John C. Dixon

Applications of fuzzy logic to the prediction of soil erosion in a large watershed

There is a need in many emerging nations to develop simple methods for predicting areas of extensive soil erosion using imprecise, but real-world, input data at low cost with considerable accuracy. The objectives of this study are to (1) develop fuzzy logic models that predict soil erosion in a relatively large watershed using a limited number of input variables, (2) determine the effects of scale and grid-size variations in input data on fuzzy logic model output, and (3) compare the predictions of soil erosion using fuzzy logic methodologies with those of the Universal Soil Loss Equation (USLE). Two fuzzy-logic rule bases were constructed: (1) a two-variable-based model which required inputs of slope angle and landuse ratio or landuse, and (2) a three-variable-based model which required inputs of slope length (FLS), soil erodibility (FK) and vegetative cover (FC). Reducing the grid size of input data resulted in a decrease in the areal extent of predicted high soil erosion. The more dispersed pattern of soil erosion, observed with a 4-mile grid at a scale of 1:250,000, became more clustered in the 2-mile grid and even more clustered in a 2-mile grid at a scale of 1:24,000. The trend of clustering towards smaller areas of high erosion potential as map scale increased was also found at the grid sizes 1 and 0.4 miles. Soil erosion, predicted with the two-variable fuzzy logic model using 30 m resolution GIS-based data sets of slope and landuse, was similarly distributed among the low, moderately low and moderate soil erosion categories. This was attributed to the lack of inherent fuzziness in the input data obtained from raster format. The areal extent and locations of soil erosion predicted by the USLE model and by the two-variable-fuzzy logic model were similar. Differences between the predictions of the USLE model and the three-variable fuzzy logic model were primarily in the moderately low and moderate soil erosion categories and were attributed to the effects of the two non-fuzzy variables used in the USLE model, annual rainfall erosivity and cropping practices, which were not used in the fuzzy logic model. Compared with the USLE model predictions, the fuzzy logic-soil erosion prediction models were successful at locating and differentiating areas of soil erosion with minimum input data.

Weathering implications of water chemistry in an arctic–alpine environment, northern Sweden

This paper reports on some of the chemical characteristics of late melt-season water from Karkevagge (“valley of the boulders”) above the Arctic Circle in northern Sweden. Included in the analyses were temperature, electrical conductivity, pH, SO4, NO3, K, SiO2, Mg, Mn, Na, Fe, and Al. These were measured in rain, late-lying snow, and water from the major stream and lake, as well as from pond, tributary, and seep sources in the valley. A total of 71 samples was collected at 57 sites between August 6 and August 23, 1996 for the purpose of characterizing the present weathering regime within this classic U-shaped glacial valley. Evidence of chemical weathering included increases in solute concentrations over precipitation inputs and a source-related, wide variation in water chemistry. The dominant anion measured in surface water was SO4. That, along with the presence of CaSO4 coatings on streambeds, indicates that pyrite oxidation may contribute to the weathering regime. High SO4 concentrations were associated with gypsum-coated streambeds and seeps that emerge from the bedrock. Low SO4 concentrations were associated with tributaries flowing primarily on fresh rock and originating from melting snow. Estimated chemical denudation rate for the valley, corrected for atmospheric inputs, was 19.2 tons/km2/yr. Although this is lower than previously reported, our research supports earlier work indicating that chemical weathering is a major component of mass wasting in this arctic–alpine environment.

Weathering rinds and rock coatings from an Arctic alpine environment, northern Scandinavia

Coarse rock debris exposed in the subaerial environment of northern Sweden displays the development of a wide variety of surface coatings. These include weathering rinds as well as a great diversity of geochemical coatings, including those dominated by Ca, Fe, Si, and Al. Each of these types of rock coatings displays a high degree of geochemical complexity. The weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores, including extensive dissolution, oxidation, and hydration as well as disaggregation, fracturing, and cementation by secondary geochemical coatings. Chemical breakdown of the rock to form weathering rinds includes loss of K, Si, Mg, and Ca and buildup of Fe. Weathering rinds are fundamentally the result of dissolution, as no clay minerals were identified in the rinds. Rock coatings are distinguished from rinds by their clear accretionary nature. Despite the distinction made between weathering rinds and rock coatings, it is important to note that often the two are intimately related. The presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the Arctic alpine climate of northern Sweden in particular, as well as its significance in landscape evolution in such environments in general.

The chemical weathering regime of Kärkevagge, arctic–alpine Sweden

Abstract Karkevagge is a valley located in Swedish Lapland at approximately 68°N and represents an arctic–alpine landscape. It is a presently periglacial, glaciated trough incised into essentially horizontal metamorphic rocks, some of which are presumably pyrite-rich. A set of coordinated studies was undertaken to investigate the nature of chemical weathering and pedogenesis in the valley and upon the abutting ridges. August 1996 water quality measures reveal considerable spatial variation in solute totals with the highest Total Dissolved Solute abundances being correlated with high sulfate abundances. Ridge-crest soils exhibited poor horizonation, but more extensive development of secondary clay minerals developed in situ than was found in valley-flank and valley-bottom soils. Valley soils exhibited multiple thin horizons, many of which were buried, and are taken to reflect great paraglacial and periglacial instability. Favorable microenvironments in the valley permit significant development of Spodosols. Coarse debris along and across the valley bears both weathering rinds and rock coatings. Rock coatings in the valley include several types of iron films, sulfate crusts, carbonate skins, and heavy metal skins. Karkevagge represents a mild arctic environment, which does not preclude substantial chemical weathering in locations where abundant pyrite-rich bedrock and water coincide. This weathering follows pathways which are eminently expectable given that weathering of the pyrite-rich rock permits generation of sulfuric acid which, in turn, weathers muscovite mica and calcite in local schists and marble, respectively. Zones of intense chemical weathering also generate clearly visible deposits of gypsum and iron sulfate deposits such as jarosite. Not all arctic and/or alpine environments are likely to be so active chemically, but the results from Karkevagge clearly show that dismissal of chemical weathering in cold regions on the basis of presumed first principles is erroneous. Consequently, chemical weathering in such environments merits substantially more attention than it has hitherto received.

