Comparative zinc dynamics in Atlanta metropolitan region stream and street runoff

Zinc, major ion, and other trace metal (V, Cr, Co, Ni, Cu, Cd, and Pb) concentrations were measured within 172 street and stream runoff samples in the Atlanta metropolitan region and in relatively undeveloped watersheds within the Georgia Piedmont and Blue Ridge Provinces. Peachtree Creek, draining a densely populated area of Atlanta, was the primary sampling location and samples were acquired under a wide range of hydrological conditions. Zinc concentrations within street runoff [median (Zn)_{urban street runoff}=905 µg/l] were significantly greater than zinc concentrations within storm runoff [median (Zn)_{Peachtree Creek}=60 µg/l], which were, in turn, greater than zinc concentrations within non-storm runoff [median (Zn)_{Peachtree Creek}=14 µg/l]. Zinc concentrations were not significantly greater within urban base flow than within non-urban base flow, indicating that the primary source of pollution is "event water" or street runoff. Zinc was the only heavy metal present in greater than "background" concentrations (i.e., >10 µg/l), which is likely the result of automotive pollution that is omnipresent within the study area. Analysis of storm alkalinity dilution trends indicate that simple mixing between polluted street runoff and groundwater cannot account for the zinc concentrations observed within storm and recession flows. A two end member mass balance model suggests that a large proportion of the zinc present in the street runoff is adsorbed and transported on surfaces of the suspended sediment. Adsorption is readily possible at the near neutral pH (~6.5) of turbid storm discharge.     

Chemical Characteristics of Stream Draining fromDudu Glacier: An Alpine Meltwater Stream inGanga Headwater, Garhwal Himalaya

I-DtjcrONAlpine environment enjoys a distinct set of physicochemical conditions asl compared to other aqueous systems. Thehydrochemical characteristics of meltwater draining from thisenvironment are different from the other aqueous ecosystemsdue to their mountainous nature and extreme cold climatic conditions. The high concentration of various chemical constitu.ents in meltwater shows the intensive chemical weathering inthe basin. The rapid physical weathering due tO grinding actionof the gl…     

Strontium Isotopic Signatures of Streams from Taylor Valley, Antarctica, Revisited: The Role of Carbonate Mineral Dissolution

We have collected and analyzed a larger set of stream waters for major ions and strontium isotopes in Taylor Valley, McMurdo Dry Valleys, Antarctica. These new data substantiate the concept that the dissolution of carbonate minerals is a significant source of strontium, even in polar desert environments where liquid water is primarily limited to stream channels. In Taylor Valley, most of the carbonate minerals present are the result of secondary processes, such as mineral precipitation and/or eolian deposition, and not through primary geologic sources, such as bedrock or till sources. In Von Guerard Stream (Lake Fryxell basin) and Andersen Creek (Lake Hoare basin), water samples were collected during the austral summer to determine short-term ⁸⁷Sr/⁸⁶Sr patterns. The observed variability in both time and space may be dependent on the relative amounts of primary and secondary carbonates present in the streambeds and hyporheic zone as well as contingent on the relative proportions of carbonate and aluminosilicate weathering.     

Hydrochemistry of reservoirs of Damodar River basin, India: weathering processes and water quality assessment

Water samples collected from the six reservoirs of Damodar River basin in pre- and post-monsoon, have been analysed, to study the major ion chemistry and the weathering and geochemical processes controlling the water composition. Ca, Na and HCO₃ dominate the chemical composition of the reservoir water. The seasonal data shows a minimum concentration of most of the ions in post-monsoon and a maximum concentration in pre-monsoon seasons, reflecting the concentrating effects due to elevated temperature and increased evaporation during the low water level period of the pre-monsoon season. Water chemistry of the reservoirs strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area. Higher concentration of SO₄ and TDS in Panchet, Durgapur and Tenughat reservoirs indicate mining and anthropogenic impact on water quality. The high contribution of (Ca+Mg) to the total cations, high concentration of dissolved silica, relatively high (Na+K)/TZ⁺ ratio (0.3) and low equivalent ratio of (Ca+Mg)/(Na+K) suggests combined influence of carbonate and silicate weathering. Kaolinite is the possible mineral that is in equilibrium with the water, implying that the chemistry of reservoir water favours kaolinite formation. The calculated values of SAR, RSC and sodium percentage indicate the ‘excellent to good quality’ of water for irrigation uses.     

