A new method for determining weathering rates in weathering pits

Determining the rates of rock weathering is difficult because, firstly, the weathering rate of rocks is usually so slow that it is difficult to measure; secondly, it is also difficult to determine the start time and duration of weathering. The Shanxi River Valley in Fujian, China dried up after a reservoir was built upstream in 1959, and became a stone quarry site. Quarrying ceased in 1977, so a large amount of quarry wastes with artificially excavated surfaces were left in the valley. The concave-upward curved rocky surface, broken by manual excavation, easily contains rainwater in its central part, which was easily weathered into a more concave surface. Plaster mould casting was performed in situ on such a concave surface of an excavated stone rock in the valley and scanned with a high-precision 3D scanner to obtain 3D data of the concave-upward rock surface and its more concave middle part, which was considered as an initial weathering pit. The 3D model provided an in-depth understanding of the initial formation process of weathering pits, indicating that: (1) the average weathering rate of a weathering pit is 10.8 ± 0.49 cm ka⁻¹; (2) weathering pits are generally formed by standing water in depressions on a flat near-horizontal rock surface due to weathering actions involving water; (3) the deepening rate of a weathering pit is about four times greater than that of the surrounding area; (4) the growth of a weathering pit can begin in some small concavities on the flat rock surface without pre-existing depressions and gradually expands; (5) a weathering pit is generally wider than deep or with a flat bottom due to expansion with a lateral weathering rate that is greater than that of the vertical, and the lamination of the host rock is not necessary for the formation of flat-floored weathering pits. © 2020 John Wiley & Sons, Ltd.     

Differential weathering of feldspar and pyroxene in an arctic-alpine environment

The relative relief of adjacent plagioclase and pyroxene minerals was accurately measured on a recently-exhumed outcrop of gabbroic rocks in Leirdalen, southern Norway. Above the level of the former soil surface the feldspars protrude above the pyroxenes whereas below that level the pyroxenes are higher. Differential relief declines with increasing depth of burial down to 80 cm. On exposed surfaces the mean loss of pyroxene relative to feldspar is 103 cm³ m^?2 of rock surface. With burial down to 50 cm in an arctic-alpine Brown Soil the mean loss of feldspar relative to pyroxene is 179 cm³ m^?2. These figures represent minimum amounts of weathering over about 9000 years. The results confirm the importance of chemical weathering in arctic-alpine environments and the techniques may provide useful physical measures of degree of weathering for use in rate studies and relative-dating.     

The application of uranium series disequilibrium concepts to sediment yield determination

The determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, ²³⁴U is more mobile than ²³⁸U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, teaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, U_S/U_W can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred. The Witham catchment in Lincolnshire has been used to test the proposed method. A U_S/U_W ratio of between 5 and 7 is determined and a sediment yield of 2.51 ± 2.12 tonnes yr^?1 km^?2 is proposed. Although some problems concerning environmental chemistry have arisen, the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods.     

Hydrological regulation of chemical weathering and dissolved inorganic carbon biogeochemical processes in a monsoonal river

To better understand the mechanisms relating to hydrological regulations of chemical weathering processes and dissolved inorganic carbon (DIC) behaviours, high-frequency sampling campaigns and associated analyses were conducted in the Yu River, South China. Hydrological variability modifies the biogeochemical processes of dissolved solutes, so major ions display different behaviours in response to discharge change. Most ions become diluted with increasing discharge because of the shortened reactive time between rock and water under high-flow conditions. Carbonate weathering is the main source of major ions, which shows strong chemostatic behaviour in response to changes in discharge. Ions from silicate weathering exhibit a significant dilution effect relative to the carbonate-sourced ions. Under high temperatures, the increased soil CO₂ influx from the mineralisation of organic material shifts the negative carbon isotope ratios of DIC (δ¹³C_DIC) during the high-flow season. The δ¹³C_DIC values show a higher sensitivity than DIC contents in response to various hydrological conditions. Results from a modified isotope-mixing model (IsoSource) demonstrate that biological carbon is a dominant source of DIC and plays an important role in temporal carbon dynamics. Furthermore, this study provides insights into chemical weathering processes and carbon dynamics, highlighting the significant influence of hydrological variability to aid understanding of the global carbon cycle.     

