NRES 517 MOOC 1 Module 2 Scripts PDF

NRES 517_MOOC 1 Module 2 |Field Indicators for Hydric Soils Learning Objectives: 1. Understand why and how hydric soils are assessed for wetland delineation 2. Describe field indicators used for all hydric soils 3. Describe field indicators used for sandy or loamy soils...

NRES 517_MOOC 1 Module 2 |Field Indicators for Hydric Soils Learning Objectives: 1. Understand why and how hydric soils are assessed for wetland delineation 2. Describe field indicators used for all hydric soils 3. Describe field indicators used for sandy or loamy soils Videos 2.0 | Module Introduction 2.1 | Basics of Hydric Soil Assessment 2.1a | Overview of Hydric Soils and their Role in Wetland Delineations 2.1b | Preliminary Assessment of Hydric Soils before On-Site Delineation 2.1c | Field Sampling Protocol for On-Site Delineations 2.2 | Field Indicators for All Hydric Soils 2.2a | Overview of Hydric Soil Indicators 2.2b | Characterizing Soil for Wetland Delineation 2.2c | Indicators for the Accumulation of Organic Matter 2.2d | Indicators for Redox Depletions 2.2e | Indicators for Redox Concentrations 2.3 | Field Indicators for Sandy and Loamy Soils 2.3a | Sandy Soil Indicators 2.3b | Loamy Soil Indicators 2.4 | Module Wrap-up 2.0 | Module Introduction Soil provides a reliable method of delineating wetlands. The formation of soils under conditions of saturation, flooding or ponding typically observed in wetlands results in anaerobic conditions occurring within the upper part of the soil profile. This depletion of oxygen promotes geochemical processes, such as the accumulation of organic matter or reduction of elements, which can be observed in soil samples obtained from wetlands. Importantly, most of these processes do not occur in aerated, non-wetland soils and can be used as indicators for wetland delineation. In this module, we will explore field indicators used to determine whether hydric soils are present at a site for wetland delineation purposes by: Discussing why and how hydric soils are assessed for wetland delineation. Describing field indicators that are used for all hydric soils. Examining field indicators that are used for specifically sandy or loamy soils. Let’s begin with an overview of hydric soils and their importance to wetland delineation procedures. 2.1a | Overview of Hydric Soils and their Role in Wetland Delineations In this video, we will discuss the importance and role of hydric soil for wetland delineation. The importance of the chemical and biological activity residing in wetlands soils cannot be understated as they provide a vital link between the non-living and living components of a wetland. Soils also provide a reliable method of delineating wetlands, especially in areas where wetland hydrology or vegetation has been modified. As such, it is important to understand how we identify and delineate hydric soils from upland, non-hydric soils. Hydric soils, according to the USDA Natural Resources Conservation Service, are soils that formed under Commented [CD1]: Citation: United States Department of conditions of saturation, flooding or ponding long enough during the growing season to develop Agriculture, Natural Resources Conservation Service. 2018. Field Indicators of Hydric Soils in the United States, Version anaerobic conditions in the upper part of the soil. Nearly all hydric soils exhibit characteristic 8.2. L.M. Vasilas, G.W. Hurt, and J.F. Berkowitz (eds). USDA, morphologies that result from repeated periods of saturation or inundation that last more than a few NRCS, in cooperation with the National Technical Committee days. Soil microbes quickly use available oxygen within water saturated soils resulting in anaerobic for Hydric Soils. conditions within the upper part of wetland soils. This promotes certain biochemical processes that result in distinctive characteristics that persist in hydric soils during both wet and dry periods, making them particularly useful for identifying hydric soils in the field. A national list of these distinctive soil characteristics is published by the USDA Natural Resources Conservation Service in a document title: “Field Indicators of Hydric Soils in the United States: A Guide for Identifying and Delineating Hydric Soils”. Hydric soil indicators are formed predominately by the accumulation or loss of iron, manganese, sulfur, and carbon compounds under saturated or anaerobic conditions. One of the most common indicators associated with hydric soils is the accumulation of organic matter driven by the decrease in microbial activity and decomposition that occurs in anaerobic soil. This is observed as a layer of organic soil consisting of peat (fibrist) or muck (saprist) material on the surface of the soil profile. Various hydric soil indicators are driven by reduction, translocation and oxidation of iron and manganese in wetland soils. Evidence of iron reduction is commonly observed as bluish gray or greenish gray colors in saturated, anaerobic soils. If the wetland enters a dry period and the soil becomes aerobic, re-oxidation of iron can occur and be observed as reddish-orangish colors along pores and root channels. Finally, a “rotten egg” odor produced by sulfide gas in the upper foot of the soil can be used as a reliable hydric soil indicator. This odor results from microbial transformation of sulfate into sulfide gas; however, this indicator is typically observed in hydric soils that have prolonged or permanent inundation or saturation as sulfate is one of the last elements to be reduced by microbes. While these indicators are valuable features to help identify hydric soils, they are not intended to replace the requirements contained in the definition of a hydric soil. In other words, a soil that meets the definition of a hydric soil is hydric whether it exhibits indicators or not. Hydric soils that are wet long enough to develop anaerobic conditions in the upper part of the soil may lack field indicators if the soil has black or red parent material which can mask coloration. If the wetland site has been disturbed by human development, for example through plowing for agriculture, this can mix or remove specific soil indicators used to identify hydric soils. IIn these cases, you would rely on previous knowledge of soils within the area or use stream gauge data to determine if it is saturated for a sufficient time to develop anaerobic soils. While no list for hydric soil indicators will be comprehensive and work in every situation, the national list provided by the USDA works for nearly all hydric soils and an important part of verifying hydric soils for wetland delineation and determinations. It is important to note that this list is not static, changes and additions are expected with additional research and field testing. As such, it is important to be aware of revisions to the USDA document detailing Field Indicators for Hydric Soils in the United States. 