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Snowmelt‐fed springs and small (0.5 km2) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca2+, Na+, and HCO3−, locally SO42−. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na+ and Si. Concentrations of Ca2+ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca2+ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m−2·s−1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments. [ABSTRACT FROM AUTHOR]

Long‐term decreases in acidic precursors have changed the chemistry of precipitation and streamflow in two moderately to well‐buffered, forested headwater catchments in the Taconic Range of western New England, USA. We report 30‐year geochemical trends from Birch Brook and annual and seasonal variations from Birch Brook and adjacent Ford Glen, which drain phyllitic and carbonate bedrock. Median pH of precipitation has increased irregularly since 1983, consistent with regional trends. Increases in precipitation pH and decreases in sulfate (SO42−) correspond with increasing stream pH and decreasing SO42− concentration and flux over at least the past 30 years. Calcium (Ca2+) concentration and acid‐neutralizing capacity (ANC) in Birch Brook began to increase about 2005, in contrast to geochemical indicators from some poorly buffered catchments in the NE USA. Point and longitudinal sampling over a range of flows show that Birch Brook chemistry is a mixture of upstream source waters (throughfall, soil water, and ground water) with different chemistries. Acidic precipitation and shallow soil water affect stream chemistry directly only in the upper reaches of Birch Brook and during periods of extremely high flow, such as snowmelt. Ford Glen has high ANC and is near saturation with calcite at most flows. Long‐term trends measured at Birch Brook and at other streams in western Massachusetts show that stream chemistry reflects changes in acidic deposition in upland catchments, even where ecosystem geochemistry is well buffered by bedrock composition. [ABSTRACT FROM AUTHOR]

Abstract: Infrequent, high‐magnitude events cause a disproportionate amount of sediment transport on steep hillslopes, but few quantitative data are available that capture these processes. Here we study the influence of wildfire and hillslope aspect on soil erosion in Fourmile Canyon, Colorado. This region experienced the Fourmile Fire of 2010, strong summer convective storms in 2011 and 2012, and extreme flooding in September 2013. We sampled soils shortly after these events and use fallout radionuclides to trace erosion on polar‐ and equatorial‐facing burned slopes and on a polar‐facing unburned slope. Because these radionuclides are concentrated in the upper decimeter of soil, soil inventories are sensitive to erosion by surface runoff. The polar‐facing burned slope had significantly lower cesium‐137 (137Cs) and lead‐210 (210Pb) inventories (p < 0.05) than either the polar‐facing unburned slope or equatorial‐facing burned slope. Local slope magnitude does not appear to control the erosional response to wildfire, as relatively gently sloping (~20%) polar‐facing positions were severely eroded in the most intensively burned area. Field evidence and soil profile analyses indicate up to 4 cm of local soil erosion on the polar‐facing burned slope, but radionuclide mass balance indicates that much of this was trapped nearby. Using a 137Cs‐based erosion model, we find that the burned polar‐facing slope had a net mean sediment loss of 2 mm (~1 kg m−2) over a one to three year period, which is one to two orders of magnitude higher than longer‐term erosion rates reported for this region. In this part of the Colorado Front Range, strong hillslope asymmetry controls soil moisture and vegetation; polar‐facing slopes support significantly denser pine and fir stands, which fuels more intense wildfires. We conclude that polar‐facing slopes experience the most severe surface erosion following wildfires in this region, indicating that landscape‐scale aridity can control the geomorphic response of hillslopes to wildfires. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Historic charcoal hearth remains provide a unique archive of the long-term interaction between biochar, soil development, and plant growth. Charcoal as raw material was crucial for production of iron in iron works, and hence numerous charcoal hearths can be found in the forests near historic iron works in Europe and in the eastern united States. Charcoal hearths are round to elliptical forms often around 10 m in diameter and consist of several-decimeter-thick layers that contain charcoal fragments, ash, and burnt soil. We studied the soil chemistry of 24 charcoal hearths and compared them with the surrounding "natural" soils in the northern Appalachians of northwestern Connecticut. The thickness of the topsoils on the charcoal hearths and their carbon content are remarkably higher than in the surrounding topsoils. The presence of residual products from charcoal production classifies the soils as Anthropic Udorthents (US Soil Taxonomy) or Spolic Technosols (Humic) according to the World Reference Base for Soil Resources. The widespread occurrence of charcoal hearth remains, and their high spatial density in different ecosystems underlines their importance for further pedological research. [ABSTRACT FROM AUTHOR]

