Surface Water Chemistry Research Articles

New insights into fluid-rock interaction mechanisms at mud volcanoes: Implications for fluid origin and mud provenance at Bahar and Zenbil (Azerbaijan)

Understanding the fluid-rock interactions occurring in terrestrial mud volcanoes is a premise for elucidating the (bio)geochemical processes involved in the release of aqueous fluids, mud and gases to the Earth's surface and atmosphere. For the first time, fluid and mud ejecta from the mud volcanoes at Bahar and Zenbil, located in eastern Azerbaijan and in the shallow coastal water of the South Caspian, were collected and analyzed for their mineralogical, textural and chemical composition. The expelled aqueous fluids have a Na-Cl-(HCO3) composition and are generated by the mixing of evaporitic Caspian seawater and ancient, low- to high-salinity, sedimentary pore water at temperatures of 32 ± 3 °C and 42 ± 5 °C for the mud volcanoes at Bahar and Zenbil, consistent with mud chambers to be situated in the Pliocene sediments at 2–3 km depth. These aqueous fluids are strongly enriched in major solutes, like Na, Cl, HCO3, B, Br, NH4 and DOC, as well as in some trace elements (As, Ba, Cu, Fe, Li, Sr and Zn), with concentrations up to 220 times that of the current Caspian seawater. This chemical concentration is caused mainly by a combination of (i) strong surface evaporation, ion exchange and adsorption-desorption involving smectite clays, redox-driven reactions and carbonate mineral precipitation at relatively shallow depths (not deeper than 4 km) as well as (ii) thermal breakdown of organic matter and methane production in deeply buried (4 to 7 km depth) organic-rich strata. Biogenic processes are only of minor importance. The mud is sourced from all horizons the mud volcanoes are cross-cutting, partly altered by diagenetic processes. Alteration is comprised of illitization of smectite during burial diagenesis (120 to 150 °C), replacements of feldspar by kaolinite and smectite, weathering of sulfide minerals, Fe-(oxy)hydroxide formation, as well as oxidation of methane and organic matter in the near sub-surface environments at low temperature (<40 °C). Our results indicate that fluid-mud mixtures expelled from mud volcanoes of the South Caspian basin can influence the chemistry of local surface and ground water as well as of (sub-)surface sediments.

Comparative study of physicochemical parameters of groundwater and surface water of rawatsar, Hanumangarh (Rajasthan)

A study on the comparison of surface water and groundwater quality in Rawatsar Tehsil of Hanumangarh district (Rajasthan) was carried out. Different sites were selected for analysis of groundwater and surface water. Physicochemical parameters of water such as pH, EC, TDS, Turbidity, Alkalinity, Chloride, DO, COD, Na and K were analyzed using standard methods for all the samples. It was found that pH and EC were within the BIS permissible limit. All water samples have chloride content more than BIS standard values, showing the dominance of chloride ions in the study area. From the present study, surface water and groundwater samples have higher turbidity and high content of total dissolved solids, alkalinity, chloride, sodium and potassium. Groundwater dominates chloride, carbonate, sodium and potassium ions. Hence, surface water and groundwater need to be treated before end-use. This preliminary study needs to be researched further for a better understanding of hydrogeochemistry of groundwater and chemistry of surface water in Rawatsar.

The combined effects of surface texture, flow patterns and water chemistry on corrosion mechanisms of stainless steel condenser tubes

Detailed failure analysis was carried out for a set of leaking vertical condenser tubes made from AISI 304L-type stainless steel. Experimental part of the analysis included non-destructive testing (eddy current testing and dye-penetrant testing), visual and stereoscopic examination, mechanical testing, chemical analysis, optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The present failure was found to be a result of a sequence of several interrelated actions. Experimental evidence indicated the leaking to be caused by surface-breaking pitting resulting mainly from under deposit corrosion (UDC) mechanism. The observed UDC, however, was associated with the presence of distinct surface features promoting low local flow velocities and stagnation conditions. These features are believed to be the result of the specific inside diameter (ID) weld scarfing process. The present results also indicated that UDC was followed by flow accelerated corrosion (FAC) upon tube wall perforation. Computational fluid dynamics (CFD) was used to simulate water flow conditions inside the condenser tubes before and after perforation in order to evaluate the suggested failure sequence and the involved damage mechanisms. CFD results were found to be in strong support of the observed experimental evidence and the proposed failure mechanisms. Finally, the three interacting factors, i.e.; surface texture, flow conditions and water chemistry, are discussed in terms of their effects in leading to the observed final failure and forming its distinct morphology.

