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1.
The soil aggregate stability is a key property of soil quality and reflects soil quality and anti‐erosion ability. The transition matrix between initial and final aggregates condition was established by modifying Niewczas and Witkowska‐Walczak's method by not considering the artificial weights and each size of aggregates fraction on the basis of three reasonable assumptions, and soil aggregate stability index (ASI) was formed through preserving each size of aggregates probability. This ASI is identical to the result by reference, and the transition matrix can be showed to evaluate the soil aggregates stability. Using the transition matrix was furthermore to analyze anti‐breaking ability of different size aggregate by reference material. We found there were different effects for each size aggregate by four methods, simulation rainfall, one cycle of wetting–drying, ten cycles of wetting–drying, and Yoder wetting–sieving. The Yoder wetting–sieving is a severe method that destructed soil aggregates. The ASI by modifying transition matrix method was used to evaluate the aggregates stability under different land utilization in Karst region in Chongqing, China. The ASI of agricultural utilization was lower than abounded cultivated land, shrub‐grass land, secondary forest land, and primeval forest land. For some selected soil properties, when SOM content was <60 g/kg, ASI increased along with the SOM increase. Once the SOM content was >60 g/kg, the ASI was almost unchanged. The sorption moisture content of air‐drying acutely affected ASI too, and the ASI increased along the sorption moisture increasing. SOM content and sorption markedly affected the preserving probability of larger aggregates such as 10–5, 5–3, 3–2, 2–1, and 1–0.5 mm size class. Although CaCO3 and clay content did not influence preserving probability of each size class of aggregates fiercely, but the influence on small aggregates was higher than that of larger aggregates. The modified transition matrix method could not only calculate soil aggregates stability index, but also analyze more parameters of aggregate experiment, and bring out the each size aggregates characteristics. Thus, the modified transition matrix method could be a better tool to understand soil quality.  相似文献   

2.
In this study our main objective was to quantify water interrill erosion in the sloping lands of Southeast Asia, one of the most bio‐geochemically active regions of the world. Investigations were performed on a typical hillslope of Northern Laos subjected to slash and burn agriculture practiced as shifting cultivation. Situations with different periods of the shifting cultivation cycle (secondary forest, upland rice cultivation following a four‐year fallow period and three‐year continuous upland rice cultivation) and soil orders (Ultisols, Alfisols, Inceptisols) were selected. One metre square micro‐plots were installed to quantify the soil material removed by either detachment of entire soil aggregate or aggregate destruction, and the detached material transported by thin sheet flow, the main mechanisms of interrill erosion. In addition, laboratory tests were carried out to quantify the aggregate destruction in the process of water erosion by slaking, dispersion and mechanical breakdown. The average runoff coefficient (R) evaluated throughout the 2002 rainy season was 30·1 per cent and the interrill erosion was 1413 g m?2 yr?1 for sediments and 68 g C m?2 yr?1 for soil organic carbon, which was relatively high. Among the mechanisms of interrill water erosion, aggregate destruction was low and mostly caused by mechanical breakdown due to raindrops, thus leading to the conclusion that detachment and further transport by the shallow runoff of macro‐aggregates predominates. R ranged from 23·1 to 35·8 per cent. It decreased with the proportion of mosses on the soil surface and soil surface coverage, and increased with increasing proportion of structural crust, thus confirming previous results. Water erosion varied from 621 to 2433 g m?2 yr?1 for sediments and from 31 to 146 g C m?2 yr?1 for soil organic carbon, and significantly increased with increasing clay content of the surface horizon, probably due to the formation of easily detachable and transportable sand‐size aggregates, and proportion of macro‐aggregates not embedded in the soil matrix and prone to transport. In addition, water erosion decreased with increasing proportion of structural crusts, probably due to their higher hardness, and when cultivation follows a fallow period rather than after a long period of cultivation due to the greater occurrence of algae on the soil surface, which affords physical protection and greater aggregate stability through binding and gluing. This study based on simultaneous field and laboratory investigations allowed successful identification and quantification of the main erosion mechanisms and controlling factors of interrill erosion, which will give arguments to further set up optimal strategies for sustainable use of the sloping lands of Southeast Asia. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
Wischmeier's soil erodibility factor K calculated for 10 surface soils in the Hornos area, S. Spain, is compared with 3 aspects of aggregate stability. A significant correlation is found with the percentage of particles < 100 μm after aggregate breakdown, which is used as a measure of the vulnerability of the soil to erosion by overland flow. No significant correlation exists with the number of water drops required to cause breakdown of the aggregates nor with the mean size of the shattered aggregates, both being aspects of the resistance of aggregates to splash erosion. Of the micromorphological and analytical soil properties explaining aggregate stability, only the clay and silt content and the number of closed voids are significantly correlated with the factor K. The aggregate stability of the investigated soils is mainly determined by soil properties inherited from the parent material; the stabilizing effect of pedological features is small.  相似文献   