祁连山中段排露沟流域水化学特征及成因

2012年11月-2013年10月,在祁连山中段排露沟流域持续采集1 a的大气降水和出口断面径流样品,对主要可溶离子、pH、电导率EC和总溶解固体TDS进行了分析。结果表明：流域径流与大气降水相比,各项对应离子浓度显著增加,径流TDS均值（255.50 mg·L^-1）远大于降水（46.77 mg·L^-1）。径流离子类型为Ca²⁺-Mg²⁺-HCO₃^-,呈弱碱性。大气降水离子类型为Ca²⁺-HCO₃^-,接近中性。所有径流样品都落在Gibbs分布图的左中端,表明径流离子组成主要受流域岩石风化作用控制。根据Piper图和主要离子的摩尔比值,综合分析得出控制径流离子过程主要是流域碳酸盐岩风化,其次伴随部分硫酸盐和硅酸盐岩石风化。并通过海盐校正分析方法,得出大气降水对出口断面径流主要离子贡献率仅为4.58%。     

The effect of organic matter on chemical weathering: study of a small tropical watershed: nsimi-zoétélé site,cameroon

The effect of organic matter during soil/water interaction is still a debated issue on the controls of chemical weathering in a tropical environment. In order to study this effect in detail, we focused on the weathering processes occurring in a small tropical watershed (Nsimi-Zoetélé, South Cameroon). This site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry.The lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones: unsaturated slope soils on the hills and/or elevated areas; and water-saturated soils in the swamp zone which represent 20% of the basin surface. The study present chemical analysis performed on water samples collected monthly from different localities between 1994–1997 and on soil samples taken during a well drilling in December 1997. The results suggest the existence of chemical and spatial heterogeneities of waters in the basin: colored waters flooding the swamp zone have much higher concentrations of both organic matter (i.e., DOC) and inorganic ions (e.g., Ca, Mg, Al, Fe, Th, Zr) than those from springs and groundwater from the hills. Nevertheless, these organic-rich waters present cation concentrations (Na, Ca, Mg, K) which are among the lowest compared to that of most world rivers. The main minerals in the soils are secondary kaolinite, iron oxi-hydroxides, quartz, and accessory minerals (e.g., zircon, rutile). We mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through SEM observations the textural characterization of weathered minerals such as kaolinite, zircon, rutile, and the secondary recrystallization of kaolinite microcrystals within the soil profile. Water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin. Thus, in order to explain the increase of element concentration in the organic-rich waters, we suggest that organic acids enhance dissolution of minerals such as kaolinite, goethite, and zircon and also favors the transport of insoluble elements such as Al, Fe, Ti, Zr, and REE by chemical complexation. SiO₂(aq) concentrations in these waters are above saturation with respect to quartz. Dissolution of phytholithes (amorphous silica) may be responsible for this relatively high SiO₂(aq.) concentration. Al/Mg ratios obtained for the soil and the Mengong river waters show that a significant amount of Al does not leave the system due to kaolinite recrystallisation in the swamp zone soils. Geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone. Quantitatively we propose that the increasing amount in total dissolved solid (TDS) due to organic matter and vegetation effect is about 35%. In summary, this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements. Thus, the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils.     

