Chemical weathering of carbonates and silicates in the Han River basin,South Korea

A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO₂. The Han River drains approximately 26,000 km² and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Han River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved solids (TDS), Sr, and major ion concentrations but a higher Si concentration and ⁸⁷Sr/⁸⁶Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55 ± 11%), with a relatively small portion from carbonates (30 ± 14%), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82 ± 3%), with only 11 ± 4% from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the NHR and SHR basins, but the rate of CO₂ consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation.     

Chemical weathering in the Hong (Red) River basin: Rates of silicate weathering and their controlling factors

The Hong (Red) River drains the prominent Red River Fault Zone that has experienced various tectonic activities—intrusion of magma, exhumation of basement rocks, and influx of thermal waters—associated with the Cenozoic collision of India and Eurasia. We report dissolved major element and Sr isotope compositions of 43 samples from its three tributary systems (Da, Thao/Hong main channel, and Lo) encompassing summer and winter seasons. Carbonic acid ultimately derived from the atmosphere is the main weathering agent, and sulfuric acid from pyrite oxidation plays a minor role. Seasonality is manifested in higher calcite saturation index and Mg/TZ⁺ and lower Ca/Mg in summer, suggesting calcite precipitation, and in higher Si/(Na^∗ + K) ratios in summer suggesting more intensive silicate weathering. We quantified the input from rain, evaporite, carbonate, and silicate reservoirs using forward and inverse models and examined the robustness of the results. Carbonate dissolution accounts for a significant fraction of total dissolved cations (55-97%), and weathering of silicates makes a minor contribution (1-40%). Our best estimate of the spatially averaged silicate weathering rate in the Hong basin is 170 × 10³ mol/km²/yr in summer and 51 × 10³ mol/km²/yr in winter. We tested for correlations between the rate of CO₂ consumption by silicate weathering and various climatic (air temperature, precipitation, runoff, and potential evapotranspiration) and geologic (relief, elevation, slope, and lithology) parameters calculated using GIS. Clear correlations do not emerge (except for ?CO₂ and runoff in winter) which we attribute to the complex geologic setting of the area, the seasonal regime change from physical-dominant in summer to chemical-dominant in winter, and the incoherent timescales involved for the different parameters tested.     

重新认识鄂尔多斯南部早奥陶世马家沟期碳酸盐台地沉积模式

地层、沉积岩组合及古地貌特征显示,鄂尔多斯盆地南部地区早奥陶世马家沟期为3个沉积单元区,即:北东部区为白云岩-蒸发盐组合;南部区为白云岩-少量蒸发盐组合;西部区以石灰岩为主。相应地北东部区以发育台内盆地-盆缘坪为主;南部区发育洼地-台坪-台地边缘-海槽;西部区则发育台地边缘-海槽。野外剖面与钻井岩心观测以及区域资料研究表明,鄂尔多斯盆地南部边缘大致在洛南瓦窑沟—西安—宝鸡一带。马家沟期研究区沉积模式总体上为:横向上"西槽、南洼、东坪、北盆",纵向上"咸-淡交替";灰岩-白云岩-蒸发岩横向上呈带状展布,纵向上则为不等厚交替沉积。     

An experimental study of a minette from the Milk River area, southern Alberta, Canada

Buhlmann et al. (Can J Earth Sci 37: 1629–1650, 2000) studied the minettes and xenoliths from the Milk River area of southern Alberta, Canada. Based on previous work, they hypothesized that the minettes were derived from a source containing phlogopite?+?clinopyroxene?±?olivine, at pressures ≥1.7?GPa. To test this hypothesis, liquidus experiments were performed on a primitive minette between 1.33 and 2.21?GPa and between 1,300 and 1,400?°C to constrain the mineralogy of its source region. We found a multiple saturation point along the liquidus at 1.77 GPa and 1,350?°C, where the liquid coexists with orthopyroxene and olivine. Neither phlogopite nor clinopyroxene were found to be liquidus phases, which is inconsistent with Buhlmann et al.’s hypothesis. We suggest that our minette is not primary, but had re-equilibrated with harzburgitic mantle subsequent to formation. In such a scenario, partial melting of a veined source containing mica and clinopyroxene occurred at or near the base of the Wyoming craton (~200?km). Minimal heating or the introduction of hydrous fluids into the source would be required to induce partial melting. Rapid ascent rates, coupled with slow cooling rates, of the “primary minette magma” would preserve the high temperature observed in our experiments. At ~58?km, our “primary minette magma” likely stalled and re-equilibrated with the harzburgite surroundings.     