4.
Two rainfall simulators of different plot sizes were used to test whether sediment in runoff could be used to measure aggregate breakdown in the surface of a cracking clay soil under rain. Plots were prepared with either levelled or furrowed surfaces. Samples of the soil surface under rain were taken from furrow ridges or levelled surfaces, and from areas of deposited sediment. These were compared with samples of sediment in runoff taken at the same times. On both furrowed and levelled plot surfaces and for both simulators, aggregate sizes were significantly finer in sediment in runoff than in samples of the soil surface taken with a spatula. No significant differences in surface aggregate size distributions were found between rainfall simulators, or between furrowed and levelled plot surfaces. Regression lines fitted to the data on size distributions of sediment or of aggregates in the soil surface showed no significant changes through time. The fitted lines showed sediment in runoff to be still significantly finer than aggregates in the soil surface after 50 min rain at 95 mm h?1, except for levelled plots under the rotating disc rainfall simulator, where extreme variability of data meant that even relatively large differences were not statistically significant. Size distributions of deposited sediment were similar to those of the surface of adjacent furrow ridges exposed to raindrop impact. This provides evidence that sampling the soil surface with a spatula gives a representative sample of the material available for rain-flow transport.  相似文献   

5.
Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m−2 mm−1 and 12 m−2 mm−1. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.  相似文献   

6.
To obtain a better understanding of the colluvial deposits in two catchments in the Luxembourg Ardennes, structural aggregates from forest and farmland soils were subjected to the impact of falling water drops. The changes that the aggregates underwent and the material eroded from them were studied in thin section. Predictably, forest aggregates were more resistant to water-drop impacts than those from farmland. Farmland aggregates tended to slake upon wetting and to break down into many micro-aggregates having a size-frequency distribution similar to that of the micro-aggregates in the undisturbed soil. The forest aggregates were eroded slowly under water-drop impact, losing material from their surfaces or occasionally shearing into several smaller equally resistant aggregates. The size-frequency distributions of the break-down products differed from the micro-aggregates in the untreated aggregates or original forest soil, probably because of bonding by organic material. The differing composition of the aggregates points to the importance of oriented clay and planes for the lack of stability of the farmland aggregates. It can be concluded that agricultural colluvium is probably largely deposited by processes other than splash and that splash is an important process, but not the only one, in the formation of colluvium under forest.  相似文献   

