Geochemical Weathering Research Articles

Chemical weathering of new pyroclastic deposits from Mt. Merapi (Java), Indonesia

The Java Island, Indonesia with abundant amount of pyroclastic deposits is located in the very active and dynamic Pacific Ring of Fires. Studying the geochemical weathering indices of these pyroclastic deposits is important to get a clear picture about weathering profiles on deposits resulting from the eruption of Mt. Merapi. Immediately after the first phase of the eruption (March to June 2006), moist and leached pyroclastic deposits were collected. These pyroclastic deposits were found to be composed of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole and titanomagnetite. The total elemental composition of the bulk samples (including trace elements and heavy metals) was determined by wet chemical methods and X-ray fluorescence (XRF) analyses. Weathering of the pyroclastic deposits was studied using various weathering indices. The Ruxton ratio, weathering index of Parker, Vought resudual index and chemical index of weathering of moist pyroclastic deposits were lower than those of the leached samples, but the alteration indices (chemical and plagioclase) were slightly higher in the moist compared to the leached pyroclastic deposits.

Recent developments in the application of proteomics to the analysis of plant responses to heavy metals

Pollution of soils by heavy metals is an ever-growing problem throughout the world, and is the result of human activities as well as geochemical weathering of rocks and other environmental causes such as volcanic eruptions, acid rain and continental dusts. Plants everywhere are continuously exposed to metal-contaminated soils. The uptake of heavy metals not only constrains crop yields, but can also be a major hazard to the health of humans and to the entire ecosystem. Although analysis of gene expression at the mRNA level has enhanced our understanding of the response of plants to heavy metals, many questions regarding the functional translated portions of plant genomes under metal stress remain unanswered. Proteomics offers a new platform for studying complex biological functions involving large numbers and networks of proteins, and can serve as a key tool for revealing the molecular mechanisms that are involved in interactions between toxic metals and plant species. This review focuses on recent developments in the applications of proteomics to the analysis of the responses of plants to heavy metals; such studies provide a deeper understanding of protein responses and the interactions among the possible pathways that are involved in detoxification of toxic metals in plant cells. In addition, the challenges faced by proteomics in understanding the responses of plants to toxic metal are discussed, and some possible future strategies for meeting these challenges are proposed.

Analytical Framework for a Risk-based Estimation of Climate Change Effects on Mine Site Runoff Water Quality

A conceptual analytical framework was developed for the risk-based estimation of climate change effects on mine waste runoff water quality. The modeling approach incorporates temporal variability in both precipitation and temperature using trend analyses from historical datasets and the resulting effects on water balances and geochemical weathering rates. A case-study method was used to develop and present the model for regions near the city of Yellowknife, Northwest Territories, Canada. Time-resolved relative precipitation and weathering factors can be calculated using climate data and site-specific estimates regarding mine waste properties. Interpretation of these factors allows an assessment of when the period of highest analyte concentrations are expected to occur under a given risk scenario over a modeling timeframe, whether low precipitation or warming effects are more important in determining water quality issues, and the relative magnitudes of water quality under differing risk scenarios.

The Geochemistry of Supraglacial Streams of Canada Glacier, Taylor Valley (Antarctica), and their Evolution into Proglacial Waters

We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the 2001–2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and proglacial stream geochemistry with average concentrations of 49.1 μeq L−1 Ca2+, 19.9 μeq L−1 SO42−, and 34.3 μeq L−1 HCO3−. Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO42−:HCO3− equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve in the western supraglacial streams. A graph of HCO3− versus Ca2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R2 values of 0.84 and 0.83. Low concentrations of reactive silicate (> 10 μmol L−1) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception of cryoconite holes (1000 μmol L−1). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution. Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times the Ca2+ and 10 times the SO42−. Canada Glacier proglacial streams also contain higher concentrations (16.6–30.6 μeq L−1) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves. Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical, low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming events, such as the 2001–2002 austral summer produce supraglacial streams that are a major source of water to Lake Hoare.