A carbonate submarine fan in a fault-controlled basin of the Upper Jurassic, Betic Cordillera, southern Spain

ABSTRACT The middle member of the Loma del Toril formation (Kimmeridgian-Lower Tithonian, Intermediate units, Betic Cordillera) consists of up to 250 m of resedimented carbonate material. Three units have been distinguished. The lower, Unit A, is composed of conglomerates that are interpreted as deposited in a major valley on the lower slope of a basin margin. Unit B, calcarenites with some conglomerate intercalation, is interpreted as distributary channel deposits and Unit C, calcarenites, as the result of poorly developed depositional lobes of a submarine fan. The three units form a recessional sequence. They cannot be related to a transgression because the Kimmeridgian-Lower Tithonian in the Prebetic zone, where epicontinental sediments exist, is clearly regressive. The upper member of the Loma del Toril formation, made up of pelagic limestones with sporadic calcarenites or even thin conglomerate intercalations, is best interpreted as a basin plain facies. Lateral facies relationships suggest that down-faulting of the basin floor controlled the development of the fan. The scarce occurrence of turbidite beds in the basin plain facies, the prevailing channelized facies and the obvious lack of overbank deposits, suggest a transport system of low efficiency, with fan deposition at the base of slope. The underlying Jurassic strata cropping out along fault scarps, coeval carbonate shelf material, and upper slope deposits were the main sources of turbiditic resediments. With respect to basin morphology sedimentary processes and fan geometry, this Jurassic turbidite basin can be compared with the modern California continental borderland. Ancient analogues have been described by Reinhart (1977) and Price (1977).     

Chemical weathering in a tropical watershed,Luquillo Mountains,Puerto Rico III: quartz dissolution rates

The paucity of weathering rates for quartz in the natural environment stems both from the slow rate at which quartz dissolves and the difficulty in differentiating solute Si contributed by quartz from that derived from other silicate minerals. This study, a first effort in quantifying natural rates of quartz dissolution, takes advantage of extremely rapid tropical weathering, simple regolith mineralogy, and detailed information on hydrologic and chemical transport. Quartz abundances and grain sizes are relatively constant with depth in a thick saprolite. Limited quartz dissolution is indicated by solution rounding of primary angularity and by the formation of etch pits. A low correlation of surface area (0.14 and 0.42 m² g⁻¹) with grain size indicates that internal microfractures and pitting are the principal contributors to total surface area.Pore water silica concentration increases linearly with depth. On a molar basis, between one and three quarters of pore water silica is derived from quartz with the remainder contributed from biotite weathering. Average solute Si remains thermodynamically undersaturated with respect to recently revised estimates of quartz solubility (<180 μM) but exceeds estimated critical saturation concentrations controlling the initiation of etch pit formation (>17–81 μM). Etch pitting is more abundant on grains in the upper saprolite and is associated with pore waters lower in dissolved silica. Rate constants describing quartz dissolution increase with decreasing depth (from 10^−14.5–10^−15.1 mol m⁻² s⁻¹), which correlate with both greater thermodynamic undersaturation and increasing etch pit densities. Unlike for many aluminosilicates, the calculated natural weathering rates of quartz fall slightly below the rate constants previously reported for experimental studies (10^−12.4–10^−14.2 mol m⁻² s⁻¹). This agreement reflects the structural simplicity of quartz, dilute solutes, and near-hydrologic saturation.     

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.     