2.1b | Preliminary Assessments of Hydric Soils before On-Site Delineation Prior to any onsite identification or delineation of hydric soils, all available offsite information should be evaluated. Offsite information includes published soil surveys of the National Cooperative Soil Survey, National Wetlands Inventory Maps produced by the U.S. Fish and Wildlife Service, topographical maps produced by the U.S. Geological Survey, and maps of areas subject to flooding produced by the Federal Emergency Management Agency. Reviewing these sources before attempting to identify or delineate Commented [CD2]: Much of this taken from: hydric soils can significantly reduce time spent in the field. It will also facilitate most onsite identification Ch 8: Delineating Hydric Soils by G.W. Hurt and V.W. Carlisle in Wetland Soils: Genesis, Hydrology, Landscapes, and and delineation procedures. Classification (eds: JL Richardson and MJ Vepraskas) The USDA Natural Resources Conservation Service has been conducting soil surveys throughout the United States since 1896. Originally used to help farmers locate suitable soils, these surveys now provide valuable information for engineers, wetland scientists and natural resource planners. The result of soil surveys consists of technical reports detailing the location, classification, use and management of soils in a specific county which was then used to generate maps to visualize the soil data. Online soil maps are available via the Web Soil Survey web page that has links to the mapper, survey reports, and other soil data. By using the hydric soil rating feature in the Web Soil Survey, users can identify the likely presence of wetlands in a given area. Some units rated as 100% hydric, as shown in the red colored units on the Commented [CD3]: Figure 10.6 in Wetland Indicators: A map, indicate obvious wetlands. While orange and green colored units show the expected occurrence of Guide to Wetland Formation, Identification, Delineation, Classification and Mapping by Ralph W. Tiner hydric soils in the area ranging from 66-99% likelihood of hydric soils for areas in orange to 1-32% in light green areas. The Web Soil Survey gives wetland delineators a good sense of what to expect in the field Commented [CD4R3]: https://websoilsurvey.nrcs.usda.g ov/app/WebSoilSurvey.aspx regarding hydric soils and contains descriptions of the soil on the site. However, it is important to note that soil surveys do have limitations. First, most of these maps were published at a scale of 1:12000 or 1:24000 so not all hydric soils may be captured on these soil surveys. Second, even if a soil unit has been designated as hydric soil on the Web Soil Survey does not mean it is hydric. This is only an interpretive rating and must be verified in the field. Finally, it is important to note the date that the soil survey was carried out and if any development has occurred on the site. Soil maps should be used with other map types to identify the likely presence of hydric soils encountered during field inspections. For example, wetland maps produced by the US Fish and Wildlife Service’s National Wetland Inventory program can be accessed online via the “Wetlands Mapper” tool. While Commented [CD5]: https://fwsprimary.wim.usgs.gov/wet these maps have identified many wetlands, they often underestimate the extent of wetland and might lands/apps/wetlands-mapper/ miss drier-end wetlands or wetlands that are difficult to detect with imagery. Another source of Commented [CD6R5]: OR. Fig 10.2 in Wetland Indicators information are topographical maps produced by the US Geological Survey. These maps contain Book by Ralph Tiner elevation contours that can be used to check for locations on sites where hydric soils may differ from Commented [CD7]: https://ngmdb.usgs.gov/topoview/vi upland soils and contain swamp and marsh symbols that can be used to mark points of interest. ewer/#15/40.1935/-88.4004 However, field verification is needed to determine hydric soil conditions. Finally, maps produced by the Federal Emergency Management Agency can be used to determine areas that are flood prone and can Commented [CD8]: https://msc.fema.gov/portal/search? indicate areas that might have flooding or ponding for long enough duration to become hydric soil. AddressQuery=mahomet%20IL Because of these limitations, onsite investigation is recommended to decide if hydric soils occur and to determine the exact location and extent of hydric soils. However, valuable insight can be gained by reviewing these off-site sources of information and might be needed if problematic or atypical situations arise during wetland delineation. 2.1c | Field Sampling Protocol for On-Site Delineations In this video, we will be discussing the field sampling protocol for onsite delineations of hydric soils. This generalized protocol is described in detail within the USDA Natural Resources Conservation Service document “Field Indicators of Hydric Soils in the United States” and follows the US Army Corps of Engineers Wetland Delineation Manual. All wetland delineation methods described in the 1987 Army Corps Manual can be grouped into two general types: routine and comprehensive. For hydric soil determinations, the field sampling protocol is nearly identical between the two methods and follows a transect approach based on either recognizable plant communities for routine delineations or fixed sampling intervals for more comprehensive delineations. Before making any decisions about the presence or absence of hydric soils, the overall site and how it interacts with the soil should be considered. Using preliminary assessments obtained from soil surveys and national wetland inventory maps, examine the soil and plant community boundaries in the field contrasting the wet and dry sites close to them. While walking around the site, note the number and location of plant communities and determine whether there is any evidence of natural or human alterations on the site that might make hydric soil delineation challenging. If a problem or atypical situation exists, such as recent development or sediment dredging, you may have to rely on additional site information to determine whether a soil is hydric or not based on the USDA definition. For example, documentation of standing water or depth of water table can help determine whether a long enough duration of saturation, flooding or ponding has occurred to develop anaerobic conditions in the upper part. After observing and documenting plant communities in the site, establish a baseline for setting up transects. The baseline should be parallel to the major river course or perpendicular to the hydrological gradient. Determine the number and position of transects based on the length of the baseline. For Commented [CD9]: Figure 6.3 in Wetland Indicators by example: if the baseline is 1-2 miles long, then 3-5 transects are needed for delineation based on the Tiner. 