Implications For Chemical Weathering Research Articles

Geochemical Compositions of Size‐Fractioned Sediment Samples From the Yangtze and Yellow Rivers: Implications for Chemical Weathering, Fractionation Behavior of Provenance Tracers, and Sources of Radial Sand Ridges

AbstractRiver sediments are valuable archives of the environmental conditions within their catchments. The Yangtze and Yellow Rivers are the most active fluvial systems for sediment transport in East Asia, and they are regarded as potential sediment sources for the radial sand ridges (RSRs) in the southwestern Yellow Sea. We used the geochemical compositions of size‐fractioned sediment samples from the Yangtze and Yellow Rivers to characterize chemical weathering, the fractionation behavior of provenance tracers, and the sources of RSRs. For the Yangtze and Yellow River sediments, the (Rb + Sr)/Ti ratio is a reliable chemical weathering proxy that is grain‐size independent. The chemical indices of Chemical Index of Alteration, Rb/Sr, (Rb + Sr)/Ti, and acid‐leached elements from common grain‐size fractions together reveal that the Yangtze River basin undergoes stronger chemical weathering than the Yellow River basin, indicating that the chemical weathering is dominated by latitudinally‐dependent climatic variations. The dissolution and precipitation of amorphous Fe‐Mn oxides can result in the significant fractionation of La/Y, La/Sc, Nb/Co, La/Co, (La/Sm)N, (La/Yb)N, Ti/Sc, Zr/Y, Zr/Co, and Cr/Ta, whereas Zr/Ti and Zr/Nb are largely unaffected. Based on the robust provenance tracers of Zr/La, La/Hf, (La/Yb)N, Zr/Nb, Ti/Zr, and Hf/Ta, we conclude that the RSRs in the southwestern Yellow Sea are mainly derived from Yangtze River sediments, and that part of the clay fraction is from the Yellow River. In future research, we suggest that established geochemical indicators of chemical weathering and sediment provenance can be applied to the deposits of the Yangtze and Yellow River Deltas, the Yellow Sea, and the East China Sea.

Depositional processes of Marinoan-age diamictites and cap carbonates in northwestern Tarim, China: Implications for chemical weathering following the Marinoan deglaciation

The Marinoan diamictites and the overlying cap carbonates at continental margins bear key information on the paleo-environment evolution during the collapse of Snowball Earth, such as the timespan of intense chemical weathering. Such a sedimentary suite has been recently discovered in the northwestern Tarim Craton of China, but its depositional processes remain controversial. Here, we present stratigraphic and isotope geochemical studies on the diamictites of the Yuermeinak Formation and the overlying cap carbonates of the Sugetbrak Formation in the Aksu region of the northwestern Tarim Craton. Multiple unconformities in the region suggest major tectonic uplifting during the Cryogenian, probably resulting in a mountainous topography and varying dip directions of the overlying cap carbonates. The paleo-elevation of these mountains might have been higher and above sea level. We propose new depositional processes that involved four stages from glacial continental facies to neritic facies and/or alluvial fan systems. The first stage formed the massive diamictites and stratified siltstones with dropstones, recording cycles between glacier retreat and advance. The second stage involved the late transgression at the end of the deglaciation and the formation of calcareous massive diamictites with negative δ13C. The third stage included the onset of cap carbonate deposition and the alternating precipitation of calcareous mudstones and carbonates, reflecting frequent sea-level changes. The fourth stage was related to a widespread marine regression that developed a terrestrial environment and the sedimentation of the sandstones of the Sugetbrak Formation. Furthermore, we suggest that intense chemical weathering on exposed continents after the Marinoan deglaciation likely lasted for only hundreds of thousands of years, releasing ample alkalis into the ocean and facilitating the precipitation of the cap carbonates.