Relict charcoal hearths are round or elliptical earthen platforms up to 11 m in diameter and a widespread feature of historical industry that supplied charcoal used in the production of iron in furnaces or smelters. The iron industry dominated Litchfield County, Connecticut, and surrounding areas in the northeast United States throughout the 19th century, peaking in ∼1850. The large number of charcoal hearths in this region is a relic of >150 years of widespread iron production. In this study, we describe the architecture and soil stratigraphy of 26 charcoal hearths in Litchfield County. This contribution aims to (1) compare soils that comprise the charcoal hearths with 'natural' adjacent soils, (2) measure the thickness of topsoil developed upon the hearths, and (3) characterize the stratigraphy associated with these features. Results indicate that the black topsoils overlying the charcoal hearths contain residual charcoal and are on average 2.6 times thicker than adjacent Cambisols. Charcoal hearths display two or more black, charcoal-rich strata separated by layers of reddish-brown soil low in charcoal content indicating multiple episodes of use. We also find that many charcoal hearths have been stabilized with boulders on the downslope side during construction and repeated use. Overall, the results presented here provide significant information regarding the construction, use, and associated impacts of earthen platforms for charcoal production in the northeast United States, with further relevance to other areas where historical charcoal production occurred. [ABSTRACT FROM AUTHOR]

The architecture of the critical zone includes the distribution, thickness, and contacts of various types of slope deposits and weathering products such as saprolite and weathered bedrock resting on solid bedrock. A quantitative analysis of architecture is necessary for many model-driven approaches used by pedologic, geomorphic, hydrologic or biologic studies. We have used electrical resistivity tomography, a well-established geophysical technique causing minimum surficial disturbance, to portray the subsurface electrical resistivity differences at three study sites (Green Lakes Valley; Gordon Gulch; Betasso) at the Boulder Creek Critical Zone Observatory (BcCZO). Possible limitations of the technique are discussed. Interpretation of the specific resistivity values using natural outcrops, pits, roadcuts and drilling data as ground truth information allows us to image the critical zone architecture of each site. Green Lakes Valley (3700 MASL), a glacially eroded alpine basin, shows a rather simple, split configuration with coarse blockfields and sediments, partly containing permafrost above bedrock. The critical zone in Gordon Gulch (2650 MASL), a montane basin with rolling hills, and Betasso (1925 MASL), a lower montane basin with v-shaped valleys, is more variable due to a complex Quaternary geomorphic history. Boundaries between overlying stratified slope deposits and saprolite were identified at mean depths of 3.0 ± 2.2 m and 4.1 ± 3.6 m in the respective sites. The boundary between saprolite and weathered bedrock is deeper in Betasso at 5.8 ± 3.7 m, compared with 4.3 ± 3.0 m in Gordon Gulch. In general, the data are consistent with results from seismic studies, but electrical resistivity tomography documents a 0.5-1.5 m shallower critical zone above the weathered bedrock on average. Additionally, we document high lateral variability, which results from the weathering and sedimentation history and seems to be a consistent aspect of critical zone architecture within the BcCZO. [ABSTRACT FROM AUTHOR]

In the critical zone of the upland Boulder Creek (Colorado) catchment, a weathered mantle consisting of 3 to 10 m of oxidized bedrock, saprolite, and mobile regolith (grus and soil) overlies fresh and locally hydrothermally altered bedrock that is exposed beneath a low-relief surface. Saprolite forms from isovolumetric alteration of primary rock materials to secondary minerals by percolating water; mobile regolith includes rock materials in transport downslope, mixed by a variety of biologic and physical processes. Analysis of vadose zone samples by petrographic, inductively coupled plasma mass spectroscopy (ICP-MS) and X-ray diffraction (XRD) techniques demonstrates that weathering of Precambrian Boulder Creek Granodiorite and Silver Plume Granite has formed small amounts of clay and iron oxides. Bulk geochemical changes during alteration are minor except in the transformation of saprolite to regolith, which is enriched in neoformed minerals. In saprolite, the alteration sequence is: plagioclase > biotite > microcline > quartz. Quantitative XRD analysis shows that smectite and kaolinite form <10% of the rock in weathered samples and that smectite is absent and kaolinite and illite comprise >15% of the rock at several hydrothermally altered sites. Iron oxide and hydroxide minerals, such as goethite and hematite, have formed by weathering and by hydrothermal alteration. Hydrothermal alteration of granodiorite to saprolite at the Hurricane Hill site resulted in substantial losses of CaO, MgO and Na2O, Sr and metals such as Cd and Pb, and enrichment in K2O and the trace elements Cs, Sb, and W. At four critical-zone profiles studied in detail: (i) increases in kaolinite, smectite, and Fe oxides and decreases in magnetite concentration due to weathering are significant if fresh rock is compared to regolith; (ii) illite is enriched in soil; (iii) minor amounts of clay minerals are inherited from fresh rock; and (iv) clay minerals and Fe oxides are abundant only in hydrothermally altered saprolite. Some of the apparent enrichment of secondary minerals in weathered profiles likely results from dustfall and from material mixed into mobile regolith from heterogeneous bedrock sources. If some portion of the clay minerals in regolith and some fraction of dissolved material leaving Boulder Creek catchments are exotic, rates of clay and Fe oxide formation in the Boulder Creek area must be slow, and the alteration of granitic rocks during the conversion of saprolite to regolith may be driven mainly by volume expansion in this cool, continental climate. [ABSTRACT FROM AUTHOR]