Accelerated Weathering of Biosolid‐Amended Copper Mine Tailings

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.

Impact of Douglas-fir and Scots pine seedlings on plagioclase weathering under acidic conditions

The weathering of soil minerals in forest ecosystems increases nutrient availability for the trees. The rate of such weathering and its relative contribution to forest tree nutrition, is a major issue when evaluating present and potential forest stand productivity and sustainability. The current paper examines the weathering rate of plagioclase with and without Douglas-fir or Scots pine seedlings, in a laboratory experiment at pH 3–4 and 25 °C. All nutrients, with the exception of Ca, were supplied in sufficient amounts in a nutrient solution. The objective of the experiment was to evaluate the potential of trees to mobilise Ca from the mineral plagioclase that contained 12% of Ca. Amounts of nutrients supplied in the nutrient solution, amounts accumulated in the living tissue of the seedlings and amounts leached from the experimental vessels, were measured. A weathering balance, accounting for leached + accumulated − supplied amounts, was established. Bio-induced weathering, defined as the weathering increase in the presence of trees, relative to the weathering rate without trees (geochemical weathering; control vessels), under the present experimental conditions, explained on average, 40% of total weathering (biological + geochemical). These conditions appeared more beneficial to Scots pine (higher relative growth rate, higher Ca incorporation) than to Douglas-fir.

Transport and geochemical controls on the distribution of solutes and stable isotopes in a thick clay-rich till aquitard, Canada

A comprehensive understanding of the transport and geochemical processes controlling solutes in clay-rich aquitard confining units is needed to accurately predict the long-term migration of contaminants into the subsurface. To this end, the geochemical and stable isotopic composition of porewaters in the upper 22 m of a thick, unoxidized and nonfractured clay-rich, till aquitard (Sutherland Group) was examined in detail. The aquitard is overlain by about 8 m of oxidized and fractured till (Floral Fm). Concentrations of TDS, SO4 2−, HCO3 −, Cl−, Na+, Mg2+, Ca2+ and porewater deuterium were greater in the Floral Fm and decreased with depth through the aquitard. The elevated and seasonably variable solute concentrations in the oxidized Floral Fm were attributed to geochemical weathering and dynamic water movement through fractures. Good fits between measured δ2H, TDS, SO4 2−, Cl− and HCO3 − profiles through the aquitard and simulated solute transport profiles were obtained by diffusion (without advection) with transport times of 4–6 ka. The deficiency of geochemical reactions affecting HCO3 − and SO4 2− in the aquitard was supported by δ13CDIC and δ34SSO4 analyses. Geochemical and isotope mass balance modelling (NETPATH) indicated that diffusive mixing with minor calcite dissolution and ion exchange could account for the distribution of Na+, Ca2+ and Mg2+ in the aquitard. Results of this study further suggested that microbiological activity in the aquitard was limited. With minor exceptions, the solute and isotopic profiles, their transport and the controlling geochemical reactions in the Sutherland are similar to those determined at another clay-rich till aquitard, 160 km south of this site, suggesting that geochemical and biological processes in some clay-rich aquitards may have a minimal effect on the migration of dissolved constituents.

Tephrostratigraphical evidence for the timing of pleistocene explosive volcanism at Jan Mayen

AbstractWavelength dispersive (WDS) electron microprobe analysis of glass shards recovered from Pleistocene sediments at Ocean Drilling Program Hole 907A (Leg 151) has been used to define key Pleistocene tephrochronostratigraphical markers for the Greenland–Iceland–Norwegian (GIN) seas. Two tephras have particularly distinctive geochemistry, making them useful as marker horizons in cores from the Iceland Plateau, and potentially further afield. These tephras enable the construction of a sedimentation rate history that indicates reduced sediment deposition in the mid‐Brunhes magnetochron, possibly through reduced carbonate preservation. No significant geochemical weathering of the Iceland Plateau tephra sequence has occurred. The geochemical signature of a key tephra, dated to 577–640 ka, can be attributed to the Jan Mayen rock suite, demonstrating unambiguously the explosive potential of Jan Mayen and its potential to contribute to the North Atlantic tephra record. Copyright © 2004 John Wiley &amp; Sons, Ltd.