Oxygen and carbon isotope composition of structural carbonate in weathering apatites from laterites, southern Brazil and western Senegal

The oxygen (δ¹⁸O_c) and carbon (δ¹³C_c) isotope compositions of the structural carbonate group (CO₃) in apatites from lateritic profiles were investigated. The weathering profiles, located in southern Brazil and in western Senegal, are developed on three different types of apatite-rich parent rock: carbonatite, metamorphosed marine phosphorite and sedimentary marine phosphorite. The parent rock apatites are of magmatic, hydrothermal, metamorphic and sedimentary origins. The in situ formation of apatite of weathering origin in the profiles is well documented petrographically and geochemically.The overall range of measured δ¹⁸O_c and δ¹³C_c values of apatites of weathering origin (22 to 27 SMOW for δ¹⁸O_c and −15 to −10 PDB for δ¹³C_c) is much smaller than the range of measured and/or published isotope compositions of parent rock apatites (4–35 for δ¹⁸O_c and −11 to +1 for δ¹³C_c). In any profile, the apatites of weathering origin can exhibit lower, similar or higher δ¹⁸O_c values than parent rock apatites. In contrast, their δ¹³C_c values are systematically and significantly lower than those of the parent rock apatites. Apatites formed as a result of weathering in laterites can therefore be readily distinguished from apatites of other origin on the basis of their isotope composition.Assuming that apatite CO₃ fractionates O in a way similar to calcite CO₃, the structural carbonate group of the apatites of weathering origin appears to form in approximate isotopic equilibrium with the weathering solutions. The very low δ¹³C_c values exhibited by these apatites indicate that the dominant sources of dissolved CO₂ in the soil water are organic. The isotope composition of structural carbonate in apatite of weathering origin in lateritic profiles may provide useful information for paleoenvironmental studies.     

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates

The spatial and temporal changes in hydrology and pore water elemental and ⁸⁷Sr/⁸⁶Sr compositions are used to determine contemporary weathering rates in a 65- to 226-kyr-old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Soil moisture, tension and saturation exhibit large seasonal variations in shallow soils in response to a Mediterranean climate. These climate effects are dampened in underlying argillic horizons that progressively developed in older soils, and reached steady-state conditions in unsaturated horizons extending to depths in excess of 15 m. Hydraulic fluxes (q_h), based on Cl mass balances, vary from 0.06 to 0.22 m yr⁻¹, resulting in fluid residence times in the terraces of 10-24 yrs.As expected for a coastal environment, the order of cation abundances in soil pore waters is comparable to sea water, i.e., Na > Mg > Ca > K > Sr, while the anion sequence Cl > NO₃ > HCO₃ > SO₄ reflects modifying effects of nutrient cycling in the grassland vegetation. Net Cl-corrected solute Na, K and Si increase with depth, denoting inputs from feldspar weathering. Solute ⁸⁷Sr/⁸⁶Sr ratios exhibit progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. While net Sr and Ca concentrations are anomalously high in shallow soils due to biological cycling, they decline with depth to low and/or negative net concentrations. Ca/Mg, Sr/Mg and ⁸⁷Sr/⁸⁶Sr solute and exchange ratios are similar in all the terraces, denoting active exchange equilibration with selectivities close to unity for both detrital smectite and secondary kaolinite. Large differences in the magnitudes of the pore waters and exchange reservoirs result in short-term buffering of the solute Ca, Sr, and Mg. Such buffering over geologic time scales can not be sustained due to declining inputs from residual plagioclase and smectite, implying periodic resetting of the exchange reservoir such as by past vegetational changes and/or climate.Pore waters approach thermodynamic saturation with respect to albite at depth in the younger terraces, indicating that weathering rates ultimately become transport-limited and dependent on hydrologic flux. Contemporary rates R_solute are estimated from linear Na and Si pore weathering gradients b_solute such that

     

Northern latitude chemical weathering rates: clues from the Mackenzie River Basin, Canada