Chemical weathering and related controls on surface water chemistry in the Absaroka Mountains,Wyoming

Chemical relationships among surface waters, soils and rocks were investigated in the drainage basin of the North Fork of the Shoshone River in northwestern Wyoming. The area is underlain entirely by andesitic volcanic rocks. Smectite is the only clay mineral forming in soils over much of the area, although minor kaolinite occurs in a few areas of higher-than-average rainfall.Mass-balance calculations relating stream water chemistry to rock alteration indicate that controls on the chemistry of surface waters take place not in the soil zone but in the altered rock zone. The dominant weathering process which controls the water chemistry is slight alteration of large volumes of rock, rather than development of chemical equilibria involving secondary phases in the soil zone. The altered rock is enriched in feldspars and depleted in ferromagnesian minerals compared to fresh rock. The high rate of physical erosion of the area is enough to remove the residue, reexpose the bedrock, and continue the weathering process.     

Dissolved constituents and Sr isotopes in river waters from a mountainous island – The Danshuei drainage system in northern Taiwan

Taiwan is a typical active orogenic belt situated at the collision boundary between the Eurasian Continental Plate and the Philippine Sea Plate. Dissolved major and trace constituents, as well as Sr and Sr isotopes in river waters collected from the Danshuei River basin in northern Taiwan have been studied to evaluate chemical weathering processes. The results of principal component analysis show that the ion sources in these river waters can be categorized into 3 major components: chemical weathering, seasalt contribution and local anthropogenic input. The chemical weathering is the most dominant factor that contributes about 85% of total variances. Significantly increased Na/Cl and Ca/Cl, as well ⁸⁷Sr/⁸⁶Sr, were observed in most upper stream samples. The Na/Cl and Ca/Cl ratios in the Dahan Stream, however, are much higher than the Shindien Stream. Even though average rainfall is stronger in the Shindien drainage basin, chemical evidence from river waters supports less intense weathering in the region. Selective dissolution of secondary calcites explains the observed high Ca/Cl, Sr/Cl and Ca/Na in the Dahan Stream. These results highlight the potential importance of tectonic factors, such as uplift and physical erosion in studying chemical weathering in an active orogenic belt.     

Major ion chemistry of Renuka Lake and weathering processes, Sirmaur District, Himachal Pradesh, India

Renuka Lake in the Lesser Himalaya, Himachal Pradesh is in a valley surrounded by mountains comprised of highly crumpled, shattered, crushed, folded and dislocated rocks consisting of carbonaceous shales-slates often pyrite-ferrous, limestone, quartzites, boulder beds, etc. A detailed and systematic study of the major ion chemistry of the lake, clay mineral composition of the bed and core sediments and the Pb²¹⁰ isotope estimation in the latter was conducted. The chemistry is dominated by carbonate weathering and (Ca + Mg) and (HCO₃ + SO₄) accounts for about 90% of the cations and anions. The SO₄ content is almost the same as the HCO₃. The low contribution of (Na + K) to the total cations and the (Ca + Mg) and HCO₃ data tends to indicate that silicate weathering has not been the potential source of major ions to the lake waters. This difference may be related to the increasing susceptibility to weathering of carbonate over silicate rocks exposed in the catchment and also seepage of water at the bottom. The high sulphate content in waters is derived from dissolution of pyrite-ferrous reduced black shales, which constitute a significant lithology in the catchment. The chemical index of alteration (CIA) value in core sediments is on an average 76, which is comparable with average shale (70-75) and the rate of sedimentation 3.3 mm/year based on measurement of Pb²¹⁰, indicating a fairly high weathering rate in the catchment. Illite is the dominant clay mineral (52-90%) in the bed and core sediments, chlorite constitutes 7-48% and the kaolinite-chlorite mixed silicate layer is l-2%. This is consistent with the shale-slate, sandstone lithology in the valley.     

