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Redoximorphic Features and Seasonal Water Table Relations, Upper Coastal Plain, Virginia
Abstract
Redoximorphic features are routinely used by soil scientists to predict the depth, duration, and timing of soil saturation. Yet, there are few published studies which examine the validity of commonly held assumptions regarding relationships between periods of soil saturation and the occurrence of redoximorphic features. We initiated this study to relate certain redoximorphic features to seasonal water table fluctuations in an Upper Coastal Plain landscape in Virginia. Soils were sampled along seven catenas. Pedons were auger-sampled on 15-m spacings to a depth of 150 cm, and classified in the field using National Cooperative Soil Survey (NCSS) methods. Water-table monitoring wells were established in 33 pedons spanning the range of observed soil drainage classes. Water table elevations were recorded weekly for 3 yr, beginning in March 1991. Seasonal high-water tables occurred during February and March, regardless of soil drainage class. Seasonal low-water tables occurred during September and October. We used simple linear regression to quantify the relationships between: (i) seasonal high-water tables and the depth to the shallowest Fe depletions or Fe-depleted matrices of Munsell chroma ≤2(r2=0.73), and (ii) the seasonal high-water tables and the depth to the shallowest Fe concentrations of chroma ≥6 (r2= 0.64). Seasonal high-water tables in welland moderately well-drained soils rose above the shallowest occurring redoximorphic features for periods of up to 30 d. Conversely, the highest water table elevations in poorly and very poorly drained soils often occurred below the depth of the shallowest Fe-depleted matrices.
... Similarly featured soil horizons were saturated for approximately the same amount of time in any given month, regardless of soil drainage class. However, the authors found that the frequency of saturation of soil materials at a given height above the featured horizon varied by drainage class, with more frequent saturation of materials in somewhat poorly drained soils> moderately well-drained soils> well-drained soils (Genthner et al., 1998). ...
... At this condition redox processes may continue throughout the peds. During this time period, the formation of highchroma Fe concentrations could occur only in the capillary fringe, where there is presumably considerable microsite variation in the soil redox environment (Genthner et al., 1998). This is called Endosaturation. ...
... Fe oxides hypocoating around the voids showed reduced condition interior the peds which caused the migration of Fe oxides to macropores. The occurrence of some high chroma Fe concentrations at depths slightly above the shallowest Fe depletions may indicate that some Fe also diffuses upward along saturated macropores and is precipitated at the interface between oxidized and reduced portions of the soil profile (Genthner et al., 1998). Figure 3c, shows precipitated Iron oxides on external ped surfaces between oxidized and reduced part of horizon. ...
Land drainage is an operation which increases land production and ensures sustainable land use. Soil scientists attempt to arrive a scientific procedure for assessing the efficiency of drainage system, among the correlation between soil morphological characteristics, mainly soil color and redoximorphic features and water table behavior. The aims of this study were investigating the efficiency of drainage system through soil morphological and micromorphological characteristics and judge about the existence of episaturation or endosaturation, in Khuzestan sugarcane cultivated lands after years of artificial drainage. 5 pedons were dug and characterized based on their morphological and micromorphological features. The characteristics of redoximorphic features showed no considerable differences in drainage class between artificial drained field and virgin land. The only contrast was shallower ground water table in virgin lands. 4 pedons were classified as somewhat poorly drained and one as well drained. These drainage classes show that despite the existence of artificial drainage system, the problems haven't been eliminated yet. All pedons showed horizons with low chroma colours in deeper horizons and different types of redoximorphic feature. Micromorphological observations proved that the lands were involved in Endosaturation due to high ground water level.
... Preliminary site designs frequently use the depth to significant redox depletions/concentrations to estimate the top of the winter high saturated zone along with depth to the complete lack of redox concentrations to indicate the maximum depth of summer water table draw-down. However, great caution must be taken in the interpretation of the type and abundance of redoximorphic features with respect to the length of duration of seasonal saturation at a given depth (Genthner et al., 1998). We strongly believe that wherever possible, an appropriate array of water table monitoring wells and nested piezometers should be installed at any proposed mitigation site and monitored for at least one full fall/winter/spring season to establish the local seasonal hydroperiod (high/low cycle), ground water gradients, and epi-versus endosaturation. ...
