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Peter J. Dillon - One of the best experts on this subject based on the ideXlab platform.
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Chironomidae (Diptera) larvae of Precambrian Shield headwater streams, Canada
Zootaxa, 2012Co-Authors: Armin Namayandeh, Bohdan Bilyj, David V. Beresford, Keith M. Somers, Peter J. DillonAbstract:A taxonomic diagnosis of chironomid larvae collected from Precambrian Shield headwater streams, Canada, is providedfor 51 species. In addition, the Nearctic distribution is given for each species, including 17 new records, along with and information on their ecology and habitat.
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the effects of dissolved organic carbon acidity and seasonality on metal geochemistry within a forested catchment on the Precambrian Shield central ontario canada
Biogeochemistry, 2009Co-Authors: Amanda L Landre, Shaun A Watmough, Peter J. DillonAbstract:Metal pollution, in combination with other environmental stressors such as acid deposition and climate change, may disturb metal biogeochemical cycles. To investigate the influence of dissolved organic carbon, acidity and seasonality on metal geochemistry, this study has described concentrations of 19 metals as they pass through an acidified forested catchment on the Precambrian Shield in south-central Ontario, Canada. Metal, dissolved organic carbon (DOC) and sulphate (SO4 2−) concentrations fluctuate throughout the catchment compartments as the water passes through and interacts with vegetation, soils and bedrock. Relationships among metals, DOC and SO4 2− are most pronounced in compartments where DOC and SO4 2− exhibit high variability, namely in the throughfall, organic horizon soil water, and wetland-draining stream. Metal, DOC and SO4 2− concentrations varied seasonally in the streams, and temporal coherence occurred among metal, DOC and SO4 2− concentrations in the organic horizon soil water and the wetland-draining stream (PC1). In the wetland-draining stream, the highest DOC, Cr, Cu, Fe, Pb, and V concentrations occur in the summer, whereas concentrations of SO4 2− and most other metals peak in the fall after a period of drought. Despite the rural location, provincial water quality objectives for surface water were exceeded for many metals when the peak fall values occurred.
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detecting the transport of toxic pesticides from golf courses into watersheds in the Precambrian Shield region of ontario canada
Environmental Toxicology and Chemistry, 2007Co-Authors: Tracy L Metcalfe, Peter J. Dillon, Chris D MetcalfeAbstract:Golf courses impact the environment through alterations to habitat and through the release of nutrients and pesticides. The Precambrian Shield region of central Ontario, Canada, which is a major recreational area, is especially susceptible to the impacts of golf courses as a result of the geology and hydrology of the region. In a monitoring program at two golf courses in the Muskoka region conducted during the spring, summer, and fall of 2002, semipermeable membrane devices (SPMDs) were deployed into streams that drain the golf courses. The extracts from the SPMDs were tested for toxicity using bioassays with early life stages of an aquarium fish, the Japanese medaka (Oryzias latipes). Toxicity was assessed using a scoring system developed for the present study. The bioassays with medaka indicated that toxicity was highest in extracts from SPMDs deployed during the spring and the fall. The peaks in toxicity for the SPMDs deployed at the two golf courses corresponded with the presence in the SPMD extracts of pentachloronitrobenzene (PCNB) at concentrations up to 334 ng/SPMD. Quintozene is the turfgrass fungicide in which PCNB is the active ingredient. Pentachlorothioanisole, an anaerobic degradation product of PCNB, also was detected in the SPMDs deployed during the spring. Extracts prepared from SPMDs with high toxicity contained residues of a surfactant used in pesticide formulations, nonylphenol, at concentrations up to approximately 20 μg/SPMD. Overall, these data indicate that some pesticides applied to golf courses in the Precambrian Shield of central Ontario may have the potential to cause toxic impacts to aquatic organisms in adjacent watersheds.
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export of nutrients from golf courses on the Precambrian Shield
Environmental Pollution, 2006Co-Authors: Jennifer G Winter, Peter J. DillonAbstract:Abstract Annual export rates, or fluxes, of total nitrogen (TN), nitrate, total phosphorus (TP) and potassium from four streams on two golf courses on the Precambrian Shield were compared with those from forested reference locations. Overall, the mean annual fluxes of K, TN, NO 3 and TP from golf courses were greater than from forested areas by 10, 2, 6 and 2 times, respectively. The overall mean export coefficients (kg/ha/yr) were 16 for K, 5.2 for TN, 2.1 for NO 3 and 0.14 for TP. For TN and TP, these are similar to those reported from cropland in Canada by Chambers and Dale (1997. Contribution of industrial, municipal, agricultural and groundwater sources to nutrient export, Athabasca, Wapiti and Smoky Rivers, 1980 to 1993. Northern River Basins Study Project Report No. 110. Northern River Basins Study, Edmonton, Alberta).