Study of hydrogeochemical processes of the groundwater in Ghatprabha river sub-basin, Bagalkot District, Karnataka, India

The alluvial aquifer of the Ghatprabha River comprises shallow tertiary sediment deposits underlain by peninsular gneissic complex of Archean age, located in the central–eastern part of the Karnataka in southern India. In order to establish the baseline hydrochemical conditions and processes determining the groundwater quality, groundwater samples were collected as part of an integrated investigation that coupled multivariate statistical analysis with hydrochemical methods to identify and interpret the groundwater chemistry of the aquifer system. Three main hydrochemical types (Ca–Mg–Cl, Ca–Mg–HCO₃, and Na–SO₄) were identified. Gibbs plots indicate that the evolution of water chemistry is influenced by water–rock interaction followed by evapotranspiration process. The results of factor analysis indicated the total variance explained by the extracted factor 79.9% and 87.1% for both pre- and post-monsoon, respectively. And other processes such as silicate weathering, ion exchange, and local anthropogenic activities affect the groundwater chemistry.     

Geochemical and Sr-isotopic characteristics of stream and spring waters from small-forested catchments at Seto,central Japan

Hydrogeochemical processes controlling surface water chemistry were examined in five small (<1.5 km ²) forested catchments that have contrasting bedrock lithologies of granite, and conglomerate, and are distributed in the southeast of Seto district, central Japan. Watersheds developed on these two bedrocks differ in their ability to neutralize atmospheric acid (pH ~4.5) deposition. The study was conducted to (1) characterize the hydrogeochemical processes controlling surface water chemistry, and (2) to elucidate acidification of spring and stream waters using data from three sampling campaigns conducted from August to October 2000. Stream and spring water solutes fall into two general groups according to concentration: alkaline, relatively high pH (5.2–7.7) and high cation concentrations (HCO ₃ ^-, Cl ^-, base cations), and dilute, low pH (4.2–5.5) waters. Concentrations of trace metals (Al, Ba, Sr) showed a strong negative correlation with pH, suggesting the mobility of these metals in the dissolved load of catchments underlain by Tokai conglomerate. The strontium isotope ratio ( ⁸⁷Sr/ ⁸⁶Sr) of rock and soil, plant, precipitation, and surface water samples was used to identify different reservoirs within the ecosystem. Low Si concentrations in stream and spring waters from the conglomerate area, with a relatively high pool of SiO ₂, >90 (wt%), suggest slow chemical weathering. The dissolved solute concentrations are generally of similar magnitude in stream waters within the catchments of similar bedrock lithology. The high inverse correlation ( r ²=0.72) between pH and SO ₄ ^– concentrations and the high positive correlation ( r ² =0.90) between Ba and SO ₄ ^– concentrations in waters draining Tokai conglomerate suggest that barite (BaSO ₄) is being dissolved in an acidic environment. The three catchments were identified as being sensitive to acidic deposition because the bedrock conglomerate provided little capacity to buffer acidic inputs. The soils from the granite area have a high cation-exchange capacity (CEC an average of 868 µmol/kg), and are nearly ten times greater than the soils from the conglomerate area. Because ion exchange, besides weathering, is the main source that counteracts soil acidification, the sensitivity to further acidification may increase.     

River Discharge,Major Ion Chemistry and Sediment Transport of the Bharathapuzha River,Southwest India: Implications on Catchment Erosion

The present study deals with the discharge characteristics, major ion chemistry as well as particulate and dissolved sediment transport of the Bharathapuzha river flowing across the Western Ghats through the Palghat gap - a prominent break in the Western Ghats that acts as a climate corridor in the region. While the western part of the basin in Kerala exhibits a wetter/humid climate, the eastern part in Tamil Nadu experiences a semi-arid climate. This peculiar climatic condition together with human interventions has a decisive role on the discharge characteristics as well as catchment erosion of the river basin. The dissolved and particulate contents of the river waters were found to be directly related to the geo-environmental settings of the river catchments. An intercomparison of elemental loading in the river waters in different seasons reveals notable decrease in monsoon compared to nonmonsoon seasons, which is attributed mainly to dilution of the solute contents by monsoon precipitation. The bivariate plots of Na/(Na+Ca) vs Total Dissolved Solids (TDS) and Cl/(Cl+HCO₃) vs TDS spread generally in the rock dominance sector of Gibb’s model indicating the role of chemical weathering in contributing to the major ion chemistry of the Bharathapuzha river. The intensity of weathering varied significantly among the different sub-basins of the Bharathapuzha river basin. The higher particulate load by dissolved load ratio of the Thuthapuzha and Gayathripuzha tributaries draining the humid areas compared to the Chitturpuzha tributary draining the semi-arid zones of the basin indicates the predominance of physical weathering in the former two sub-basins than the latter.     

