Bedrock Chemistry Research Articles

Microsite preferences of three conifers in calcareous and siliceous treeline ecotones in the French alps

AbstractSeedling establishment is crucial for elevational advance of tree species above the treeline ecotone, but the characteristics and availability of safe sites for tree regeneration in alpine ecosystems are not well understood. To better understand the potential of treeline ecotones to show infilling or upward shifts, we assessed microsite preferences of the conifers Larix decidua, Pinus uncinata, and Pinus cembra in upper treeline ecotones with different bedrock chemistry in the French Alps. At each of two sites on calcareous and two on siliceous bedrock, we compared microsites of 50 tree individuals to 50 randomly-selected reference microsites, considering substrate, ground cover, topography, and shelter proximity. In addition, we related these characteristics with the health of the individuals. We found that the three species were established in similar microsites, usually with some shelter. The occupied microsites reflected the available microsites in the area, but certain extreme microsite types remained unoccupied. Most individuals had a krummholz form or were bent, while only a small proportion presented signs of recent mechanical damage, desiccation, snow mold or herbivory, independent of microsite characteristics. Our study shows that the availability of safe sites unlikely limits the establishment of these conifers in the studied sites, suggesting that, instead, seed availability may be a major limitation for tree establishment in these alpine-treeline ecotones. Even in safe sites, the harsh alpine conditions limit the development of tree-species individuals into tree stature, but the strong recent length growth observed suggests favorable conditions for eventual tree expansion in and above current treeline ecotones.

Relationship of seasonal variations in drip waterδ13CDIC,δ18O, and trace elements with surface and physical cave conditions of La Vallina cave, NW Spain

Abstract. Cave-monitoring studies clarify the climatic, surface vegetation, and karst processes affecting the cave system and lay the foundation for interpreting geochemical stalagmite records. Here we report the monitoring of cave air, bedrock chemistry, and drip water δ13CDIC, δ18O, and δD, as well as 16 trace elements, covering a full annual cycle spanning the 16 months between November 2019 and March 2021 in La Vallina cave in the northwestern Iberian Peninsula. While decreased rainfall and increased evapotranspiration in the summer months lead to a strong reduction in drip rates, there is little seasonal variation in δ18O and δD in a given drip, likely reflecting the discrete moderately mixed to well-mixed karst water reservoirs. Small differences in δ18O and δD between drip sites are attributed to variable evaporation intensity and/or transit times. The carbon isotope signature of the dissolved inorganic carbon of drip water (δ13CDIC) is likely driven by seasonal changes in the temperature controlling biological processes (vegetation and microbial soil activity), resulting in minimum δ13CDIC in summer and autumn months. Increased bedrock dissolution due to higher soil pCO2 in summer and autumn results in increased trace element concentrations of congruently dissolved elements. Cave air measurements (pCO2, δ13Cair, and temperature) indicate the seasonal ventilation (winter) and stagnation (summer) of cave air. The opposite effects of reduced cave air pCO2, seasonally variable biological activity, and increased drip rate limit the extent of the seasonal variation in degassing and prior calcite precipitation (PCP) supported by trace elements (Sr/Ca index). Estimated stalagmite growth rates using monitoring data suggest biannual phases of potential calcite precipitation in summer and winter and growth cessation during spring and autumn, depending on cave and drip water conditions and the location within the cave, which has important implications for the proxy interpretation of stalagmite records.

GEOTECHNICAL ASSESSMENT OF SUB-GRADE SOILS ALONG STABLE AND UNSTABLE PAVEMENTS OF SUPARE-EMURE EKITI ROAD, SOUTHWESTERN NIGERIA

The qualities of road construction materials are essential in their choice for various civil works. Therefore, engineering geological properties of the sub-soil that constitute sub-grade materials along Supare- Emure road were investigated in order to determine the causes of the failure of the pavement along the unstable sections. A total of twelve (12) sub- grade soil samples were collected from unstable and stable sections of the road and were subjected to various geotechnical tests. These tests include natural moisture content, atterberg limits, linear shrinkage, plasticity index and grain size. Results showed that the natural moisture content of the stable sections range from 5% to 11%, while those of unstable sections range from 23.8% to 37.2%. The range of the unstable sections fell short of required specification. For the plasticity index, both sections have values less than required 30%, while the unstable sections had linear shrinkage above 8%. On the grain size results, unstable sections have values greater than the specified 35% passing. Bedrock chemistry and clayey nature of sub-grade soils have been found to be responsible for the failed sections of the road investigated.