Geochemical and statistical evaluation of spring water in Sarduiyeh Basin, SE Iran

This study investigates the natural processes that influence the chemistry of surface and spring water within the Sarduiyeh region using correlation matrix and factor analysis techniques. A total of 27 spring samples were collected during April 2011, and analyzed for their physico-chemical constituents. Hydrogeochemical data of samples suggested that the water types are: Na–Cl (40.74%), Ca–Mg–HCO3 (37.04%), Na–HCO3–Cl–Mg (14.81%) and Ca–Mg–SO4–Cl (7.41%). The order of cations and anions abundance is Na+> K+> Mg2+> Ca2+ and Cl− > SO42− > HCO3− > NO3−. The very high As concentrations are observed in three samples (numbers 24, 3 and 2) with value 25,000, 2327 and 2178 µg/L. The multivariate statistical methods indicate that hydrogeochemistry of the spring water in study area is mainly controlled by water–rock interaction, and weathering and dissolution of silicate minerals mainly extend in the area.

Design and applications of metal-based molecular receptors and probes for inorganic phosphate.

Inorganic phosphate has numerous biomedical functions. Regulated primarily by the kidneys, phosphate reaches abnormally high blood levels in patients with advanced renal diseases. Since phosphate cannot be efficiently removed by dialysis, the resulting hyperphosphatemia leads to increased mortality. Phosphate is also an important component of the environmental chemistry of surface water. Although required to secure our food supply, inorganic phosphate is also linked to eutrophication and the spread of algal blooms with an increasing economic and environmental burden. Key to resolving both of these issues is the development of accurate probes and molecular receptors for inorganic phosphate. Yet, quantifying phosphate in complex aqueous media remains challenging, as is the development of supramolecular receptors that have adequate sensitivity and selectivity for use in either blood or surface waters. Metal-based receptors are particularly well-suited for these applications as they can overcome the high hydration enthalpy of phosphate that limits the effectiveness of many organic receptors in water. Three different strategies are most commonly employed with inorganic receptors for anions: metal extrusion assays, responsive molecular receptors, and indicator displacement assays. In this review, the requirements for molecular receptors and probes for environmental applications are outlined. The different strategies deployed to recognize and sense phosphate with metal ions will be detailed, and their advantages and shortfalls will be delineated with key examples from the literature.

Groundwater Carbon Within a Boreal Catchment: Spatiotemporal Variability of a Hidden Aquatic Carbon Pool

AbstractGroundwater is an essential resource providing water for societies and sustaining surface waters. Although groundwater at intermediate depth could be highly influential at regulating lake and river surface water chemistry, studies quantifying organic and inorganic carbon (C) species in intermediate depth groundwater are still rare. Here, we quantified dissolved and gaseous C species in the groundwater of a boreal catchment at 3‐ to 20‐m depth. We found that the partial pressure of carbon dioxide (pCO2), the stable carbon isotopic composition of dissolved inorganic carbon (δ13C‐DIC), and pH showed a dependency with depth. Along the depth profile, a negative relationship was observed between pCO2 and δ13C‐DIC and between pCO2 and pH. We attribute the negative pCO2‐pH relationship along the depth gradient to increased silicate weathering and decreased soil respiration. Silicate weathering consumes carbon dioxide (CO2) and release base cations, leading to increased pH and decreased pCO2. We observed a positive relationship between δ13C‐DIC and depth, potentially due to diffusion‐related fractionation in addition to isotopic discrimination during soil respiration. Soil CO2 may diffuse downward, resulting in a fractionation of the δ13C‐DIC. Additionally, the dissolved organic carbon at greater depth may be recalcitrant consisting of old degraded material with a greater fraction of the heavier C isotope. Our study provides increased knowledge about the C biogeochemistry of groundwater at intermediate depth, which is important since these waters likely contribute to the widespread CO2 oversaturation in boreal surface waters.