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changes in the molecular weight distribution of dissolved organic carbon within a Precambrian Shield stream
Water Resources Research, 2006Co-Authors: Dolly N Kothawala, R D Evans, Peter J. DillonAbstract:[1] Dissolved organic carbon (DOC) is of environmental and biological significance to Precambrian Shield streams. Our objective was to determine the extent of transformations to the concentration and molecular weight distribution (MWD) of DOC along the length of Harp 4A stream, from the headwater swamp to the outflow into Harp Lake. The average MWD shifted to a smaller weight by 0.48 kDa. A rapid decline in the concentration and MWD of DOC was observed within 120 m from the main DOC source, a headwater swamp. The most significant decline in concentration and MWD was observed within the first of a series of three beaver ponds. DOC within waters downstream of the beaver ponds was resistant to further changes in concentration and MWD. The MWD within each of four stream sections with Hp 4a remained stable over 6 months, from May to October 2001.
Murray Richardson - One of the best experts on this subject based on the ideXlab platform.
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wetlands and low gradient topography are associated with longer hydrologic transit times in Precambrian Shield headwater catchments
Hydrological Processes, 2020Co-Authors: Daniel Lane, Murray Richardson, Colin P R Mccarter, Chris Mcconnell, Tim Field, George B Arhonditsis, Carl P J MitchellAbstract:The estimation of hydrologic transit times in a catchment provides insights into the integrated effects of water storage, mixing dynamics, and runoff generation processes. There has been limited effort to estimate transit times in southern boreal Precambrian Shield landscapes, which are characteristically heterogeneous with surface cover including till, thin soils, bedrock outcrops, and depressional wetland features that play contrasting hydrologic roles. This study presents approximately 3.5 years of precipitation and streamflow water isotope data and estimates mean transit times (MTTs) and the young water fraction (py) across six small catchments in the Muskoka‐Haliburton region of south‐central Ontario. The main objectives were to define a typical range of MTTs for headwater catchments in this region and to identify landscape variables that best explain differences in MTTs/py using airborne light detection and ranging and digital terrain analysis. Of the transit time distributions, the two parallel linear reservoir and gamma distributions best describe the hydrology of these catchments, particularly because of their ability to capture more extreme changes related to events such as snowmelt. The estimated MTTs, regardless of the modelling approach or distribution used, are positively associated with the percent wetland area and negatively with mean slope in the catchments. In this landscape, low‐gradient features such as wetlands increase catchment scale water storage when antecedent conditions are dryer and decrease transit times when there is a moisture surplus, which plausibly explains the increases in MTTs and mean annual runoff from catchments with significant coverage of these landscape features.
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the influence of hyporheic exchange on reach scale water budgets in a Precambrian Shield catchment quebec canada hyporheic exchange and reach scale water budgets
Hydrological Processes, 2013Co-Authors: Ryan C Zanatta, Sean K Carey, Murray RichardsonAbstract:The influence of hyporheic exchange on water and solute budgets of streams is widely identified as important; yet, there is a notable absence of research identifying its role in Precambrian Shield headwater streams. This research addressed this shortcoming by quantifying the proportions of solute mass loss, net and gross water gains and losses for selected reaches over a single summer recession period. Six conservative tracer injections were performed on nine reaches of a 2.94-km2 catchment in Gatineau Park, Quebec, Canada, from July to November, 2011. High solute exchange occurred for all reaches despite most showing positive net discharge. Solute losses in stream reaches typically exceeded 10%, and substantial gross water losses and gains indicate a high degree of bi-directional water exchange along stream reaches. Both solute loss and the fraction of channel water involved in hyporheic exchange increased throughout the summer in response to a decrease in discharge and increase in the time of contact. Results support the assertion that reductions in groundwater contributions to streamflow throughout the summer baseflow period allow for greater exchange of water through hyporheic flowpaths, which constitute the majority of gross channel losses and gains. Spatial (inter-reach) variability in mass loss has been previously ascribed to watershed control on exchange potential. In this catchment, net discharge and gross hydrologic gains were inversely related to the average flowpath gradients within the valley bottom and local hillslope contributing areas. Copyright © 2013 John Wiley & Sons, Ltd.