1987 Corps Manual. Walk each transect and conduct a soil sample for each plant community observed or at the specified sampling interval. To observe and document a hydric soil, first remove from the soil surface any woody material larger than 2 cm in cross section. Do not remove the soil's organic surface layer, which generally consists of peat or muck depending on the stage of plant decomposition. Dig a hole and describe the soil profile. For most soils, the recommended excavation depth is approximately 50 cm from the soil surface and 20 - 30 cm in diameter. Hydric soils in wetland prairies tend to have thick, dark surface layers greater than 50 cm and may require deeper excavation to observe hydric indicators. If this is the case, the use of a soil auger or a backhoe may be necessary. Depths used to make hydric soil determinations are measured from the soil surface unless otherwise indicated. Soil colors used for hydric soil indicators should be measured when the soil is moist and referenced to the Munsell Color Charts. It may also be necessary to dry out a saturated soil sample, as redox concentrations of iron or manganese may not be visible in very wet soil. Taking photos of the soil samples with clearly marked measurement scales can also improve documentation and reporting. The process of delineating hydric soil boundaries is rather simple in concept – the upland boundary of hydric soils is at a landform change that results in a slope change in the landscape. However, finding the boundary can be difficult in practice especially where the landform change is very subtle or if the microtopography is highly variable. The easiest way to delineate a hydric soil boundary is to begin on the upland side of a wetland and travel toward the wetland looking for concave slope breaks. Once the boundary is located, you would then take a series of soil samples near the soil boundary to verify that area as the wetland hydric soil boundary. 2.2a | Overview of Hydric Soil Indicators Wetlands are identified and mapped in the field based on hydrophilic vegetation, wetland hydrology, and the presence of hydric soils which possess visible soil features. The definitive guide to identifying, describing, and delineating wetland soils for regulatory purposes is “Field Indicators of Hydric Soils in the United States” published by the USDA Natural Resources Conservation Service. If a soil meets the criteria of one of the field indicators described in this document, it's considered a hydric soil. These indicators were designed to identify a variety of wetland soil types that meet the definition of hydric soil. As a reminder, a hydric soil must have saturation, flooding, or ponding for a long enough duration to develop anaerobic conditions in the upper part of the soil. Given that there are always exceptions to the rule, the absence of indicators does not prevent a soil from being hydric and additional site information can be used to assess whether soils meet the definition of a hydric soil. However, these hydric soil indicators will work for most wetland soils, especially at the edge of wetlands where the boundary between upland and wetland soils must be resolved for delineation purposes. Field indicators are listed for three soil categories: all soils, sandy soils, and loamy and clayey soils. “Sandy” soil indicators are used in soil layers with USDA textures of loamy fine sand or courser, while “loamy and clayey” soil indicators are used in soil layers with textures of loamy fine sand or finer. Indicators for “all soils” are used in any soil regardless of texture. Sandy and clayey layers can occur in the same soil profile, so it is possible for a soil to have all three types of hydric field indicators. However, a soil only needs to have one field indicator for it to be considered a hydric soil. Even though hydrology is transient, water comes and goes depending on the season or depending on the most recent weather, the field indicators of hydric soils are relatively stable. Hydric soil indicators are formed predominately by the accumulation or loss of iron, manganese, sulfur, and carbon compounds under saturated or anaerobic conditions. One of the most common indicators associated with hydric soils is the accumulation of organic matter usually observed as a thick organic surface layer consisting of peat or muck. A variety of indicators are driven by the reduction and reoxidation of iron and manganese in mineral soils which can be visibly observed in wetland soils. In wetland soils subject to prolonged saturation, the dominant color of the soil changes from reddish-brown to gray with reddish-orange colors around soil pores and roots. Similar types of indicators are used for sandy and loamy/clayey soils; however, the depth and color of these indicators can change based on the texture of the soil due to its water holding capabilities. The descriptions of hydric soil indicators provided by the USDA “Field Indicators” document also specify whether an indicator can be used throughout the United States or only in certain geographic areas. For example: indicator A1 Histosol can be used in all 50 states and with any soil texture, while indicator F16 High Plains Depressions can only be used in USDA Land Resource Region H in loamy-clayey soils typical of playas in western Kansas, southwestern Nebraska, eastern Colorado, and southeastern Wyoming. As such, special care should be taken to verify which indicators are most useful in your region for delineation. The remaining videos in this module will consist of a deep dive into hydric soil indicators for all soils, sandy soils, and loamy-clayey soils. However, before we cover the list of hydric soil indicators, we will provide a brief overview of basic soil properties used to describe soil and to differentiate hydric soils from upland soils. 2.2b | Characterizing Soil for Wetland Delineation Commented [CD10]: Much of this taken from: Ch.1 Basic Concepts of Soil Science in Wetland Soils by When describing soils, wetland delineators need to include the following features in their soil Richardson and Vepraskas descriptions: horizon depth, color, redoximorphic features, and an estimate of texture. In this video, we Ch. 5 Soil Indicators of Wetlands in Wetland Indicators by Tiner will give a brief overview of soil properties used to describe hydric soils for delineation purposes. Formal procedures for describing soils can be found in the USDA’s Soil Survey Manual. There are approximately 20,000 named soils in the United States, and they are differentiated from each other based on the presence and sequence of soil layers, as well as external factors such as climate and parent material. For wetland delineation purposes, the type and thickness of each soil layer is recorded when describing soils. The top of the first horizon is the soil surface. Subsequent horizons are distinguished from those above by changes in soil color, texture, structure, or presence/absence of redoximorphic features. In general, there are six major layers (also called master horizons) recognized by soil scientists. Organic horizons, or O horizons, are most prominent in organic soils consisting of peat or Commented [CD11]: Fig. 1.1 in Wetland Soils muck horizons on the top layer of the soil. The A horizon is the uppermost mineral layer and is commonly called topsoil. This layer is typically the darkest layer of soil and varies in thickness between 5 and 30 cm. It is