Hydrochemical Characteristics and Quality Assessment of Stream Water in Parts of Gadag, Koppal and Ballery Districts of Karnataka, India

Seventeen water samples were collected from various streams in parts of Gadag, Koppal and Ballery districts of Karnataka and analyzed for major ions and heavy metals to determine the processes controlling surface water chemistry and suitability of water for drinking, livestock uses and irrigation purposes. The water samples are moderately alkaline to alkaline in nature and soft to moderately hard. The order of cations is Na>Ca>Mg>K, of anions is HCO3>Cl>SO4>CO3>NO3 and heavy metals Sr>Fe>V>Ba>Zn>Ni>Mn>As>Cu>Cr>Pb>Co. According to Gibbs diagram, the water samples fall in the dominant rock-water interaction area, suggesting chemical weathering of the rock forming minerals as the main process contributing ions to the surface water. Scatter plots of Ca + Mg vs HCO3 + SO4 and Ca/Na vs HCO3/Na clearly indicate the silicate weathering playing a dominant role on water chemistry. The evolution of surface water into Ca-Na-HCO3 and Ca-HCO3 water types is due to easy dissolution of silicate minerals and less time for water-rock interaction. Surface water samples are characterized by Na-Ca-HCO3-Cl the principal water type of schoeller’s plot, which can be related to the weathering of the silicate rocks along with some anthropogenic input. The physical parameters, major ions and heavy metals are within the permissible limits of WHO and BIS standards except for two samples, suggesting the water as suitable for domestic and livestock uses. The stream water is suitable for irrigation as per the quality parameters and plots including EC, sodium percent, sodium adsorption ratio, Wilcox and USDA classification diagrams.

Global warming and acid atmospheric deposition impacts on carbonate dissolution and CO2 fluxes in French karst hydrosystems: Evidence from hydrochemical monitoring in recent decades

The long-term change in surface water chemistry over time in remote areas is usually related to global change, including several processes such as global warming and acid atmospheric pollution. These cumulative factors limit the quantitative interpretation of the global warming effect on surface water acidification in relation to the atmospheric CO2 sink. To quantitatively estimate the impact of global warming on the atmospheric/soil CO2 uptake by carbonate weathering, the approach proposed here involves discriminating the proportion of [Ca + Mg] in waters resulting from soil carbonic acid dissolution (equal to the amount of CO2 uptake from soil/atmosphere) from the proportion resulting from strong acid pollution. This approach was applied to 5 karst hydrosystems located in France, far from local pollution sources and with several decades of hydrochemical monitoring.[Ca + Mg] from acid deposition represented between 16 and 25% of the total [Ca + Mg] concentration and the flux was positively correlated with the atmospheric deposition flux. This [Ca + Mg] increase is associated with increasing [Mg] and was found to be driven by the acid pollution inputs. Equilibrating water with calcite in presence of carbonic acid will release [Ca + Mg] into solution. The input of strong acids from atmospheric pollution contributes more to magnesian calcite dissolution because its solubility is lower than that of calcite.Since the 1980s, the decrease in [Ca + Mg] production due to the decrease in acid atmospheric deposition has minimized the increase in [Ca + Mg] linked to CO2 partial pressure (pCO2) increasing with global warming. It was found that [Ca + Mg] from H2CO3 dissolution did not decrease with an increase in air temperature, as suggested by carbonate solubility. The annual fluxes of Ca + Mg from H2CO3 dissolution, calculated for an average flow, showed a positive gradient with air temperature, of about 0.061 mol m2 yr−1 °C−1 (±0.006). In low rainfall areas, the pCO2 increase with air temperature was stronger than in rainy areas. For an average specific discharge of 300 L m−2 yr−1, global warming is estimated to increase the CO2 uptake flux by about 204 micromol L−1 °C−1 (5.7% of the observed flux).

Using stream-side groundwater discharge for geochemical exploration in mountainous terrain

