Search

Manganese (Mn) and Fe indicator of reduction in soils (IRIS) devices are low‐cost, convenient tools for identifying reducing conditions in soils. Because Mn is reduced at similar redox potentials as nitrate, there is considerable interest in using Mn IRIS tools for understanding microbial reduction of Mn as a surrogate for processes such as denitrification. However, the sensitivity of these devices to differences in Mn‐reducing capacity has not been empirically investigated. Here we have found that the rate of birnessite paint removal from Mn IRIS films exposed to a twofold dilution series of the Mn‐reducing bacterium Shewanella oneidensis is directly proportional to the number of S. oneidensis cells added. Thus, regularly monitored birnessite IRIS sensors are capable of indicating twofold differences in Mn reduction in soil and can be used to measure relative Mn reduction rates over time in a single location or compare and contrast Mn reduction rates across soil types. Core Ideas: Manganese indicator of reduction in soils film sensitivity was determined using a Shewanella oneidensis dilution series.Manganese indicator of reduction in soils films are sensitive tools for measuring Mn reduction rates in soil.Timing of Mn indicator of reduction in soils film deployment and observation is critical for maximum sensitivity. [ABSTRACT FROM AUTHOR]

Soil organic C (SOC) content is one of the most dynamic of soil properties. In this study, we examined the effects of land use change on SOC pools for a single soil series and developed a mapping approach to relate SOC dynamics to land use change. Six paired sites, consisting of adjacent agricultural field and forest within a single delineation, were sampled and the SOC pools determined. The average forest SOC pool (157 Mg [ha.sup.-1]) was significantly higher (P < 0.05) than the field pool (103 Mg [ha.sup.-1]), supporting the importance of land use on SOC pools. We propose the development of a SOC phase based on land use to map such differences. Master O and A horizon data should be used to establish SOC phases. Data can be obtained from existing soil surveys, updates, or C accounting activities. Land use classes can be identified with digital imagery and SOC phases can be assigned to all mapping units. Mapping units sampled for C accounting can be resampled to detect patterns and rates of change. This approach provides a robust data set to effectively map and model SOC pools and change across the landscape, doi: 09.0228/sssaj2009.0326N

Commercial sod farms occupy about 1.62 x [10.sup.3] [km.sup.2] of the landscape of the United States. Land managers generally consider sod farms on an equal footing with other, sustainable agricultural land uses. We measured soil losses associated with sod harvesting in farms in the northeastern United States. Sod harvest resulted in soil losses ranging from 74 to 114 Mg [ha.sup.-1] [yr.sup.-1,] considerably higher than the tolerable soil loss of 6.7 Mg [ha.sup.-1] [yr.sup.-1]. Soil losses were proportional to time under sod production, with soil removal rates of 0.833 cm [yr.sup.-1]. We estimate that sod harvesting in the United States results in the net, permanent loss of 12.0 to 18.7 Tg of agriculturally productive soil from sod farms--and associated ecosystem services--every year. The soil losses reported here have important implications in terms of land use planning, transactions involving the purchase of development rights, and tax deductions for soil depletion. doi: 10.2136/sssaj2009.0239

Soil C supplies vary spatially within and among riparian wetlands. Understanding this variability is essential to assessments of C-dependent riparian wetland functions such as water quality enhancement and C storage. In this study, we examined the distribution of C with depth across the riparian landscape. Our objectives were to describe the spatial distribution of various C forms in the subsurface of riparian wetlands, and to identify the watershed, landscape, and soil characteristics that govern the distribution of these forms. Twenty-two riparian sites, mapped as alluvial or outwash soils, were examined along first- through fourth-order streams. Soils were described from pits and auger borings along transects established perpendicular to the stream. Roots and buried A horizons represent the majority of C in the subsurface, representing an important source of C for riparian zone functions. Buried A horizons and C-rich lenses, indicative of alluvial soils, were identified in 21 of the 22 sites. Higher order riparian zones tended to have greater quantities of alluvium. Roots were generally distributed to the greatest depths close to the streams where alluvial deposits were thickest. All first-, second-, and third-order riparian zones were mapped as outwash soils on county-scale soil surveys. These sites, however, contained predominantly alluvial soils, suggesting that soil surveys at the 1:15,840 scale are inadequate for identifying alluvial soils along lower order streams. To assess the best predictors of alluvium distribution within riparian zones, 11 watershed characteristics were examined. A forward stepwise regression revealed that watershed size and floodplain width are two of the most important indicators of the quantity, width, and depth of alluvium, and subsequently subsurface C, within glaciated riparian zones. Abbreviations: FOM, fragmental organic matter.