Terrigenous provenance of late Oligocene–Miocene sediments in the central basin of the South China Sea and its implications for chemical weathering and climate change

The oceanic red beds (ORB) are unique pelagic sediments in the global ocean, providing excellent archives for understanding the chemical weathering and relevant climate change in their source areas. Clay minerals, Nd and Sr isotopes, and major elements of terrigenous components were investigated on the ORB (27.0–10.6 Ma) recovered at International Ocean Discovery Program (IODP) Expedition 367 Site U1499 in the central basin of the South China Sea, to determine the terrigenous provenance and constrain the main factors controlling terrestrial chemical weathering during the late Oligocene–Miocene. The clay mineral assemblage of the ORB is characterized by dominant smectite (52–95%), moderate illite (4–23%), and minor kaolinite (0–19%) and chlorite (0–7%). Nd isotope value (εNd) and 87Sr/86Sr ratio vary from −12.1 to −6.4 and from 0.7122 to 0.7275, respectively. These results display a three-stage temporal variation pattern with the most significant shift in the sedimentary sources at ∼23 Ma. Stage I (27.0–23.0 Ma) sediments were mainly derived from Palawan, whereas Stages II (23.0–14.0 Ma) and III (14.0–10.0 Ma) sediments were derived from South China and Luzon. Simple NdSr isotope mixing model result shows the greater terrigenous contribution of South China from Stage II (49–60%) to Stage III (64–80%), consistent with an increase in illite, chlorite, and kaolinite contents. Chemical index of alteration, K2O/Na2O ratio, Al2O3/TiO2 ratio, smectite/(illite + chlorite) ratio, and illite crystallinity indicate moderate chemical weathering intensity through the late Oligocene to the Miocene. The weathering was influenced by the lithology of parent rocks in Stage I and primarily by the climatic evolution during Stages II and III. The synchronous reduction of various indicators from the ORB reveals the weakening of terrestrial weathering around the South China Sea at ∼14 Ma, induced by the global cooling at the Middle Miocene Climate Transition.

Tectonic controls on the isotopic juvenility of mid-Cretaceous continental arcs: Global compilations and implications for chemical weathering

Continental arcs influence the global carbon cycle via degassing and chemical weathering. Several studies also suggested that the isotopic composition of continental arcs plays an important role in controlling the strontium (Sr) isotopic composition of seawater through chemical weathering. Yet, geological or tectonic drivers of isotopic variations of continental arcs on a global scale are missing in previous studies. Here, we compiled two independent global databases for mid-Cretaceous (125-85 Ma) continental arcs. The first database maps the location, geometry, and tectonic nature of the basements upon which the arcs were built. The second compiles Sr-Nd-Hf isotopes data for these continental arcs. We find that isotopically-juvenile arcs form when their basements are generated by tectonic processes such as oceanic terrane accretion, upper plate extension, slab breakoff, and ridge subduction. During the mid-Cretaceous, most continental arcs were fully or partially built on juvenile basements and yielded juvenile isotopes on a global scale. Our compilation reinforces the importance of isotopically-juvenile continental arcs observed in the global Hf isotopes in detrital zircon for the mid-Cretaceous, but also provides the geological context for these trends. Since many of these isotopically-juvenile arcs were located in tropical or warm-temperate regions during the mid-Cretaceous, these uplifted rocks were preferentially eroded and weathered providing juvenile Sr isotopes to the oceans. This study highlights the importance of tectonic processes in controlling isotopic compositions of continental arc, which has implications for ocean chemistry, global chemical weathering feedback, and the long-term carbon cycle.