Groundwater chemistry has been predominantly used in geochemical exploration studies to identify mineralized targets concealed under transported cover in areas with gentle topography. Another potentially valuable application that has received little attention is using groundwater chemistry to identify deposits concealed within mountain ridges. A number of geochemical exploration studies have employed surface water chemistry in hilly and mountainous terrain and have demonstrated mixed success. However, groundwater chemistry is potentially a more refined and powerful tool because groundwater sample locations can be selected to target a specific hillslope zone, whereas surface water integrates the geochemical signature of the entire watershed area above the sample site. In this study, we propose an approach that utilizes shallow groundwater samples collected from near-stream, hand-installed sampling points. We tested this approach in Handcart Gulch, an unmined catchment in the Montezuma Mining District, Colorado, USA, where previous studies suggested the possible presence of a concealed mineral occurrence. Seventeen near-stream mini-boreholes were drilled in a stream-parallel 3.3-km-long transect to depths of ~2 m in ferricrete (iron-oxide cemented colluvium and alluvium) using a handheld rock-coring drill. Groundwater in the mini-boreholes was sampled for major and trace element chemistry, as well as environmental tracers including stable water isotopes, dissolved noble gases, helium isotopes, and tritium, to identify possible variations in groundwater age and recharge conditions/sources. Chemistry data delineate a well-defined 900-m-wide zone of elevated SO4, Cu, and other metal concentrations on the east side of the stream. In this zone, Cu concentrations up to 2670 μg/L are 1–3 orders of magnitude greater than concentrations in upstream and downstream areas. Environmental tracer data show no corresponding anomalies in groundwater age or recharge conditions/sources within the zone, suggesting that the source of the elevated metals is a change in bedrock mineralogy as opposed to other hydrologic factors. The groundwater samples therefore successfully identify and refine the location of a potential concealed high-Cu mineral occurrence in the watershed, demonstrating that near-stream groundwater discharge may be a valuable medium for geochemical exploration in mountainous areas.

Natural Radionuclides 238U, 226Ra, and 222Rn in the Surface Water of the El’konskii Uranium Ore Region, Southern Yakutia

Surface water chemistry and content of radionuclides 238U, 226Ra, and 222Rn were studied in both natural and technogenic landscapes of Southern Yakutia. The technogenically disturbed landscapes of the El’konskii Uranium Ore Region showed intense migration of these radionuclides in water from dumps of radioactive rocks that had formed during large-scale exploration works for radioactive ore in the late XX century. A dispersion halo of 238U and 226Ra in water was detected in groundwater over a distance of more than 2 km downstream of the radioactive pollution sources.

Hydrogeochemistry as a Tool for Platinum Group Element (PGE) Exploration — A Case Study from Sittampundi Anorthosite Complex, Southern India

The use of surface and ground water for exploration of platinum group elements (PGE) has been studied in the Sittampundi anorthosite complex, Tamil Nadu, south India, where PGE mineralization is known to occur in basic and ultrabasic rocks. Groundwater interacting with mineralized rocks creates a geochemical signature which can be linked to the occurrence and distribution of PGE, especially Pd because of its leachability and relatively high mobility in aqueous environment. Forty surface and ground water samples collected from the area were analyzed for PGE and several other major, minor and trace elements using high resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) to investigate the distribution patterns of individual PGE and other elements for the purpose of evaluating the utility of hydrogeochemistry as a tool for PGE exploration studies. Ground and surface water chemistry reflected the chemical composition of host lithology, particularly the basic-ultrabasic rocks of the region, with the dispersion of PGE and high anomalous concentrations of Pd, Ru and Rh along with several other metals such as Zn, V, Cr and Ni indicating PGE mineralization. The results of this study suggest that groundwater chemistry has significant potential as a PGE exploration tool with advantages such as rapid and low-cost sampling, high contrast anomalies and a uniform sampling medium.

Environmental State of a Small Northern River after an Emergency Discharge of Oil Products

The chemistry of surface water, bottom sediments, and zoobenthos communities is studied in a small forest watercourse after an accident on a petroleum pipeline. Nine months after the oil spill, the surface water downstream of the site of emergency discharge of oil-containing liquid still shows higher petroleum hydrocarbon content (2.8 MAC). The determined high concentrations of ions of iron (1.1−4.6 MAC) and copper (1.2−2.6 MAC), as well as difficult to decompose organic compounds (1.2−3.3 MAC), are also typical of the background area, thus suggesting their predominantly natural origin. The concentration of petroleum hydrocarbons in bottom sediments in water downstream of the emergency petroleum discharge site is 7–214 times its background value. The zoobenthos in the streams in the study area is represented by 18 groups of aquatic organisms, of which 14 are detected in the polluted zone. In the direction from the oil spill zone toward the mouth of the Vozei-shor Creek, the structure of zoobenthos changes and its quantitative characteristics decrease. Crustaceans and oligochaetes were found to dominate in the benthic communities of oil-polluted areas.