Soil phosphorus status and P nutrition strategies of European beech forests on carbonate compared to silicate parent material

Sustainable forest management requires understanding of ecosystem phosphorus (P) cycling. Lang et al. (2017) [Biogeochemistry,https://doi.org/10.1007/s10533-017-0375-0] introduced the concept of P-acquiring vs. P-recycling nutrition strategies for European beech (Fagus sylvatica L.) forests on silicate parent material, and demonstrated a change from P-acquiring to P-recycling nutrition from P-rich to P-poor sites. The present study extends this silicate rock-based assessment to forest sites with soils formed from carbonate bedrock. For all sites, it presents a large set of general soil and bedrock chemistry data. It thoroughly describes the soil P status and generates a comprehensive concept on forest ecosystem P nutrition covering the majority of Central European forest soils. For this purpose, an Ecosystem P Nutrition Index (ENIP) was developed, which enabled the comparison of forest P nutrition strategies at the carbonate sites in our study among each other and also with those of the silicate sites investigated by Lang et al. (2017). The P status of forest soils on carbonate substrates was characterized by low soil P stocks and a large fraction of organic Ca-bound P (probably largely Ca phytate) during early stages of pedogenesis. Soil P stocks, particularly those in the mineral soil and of inorganic P forms, including Al- and Fe-bound P, became more abundant with progressing pedogenesis and accumulation of carbonate rock dissolution residue. Phosphorus-rich impure, silicate-enriched carbonate bedrock promoted the accumulation of dissolution residue and supported larger soil P stocks, mainly bound to Fe and Al minerals. In carbonate-derived soils, only low P amounts were bioavailable during early stages of pedogenesis, and, similar to P-poor silicate sites, P nutrition of beech forests depended on tight (re)cycling of P bound in forest floor soil organic matter (SOM). In contrast to P-poor silicate sites, where the ecosystem P nutrition strategy is direct biotic recycling of SOM-bound organic P, recycling during early stages of pedogenesis on carbonate substrates also involves the dissolution of stable Ca-Porg precipitates formed from phosphate released during SOM decomposition. In contrast to silicate sites, progressing pedogenesis and accumulation of P-enriched carbonate bedrock dissolution residue at the carbonate sites promote again P-acquiring mechanisms for ecosystem P nutrition.

Soil-sample geochemistry normalised by class membership from machine-learnt clusters of satellite and geophysics data

The primary aim of mineral exploration is to focus the search space from regional scale (1000 s km2) to prospect scale (1–10 km2), identify areas that warrant further investigation, and ultimately drill a target. Mineral deposits typically display geochemical anomalism related to the conditions of their formation, or the weathering and mass transport of sediment away from a mineral deposit. However, this anomalism can be obscured in soil-sample surveys due to background variations in host bedrock chemistry and the transformation and redistribution of original minerals during surface weathering, regolith development, and supergene processes. This contribution uses machine-learnt map products to aid in the interpretation of a regional-scale soil-sample dataset. ASTER (satellite spectral) data were combined with airborne radiometric data using Self-Organising Maps (SOM) to generate a map of regolith type. A map of bedrock geology was previously derived by the authors from airborne geophysical data using Random Forests. These two products are used to classify soil samples with an objective bedrock-geology and regolith-type classification. A z-score normalisation was implemented on the soil-sample geochemical data, using two different matrices (regolith type and bedrock geology) to remove the bias of bedrock geology and regolith type from the soil sample chemistry. The signal that remains likely reflects metasomatic processes, and associated elemental anomalism, potentially linked to mineralisation. These data can then be plotted to provide maps of (pathfinder) element anomalies, thus identifying potential exploration targets. We explore this approach to normalise geochemical data in a dataset of 9,924 soil samples collected over an area of 1,028 km2, from Kerkasha, Eritrea (Nubian Shield). The Kerkasha project is an early-stage exploration project, with a limited understanding of the local geology and mineral deposit types; however, it contains many Au and Cu prospects that have received minimal exploration work.