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contributions of streamflow variability concentration discharge shifts and forested wetlands to terrestrial aquatic solute export in Precambrian Shield headwater catchments
Ecohydrology, 2012Co-Authors: Murray RichardsonAbstract:Hydrological and biogeochemical processes in terrestrial watershed compartments are an important source of short- and long-term physico-chemical dynamics in Precambrian Shield headwater lakes. In this study, a residual analysis of concentration discharge models based on the composite method of stream solute flux estimation was conducted to quantify two key factors contributing to terrestrial–aquatic export of sulphate (SO42−), dissolved organic carbon (DOC), hydronium ion (H+) and colour for ten Precambrian Shield catchments in three lake basins: (1) advective transport capacity, as influenced by variations in runoff, and (2) the terrestrial supply of mobilizable solute, as influenced by terrestrial biogeochemical cycling and associated controlling variables. Overall, annual fluxes associated with mechanism (2) were approximately equal to those associated with mechanism (1) in driving inter-annual deviations from long-term mean annual solute export. There was considerable variation in the relative contributions of these mechanisms among solutes and watersheds, and % wetland area could not explain these differences. However, mean annual terrestrial-aquatic fluxes of DOC and colour were highly correlated with % wetland area, as were inter-annual variations in mean annual flux. The corresponding relationships between H+ and % wetland area were moderate but also significant. Annual fluxes SO42− were negatively associated with wetlands but there was no relationship between inter-annual variations in mean annual SO42− flux and % wetland area. The contribution of forested wetlands to annual flux variability for DOC, colour and H+ was primarily driven by inter-annual differences in runoff and associated mobilization of large solute pools within these critical source areas of organic carbon and acidity. Copyright © 2011 John Wiley & Sons, Ltd.
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Contributions of streamflow variability, concentration–discharge shifts and forested wetlands to terrestrial–aquatic solute export in Precambrian Shield headwater catchments
Ecohydrology, 2011Co-Authors: Murray RichardsonAbstract:Hydrological and biogeochemical processes in terrestrial watershed compartments are an important source of short- and long-term physico-chemical dynamics in Precambrian Shield headwater lakes. In this study, a residual analysis of concentration discharge models based on the composite method of stream solute flux estimation was conducted to quantify two key factors contributing to terrestrial–aquatic export of sulphate (SO42−), dissolved organic carbon (DOC), hydronium ion (H+) and colour for ten Precambrian Shield catchments in three lake basins: (1) advective transport capacity, as influenced by variations in runoff, and (2) the terrestrial supply of mobilizable solute, as influenced by terrestrial biogeochemical cycling and associated controlling variables. Overall, annual fluxes associated with mechanism (2) were approximately equal to those associated with mechanism (1) in driving inter-annual deviations from long-term mean annual solute export. There was considerable variation in the relative contributions of these mechanisms among solutes and watersheds, and % wetland area could not explain these differences. However, mean annual terrestrial-aquatic fluxes of DOC and colour were highly correlated with % wetland area, as were inter-annual variations in mean annual flux. The corresponding relationships between H+ and % wetland area were moderate but also significant. Annual fluxes SO42− were negatively associated with wetlands but there was no relationship between inter-annual variations in mean annual SO42− flux and % wetland area. The contribution of forested wetlands to annual flux variability for DOC, colour and H+ was primarily driven by inter-annual differences in runoff and associated mobilization of large solute pools within these critical source areas of organic carbon and acidity. Copyright © 2011 John Wiley & Sons, Ltd.
Nigel T Roulet - One of the best experts on this subject based on the ideXlab platform.