Identification of major sources controlling groundwater chemistry from a hard rock terrain — A case study from Mettur taluk,Salem district,Tamil Nadu,India

The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO₄) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO₃ indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO₃ values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right in plot for Ca + Mg to SO₄ + HCO₃. The plot of Na-Cl to Ca + Mg-HCO₃-SO₄ confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions from anthropogenic impact.     

Controls of phosphorus loading and transport in the Cuyahoga River of northeastern Ohio,USA

An urban stream differs from a natural stream in that it commonly contains anthropogenic nutrients from a variety of diffuse and point sources (e.g., urban runoff, industrial and municipal effluents). The Cuyahoga River as one of such stream systems receives on average 30% of water from over a dozen wastewater treatment plants (WWTPs) and exports over 300 Mg/yr of total phosphorus (TP) into Lake Erie. Municipal effluents account for at least two thirds of the TP loading and 90% of the effluent TP is in the form of soluble reactive phosphorus (SRP), i.e., the highly bioavailable form in aquatic ecosystems. Owing to its dominance of the effluent P, the Cuyahoga River may pose a disproportionately greater ecological risk to Lake Erie. Here we report results of TP and SRP as measured on water samples collected from 12 locations along the Cuyahoga River and its major tributary – Tinkers Creek under three different flow conditions in July 2007 through May 2008. Our results show that the loadings of SRP and TP increased progressively with the effluent inputs increasing from the upper basin downstream. We found the loadings of SRP and TP are not only affected by the amount of effluent P input but also regulated by stream flow regimes. Effluent P is more likely to be transformed during storm runoff events, whereas TP is more likely to be retained under low flow conditions. As a result, most of the TP loading was exported during the storm and intermediate flow conditions, whereas most of the SRP loading was delivered during the low and intermediate flow conditions. These results suggest that stream hydrology has played an important role in the loading and transport of P across the Cuyahoga River as it dictated the amount, form, and timing of P exported to Lake Erie.     

Environmental geochemistry of Damodar River basin, east coast of India

 Water and bed sediment samples collected from the Damodar River and its tributaries were analysed to study elemental chemistry and suspended load characteristics of the river basin. Na and Ca are the dominant cations and HCO₃ is the dominant anion. The water chemistry of the Damodar River basin strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area. High concentrations of SO₄ and PO₄ at some sites indicate the mining and anthropogenic impact on water quality. The high concentration of dissolved silica, relatively high (Na+K)/TZ⁺ ratio (0.2–0.4) and low equivalent ratio of (Ca+Mg)/(Na+K) indicate that dissolved ions contribute significantly to the weathering of aluminosilicate minerals of crystalline rocks. The seasonal data show a minimum ionic concentration in the monsoon season, reflecting the influence of atmospheric precipitation on total dissolved solids contents. The suspended sediments show a positive correlation with discharge and both discharge and suspended load reach their maximum value during the monsoon season. Kaolinite is the mineral that is possibly in equilibrium with the water. This implies that the chemistry of the Damodar River water favours kaolinite formation. The concentration of heavy metals in the finer size fraction (<37 μ m) is significantly higher than the bulk composition. The geoaccumulation index values calculated for Fe, Mn, Zn, Ni and Cr are well below zero, suggesting that there is no pollution from these metals in Damodar River sediments. Received: 21 January 1998 · Accepted: 4 May 1998     