A European map of groundwater pH and calcium

Abstract. Water resources and associated ecosystems are becoming highly endangered due to ongoing global environmental changes. Spatial ecological modelling is a promising toolbox for understanding the past, present and future distribution and diversity patterns in groundwater-dependent ecosystems, such as fens, springs, streams, reed beds or wet grasslands. Still, the lack of detailed water chemistry maps prevents the use of reasonable models to be applied on continental and global scales. Being major determinants of biological composition and diversity of groundwater-dependent ecosystems, groundwater pH and calcium are of utmost importance. Here we developed an up-to-date European map of groundwater pH and Ca, based on 7577 measurements of near-surface groundwater pH and calcium distributed across Europe. In comparison to the existing European groundwater maps, we included several times more sites, especially in the regions rich in spring and fen habitats, and filled the apparent gaps in eastern and southeastern Europe. We used random forest models and regression kriging to create continuous maps of water pH and calcium at the continental scale, which is freely available also as a raster map (Hájek et al., 2020b; https://doi.org/10.5281/zenodo.4139912). Lithology had a higher importance than climate for both pH and calcium. The previously recognised latitudinal and altitudinal gradients were rediscovered with much refined regional patterns, as associated with bedrock variation. For ecological models of distribution and diversity of many terrestrial ecosystems, our new map based on field groundwater measurements is more suitable than maps of soil pH, which mirror not only bedrock chemistry but also vegetation-dependent soil processes.

Controls on δ26Mg variability in three Central European headwater catchments characterized by contrasting bedrock chemistry and contrasting inputs of atmospheric pollutants.

Magnesium isotope ratios (26Mg/24Mg) can provide insights into the origin of Mg pools and fluxes in catchments where Mg sources have distinct isotope compositions, and the direction and magnitude of Mg isotope fractionations are known. Variability in Mg isotope compositions was investigated in three small, spruce-forested catchments in the Czech Republic (Central Europe) situated along an industrial pollution gradient. The following combinations of catchment characteristics were selected for the study: low-Mg bedrock + low Mg deposition (site LYS, underlain by leucogranite); high-Mg bedrock + low Mg deposition (site PLB, underlain by serpentinite), and low-Mg bedrock + high Mg deposition (site UDL, underlain by orthogneiss). UDL, affected by spruce die-back due to acid rain, was the only investigated site where dolomite was applied to mitigate forest decline. The δ26Mg values of 10 catchment compartments were determined on pooled subsamples. At LYS, a wide range of δ26Mg values was observed across the compartments, from -3.38 ‰ (bedrock) to -2.88 ‰ (soil), -1.48% (open-area precipitation), -1.34 ‰ (throughfall), -1.19 ‰ (soil water), -0.99 ‰ (xylem), -0.95 ‰ (needles), -0.82 ‰ (bark), -0.76 ‰ (fine roots), and -0.76 ‰ (runoff). The δ26Mg values at UDL spanned 1.32 ‰ and were thus less variable, compared to LYS. Magnesium at PLB was isotopically relatively homogeneous. The δ26Mg systematics was consistent with geogenic control of runoff Mg at PLB. Mainly atmospheric/biological control of runoff Mg was indicated at UDL, and possibly also at LYS. Our sites did not exhibit the combination of low-δ26Mg runoff and high-δ26Mg weathering products (secondary clay minerals) reported from several previously studied sites. Six years after the end of liming at UDL, Mg derived from dolomite was isotopically undetectable in runoff.