important to recognize the A horizon because hydric soils are usually identified from features immediately below it. The E horizon, when present, is a layer from which clay and iron oxides have been leached or “eluviated” resulting in a gray or white coloration in the soil. E horizons in hydric soils typically contain redox concentrations observed as reddish mottles in the grey-white soil. Below the E horizon is the B horizon, or subsoil layer. Most hydric soils have a B horizon that is seasonally anaerobic, and this can result in gleyed colors and redox features within this subsoil. Finally, the C horizon and R horizon are formed below the B horizon and consist of parent geological material or bedrock. Wetland delineators record the horizon depths for each soil layer and denote the coloration and texture of each layer to determine whether a soil is hydric or not. Hydric mineral soils are identified based mainly on soil color described by 3 characteristics: hue, value, and chroma. Hue is related to the spectral wavelength of color. Value describes how much light is reflected by the soil, in other words does that soil look bright or dark. Chroma is the strength or purity of the color. Wetland delineators use Munsell Soil Color Charts to characterize the color of soil samples. Each chart consists of 29 to 42 color chips that differ in value (darkness of soil) and chroma (purity of color) for a specific hue. For example, this is a 10YR color chart. This represents a soil with a hue Commented [CD12]: Fig. 5.3 in Wetland Indicators consisting of 50% yellow and 50% red. A 10R color chart would represent a soil consisting of 100% red coloration. Hues are further subdivided based on the percentage of each color present in the mix. For example, 5YR color charts are 25% yellow and 75% red coloration. The next color characteristic is value, or the darkness or lightness of the soil which ranges from black to white on a scale from 0 to 10 and is shown vertically across these charts. Chroma also ranges from 0 to 10, as shown across the page left to right, with high chroma colors being richly pigmented and low chroma colors having little pigmentation and look dull and grayish. Wetland delineators may have to use special “gley” soil color charts for hydric soils that are waterlogged for most of the year that tend to have B horizons that look grayish and have low chroma. It is important to note that soil color must be observed under standard conditions: full midday sunlight and soil needs to be moist. Another important soil characteristic for wetland delineation purposes is soil texture. Soil is usually made up of a combination of sand, silt, clay, and organic matter. Soil texture as defined by the USDA is related to the relative proportion of sand, silt and clay within the soil and can be determined in the field Commented [CD13]: Figure 5.1 in Wetland Indicators by feel. Sand has the largest particle size, 0.05 – 2 mm, and is typically spherical and feels slightly gritty when rubbed between fingers. Silt particles are smaller than sand and feel like flour when rubbed. Clay particles are the smallest at less than 2 microns in size and feel sticky. Soil texture is important because it can have a significant effect on the soil’s ability to retain water. For example, sandy soils have larger pore spaces and tend to have better drainage than clayey soils which can alter the types and depths of hydric soil indicators. Because natural soils rarely consist of just one particle size, the USDA has created 12 different textural classes for describing and classifying soils by texture based on the percentage of clay, silt and sand. For soils that consist of a significant mixture of particle sizes, the word “loam” is used to describe the soil mixture. With training and practice, wetland delineators can estimate soil texture in the field by rubbing a moistened soil sample between their fingers and testing for specific soil properties. The first step is to Commented [CD14]: Figure 5.2 in Wetlands Indicators wet the soil in the palm of your hand to create a putty-like, moldable soil ball. If the soil ball breaks apart when you squeeze it, the soil texture is sand and consists of 90% sand particles. If the soil texture is not sand, the next step is to place the soil ball between your thumb and forefinger and push soil towards the thumb creating a ribbon. The length of the ribbon that can be created reflects the soil’s clay content with longer ribbons having a greater proportion of clay particles. The grittiness or smoothness of the ribboned soil indicates a high content of sand or silt. Soil texture is also important in determining whether “sandy” or “loamy/clayey” indicators should be used during wetland delineation. A rule of thumb for determining whether the indicators for sandy or loamy soils should be used is to take a moist soil sample and roll it into a one-inch ball. Drop the ball into the palm of your hand from a height of 10 inches. If no ball can be formed or falls apart when dropped, use indicators for sandy soils. If the ball stays intact, use indicators for loamy or clayey soils. Commented [CD15]: In Ch.1 of Wetland Soils book Wetland soil investigations and delineation follow the same protocols used for standard soil surveys conducted by the USDA. As such, it is important to understand how to read and interpret a soil profile and label specific coloration and texture information for each soil horizon. This knowledge is necessary to effectively and correctly use the hydric soil indicators and mistakes can lead to improper wetland delineations and loss of essential wetland habitat for plants, animals and humans. 2.2c | Indicators for the Accumulation of Organic Matter There are two major categories of wetland hydric soils: organic soils and mineral soils. Organic soils form from organic material produced through the incomplete decomposition of plant debris; while mineral soils consist of different amounts of sand, silt, clay, and organic matter. Distinguishing between organic and mineral soil material is important for wetland delineation, as many hydric soil indicators require the identification of specific types of organic matter within soils. Soil materials fall into three categories based upon their organic carbon content: organic soils, mucky mineral soils, and mineral soils. In general, organic soils such as peat and muck consist of 12-18% Commented [CD16]: Figure 1.2 in Wetland Soils organic carbon based on the amount of clay present in the soil. Mucky mineral soils contain 5-12% organic carbon and tend to have darker organic-rich surface layers. Mineral soils, in contrast, have the least amount of organic carbon with less than 5% in sandy soils. To classify soil materials in the field, gently rub wet soil material between the forefinger and thumb. If the material feels gritty following the first or second rub, it is a mineral soil. If the material feels greasy after the second rub, it is either a mucky mineral or an organic soil. If additional rubs results in a gritty or plastic feel, it is a mucky mineral soil. If the