The main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate. More than 110 river water samples from the Mackenzie River system (northern Canada) have been sampled and analyzed for major and trace elements and Sr isotopic ratios in the dissolved phase. The three main morphological units are reflected in water chemistry. Rivers from the Canadian Shield are very dilute, dominated by silicate weathering (Millot et al., 2002), whereas the rivers of the Rocky and Mackenzie Mountains as well as the rivers of the sedimentary Interior Platform are dominated by carbonate weathering and are SO₄ rich. Compared to the rivers of the Mackenzie and Rocky Mountains, the rivers of the interior plains are organic, silica, and Na rich and constitute the dominant input term to the Mackenzie River mainstream. Rivers of the Canadian Shield area do not significantly contribute to the Mackenzie River system. Using elemental ratios and Sr isotopic ratios, a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering. Carbonate weathering rates are mostly controlled by runoff, which is higher in the mountainous part of the Mackenzie basin. These rates are comparable to the carbonate weathering rates of warmer areas of the world. It is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering, but its extent remains difficult to assess. Conversely to what was stated by Edmond and Huh (1997), overall silicate weathering rates in the Mackenzie basin are low, ranging from 0.13 to 4.3 tons/km²/yr (Na + K + Ca + Mg), and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates. In contrast to what has been observed in other large river systems such as the Amazon and Ganges Rivers, silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters. This contradicts the “Raymo hypothesis” (Raymo and Ruddiman, 1992). Isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains (e.g., by glaciers) and deposited in the plains. Rather, the relatively high chemical denudation rates in the plains are attributed to lithology (uncompacted shales), high mechanical denudation, and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation. The three- to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by Moulton et al. (2000) between unvegetated and vegetated watershed. This study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors, such as organic matter, associated with northern watersheds are able to counteract the effect of temperature. This acceleration by a factor of 4 in the plains is equivalent to a 6°C increase in temperature.     

西南喀斯特流域碳酸盐岩的硫酸侵蚀与碳循环

流域化学侵蚀及其速率与流域生态和环境之间的关系是当前地表地球化学研究的重要前沿领域,其中碳酸盐岩的硫酸风化机制及其与区域碳循环的关系则是科学家们最为关注的科学问题.因此,近年通过研究西南喀斯特流域地表水地球化学对这一科学问题进行了研究,发现西南喀斯特地区河水一般含有较多的SO2-4,从化学计量学、SO2-4的δ34S和溶解无机碳(DIC)的δ13S分析发现,硫循环中形成的硫酸广泛参与了流域碳酸盐矿物的溶解和流域侵蚀:西南喀斯特流域碳酸盐岩的侵蚀速率为97 t/(km2?a),消耗CO2量为25 t/(km2?a).对乌江流域河水硫酸盐离子的硫同位素研究结果认为:参与流域侵蚀的硫酸主要来自煤系地层硫化物和矿床硫化物的氧化及大气酸沉降,分别对河水SO2-4的贡献为50%、27% 20.5%(其余2.5%的SO2-4为硫酸盐蒸发岩的溶解);硫酸风化碳酸盐岩向大气净释放CO2的总通量为8.2 t/(km2?a),依此计算西南喀斯特区域向大气释放CO2的通量为4.4×1012g/a,相当于每年西南碳酸盐岩风化消耗CO2总通量的33%.将乌江流域的研究结果对我国大陆碳酸盐岩分布区域进行相应计算发现,硫酸风化碳酸盐矿物向大气释放的CO2总通量为28×1012g/a,相当于全球硅酸盐风化消耗CO2量的26%.硫酸参与流域侵蚀改变了区域碳循环,人为过程可以通过释放酸沉降、矿业活动和土地利用等形式加速流域侵蚀和影响流域元素的生物地球化学循环.     

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.     

Chemical weathering processes in the Yalong River draining the eastern Tibetan Plateau,China

To better understand chemical weathering and controlling processes in the Yalong River of the eastern Tibetan Plateau, this study presents major ion concentrations and stable isotopes of the dissolved loads. The isotopic compositions (δ¹³C-DIC, δ³⁴S and δ¹⁸O-SO₄) of the dissolved loads are very useful to quantify solute sources and define the carbon budget related with chemical weathering in riverine systems. The isotopic composition of sulphate demonstrates that most of the sulphate is derived from sulphide oxidation, particularly in the upper reach of the Yalong River. The correlations between δ¹³C-DIC, water chemistry and isotopes of sulphate, suggest that the carbon dynamics are mainly affected by carbonate weathering by sulphuric acid and equilibration processes. Approximately 13% of the dissolved inorganic carbon in the Yalong River originates from carbonate weathering by strong acid. The CO₂ consumption rates are estimated to be 2.8 × 10⁵ mol/km²/yr and 0.9 × 10⁵ mol/km²/yr via carbonate and silicate weathering in the Yalong River, respectively. In this study, the influence of sulphide oxidation and metamorphic CO₂ on the carbon budget is estimated for the Yalong River draining the eastern Tibetan Plateau.     