Dust, impure calcite, and phytoliths: Modeled alternative sources of chemical weathering solutes in shallow groundwater

In highly reactive, carbonate terrains that constitute more than one-fifth of critical zone landscapes, quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility, biotically-produced minerals as an integral part of leaky biogeochemical cycles, and dust-deposited minerals as important high-surface-area, first-contact solute sources. The potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock, although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems, including those in mountain and tropical settings. We present results of computer and hand-calculated (manual) inverse modeling of two years of stream-water chemistry, spanning a dry and a wet year, for a groundwater-fed headwater stream at the Konza Tallgrass Prairie Long-Term Ecological Research Site in northeastern Kansas. Weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater-fed stream, but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock. We used the mineralogy and geochemistry of local dust collected previously, estimates of a possible chemical composition of phytolith containing potassium, and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry. Average annual amounts were about: 1) 380 kg ha−1 yr−1 dust dissolved, 2) 80 kg ha−1 yr−1 bedrock carbonate dissolved, and 3) 320 kg ha−1 yr−1 phytoliths precipitated. Small amounts of cation exchange were also required to balance the models. There were only small differences between the computer and manual inverse models; both methods resulted in up to 4.6 times more mass of dust dissolved than bedrock. We suggest that dust weathering may be a process that occurs widely, considering the ubiquitous dust flux in continental regions. Significance of researchSolutes in groundwater and in streams fed by groundwater are thought to be mostly derived from aquifer bedrock and soil water recharging the aquifer. This paradigm may fail for landscapes that have been subaerially exposed for 10's to 100's of millions of years in terrains where relatively rapid dissolution of minerals dominates, such as carbonate-mineral dominated rocks like limestone. Here we test whether dust, having high surface area and being the first inorganic solid encountered by meteoric precipitation, could provide enough solutes water to reduce the amount of bedrock that dissolves, extending the timeframe of landscape evolution. We found, through inverse modeling with PHREEQC, that dust can provide 4.6 times as much mass to stream water in merokarst than calcite and that the mass of dust dissolved was the same order of magnitude as local dust deposition. These results give permissive evidence that dust is important to understanding groundwater chemistry.

Controls on dripwater chemistry of Oregon Caves National Monument, northwestern United States

Cave dripwater chemistry of Oregon Caves National Monument (OCNM) was studied, where the parameters pH, total alkalinity, calcium, magnesium, strontium, sodium and barium were analyzed at quasi-monthly intervals from 2005 to 2007. Different statistical analyses have been used to investigate the variability of the chemical parameters in the different sites in the OCNM cave system. The dripwater varies in response to seasonal changes in rainfall. The drip rates range from zero in summer to continuous flow in winter, closely following the rainfall intensity. Spatial variations of dripwater chemistry, which is nonlinearly related to dripwater discharge likely, reflect the chemical composition of bedrock and overlying soil, and the residence time of the ground water within the aquifer. The residence time of infiltrated water in bedrock cracks control the dissolution carbonate bedrock, reprecipitation of calcium carbonate and the degree of saturation of dripwater with respect to calcium carbonate minerals. Spatiotemporal fluctuations of dripwater Mg/Ca and Sr/Ca ratios are controlled by dissolution of carbonate bedrock and the degree of calcite reprecipitation in bedrock cracks. This suggests that trace elements in speleothem deposits at the OCNM may serve as paleoclimatological proxies for precipitation, if interpreted within the context of understanding local bedrock chemistry.

Nonpoint Source Contributions Drive Elevated Major Ion and Dissolved Inorganic Carbon Concentrations in Urban Watersheds

The rapid expansion of urban land cover is associated with negative impacts on stream ecosystems. Elevated specific conductance (SC) and major ion concentrations are increasingly documented in urban streams. However, the degree to which nonpoint sources contribute to elevated ion concentrations is unclear. We characterized SC and major ion concentrations in five small watersheds along a forested-to-urban gradient with impervious surface cover (ISC) ranging from 0–25%, no major point sources such as wastewater treatment plants, and similar bedrock chemistry. Ion concentrations increase by an average of 27 times along the forested-to-urban gradient, including an increase of 10 times in dissolved inorganic carbon (DIC). Inputs from road salt caused large increases in Na+ and Cl– concentrations as well as high seasonal variability. Significant increases in Ca2+, Mg2+, DIC, and SO42– concentrations in watersheds with high ISC provide the best evidence to date that concrete is a substantial nonpoint source cont...