soil still feels greasy, then it is organic soil. Being able to separate organic materials from mucky mineral materials is important for specific types of hydric soil indicators. Organic materials are further classified as fibric, hemic, or sapric based on the percentage of visible plant fibers within the soil. Saprist soil, commonly referred to as muck, consists of organic matter where less than 1/6 of the plant material can be identified and tends to break down into a greasy mess upon rubbing. If 3/4 of plant material is identifiable, then the soil is considered peat or fibric. Hemist soil is intermediate to muck and peat. Organic soil can easily be recognized by a black muck layer or orange- brown peat layer. If this organic layer is greater than 40 cm in depth, the soil would show our first indicator for hydric soil (A1 – Histosol) which can be used throughout the United States and in any USDA soil texture. If the organic layer is less than 40 cm thick but overlays a mineral soil material, then the soil is classified as mineral soil. When peat or muck layers are 20 to 40 cm thick, they are called histic epipedons and tend to form in areas with an abundance of soil moisture. Hydric Soil Indicators A2 (histic epipedons) and A3 (black histic) are examples of mineral soils that have deep layers of organic materials. Indicator Commented [CD17]: Figure 8 in Field Indicators of Hydric A3 requires specific coloration (hue 10YR or yellower, value of 3 or less, and chroma of 1 or less) but Soils does not require proof of aquic conditions that is needed for Indicator A2. Organic materials may also accumulate on the surface of hydric soil in thin layers. A 2 cm layer of muck should be a reliable indicator of hydric soils in many areas, meeting hydric soil indicators A8 through A10. Be sure that this muck layer Commented [CD18]: Figure 14 in Field Indicators of meets coloration requirements for the specific indicator, and you use the correct indicator based on your Hydric Soils USDA land resource region. For example, the mere presence of muck is a hydric soil indicator for hydric soils for wetlands in the southeastern United States (Indicator A8) while 2 cm of muck is required for wetlands in the Midwest (Indicator A10). Mucky mineral soil material, which contains 5-12% organic carbon, can also be used as an indicator for hydric soils. For example, wetland delineators in the southeastern US can use Indicator A7 – 5 cm mucky mineral to distinguish between upland and hydric wetland soils. Thin layers of mucky-mineral soil Commented [CD19]: Figure 13 in Field Indicators of material deposited between mineral layers can also be used as indicators for hydric soils. This indicator Hydric Soils is observed in alluvial or floodplain wetlands due to the frequent deposition of sediment from flooding. To be considered hydric, Indicator A5 (stratified layers) requires that at least one layer within 15 cm of Commented [DC20]: Figure 10 in Field Indicators of the soil surface must consist of organic or mucky-mineral material with low chroma and value resulting Hydric Soils in a dark, dull coloration relative to the other stratified soil layers. Lastly, hydric soil Indicator A6 uses the Commented [DC21]: Figure 11 in Field Indicatory of presence of organic bodies made of muck or mucky-mineral material along roots of plants to delineate Hydric Soils wetland soils from upland soils. Organic bodies form due to the frequent dieback of some roots under long duration of saturation, flooding, or ponding. Organic matter can even stain mineral soil and lead to the development of dark surface layers. This type of mucky mineral soil can develop in prairie soils, as observed in Indicators A11 (depleted below dark Commented [CD22]: Figure 12 in Midwest Regional surface) and A12 (thick dark surface). To be a hydric soil, soil with dark surface layers appear dark and Supplement to USACE Delineation Manual dull in coloration (value: 3 or less and chroma: 2 or less) and either need to be 30 cm thick or underlaid by a reduced matrix. The soil particles in the dark surface layer must also be masked by organic matter, such that 70% of soil particles are masked when observed through a power hand lens. It is important to note that these hydric soil indicators that require a dark surface layer also require that you look for features below the A horizon that might indicate prolonged wetness such as a depleted subsoil or redox concentrations or depletions. In summary, the presence of organic materials within the soil is usually a good indicator of hydric soils. Organic material indicators can range from organic soils, peat or muck that is at least 40 cm thick, to thin layers of muck or mucky-mineral soil that occur in floodplains. As such, wetland delineators need to determine the type of organic material present within a soil and accurately document their features with it. 2.2d | Indicators for Redox Depletions The reduction, translocation, and precipitation of iron and manganese in wetland soils provide visible evidence of past anaerobic conditions within hydric soils. In this video, we will focus on indicators related to the reduction of iron and manganese within hydric soils. Iron is typically the most abundant chemical element in soil. In its oxidized state, iron gives well-drained soils their characteristic yellowish, reddish, orangish, or brown colors. Prolonged saturation of mineral soil results in microbes converting iron from its stable oxidized form (ferric iron) to its mobile reduced state (ferrous iron). When iron is reduced, it is soluble and usually moves within or out of the soil leaving parts of the soil grayish in appearance which is called a redox depletion. When the dominant color of a soil horizon is the result of iron depletion, it is called a depleted matrix. When reduced iron is completely removed from the soil, the soil usually takes on a grey color with a blueish, greenish, or purplish tint and is classified as a “gleyed matrix”. If water recedes and the soil reverts to an oxidized state, reduced iron in solution will oxidize and become concentrated in patches and along root channels. These areas of oxidized iron are known as redox concentrations. Water movement within soil can be multidirectional, for example groundwater can move water upward through the soil, which means that redox depletions and concentrations can occur anywhere in the soil and have irregular shapes and sizes. Redox concentrations and depletions, along with reduced and gleyed matrixes, are collectively referred to as redoximorphic features and are used as indicators for hydric soils. Some of the wettest hydric mineral soils are typically gleyed in the subsoil and are said to have a “gleyed matrix”. These soils are neutral gray in color due to aluminosilicates within the soil and can occasionally be greening or bluish gray depending on other chemicals in the soil such as ferrous sulfide. To be Commented [CD23]: Figure 5.18 in Wetland Indicators considered a gleyed matrix, the soil color must match a color chip on one of the two gley charts in the Munsell