A buried palaeosol and late Pleistocene unconformity in coastal deposits of the eastern Yellow Sea, East Asia

Deep-drill core sampling with a high-resolution seismic survey was carried out to identify a Holocene–late Pleistocene boundary in the eastern coast of the Yellow Sea, East Asia. Analysis of core sections revealed the existence of an oxidized and desiccated sedimentary layer, lying directly below a Holocene horizon (Unit I) and being developed at the top of a late Pleistocene (Unit II), possibly last interglacial tidal deposit. The buried oxidized-sedimentary layer is characterized by semi-consolidated, yellowish sediments showing signs of desiccation and alteration such as periglacial cryogenic structures, lithified trace fossils, depletion of smectite, and high geochemical weathering index (Ba/Sr ratio). These features, together with radiocarbon ages, suggests that the layer, defined as a palaeosol developed in marine sediments, has formed as a result of prolonged subaerial exposure of Unit II sediments during the Wisconsinan sea-level lowstand, producing a regional unconformity (late Pleistocene unconformity). This unconformable bounding surface corresponds to a prominent near-surface reflector (R), which is observed in seismic profiles obtained across the drilled-core sections and further is traced ubiquitously across the Yellow Sea shelf. Consequently, the buried palaeosol layer associated with the seismic reflector presents a key horizon for the understanding of late Quaternary environmental changes and integrated stratigraphical correlation in the East Asian marginal seas.

A buried palaeosol and late Pleistocene unconformity in coastal deposits of the eastern Yellow Sea, East Asia

Deep-drill core sampling with a high-resolution seismic survey was carried out to identify a Holocene–late Pleistocene boundary in the eastern coast of the Yellow Sea, East Asia. Analysis of core sections revealed the existence of an oxidized and desiccated sedimentary layer, lying directly below a Holocene horizon (Unit I) and being developed at the top of a late Pleistocene (Unit II), possibly last interglacial tidal deposit. The buried oxidized-sedimentary layer is characterized by semi-consolidated, yellowish sediments showing signs of desiccation and alteration such as periglacial cryogenic structures, lithified trace fossils, depletion of smectite, and high geochemical weathering index (Ba/Sr ratio). These features, together with radiocarbon ages, suggests that the layer, defined as a palaeosol developed in marine sediments, has formed as a result of prolonged subaerial exposure of Unit II sediments during the Wisconsinan sea-level lowstand, producing a regional unconformity (late Pleistocene unconformity). This unconformable bounding surface corresponds to a prominent near-surface reflector (R), which is observed in seismic profiles obtained across the drilled-core sections and further is traced ubiquitously across the Yellow Sea shelf. Consequently, the buried palaeosol layer associated with the seismic reflector presents a key horizon for the understanding of late Quaternary environmental changes and integrated stratigraphical correlation in the East Asian marginal seas.

Modeling biogeochemistry, the key for understanding environmental chemistry of a Semi-Arid soil in Egypt

Modeling geochemistry of the studied Bahtim catchment in Egypt provides a powerful tool for untangling various connections and feedbacks between atmospheric inputs, vegetation, soil and hydrology within the system. The biogeochemical PROFILE model was used to study the integrated environmental monitoring of different environmental compartments as well as calculating geochemical weathering rate. The model is in steady state and includes multi-layers which have the mineralogical, physical and chemical attributes measured for individual soil layers. In this study, the base cations (Ca2+, Mg2+, Na+, K+) are produced from the minerals through chemical weathering. The total chemical weathering rate of base cations is 6.5 keq-1. ha-1. a-1. In addition, the output results indicate that a small amount of dark minerals like hornblende, pyroxene and plagioclase largely contribute the field weathering rate in Egyptian Vertisols.