Major element chemistry of the Huai River basin, China

The chemistry of major ions (Ca, Mg, Na, K, HCO₃, SO₄, Cl and Si) in the water of the Huai River basin was studied, based on samples from 52 sites from nine different water bodies in July 2008. Ions and total dissolved solids (TDS) displayed clear spatial patterns with lower concentrations in the south and higher in the north of the basin; the same conditions were also found in the East Line of South-North Water Transfer Project (SNWTP) in this region. The Huai River main channel and Hongze Lake have moderate ion concentrations relative to the whole basin. TDS concentrations versus the weight ratios of Na/(Na + Ca) and ternary ions demonstrate that the southern rivers (Shi R. and Pi R.) are mainly controlled by the weathering of carbonates, whereas the northern water systems (Guo R., Shaying R., Nansi Lake and its tributaries) are dominated by the weathering of evaporites. The Huai River main channel, Hongze Lake and the East Line of SNWTP are synergistically influenced by weathering of evaporites and carbonates, yet Hongze Lake and the East Line of SNWTP are mainly controlled by evaporation and crystallization processes. This study also confirmed that the Huai River is the geographic division between southern and northern China. Most rivers of this basin have very high ionic composition relative to the global median and other world rivers. The spatial patterns and ionic composition also suggest that intensive anthropogenic activities in northern areas of this basin are well characterized. A comparison with WHO and Chinese standards for drinking water indicates that the northern water systems of this basin are not suitable for use as drinking water sources, and pollution control should be improved and enhanced in northern areas of the basin.     

Origin and evolution of major salts in the Darling pans,Western Cape,South Africa

Sediment and water samples from 12 saline pans on the semi-arid west coast of South Africa were analysed to determine the origin of salts and geochemical evolution of water in the pans. Pans in the area can be subdivided into large, gypsiferous coastal pans with 79–150 g/kg total dissolved salt (TDS), small inland brackish to saline (2–64 g/kg TDS) pans and small inland brine (168-531 g/kg TDS) pans that have a layer of black sulphidic mud below a halite crust. The salinity of coastal pan waters varies with the seasonal influx of dilute runoff and dissolution of relict Pleistocene marine evaporite deposits. In contrast, inland pans are local topographic depressions, bordered on the north by downslope lunette dunes, where solutes are concentrated by evaporation of runoff, throughflow and groundwater seepage. The composition of runoff and seepage inflow waters is determined by modification of coastal rainfall by weathering, calcite precipitation and ion exchange reactions in the predominantly granitic catchment soils. Evaporation of pan waters leads to precipitation of calcite, Mg–calcite, dolomite, gypsum and halite in a distinct stratigraphic succession in pan sediments. Bicarbonate limits carbonate precipitation, Ca limits gypsum precipitation and Na limits halite precipitation. Dolomitisation of calcite is enhanced by the high Mg/Ca ratio of brine pan waters. Brine pan waters evolve seasonally from Na–Cl dominated brines in the wet winter months to Mg–Cl dominated brines in the dry summer months, when 5–20 cm thick halite crusts cover pan surfaces. Pan formation was probably initiated during a drier climate period in the early Holocene. More recent replacement of natural vegetation by cultivated land may have accelerated salt accumulation in the pans.     

Climatic and lithologic controls on the temporal and spatial variability of CO2 consumption via chemical weathering: An example from the Australian Victorian Alps