Soil Color book. Soils with a gleyed matrix typically have a value of 4 or more, meaning they are lighter in color, and have either no or low chroma resulting in a neutral, grey coloration or a very dull yellow, green, blue or purple hue. A few hydric soil indicators require a gleyed matrix. In all states, except Alaska, Indicators S4 and F2 require a layer of gleyed matrix near the soil surface that makes up at least 60% of a soil horizon in either sandy or loamy soils. In Alaska, many upland soils look naturally gray, so indicator A13 – Alaska Gleyed is used to confirm that surface soil layers have undergone reduction Commented [CD24]: Figure 18 in Field Indicators for and represent a different color than surrounding parent soil material. Wetland Soils Most hydric mineral soils are characterized by low-chroma subsoils known as a depleted matrix. A depleted matrix can occur in soils with any hue (color spectrum wavelength), which differs from a gleyed matrix that is restricted to neutral or blueish/purplish colors. Depleted soils also appear lighter, with a value of 4 or greater, and have a dull-gray coloration with chroma of 2 or less. Another characteristic of a depleted matrix is the likely presence of red-orange mottles within the subsoil which provides evidence of re-oxygenation of the soil and the conversion of ferrous iron back to ferric iron. This differs from hydric soils that have a gleyed matrix which tend to not have red-orange mottles due to long periods of saturation or ponding in these wetter hydric soils. Indicators requiring a depleted matrix are common in prairie wetlands, A11 - Depleted Below Dark Surface and A12 – Thick Dark Surface, and in loamy/clayey Commented [CD25]: Figure 5.19 in Wetland Indicators soils. Special care must be taken to follow the specific value and chroma requirements needed for hydric soils dependent on their texture (sandy, loamy or any texture indicators) and whether mottles are present within the matrix. Being able to identify evidence of redox depletions within the soil profile is an important skill for wetland delineation. Prolonged saturation of soils leads to anaerobic conditions that result in the reduction and translocation of iron and manganese within the subsoil. This reduction can be observed through the presence of depleted and gleyed matrix in hydric soils. 2.2e |Indicators for Redox Concentrations Prolonged saturation of soils leads to anaerobic conditions that result in the reduction and translocation of iron and manganese within the subsoil. This reduction can be observed through the presence of a depleted or gleyed matrix. If water recedes and the soil reverts to an oxidized state, reduced iron and manganese in solution will oxidize and become concentrated in mottles or along root channels. These areas of oxidized iron are known as redox concentrations. Redox concentrations are features formed when iron or manganese oxides have accumulated within specific areas of a subsoil or around a large pore such as a root channel. These concentrations occur when soil is saturated and iron/manganese are reduced and soluble within the soil, these soluble elements can then move in the direction of water flow and become more concentrated in certain areas of the soil. If the soil becomes re-oxygenated, these reduced elements are oxidized and precipitate in the soil as brighter colors than the original soil matrix. Three kinds of redox concentrations have been defined: masses, pore linings and nodules/concretions. Masses are simply soft accumulations of iron or manganese oxides that occur in the soil matrix away from cracks or root channels. The masses can be of any shape and can be easily crushed by hand Commented [CD26]: Figure 5.20 in Wetland Indicators because the concentration of metal is not great enough to cement soil and are thus called soft masses. The color of these masses is variable but are typically red, orange, yellow or brown with relatively high chroma and value. Pore linings are accumulations of iron or manganese oxides that lie upon open pores in the soil matrix or root channels. This can occur in both anerobic and aerobic soils. In anaerobic soils, Commented [CD27]: Figure 5.9 in Wetland Indicators wetland plant roots can leak oxygen and soluble ferrous iron can become oxidized and create reddish- orange precipitates near root channels. These redox concentrations surrounding roots are called oxidized rhizospheres. In other cases, oxygen can enter pores in the soil resulting in redox concentrations in soil lining these pores. Finally, nodules and concretions are hard spherical bodies made of soil particles cemented by iron or manganese oxides. These range in size from less than 1 mm to over 15 cm in diameter. When found in soils, it is not clear whether these features formed in place or were brought into the soil by flooding or deposition from upland erosion. For this reason, nodules and concretions are specifically not used as evidence for redox concentrations in hydric soils. The only exception is Indicator F16 – High Plains Depressions which specifically notes that nodules and concretions can be used. Most hydric mineral soils rely on redoximorphic features for identification and delineation. For example, indicators that rely on a depleted subsoil matrix sometimes have a requirement for redox concentrations to be present as either soft masses or pore linings. A11 – Depleted Below Dark Surface requires redox concentration in soils with specific matrix colors. The depleted matrix must have redox concentrations in Commented [CD28]: Figure A1 in Midwest Regional at least 2% of the subsoil. The color of the redox concentrations must also differ enough from the Supplement surrounding matrix coloration to be considered either prominent or distinct. Wetland soil sampling requires a thorough description of these redox concentrations including their color, abundance, size, contrast and location. Color can be described using standard Munsell Soil Color Charts. Abundance is the percentage of soil horizon that contains redox concentrations ranging from few (less than 2%), common (2-20% of matrix), and many (greater than 20%). To determine whether the color of the redox concentrations differs enough from the surrounding matrix, you must determine its contrast as either faint (hard to see), distinct (easily seen), or prominent (striking, obvious). This involves comparing the Commented [CD29]: Table A1 in Midwest Regional color of redox concentrations with the surrounding matrix and then calculating the difference in hue, Supplement. value and chroma between these two soil features. Observations of redox concentrations are especially important in areas where mineral topsoil and subsoil do not meet the minimum requirements for hydric soil. Redox concentrations are used for any soil texture in Alaskan wetlands (A14) and coastal prairie wetlands (A16). There are also specific sandy and loamy/clayey indicators that use redox concentrations, and these will be further explored later in this module. In all these cases, a minimum of 2-20% redox concentration is required for identification of hydric soil depending on the soil texture and must have a contrast that is distinct or prominent. Accurate reporting of redox concentrations can drastically change wetland delineation boundaries, especially for wetlands that vary seasonally or naturally drier habitats where hydrology does not promote organic matter buildup or depleted/gleyed subsoils. 