Are spherulitic lacustrine carbonates an expression of large-scale mineral carbonation? A case study from the East Kirkton Limestone, Scotland

Lacustrine carbonate deposits with spherulitic facies are poorly understood, but are key to understanding the economically important “Pre-Salt” Mesozoic strata of the South Atlantic. A major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite-dominated deposits which are known in outcrop. Stratigraphy and petrography suggest one of the best analogue systems is found in the Carboniferous of Scotland: the East Kirkton Limestone. Here we propose a hydrogeochemical model that explains why the CaCO3, SiO2, Mg-Si-Al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock. Demonstrating links between igneous bedrock chemistry, lake and spring water chemistry and mineral precipitation, this model has implications for studies of lacustrine sediments in rift basins of all ages. Using empirical and theoretical approaches, we analyze the relationship between metal mobilization from sub-surface volcaniclastic rocks and the potential for precipitation of carbonate minerals, various Mg-bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting. This suite of minerals is most likely formed by in-gassing of CO2 to a carbon-limited alkaline spring water, consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater. We suggest that an analogous system to that at East Kirkton caused development of the ‘Pre-Salt’ spherulitic carbonate deposits.

Hydrochemical Fluxes and Bedrock Chemistry in three Contrasting Catchments Underlain by Felsic, Mafic and Ultramafic Rocks

Bedrock chemistry from three drill cores and fluxes of precipitation, throughfall and runoff from the 2015 water year were examined in three forested catchments in the western Czech Republic. The coefficient of alkalinity of rocks at the granitic (felsic) LYS catchment fall in the low chemical reactivity category. Rocks from the amphibolitic (mafic) NAZ catchment have high reactivity and rocks from the serpentinitic (mostly ultramafic) PLB catchment have high or even very high reactivity. Streamwater fluxes reflected the composition of the underlying bedrock lithologies, especially for magnesium, nickel and chromium at PLB, and for calcium, arsenic and sulfur at NAZ. Streamwater at LYS reflected incomplete neutralization of acidic deposition in the catchment and had mostly negative alkalinity and correspondingly very high fluxes of potentially toxic inorganic monomeric aluminum. Internal cycling of magnesium and calcium in spruce canopy throughfall was influenced by substrate chemistry at PLB and NAZ. About half of streamwater nitrogen left the catchments in the organic form.

A two-year automated dripwater chemistry study in a remote cave in the tropical south Pacific: Using [Cl−] as a conservative tracer for seasalt contribution of major cations