A detailed geochemical study on river waters of the Australian Victorian Alps was carried out to determine: (i) the relative significance of silicate, carbonate, evaporite and sulfide weathering in controlling the major ion composition and; (ii) the factors regulating seasonal and spatial variations of CO₂ consumption via silicate weathering in the catchments. Major ion chemistry implies that solutes are largely derived from evaporation of precipitation and chemical weathering of carbonate and silicate lithologies. The input of solutes from rock weathering was determined by calculating the contribution of halite dissolution and atmospheric inputs using local rain and snow samples. Despite the lack of carbonate outcrops in the study area and waters being undersaturated with respect to calcite, the dissolution of vein calcite accounts for up to 67% of the total dissolved cations, generating up to 90% of dissolved Ca and 97% of Mg. Dissolved sulfate has δ³⁴S values of 16 to 20‰_CDT, indicating that it is derived predominantly from atmospheric deposition and minor gypsum weathering and not from bacterial reduction of FeS₂. This militates against sulphuric acid weathering in Victorian rivers. Ratios of Si vs. the atmospheric corrected Na and K concentrations range from ~ 1.1 to ~ 4.3, suggesting incongruent weathering from plagioclase to smectite, kaolinite and gibbsite.Estimated long-term average CO₂ fluxes from silicate weathering range from ~ 0.012 × 10⁶ to 0.039 × 10⁶ mol/km²/yr with the highest values in rivers draining the basement outcrops rather than sedimentary rocks. This is about one order of magnitude below the global average which is due to low relief, and the arid climate in that region. Time series measurements show that exposure to lithology, high physical erosion and long water–rock contact times dominate CO₂ consumption fluxes via silicate weathering, while variations in water temperature are not overriding parameters controlling chemical weathering. Because the atmospheric corrected concentrations of Na, K and Mg act non-conservative in Victorian rivers the parameterizations of weathering processes, and net CO₂ consumption rates in particular, based on major ion abundances, should be treated with skepticism.     

The Drenchwater deposit,Alaska: An example of a natural low pH environment resulting from weathering of an undisturbed shale-hosted Zn–Pb–Ag deposit

The Drenchwater shale-hosted Zn–Pb–Ag deposit and the immediate vicinity, on the northern flank of the Brooks Range in north-central Alaska, is an ideal example of a naturally low pH system. The two drainages, Drenchwater and False Wager Creeks, which bound the deposit, differ in their acidity and metal contents. Moderately acidic waters with elevated concentrations of metals (pH ? 4.3, Zn ? 1400 μg/L) in the Drenchwater Creek drainage basin are attributed to weathering of an exposed base-metal-rich massive sulfide occurrence. Stream sediment and water chemistry data collected from False Wager Creek suggest that an unexposed base-metal sulfide occurrence may account for the lower pH (2.7–3.1) and very metal-rich waters (up to 2600 μg/L Zn, ? 260 μg/L Cu and ?89 μg/L Tl) collected at least 2 km upstream of known mineralized exposures. These more acidic conditions produce jarosite, schwertmannite and Fe-hydroxides commonly associated with acid-mine drainage. The high metal concentrations in some water samples from both streams naturally exceed Alaska state regulatory limits for freshwater aquatic life, affirming the importance of establishing base-line conditions in the event of human land development. The studies at the Drenchwater deposit demonstrate that poor water quality can be generated through entirely natural weathering of base-metal occurrences, and, possibly unmineralized black shale.     

Major ion chemistry,weathering processes and water quality assessment in upper catchment of Damodar River basin,India

The chemical characteristics of surface, groundwater and mine water of the upper catchment of the Damodar River basin were studied to evaluate the major ion chemistry, geochemical processes controlling water composition and suitability of water for domestic, industrial and irrigation uses. Water samples from ponds, lakes, rivers, reservoirs and groundwater were collected and analysed for pH, EC, TDS, F, Cl, HCO₃, SO₄, NO_3, Ca, Mg, Na and K. In general, Ca, Na, Mg, HCO₃ and Cl dominate, except in samples from mining areas which have higher concentration of SO₄. Water chemistry of the area reflects continental weathering, aided by mining and other anthropogenic impacts. Limiting groundwater use for domestic purposes are contents of TDS, F, Cl, SO₄, NO₃ and TH that exceed the desirable limits in water collected from mining and urban areas. The calculated values of SAR, RSC and %Na indicate good to permissible use of water for irrigation. High salinity, %Na, Mg-hazard and RSC values at some sites limit use for agricultural purposes.