... We strongly believe that wherever possible, an appropriate array of water table monitoring wells and nested piezometers should be installed at any proposed mitigation site and monitored for at least one full fall/winter/spring season to establish the local seasonal hydroperiod (high/low cycle), ground water gradients, and epi-versus endosaturation. The level and duration of winter/spring saturation is particularly important to mitigation site design, and fortunately, for endosaturated soils, winter high levels are much more consistent from year-to-year than the dynamics of the summer/fall water table (Genthner et al., 1998). ...
... The identifiable color patterns that result from these processes enable users to make predictions concerning the depth to the SHWT (Latshaw and Thompson, 1968; Daniels et al., 1971; Simonson and Boersma, 1972; Franzmeier et al., 1983; Cogger and Kennedy, 1991; James and Fenton, 1993; Veneman et al., 1998). Although the use of RMFs to identify a depth to the SHWT is a proven approach, a number of studies have observed saturated soil horizons without RMFs (Daniels et al., 1973; Franzmeier et al., 1983; Pickering and Veneman, 1984; Evans and Franzmeier, 1986; Genthner et al., 1998; Calmon et al., 1998). These studies suggested that the presence of RMFs is not necessarily indicative of the depth of the water table, but how long the water table is at that depth or above (cumulative saturation). ...
... at there is not a standard method to define a SHWT. The difficulty can be seen in a typical hydrograph where the depth of the water table varies widely during the wet season and that these variations change from year to year (Fig. 1). To account for this fluctuation, some researchers have used monthly averages to define seasonal water table levels. Genthner et al. (1998) defined the SHWT as the average depth to the water table during the month of March, averaged over the 3 yr of the study. In a study on the coastal plain of Maryland, Galusky et al. (1998) aggregated 5 yr of water table measurements, taken four to five times monthly, to produce averages monthly water table levels. In this study, we defin ...
Although redoximorphic features (RMFs) are commonly used in place of direct observation to estimate the depth of the seasonal high water table (SHWT), little is known about the relationships between RMFs and the duration of the water table. The objective of this study was to gain a better understanding of how the expression of RMFs relates to the depth and duration of the water table in moderately well-drained soils of southern New England. The 20 soils studied included Dystrudepts, Quartzipsamments, and Psammaquents; of these, 17 met the criteria for Oxyaquic (8) or Aquic (9) subgroup classification. Water table levels were monitored for 18 mo from February to July of the following year to compare the depth and cumulative duration of the water table (cumulative saturation) to RMFs within soil horizons. Average seasonal high water table level (ASHWT) was correlated (p < 0.05) to the depth of the first loamy horizon with >2% RMFs (r² = 0.65-0.72). Water table levels occurred within horizons with no RMFs for as much as 13% of the 18 mo study period. Mean cumulative saturation for soils with textures finer than loamy sand ranged from 3% for horizons with no RMFs to 36% for horizons with a depleted matrix. For horizons with textures of loamy sand and coarser, the mean cumulative saturation ranged from 8% for horizons with no RMFs to 45% for horizons with >2% depletions. (Percentage of cumulative saturation would have likely been less if we monitored for a full 2 yr, as the late summer and fall of the second year were not monitored.) Our results suggest that the abundance of RMFs increases as the percentage of time the water table is present within a horizon increases. Additionally, coarse-textured horizons are less expressive in regards to RMF abundance than are loamy-textured horizons with similar cumulative saturation. For land-use decisions, soil morphology should be used to provide both an estimate of the depths of a defined SHWT and cumulative saturation.