Field evidence for the influence of weathering on rock erodibility and channel form in bedrock rivers

Erosion processes in bedrock‐floored rivers shape channel cross‐sectional geometry and the broader landscape. However, the influence of weathering on channel slope and geometry is not well understood. Weathering can produce variation in rock erodibility within channel cross‐sections. Recent numerical modeling results suggest that weathering may preferentially weaken rock on channel banks relative to the thalweg, strongly influencing channel form. Here, we present the first quantitative field study of differential weathering across channel cross‐sections. We hypothesize that average cross‐section erosion rate controls the magnitude of this contrast in weathering between the banks and the thalweg. Erosion rate, in turn, is moderated by the extent to which weathering processes increase bedrock erodibility. We test these hypotheses on tributaries to the Potomac River, Virginia, with inferred erosion rates from ~0.1 m/kyr to >0.8 m/kyr, with higher rates in knickpoints spawned by the migratory Great Falls knickzone. We selected nine channel cross‐sections on three tributaries spanning the full range of erosion rates, and at multiple flow heights we measured (1) rock compressive strength using a Schmidt hammer, (2) rock surface roughness using a contour gage combined with automated photograph analysis, and (3) crack density (crack length/area) at three cross‐sections on one channel. All cross‐sections showed significant (p < 0.01 for strength, p < 0.05 for roughness) increases in weathering by at least one metric with height above the thalweg. These results, assuming that the weathered state of rock is a proxy for erodibility, indicate that rock erodibility varies inversely with bedrock inundation frequency. Differences in weathering between the thalweg and the channel margins tend to decrease as inferred erosion rates increase, leading to variations in channel form related to the interplay of weathering and erosion rate. This observation is consistent with numerical modeling that predicts a strong influence of weathering‐related erodibility on channel morphology. Copyright © 2017 John Wiley & Sons, Ltd.     

Processes controlling rapid temperature variations on rock surfaces

In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0·375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C min^?1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C min^?1 and the average percentage time spent above 2°C min^?1 was ～70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C min^?1. Simultaneous measurements of two thermocouples 5·5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ～10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.     

The physical properties of quartz-micaschist and their application to freeze-thaw weathering studies in the maritime antarctic

As part of a study on freeze-thaw weathering in the maritime Antarctic an investigation was made of the physical properties of the local rock. Tests were made of point-load compressive strength, Schmidt hammer in situ rock strength, moisture content, indentor resistance and the size range of weathering products. The resulting data were used to consider the form of freeze-thaw weathering operative in the field and its relationship to laboratory simulations. A distinct difference between ‘massive rock’ and ‘intact rock’ is observed in the field. It is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weathering.     

粤东五华河流域的化学风化与CO2吸收

基于对粤东五华河干流和支流水体的物理、化学组成测试数据,应用质量平衡法和相关分析法探讨湿热山地丘陵地区岩石化学风化过程对大气CO₂的吸收.结果表明:五华河水体的总溶解性固体含量(77.11 mg/L)接近于世界河流的平均值(65 mg/L);离子组成以Ca²⁺、Na⁺和HCO₃^-为主,可溶性Si次之.五华河流域化学径流组成主要源自硅酸盐矿物化学风化过程的贡献,碳酸盐矿物的贡献较少;大气和土壤CO₂是流域内岩石化学风化的主要侵蚀介质.与同一气候带其他河流相比较,五华河流域岩石化学风化过程对大气CO₂的吸收通量(2.14×105mol/(km²·a))较低,这主要是由于流域内缺乏碳酸盐岩所导致.     

The hydrochemistry of meltwaters draining a polythermal-based,high Arctic glacier,south Svalbard: I. The ablation season

Solute and runoff time-series at Finsterwalderbreen, Svalbard, provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments. The hydrochemistry of a subglacial upwelling provides evidence for a snowmelt-fed subglacial reservoir that dominates bulk runoff during recession flow. High concentrations of Cl⁻ and crustal ions, high pCO₂ and ratios of [*SO²⁻₄/(*SO²⁻₄+HCO⁻₃)] close to 0·5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock:water ratios, prolonged residence times and restricted access to the atmosphere. At higher discharges, bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock:water ratios, short residence times and free contact with atmospheric gases. These observations suggest that icemelt is routed via a hydrological system composed of basal/ice-marginal, englacial and supraglacial components and is directed to the glacier margins by the ice surface slope. Upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system, possibly constituting flow through a sediment layer. Cold basal ice at the terminus forces it to take a subterranean routing in its latter stages. The existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal-based glaciers on Svalbard. Proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm-based glaciers. These hydrochemical characteristics of bulk runoff have not been documented on any other glacier on Svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology. © 1998 John Wiley & Sons, Ltd.     