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California I: Interpreting rates and controls based on soil concentration-depth profiles

The spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal California are interpreted in terms of chemical weathering rates and processes. In regoliths up to 15 m deep and 226 kyrs old, quartz-normalized mass transfer coefficients indicate non-stoichiometric preferential release of Sr > Ca > Na from plagioclase along with lesser amounts of K, Rb and Ba derived from K-feldspar. Smectite weathering results in the loss of Mg and concurrent incorporation of Al and Fe into secondary kaolinite and Fe-oxides in shallow argillic horizons. Elemental losses from weathering of the Santa Cruz terraces fall within the range of those for other marine terraces along the Pacific Coast of North America.Residual amounts of plagioclase and K-feldspar decrease with terrace depth and increasing age. The gradient of the weathering profile b_s is defined by the ratio of the weathering rate, R to the velocity at which the profile penetrates into the protolith. A spreadsheet calculator further refines profile geometries, demonstrating that the non-linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface-to-volume ratios and at high residual feldspar concentrations, at greater depth, by the approach to thermodynamic saturation. These parameters are of secondary importance to the fluid flux q_h, which in thermodynamically saturated pore water, controls the weathering velocity and mineral losses from the profiles. Long-term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute Cl balances (q_h = 0.025-0.17 m yr⁻¹).During saturation-controlled and solute-limited weathering, the greater loss of plagioclase relative to K-feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics. The steady-state weathering rate under such conditions is defined as

     

Hydrogeochemistry in the Vouga River basin (central Portugal): Pollution and chemical weathering

To quantify and explain the contributions by pollution and chemical weathering to their composition, we studied the chemistries of springs and surface waters in the mountainous part of the Vouga River basin. Water samples were collected during a number of consecutive summer campaigns. Recharge rates were derived from monitored discharge rates within the basin. Very large contributions by meteoric, agricultural and domestic sources to the water chemistries were found, identified by the chloride, sulfate and nitrate concentrations: on average only 1/4 to 1/3 of the solutes could be attributed to chemical weathering. Two petrologic units characterize the river basin: granites and metasediments. The waters collected within metasediment units are distinct from those in granite terrain by a higher magnesium concentration. On that basis, it could be estimated that the Rio Vouga, when leaving the mountainous part of the basin, has for some 2/5 a signature determined by chemical weathering in the metasediments. The dominant primary minerals subject to chemical weathering are plagioclase (Pl) and biotite (in granite) or Pl and chlorite (in metasediment). Kaolinite, gibbsite and vermiculite are the major weathering products where annual precipitation (P) > 1000 mm y⁻¹, and kaolinite, vermiculite and smectite where P was lower. Using an algorithm based on the ratio of dissolved silica to bicarbonate, the contributions of chemical weathering of primary minerals could be unraveled. The results show that in granite the export rate (as mol ha⁻¹ y⁻¹ wt%mineral⁻¹) of oligoclase (Pl with An_10–30) was 5.0 ± 2.6 and of biotite 3.2 ± 2.6, while in metasediment these rates for albite (Pl with An_0–10) are 16.5 ± 8.9 and for chlorite are 0.5 ± 0.5. The observed decrease of dissolved silica in surface waters relative to springs was ascribed to (summer) uptake by aquatic biota.     

Flow dynamics and erosion rate of a representative karst basin (Upper Aniene River,Central Italy)

Experimental data refer to a preliminary estimate of suspended solid and solute load of a perennial river. The basin is composed almost entirely of bare mesozoic, highly fractured, karstified carbonate rocks of the central Apennine range. The suspended solid load related to stormflow events in 1991 corresponds to about 14,970 t yr^–1. For the same period the solute load is 60,060 t yr^–1 for a mean base flow discharge of 9.4 m³ s^–1. Based on the mean concentration of Ca + Mg in water, the value of dissolution of carbonate rocks of 37.1 m³ km^–2 (equivalent approximately to 0.04 mm yr^–1) was calculated. Physical and chemical variations that occur during storm events indicate the complex dynamic processes in the karst aquifer and the role undertaken by the epikarst as perched water reservoir and by the major conduits that develop through the vadose and saturated zones of the karst system.