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the hydrology and methylmercury dynamics of a Precambrian Shield headwater peatland
Water Resources Research, 1996Co-Authors: Brian A Branfireun, Andrew Heyes, Nigel T RouletAbstract:A hydrobiogeochemical investigation of a small headwater peatland located in the Experimental Lakes Area, northwestern Ontario, Canada, examined the surface and subsurface hydrologic pathways and their relation to the movement and spatial variability of methylmercury (CH3Hg+). The hydrology of the peatland controls the mass flux of CH3Hg+ to a downstream pond from the terrestrial ecosystems, and influences the production and/or accumulation of CH3Hg+ in the peatland. Distinct zones of groundwater recharge and discharge were observed within the peatland, and these corresponded, to low and high CH3Hg+ concentrations, respectively, in pore water. The magnitude and flux of CH3Hg+ from the peatland was governed by the area of the peatland and surrounding uplands contributing runoff. There was a threefold increase in CH3Hg+ concentration as stream base flow passed from the origin of the stream at the hillslope-peatland margin to the stream outlet at the peatland-lake interface. This relative increase in concentration was maintained during storm flow conditions even though the discharge was up to 10 times greater, indicating that the peatland is a large source of CH3Hg+. Methylmercury-laden peat pore water found near the surface of the peatland in areas of groundwater discharge moves to the stream as the water table rises to the peat surface. Of a total of 12.6 mg CH3Hg+ leaving the peatland during the 112-day study period, less than 1% was transported directly by groundwater, 41% was transported in stream base flow, and the remaining 58% was transported by storm flow. However, storm flow conditions occurred only 16% of the time, indicating the significance of episodic CH3Hg+ flux from headwater catchments on the Precambrian Shield.
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Runoff generation in zero‐order Precambrian Shield catchments: The stormflow response of a heterogeneous landscape
Hydrological Processes, 1994Co-Authors: Craig J. Allan, Nigel T RouletAbstract:Hydrometric and isotopic (oxygen-18) observations were used to delineate the runoff processes operating in several headwater catchments on the Precambrian Shield of Canada. The catchments comprise patches of conifer forest situated on thin soils among areas of lichen-covered granitic bedrock. Horton overland flow occurred from the lichen-bedrock areas in all precipitation events that exceeded 4–6 mm. Runoff from the forest stands occurred mainly as subsurface stormflow, but in some instances saturation overland flow was observed. The occurrence of saturation overland flow was controlled by the topography of the bedrock beneath the forest soils. The area contributing runoff and the pathway by which water was conveyed to the catchment outflow switched from the open lichen-bedrock areas producing overland flow on the rising limb of the storm hydrograph to the forest stands contributing subsurface stormflow on the recession limb of the hydrograph. The areal extent and position of the landscape units in the basin were important to the rate and magnitude of stormflow production. Runoff was generated from the catchments only during and immediately after snowmelt and/or rainfall events. The catchments were dry and/or frozen for about 70% of the year.
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runoff generation in zero order Precambrian Shield catchments the stormflow response of a heterogeneous landscape
Hydrological Processes, 1994Co-Authors: Craig J. Allan, Nigel T RouletAbstract:Hydrometric and isotopic (oxygen-18) observations were used to delineate the runoff processes operating in several headwater catchments on the Precambrian Shield of Canada. The catchments comprise patches of conifer forest situated on thin soils among areas of lichen-covered granitic bedrock. Horton overland flow occurred from the lichen-bedrock areas in all precipitation events that exceeded 4–6 mm. Runoff from the forest stands occurred mainly as subsurface stormflow, but in some instances saturation overland flow was observed. The occurrence of saturation overland flow was controlled by the topography of the bedrock beneath the forest soils. The area contributing runoff and the pathway by which water was conveyed to the catchment outflow switched from the open lichen-bedrock areas producing overland flow on the rising limb of the storm hydrograph to the forest stands contributing subsurface stormflow on the recession limb of the hydrograph. The areal extent and position of the landscape units in the basin were important to the rate and magnitude of stormflow production. Runoff was generated from the catchments only during and immediately after snowmelt and/or rainfall events. The catchments were dry and/or frozen for about 70% of the year.
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the biogeochemistry of pristine headwater Precambrian Shield watersheds an analysis of material transport within a heterogeneous landscape
Biogeochemistry, 1993Co-Authors: C.j. Allan, Nigel T Roulet, Alan R HillAbstract:The hydrology and elemental transport within five low order Precambrian Shield catchments was investigated during 1988–90. Catchments were subdivided and instrumented to examine the vertical and horizontal fluxes of elements within and between two distinct landscape types: open, lichen-covered bedrock outcrops and patches of conifer forest. The dominant hydrologic pathways were Horton overland flow in the lichen-bedrock areas and shallow subsurface flow through organic rich LFH (forest floor) and Ah soil horizons in the forested areas. Annual runoff coefficients ranged from 0.3 to 0.7.