Controls on Holocene denudation rates in mountainous environments under Mediterranean climate

The Mediterranean domain is characterized by a specific climate resulting from the close interplay between atmospheric and marine processes and strongly differentiated regional topographies. Corsica Island, a mountainous area located in the western part of the Mediterranean Sea is particularly suitable to quantify regional denudation rates in the framework of a source‐to‐sink approach. Indeed, fluvial sedimentation in East‐Corsica margin is almost exclusively limited to its alluvial plain and offshore domain and its basement is mainly constituted of quartz‐rich crystalline rocks allowing cosmogenic nuclide ¹⁰Be measurements. In this paper, Holocene denudation rates of catchments from the eastern part of the island of Corsica are quantified relying on in situ produced ¹⁰Be concentrations in stream sediments and interpreted in an approach including quantitative geomorphology, rock strength measurement (with a Schmidt Hammer) and vegetation cover distribution. Calculated denudation rates range from 15 to 95 mm ka^‐1. When compared with rates from similar geomorphic domains experiencing a different climate setting, such as the foreland of the northern European Alps, they appear quite low and temporally stable. At the first order, they better correlate with rock strength and vegetation cover than with morphometric indexes. Spatial distribution of the vegetation is controlled by morpho‐climatic parameters including sun exposure and the direction of the main wet wind, so‐called ‘Libecciu’. This distribution, as well as the basement rock strength seems to play a significant role in the denudation distribution. We thus suggest that the landscape reached a geomorphic steady‐state due to the specific Mediterranean climate and that Holocene denudation rates are mainly sustained by weathering processes, through the amount of regolith formation, rather than being transport‐limited. Al/K measurements used as a proxy to infer present‐day catchment‐wide chemical weathering patterns might support this assumption. Copyright © 2016 John Wiley & Sons, Ltd.     

A Rb/Sr record of catchment weathering response to Holocene climate change in Inner Mongolia

Variation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by ²¹⁰Pb, ¹³⁷Cs and AMS‐¹⁴C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp , accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp . However, weathering was reduced between c. 8·25 and 7·90 ka bp , which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp , increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd.     

Classification of rock weathering at writing-on-stone Provincial Park,Alberta, Canada: A study in applied geomorphology

At Writing-On-Stone Provincial Park in southern Alberta, Canada, weathering is causing deterioration and loss of archaeologically important Indian rock art. A procedure devised for the use of park personnel identified four classes of weathering ranging from largely unweathered rock to severely weathered. The technique employed simple visual, qualitative assessment and photo interpretation of 50 sample sections of sandstone cliff face covering a total area of 354 m². Schmidt hammer tests indicated large variations in rock strength and provided a numerical basis for the visual assessment. About 43 per cent of the cliffs are severely to completely weathered, 41 per cent show moderate weathering.     

Where fast weathering creates thin regolith and slow weathering creates thick regolith

Weathering disaggregates rock into regolith – the fractured or granular earth material that sustains life on the continental land surface. Here, we investigate what controls the depth of regolith formed on ridges of two rock compositions with similar initial porosities in Virginia (USA). A priori, we predicted that the regolith on diabase would be thicker than on granite because the dominant mineral (feldspar) in the diabase weathers faster than its granitic counterpart. However, weathering advanced 20× deeper into the granite than the diabase. The 20 × ‐thicker regolith is attributed mainly to connected micron‐sized pores, microfractures formed around oxidizing biotite at 20 m depth, and the lower iron (Fe) content in the felsic rock. Such porosity allows pervasive advection and deep oxidation in the granite. These observations may explain why regolith worldwide is thicker on felsic compared to mafic rock under similar conditions. To understand regolith formation will require better understanding of such deep oxidation reactions and how they impact fluid flow during weathering. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantifying weathering on variable rocks,an extension of geochemical mass balance: Critical zone and landscape evolution