... Individual hydrologic variables are often inadequate for simply relating RMFs to hydrology, as a combination of various hydrological and soil physicochemical attributes like soil texture, pH, redox potentials, and historic rainfall and water table levels influence RMF formation (Genthner et al. 1998;Jacobs et al. 2002;He et al. 2003;Vepraskas 2015); however, multiple indicators of hydrologic and soil physicochemical settings may be apt for the genesis of RMF color classes. Certain hydro-physicochemical (HP) soil attributes are not only ubiquitously and simply measured for various applications of soil and ecological research (Bestelmeyer et al. 2009;Kachergis et al. 2011), but also hold evidenced relationships to wetland development, including RMFs. ...
We assessed hydro-physicochemical (HP) settings and soil color attributes including redoximorphic features (RMFs) at four forested wetlands in Northern Virginia, USA, to identify whether four simply measurable HP attributes—inundation/saturation frequency, bulk density, soil moisture, and percent sand—can provide an explanatory framework for characterizing and classifying soil color attributes related to hydric soil field indicators. Study plots (n = 16) were grouped by site for initial characterizations and comparisons of HP (n = 4) and color attributes (n = 11); each attribute was additionally characterized and compared between three HP-based clusters formulated through k-means clustering analysis. Whereas only one HP attribute (inundation/saturation frequency) significantly differed between sites, all HP attributes but percent sand differed between HP-based clusters (p < 0.05), with PCA Dimensions 1 and 2 explaining over 80% of variability in plot HP attributes. Moreover, more sets of color attributes were significantly different when plots were grouped by HP-based cluster (n = 5: frequency of concentrations, non-matrix color count, hue, chroma, and depth to concentrations) compared to by site (n = 3: value, frequency of depleted matrices, depth to depletions) (p < 0.10). Simply measurable HP attributes are thus closely associated with certain soil RMF and color characteristics beyond site identity, potentially serving as a suite of measurements that can be adopted to assess and monitor redoximorphic features indicative of wetland soils.
... The relation between the reduction horizon and the MLW was good. Also, Genthner et al. (1998) reported underestimation of high water levels and attributed this to the lack of easily oxidisable organic carbon. Overestimations have also been reported (Jacobs et al., 2002), but in relict landscape features in regions which are not comparable with the Belgian situation. ...
The predictive quality of the current drainage class map of Flanders was evaluated using data from two monitoring networks: one with good spatial coverage but poor temporal coverage and another with better temporal but poor spatial coverage. We combine both networks to obtain 1678 point predictions for mean highest water (MHW) and mean lowest water (MLW) tables by applying time series modelling and total least squares regression. The resulting MHW and MLW point data set was used to evaluate the currency of the existing map and to identify regional differences. The quality of the current map is moderate, and large differences occur between regions. Especially the Campine region shows large and systematic differences, whereas the southeastern hills and chalk–loam region is relatively accurate. If more weight is given to errors in the wetter drainage classes, about 50% of the area of Flanders would benefit from remapping. Copyright © 2011 John Wiley & Sons, Ltd.
... The main driver of these developments seems to be the relationship between the ochre and pale-brown volumes. Water percolates more rapidly through the white-grey and palebrown volumes than through the ochre ones (Frison et al., 2009), which results in more favourable conditions for particle eluviation in white-grey and pale-brown volumes and causes redox processes in ochre volume because these processes require long contact times for the reductive phase and consecutive bleaching to occur (Brouwer and Fitzpatrick, 2002; Genthner et al., 1998; He et al., 2003; Morgan and Stolt, 2006). This difference is enhanced by the connectivity of these volumes. ...