7.
Soil detachment in concentrated flow is due to the dislodging of soil particles from the soil matrix by surface runoff. Both aggregate stability and shear strength of the topsoil reflect the erosion resistance of soil to concentrated runoff, and are important input parameters in predicting soil detachment models. This study was conducted to develop a formula to predict soil detachment rate in concentrated flow by using the aggregate stability index (As), root density (Rd) and saturated soil strength (σs) in the subtropical Ultisols region of China. The detachment rates of undisturbed topsoil samples collected from eight cultivated soil plots were measured in a 3.8 m long, 0.2 m wide hydraulic flume under five different flow shear stresses (τ = 4.54, 9.38, 15.01, 17.49 and 22.54 Pa). The results indicated that the stability index (As) was well related with soil detachment rate, particularly for results obtained with high flow shear stress (22.54 Pa), and the stability index (As) has a good linear relationship with concentrated flow erodibility factors (Kc). There was a positive linear relationship between saturated soil strength (σs) and critical flow shear stress (τc) for different soils. A significant negative exponential relationship between erodibility factors (Kc) and root density (Rd) was detected. This study yielded two prediction equations that allowed comparison of their efficiency in assessing soil detachment rate in concentrated flow. The equation including the root density (Rd) may have a better correlation coefficient (R2 = 0.95). It was concluded that the formula based on the stability index (As), saturated soil strength (σs) and root density (Rd) has the potential to improve methodology for assessing soil detachment rate in concentrated flow for the subtropical Chinese Ultisols. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

8.
The factors influencing soil erosion may vary with scale. It remains unclear whether the spatial variation in soil erosion resistance is controlled by regional variables (e.g. precipitation, temperature, and vegetation zone) or by local specific variables (e.g. soil properties, root traits, land use, and farming operations) when the study area enlarges from a hillslope or catchment to the regional scale. This study was performed to quantify the spatial variations in soil erosion resistance to flowing water under three typical land uses along a regional transect on the Loess Plateau and to identify whether regional or local specific variables are responsible for these changes. The results indicated that the measured soil detachment capacities (Dc) of cropland exhibited an irregular trend along the regional transect. The Dc of grassland increased with mean annual precipitation, except for two sites (Yijun and Erdos). The measured Dc of woodland displayed an inverted ‘U’ shape. The changes in rill erodibility (Kr) of three land uses were similar to Dc, whereas no distinguishable trend was found for critical shear stress (τc). No significant correlation was detected between Dc, Kr and τc, and the regional variables. The spatial variation in soil erosion resistance could be explained reasonably by changes in soil properties, root traits, land use, and farming operations, rather than regional variables. The adjustment coefficient of Kr for grassland and woodland could be well simulated by soil cohesion and root mass density (R2 = 0.70, P < 0.01), and the adjustment coefficient of critical shear stress could be estimated with aggregate stability (R2 = 0.57, P < 0.01). The results are helpful for quantifying the spatial variation in soil detachment processes by overland flow and to develop process‐based erosion model at a regional scale. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
Two methods for sampling aggregates in the soil surface under simulated rain were compared using two soil types. Results showed that aggregate size distributions obtained by spatula sampling were not significantly different from those obtained using rings buried in the soil surface, provided both were sampled to the same depth. The effect of transporting samples over a distance of 60 km was non-significant when samples were placed in bottles half-filled with rainwater and transported in an upright position. The per cent aggregates > 0.125 mm was found to be the most suitable index of aggregate stability for both soils.  相似文献   

10.
Organic carbon (OC) is easily enriched in sediment particles of different sizes due to aggregate breakdown and selective transport for sheet erosion. However, the transport of aggregate-associated OC has not been thoroughly investigated. To address this issue, 27 simulated rainfall experiments were conducted in a 1 m × 0.35 m box on slope gradients of 15°, 10°, and 15°and under three rainfall intensities of 45 mm h−1, 90 mm h−1 and 120 mm h−1. The results showed that OC was obviously enriched in sediment particles of different sizes under sheet erosion. The soil organic carbon (SOC) concentrations of each aggregate size class in sediments were different from those in the original soil, especially when the rainfall intensity or slope was sufficiently low, such as 45 mm h–1 or 5°, respectively. Under a slope of 5°, the SOC enrichment ratios (ERocs) of small macroaggregates and microaggregates were high but decreased over time. As rainfall intensity increased, OC became enriched in increasingly fine sediment particles. Under a rainfall intensity of 45 mm h–1, the ERocs of the different aggregate size classes were always high throughout the entire erosion process. Under a rainfall intensity of > 45 mm h–1 and slope of > 5°, the ERocs of the different aggregate size classes were close to 1.0, especially those of clay and silt. Therefore, the high ERocs in sediments resulted from the first transport of effective clay. Among total SOC loss, the proportion of OC loss caused by the transport of microaggregates and silt plus clay-sized particles was greater than 50%. We also found that low stream power and low water depth were two requirements for the high ERocs in aggregates. Stream power was closely related to sediment particle distribution. Flow velocity was significantly and positively related to the percentage of OC-enriched macroaggregates in the sediments (P > 0.01). Our study will provide important information for understanding the fate of SOC and building physical-based SOC transport models. © 2019 John Wiley & Sons, Ltd.  相似文献   

