Sandy Till Research Articles

Spatial pattern consistency and repeatability of proximal soil sensor data for digital soil mapping

AbstractData from proximal soil sensors can facilitate digital soil mapping at high spatial resolutions. However, their use for predicting static soil properties, such as texture, is affected by spatio‐temporal changes in environmental and measurement conditions. In this research study, seasonal changes in spatial patterns and repeatability of data provided by a platform that simultaneously measures the red (Red) and near infrared (NIR) reflectance, apparent soil electrical conductivity (ECa), temperature, and volumetric moisture content of topsoil (at 3–6 cm depth) were assessed. Test fields are located in Southern Finland with textures dominated by clay and fine sandy till. During single scans, mean relative differences between the data from duplicated measurement points ranged from ~4% to 6% and were the highest for temperature and Red values. The consistency of spatial patterns across seasons (spring and autumn 2021 and 2022) was the highest for ECa values, and the lowest for NIR. ECa and moisture were significant for predicting the clay contents at a cereal grain crop site, whereas temperature was significant at grass ley sites. Errors were generally lower when using spring data compared with autumn data (RMSE ranging from 4.8% to 11.1% for the data from different fields and measurement dates). For the fields, where static soil properties change at small spatial scales, spatially detailed moisture and temperature data support the understanding of seasonal changes in the spatial patterns derived from multi‐sensor data, and the corresponding changes in the performance of calibration models.

Assessing Contaminant Mass Discharge Uncertainty With Application of Hydraulic Conductivities Derived From Geoelectrical Cross‐Borehole Induced Polarization and Other Methods

AbstractA new methodology was developed to support contaminant mass discharge (CMD)‐based risk assessment of groundwater contamination downgradient of point source zones. Geoelectrical cross‐borehole induced polarization (IP) data were collected at a site undergoing in situ remediation of chlorinated solvents for determining 2D hydraulic conductivity (K) distributions with an inversion model resolution of 0.15 m (vertically) x 0.50 m (horizontally) in three control planes from 10 to 20 m depth. Additionally, 18 slug tests and 31 grain size distribution analyses (GSA) from the control planes, were used for K‐estimation. The geometric means and variance of the IP, slug test, and GSA derived K‐estimates were consistent with previously studied sandy aquifers. Furthermore, the vertical variation in K between two geological settings, a sandy till and a meltwater sand formation, was clearly identified by the IP K‐estimates. The vertical variation was backed up by hydraulic profiling tool (HPT) measurements. Random realizations of CMD were simulated based on the cross‐borehole IP derived K‐values. For comparison, the CMD was also estimated with a geostatistical conditional simulation approach, using the data from slug tests and GSAs. The high IP resolution captured the small scale variations in K across the transects and led to CMD predictions with a narrow uncertainty interval, whereas slug test and GSA either under‐ or overestimated the magnitude of the areas with the highest CMD. Applying the geophysical cross‐borehole method for estimating K‐distributions in addition to traditional methods would improve CMD‐based risk assessment and evaluation of remediation performance at contaminated sites.

Forward modeling and 3D inversion of electromagnetic data collected over the McArthur River uranium deposit in the Athabasca Basin, Canada

Detection and assessment of the deeply buried high-grade uranium deposits in the Athabasca Basin rely on geophysical methods to map conductive rocks. Variable Quaternary surface cover can mask the anomalous signals from depth and affect the interpretation of inverted conductivity models. We present the analysis of several electromagnetic (EM) modeling studies and two field data sets to demonstrate the effects of varying Quaternary cover resistivity and thickness, on the ability to resolve the parameters of underlying sandstone, alteration, and basement conductors. Synthetic data, assuming a typical shallow EM sounding system and realistic resistivities found in the Athabasca Basin, indicate that resistivity and thickness parameters of the Quaternary cover can be separately recovered in cases in which this cover is more conductive than the underlying sandstone, but not when the cover is significantly more resistive. A 3D modeling study indicates that by using airborne EM data, it is possible to detect a basement conductor of 20 S at a depth of at least 600 m below the surface, even in the presence of Quaternary cover thickness variations of the up to 20% (40–60 m). Furthermore, although Quaternary cover variations and deeper sandstone alteration can produce comparable anomalous signal amplitudes in a time-domain EM response, their effects are most visible in distinctly separate time windows. Ground-penetrating radar and other data to characterize the Quaternary cover in the McArthur River area indicate that this cover consists mostly of sandy tills ranging in thickness from 0 to 117 m. Constrained 3D inversion of an airborne EM data set from the same area indicates basement conductors consistent with the depth and location of a known fault. Elevated conductivity in the sandstone by up to a factor of two over the background values could indicate possible alteration.