Stalagmite Mg/Ca and Sr/Ca ratios are commonly interpreted as proxies for past hydrologic conditions and are often used to supplement carbon and oxygen stable isotope records. While the processes that control these element ratios, including water–rock interaction, dripwater residence time, and upstream precipitation of calcite, are well understood in continental caves, there have been few investigations of dripwater Element/Ca (X/Ca) evolution in coastal marine caves where seasalt can have a strong influence on the incoming Mg/Ca ratio.We instrumented a marine cave on the remote South Pacific island of Niue to record daily cave microclimate, as well as weekly-integrated drip rates, dripwater oxygen and hydrogen isotopes, and dripwater chemistry over a period of twenty-two months. Using chloride as a conservative tracer for sea-spray, we calculate that seasalt input accounts for a large portion of dripwater Na, SO4, and Mg (89%, 93%, and 85% respectively) and a smaller portion of the Ca and Sr (19% and 17%). During the second year of this study a gradual decrease (by ∼18%) in dripwater chlorinity was observed, suggesting that an epikarst-hosted seasalt aerosol inventory was being diluted over time. Minor element to calcium ratios for B, K, Cl, SO4, Mg, Na, Sr, and Fe all strongly covary over the observation period, suggesting that although sea-spray plays a significant role in modulating incoming drip chemistry, prior calcite precipitation (PCP) dominates chemical evolution within the epikarst. During a prolonged drought episode, evaporative enrichments in dripwater δD and δ18O (+4‰ and 0.5‰, respectively) were observed to coincide with increased cation and anion concentrations, strong Ca removal via PCP, and increases in Sr/Ca and Mg/Ca ratios (28% and 34%, respectively), suggesting that concomitant enrichment in speleothem δ18O and X/Ca ratios may be interpreted as multi-proxy evidence for dry climate conditions.We use modern dripwater chemistry and empirical water-calcite distribution coefficients to predict a range of stalagmite X/Ca ratios. We then forward model a number of scenarios that could modulate stalagmite chemistry, including increased/decreased seasalt input and changing dripwater flow path through calcite, dolomite, and aragonite bedrock. One major implication from this study is that even if PCP and flow path lithology remain constant over time, changing seasalt input can drive stalagmite Mg/Ca and Sr/Ca ratios away from PCP-controlled covariation, and lead to strongly varying Sr/Mg ratios. Thus in order to interpret coastal cave stalagmite X/Ca records accurately, it is necessary to estimate seasalt input and analyze parent drip and bedrock chemistry to quantify the influence of each contributing process.

What controls plant nutrient use in high elevation ecosystems?

The importance of rock-derived mineral nutrients (P, K, Mn, Mg, and Ca) in plant physiological function is well established. However, one important and relatively unexplored question is whether or not the same rules of plant nutrient use efficiency apply to these essential elements even if they are not limiting to primary production. We examined conifer growth and nutrient use dynamics across sites with contrasting geologies (sedimentary and volcanic) that vary in both rock-derived mineral nutrient and N availability. Differences in bedrock geochemistry generally corresponded to differences in available soil nutrients, such that the volcanic site tended to have greater available nutrients. Foliar nutrient concentrations reflected both differences in bedrock chemistry and indices of available soil nutrients for P, K, and Mn. Aboveground biomass production did not follow expected patterns and was greater for trees growing on low nutrient sites, but only with respect to the annual woody increment. Fine litter production did not differ between sites. Finally, we found evidence for trade-offs between two commonly examined components of nutrient use efficiency (NUE): nutrient productivity (A n) and mean residence time of nutrients. However, we did not find evidence for higher plant NUE in soils with lower nutrient availability for N or rock-derived nutrients.

Geochemical mapping of New Mexico, USA, using stream sediment data

The spatial analysis of geochemical data has several environmental and geological applications. The present study investigated the regional distribution of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, Pb, Sc, Th, Ti, U, V, and Zn elements in stream sediment samples from New Mexico State. These elements were studied in order to integrate them with geological and environmental characteristics of the area. Data are used from 27,798 samples that were originally collected during the national uranium resource evaluation (NURE) Hydrogeochemical and stream sediment reconnaissance (HSSR) program in the 1970s. The original data are available as U.S. Geological Survey Open-File Report 97-492. The study used a variety of data processing and filtering techniques that included univariate, bivariate, factor analyses and spatial analyses to transform the data into a useable format. Principal component analysis and GIS techniques are applied to classify the elements and to identify geochemical signatures, either natural or anthropogenic. The study found that the distribution of the investigated elements is mainly controlled by the bed rock chemistry. For example, along the Rio Grande rift and Jemez lineament a strong association between Co, Cr, Cu, Fe, Ni, Sc, Ti, V and Zn was observed and indicates that elements distribution in the area controlled by the mafic factor. The rare earth elements (REE) factor which is consists of Ce, La and U, also has strong, localized, clusters in the felsic centers in New Mexico.