11.
This paper describes laboratory testing of 148 samples collected from Southern Alberta for erosion by wash and splash. Rainfall intensity was held constant during these tests. Soil aggregation was the most significant variable explaining soil loss. The significance of other soil properties, such as organic carbon and clay content is variable, depending on the interrelationships among aggregate stability, organic content, and clay content of particular soils. Variations in erodibility of the major soils examined are explained by the resistance of aggregates to compaction and dispersion. Splash detachment and wash transport are the dominant erosion mechanisms in inter-rill areas.  相似文献   

12.
Topography and land use affect soil organic carbon(SOC) storage, stabilization, and turnover, through several biogeochemical processes. This study investigated the aggregate composition and SOC content of bulk soils and aggregates at different slope positions under different land uses in a typical karst catchment of southwestern China. Our results show that the proportion of macro-aggregates and the SOC content of bulk soils and aggregates at different slope positions decreased from the upper to the lower slope. The SOC content generally increased with an increase in the mean weight diameter and proportion of macro-aggregates under different land uses. Our results indicate that macro-aggregates in forest and grassland soils make a greater contribution to both aggregate composition and SOC content than that in arable land soils. Therefore,converting farmland to forest or grassland can facilitate the accumulation of macro-aggregates as well as the storage of SOC.  相似文献   

13.
R. M. Bajracharya  R. Lal 《水文研究》1998,12(12):1927-1938
Sealing and crusting of soil surfaces have dramatic effects on water infiltration into and runoff from soils, thereby greatly influencing erosion processes. This study focused on the effect of the initial stage of crusting on inter-rill erosion processes for a crust-prone Alfisol sampled from south-central India. Soil aggregates ranging from 2·4 to 8 mm collected from ploughed (PL) and naturally vegetated (NV) treatments were subjected to rainfall simulation under laboratory conditions. Runoff from PL soil aggregates was 2–2·5 times higher, while percolation was 20–100% lower, than for NV aggregates. Soil wash and splash losses were 0·5–3 times greater for PL than for NV soil. Runoff and inter-rill erosion were significantly higher during the wet simulation run compared with the dry run. The results indicated that NV soil aggregates were more resistant to breakdown from raindrop impact and slaking, and subject to less rapid sealing, than PL soil. Total soil loss was influenced most by initial aggregate stability and the extent of seal development. Splash and wash losses of soil both increased as a result of surface sealing regardless of soil condition for short (30–60 min) rainfall durations. High drying rates resulted in the highest crust bulk densities. Increased crust strength for PL soil compared with NV soil reflected the greater susceptibility of cultivated soil to surface sealing and crusting. © 1998 John Wiley & Sons, Ltd.  相似文献   

