Linda R. Barrett

A strand plain soil development sequence in Northern Michigan, USA

Abstract A practical problem limiting the theoretical application of a soil chronosequence study lies in the difficulty of identifying an appropriate geomorphic age sequence with more than a few surfaces. A sequence of approximately 75 strand plain beach ridges located along the northern shore of Lake Michigan, USA, overcomes this problem, and was used to explore rates of soil development in the initial stages of podzolization. Well drained pedons were sampled on 24 of the ridges, with an age range of 10 to 5200 years. Chronofunctions were developed using statistical regression techniques. For most forms of extractable Fe and Al, both linear and log–linear functions adequately describe the changes in property with surface age. Dithionite–citrate extractable Fe content, however, shows little correlation with surface age. High r 2 values (>0.7) for chronofunctions representing most extractable sesquioxide forms suggest that B horizon sesquioxide content increases with surface age, as expected for soils undergoing podzolization. Visual inspection of chronofunction data suggests that scatter increases on surfaces older than 3000 years, possibly because soil spatial variability increases with surface age. Theory suggests that the log–linear form of chronofunctions may be preferable to the linear form for these pedons. In general, equation slopes are steeper for chronofunctions representing only the initial 1650 years of soil development than for those representing the entire 5200-year sequence, suggesting that initially rapid pedogenesis slows over time. Most chronofunctions for pH and weighted profile organic C are not statistically significant, possibly because the temporal resolution of the chronosequence is too coarse to detect valid trends for properties that rapidly approach a steady state.

Spectrophotometric color measurement in situ in well drained sandy soils

Abstract A method for measuring spectral reflectance of samples in place on the face of a soil pit was developed for well drained, sandy soils. Spectrophotometer readings were taken directly on the pit face immediately after scraping a fresh, flat surface to ensure uniform soil moisture content. Measurements taken in this manner were compared to field-based visual estimates and to laboratory-based spectrophotometric measurements of sieved, air-dried samples. While overall reflectance was shown to decrease with increasing moisture content in the laboratory, little change was noted over the 1–7% moisture content range encountered for most samples in the field. The interaction between the “granular materials cover” (a glass window used to protect the integrating sphere) and the “specular reflectance included” viewing geometry resulted in hue shifts for some samples at higher moisture contents, suggesting that the “specular reflectance excluded” mode is more appropriate for in situ measurements of soil samples. A moderately strong correlation exists between spectrophotometer measurements and visual estimates of Munsell parameters in the field, but the spectrophotometer provides a higher degree of precision. Soil features smaller than the 8-mm diameter instrumental measurement area are averaged with the surrounding matrix, however. The research suggests that for well drained, sandy soils, a spectrophotometer can be used in situ to provide reliable, repeatable measurements of spectral reflectance.

SOIL DEVELOPMENT AND SPATIAL VARIABILITY ON GEOMORPHIC SURFACES OF DIFFERENT AGE

Twenty-four soil pedons on each of four sandy lake terraces in northwestern lower Michigan that ranged in age from 3000 to 11,000 years BP were studied to assess trends in soil morphological variability with time. After verifying the general uniformity of parent materials within and between the four surfaces, we examined temporal trends in the spatial variability of soil color, cementation, horizon thickness and development. E horizons attained high color values (lightness) by 3000 years and changed little after that time, whereas B horizons continued to get darker with time. Cementation within B horizons increased in strength and amount with time, as did B horizon thickness. Soils ≥4000 years old had deeper eluvial zones but much greater variabilities in the thickness of that zone than did younger soils. Soil development increased with time, but spatial variability in degree of development also increased with time. These patterns are best explained by invoking spatially random soil mixing upon a surface ...

Relationships Between Soils and Presettlement Forests in Baraga County, Michigan

-Soils data and data on the presettlement forests of Baraga County, taken from the General Land Office (GLO) Survey, were stored and analyzed in a geographic information system (GIS). The purpose of the research was to determine county-wide witness tree distributions and autecological relationships among 14 major tree species and soil wetness and texture, in this geologically and edaphically diverse region of northern Michigan. In all, 12,760 trees were coded by species, location and diameter from the GLO data, which were recorded between 1846 and 1853. Tree data were overlain on soil mapping units which were coded by natural drainage class and particle-size family. All trees located in mapping unit complexes (two or more soil types) or within 25 m of certain soil boundaries were eliminated from further consideration through a selection/buffering procedure leaving 6210 trees of 14 species for use in the analysis. Contingency tables were calculated to assess the strength and direction of the relationships between each tree species and soil texture, soil wetness and texture/wetness combinations. County-wide distributions of species were strongly related to soil patterns, with a prominent forest ecotone occurring near the boundary between two distinct till provinces. Most upland forests were dominated by sugar maple and yellow birch; prevalent lowland species included balsam fir, black spruce and white cedar. Hemlock was common only near Lake Superior on sandy tills that lacked a silt cap. Especially notable was the association between a nearly pure stand of jack pine and the dry sandy soils of the Baraga (glacial outwash) Plains. Evidence for widespread disturbance by wildfires on the level plains contrasts with the relatively long period of only small gap-scale disturbances that existed on more rolling, mesic and wet sites.