Water quality and some nutrient levels in Shiroro Lake, Niger State, Nigeria

Water physical and chemical properties and nutrient levels of the surface water of Shiroro Lake (Nigeria) were determined over a period of eighteen months from June 1999 to December 2000. Five sampling stations were located within the lake basin. The wet season mean values for water temperature, and turbidity, were significantly (P < 0.05) higher than those for the dry season at all stations. However, for pH, and phosphate- phosphorus, the dry season mean values were higher than the wet season mean values. As in most other African inland water bodies, there was seasonality in the limnological variables. The hydrological regime of the lake, precipitation chemistry, bedrock chemistry and inputs resulting from hydro-electric power generation were observed to influenced and determined the quantity of dissolved organic carbon, nutrient levels and water quality of the lake. Nutrients added to the lake by the major tributary rivers and inundation of surrounding areas influenced water quality of the reservoir. From the nutrient levels, it could be concluded that Shiroro Lake is still an oligotrophic lake. Key Words: Nutrient, water parameters, Shiroro Lake tributaries, Nigeria. Journal of Aquatic Sciences Vol.19(2) 2004: 99-106

Effects of pH, alkalinity and bedrock chemistry on metal concentrations of springs in an acidified catchment (Ecker Dam, Harz Mountains, FRG)

Thirty-four springs were sampled on five different source rocks in the upper Ecker watershed of the Northern Harz Mountains (Germany) four times during the course of 1995. The analyses included 41 cations and the major anions. Approximately 90% of the rocks in the upper Ecker watershed are low in basic cations, which inhibit the neutralisation of hydrogen-ion loading. As a consequence, the concentrations of Al, Fe, Mn, Zn, Pb, Y, Ce, As, La, Nd, Cd, Be, Co, Sb, Pr, Gd, Dy, Yb, Er, Sm, U, Tl, Ho and Tb of the Ecker dam water (pH=5.1) exceed those of the nearby Söse Dam water (pH=6.5) by almost one order of magnitude or more. With the exception of the spring waters on gabbro (pH up to 7.7) all waters on the highly siliceous rocks (quartzite, granite and gneiss) are dominated by sulfate anions with a pH range of 4–6. The concentrations of major conservative ions show a progressive increase with decreasing catchment elevation and decreasing average precipitation. Trace elements such as Sr, Be, Zn, Cd, Ba, Y, La, lanthanides, U, Li, Ni, Al, Mn, Co, Cu, Pb, As, Sb and Tl are increased in the low acid neutralizing capacity (ANC (aq)) spring waters. The behaviours of Sr, Be, Zn, Cd, Ba, Y, La, lanthanides and U resemble that of the major cations. The highest concentrations of Li and Ni are found on quartzite. Al, Mn, Co and Cu exhibit no clear correlation with catchment elevation and one particular bedrock. The concentrations of V and Cr show a distinct increase in high ANC (aq) spring waters on gabbro. Pb, As, Sb and Tl are characterized by being found in relatively high concentrations on granite at higher altitudes. Pb, As and Sb are affected by contaminated soils. The extreme variability of trace element concentrations of low ANC (aq) spring waters cannot be explained by the rock data. It is mainly controlled by the topography-dependent weathering rates of the different rock-types and the decreasing dilution with decreasing catchment elevation.

Environmental impact of metalliferous black shales at Talvivaara in Finland, with indication of lake acidification 9000 years ago

Environmental impact of metalliferous black shales was studied in the Talvivaara area in eastern Finland with 194 lake sediment and 48 organic stream sediment samples and 57 surface water and 9 ground water samples. The samples were analysed using a combination of ICP–MS and ICP–AES methods. Continuous undisturbed lake sediment cores were obtained from seven lakes. Cores from three of the lakes penetrated through the sediment column into the underlying clay, which was deposited in a late glacial ice-dammed lake between 12,000 and 9000 years ago. The concentrations of Ni, Zn, and Cd in surface water and organic stream and lake sediments were significantly greater if the bedrock of the catchment area consisted of black shales than if it consisted of gneiss granite or quartzite. It appeared that this was also the case in the past. The influence of bedrock chemistry is particularly pronounced in the Lake Härkälampi profile at a depth of 358 cm, which records the abrupt isolation of the lake from the Sotkamo ice-dammed lake 9000 years ago. At this time, the metalliferous black shales of the catchment area were exposed to prolonged wave action and erosion, and pH dropped to as low as 3.8. Following isolation of the lake the organic content of the sediment steadily increased, attaining a maximum value of 13% at a depth of 310 cm. Maximum Ni (0.1%), Cu (0.03%), Zn (0.5%), and Al (3.4%) concentrations are recorded shortly after isolation, when the proportion of organic material was still as low as 2.7%. Evidently vegetation effectively reduces bedrock weathering even in cool climate, since Ni, Cu, Zn, and Al concentrations decreased and pH increased in Lake Härkälampi due to colonization of tundra vegetation.