Soils are a non-renewable resource and evolve through time in response to changes in land-use and environmental conditions. To predict this soil evolution requires the development of mechanistic modelling. Only a few attempts of this kind exist in the literature, and these often use an extremely simplified representation of soil structure, with the soil being frequently considered as a succession of homogeneous “boxes”. In this paper we have quantified the evolution of the soil structure during pedogenesis using image analysis. This analysis was performed along a sequence of morphological degradation in an Albeluvisol perpendicular to a drain. These soils, which are commonplace in Europe, are characterised by horizons consisting in a juxtaposition of soil volumes differing in texture (silty to clayey) and colour (ochre, pale-brown, white-grey and black). The image analysis approach was based on these differences in colour and combined i) a supervised training method using ERDAS IMAGINE® to assign the different pixels to the different types of soil volumes and ii) ARCInfo™ for characterisation of the morphology of the different soil volumes. The organisation of the different volumes in space suggests that ochre volume is transformed to pale-brown one and then to grey-white one, whilst black volume is formed within the residual ochre one, due to precipitation of Mn. As the process progresses along the drainage sequence, progressive indentation and final disintegration of the ochre volume are responsible for the release of the black volume into the pale-brown matrix. Ochre volume alteration takes place mainly at the border of the volume which is indicated by the geometry of the pale-brown and ochre volumes. Finally, the formation of the white-grey volume from the pale-brown one occurs in the core of the latter, mainly by eluviation, and is centripetal. We conclude that soil structure needs to be considered when modelling pedogenetic soil evolution.
... The presence of SRFs has been used by pedologists and field scientists to infer soil moisture regimes for approximately 60 years (Veneman et al., 1998). Quantitative relationships between water table depths and soil redoximorphic features have been documented by various authors (e.g., Zampella, 1994;Genthner et al., 1998;He et al., 2003;and Morgan and Stolt, 2006), suggesting monitoring of water tables may be substituted by field description of SRFs (Vepraskas and Caldwell, 2008). This association of SRFs with soil hydrology has provided U.S. agricultural agencies with field methods necessary for identifying wetlands and enforcing farm commodity programs (e.g., 1985 USDA Farm Bill Swampbuster provisions). ...
Photography has been a welcome tool in documenting and conveying qualitative soil information. When coupled with image analysis software, the usefulness of digital cameras can be increased to advance the field of micropedology. The determination of a representative elementary area (REA) still remains a critical information need for soil scientists so that field measurements are independent of sample size and account for spatial heterogeneity. An objective of this study was to define and determine an REA for Low Chroma and High Chroma soil redoximorphic features (SRFs) present in claypan soils of northeastern Missouri, USA using a digital camera and image classification techniques. An additional objective was to examine REA differences between these two SRF types, soil depths, and landscape positions to highlight sampling considerations when quantifying SRFs in the field. Three metrics were chosen to quantify SRF heterogeneity, including percent occurrence, mean Euclidean distance, and the Interspersion/Juxtaposition Index. The relative change in these metrics was determined for 16 image sizes ranging from 2.5 cm(2) to 40 cm(2) and used to identify an REA. Results showed REAs (mean +/- SE) for Low Chroma (17.7 cm(2) +/- 0.4) and High Chroma (25.4 cm(2) +/- 0.7) were significantly different (alpha = 0.05). Further review of REAs indicated large sampling diameters (>8 cm) are necessary to simultaneously capture REAs of Low Chroma and High Chroma SRFs. When SRFs were considered separately, a >= 5 cm diameter core is recommended to reach an REA for Low Chroma, allowing accurate quantification for soil classification purposes and hydric soil determinations. Federal and state agencies requiring quantifiable SRF measures for land management decisions may greatly benefit from determining these minimum measurement scales, ensuring appropriate data collection methods in the future.
... More recently, measured and predicted water table depths have been correlated with SRF estimates of presence and abundance made by human observers (Genthner et al., 1998;He et al., 2003;Morgan and Stolt, 2006). These findings suggest that SRF estimations made in the field by human observers can substitute for monitoring soil water regimes in legal designations of wetlands (Vepraskas and Caldwell, 2008a,b). ...