Parastā oša (Fraxinus excelsior) stāvoklis Latvijā mežaudžu destrukcijas aktīvajā fāzē. Meža augšanas apstākļi un kvartāra nogulumi

At present, 87.9% of all ash stands in Latvia are found on dry soils, where groundwater does not affect the root system of trees, and 94.3% of ash stands are distributed in eutrophic habitats, saturated with exchange bases and biologically active nitrogen. In Latvia, ash stands are found mainly on the loose sediments of sandy till and clayey till in highland and rise landscapes, as well as on silty glaciolymnic sediments in the lowlands. Sand sediments in the coastal lowlands and riverine landscapes, as well as peat sediments in both highland and lowland landscapes are not suitable for ash forest stands.

Biochar addition affected nutrient leaching and litter decomposition rates in boreal sandy soils

Effects of biochar addition on litter decomposition rates, nutrient leaching and soil moisture were tested in two boreal agricultural soils; a sandy till and a medium fine sand. Three litter bags were buried in soil basins, which were stored in the dark for 31 and 19 weeks in the sandy till experiment and medium fine sand experiment, respectively. Once per each temperature period, the soil was saturated in order to collect excess water for nutrient analyses. Biochar increased the decomposition rate of N-rich litter but did not affect the decomposition of N-poor litter. PO43--P and NO2--N were released from the biochar to the leached water and thus leaching of PO43--P, NO2--N and total P was increased in the soil with the finer texture. However, biochar retained water after heavy irrigation and leaching of PO43--P and total P was not increased on the coarser soil. Although pure biochar adsorbed NH4+-N from nutrient solutions, NH4+-N leaching from both soil types was generally not affected by biochar. Leaching of nitrate NO3--N and total N was decreased on both soils due to retention by the biochar.

Indicator mineral and till geochemical signatures of the Broken Hammer Cu–Ni–PGE–Au deposit, North Range, Sudbury Structure, Ontario, Canada

The Broken Hammer Cu–Ni–PGE–Au footwall deposit in the North Range of the Sudbury Structure in Canada consists of a shallow surface zone of vein-hosted and vein stockwork-hosted mineralization within Sudbury breccia developed in the quartz monzonite Levack Gneiss Complex. The surface of the deposit consists of a 2–120 cm wide chalcopyrite vein and numerous smaller veins dominated by chalcopyrite–magnetite–millerite with trace gold, platinum group minerals, tellurides, bismuthides and selenides. The Laurentide Ice Sheet flowed southward across the region depositing a sandy till that contains abundant sperrylite (hundreds of grains), chalcopyrite, pyrite and gold in the heavy mineral fraction down-ice of mineralization. Mineral liberation analysis of the <0.25 mm heavy mineral fraction of metal-rich till identified a broader suite of PGM and sulfides than visual identification methods. The <0.063 mm fraction of till displays a strong geochemical signature of the mineralization for Pd, Pt, Au, Cu and Ag and, to a lesser extent, Bi, Te and Sn; however, geochemical signatures are not detectable as far down-ice as indicator minerals. Till sampling has not been used for exploration in the Sudbury region because of the abundant outcrop and the use of geophysical and prospecting techniques. This study demonstrates that indicator mineral and till geochemical methods are useful exploration tools for the region. The presence of sperrylite and chalcopyrite in oxidized till indicates that even thin (<1 m) highly weathered till is an effective sample medium here.