Pedogenic Influence on Base Saturation and Calcium/Magnesium Ratios in Soils of Southeastern Ohio

AbstractContiguous Alfisols and Ultisols occur across the unglaciated, upland landscape of southeastern Ohio. Difficulties are encountered in distinguishing and mapping these soils due to morphological similarities and base saturation differences. The soils have formed in a loess mantle of varying thickness overlying colluvium and residuum derived from sedimentary bedrocks. Four pedons were studied to evaluate the influence of the loess mantle and bedrock chemistry on base saturation and extractable Ca/Mg ratios in order to facilitate soil mapping in southeastern Ohio. Loess thickness and Cr horizon chemistry could adequately account for base saturation and extractable Ca/Mg ratios in three of the four pedons, but a pedogenic effect is essential to explain extractable Ca/Mg ratios in the other pedon. In the latter pedon, extractable Ca exceeded Mg in both the loess mantle (upper solum) and deep Cr horizons, but extractable Mg exceeded Ca in the lower solum and uppermost Cr horizons. We conclude that bases leached from the loess mantle accumulate in the underlying residuum and that Mg is preferentially retained during base recharge. We speculate that a transient Mg‐Al double hydroxide is formed in the residuum during base recharge and is responsible for preferential Mg retention.

CONTROLS ON SURFACE WATER CHEMISTRY IN THE UPPER MERCED RIVER BASIN, YOSEMITE NATIONAL PARK, CALIFORNIA

Surface water draining granitic bedrock in Yosemite National Park exhibits considerable variability in chemical composition, despite the relative homogeneity of bedrock chemistry. Other geological factors, including the jointing and distribution of glacial till, appear to exert strong controls on water composition. Chemical data from three surface water surveys in the upper Merced River basin conducted in August 1981, June 1988 and August 1991 were analysed and compared with mapped geological, hydrological and topographic features to identify the solute sources and processes that control water chemistry within the basin during baseflow. Water at most of the sampling sites was dilute, with alkalinities ranging from 26 to 77 pequiv. I-'. Alkalinity was much higher in two subcatchments, however, ranging from 51 to 302 pequiv. 1-'. Base cations and silica were also significantly higher in these two catchments than in the rest of the watershed. Concentrations of weathering products in surface water were correlated to the fraction of each subcatchment underlain by surficial material, which is mostly glacial till. Silicate mineral weathering is the dominant control on concentrations of alkalinity, silica and base cations, and ratios of these constituents in surface water reflect the composition of local bedrock. Chloride concentrations in surface water samples varied widely, ranging from < 1 to 96 pequiv. 1-'. The annual volume-weighted mean chloride concentration in the Merced River at the Happy Isles gauge from 1968 to 1990 was 26 pequiv. l-', which was five times higher than in atmospheric deposition (4-5 pequiv. l-'), suggesting that a source of chloride exists within the watershed. Saline groundwater springs, whose locations are probably controlled by vertical jointing in the bedrock, are the most likely source of the chloride. Sulphate concentrations varied much less than most other solutes, ranging from 3 to 14 pequiv. 1-'. Concentrations of sulphate in quarterly samples collected at the watershed outlet also showed relatively little variation, suggesting that sulphate may be regulated to some extent by a within-watershed process, such as sulphate adsorption.