Soil redoximorphic features (SRFs) have provided scientists and land managers with insight into relative soil moisture for approximately 60 years. The overall objective of this study was to develop a new method of SRF identification and quantification from soil cores using a digital camera and image classification software. Additional objectives included a determination of soil moisture effects on quantified SRFs and image processing effects on interpretation of SRF metrics. Eighteen horizons from selected landscapes in the Central Claypan Area, northcentral Missouri, USA were photographed from exposed soil cores under controlled light conditions. A 20 cm2 area was used for SRF quantification following a determination of the initial gravimetric water content of horizon faces. Overall color determination accuracy was 99.6% based on Munsell soil color groupings used for SRF identification. Rewetting of air-dry horizon faces by successive application of 1 mL of deionized water demonstrated little change in identified SRFs after seven applications. Mean change in identified Low Chroma and High Chroma SRFs between the seventh and tenth rewetting sequences was 2% (SD ± 4) and 0.03% (SD ± 0.3), respectively. However, ten of eighteen horizons contained a greater area of Low Chroma after ten rewetting sequences compared to the same horizon at the initial moisture state. Metrics characterizing SRF boundaries, shapes, number of SRFs, and mean area of SRFs were sensitive to post-classification image smoothing. Methods demonstrated by this study provide an opportunity to better integrate pedology with other related earth sciences by allowing standardized quantification of SRFs as well as a determination of human error associated with current visual estimates.
While the Munsell Soil Color Chart (MSCC) is the most frequently used, well-established field method for reading soil color, the Nix Color Sensor (NCS) is an inexpensive, app-based alternative that can complement or potentially substitute for the MSCC. Soils were collected and their colors were measured from four forested sites across Northern Virginia within the Chesapeake Bay Watershed with both the MSCC and NCS. Three MSCC variables and 15 NCS variables were collected in the field; a methodology was established to use these "measured" (M) variables to derive 9 NCS calculated (C) variables. A stepwise correlation identified NCS variables most suitable for relating the NCS to each of the MSCC attributes: hue (H), value (V), and chroma (CM). Ultimately, H, V, and CM were deemed to be best represented by HRGB calculated from the RGB color space (ρ = 0.56), L from the CIE-Lab color space (ρ = 0.73), and ẑ = Z/(X+Y+Z) from the XYZ color space (ρ = -0.80), respectively (p < 0.001). The corresponding explanatory powers of final NCS variables (i.e., HRGB, L, and ẑ) for H, V, and CM are 26%, 54%, and 62%, respectively (p < 0.01). Significant differences in ẑ between soils identified as hydric and nonhydric, but lack of nonoverlapping ranges, indicate a potential for the NCS to complement the MSCC in assessing wetland soil color in an accessible and reproducible manner, including hydric soil identifications for wetland delineation practices. Further study with more data over various types of soils is necessary to establish stronger relationships between the NCS and MSCC. Nonetheless, the method of characterizing soil color variables from the two field methods presented in the study can serve as a template for future studies or environmental education programs desiring to use the NCS as a complement to the MSCC.
The identification of the depth of seasonal saturation in soils is critical for a multitude of land uses including the siting and design of septic systems and delineation of wetlands. Often 2 chroma redox depletions are used to make this determination; however, other redoximorphic features are also related to saturation. With increasing land use intensities and environmental concerns it is important to understand exactly how redoximorphic features (RMFs) relate to saturation. The objective of this research is to relate RMFs to saturation in a coarse-loamy catena in the lower coastal plain in North Carolina. A relatively undisturbed site in eastern NC was identified and three transects were instrumented with recording wells, redox probes and thermocouples. A rain gauge was also located at the site. In all the soils investigated, ≤2 chroma redox depletions related to an average cumulative annual saturation percentage (CSP) of 15%. However, the ≤2 chroma redox depletions indicated a larger CSP in the MWD soils (19%) as compared to the SWPD soils (11%). This suggests that ≤2 chroma redox depletions do not mean the same thing in all soils. Regulations that rely on this single feature may be identifying different degrees of saturation and thus may have a varying implication to wastewater treatment and water quality.