We present a statistical model of soil and rock weathering in deep profiles to expand the capacity to assess weathering to heterogeneous bedrock types, which are common at the Earth's surface. We developed the Weathering Trends (WT) model by extending the fractional mass change calculation (tau) of the geochemical mass balance model in two important ways. First, WT log transforms the elemental ratio data, to discern the log‐linear patterns that naturally develop from thermodynamic and kinetic laws of chemistry. Second, WT statistically fits log‐transformed element concentration ratio data – log(c_j/c_i), the only depth‐varying term in tau – as a function of depth to determine characteristic depths of transitions in weathering processes, along with confidence intervals. With no prior assumptions, WT estimates average parent material composition, average composition of the upper weathered zone and mean fractional mass change of each element over the entire weathering profile. WT displays the mean shape of weathering profiles of log‐transformed geochemical data bounded by calculated confidence intervals. We share the WT model code as an open‐source R package ( https://github.com/fisherba/WeatheringTrends ). The WT model was designed to interpret two 21 m cores from the Laurels Schist bedrock in the Christina River Basin Critical Zone Observatory in the Pennsylvania Piedmont, where our morphological and elemental data provided inconclusive estimates of bedrock depth. The WT model differentiated between rock variability and weathering to delineate the maximum extent of weathering at 12.3 m (CI 95% [9.2, 21.3]) in Ridge Well 1 and 7.2 m (CI 95% [4.3, 13.0]) in Interfluve Well 2. The water table was 5–8 m below fresh rock at Ridge Well 1, but at the same depth as fresh rock at the lower elevation interfluve. We assess statistical approaches to identify the best immobile element for use in WT and tau calculations. Copyright © 2017 John Wiley & Sons, Ltd.     

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic V_p and V_s profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.     

A Morphological Study of Greenschist Weathering on Dated Coastal Structures,South Devon,UK

Three dated structures up to 450 years in age display the effects of coastal weathering of the greenschist of which they are constructed. A variety of weathering forms is present. The various topographic surfaces of the structures create variation in weathering environments and consequent weathering processes and rates. Weathering is enhanced by direct exposure to salt-bearing spray and by humid conditions, and apparently limited by direct exposure to solar radiation. The maximum rates of weathering on the three surfaces approximate to 0·6 mm a⁻¹ over this period, consistent with measured contemporary weathering rates for a natural surface formed by this rock type in a nearby coastal location. © 1997 by John Wiley & Sons, Ltd.     

Spatial characteristics and controlling factors of chemical weathering of loess in the dry season in the middle Loess Plateau,China

Hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle Loess Plateau (MLP), one of the most severely eroded areas and turbid riverine systems in the world. River waters were neutral to slightly alkaline with pH varying from 7.6 to 9.6. The total dissolved solids decreased from northwest to southeast with a mean value of 804 mg/l, much higher than the global average and other large rivers in China. Ternary diagram showed that river waters were dominated by Na⁺, HCO₃^?, and Cl^? with the main water‐type of HCO₃^?–Cl^?–Na⁺. Saturation index values, Mg²⁺, Ca²⁺, and HCO₃^? analyses indicated the preferential Ca²⁺ removal by calcite precipitation. Gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs. Samples in the northwestern basin are also influenced by evaporation. A forward model of mass budget calculation showed that, owing to high soluble characteristics, evaporite dissolution was a major feature of river waters and contributed 41% to the total dissolved cations on average, while carbonate and silicate weathering contributed 28%,and 25% on average, respectively. Besides evaporite dissolution, cation exchange is also responsible for the high concentrations of Na⁺ in river water. Spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin, whereas carbonate weathering was higher in the southern basin. Different from most rivers in the world, the physical erosion rates (varying from 117.7 to 4116.6 t/km²y) are much higher than the chemical weathering rates (varying from 3.54 to 6.76 t/km²y) in the MLP because of the loose structure of loess and poor vegetation in the basin. In the future, studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry, denudation rates, and water quality should be strengthened in the MLP. These results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time‐series sampling strategy for river water chemistry. Copyright © 2016 John Wiley & Sons, Ltd.     