Modeling the effect of mineral armoring on the rates of coupled dissolution-precipitation reactions: Implications for chemical weathering

One of the mechanisms influencing weathering rates is mineral armoring, which is the build-up of insoluble coatings on primary mineral phases. Such armoring is often the result of coupled dissolution-precipitation reactions that occur during weathering. While the role of armoring in reducing dissolution rates is widely recognized, a quantitative mechanistic description of the way it impacts mineral weathering rates has not yet been developed. This paper demonstrates how a diffusion boundary layer model can simulate the effect of a porous secondary mineral layer on the rate of primary mineral dissolution under acidic conditions. In the model, the rates are affected by 3 parameters: layer thickness, the ratio of porosity to tortuosity, and the Biot number, which defines the ratio of dissolution to diffusion. Numerical solutions to the equations show that when the porosity/tortuosity ratio is low (~0.01), dissolution rates can be reduced by several orders of magnitude relative to armor-free minerals. Biot numbers greater than 1 were also found to lead to a significant reduction in the dissolution rate. Moreover, comparison with reported experimental data shows that the model can accurately simulate the change in thickness of the secondary mineral coating with time. The dissolution rates of pristine coating-free minerals in laboratory experiments can be orders of magnitude higher than those observed under field conditions, and the results suggest that mineral armoring can account for much of this discrepancy.

Experimental investigation of lithium isotope fractionation during kaolinite adsorption: Implications for chemical weathering

The feedback between CO2 sources and sinks through chemical weathering is one of the important reasons why Earth has maintained a habitable climate for over four billion years. The lithium (Li) isotopic system is a promising tracer of silicate weathering, but the mechanisms causing its isotope fractionation during weathering remain ambiguous. Here, we performed batch experiments of Li adsorption to one of the common clay minerals -kaolinite in three sets, including the time-series, pH-dependent, and concentration-control sets. Our results demonstrate that the liquid-solid Li isotope fractionation reaches up to 36‰, with up to 99% initial Li being adsorbed on kaolinite. The magnitudes of Li adsorption and isotope fractionation increase with reaction time, and reach the steady-state after ∼1000 min. The magnitude of Li isotope fractionation increases with the adsorption ratio of Li, in positive relationships with solute pH and ionic strength. At constant solute pH = 8.5 and ionic strength of 0.001 M, the adsorption ratio and isotope fractionation of Li on kaolinite reach the maximum with the lowest initial Li concentration of 2 μM. In experiments, Li is removed by kaolinite as the inner-sphere and/or outer-sphere complexes, likely followed by structural occupation as supported by incomplete desorption. We model the Li isotope fractionation in all three sets, which can be best described by Rayleigh distillation models. In summary, significant Li isotope fractionation occurs following a kinetic law in closed-systems during adsorption on kaolinite. Adsorption-driven isotope fractionation conforms to a kinetic solid-liquid isotope fractionation factor α ∼ 0.992, consistent with theoretical ion-desolvation between complexed and dissolved ions (α = 0.9925, Hofmann et al., 2012). This study reveals a vital kinetic role of clay uptake in Li isotope fractionation during chemical weathering, suggesting rapid forward adsorption reaction versus relatively slow backward reaction. The dominance of the kinetic mechanism over the equilibrium mechanism further explains field observations from rivers worldwide. Given above, the outcome of this study calls for additional attention on low-temperature kinetic Li isotope fractionation at Earth’s surface and further refinement of quantitative models using geological Li records to trace weathering and reconstruct climate.

Experimental investigation of lithium isotope fractionation during kaolinite adsorption: Implications for chemical weathering

Experimental investigation of lithium isotope fractionation during kaolinite adsorption: Implications for chemical weathering

Millennial-scale evolution of elemental ratios in bulk sediments from the western Philippine Sea and implications for chemical weathering in Luzon since the Last Glacial Maximum