Soil Compaction Effects on Root‐Zone Hydrology and Vegetation in Boreal Forest Clearcuts

Core Ideas Impact of forwarding on soil water and vegetation was investigated after 4 to 5 years. Soil water content was highest in wheel tracks and lowest between tracks. Bare soil was more frequent in tracks and between tracks than in undisturbed soil. In wheel tracks, soil aeration may be restricted in periods with high precipitation. Simulated root‐zone pressure heads showed little variation between microsites. Soil compaction is a common consequence of forestry traffic traversing unprotected, moist soils; it decreases porosity and affects hydraulic conductivity even in coarse‐textured soils. The aim here was to study root‐zone hydrology and vegetation in three microsites (in, between, and beside wheel tracks) 4 to 5 yr after forwarder traffic, on stony and sandy till soils in two clearcuts in northern Sweden. Measurements of soil volumetric water content (VWC), vegetation indicators and one‐dimensional hydrological modeling (Hydrus‐1D) of wheel tracks and undisturbed soil were conducted. Soil VWC was monitored hourly during 2017 and 2018 in three or four plots along a slope on each site. Soil VWC was also measured once with a portable sensor in 117 plots along two slopes at each site, where the vegetation was recorded and analyzed using Ellenberg indicator indexes. Soil VWC was highest in wheel tracks and lowest between tracks; this was corroborated by the species composition in the wheel tracks (Ellenberg indicator for soil moisture). Bare soil was more frequent in wheel tracks and between tracks than in undisturbed soil. The model simulations indicated that the changed soil hydraulic properties influenced the VWC results in the wheel tracks. However, the differences in average pressure heads in the root zone were small between the microsites and only apparent during dry periods. In the wheel tracks, air‐filled porosity was <0.10 m3 m−3, indicating insufficient soil aeration during 82% (Site T) and 23% (Site R) of the 2017 growing season. Insufficient aeration could be one explanation for the presence of some still unvegetated areas.

Study of the tree species effect on the soil by means of discriminant analysis

A multi-sided study of the interactions between forest and soil requires choosing sample plots in such a way when their soil characteristics are as similar as possible but the types of biocoenoses are different. This study employed materials from the database “Soils of Karelia”, which has pooled together long-term data on soils of the Republic of Karelia. The aim of the analysis was to identify the soil traits that are the most sensitive to the type of biocoenosis. The biocoenoses chosen for the analysis were automorphic pine, spruce and birch communities, collectively accounting for 99 % of forest stands in Karelia, growing on podzolic-type Al-Fe-humus soils with sandy texture over sandy or loamy-sand till, which represent the most widespread type of soils in the study area. The analysis was performed for the following soil horizons: forest floor (O), eluvial (E) and illuvial (B). In order to characterize the soil horizons the physico-chemical parameters were used: рН (KCl), total С and N content, labile P 2 0 5 and K20 compounds content, and gross content of SiO 2 , TiO 2 , Al 2 O 3 , Fe 2 O 3 , MnO, MgO, CaO, Na 2 O, K 2 O, P 2 O 5 . Discriminant analysis was employed to determine the traits contributing the most to the differentiation of biocoenosis types. The contribution of the traits to differentiation between groups was measured by Wilks’ lambda. Overall, the analysis has shown that N and C content the most significantly reflect the changes happening under the effect of the forest, both in the organic and in the mineral parts of the soil, as corroborated by the findings of numerous Russian and foreign researchers.

Formy pierścieniowe w rejonie Wejherowa jako prawdopodobne pozostałości po-pingo i ich znaczenie dla paleogeografii późnego glacjału w północnej Polsce = Ring forms in the area of Wejherowo as likely remnants of pingos, and their significance for Late-Glacial paleogeography in Northern Poland

