Precision, particularly in terms of repeatability in particle size analysis (PSA), has recently resurfaced as an issue due to the increased use of laser PSA for PSA. Because laser diffractometry ...produces much more detailed data than does traditional pipette analysis, and because a much smaller sample is used in the analysis, precision or repeatability of laser‐produced PSA data is a legitimate concern. For example, of the 1485 soil samples analyzed in our study, most of which are silty or loamy and each of which was analyzed at least twice, 11.5% changed texture class, from the first to the second PSA measurement. Statistical analysis of these paired, subsample data was therefore used to establish a standard for normal variance among the subsamples, as a test of precision. Subsample pairs with an absolute cumulative bin difference (CBD) of <1 SD above the population's mean CBD were determined to have acceptable precision. This approach provides both a simple method for assessing the variation in PSA data sets and establishes a comparable standard for determining when additional measurements are needed to find a more precise result. Researchers may be tempted to simply use mean PSA data for samples that have been run multiple times. However, we found that using the per bin mean for only the two best matching subsamples was the optimal approach. Our analysis also indicates that, as particle size gets coarser (at least within silty/loamy samples), the precision of laser‐generated particle size data generally decreases.
Large parts of the upper Midwest, USA were impacted by permafrost during the Last Glacial Maximum (LGM). Even though permafrost persisted as the Laurentide Ice Sheet began to recede, direct age ...control of this interval is largely lacking. To better temporally constrain the permafrost interval in western Wisconsin, we identified two sites, outside the Late Wisconsin (MIS 2) glacial limit, that contain relict, ice‐wedge pseudomorphs, initially interpreted to be sand wedges, hosted within well‐drained outwash deposits. The pre‐Wisconsin (>MIS 5) host material commonly displays up‐turned bedding near the contact with the wedges, indicative of well‐formed features. The wedges are filled with well‐sorted, gravel‐free, medium and fine sands, and lack evidence of post‐formational disturbance, pointing to an aeolian sand infill and confirming them as sand wedges. Ventifacts on nearby uplands attest to windy conditions here in the past. Optically stimulated luminescence (OSL) ages on five sand wedges indicate that they filled with sand between c. 19.3 and 18.3 ka at the southerly site and between c. 15.1 and 14.7 ka at the northerly site, which is closer to the LGM margin. Sand wedges at the latter site were wider and had more complex morphologies, possibly suggesting a longer interval of formation and/or more intense permafrost. We also examined a site along a ridge crest, between the two wedge sites, which displayed interbedded loess and sand, dated by OSL to 12.7 ka. Together, these results point to dry, cold, windy conditions in west‐central Wisconsin, within 100 km of the LGM limit. At this time, aeolian sands were being transported across a landscape with (at least scattered) permafrost. The OSL results suggest multiple phases, or perhaps time‐transgressive, sand‐wedge formation, associated with permafrost between c. 19 and 15 ka, with dry, windy (and likely, cold) conditions persisting until at least 12.7 ka.
The purpose of this research was to characterize and interpret the coarse basal zones that are common in thin loess deposits that overlie coarser-textured sediment. To that end, we sampled nine ...pedons in northeastern Wisconsin and the Upper Peninsula of Michigan, each of which had formed in thin (≤55cm) loess over sandy glacial sediment. At most of these sites, the loess became noticeably coarser near the lithologic discontinuity. The loess has a primary particle size mode in the coarse silt or fine, very fine sand fraction (≈30–65μm) and a secondary mode in the fine or medium sand fraction (≈200–400μm). We attribute the secondary mode to mixing of underlying sands into the loess, either during loess deposition or by post-depositional pedoturbation. In thin loess, pedoturbation processes can penetrate into the underlying sediment, facilitating mixing upward as far as 50cm into the loess. Silt from the loess has also been mixed into the underlying sandy sediment. Alternatively, in some pedons, the loess itself coarsens with depth; the particle size mode for the loess becomes increasingly coarser with depth. This coarsening suggests that, during loess deposition, one or more of the following was occurring: (1) wind velocities were decreasing over time, (2) the textural character of the loess source area(s) were changing/decreasing, or (3) additional source areas—with finer-textured sediment—became more dominant over time. Our research demonstrates the utility of detailed particle size data for detecting and interpreting the paleoenvironmental history of loess. We also document the extent to which pedoturbation can impact the original textural characteristics of loess (or any sediment) that occurs as a thin surficial mantle.