To reconstruct the chemical weathering history in Luzon, Philippines, since the Last Glacial Maximum (LGM), major and trace elements (Ti, Al, Fe, K, Ba, Rb, V, Sc, Cr, and Th) and grain size were determined for core MD06-3054 as well as the bulk and detrital fractions of three core-top samples from the western Philippine Sea (WPS). In combination with previously published Sr-Nd isotopes, our new results indicate that Ti-normalized elemental ratios in the study samples were not controlled by the quantity of biogenic, authigenic, or diagenetic materials, sediment provenance, or grain size. Instead, variations in Ti-normalized elemental ratios mainly reflect changes in chemical weathering intensity, with lower values representing stronger chemical weathering in Luzon. To assess long-term integrated chemical weathering patterns, we defined a stacked chemical weathering index (SCWI) based on all elemental ratios in the study core. Downcore SCWI records indicate that sediments deposited during the LGM underwent a degree of chemical weathering equal to that during the Holocene, and sediments deposited during the last deglaciation exhibit rapid changes in chemical weathering, with higher intensity during the Heinrich event 1 (H1) and Younger Dryas (YD), and lower intensity during the Bølling-Allerød (B/A) in the WPS. These observations are in excellent agreement with chemical weathering proxies, such as the K/Al ratios and chemical index of alteration when applied to the same core. We infer that persistent sea-level lowstand and induced reworking of poorly consolidated sediments on the eastern Luzon continental shelf during the LGM accounted for equal or slightly stronger chemical weathering for the LGM sediments relative to the Holocene sediments. Rainfall, rather than air temperature, in Luzon was responsible for the rapid changes in chemical weathering during the last deglaciation, with higher precipitation generating stronger chemical weathering during the H1 and YD than during the B/A. Our observations, combined with existing data, suggest that strong weathering of marine sediments during colder intervals of the middle–late Quaternary is likely to be a general feature of the tropical West Pacific, although the mechanism that underlies this phenomenon remains controversial.

Hydro‐Geochemical and Sr Isotope Characteristics of the Yalong River Basin, Eastern Tibetan Plateau: Implications for Chemical Weathering and Controlling Factors

AbstractMajor ions and Sr isotope compositions of waters in the Yalong River basin in the eastern Tibetan plateau were investigated to explore the sources of dissolved loads and the controls on chemical weathering rates. Measured radiogenic 87Sr/86Sr ratios of water samples are most likely derived from the weathering of metamorphic carbonates or the Precambrian silicate rocks. Quantitative analysis of water geochemistry shows that carbonate weathering dominates the chemical characteristics of the river water. The chemical weathering rate of the whole Yalong River basin is calculated to be 7.6 ton·km−2·year−1 by silicate weathering and 44.7 ton·km−2·year−1 by carbonate weathering, which consumes 158.5 × 103 and 885.0 × 103 mol·km−2·year−1 of atmospheric CO2, respectively. The highest carbonate weathering rate (116.3 ton·km−2·year−1) in the Yalong River basins is observed from the basin with the steepest catchment average slope. This highest magnitude of carbonate weathering is comparable to the rates from catchments in the southern Himalayas. Positive relationships are observed between silicate weathering rates and both climatic (precipitation and temperature) and topographic (relief and slope) controls. The combined climatic and tectonic effects increase silicate weathering and counterbalance the dilution effect. However, the relationship between silicate weathering rate and climatic and topographic controls varies with hydrologic conditions. The rate for low‐discharge catchments is more closely related to climatic parameters, while the rate for high‐discharge catchments is more closely related to local topography.

Water geochemistry of rivers draining karst-dominated regions, Guangxi province, South China: Implications for chemical weathering and role of sulfuric acid