Regressive pedogenesis following a century of deforestation : Evidence for depodzolization

After the logging and fires of the late nineteenth century, the upland stump prairies of Michigans Upper Peninsula, which had previously supported dense forest, have remained deforested. Surrounding areas in similar geomorphologic settings have returned to forest. We investigated whether soil B horizon properties have degraded in response to the removal of podzolization-promoting vegetation by studying pedons under forest and stump prairie. Active soil processes were examined by analyzing ions sorbed on cation exchange resins and chelating resins that had been buried in the pedons, at three depths, for approximately 1 year. In both vegetation types, patterns of sorbed Fe and Al indicate that podzolization is on-going, with active translocation of sesquioxides into the B horizon. Larger absolute amounts of sesquioxides were sorbed on resins in forested pedons compared with stump prairie pedons, however, suggesting that podzolization processes are more active in forested than in stump prairie environments. The chemical and morphological properties of forested and stump prairie pedons were examined by analyzing the organic C and extractable Fe and Al content of horizon-based samples. Strength of podzol development was greater, in general, for forested than for stump prairie soils. The primary chemical difference between the two types was found in organic C content and in properties associated with organic C, including pyrophosphate-extractable Fe and Al. Differences between forested and stump prairie soils were much smaller for inorganic constituents. Depodzolization (the degradation of existing podzol features) in stump prairie B horizons is most evident in morphological properties associated with organic C, which are dependent on continued input of organometallic complexes. Depodzolization has occurred in the stump prairie soils because the balance between progressive development (podzolization) and regressive development (depodzolization) has been altered under stump prairie vegetation.

Forecasting Climate Change Impacts on the Distribution of Wetland Habitat in the Midwestern United States

Shifting precipitation patterns brought on by climate change threaten to alter the future distribution of wetlands. We developed a set of models to understand the role climate plays in determining wetland formation on a landscape scale and to forecast changes in wetland distribution for the Midwestern United States. These models combined 35 climate variables with 21 geographic and anthropogenic factors thought to encapsulate other major drivers of wetland distribution for the Midwest. All models successfully recreated a majority of the variation in current wetland area within the Midwest, and showed that wetland area was significantly associated with climate, even when controlling for landscape context. Inferential (linear) models identified a consistent negative association between wetland area and isothermality. This is likely the result of regular inundation in areas where precipitation accumulates as snow, then melts faster than drainage capacity. Moisture index seasonality was identified as a key factor distinguishing between emergent and forested wetland types, where forested wetland area at the landscape scale is associated with a greater seasonal variation in water table depth. Forecasting models (neural networks) predicted an increase in potential wetland area in the coming century, with areas conducive to forested wetland formation expanding more rapidly than areas conducive to emergent wetlands. Local cluster analyses identified Iowa and Northeastern Missouri as areas of anticipated wetland expansion, indicating both a risk to crop production within the Midwest Corn Belt and an opportunity for wetland conservation, while Northern Minnesota and Michigan are potentially at risk of wetland losses under a future climate.

Teaching Archaeogeophysical Survey and Mapping any Time of the Year: An Interdisciplinary Course

One of the fastest-growing areas of archaeological fieldwork is the use of subsurface geophysical survey techniques to map ancient remains without excavation. Growing interest in this technology, coupled with the availability of commercial data collectors tailored to archaeological needs, presents a challenge to educators. Specifically, this challenge is to create an integrated, interdisciplinary, active learning curriculum, providing students with: (1) a competent theoretical understanding of basic geophysical processes underlying these survey techniques; (2) an appreciation of the implications these technologies have for research design and methodology and (3) a working knowledge of appropriate mapping and imaging theory and technology. We designed and implemented a course focusing on these outcomes that was taught at the University of Akron for the first time in Spring 2002. This course was offered to advanced undergraduate and graduate students through a cooperative effort between the Geology, Archaeology and Geography programs. Positive outcomes were measured in terms of overall student responses to course content, a dynamic teaching environment for faculty, successful field studies and the placement of students in post-course research projects. At the same time, course logistics, managing student group dynamics and the difficulty in selecting “real” but appropriate test sites warrant further discussion and modification of the course syllabus for future offerings.