Search

This module begins with a review of redox reactions and redoximorphic features. Reduction and concurrent oxidation (redox) are the dominant chemical processes taking place in wetland soils. There are abiological and biological driven redox reactions in wetland soils. The module will focus on the reactions driven by microbial breakdown of organic matter in soils under saturated conditions that lead to unique anaerobic conditions that meet the hydric soil definition of USDA. The redox reactions lead to mobilization of soluble Fe and Mn (depletion zones and surfaces) and subsequent reoxidation (concentration zones and surfaces), collectively called redoximorphic features. Redox feature types are identified through images. Description of the features will be briefly reviewed, in preparation for use as components of field indicators of hydric soils.

The module focuses on wetland functions attributed directly to hydric soils. Functions are the biological, chemical, and physical processes that occur in wetlands. Hydric soils play a direct role in the wetland functions of water retention (short term and long term), sedimentation, carbon sequestration and biogeochemical cycling of nutrients. Due to their capacity to become anaerobic close to the surface, hydric soils support unique plant communities and wildlife habitat unlikely to be found in uplands. Functional capacity is influenced by landscape position, hydrologic characteristics, and soil characteristics. Soil characteristics that affect wetland functions include porosity, permeability, drainage class/hydroperiod, organic matter content, slope, micro-topography, and chemical properties.

The module focuses on the Hydric Soil Technical Standard. The Hydric Soil Technical Standard (HSTS) provides a quantitative method of determining if a soil meets the definition of a hydric soil. The HSTS can be used to: 1) Identify a soils forming as hydric soils when a field indicator may not be present (e.g. wetland creation sites, problematic hydric soils); 2) Evaluate the current functional status of a hydric soil (e.g. change to hydrology); and 3) Propose changes to hydric soil indicators (e.g. expanding jurisdictional extent of an indicator, revising an existing indicator, adding a newly developed indicator). The HSTS requires quantitative measurements showing the soil becomes saturated and anaerobic in the upper part during normal precipitation years.

The module focuses on typical hydric soil morphologies associated with major wetland types-tidal marshes, peat bogs, perennially-inundated swamps, mineral soil flats, floodplains, depressions, and slope wetlands. The roles of landscape position, hydroperiod, and hydrodynamics on soil morphology will be emphasized. Soil morphology is impacted by the duration of inundation, and the seasonal vertical fluctuations in water tables. Water collecting surfaces such as closed depressions facilitate ponding; water shedding surfaces on slopes promote rapid movement of surface water through the wetland. Peat bogs are hydrologically isolated and permanently saturated; floodplains receive hydrologic inputs from overbank flow and groundwater discharge, and exhibit short-term inundation. Therefore, because of differences in landscape position and associated hydrologic characteristics different types of wetlands produce distinctive hydric soils.

The module focuses on problematic landscapes and parent materials. Most hydric soils exhibit certain common morphological characteristics that allow you to identify them as a soil that meets the hydric soil definition. Problem soils are hydric soils that do not exhibit these common hydric soil morphologies. The lack of a morphological indicator despite the soil developing anaerobic conditions in the upper part can be caused by many things including problematic parent material, certain environmental conditions, and the replenishment of iron oxides or new sediments in the upper part of the soil. For some problem soils, alternate morphologies that can only be used in specific problematic situations have been developed. For those problematic situations where an indicator has not been identified, alternative methods of identifying the soil as hydric must be employed. These techniques are outlined in chapter 5 of the Corps of Engineers Regional Supplements.

The module focuses on the Hydrogeomorphic (HGM) system and hydric soils. The classification of wetlands in the HGM system is based on landscape position, dominant water source, and hydrodynamics – the magnitude and direction of water inflow and outflow. Information on these parameters is contained in soils information, which is housed in the Web Soil Survey and the soils database. While HGM interpretations are not provided directly, knowledge of soils attributes can be readily applied to make HGM class and sub-class designations. These attributes can be used to aggregate soil map units into HGM site concepts. A site concept is valid when all map units have similar water budgets, are in the same watershed position, and have the same water movement vectors. The HGM system also requires the definition of a Reference Domain, within which HGM classifications are valid. Since soil map unit concepts are generally consistent within a Major Land Resource Area, this boundary is the first selection for the Reference Domain. Since landscape position is more meaningfully defined as watershed position, the HUC-12 watershed scale is useful for heads-up testing of map unit aggregations. Since map units often need to be either aggregated, or disaggregated into components, the use of Digital Elevation Data is useful for performing these “lumping” or “splitting” operations. The final result should be a HGM sub-class with associated map units, or components, which can be mapped across the MLRA extent, and which is useful for land managers and conservation planners.

The module focuses on using the NTCHS Indicators of Hydric Soils (Version 7.0) for onsite decision making about soils in the field. This module shares what resources you will need to use the indicators, how to access the electronic resources (including guides, errata sheets and more). The module will help participants understand the definitions of key terms for this work, as well as show how to combine the use of these resources effectively to aid decision making in the field. This module brings together many of the main concepts from earlier modules (e.g. soil textures, colors, landforms) and helps the participant understand their application in an applied setting. The module will cover important indicator caveats and provide other useful guidance for working with NTCHS Indicators of Hydric Soils in the field. Note: If you are not familiar with the basics of hydric soils, we recommend that you complete the earlier modules in the series prior to participating in Modules 10, 11 and 12 to optimize your learning experience.

The module focuses on how wetland professionals can use soil science principles in onsite decision making for work in the areas of wetland mitigation, voluntary wetland restoration and wetland creation. The module identifies common fallacies about wetland creation and reviews wetland soil reconstruction guidance protocols. The module includes a review of learning from 20 years of collaborative research on the limitations of created wetland soils. Note: If you are not familiar with the basics of hydric soils, we recommend that you complete the earlier modules in the series prior to participating in Modules 10, 11 and 12 to optimize your learning experience.