2.3a | Sandy Soil Indicators Hydric soil indicators occur in three groups. Indicators for “All Soils”, or A indicators, are used for any soil regardless of texture. Indicators for “Sandy Soils”, or S indicators, are used for soil layers with USDA textures of loamy fine sand or coarser. The last group of indicators are for “Loamy or Clayey Soils”, of F indicators, used for soil layers with USDA textures of loamy very fine sand and finer. In this video, we will be discussing sandy soil indicators for hydric soils. Many of the same characteristics, such as the accumulation of organic matter on the soil surface and redoximorphic features in subsoil layers, are used to identify and delineate sandy wetland soils. However, slight changes in coloration and horizon thickness/depth where hydric soil indicators develop in sandy wetlands required the use of different indicators for sandy soils. For example, organic matter accumulation of peat or mucky peat needs to be greater than 2 cm in sandy wetland soils in the Midwest US to be considered a hydric soil according to sandy soil indicators S2 and S3. This is in contract to Indicator A10 which allows for only 2 cm of muck to act as an indicator for hydric soils. Similarly, mucky mineral soil is used as a hydric soil indicator in the southeast US for all soil types (A7); however, this indicator can be applied to all other US wetlands if this 5 cm of mucky mineral soil occurs in sandy soils (S1). Commented [CD30]: Figure 14 in Midwest Regional Supplement In addition to organic matter, redoximorphic features such as a gleyed matrix or redox concentrations can also be used to identify hydric sandy soils. For areas outside of Alaska, a gleyed matrix observed within 15 cm of the soil surface can be used in sandy soils (Indicator S4) which is nearer to the surface compared to the 30 cm needs for loamy or clayey soils. Redox concentrations observed as orangish-red soft masses or pore linings can also be used to identify sandy hydric soils. Indicator S5, sandy redox, Commented [CD31]: Figure 16 in Midwest Supplement requires redox concentrations to begin closer to the soil surface, 15 cm compared to 20 cm for loamy soils or 30 cm for all soils in Alaska, but need the least amount of redox concentrations within this layer, only 2% redox for sandy soils compared to 2-5% in loamy soils or 10% in Alaska. Redox concentrations are also used for hydric soil identification in wetlands near shorelines near the Great Lakes because naturally occurring high chroma sandy soil is usually considered non-hydric soils. However, sandy soil indicator S11 (high chroma sands) allows for a soil layer with chroma of 4 or greater if this layer has 2% redox concentrations. This redox concentration is important as nearby upland areas tend to meet the chroma requirement, but the redox concentration is absent. An indicator that is unique to sandy soils, and a very common hydric soil indicator in the midwestern united states, is the presence of a stripped matrix. A stripped matrix is a layer of soil starting within 15 Commented [CD32]: Figure 17 in Midwest Supplement cm of the soil surface in which iron/manganese oxides and organic matter have been stripped from the matrix and the primary base color of the soil material has been exposed. The stripped areas are typically 1-3 cm in size, and commonly have a value of 5 (or more) and a chroma of less than 2. However, there are no specific color requirements for this indicator. The mobilization and translocation of the oxides and organic matter are the important processes and results in splotchy coated and uncoated soil areas. Similarly, indicator S8 (polyvalue below surface), also results from the mobilization and translocation of Commented [CD33]: Figure S8 in Field Indicators of organic matter within sandy soils. This indicator applies to soils with a very dark surface less than 10 cm Hydric Soils in depth that is then underlain by layer of sandy soil that contains organic matter that has been differentially distributed within the soil by water movement. In conclusion, sandy soil indicators use many of the same type of hydric soil indicators used for any soil texture including redox concentrations and organic matter build-up. However, important distinctions between soil horizon depths, content and color exist due to the reduced water-holding capability of sandy soils and increased ability of organic matter to percolate through soil pores. These specifications need to be followed to correctly delineate between hydric and non-hydric sandy soils. 2.3b | Loamy Soil Indicators The last group of hydric soil indicators are for “Loamy or Clayey Soils”, of F indicators, used for soil layers with USDA textures of loamy very fine sand and finer. Soil texture plays a significant role in its ability to retain water and become a hydric soil. Soils with fine texture, such as silt or clay materials, result in a soil with smaller pore spaces as the soil particles can fit closer together. Water can be held above the water table within these pores through tension and can saturate upper horizons of the soil. The zone saturated above the water table is called the capillary fringe. The thickness of this capillary fringe is strongly correlated with soil texture. Clayey soils have the smallest pore spaces and thickest capillary fringe meaning they can hold water under tension at higher levels than sandy soils. This allows loamy and clayey soils to be hydric soils even in areas with considerable slopes as the fine texture allows soils to be saturated for longer periods. The specific characteristics of loamy and clayey soils resulted in a list of hydric soil indicators used specifically for loamy very fine sand and finer. As of the 2018 USDA’s Field Indicators of Hydric Soils in the United States document, there are currently 17 hydric soil indicators for loamy and clayey soils. Six of these indicators are widely applicable throughout the US, while the other 11 are used in specific regions of the US where highly specialized hydrological, geochemical, and biological processes result in hydric soils. We will focus on the six indicators that can be used in most land resource regions of the United States and highlight a few other examples of loamy and clayey hydric soil indicators. Unless otherwise noted, all mineral layers above any of the layers meeting an F indicator must have a dominant chroma of 2 or less, or the layer with a dominant chroma greater than 2 must be less than 15 cm thick. The first loamy or clayey hydric soil indicator, F1 – loamy mucky mineral, can be applied to most soils outside of Alaska or the eastern coast of the US. This indicator requires the organic carbon content of a soil