hydric Soils in the United States attempts to address the issue by using test indicator TF2. This study was undertaken in an attempt to develop an approach for quantifying the inherent tendency of soils to form redoximorphic features under reducing conditions. Thirty soils from diverse parent materials in the Mid‐Atlantic region was studied, including 13 thought to be problematic soils formed from red parent materials. Samples were treated using a citrate‐buffer and Na dithionite at room temperature (25°C) for periods of time ranging from 0.5 to 72 h, and also at 80°C for 4 h. Colors were measured using a digital colorimeter to document changes in Munsell hue, value, and chroma. By comparing initial soil colors with those measured under the treatments of 25°C for 1 h and at 80°C for 4 h, a color change propensity index (CCPI) was developed that effectively discriminated between soils which were and were not thought to be problematic. The utility of the CCPI was tested using 14 additional soil samples, six of which came from outside the Mid‐Atlantic region. Recommendations are made to differentiate between problematic and nonproblematic soils based on values of CCPI.

Dynamics of hydric soil formation across the edge of a created deep marsh

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 a created 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, Aquic Hapludalf, 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 and edge 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 the soil matrix, gave the most consistent results for identifying hydric soils. 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 marsh within this period.

Hydric Conditions and Hydromorphic Properties within a Mollisol Catena in Southeastern Minnesota

AbstractWetlands are characterized by wetland hydrology, hydrophytic vegetation, and hydric soils. The multiparameter approach to wetland identification and delineation requires independent evaluation of all three diagnostic characteristics. Hydric soils can be determined from data collected under saturated and anaerobic soil conditions or by using accepted field indicators. The objectives of this research were to: (i) evaluate the presence of wetland hydrology and hydric soil conditions, (ii) examine associations between observed soil hydrology and soil morphologic properties, and (iii) evaluate current field indicators of hydric soils for their applicability to presumed hydric Mollisols. We used wells, piezometers, and tensiometers to measure saturated conditions, and Pt electrodes to measure anaerobic and reducing conditions for five soils along a hillslope transect from summit to drainageway in southeastern Minnesota. Saturated conditions were observed within 25 cm of the soil surface for all five soils for at least a few days each year between 1992 and 1995, mainly in the early spring and the late fall when soil temperatures at 50 cm were not always &gt;5°C. Only the soil in the drainageway was saturated and anaerobic during the microbial activity season in more than one year. Soil morphology reflects the presence of saturated and anaerobic conditions in the form of thick, black surface horizons. Absence of Fe concentrations and depletions in the upper 30 cm of presumed hydric soils may reflect the absence of Fe‐reducing conditions as a result of saturated conditions when soil temperatures do not facilitate abundant microbial activity.