Guangxi province, located in South China, is a typical karst region affected by acid depositions for a couple of decades. Water samples from the major river basins in this region were collected and the chemical compositions were measured with a main purpose to quantify chemical weathering rates and associated CO2 budget. The average total dissolved solids (TDS) of the river waters (232 mg/l) are comparable with other karstic rivers. The major ion compositions of the river waters are characterized by the dominance of Ca2+, Mg2+, HCO3−, and are significantly rich in SO42−. The chemical compositions of the river waters indicate that four major reservoirs (atmospheric, anthropogenic, carbonate and silicate inputs) contribute to the dissolved loads. The carbonate chemical weathering rates range from 61.4 t/km2/yr for the Qingshuihe river basin to 93.3 t/km2/yr for the Zuojiang river basin. The silicate chemical weathering rates range from 2.9 t/km2/yr for the Qingshuihe river basin to 7.9 t/km2/yr for the Liujiang river basin. The CO2 consumption rates by carbonate weathering range from 559 × 103 mol/km2/yr for the Qingshuihe river basin to 817 × 103 mol/km2/yr for the Zuojiang river basin. The CO2 consumption rates by silicate weathering range from 19 × 103 mol/km2/yr for the Zuojiang river basin to 85 × 103 mol/km2/yr for the Liujiang river basin. Sulfuric acid is involved as a proton donor in weathering reactions, and about 9–15% of the chemical weathering rates of the river basins are sulfuric acid-induced. The CO2 consumption rates are only 85–91% of the value when assuming carbonic acid provides all the protons in the weathering reactions. The CO2 released from sulfuric acid-induced carbonate weathering would exceed the CO2 consumed by silicate weathering, making the river basins in Guangxi net CO2 sources on geological timescales. The total net CO2 releasing flux is approximately 15.7 × 109 mol/yr (0.19 × 1012 gC/yr). This result quantitatively highlights the fact that CO2 budget by chemical weathering will be largely modified by sulfuric acid, especially in seriously acid deposition affected region.

Changes in mineral reactivity driven by pore fluid mobility in partially wetted porous media

Microfluidics experiments were used to examine mineral dissolution-precipitation reactions under evaporative conditions and identify pore-scale processes that control reaction rate. The entrainment of reacting mineral particles by a mobile water-gas interface driven by evaporation dramatically altered the relative abundance of reactive mineral surface area to fluid reservoir volume. This ratio, which directly influences reaction rate and reaction progress, was observed to vary by nearly two orders of magnitude as evaporation progressed in the experiments. Its dynamic evolution may have a correspondingly large impact on mineral-fluid reaction in Earth's shallow subsurface. We predict that the spatial and temporal variability of pore-scale reaction rates will be significant during evaporation, imbibition, or drainage in the vadose zone, with implications for chemical weathering, soil quality, and carbon cycling. Variable reaction rates during particle mobility are likely to be of increased significance as global rainfall patterns and soil moisture contents evolve in response to climate change.

40Ar/39Ar dating of supergene Mn-oxides from the Zunyi Mn deposit, Guizhou Plateau, SW China: Implications for chemical weathering and paleoclimatic evolution since the late Miocene

40Ar/39Ar laser incremental heating analyses of potassium-bearing Mn-oxides from a weathering profile at the Zunyi manganese deposit, northern Guizhou Plateau, SW China, were applied to constrain the timing and rate of chemical weathering in critical zone and to provide insights into paleoclimatic conditions under which the weathering profile and associated Mn-oxides formed. Eighteen Mn-oxide grains from nine samples at three sites in saprolite zone of a single weathering profile yield well-defined plateau or pseudo-plateau ages ranging from 13.1±0.3 to 0.1±0.4Ma (2σ). The Mn-oxide ages are progressively younger toward lower elevations (13.1±0.3 to 11.0±1.8Ma at 951m; 3.69±0.07 to 2.16±0.16Ma at 922m; <1.3±0.2Ma at 914m), yielding an average weathering front propagation rate at 3.3m/Ma for the past 13.1Ma. The calculated weathering front propagation rate corresponds to a chemical denudation rate of 4.6±0.2t/km2/yr., which is consistent with values deduced from mass balance calculation for suspended and dissolved loads of river discharge across the Guizhou Plateau. The Mn-oxide 40Ar/39Ar ages suggest that humid climate conducive to intense weathering has prevailed over the Guizhou Plateau at least since the late Miocene. The climatic conditions inferred from the weathering geochronology are consistent with the continuous sedimentary and paleontological records from many Cenozoic basins over the Guizhou Plateau, confirming that supergene Mn-oxides can serve as a paleoclimate proxy for the past climatic condition. The present 40Ar/39Ar dating results, when combined with previous geochronological data of weathering profiles in the Yunnan–Guizhou Plateau and coastal areas of South China, document progressively intensive erosion toward areas proximal to the eastern margin of the Tibet Plateau.

