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Hydropedology: Genesis, Properties, and Distribution of Hydromorphic Soils
Department of Plant and Soil Sciences
Because of the environmental and economic importance of riverine resources as well as wetlands in the region, pedologists working together under NE-1021 have been developing expertise in the identification, characterization, classification, and land use interpretations for hydromorphic soils (soils that have formed in the presence of excess water) within these areas. The key linkage among these soils and resources across the landscape is the hydrology. Understanding the integrated effects of the hydrologically-driven processes associated with saturation, inundation, and transport across the landscape is critical for the development of numerous soil based land use interpretations. For example, understanding soil morphology/water table relationships is critical in developing interpretations for the construction of buildings and roads, surface application of waste, the use of on-site waste disposal systems, and the function of various wetlands in storing carbon (C) and providing beneficial ecological services. Wetland delineation is a multi-million dollar industry.
New techniques in landscape modeling are allowing investigators to identify wetlands using geospatial analysis and remote sensing (Pantaleoni et al., 2011a and 2011b). The improved mapping of wetlands is intended to improve the comprehensive National Wetland Inventory maps used as a basis for legislative decisions and wetland monitoring. Identification of hydric soils is essential in the on-site delineation process. Field indicators of hydric soils were developed to facilitate jurisdictional determinations of wetlands by identifying hydric soils (USDA-NRCS, 2006). Several field indicators rely on the quantity of soil C and may prove useful in predicting the amount of soil C in the surface of wetland soils. Some hydric soils, however, fail to develop the typical morphology found in most wetland soils. These so called "problem hydric soils" occur across the entire region and need to be addressed from a regional perspective (Vepraskas and Sprecher, 1997; Castenson, 2004; Zurheide, 2011).
Across the United States efforts have been ongoing to develop regional supplements to the ACOE Wetland Delineation Manual (Environmental Laboratory, 1987). These supplements would provide guidelines for identifying hydric soils using regional hydric soil indicators. Working within the proposed regional framework will allow for testing of hypotheses across climatic gradients, across parent material types (coastal plain, residual, and glacial), and among different types and settings of coastal, riverine, and subaqueous soils. Testing these hypotheses is not possible for a single investigator working within a single state and must be done at the regional level. Addressing these questions within a regional framework is also critical because the major agencies that use the soils information that pedologists collect, such as USDA-NRCS, USACOE, USEPA, all work in a region-wide context. Data gathered, relationships that are established, and interpretations that are made are therefore much more meaningful to the user if the science was tested within a region-wide context.
2011 Project Description
Appalachian mountain wetlands are uncommon and diverse ecosystems however, they are often susceptible to extensive alteration or destruction due to coal mining, highway construction, and quarrying. This study aimed to determine vegetation composition at three pristine wetlands and establish relationships with previously reported hydrologic, edaphic, and porewater characteristics to provide baseline data that could enhance wetland mitigation or restoration projects.
Herbaceous vegetation was assessed by visually estimating percent cover for bryophyte and vascular species and by determining stem density for vascular taxa using 1 m2 quadrats located along transects. Multiple response permutation procedures (MRPP) based upon importance values confirmed that species composition differed significantly (P < 0.001) among the sites. Nonmetric multi-dimensional scaling (NMDS) indicated that piezometric water levels, soil properties, and porewater chemical composition influenced plant community composition.
The first wetland (Martins Fork) was primarily dominated by Osmunda ferns and Sphagnum palustre in response to variable soil saturation levels and weak minerotrophy. The second wetland (Kentenia) was overwhelmingly dominated by Sphagnum palustre due to persistently high water levels. Vegetation at the third wetland (Four Level) was distinguished by strongly dominant Scirpus polyphyllus and Glyceria striata and responded to higher soil and porewater base richness as well as distinct sunny and shaded areas. The diverse vegetation and physico-chemical characteristics indicate that these sites, although small in size, support regional biodiversity and are also potential reference wetlands.
Plant Community assessments of the wetlands suggested each site to be floristically unique. Variable soil and porewater base richness and water level gradients diversely affected plant community associations. All three wetlands all exceeded the regulatory criterion for vegetation by having more than 80% of the dominant taxa at each site within the obligate wetland (OBL) or facultative wetland (FACW) wetland indicator categories for the northeast region. Although these sites are in fairly close proximity to one another, striking differences in vegetation composition reflected varying hydrology, edaphic characteristics, and porewater composition.
A range of environmental properties including comparatively dry soil conditions and weak minerotrophy at Martins Fork, persistent high water levels at Kentenia, and more minerotrophic soil and porewater at Four Level was associated with significant differences in plant community composition. The diversity shown among these wetlands illustrates their contribution to regional biodiversity as well as their value as reference sites for mitigation or restoration efforts.
Thompson, Y.L., E.M. D Angelo, A.D. Karathanasis, and B. Sandefur. 2011. Plant Community Composition as a Function of Geochemistry and Hydrology in three Appalachian Wetlands. Ecohydrology (DOI:10.1002/eco.228).