Clay mineralogy, chemical weathering and landscape evolution in Arctic–Alpine Sweden

Abstract The purpose of this research was to: (1) characterize the clay mineralogy of soils in and adjacent to Karkevagge, a recently deglaciated valley in Arctic Sweden, (2) document chemical weathering in a periglacial environment and (3) use the mineralogy to help explain landscape evolution. Soil samples were analyzed from 11 sites that differ in elevation, parent material, drainage, slope and vegetation. Parent materials include residuum, alluvium, colluvium and glaciofluvial material derived from garnet–mica–schist, plus, in one locality, a till of granitic origin. X-ray diffraction (XRD) was used to characterize the clay-size fraction (

CHEMICAL WEATHERING PROCESSES ON THE VANTAGE PEAK NUNATAK, JUNEAU ICEFIELD, SOUTHERN ALASKA

On the Vantage Peak nunatak in the Juneau Icefield of southeastern Alaska, grus and soils display evidence of extensive chemical alteration in a self-evidently periglacial environment. Accompanying the alteration of bedrock to grus and soil is a decrease in grain size. Grus is dominated by very coarse sand while the soils are predominantly fine sand. Grain-size reduction is attributed primarily to mineral grain dissolution. Total chemical analyses show that alkali earths (calcium and magnesium) and alkalis (sodium and potassium) are lost as weathering progresses, while silicon and iron increase relative to resistant elements. Secondary clay minerals present in the grus and soils appear to have been derived from clay-size primary minerals. Vermiculite is the principal secondary clay mineral and appears to have formed by the alteration of biotite. Scanning electron microscopy shows that quartz and feldspars are primarily weathered by dissolution with no evidence of feldspar transformation to secondary clays...

Character and origin of deep arenaceous weathering mantles on the bega batholith, southeastern Australia

Summary Arenaceous weathering mantles on the Bega batholith, southeastern Australia, are similar to those described from Europe by MILLOT. As in Europe, they have been formed by hydrothermal alteration of the parent rock, and later by chemical weathering of biotites and feldspars. But comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock. Unlike the examples cited by MILLOT, in the Bega mantles kaolinite is the dominant clay mineral. Nonetheless these mantles seem to be contemporary, not relict features, and apparently formed under a temperate climate.

Aridic Soils, Patterned Ground, and Desert Pavements

Pedogenic and geomorphic processes operating in deserts are inextricably linked. These linkages are particularly well expressed in the development of patterned ground and desert pavement. In addition, the nature and efficacy of hydraulic, gravitational, and aeolian processes on desert surfaces are strongly influenced by the physical and chemical characteristics of the underlying soils. As a result, the evolution of a diversity of desert landforms is either directly or indirectly linked to pedogenic processes.

Statistical relationships between daily and monthly air and shallow-ground temperatures in Kärkevagge, Swedish Lapland

Single-year air and ground temperature records from 1995 to 1996 in Karkevagge (approximately 68 °26′N, 18 °18′E), a glaciated trough in northern Sweden, are compared using reduced major axis analysis (RMAA) to demonstrate the limitations in using air temperatures as indicators of ground temperatures in an Arctic–alpine environment. While air temperatures predict some 10 and 50 cm level ground temperatures with as much as 95% explanatory power at daily and monthly scales, other ground sites are predicted with as little as ∽20% explanatory power. Such variability, found over sites differing in elevation, aspect and vegetation cover, is assigned to the influence of snow cover, which was not measured. As would be expected, the smoothing of data from daily to monthly scales generally improves the correlation between air and ground temperatures; this phenomenon is also due, in part, to lag effects associated with heat conductance. The 1995–96 record appears to be drawn from a period that is probably somewhat warmer than the average over the last 47 years: a conclusion drawn by examining the 1951–97 record from two nearby weather stations. Copyright

Chemical denudation rates in Kärkevagge, Swedish Lapland

This study examines the spatial and temporal variability of chemical denudation rates in Kärkevagge, northern Sweden. The chemical flux rates within the valley are strongly influenced by the local geology. Chemical denudation rates determined for the study period are more than double those previously reported in the literature for this valley. Rates of greater than 46t km−2 a−1 were measured at the valley mouth over the course of the melt season. This difference is likely due to differences in measurement technique compared to that used by past researchers. This rate is also much higher than for other arctic and alpine watersheds. Chemical denudation in Kärkevagge is comparable to larger temperate rivers. The rapid chemical denudation in Kärkevagge is likely due to sulfide weathering creating acid solutions.