The weathering effects of the lichen Lecidea aff. Sarcogynoides (Koerb.) on magaliesberg quartzite

The effect of the weathering processes generated by Lecidea aff. Sarcogynoides (Koerb.) on the substrate was studied by means of a scanning electron microscope. The elements present in the substrate (Magaliesberg quartzite) and in the lichen thallus were determined by X-ray fluorescence spectrometry for the purpose of comparison. The elements present were mostly similar although a few were present in the thallus which were not observed in the quartzite. It is possible that those elements present in the lichen thallus which were not present in the substrate may have been extracted from the atmosphere. The occurrence of small hollows (weathering pits) in which the early stages of plant development occurs, and the disintegration of the rock indicate that Lecidea aff. sarcogynoides (Koerb.) contributes to the chemical weathering processes by chelation and mechanically by the penetration and expansion of hyphae. A model is proposed in which a possible mechanism for these weathering processes is suggested.     

The spatial variation of weathering and soil depth across a Triassic sandstone outcrop

In this study, we used an archive of borehole logs from the British Geological Survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the Triassic Sherwood Sandstone Group outcrop (750 km²), in the East Midlands, UK. The borehole logs were used to estimate the thickness of the soil (n = 280) and soil and saprolite (S&S) to competent rock (n = 500). The weathering profile of the sandstone consisted of soil (median thickness ～ 1·5 m) overlying a transition zone of compacted and weakly cemented weathered sandstone saprolite over bedrock. Topographic analysis using a NEXTMAP 5 m × 5 m digital elevation model (DEM) revealed no significant relationships between slope properties (relief, flow length, flow accumulation or slope angle) and soil or S&S thickness. A weak, but statistically significant correlation was found between the thickness of the soil and S&S (r_s = 0·25, p < 0·001, n = 192). The variation in soil thickness may be related to changes in current and historic and land‐use, variation in sandstone properties and the influence of glacial/peri‐glacial processes. The thickness of the saprolite was more variable towards the southern part of the study area, where it increased to a maximum 40 m. We hypothesize and provide evidence that the greater weathering thickness is related to the occurrence of increased faulting in this part of the study region, allowing increased access to meteoric waters. A possible source of increased water supply is meltwater from Quaternary ice sheets; the overburden of ice may have increased sub‐glacial pore water pressure, with the fractures and faults acting as a drainage system for the removal of dissolved weathering products. British Geological Survey © NERC 2010     

喀斯特地区梯级水库建造对水化学分布的影响

为深入了解河流梯级筑坝对喀斯特地区河流水化学分布的影响,于2017年1、4、7和10月别对乌江干流洪家渡水库(多年调节)、乌江渡水库(季调节)和索风营水库(日调节) 3个具有不同滞留时间的水库进行水样采集,分析入库水、坝前剖面水和下泄水的水化学特征,探讨河流梯级筑坝对水化学分布及风化速率估算的影响.研究结果表明:3个水库深层水比表层水HCO3-浓度分别高12.9%、5.5%和8.0%,Ca~(2+)浓度分别高15.9%、2.4%和8.5%.河流梯级筑坝一定程度上改变了水体水化学组成,从而影响碳酸盐岩风化速率估算.整体上,洪家渡水库、索风营水库和乌江渡水库的全年风化速率变化范围分别为:-1.7%～15.4%、-5.6%～1.1%和-0.3%～3.4%.河流筑坝作用对风化速率估算及主量离子浓度的影响:HCO_3~-与Ca~(2+)浓度分布均为:洪家水库乌江渡水库索风营水库,这与水体滞留时间长短规律一致,表明水体滞留时间影响着水化学的组成分布.同时水体离子浓度表现出明显的季节性差异,丰水期各水库变化率明显大于枯水期.上述结论表明喀斯特地区河流连续筑坝后水化学组成及分布特征发生了一定程度改变,影响流域化学风化速率的估算,且影响程度随水体滞留时间延长而增大,并受气温影响.因此,今后在估算流域风化速率及探究水化学空间变化时应对筑坝作用加以考虑,以便更加准确地评估喀斯特流域岩石风化在全球碳循环中的作用.