to be at least 8 – 18% depending on the amount of clay. For loamy/clayey soils, a 10 cm thick layer of mucky mineral material that starts within 15 cm of the soil surface is needed. In the midwestern US, this indicator is commonly associated with the interiors of prairie potholes. The next two indicators rely on the observation of redox depletions within hydric soils. Loamy soils that have a gleyed matrix (indicator F2), or a depleted matrix (indicator F3), are excellent indicators that reducing conditions existed within the soil for long enough periods to cause anaerobic conditions in the surface layer. In loamy soils, a gleyed matrix must begin within 30 cm of the soil surface and match Commented [CD34]: Figure 18 in Midwest Supplement coloration on the gley pages of the Munsell Soil Color Charts. The loamy gleyed matrix, F2 indicator, is typically not observed near the wetland-upland boundary due to the duration of water saturation that is needed to produce a gleyed matrix. In contrast, Indicator F3 – Depleted Matrix, is one of the most Commented [CD35]: Figure 19 in Midwest Supplement observed hydric soil indicators at wetland boundaries. A depleted matrix results from a cycle of wet and dry periods within wetland soils resulting in redoximorphic features developing in the subsoil. This subsoil is typically dull, low chroma (2 or less) and light in color (value of 4 or more). Redoximorphic features, such as a depleted matrix and redox concentrations, are also used to identify loamy or clayey soils that contain dark-colored surface layers. This indicator often occurs in prairie soils (mollisols) and at the boundaries of pothole wetlands. Redox concentrations, observed as either soft masses or along pore linings, are used in loamy indicator F6 to identify hydric soils with dark surface Commented [CD36]: Figure 30 in Field Indicators for layers. Organic matter can mask some or all the redox concentrations in the dark surface layer, so careful Hydric Soils examination is required. It may also be necessary to let soil samples dry at least to a moist condition for redox conditions to become visible. The amount of redox concentrations needed in this dark layer ranges from 2-5% of the matrix and depends on the coloration of the surrounding matrix. Redox depletions can also be observed in dark surface layers of loamy/clayey soils, as observed for hydric soil indicator F7 – Depleted Dark Surface. Redox depletions must occur within either 10-20% of the soil Commented [CD37]: Figure 22 in Midwest Supplement matrix and have a dull, whitish color (value of 5 or more, chroma of 2 or less). If a dark surface layer has depletions, it most likely also has concentrations and will meet the requirements of loamy indicator F6 (redox dark surface). Lastly, there are a variety of loamy/clayey hydric soil indicators specific to wetland type or region. For example, indicator F8 is used throughout the US (except Alaska) to identify hydric soils in depressional Commented [CD38]: Figure 23 in Midwest Supplement wetlands such as vernal pools, playa lakes, rainwater basins and potholes. This indicator requires a 5 cm thick layer that contains 5% or more distinct or prominent redox concentrations. Note that there is no color requirement for the soil matrix, just a 5 cm soil horizon thickness that starts within 10 cm of the soil surface. Several indicators are specific to the Mississippi River delta and floodplains in the southeastern part of the US. For example, indicator F12 is used in floodplain wetlands near the Commented [CD39]: Figure 36 in Field Indicators of Mississippi River and relies on the observation of iron and manganese masses to identify hydric soils. Hydric Soils Unlike most hydric soils, manganese oxides can dominate the redox concentrations in these soils which results in low value and chroma masses in the soil that look black rather than reddish-orange. Other indicators, such as F20 (anomalous bright loamy soils) or F21 (red parent material), might be needed in Commented [CD40]: Figure 39 and 40 in Field Indicators of Hydric Soils specific regions of the US due to natural soil matrix coloration that might mask redoximorphic features or result in soil matrix coloration that is too bright or pigmented for typical hydric soil colors. As such, wetland delineators need to pay special attention to the variety of hydric soil indicators that can be used in their specific region of the US. 2.4 | Module Wrap-up Most regulated wetlands must have three essential components: hydrophytic vegetation, wetland hydrology, and hydric soils. The formation of hydric soils under conditions of saturation, flooding or ponding typically observed in wetlands results in anaerobic conditions occurring within the upper part of the soil profile. These anaerobic soil conditions are responsible for many of the important ecosystem services that wetlands provide so being able to accurately document hydric soils is important for identifying and delineating the boundaries of wetlands. We began this module by discussing why and how hydric soils are assessed for wetland delineation purposes. Regulators must provide evidence that a soil fulfills the definition of a hydric soil as defined in the 1987 USACE Wetland Delineation Manual. Preliminary assessments using the Web Soil Survey and other wetland mapping tools can help determine where hydric soils might exist on a field site; however, on-site investigation is usually necessary to verify and delineate hydric soil boundaries. We then discussed the use of field indicators to identify and delineate hydric soils following the guide developed and tested by the USDA Natural Resources Conservation Service. Hydric soil indicators are formed predominantly by the accumulation or loss of iron, manganese, sulfur, or carbon compounds under anerobic conditions. To document these hydric soil indicators, wetland delineators need to identify soil horizon depth and content (organic or mineral soil), texture, and coloration. Hydric soils tend to have: an accumulation of organic matter (peat or muck), a gleyed/depleted matrix that results from redox depletions, or reddish-orange mottles in the soils or near root channels that results from redox concentrations. Finally, we discussed the difference between sandy soils and loamy/clayey soils and described the types of hydric soil indicators that are used in these different types of soil texture. Sandy soils tend to have large pore sizes which can result in organic matter percolating into the subsoil layers. Loamy and clayey soils tend to hold water better than sandy soils which results in different types of soil indicators. The ability to effectively and correctly use these soil indicators to identify hydric soils is incredibly important, as mistakes can lead to improper wetland delineations and loss of essential wetland habitat for plants, animals, and humans. As such, it is important to take special care when sampling soils for wetland delineation and follow the procedures outlined by the US Army Corps of Engineers and the USDA Natural Resources Conservation Service.