Elemental distribution in the topsoil of the Lake Qinghai catchment, NE Tibetan Plateau, and the implications for weathering in semi-arid areas

An understanding of topsoil geochemistry within a watershed helps to identify the influence of natural processes and anthropogenic activities in the environment. Fifteen elements were measured in 73 topsoil samples (top 30cm) from the Lake Qinghai catchment, NE Qinghai–Tibetan Plateau (QTP) in 2009, to investigate geochemical patterns, identify possible sources and explore the implications of chemical weathering. Compared with their content in the upper continental crust (UCC), a deficit of Cu and Zn and an enrichment of Pb were identified in the study area. Enriched Ca levels were observed in alpine soil and pedocal, solonchak and aeolian sand soils, whereas there was a loss in hydromorphic and semi-hydromorphic soils. High Na in marsh solonchak indicated the possible presence of evaporites. Cluster analysis (CA) and principal component analysis (PCA) indicated the dominance of carbonate and the accumulation of P, possibly from grassland litterfall in topsoil. Some human activities have exerted an influence on virgin topsoil, as revealed by GIS mapping. The implications for chemical weathering, based on a chemical index of alteration (CIA) and an Al2O3–(CaO*+Na2O)–K2O (A–CN–K) diagram were characterised by a major carbonate control of the primary weathering stage under cold-dry climatic conditions with Ca and/or Na removal.

Elemental and strontium isotopic geochemistry of the soil profiles developed on limestone and sandstone in karstic terrain on Yunnan-Guizhou Plateau, China: Implications for chemical weathering and parent materials

The limestone and yellow sandstone soil profiles from SW China were measured for chemical and Sr isotope compositions of the bulk soils and their sequential leachates (labile, carbonate, and residue or silicate fraction), aiming to characterize the parent materials of the soils, to understand the soil weathering and formation processes, and to discuss the origin of the red residua (terra rossa). The studied yellow sandstone soil, yellow limestone soil, and black limestone soil show different pH values, SiO2 contents, Rb/Sr abundance ratios, and 87Sr/86Sr ratios. The sequential leachates of different soil types also have different 87Sr/86Sr and Ca/Sr ratios. The major chemical compositions of the studied soil profiles suggest that all the sandstone and limestone soils are developing at a stage that feldspar is exhausting and the clay minerals are changing from smectite to kaolinite and gibbsite. As compared with the red residua distributed in the karst region, the soils studied here show lower CIA values (58–84), but both higher Na2O/K2O (0.9–2.7) and Na2O/Al2O3 concentration ratios (0.07–0.26) on average, suggesting a lower weathering intensity than that of the red residua. The depth profiles of soil CIA values, Na2O/K2O and Rb/Sr ratios, and 87Sr/86Sr ratios indicate that the weathering intensity is slightly lower for the upper and higher for the deeper soils, which suggest that the sandstone and limestone soil profiles were formed through both accumulation and weathering of in situ weathering residue and input of external detritus or soil from upper land. During weathering of the soils, preferential release of Ca and retention of Sr in soil result in higher Ca/Sr ratios in both labile and carbonate fractions than those in the residue fractions of all soil profiles. The co-variations of Hf/Nb and Zr/Nb ratios, together with those Rb/Sr and 87Sr/86Sr ratios of limestone soils, sandstone soils, and the red residua, demonstrate that their parent materials are distinct, and support the point that the widely distributed red residua is originated from the weathering residua of both carbonate and silicate clastic rocks, and further weathering of the weathering residua resulted in intensive release of Si, Na, Ca and relative enrichment of Al, K and other immobile elements in the red residua.