14.
Olive cultivation is a widespread land use in Mediterranean climates. The proper implementation of soil and water conservation practices in groves requires detailed knowledge of the governing hydrological processes. In this work topsoil moisture dynamics under wet and dry conditions and across a small catchment was investigated in the inter row (IR) and directly under the olive tree canopies (UC). We do this using a sensor network (11 stations) and a simple bucket model which was calibrated (June, 2011–2012) and validated (June, 2012–2013). During most of the year the normalized soil moisture contents (s) were greater in the IR than under UC, with an average normalized soil moisture difference of 0.12. The difference between UC and IR normalized soil moisture followed a seasonal pattern, reaching a maximum near 0.30 during spring. An analysis of the normalized soil moisture probability density functions (pdfs) was bimodal, showing characteristic dominant wet and dry soil moisture states, with the highest probability densities for the dry state. Overall the spatial variability of soil moisture was lower UC than in the IR. This was a result of the soil moisture buffering capacity of the canopy with respect to rainfall and evaporation, in addition to observed differences in soil properties. Hourly soil moisture data were successfully modelled (R2 > 0.85), both UC and in the IR, yet with the inclusion of a simple formulation for canopy interception for the former. The results provide insight into how olive trees change hydrological processes in their neighbourhood. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
In the northern Loess Plateau that has been severely affected by wind–water erosion, shifts from arable land to forest or grasslands have been promoted since 1998, using both native and introduced vegetation. However, there is little knowledge of the ecological consequences and effectiveness of the vegetation restoration in the region. Therefore, relationships between watershed‐scale soil physical properties and plant recovery processes were analyzed. The results show that soil physical properties such as bulk density, hydraulic conductivity, mean weight diameter, and the stability of >1 mm macro‐aggregates have been significantly ameliorated in the 0–20 cm soil layer under secondary natural grasslands. In contrast, re‐vegetation with introduced species such as Caragana korshinskii or Medicago sativa had adversely affected the soil physical properties, probably due to the deterioration of soil water conditions and lower organic matter inputs resulting from severe erosion. Reductions in bulk density and increases in saturated hydraulic conductivity could be used as indicators of soil structure amelioration since they are closely related to most other measured properties. Practical considerations for future re‐vegetation projects are suggested, particularly that native species with lower water consumption rates than the introduced species should be used to avoid further soil degradation.  相似文献   

16.
Soil surface crusting, a common phenomenon on cultivated soils, has major implications for agriculture and the environment because of its effects on soil hydrological properties, erosion and crop establishment. The objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a Patancheru series soil (clayey skeletal, mixed, isohyperthermic Udic Rhodustalf) in south‐central India. Soil aggregates, obtained from cultivated (PL) and naturally vegetated fallow (NV) land, were packed into sample trays and subjected to laboratory rain simulation to form crusts. Thin sections and visual observation indicated that crust development reached a more advanced stage in the PL case compared with NV following 90 min of rain at 40–80 mm h−1 intensity. This was reflected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter. The hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on NV than on PL soil. The results suggested that NV soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable PL aggregates. A structural crust‐type formed on the Patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products, and raindrop compaction and particle rearrangement. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

17.
Fault gouges have been observed in the surface outcrops, in shallow excavations, and in deep (300 meters below the surface) tunnels and mines in fault zones. The 2-microns fractions in these fault gouges may compose a few percent to more than fifty percent of the total mass in the outcrops, and the mineralogy of the 2-microns fractions consists of a variety of clays (the common ones are montmorillonite, illite, kaolinite, chlorite, vermiculite and mixed-layer clays) and some quartz, feldspars, etc.Although we cannot yet conclude directly from the studies of gouges that similar gouges exist at depths where many large shallow earthquakes are generated, there is a strong possibility that they do, based on (1) available equilibrium data on various clays — for example, kaolinite has been found to exist at 4 kb and 375°C (±15°C) (Thompson, 1970) and montmorillonite + kaolite has been found to exist at 450°C and 4 kb (Velde, 1969); (2) the compatibility of laboratory velocity data in gouge (Wang et al., 1977) with those in a model for central California (Healy andPeake, 1975); (3) the capability of clays to undergo sudden earthquake-like displacements (Summers andByerlee, 1977); (4) the petrology of intrafault cataclastic rocks in old fault zones (Kasza, 1977); and (5) the compatibility of gouge mineralogy with the mineralogy of hydrothermal clay deposits.If clay gouges are indeed significant components of the fault zone at depth, then the mechanical properties of clays under confining pressures up to 4 kb are important in the behavior of faults. Very few experiments have been performed under such high pressures. But from the physical makeup of clays, we can infer that (1) the range of possible behavior includes stable sliding with vermiculite and montmorillonite (asByerlee andSummers, 1977, have proven) to stick-slip-like behavior with kaolinite, chlorite, etc.; (2) the absence or presence of water will greatly affect the strengths of gouges — it is possible that water may reduce the strength of gouge to a fairly small value.  相似文献   