Several potential Polish locations for the occurrence of fossil pingos were determined on the basis of analyses of a digital terrain model. Subsequent field reconnaissance connected with drilling into the geological structure, confirmed that one form located NW of Gdańsk, was indeed a fossil pingo. The aforementioned forms occur in a moraine plateau area related to the last ice-sheet retreat towards the Gardno phase moraine. This surface of the plateau is noticeably inclined south-north, at elevations of between 170 and 110 metres. It in fact proved possible to identify more than 80 very well-developed fossil pingos in the area investigated, with each found to consist of a central depression of average diameter 60‒80 m, as surrounded by a rampart 3–7 m high. By drilling into the central parts of the fossil pingos, we found them to be filled with organic sediments up to 6 or 7 m deep. The bottom layer of infill has carbonate and mineral-carbonate gyttjas up to 2 m thick. These are overlain by a peat layer up to 4 m thick, while these organic sediments are underlain by gley till sand. The ramparts are of sandy till frequently intercalated with silty sand. The established sequence of infilling of the central parts of the fossil pingos indicates that, in the immediate aftermath of ice-core melting, these played host to small ponds in which the accumulation of gyttja was able to take place. The gradual accumulation of lake-bottom sediments resulted in a shallowing of the ponds and the development of peat bogs. The morphological image of the above forms and initial drilling in the studied area suggest an association between their genesis and the presence of an ice-cored mound of the pingo type, experiencing subsequent degradation in the direction of the current, fossil pingo, form. Besides the classical, literal morphology of these forms, a decisive argument for acceptance of the above concept is provided by rampart lithology indicating how essential slow processes were in their accumulation. The nature and thickness of the organic infilling in the central part of a post-pingo prove equally important, suggesting an extended period of lake and peat-bog accumulation, probably lasting for the entire Holocene. The aforementioned arguments allow for the precluding of any origin linked with direct human activity (ground construction, bomb craters). The high density and close proximity and morphological similarity of the forms are likewise inimical to an identification as craters caused by above-ground meteorite explosions. Likewise, comparative analysis of the studied forms and kettle holes (usually larger irregularly-shaped larger forms of varied bottom topography) fails to indicate that the ring forms under study here have somehow arisen through the melting of buried dead ice. Analysis of deep boreholes made previously may support a geological structure of the analysed area consisting of a sand layer over 90 metres thick covered by a discontinuous till moraine several metres thick. The thick sand layer in question consists of differently-aged glaciofluvial sediments. This is a hydrogeological window connecting three main Quaternary aquifers and offering a perfect location for the ascension of groundwater. In conditions of developing discontinuous permafrost, this movement led to the creation of pingo forms in open systems on the surface. It is clear that investigation work is not currently at a stage allowing for about as to age to be made, or all details regarding evolution provided. However, the results of planned geomorphological, hydrogeological and geochronological studies should provide for both the recognition and detailed definition of the forms, thereby prompting discussion as to the evolution of permafrost during the late Weichselian transgression and recession in Central Europe.

Terrain mobility estimation using TWI and airborne gamma-ray data

Since one purpose of forestry laws and certification standards is to guide loggers to minimize the damage caused by forest operations, information regarding internal variations in site trafficability is needed for both economic and ecological reasons. The aim of this work was to test the prediction of terrain mobility from open data sources in Finland. New Lidar-based data sources were available for calculating terrain features and a gamma-ray-based soil wetness parameter. Rut depths were measured and can bus data were collected from a forwarder in two logging areas. Net power at the forwarder's drive shaft, total resistance and rolling resistance were calculated from the can bus data and augmented by means of a digital elevation model (DEM), soil data, aerogeophysical gamma-ray radiation data and a topographic wetness index (TWI). The rut depth was explained best either by TWI calculated from a 2 m grid DEM or the combination of a 16 m grid TWI, gamma radiation from thorium and engine net power (r2 = 0.20–0.33). In the areas concerned here the gamma-ray results may have detected the soil type more precisely than the soil type class, and the gamma radiation from thorium may also have detected wet places inside the site type, labelled as sandy till, and will therefore have explained the variation in rut depth.

Subglacial till formation: Microscale processes within the subglacial shear zone

This was a study of subglacial deformation till genesis from a modern temperate glacier, at Skálafellsjökull, Iceland. Detailed microscale properties of till samples (from Scanning Electron Microscope [SEM] and thin section analysis) were examined from a glacial site with in situ subglacial process monitoring and an exposed subglacial surface in the foreland. Two lithofacies were examined, a grey sandy till derived from the ash and basalt, and a silty reddish brown till derived from oxidized paleosols and/or tephra layers. These also represented a clay-content continuum from low (0.3%) to high (22.3%). The evolution from debris to subglacial till was investigated. This included a reduction in grain-size (21% for grey lithology, 13% reddish brown lithology), and reduction in rounding (RA) (32% for the grey lithology, 26% for the reddish brown lithology), and the quantification and analysis of the different grain erosion/comminution processes in the resultant till. It was shown that the microstructures within a till were dependent on shear strain and glaciological conditions (deformation history). The low clay content tills were dominated by linear structures (lineations and boudins, and anisotropic microfabric) whilst the higher clay content tills were dominated by rotational structures (turbates and plaster, and isotropic microfabric). These results are important in our understanding of the formation of both modern and Quaternary tills and informs our reconstruction of past glacial dynamics.