► In this study we examined nine pedons that have thin loess mantles over sandy glacial sediment. ► In most of these pedons, the loess becomes increasingly coarser with depth. ► In some pedons, pedoturbation has mixed some of the sands into the basal loess. ► In some pedons, the loess coarsens with depth, possibly due to changing depositional conditions. ► Detailed particle size curves help explain the origins of coarse-textured basal zones in loess.
Charles Darwin and Vasily Dokuchaev made early and important, but quite different, contributions to pedogenic theory. Their major contributions were both written as books — Darwin's, 1881 The ...Formation of Vegetable Mould, Through the Action of Worms, With Observation on Their Habits, and Dokuchaev's, 1883 Russian Chernozem. Although most soil scientists are familiar with Dokuchaev's legacy and lasting impact, far fewer know about or value equally Darwin's “worm book.”
Dokuchaev's factorial approach to soil science, drawn from observations across the Eurasian steppe, helped map, classify, and place economic value on soils, while also providing key insight into their formation. This approach gained visibility in the 1930s and 1940s, when personnel at the U.S. Department of Agriculture, and some academic pedologists, recognized its utility for soil survey and for interpreting pedogenesis. Jenny's (1941) book, Factors of Soil Formation, helped the model to gain acceptance, and it eventually became entrenched as the core pedogenic model for North America, if not the world. Dokuchaev's legacy is tied to this model. Alternatively, Darwin's main contribution to the field was to shed light on soil processes, particularly faunal mixing (bioturbation) and the textural sorting it can produce. Although Darwin's findings fostered an array of multidisciplinary studies on pedogenic processes during the ensuing 50years, his work languished in the broad shadow cast by Dokuchaev's model. In 1975, Darwin's ideas reappeared in Soil Taxonomy — associated with rudimentary biomantle concepts. Recently, empowered with new concepts and language, bioturbation concepts have gained considerable traction.
We briefly summarize the backgrounds of Darwin and Dokuchaev, and compare their fundamentally different approaches to pedogenesis. But insofar as Dokuchaev's approach is more mainstream, we emphasize Darwin's, for balance. We show how Darwin's model, updated with current understandings of biomantle formation, is allowing new questions to be asked about pedogenesis and landscape evolution, and formerly intractable ones to be answered. We stress the profound role of conceptual models in guiding explanatory thought, and end by positing that both Darwin's and Dokuchaev's approaches, while different in their basic structure and goals, provide together a more complete view of pedogenesis than either can do singly.
•Charles Darwin and Vasily Dokuchaev are acknowledged giants of soil science.•Both made key fundamental contributions to pedogenic theory.•Darwin's research on bioturbation and sorting has been comparatively overlooked.•Bioturbation theory helps explain genesis of stone lines and Mima mounds.•Science is stronger when both models are used to explain soil-landscape genesis.
Progress in soil geography I: Reinvigoration Miller, Bradley A; Brevik, Eric C; Pereira, Paulo ...
Progress in physical geography,
12/2019, Letnik:
43, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The geography of soil is more important today than ever before. Models of environmental systems and myriad direct field applications depend on accurate information about soil properties and their ...spatial distribution. Many of these applications play a critical role in managing and preparing for issues of food security, water supply, and climate change. The capability to deliver soil maps with the accuracy and resolution needed by land use planning, precision agriculture, as well as hydrologic and meteorologic models is, fortunately, on the horizon due to advances in the geospatial revolution. Digital soil mapping, which utilizes spatial statistics and data provided by modern geospatial technologies, has now become an established area of study for soil scientists. Over 100 articles on digital soil mapping were published in 2018. The first and second generations of soil mapping thrived from collaborations between Earth scientists and geographers. As we enter the dawn of the third generation of soil maps, those collaborations remain essential. To that end, we review the historical connections between soil science and geography, examine the recent disconnect between those disciplines, and draw attention to opportunities for the reinvigoration of the long-standing field of soil geography. Finally, we emphasize the importance of this reinvigoration to geographers.