18.
Steep erosion‐prone and vegetation‐free slopes are widespread in alpine areas and are often discussed since they have a high socio‐economic damage potential. We present an eco‐engineering approach to test whether a mycorrhizal inoculum improves the establishment of hedge brush layers and in turn soil structural stability on a steep, coarse‐grained vegetation‐free slope in the eastern Swiss Alps. We established (i) mycorrhizal and (ii) non‐mycorrhizal treated eco‐engineered research plots on a field experimental scale, covering a total area of approximately 1000 m2 on an east‐northeast (ENE) exposed slope, where many environmental parameters can be regarded as homogeneous. After a full vegetation period, we quantified soil aggregate stability, the formation of water stable aggregates and the fine‐root development. Our results illustrate that the establishment of brush layers without mycorrhizal inoculum increased aggregate stability significantly. Against our expectation and glasshouse experiments, the addition of mycorrhizal inoculum did not have a statistically significant effect after one vegetation period although it tended to increase aggregate stability. Analogously, root length density (RLD) tended to be higher at the non‐mycorrhizal treated site. Aggregate stability was significantly correlated with RLD. Studies on a bigger field experimental scale are inevitable, complement glasshouse studies and lead to a better understanding for a successful application of sustainable eco‐engineering measures in alpine environments. Based on our results and considering the fact that the response time in natural ecosystems may be slower than in laboratory approaches, we conclude that long‐term field studies are necessary to validate results gained through laboratory experiments. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Soil piping is a widespread land degradation process that may lead to gully formation. However, the processes involved in sediment detachment from soil pipe walls have not been well studied, although their recognition is a crucial step to protect soils from piping erosion. This study aims to recognize the factors affecting cohesion and to identify the mechanisms which are likely to be responsible for the disintegration of soil. The study has been conducted in mid-altitude mountains under a temperate climate (the Bieszczady Mountains, the Carpathians, SE Poland). The research was based on the detailed field and laboratory analyses of morphology, and the physical and chemical properties of soil profiles with and without soil pipes. Moreover, experiments with flooding the undisturbed soil samples using different solutions (deionized water, ammonium oxalate, dithionate citrate, 35% hydrochloric acid and 30% hydrogen peroxide) were conducted in order to check the role of air slaking, the removal of soil organic carbon (SOC), and Fe and Al oxides on sediment detachment. The obtained results have confirmed that soil pipes develop in quite cohesive soils (silt loams), which allow the formation and maintenance of pipes with a diameter up to 30 cm. Soil cohesion, and thus susceptibility to piping, are impacted by the content of major oxides, soil particle size distribution, biological activity and porosity. The tested soils affected by piping erosion have a lower content of Al2O3 and Fe2O3, and free Fe (Fe(DCB)), lower clay content, higher biological activity (more roots and animal burrows), higher porosity, and more and larger pores than the profile without soil pipes. The experiments have indicated that especially SOC along with Fe and Al oxides are an important cohesion source in the study area. This suggests that the removal of SOC, and Fe and Al oxides may weaken and disintegrate aggregates in soil pipes. Further study of soil leaching and tensile strength will broaden understanding of which chemical processes control where pipes will develop in other cohesive piping-prone soils. © 2020 John Wiley & Sons, Ltd.  相似文献   

20.
The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (C–Q) patterns. Hydrologists often use C–Q analyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping stream C–Q patterns. However, few C–Q studies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of important C–Q controls such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyse C–Q relations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x-ray diffraction and soil cation-extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact stream C–Q trends. We show that as groundwater age increases, C–Q slope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on stream C–Q highlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge.  相似文献   

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