Seasonal changes in the radiogenic and stable strontium isotopic composition of Xijiang River water: Implications for chemical weathering

Seasonal changes in strontium (Sr) isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering, and help to better constrain the Sr isotopic budget of global oceans. However, such records are scarce. Here we present a year-long time-series of both radiogenic and stable Sr isotope measurements (87Sr/86Sr and δ88Sr) from river water at Guiping, in the middle reaches of the Xijiang River, South China. Temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both Sr isotopes and major ions in the river water. River water 87Sr/86Sr values range from 0.708487 to 0.710336, with most values being <0.7092, indicating a dominant contribution from the weathering of carbonate rocks. High 87Sr/86Sr values (>0.7092) are generally accompanied by high Rb/Sr ratios, and low pH and δ13C of dissolved inorganic carbo (DIC) and occur during periods of large river flux. This indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons. Seasonal variation in river water δ88Sr is large, from 0.147‰ to 0.661‰, with higher δ88Sr values generally corresponding to higher 87Sr/86Sr values. Again, low δ88Sr values (<0.3‰) suggest a dominant contribution from the weathering of carbonate rocks, whereas the high δ88Sr values may represent a contribution from intensive weathering of silicate rocks. Using the time-series data, we estimated the flux-weighted averages of Sr concentration, 87Sr/86Sr, and δ88Sr for the Xijiang River to be 1.00μmol/L, 0.70960, and 0.38‰, respectively. The Sr concentration and 87Sr/86Sr results are close to previous estimates, while the δ88Sr value is amongst the highest recorded for the large rivers of the world, and is close to that of seawater. Our results indicate that large rivers draining through tropical/sub-tropical regions could play an important role in regulating the stable Sr isotopic budget of global oceans.

Diurnal and seasonal water variations of temperature, pH, redox potential and conductivity in gnammas (weathering pits): Implications for chemical weathering

A gnamma or weathering pit is a small-sized cavity sculpted into solid rock which refills with rainwater. This study describes the main hydrological processes in gnammas and the underlying chemical interactions with the environment. Four gnammas developed in a granite tor from central Spain were chosen for monitoring and studying the dynamics of the gnamma–water system. Parameters monitored were air and water temperature, pH, ORP (redox potential), and conductivity. These measurements describe the system dynamics, without the need for special sampling or other potential interferences under low water volumes. Additionally, chemical analyses were carried out to contrast the chemical properties with the chemical composition. As a consequence of water volumes less than 100 L, daily fluctuations tended to cause the largest amplitude changes. Photosynthesis and respiration/putrefaction processes in the gnamma are responsible for daily pH fluctuations up to 4 units, with pH values often greater than 9. ORP generally alternates from positive to negative values as the solution oscillates diurnally between basic and acidic conditions. Conductivity values ∼ 10 μS/cm occur most of the year, with only minor daily oscillations. During dry periods, conductivity increases significantly with maximum values > 400 μS/cm. These high conductivity values reflect atmospheric inputs by summer rainstorms after prolonged dry periods. Therefore, conductivity does not relate directly with chemical species dissolved from the host rock. Silica was the main weathering product of granite dissolution during the year, with highest concentrations (> 200 ppm) in the rainy season. Low Si values measured during the dry season are in accordance with observed precipitation of amorphous silica within the gnamma. Seasonal variations in concentration are also present in Al and Fe as a response to ORP variations and evaporative dynamics, causing mineral dissolution and new mineral precipitation during the year. Relations among the measured parameters are influenced by several factors, including biological processes, temperature effects and water level variations. Factors such as large pH oscillations, basic pH values, acids from biological activity, and alkali cations all increase silicate solubility, thus favoring granite dissolution. Overflow of water during the winter, when the water is chemically enriched, is an effective mechanism to remove weathering products.