Till Geochemistry in West-Central Manitoba: Interpretation of Provenance and Mineralization Based on Glacial History and Multivariate Data Analysis

Till geochemical datasets from archived samples in west-central Manitoba are interpreted using multivariate data analytical techniques such as principal component analysis and pathfinder element index methods, combined with a spatial representation of the data in a geographic information system (GIS). Results show that carbonate till derived from Hudson Bay, as expressed by the (Ca + Mg)/Na ratio, is found predominantly east of Leaf Rapids and extends south into the Northeastern Kisseynew Domain. A 30- to 70-km-wide zone is documented beyond the limit of dissolvable carbonate dispersal that contains till of Labradorean provenance with low Ca-Mg-Mn-Te concentrations, noncalcareous till of Keewatin provenance, and silty calcareous till at depth. The variation in till provenance, together with the predominance of southwesterly ice-flow indicators, suggests that carbonate dispersal occurred prior to deglaciation, and that surface tills in the zone of confluence between Labradorean and Keewatin ice are likely the result of recycling of calcareous tills and/or carbonate-leached sandy tills, mainly by Keewatin ice. The newly defined limits of carbonate and Ca-rich till, typically used to assess provenance and glacial transport, provide a new framework for evaluating the significance of till geochemical patterns when drift prospecting over the Trans-Hudson orogen. Several regional- to local-scale dispersal trains from geochemically distinct bedrock sources are discussed in terms of elemental association, glacial transport characteristics, and potential bedrock sources. The multivariate statistical approach combined with GIS mapping also highlights new areas with small multi- or single-element enrichments that may be of further interest for volcanogenic massive sulfide exploration or for potentially more detailed drift sampling.

Effects of meat bone meal as fertilizer on yield and quality of sugar beet and carrot

Meat and bone meal (MBM) is a by-product of the meat industry and is an important pathway for recycling of N and P. MBM contains about 8% N, 5% P, 1% K and 10% Ca. Field trials compared the effects of MBM and mineral fertilizer on yield and quality of sugar beet (2008-2009) and carrot (2010-2011) in Finland. MBM fertilisation of sugar beet grown on clay loam and sandy clay soil gave 11.4% (2008) and 19.6% (2009) lower yields than mineral fertilizers. The lower root yield in 2008 was compensated by higher extractable sugar content and lower amino-N, K and Na in root but no such compensation in root quality was detected for 2009. Mixing MBM with mineral NPK fertilizers had similar effects as MBM-alone. MBM (80 kg N ha-1 2010 and 60 kg N ha-1 2011) together with K fertilizer (Patentkali®, 180 kg K ha-1) were applied for carrot to a fine sandy till soil in 2010 and sandy loam in 2011. MBM alone gave 14% lower total and marketable root yield than mineral fertilization. The lower yield was compensated by improved quality, lower NO3- content in the carrot and good storability. Adding extra fertilizer during growth or separating fertilization applications had no effect on root yield or quality. MBM performed in these cases mainly as an organic N fertilizer. The N supply from MBM is not sufficient for achieving same yields as with mineral fertilizers. The relative N efficiency of total N of MBM was 83% that of mineral fertilizers. MBM should be targeted on soils with low P status.We conclude that MBM is a reasonably competitive alternative to mineral fertilizers, and as a recycled fertilizer it is a good option for organic production.

Dye tracer visualization of flow patterns and pathways in glacial sandy till at a boreal forest hillslope

Dyes are valuable tracers in visualizing flow patterns and pathways in soil. We applied the dye Acid Blue 9 to unsaturated and saturated soil profiles at a boreal forest hillslope consisting of glacial sandy till, and determined the soil physical properties from soil samples. The objective was to characterize preferential flowpaths, investigate their porosity, extent and connectivity, and complement earlier findings on subsurface flow formation at the site. According to the results, preferential flowpaths were formed by roots, erosion related to soil water flow, freezing–thawing cycles, and soil fauna. The role of roots and stones in the formation of preferential flowpaths was emphasized. Porosity of preferential flowpaths was 5.1±1.8%, and they extended to a depth of about 55cm from the soil surface; the deepest roots reached the same depth. When the soil saturated, individual preferential flowpaths self-organized into continuous and well-connected lateral flow systems along the slope. At the slope shoulder, preferential flow network covering the entire soil profile, as well as preferential flowpaths on the underlying bedrock surface, were considered crucial for runoff generation. In the midslope area, runoff generation was characterized by lateral preferential flow and the transmissivity feedback phenomenon. At the slope foot, preferential flowpaths in soil below the eluvial horizon were the major runoff contributors. A full saturation of the soil profile at the slope is unlikely under natural conditions. However, lateral flow was found to occur also in unsaturated soil.