Additions of human-transported materials (HTM) have significantly altered many coastal shorelines and wetlands. The hydrology and the ability of these anthropogenic soils to support ecologically important functions is poorly understood. In this study, we documented soil hydrologic patterns along disturbed estuarine shorelines and wetlands. Our goal was to determine if the soils had properties relative to the potential to support denitrification (i.e., labile C, saturation, and reducing conditions). Eleven anthropogenic sites, located in Rhode Island and 30 to >60 yr old, were studied. Auger transects were completed to characterize anthropogenic soils. Water table levels were monitored twice a month. Anthropogenic soils were described and sampled from pits at five representative locations. Soil organic C (SOC), permanganate-oxidizable C (POC), bulk density, and pH were measured. Deposits of HTM, comprised of dredge and fill materials, ranged in thickness from 26 to >285 cm, were predominantly sandy and often contained artifacts. In the thickest HTM deposits, water table levels rose as much as 2.5 m above the original buried soil surface. Redoximorphic features were identified within the range of water table activity in 16 of the 18 monitored anthropogenic soils, suggesting reducing conditions. Soil organic C ranged from 1.6 to 88.9 g [kg.sup.-1], was highest in surface horizons, and had an irregular distribution with depth. Labile C, estimated from POC measurements, followed the SOC distribution. Evidence of labile C, saturation, and reducing conditions in the majority of these soils suggest that most of the disturbed estuarine soils we studied have the capacity for denitrification. Abbreviations: HTM, human-transported materials; POC, permanganate-oxidizable carbon; RMF, redoximorphic features; SOC, soil organic carbo

Soil morphology is often used as a predictor of water table levels in hydric soil determinations or other on-site evaluations. These predictions are based on the assumption that the relationships between water table levels and morphologic properties were established during typical weather patterns. Because climatic factors such as precipitation and evapotranspiration vary widely from year to year, there are often concerns about the validity of using short-term hydrologic data to predict longer term relationships. In this study, we monitored water table levels in three soils formed in glacial fluvial and till parent materials for 18 mo. Using these data, we developed a simple model that applies archived precipitation data and established hydrologic patterns to predict water table levels and cumulative saturation. The model was calibrated for each site through an iterative process. The minimal average differences between actual and predicted water table levels (

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 Io 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 ([r.sup.2] = 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.

Soil organic matter (SOM) contains fractions that range from very active to passive, relative to microbial-driven ecosystem processes and functions. A classification system is needed that can test the hypothesis that SOM can be separated by morphology into functionally meaningful fractions. The objectives of this study were to use macro- and micromorphological techniques to classify the various C forms present in saturated (or seasonally saturated) subsurface horizons of hydric riparian soils, and to increase our understanding of their genesis. Nine soils formed in outwash or alluvium, located in Rhode Island riparian wetlands, were described and sampled up to depths of over 3 m. The majority of these soils had seasonally high water table levels at or above the soil surface. Thirty-four thin sections were constructed from undisturbed samples collected from subsurface horizons for micromorphological investigation. Six C forms (roots, fragmental organic matter [FOM], lenses, infillings, masses, and horizon C) and five root-decomposition classes were identified. All C forms were more abundant in the subsurface of alluvial soils than in the subsurface of outwash soils. Masses and roots were the most abundant C form identified. Most masses have likely formed from dispersion of C associated with decomposed roots. Alluvial deposition has resulted in considerable C in subsurface riparian zone soils in the form of buried A and O horizons, lenses, and FOM. Illuvial-horizon C was found primarily in sandy horizons having outwash parent materials. Carbon dating suggested that many of these C forms persist for thousands of years in the riparian subsurface. The variety of C forms that exist in riparian zone subsoils suggests that understanding C morphology, and how these forms are related, may prove useful for developing functionally different morphologic classes of soil C.

Understanding soil organic C (SOC) spatial variability is critical when developing C budgets, explaining the cause and effects of climate change, and for basic ecosystem characterization. We investigated delineations of four soil series to elucidate the factors that affect the size, distribution, and variability of SOC pools from horizon to landscape scales. These soils, classified as Udipsamments, Dystrudepts, Endoaquepts, and Haplosaprists, were sampled along random transects to a depth of 1 m. In very poorly and poorly drained soils 75 and 45% of total SOC was round below 30 cm, respectively. In contrast, only 30% of the total SOC could be accounted for below 30 cm in the well and excessively drained soils. Soils formed in outwash and young alluvium sequestered a greater portion of total SOC within the subsoil, while soils formed in loess held approximately 70% of the SOC within O and A horizons. Total SOC contents among the four soil types differed significantly (p < 0.001), with the wetter soils having greater accumulations of C. Soil C pools ranged from 110 Mg C [ha.sup.-1] in the excessively drained Psamments (double the mean national value) to 586 Mg C [ha.sup.-1] in the very poorly drained Saprists (30-60% lower than the mean national value). The two-fold differences between our data and the national averages support the need for regional assessments of soil C pools. Based on the coefficient of variation (CV) values, there appears to be nearly as much variability in the SOC pool within a delineation (CVs ranged 9 to 30%) as among delineations (CVs ranged from 15 to 31%) for the same soil type. Since significant differences were found for total SOC among delineations of the same soil type, we concluded that sampling from a significant number of delineations of the same series will provide a more accurate representation of SOC for scaling to the landscape or region than sampling at multiple locations within a single representative delineation.

Subaqueous soils occur from the lower limit of the intertidal zone to a depth of