Distribution of the rare earth elements in porewaters from a clay-rich aquitard sequence, Saskatchewan, Canada

A 91.4-m thick porewater profile of the rare earth elements (REEs) is presented from a thick clay-rich Pleistocene till (0–80 m) and Cretaceous clay (80–156 m) aquitard sequence, Saskatchewan, Canada. The upper 3–4 m of till is weathered. Absolute aqueous concentrations of the REEs vary by more than one order of magnitude. Aqueous REE concentrations decrease with depth through the weathered till to a depth of about 15 m below ground, below which, the concentrations in the unweathered till remain relatively consistent. The only porewater sample from the clay (91.4 m) has the highest total REE concentration. Elevated REE concentrations in the oxidized zone attributed to geochemical weathering. There is no significant seasonal variation in aqueous REE concentrations within the water columns in the piezometers. Redox conditions and solution complexation reactions exert predominant controls on the aqueous REE concentrations. The majority of REE patterns are coherent, characterized by overall negatively fractionated REE, with convex-down profiles from La to Pr or Nd, and convex-up from Nd to Tb. In the porewater sample from the clay, the LREEs are an exception, with a flat normalized profile. HREE/LREE fractionations in the porewaters are depth-dependent and are mainly controlled by solution complexation with dissolved sulfate, phosphate, free carbonate ions and DOC. Porewaters in the unweathered till (5–76.2 m) are characterized by negative Ce anomalies, which may reflect in part, negative Ce anomalies in the host till geochemistry. The negative Ce anomalies are magnified relative to the host tills during water–rock interaction and REE transportation. Porewaters from the weathered till exhibit strong positive Ce anomalies relative to PAAS, the host rocks and their leachates. The Ce anomalies are predominantly controlled by the redox conditions and solution complexation. The large positive Ce anomalies in these porewaters are probably caused by the oxidation of Ce(III) to Ce(IV) that was stabilized in solution through complexation with high contents of inorganic and organic ligands. Positive Eu anomalies relative to PAAS, the host rocks and leachates of the host rocks, result from hydrolysis of plagioclase feldspar. The limited depth profile for total dissolved REEs across the weathered–unweathered till boundary is retarded with respect to that previously established for Na +, K +, Mg 2+, SO 4 2−, and TDS, suggesting that chemical reactions control the migration of dissolved REEs.

Evaluation of an integrated biogeochemical model (PnET‐BGC) at a northern hardwood forest ecosystem

An integrated biogeochemical model (PnET‐BGC) was formulated to simulate chemical transformations of vegetation, soil, and drainage water in northern forest ecosystems. The model operates on a monthly time step and depicts the major biogeochemical processes, such as forest canopy element transformations, hydrology, soil organic matter dynamics, nitrogen cycling, geochemical weathering, and chemical equilibrium reactions involving solid and solution phases. The model was evaluated against soil and stream data at the Hubbard Brook Experimental Forest, New Hampshire. Model predictions of concentrations and fluxes of major elements generally agreed reasonably well with measured values, as estimated by normalized mean error and normalized mean absolute error. Model output of soil base saturation and stream acid neutralizing capacity were sensitive to parameter values of soil partial pressure of carbon dioxide, soil mass, soil cation exchange capacity, and soil selectivity coefficients of calcium and aluminum. PnET‐BGC can be used as a tool to evaluate the response of soil and water chemistry of forest ecosystems to disturbances such as clear‐cutting, climatic events, and atmospheric deposition.