Comparisons between macro‐ and microfabrics in a pebble‐rich, sandy till deposited by the Cordilleran Ice Sheet

It is standard practice to measure particle fabrics in glacial studies to infer palaeo‐ice flow directions and processes of till formation but few studies examine the relationships between particle fabrics at different (i.e. the macro‐ and micro‐) scales. This knowledge is critical to inform the utility of the methods and limitations of the associated interpretations. Micro‐ (sand grain) and macro‐ (pebble) fabrics of pebble‐rich, sandy subglacial till (Kamloops Lake till) deposited by the Cordilleran Ice Sheet, south‐central British Columbia, were compared to assess their similarities and differences, and therefore their utility for understanding subglacial processes. Before comparisons were made, the data were tested for robustness by assessing various controls (e.g. sampling face orientation, number of particles measured, statistical variation resulting from sampling effects, particle shape, size and concentration) on particle fabrics. A new method of microfabric analysis was applied that involves the identification and delineation of distinct clusters of similarly orientated sand grains in order to compare them with macrofabrics and inferred ice‐flow directions. The results show that microfabrics, on their own, are an unreliable indicator of ice‐flow direction in Kamloops Lake till in the study area and should not be used as a substitute for macrofabric data, as they probably record late‐stage microscale strain patterns and pore‐water flow in addition to till deposition and deformation by overriding ice. We suspect that this would also be the case for coarse‐grained till elsewhere. Our findings suggest that till microfabric interpretations should always be made after assessing corresponding macrofabric data alongside sedimentological and structural observations.

Groundwater dynamics in a till hillslope: flow directions, gradients and delay

AbstractKnowledge of groundwater dynamics is important for the understanding of hydrological controls on chemical processes along the water flow pathways. To increase our knowledge of groundwater dynamics in areas with shallow groundwater, the groundwater dynamics along a hillslope were studied in a boreal catchment in Southern Sweden. The forested hillslope had a 1‐ to 2‐m deep layer of sandy till above bedrock. The groundwater flow direction and slope were calculated under the assumption that the flow followed the slope of the groundwater table, which was computed for different triangles, each defined by three groundwater wells. The flow direction showed considerable variations over time, with a maximum variation of 75°. During periods of high groundwater levels the flow was almost perpendicular to the stream, but as the groundwater level fell, the flow direction became gradually more parallel to the stream, directed in the downstream direction. These findings are of importance for the interpretation of results from hillslope transects, where the flow direction usually is assumed to be invariable and always in the direction of the hillslope. The variations in the groundwater flow direction may also cause an apparent dispersion for groundwater‐based transport. In contrast to findings in several other studies, the groundwater level was most responsive to rainfall and snowmelt in the upper part of the hillslope, while the lower parts of the slope reached their highest groundwater level up to 40 h after the upper parts. This can be explained by the topography with a wetter hollow area in the upper part. Copyright © 2011 John Wiley & Sons, Ltd.

Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea

Passchier, S., Laban, C., Mesdag, C.S. & Rijsdijk, K.F. 2010: Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea. Boreas, Vol. 39, pp. 633–647. 10.1111/j.1502‐3885.2009.00138.x. ISSN 0300‐9483.Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice‐stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice‐sheet reconstructions.

Characterization of a Regional Aquifer System in the Maritimes Basin, Eastern Canada