Vertisols are clayey soils containing slickensides and wedge-shaped aggregates formed by shrink-swell processes in seasonally wet climates. The dynamic distribution of macro- and microvoids as a by-product of this unique pedoturbation process, accompanied by microtopographic lows and highs (gilgai), mitigate our ability to make accurate and precise interpretations of aquic and hydric conditions in these problem soils. We studied Vertisols across a subhumid to humid climosequence to assess the formation of redoximorphic features on shallow, linear (nondepressional) landscape positions in response to varying levels of rainfall. Approximately 1000 mm of mean annual precipitation (MAP) is required to form soft iron masses that then increase in abundance, and to shallower depths, with increasing rainfall. Soft iron masses with diffuse boundaries become more abundant with higher rainfall in microlows, whereas masses with nondiffuse boundaries become more common in microhighs. Most soft iron masses form in oxygenated ped interiors as water first saturates and then reduces void walls where iron depletions form. In contrast, at least 1276 mm of MAP is needed to form iron pore linings in both microlow and microhigh topographic positions. Iron depletions do not correlate with rainfall in terms of abundance or depth of occurrence. The quantity of crayfish burrows co-varies with rainfall and first appears coincidentally with soft iron masses in microlows near 1000 mm of MAP; they do not appear until nearly 1400 mm of MAP in microhighs. Dithionite-citrate extractable and ammonium-oxalate extractable iron oxides increase systematically with rainfall indicating more frequent episodes of iron reduction and precipitation into pedogenic segregations. The sum of our data suggests that Vertisols forming in the Coast Prairie of Texas with MAP greater than 1276 mm should be classified as aquerts because of the presence of aquic conditions. These same soils may also meet the definition of hydric as one criterion for the identification of Federally-protected wetlands. However, there is a considerable disjunct between protracted periods of saturation and limited periods of reduction in these soils. Based on the distribution of redoximorphic features in the study area, regional water table data, and recent electrical resistivity data from a nearby upland Vertisol, non-Darcian bypass flow is the principle mechanism governing the flux of water through deep cracks where water first accumulates and then persists in microlow bowls at depths of 1 to 2 m.
Vertisols contain slickensides and wedge-shaped aggregates formed by shrink-swell processes during wet-dry cycles in seasonal climates. The dynamic distribution of macro- and microvoids as a by-product of this unique process, accompanied by microtopographic lows and highs, mitigate our ability to make accurate and precise interpretations of aquic and hydric conditions in these problematic soils. We studied Vertisols across a subhumid to humid climosequence to assess the formation of redoximorphic features on planar landscape positions in response to varying levels of rainfall. Approximately 1000 mm of MAP is required to form soft iron masses that then increase in abundance, and to shallower depths, with increasing rainfall. More than 1200 mm of MAP is needed to form iron pore linings, regardless of microlow or microhigh topographic position. Soft iron masses with diffuse boundaries become more abundant with higher rainfall in microlows, whereas masses with nondiffuse boundaries are more common in microhighs. Iron depletions do not correlate with rainfall in terms of abundance or depth of occurrence. Most soft iron masses form in oxygenated ped interiors as water tends to first saturate and reduce voids where iron depletions form. The quantity of crayfish burrows is strongly correlated with rainfall and first appears coincidentally with soft iron masses in microlows near 1000 mm of MAP. Dithionite-citrate extractable and ammonium-oxalate extractable iron oxides increase systematically with rainfall indicating frequent episodes of iron reduction and precipitation into pedogenic forms. It appears that Vertisols forming in these landscapes with MAP greater than 1200 mm should classify as Aquerts because of the presence of aquic conditions. These same soils may also meet the definition of hydric as one criterion for the identification of Federally protected wetlands. However, there is a considerable disjunct between protracted periods of saturation and limited periods of reduction in these soils. Non-Darcian bypass flow appears to be the principle mechanism governing the flux of water through these cracking soils where water first accumulates and then persists in microlow bowls.