M C Eimers - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of physical lake processes to climate change within a large Precambrian Shield catchment
Hydrological Processes, 2016Co-Authors: J Crossman, M C Eimers, Jason Grainger KerrAbstract:Potential future changes in lake physical processes (e.g. stratification and freezing) can be assessed through exploring their sensitivity to climate change, and assessing the current vulnerability of different lake types to plausible changes in meteorological drivers. This study quantifies the impacts of climate change and sensitivity of lake physical processes within a large (5100 km2) Precambrian Shield catchment in south-central Ontario. Historic regional relationships are established between climate drivers, lake morphology, and lake physical changes through generalized linear modelling (GLM), and are used to quantify likely changes in timing of ice phenology and lake stratification across 72 lakes under a range of future climate models and scenarios. In response to projections of increased temperature (ensemble mean of +3.3 °C), both earlier ice-off and onset of summer stratification were projected, with later ice-on and fall turnover compared to the baseline. Process sensitivity to climate change varied by lake type; shallower lakes with a smaller volume (less than 15 m deep and less than 0.05 km3) were more sensitive to processes associated with lake heating (stratification onset and ice-off), and deeper lakes with a larger surface area (greater than 30 m deep and greater than 1000 ha) were more sensitive to processes associated with lake cooling (fall turnover and ice-on). These results indicate that whereas small lakes are vulnerable to climate warming because of changes that occur in spring and summer, larger lakes are particularly sensitive during the fall. The findings suggest that lake morphology and associated sensitivity should be considered in the development of sustainable lake management strategies. Copyright © 2016 John Wiley & Sons, Ltd.
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scaling and physiographic controls on streamflow behaviour on the Precambrian Shield south central ontario
Journal of Hydrology, 2009Co-Authors: J M Buttle, M C EimersAbstract:Summary Relationships explaining streamflow behaviour in terms of drainage basin physiography greatly assist efforts to extrapolate streamflow metrics from gauged to ungauged basins in the same landscape. The Dorset Environmental Science Centre (DESC) has monitored streamflow from 22 small basins (3.4–190.5 ha) on the Precambrian Shield in south-central Ontario, in some cases since 1976. The basins exhibit regional coherence in their interannual response to precipitation; however, there is often a poor correlation between streamflow metrics from basins separated by as little as 1 km. This study assesses whether inter-basin variations in such metrics can be explained in terms of basin scale and physiography. Several characteristics (annual maximum, minimum and average flow) exhibited simple scaling with basin area, while magnitude, range and timing of annual maximum daily runoff showed scaling behaviour consistent with the Representative Elementary Area (REA) concept. This REA behaviour is partly attributed to convergence of fractional coverage of the two dominant and hydrologically-contrasting land cover types in the DESC region with increasing basin size. Three Principal Components (PCs) explained 82.4% of the variation among basin physiographic properties, and several runoff metrics (magnitude and timing of annual minimum daily runoff, mean number of days per year with 0 streamflow) exhibited significant relationships with one or more PC. Significant relationships were obtained between basin quickflow ( QF ) production and the PCs on a seasonal and annual basis, almost all of which were superior to simple area-based relationships. Basin physiography influenced QF generation via its control on slope runoff, water storage and hydrologic connectivity; however, this role was minimized during Spring when QF production in response to large rain-on-snow events was relatively uniform across the DESC basins. The PC-based relationships and inter-seasonal changes in their form were consistent with previous research conducted at point, slope and basin scales in the DESC region, and perceptions of key hydrological processes in these small basins may not have been as readily obtained from scaling studies using streamflow from larger basins. This process understanding provides insights into scaling behaviour beyond those derived from simple scaling and REA analyses. The physiography of the study area is representative of large portions of the Precambrian Shield, such that basin streamflow behaviour could potentially be extended across much of south-central Ontario. This would assist predictions of streamflow conditions at ungauged locations, development and testing of hydrological models for this landscape, and interpretation of inter-basin and intra-annual differences in hydrochemical behaviour on the southern Precambrian Shield.
Craig J. Allan - One of the best experts on this subject based on the ideXlab platform.