Digital Classification of Hillslope Position Miller, Bradley A.; Schaetzl, Randall J.
Soil Science Society of America journal,
January-February 2015, Letnik:
79, Številka:
1
Journal Article
Recenzirano
Hillslope position has long been important in soil geomorphology. At the scale of county‐level soil maps, more soil boundaries are based on topography than any other soil‐forming factor. However, the ...inability to accurately delineate topographic breaks across hillslopes—either due to lack of sufficient topographic resolution or the proper technology to develop and/or model them—hinders soil mapping efforts. In this research, we developed a decision tree model for classifying hillslope position, which was calibrated and validated using the observations of soil scientists in the field. Different decision tree structures were tested with classification breaks based on calibration groups' mean midpoints, median midpoints, and fuzzy membership. The final model objectively and quantitatively classifies the five major hillslope positions and performs well on different landscapes, making it suitable for efficient application to large areal extents. The resulting maps of hillslope position represent base maps that can be used to (i) improve research on toposequences by providing explicit definitions of each hillslope element's location, (ii) facilitate the disaggregation of soil map unit complexes, and (iii) identify map unit inclusions that occur due to subtle topographic variation. Base maps developed by the model can also help identify areas of possible inaccuracies in soil maps, especially where soil boundaries cross topographic breaks. Predictions from the model enable the mapper to better place soil map unit boundaries at locations where defendable landscape breaks exist.
This study was performed in the eastern Upper Peninsula of Michigan, where Spodosols are extremely well developed. We instrumented a Typic Durorthod with zero‐tension lysimeters to capture water ...leaving the O, E, and B horizons and with sensors to determine volumetric water contents with depth. We also occasionally measured snowpack depths and determined snow water equivalents. These field data were used to validate a hydrologic model that was run for the site using nearby National Weather Service (NWS) data. Good agreement between the modeled output and field data from the site enabled us to apply 1961 to 2013 NWS data from three additional stations along a transect that spans the range of podzolization strength in Michigan as inputs to the model. Soils remain dry throughout the summer and slowly wet up in fall. The more strongly developed soils in the north are slightly wetter in fall, facilitating breakdown of fresh litter and enhancing production of soluble organic materials. Their translocation into the mineral soil is presumably deepest and most pronounced during snowmelt, facilitated by a strong “pulse” of cold snowmelt water. This pulse comprises well over half of the annual flux of water at 100‐cm depth, even though its timespan is short. Snowmelt fluxes are larger and of shorter duration in the north, where podzolization is strongest. By storing precipitation in a thick snowpack, the pedogenic system compresses inputs of water, creating deeper, more concentrated pulses of percolation when soluble organic materials are readily available; this is the essence of podzolization in this region.
•Tree uprooting can significantly contribute to soil surface microrelief.•Treethrow pit can retain water and snow, delay runoff, and facilitate infiltration.•The pit can serve as a strategic source ...of moisture and nutrients for nearby trees.•Reduced microrelief in forests may accelerate runoff and reinforce drought stress.
Forest ecosystems are known for their capacity to retain and redistribute water. Nevertheless, even in some forested watersheds, prolonged or intense rainfall events often exceed the retention threshold of the system, generating accelerated runoff. Surface microrelief is an important attribute of forest ecosystems that often act to mediate potential runoff. In most natural forests, the soil surface is typically unevenly broken with pit and mound microrelief, formed by both historical and recent tree uprooting events. In managed forests, however, tree uprooting is traditionally seen as undesirable. The systematic repression of this process may lead to gradual loss of microrelief. To date, little attention has been paid to the impacts of the pit-mound microrelief, or its absence, on forest hydrology. Restoration of naturally undulating microrelief in managed forests can help to accentuate water retention and mitigate runoff, while reducing drought stress and reinforcing forest productivity and resilience.
This paper summarizes the literature and presents insights on the effects of tree uprooting on the microrelief of forest soils and forest hydrology, focusing on its consequences to water retention, tree water supply, and forest health. Furthermore, we explore the mechanisms and possible consequences of the long-term repression of these processes in intensively managed forests, with implications for forest management and further research.
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