Controls on the distribution of major ions in pore waters of a thick surficial aquitard

Transport and geochemical processes controlling the chemical and isotopic composition of pore waters in the upper 45 m of a thick, surficial, clay‐rich till (Battleford Formation) were studied. The upper 3 m of the till is oxidized and fractured. The remaining 77 m of the till (the aquitard) is nonfractured and unoxidized. Concentrations of total dissolved solids, SO42−, Na+, Mg2+, and K+ decrease with depth through the unoxidized zone to a depth of about 15 m below ground, below which the concentrations remain constant. A similar trend was observed for alkalinity; however, the decrease in concentration occurs over 20 m. In contrast to these ions, Ca2+ concentrations increase with depth through the upper 20‐m unoxidized zone, below which the concentrations remain relatively constant. The distribution of dissolved ions shows the presence of two end‐members: elevated solute concentrations in the oxidized zone attributed to geochemical weathering that occurred since the start of the Holocene and connate Pleistocene‐age water at depths between 20 and 45 m. Abiotic and biotic geochemical reaction rates in the aquitard were shown to be extremely slow or not occurring.

Hydrogeologic and Geochemical Factors Required for the Development of Carolina Bays Along the Atlantic and Gulf of Mexico Coastal Plain, USA

More than 60 years of intense study and debate have yet to resolve the origin of the Carolina Bays. Carolina Bays are circular to elliptical depressions located along the Gulf of Mexico and Atlantic Coastal Plains. Proposed processes of initiation and development of these karst-like features include meteorite impacts, substrate dissolution, wind, ice, marine waves and currents. Based on field studies throughout the Atlantic and Gulf Coastal Plains and on review of coastal plain literature, we propose that Carolina Bays initially developed as silica-karst features. During Pleistocene sea-level lowstands, water tables in the Atlantic Coastal Plain were up to 30 m lower than today. Large volumes of surface water collected in local topographic lows and/or areas of enhanced permeability and infiltrated through sandy substrates of the low-relief coastal plain. Localized infiltration of phreatic water induced extensive desilicification of the sandy and clayey substrates, resulting in volume loss and development of karst-like depressions. Particularly relevant to initial bay development was alteration of kaolinite to gibbsite, which can produce a 34-percent loss in clay material volume, and concurrent dissolution of iron oxide. The initial silica-karst depressions along the Atlantic and Gulf coasts were later modified by eolian and, perhaps, ice-push processes, which enhanced their elliptical form. The subsequent Holocene rise in sea level caused ground-water levels in the coastal plain to equilibrate near the present-day land surface. This curtailed geochemical weathering, as well as eolian and ice-related processes. Ground-water saturation partially reversed chemical reactions associated with intensive weathering of clays beneath the bays, masking evidence of the severe leaching that occurred during their initial formation. Silica-karst features, similar to Carolina Bays in their initial stages of development, are common geologic features. Moreover, silica-karst processes are active today in warm temperate, subtropical, and tropical areas in sandy substrates where groundwater levels are well below the ground surface and can cause subsidence or disrupt developing wetlands.

Effects of lichens on the geochemical weathering of granitic rocks

This paper examined the role of lichens in geochemical weathering of granite for several lichens representative of the species colonizing granitic monuments in Galicia (N.W. Spain). The salient results were that although the lichens affected the mobility of some elements, overall geochemical weathering was similar for colonized and uncolonized rock. Where differences were detected the various lichen species generally had similar effects on the weathering of the rock. Lichens seemed to protect the exposed surface of the rock from atmospheric weathering, thereby reducing losses of the most mobile elements. However, the overriding factor determining the extent to which an element was accumulated at, or mobilized from, the surface of colonized rock was the susceptibility to weathering of the source mineral. A new term, “interphase”, was introduced to describe rock engulfed in lichen thalli.