Fecal indicator dynamics at the watershed scale: Variable relationships with land use, season, and water chemistry

Tracking fecal contamination in surface waters is critical to remediating water quality; however, general and source-specific fecal indicators often provide conflicting results. To understand the spatial and temporal dynamics of multiple fecal indicators and the sources they represent, we measured weekly concentrations of two general fecal indicator bacteria (FIB), a genetic indicator of human-associated Bacteroides (HF183), and surface water chemistry in nine mixed land-use watersheds in southwest Virginia, USA. At the watershed scale, general and source-specific indicators were decoupled, with distinct spatial, temporal, and chemical patterns. Random Forest analysis of individual sample variability identified temperature, watershed, nutrients, and cations as top predictors of indicator concentrations. However, these patterns – and the specific nutrients and cations identified – varied by indicator type. Among watersheds, FIB increased with developed land cover and during the summer months, while HF183 increased during the winter and only in urban watersheds. Nutrients generally related poorly to FIB and HF183, except E. coli, which correlated with total nitrogen. In contrast, all fecal indicators showed strong correlations with cations. FIB were more strongly related to calcium, magnesium, and potassium concentrations, while HF183 was related to sodium. These results suggest that, even at the watershed scale, 1) HF183 detects mainly human fecal contamination, while FIB detect broader ecosystem fecal inputs, and 2) poor correlation between specific and generalist fecal indicators is caused by unique spatial, temporal, and transport dynamics of different fecal sources in watersheds.

Redox conditions and pH control trace element concentrations in a meandering stream and shallow groundwater of a semiarid mountain watershed, Red Canyon, Wyoming, USA

The interface between oxic surface water and anoxic groundwater plays an important role in trace element cycling in mountains streams. In this investigation, stream water and shallow groundwater were sampled in a semiarid mountain catchment at Red Canyon, Wyoming, USA to evaluate variability in redox conditions and trace element concentrations. Samples were collected in July 2013 during summer baseflow conditions and in May 2014 during snowmelt runoff. Field measurements showed dissolved oxygen-saturated stream water and anoxic groundwater, with relatively higher pH in surface water. Groundwater and surface water chemistry were remarkably similar during both the summer and spring sampling events, indicating overall stability of the oxic/anoxic transition and trace element concentrations. Similar stable water isotope values indicate a close connection between the surface water and groundwater (δ18O and δD ranged from − 18.1 to − 18.9‰ and from − 140 to − 147‰, respectively). Concentrations of most trace and major elements were a factor of two higher in groundwater relative to surface water. Notably, Mn, Fe, and Ce concentrations were 7–90-fold higher in groundwater relative to surface water. In contrast, As, Se, and V concentrations were 3–30-fold lower in groundwater relative to surface water, likely due to pH- and redox-driven changes in speciation and sorption. This study is important for characterizing trace element cycling in mountainous areas, where measurements are rare, and has implications for furthering understanding of the key biogeochemical processes that occur during groundwater–surface water interactions.

Hydrochemical and isotopic characteristics of surface water in the Lhasa River basin

In this study, 36 surface water samples were collected to investigate the hydrochemical and isotopic characteristics of the surface water in the Lhasa River basin using mathematical statistics, a Piper diagram, Gibbs plots, ratio graphs of ions and factor analysis. The dominance of the cations and anions in the surface water was Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl−. The mean concentrations of the cations and anions of the surface water were low in the study area. Human activities have a certain influence on the hydrochemical components of surface water in the study area. HCO3·SO4 (SO4·HCO3)-Ca·Mg (Mg·Ca) types of surface water were dominant in the study area. Water-rock interactions play a dominant role in controlling the surface water chemistry in the Lhasa River basin, mainly the weathering of silicate and carbonate, as well as the dissolution of sulfate minerals and cation exchange. Isotopic analysis indicated that the surface water was of meteoric and glacial/snow meltwater origin.