A regional hydrogeological study was carried out in the Maritimes provinces, in one of the main aquifer systems in Canada. The study area covers a land surface of 10,500 km2, of which 9,400 km2 is over Carboniferous and younger rocks. The sedimentary fractured bedrock is composed of a sequence of discontinuous strata of highly variable hydraulic properties, and is overlain by a thin layer of glacial till (mostly 4 to 8 m). Depending on areas, 46 to 100% of the population relies on groundwater for water supply. Almost all residential wells are shallow (28 m on average) open holes that are cased only through the surficial sediments. This paper describes a regional hydrogeological investigation based on targeted fieldwork, the integration of a wide variety of existing multisource datasets and groundwater flow numerical modelling. The aim of this paper is to present the current state of understanding of the aquifer system in a representative area of the Maritimes Basin, along with the methodology used to characterize and analyze its distinct behaviour at the regional, local and point scales. This regional hydrogeological system contains confined and unconfined zones, and its aquifer lenticular strata extend only a few kilometers. Preferential groundwater recharge occurs where sandy tills are present. The estimated mean annual recharge rate to the bedrock aquifers ranges between 130 and 165 mm/year. Several geological formations of this Basin provide good aquifers, with hydraulic conductivity in the range of 5 × 10−6 to 10−4 m/s. Based on numerical flow modelling, faults were interpreted to play a key role in the regional flow. Pumping test results revealed that the aquifers can locally be very heterogeneous and anisotropic, but behave similarly to porous media. Work performed at the local scale indicated that most water-producing fractures generally have a sub-horizontal dip along a north-east (45°) strike.

The distribution of silty soils in the Grayling Fingers region of Michigan: Evidence for loess deposition onto frozen ground

This paper presents textural, geochemical, mineralogical, soils, and geomorphic data on the sediments of the Grayling Fingers region of northern Lower Michigan. The Fingers are mainly comprised of glaciofluvial sediment, capped by sandy till. The focus of this research is a thin silty cap that overlies the till and outwash; data presented here suggest that it is local-source loess, derived from the Port Huron outwash plain and its down-river extension, the Mainstee River valley. The silt is geochemically and texturally unlike the glacial sediments that underlie it and is located only on the flattest parts of the Finger uplands and in the bottoms of upland, dry kettles. On sloping sites, the silty cap is absent. The silt was probably deposited on the Fingers during the Port Huron meltwater event; a loess deposit roughly 90 km down the Manistee River valley has a comparable origin. Data suggest that the loess was only able to persist on upland surfaces that were either closed depressions (currently, dry kettles) or flat because of erosion during and after loess deposition. Deep, low-order tributary gullies (almost ubiquitous on Finger sideslopes) could only have formed by runoff, and soil data from them confirm that the end of gully formation (and hence, the end of runoff) was contemporaneous with the stabilization of the outwash surfaces in the lowlands. Therefore, runoff from the Finger uplands during the loess depositional event is the likely reason for the absence of loess at sites in the Fingers. Because of the sandy nature and high permeability of the Fingers' sediments, runoff on this scale could only have occurred under frozen ground conditions. Frozen ground and windy conditions in the Fingers at the time of the Port Huron advance is likely because the area would have been surrounded by ice on roughly three sides. This research (1) shows that outwash plains and meltwater streams of only medium size can be significant loess sources and (2) is the first to present evidence for frozen ground conditions in this part of the upper Midwest.

Geological controls on conifer distributions and their implications for forest management in Finnish Lapland

Soil water and nutrient regimes of naturally established old-growth conifer stands and those of intensively managed Norway spruce [Picea abies (L.) Karst.] sites were assessed over a range of lithological provinces in Finnish Lapland. Soil dielectric permittivity (ϵ), as a measure of soil water content (θ v) and soil electrical conductivity (σ a), as a measure of soil solute content, were species specific, such that high soil θ v>0.27 cm3cm−3 (ϵ>15) constitutes an edaphic constraint for Scots pine (Pinus sylvestris L.) and low soil solute content (σ a<0.5 mS m−1) is constraining for Norway spruce. The spatial pattern of the soil θ v was temporally stabile, such that intraseasonal and interseasonal soil θ v was significantly higher in silty tills of spruce stands compared to sandy tills of pine stands. Scots pine was the only conifer on tills derived from felsic rocks of Hetta granite (HG) and Lapland granulite (LG). Norway spruce dominated on tills derived from the mafic rocks of Lapland greenstone belt (LGB), but tills of LG and HG constitute a dispersal barrier for spruce. Mechanical site preparation (MSP) with ploughing (Marttiini) was not able to amend soil θ v to meet site requirements of Scots pine at former spruce sites. MSP resulted in significant reduction in soil nutrient content such that untreated control σ a>tilt/shoulder σ a>trench σ a. The results imply that MSP treatments through which cross-contour tracks are created pose a risk to the sustainability of soil quality in Lapland.