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Hydrochemical response of upland Precambrian Shield catchments to additions off H2SO4 and NH4NO3 during snowmelt
Canadian Journal of Fisheries and Aquatic Sciences, 1995Co-Authors: Craig J. AllanAbstract:Two of three upland Precambrian Shield catchments received additions of H2SO4 and NH4NO3 prior to snowmelt in 1989 and 1990; loading levels were equivalent to 18 kg∙ha−1∙yr−1 as SO42− and 2.62 kg∙ha−1∙yr−1 as N. The third catchment served as a reference. The manipulated catchments retained 96–98% of the added NH4+, 73–94% of the added NO3−, 31–48% of the added SO42−, and 72–92% of the added H+. Proton neutralization was attributed to increased cation export (Ca2+ + Mg2+ + Na+ + K+ + Aln+ + Mn2+ + Fe2+: 26–53%) and SO42− retention (48–67%). The protonation of weak organic acids accounted for a 13–34% decline in organic anions during snowmelt. No significant change in dissolved organic carbon export was observed. In manipulated catchments, inorganic monomeric Al export increased from 30 to 80% over reference levels, and the ratio of inorganic to organic monomeric Al changed from
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runoff generation in zero order Precambrian Shield catchments the stormflow response of a heterogeneous landscape
Hydrological Processes, 1994Co-Authors: Craig J. Allan, Nigel T RouletAbstract:Hydrometric and isotopic (oxygen-18) observations were used to delineate the runoff processes operating in several headwater catchments on the Precambrian Shield of Canada. The catchments comprise patches of conifer forest situated on thin soils among areas of lichen-covered granitic bedrock. Horton overland flow occurred from the lichen-bedrock areas in all precipitation events that exceeded 4–6 mm. Runoff from the forest stands occurred mainly as subsurface stormflow, but in some instances saturation overland flow was observed. The occurrence of saturation overland flow was controlled by the topography of the bedrock beneath the forest soils. The area contributing runoff and the pathway by which water was conveyed to the catchment outflow switched from the open lichen-bedrock areas producing overland flow on the rising limb of the storm hydrograph to the forest stands contributing subsurface stormflow on the recession limb of the hydrograph. The areal extent and position of the landscape units in the basin were important to the rate and magnitude of stormflow production. Runoff was generated from the catchments only during and immediately after snowmelt and/or rainfall events. The catchments were dry and/or frozen for about 70% of the year.
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Runoff generation in zero‐order Precambrian Shield catchments: The stormflow response of a heterogeneous landscape
Hydrological Processes, 1994Co-Authors: Craig J. Allan, Nigel T RouletAbstract:Hydrometric and isotopic (oxygen-18) observations were used to delineate the runoff processes operating in several headwater catchments on the Precambrian Shield of Canada. The catchments comprise patches of conifer forest situated on thin soils among areas of lichen-covered granitic bedrock. Horton overland flow occurred from the lichen-bedrock areas in all precipitation events that exceeded 4–6 mm. Runoff from the forest stands occurred mainly as subsurface stormflow, but in some instances saturation overland flow was observed. The occurrence of saturation overland flow was controlled by the topography of the bedrock beneath the forest soils. The area contributing runoff and the pathway by which water was conveyed to the catchment outflow switched from the open lichen-bedrock areas producing overland flow on the rising limb of the storm hydrograph to the forest stands contributing subsurface stormflow on the recession limb of the hydrograph. The areal extent and position of the landscape units in the basin were important to the rate and magnitude of stormflow production. Runoff was generated from the catchments only during and immediately after snowmelt and/or rainfall events. The catchments were dry and/or frozen for about 70% of the year.
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Solid phase controls of dissolved aluminum within upland Precambrian Shield catchments
Biogeochemistry, 1994Co-Authors: Craig J. Allan, N.t. RouletAbstract:Solid phase controls of dissolved aluminum chemistry of soil and surface waters were investigated in several pristine, low order Precambrian Shield catchments. Soil extraction and leaching experiments were conducted to quantify the various pools of solid phase soil aluminum and their relative mobility. Reactive soil aluminum (exchangeable + organic + amorphous forms), comprised < 20% of the total soil aluminum. Leaching soils with pH 3.0 HCl solutions indicated that Na_4P_2O_7 extractable aluminum (largely organic complexes) was the most mobile form of reactive soil aluminum. Aluminum hydroxide from vermiculate interlayers was also mobilized from all soil horizons and its contribution to dissolved aluminum increased with soil depth. Runoff and soil waters from organic LFH and Ah soil horizons were highly undersaturated with respect to Al(OH)_3 solid-phases. Several natural bedrock surfaces (metagranites) covered with moss or lichen were leached with HCl solutions. Significantly more aluminum was removed from bedrock surfaces colonized with the moss Racomitrium microcarpon compared to that of the lichen-covered surfaces. Aluminum removal increased dramatically as the acidity of the leaching solution increased to pH 3.0. Leachates solutions collected from bedrock surfaces became increasingly undersaturated with respect to Al(OH)_3 minerals at lower pH values. Aluminum solubility appears to be controlled by equilibrium with organic complexation, modified by kinetically constrained dissolution of interlayer aluminum.