Chemical Changes and Genesis of Secondary Minerals During the Alteration of Biotites from Ignimbrites in the Tazzeka Mountain (Morocco)

AbstractThe Tazzeka Mountain, located approximately 20 km south of Taza, eastern Morocco, is composed of a Westphalian volcano-sedimentary complex. It contains rhyolitic ignimbrites with the following minerals: quartz, potassium feldspar, oligoclase-andesine, and biotite. The ignimbrites are extensively altered because of a dense network of fractures in the massif. Alteration has resulted in the formation of spheroidal rocks and saprolite, the thickness of which depends on local topography. The evolution of the biotites in the ignimbrites was investigated by microprobe analysis of the mica crystals. This technique provides data that are not accessible through classical analytical methods. Biotites are transformed into secondary clay minerals, mainly chlorites and illites; intermediate stages are related to the degree of alteration of biotite, the latter being expressed by the K2O content which decreases progressively from 7.3 to 1.3%. Next come protochlorites and chlorites sensu stricto, in which the K2O content is 0.3%. Several processes including retrodiagenesis, hydrothermal activity, fumarolic activity, and geochemical weathering contributed to the transformation of the biotites at Tazzeka.

Geochemical Processes, Weathering and Groundwater Recharge in Catchments

Geochemical Processes, Weathering and Groundwater Recharge in Catchments

Could Mars be dark and altered?

There is a long known dichotomy in the martian albedo, with an associated, but mostly assumed, mineralogical split as well. The bright red regions are inferred to be weathered, oxidized dust and the dark grey regions unaltered volcanic material. A number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re‐examination of the spectra in light of potential alteration minerals. I present an alternate interpretation of the reflectance spectral characteristics of some dark regions on Mars that includes dark layer silicates. If their presence is confirmed on Mars this will have implications for sequestration of current and past volatile inventories, clues to the extent and type of geochemical weathering, and potential zones where bacterial life forms may have emerged.

Organic and inorganic nitrogen pools in talus fields and subtalus water, Green Lakes Valley, Colorado Front Range

Organic and inorganic pools of nitrogen (N) were measured in talus fines or ‘soils’ and subtalus water during the summer of 1995 in the alpine Green Lakes Valley catchment of the Colorado Front Range. Nineteen talus soil samples were divided into four classes: subtalus dry, subtalus wet, surface vegetated and surface bare. The size of the individual talus soil patches ranged from 0·5 to 12·0 m2 in area, with bulk density ranging from 0·98 to 1·71 kg m−3 and soil texture ranging from sandy gravel in the subsurface talus to a loam in the vegetated surface. All samples contained KCl-extractable NH+4 and NO−3, organic N and carbon (C), and 17 of 19 samples contained microbial biomass. The mean subtalus values for KCl-extractable NH−4, of 3·2 mg N kg−1, and NO−3, of 1·0 mg N kg−1, were comparable with developed alpine soils on Niwot Ridge. Average microbial biomass in subtalus soils of 5·4 mg N kg−1 and total N of 1000 mg N kg−1 were about an order of magnitude lower than alpine tundra soils, reflecting the reduced amount of vegetation in talus areas. However, these measurements in surface-vegetated patches of talus were comparable with the well-developed soils on Niwot Ridge. These measurements in talus of microbial biomass, total N and KCl-extractable NH+4 and NO−3, show that there is sufficient biotically conditioned ‘soil’ within talus fields to influence the solute content of interstitial waters. Mean NO−3 concentrations of 20 μeq l−1 from 29 samples of subtalus water were significantly higher than the 6·7 μeq l−1 in snow, while NH+4 concentrations in subtalus water of 0·7 μeq l−1 was significantly lower than in snow at 5·2 μeq l−1 (p = 0·001). Nitrate concentrations in subtalus water were significantly (p < 0·0001) correlated with concentrations of geochemical weathering products such as Ca2+ (r2 = 0·84) and silica (r2 = 0·49). The correlation of NO−3 in subtalus water with geochemical weathering products suggests that NO−3 concentrations in subtalus water increased with increased residence time, consistent with a biological source for this subtalus water NO−3. The high NO−3 concentrations in subtalus water compared with atmospheric deposition of NO−3 suggests that NO−3 in talus fields may contribute to NO−3 in stream waters of high-elevation catchments. © 1997 John Wiley & Sons, Ltd.