The growing season requirement is an often overlooked part of the definition for hydric soils. The current technical definition for a hydric soil states that flooding or soil saturation must occur during the portion of the year when soil temperature at 50 cm is >5°C. In this study, we defined the portion of year when soils were >5°C at 50 cm as the microbial activity season and reserved the term growing season for plant activity. In the technical criteria for hydric soils, specific microbial activity season months have been assigned to each of the soil temperature regimes. Our objectives were to determine the portion of the year when southeastern U.S. hydric soils are <5°C at 50 cm and to estimate rates of microbial activity during winter flooding. We found that 34 bottomland hardwood forest soils in South Carolina, Louisiana, and Mississippi were never <5°C at 50 cm during a period of 2 to 3 yr. Also, winter rates of soil respiration and O2 consumption (1.6 mL O2 L-1 air d-1) are apparently sufficient to cause anoxia in saturated soils. Based on the available data, we recommend a 12-mo microbial activity season for southeastern bottomland hardwood forests. Additional data will be necessary to determine the relationships between temperature, soil saturation, and development of redoximorphic features in southeastern soils.
Water table depths and precipitation were measured over a 10-yr period on four adjacent forested soils in central Ohio. The soils included a hydrosequence of well, moderately well, poorly, and very poorly drained fine-textured soils. Graphs describing the probability of observing water tables during consecutive 2-week (semi-monthly) intervals, by soil depth class, were compared with estimates reported on USDA-Soil Conservation Service forms SOIL-SOI-5 and a method proposed in the Soil Survey Manual.-from Authors
In soils of sandy, coarse loamy, fine loamy, fine silty, and fine particle‐size families, we observed some general relationship between water table depths and soil color pattern. Horizons that have dominantly gray (chroma ≤ 2) color in the matrix or argillans are saturated much of the year. Horizons that have gray mottles, but are dominantly brown, are saturated a few months of the year if they are above the dominantly gray horizons, or are saturated most of the time if these horizons are below the dominantly gray horizon. Horizons that have dominant chroma of three in the matrix, mottles, or argillans are often saturated. Those that have dominant chroma of five or six and have no mottles with chroma of three or less are seldom or never saturated. This study shows that soils with three‐chroma matrix, mottles or argillans are much wetter than they had been thought to be and are wetter than reflected in Soil Taxonomy definitions.
Four seasonally saturated Alfisols along a toposequence 56km north of Houston, Texas, were studied to determine if each soil had an aquic moisture regime. On the basis of the water table and redox potential measurements, each soil was considered to have significant periods of saturation and reduction within 75cm of the surface. Recommendations for use of color chromas of three or less for identification of aquic moisture regimes are proposed.-from Authors.
The water regime in a Dothan soil was characterized by installing piezometers at 137-, 183-, and 285-cm depths. Monthly water table measurements differed for each piezometer throughout a 4-yr study period, indicating a perched water table. There was a water table at the greatest depth on only five occasions during the study period. On all but a few occasions, a water table was encountered at the 2 shallower depths. Morphological properties and seasonal precipitation were related to the water regime. -from Authors
The frequency of occurrence of water tables at certain depths below the soil surface and the length of time water tables remained at or above these depths were calculated on the basis of rainfall records from a 29‐year period. Results were correlated with soil morphological features.
Faint and distinct mottling correlated with water table behavior. The average depth below the surface to the midpoint of the uppermost mottled horizon increased as the drainage condition of the series improved. At the depth of a given degree of mottling, the percentage of time a soil was submerged was essentially the same in a given month for all series. Color designations of Munsell value and chroma for dry crushed material were also correlated with the percentage of time a soil was submerged during the first 6 months of the year. The relations were not consistent for all soils within the drainage sequence, but the poorly‐drained Dayton and Concord soils had the highest values and lowest chromas.
Munsell hues of 10YR occurred in horizons of well‐drained soils, whereas Munsell hues of 2.5Y and 5Y occurred in horizons of poorly‐drained soils. The size and abundance of iron and manganese concretions increased in a consistent manner in the sequence from well‐drained to poorly‐drained soils. The sequence of bleached A2 horizons over “clay pan” IIB2t horizons was specifically related to the perched water tables of the Dayton and Concord series.