Statistical methods for the geochemical characterisation of surface waters: The case study of the Tiber River basin (Central Italy)

Studying the chemistry of surface waters and their resilience to compositional changes represents a global challenge to preserve them from human- and changing climate-induced modifications. River waters are sentinel parameters for all processes occurring in a river basin. This is particularly true for regional watersheds, which can include both natural- and anthropogenic-sourced solutes such as those present in the Tiber River basin, the biggest one in Central Italy. In this work, innovative applications of statistical methods are proposed, from the perspective of Compositional Data Analysis theory, in order to consider the geochemical riverine system as a whole and detect compositional changes throughout the catchment. Robust compositional biplots highlighted different sources of variability linked to geological (low variability) and anthropogenic origin (high variability) of the main compounds, thus identifying a hierarchy in the variance of the riverine geochemical processes. On a different scale, the innovative use of the robust Mahalanobis distance in an iterative way monitored spatial compositional shifts for single cases. The effectiveness of this method consists in minimising the influence of an individual anomalous point on the compositional centre and the covariance structure of the data highlighting when along the river a significant compositional shift occurs. The study provides powerful compositional tools for detecting potential contamination events or climate-induced modifications both at catchment and river scale.

Assessing the legacy of red mud pollution in a shallow freshwater lake: long-term chemical recovery in the water column

ABSTRACTLittle is known about chemical and ecological recovery following red mud leachate pollution in fresh waters. This deficiency is confounded by a lack of knowledge on the chemical composition of red mud leachate and the changes in composition that occur as a result of interactions with sediments and freshwater organisms during transport through aquatic ecosystems. We used over 30 years of data from a shallow lake (Kinghorn Loch, Fife, Scotland) with a well-documented history of several decades of red mud leachate pollution to characterise the chemical loads (during a pollution period from 1981 to 1983), resultant impacts on surface water chemistry (comparison between 1983 and 2009), and recovery trajectories following leachate diversion (1983–2010) of constituents that pose a risk to the environment. Between 1981 and 1983, the input of leachate resulted in loads of total aluminium (Al), total arsenic (As), total vanadium (V), and phosphate (PO4-P) to the lake of 107, 2.3, 3.3, and 2.3 g m−2 (lake surface area) yr−1, respectively. During the same period, the lake acted as a sink of Al, As, V, and PO4-P, retaining 63.6, 0.6, 0.8, and 1.6 g m−2 yr−1, respectively. We used generalised additive modelling to assess the response trajectories and recovery end points of these constituents. Our results demonstrate the complexity of sediment–pollutant interactions during pollutant transport through the aquatic environment and provide insight into likely recovery trajectories in other aquatic ecosystems following red mud contamination. The PO4-P, total As, and total V surface water concentration recovery times, defined statistically as the point on the time series beyond which no further significant decrease in concentrations was observed, ranged from 18 to 26 years. Total Al concentrations continued to decrease significantly following the end of the monitoring period in 2010. In Kinghorn Loch, the legacy of red mud pollution continues to represent an environmental risk, demonstrating the importance of long-term monitoring and management strategies following similar pollution events.

Response of Water Chemistry to Long-Term Human Activities in the Nested Catchments System of Subtropical Northeast India

The subtropics within the monsoonal range are distinguished by intensive human activity, which affects stream water chemistry. This paper aims to determine spatio-temporal variations and flowpaths of stream water chemical elements in a long-term anthropogenically-modified landscape, as well as to verify whether the water chemistry of a subtropical elevated shield has distinct features compared to other headwater areas in the tropics. It was hypothesized that small catchments with homogenous environmental conditions could assist in investigating the changes in ions and trace metals in various populations and land uses. Numerous physico-chemical parameters were measured, including temperature, pH, electrical conductivity (EC), dissolved organic carbon (DOC), major ions, and trace metals. Chemical element concentrations were found to be low, with a total dissolved load (TDS) below 52 mg L−1. Statistical tests indicated an increase with significant differences in the chemical element concentration between sites and seasons along with increases of anthropogenic impact. Human influence was clearly visible in the case of cations (Ca2+, K+, Mg2+, Na+) and anions (Cl−, HCO3−, NO3−, SO42−), compared to trace metals. The order of most abundant metals Fe &gt; Zn &gt; Al &gt; Sr was the same in springs and streams, regardless of population density, land use, and season. Principal component analysis (PCA) demonstrated that major ion concentrations in stream water followed the pattern forest &lt; cultivated land &lt; grassland &lt; built-up area. Surface water chemistry of the subtropical elevated shield has mixed features of tropical and temperate zones. Low concentrations of chemical elements; small seasonal differences in headwater streams; and increased concentrations of NO3−, SO42−, DOC, and Zn in the wet monsoon season are similar to those observed in the tropics. The role of long-term cultivation without chemical fertilizers in ions supply to streams is less than in other headwater areas of the tropical zone. Strong control of water chemistry in densely populated built-up areas is analogous to both tropical and temperate regions. Population density or a built-up area may be used as a proxy for the reconstruction or prediction of the anthropogenic impact on stream water chemistry in similar subtropical elevated shields.