Attempts to isolate relationships between water table regimes and a single color feature of the soil which might be useful as a tool for quantitatively appraising water table regimes were not successful. However, when color features were considered jointly, the morphological assessment of natural drainage class was found consistent with the water table regimes of the soils. The results illustrate the relationship between morphological indicators of soil drainage and water table regimes under climatic conditions peculiar to the Pacific Northwest.
Approximately 22.7 million metric tons (25 million short tons) of heavy minerals, at an average grade of 6 wt percent in 377.8 million metric tons (416 million short tons) of sand, have been delineated in 19 deposits in the upper Coastal Plain of North Carolina and Virginia. These deposits formed during a worldwide, Pliocene, transgressive-regressive event that occurred between 3.5 and 3.0 Ma. The deposits formed as beach or dune sands during the regressive phase of the event over an elevation range of 96 m (315 ft) to 53 m (175 ft). -from Authors
Moisture regimes and associated soil mottling patterns were investigated over a 2‐y period in a Paxton‐Rainbow‐Ridgebury‐Scarboro hydrosequence in central Massachusetts. Changes in physical conditions in these coarse‐loamy fragipan soils were monitored with well points, tensiometers, soil temperature probes, and redox potential electrodes. Well‐drained soils appeared uniformly brown, reflective of a generally strongly oxidized environment. They also showed the greatest seasonal fluctuations in soil temperature ranging from 0 to 23°C. Matrix colors of highest chromas (6 or higher) occurred in the moderately well‐drained (MWD) soils where reducing and oxidizing environments coexist within the profile at some time during the growing season. Prominent ferrans and albans in the 2Cx horizons of MWD soils were related to sustained groundwater levels, although higher water tables often occurred for periods too short or too cold for development of strongly reducing conditions. The characteristics grey streaking patterns of fragipans were best expressed in the 2Cx horizons of MWD soils and can be attributed to reducing environments during periods with soil temperature above biologic zero when conditions are wet but unsaturated. Significant translocation and leaching of iron occurred in the somewhat poorly drained soils, as evidenced by olive‐grey matrix colors. Channel neoferrans and some neoalbans indicated that a reducing environment may persist within the B2 horizon long after it has become unsaturated. Lowest chroma colors in this hydrosequence was found in the very poorly drained soils where perennial conditions of saturation or near saturation exists up to the soil surface resulting in the strongest reducing environment and least fluctuations in seasonal temperatures.
Depth to water table in Typic Paleudults decreases away from the dissected edge of the geomorphic surface in east central North Carolina. This relation is linear in log log form and statistically highly significant for 19 of 22 time periods tested. The greatest changes in water‐table depths and soil morphology are within the first 0.15 to 0.3 km from the surface edge. Deep water tables are associated with thick A2 horizons and fine‐textured B horizons. The shallow water tables are associated with thin A2 horizons, low‐contrast mottling, and presence of Be bodies. This close association between water‐table depths and soil morphology is interpreted as indicating that landscape dissection, acting through its influence on water‐table depths, is one of the driving forces in genesis of North Carolina Coastal Plain soils.
The weekly fluctuation of the water table was recorded for a period of 2 yr at five sites along a transect of a high plateau area in the Cerrados of Brazil characterized by minimal variation in soil morphology, color, and texture. The soil studied was a Red-Yellow Latosol, a member of the clayey, oxidic, isohyperthermic family of Typic Acrustoxes. Data suggest that reduction does not occur in the field in the lower part of the soil profile even when a high waater table is present due to the lack of a source of energy for microbial activity. The organic matter present in the lower part of the soil profile is too stable and/or too low in available nutrients for the reduction process to take place during the water logging period. -from Authors
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- E E Gamble
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-aspects of soil classificaLion with particular reference to reclaimed hydromorphic soils
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