Runoff and Solute Outputs under Different Land Uses: Long-Term Results from a Mediterranean Mountain Experimental Station

Water availability and quality in Mediterranean environments are largely related to the spatial organisation of land uses in mountain areas, where most water resources are generated. However, there is scant data available on the potential effects of land use changes on surface water chemistry in the Mediterranean mountain region. In order to address this gap in the research, this study investigates the effects of various mountain Mediterranean land covers/land uses on runoff water yielded and water chemistry (solute concentrations and loads) using data from the Aísa Valley Experimental Station (Central Pyrenees) for a long-term period (1991–2011). Nine land covers have been reproduced in closed plots, including dense shrub cover, grazing meadows, cereal, fallow land, abandoned field, shifting agriculture (active and abandoned) and 2 burned plots (one burned in 1991 and the second one burned twice in 1993 and 2001). Results show that all solute concentrations differed among land uses, with agricultural activity producing significantly higher solute loads and concentrations than the other types. Two groups have been identified: (i) the lowest solute concentrations and the smallest quantities of solute loads are recorded in the dense shrub cover, the plot burned once (at present well colonized with shrubs), meadows and abandoned field plots; (ii) the plot burned twice registered moderate values and the highest solute concentrations and loads are found in cereal, fallow land and shifting agriculture plots. Water chemistry is clearly dominated by Ca2+ and HCO3− concentrations, whereas other solutes are exported in very low quantities due to the poor nutrient content of the soil. These results complete the information published previously on soil erosion under different land uses in this experimental station and help to explain the evolution of land cover as a consequence of shifting agriculture, cereal farming on steep slopes and the use of recurrent fires to favour seasonal grazing. They also suggest that promoting the development of grazing and cutting meadows is a good strategy to reduce not only soil erosion but also the loss of nutrients.

Models for the acute and chronic aqueous toxicity of vanadium to Daphnia pulex under a range of surface water chemistry conditions

Alberta's oil sands petroleum coke (PC) generation has in recent years surpassed 10 million tonnes. Petroleum coke has been proposed as an industrial-scale sorbent to reduce concentrations of organic chemicals in oil sands process-affected water (OSPW). However, PC contains up to 1000 mg of vanadium (V) per kg of PC, and during the treatment it leaches from coke reaching levels of up to 7 mg/L in “treated” OSPW. Little information is available on how common water quality variables affect the toxicity of V to aquatic organisms. Here descriptive relationships are presented to describe how site-specific surface water characteristics representative of the Alberta oil sands region influence the toxicity of V to Daphnia pulex. Results revealed that when D. pulex was exposed to an increase in pH, a threshold relationship was found where acute V toxicity increased from a lethal median concentration (LC50) of 1.7 to 1.2 mg V/L between pH 6 and 7 and then levelled off at around 1 mg V/L. When alkalinity (from 75 to 541 mg/L as CaCO3) and sulphate (from 54 to 394 mg/L) increased, the acute toxicity of V decreased slightly with LC50s changing from 0.6 to 1.6, and from 0.9 to 1.4, respectively. When the length of V exposure was extended (from 2 to 21 d), only an increase of sulphate from 135 to 480 mg/L caused a slight increase in V toxicity from a LC50 of 0.6 to 0.4 mg V/L, the opposite trend seen in the acute exposures. In addition, the influence of two OSPW representative mixtures of increasing sodium and sulphate, and increasing alkalinity and sulphate on V acute toxicity to D. pulex were evaluated; only the mixture of increasing sodium (from 18 to 536 mg/L) and sulphate (from 55 to 242 mg/L) caused a slight decrease in V acute toxicity (LC50 1.0–2.1 mg V/L). Evidence is presented that variations in surface water chemistry can affect V toxicity to daphnids, although only to a small degree (i.e. within a maximum factor of 2 in all cases evaluated here). These relationships should be considered when creating new water quality guidelines or local benchmarks for V.