Search

In streams, short‐term element‐specific solute fluxes are often not balanced with long‐term chemical weathering fluxes determined in the residual solids from fractional element loss and denudation rate. The ratio of both estimates—the "Dissolved Export Efficiency" (DEE)—is frequently <1, indicating deficits in the stream dissolved load. To explore the cause of the stream deficits, we performed a daily water sampling campaign for one year in a forested headwater watershed in Southern Germany. We sampled surface runoff, above‐canopy and below‐canopy precipitation, subsurface flow from the organic soil layer, upper, and deep mineral soil, and groundwater. Regolith samples were obtained from a drill core and revealed the weathering front to lie between 7 and 15 m depth. We found a DEE < 1 for K, Si, Al, Fe. These elements are characterized by shallow slopes in C‐Q relationships, and the imbalances were found to originate in the deep saprolite. Their export pathway potentially includes "hidden" Critical Zone compartments or fluxes, presumably unsampled colloids that are exported preferentially during rare flushing events with stochastic temporal distribution. The DEE of nutritive elements like Ca, Mg, and P is also <1. These elements are characterized by steeper C‐Q slopes, and their imbalance can be explained by deep nutrient uptake followed by nutrient retainment in re‐growing forest biomass or export in plant debris. The collective evidence for these imbalances, including previous evidence from metal stable isotopes, suggests that the deep Critical Zone represents the location for chemical or biogenic retention and release of solutes. Plain Language Summary: Mineral dissolution by chemical weathering produces solutes in the weathering zone that are eventually exported by streams. Yet, often an imbalance between element‐specific solute export fluxes in stream water and element‐specific chemical weathering fluxes determined from residual solids in the weathering zone is apparent. This imbalance is expressed as a deficit in the stream dissolved load. To explore the origin of this deficit, we performed a daily water sampling campaign for one year in a forested watershed in Southern Germany. We studied concentration‐discharge relationships and quantified solute fluxes in stream‐ and groundwater. A comparison of solute fluxes in stream water with chemical weathering fluxes integrating mineral dissolution over the whole weathering zone revealed indeed deficits in the stream dissolved load. These deficits originate in deep isovolumetrically weathered bedrock (saprolite). The elements K, Si, Al, and Fe, which show invariant concentration changes with increasing discharge, may follow a "hidden" export pathway involving colloids that are only mobilized and exported during rare flushing events that were missed during this study's sampling period. Deficits of nutrients (Ca, Mg, P), which show dilution behavior with increasing discharge, can be explained by deep nutrient uptake and retention in growing forest biomass or plant litter erosion. Key Points: Imbalances between short‐term and long‐term estimates of element‐specific chemical weathering fluxes (DEE < 1) emerge in deep saproliteElements with shallow C‐Q slopes showing chemostatic or enrichment behavior are likely exported in colloidal form during flushing eventsElements with steeper C‐Q slopes showing weak dilution behavior remain in re‐growing biomass or are exported in particulate biogenic form [ABSTRACT FROM AUTHOR]

Chemical weathering dynamics in Greenland Ice Sheet (GrIS) catchments are largely unknown, due to a scarcity of field data. This paper presents the most comprehensive study to date of chemical weathering rates from four GrIS catchments of contrasting size. Cationic denudation rates varied greatly between catchments studied (2.6–37.6 tons km–2 a–1, world mean = 11.9 tons km–2 a–1), but were of the same order of magnitude to the world non-glacial riverine mean, and are greater than those documented in some major temperate rivers catchments (e.g., Mississippi (1.3 tons km–2 a–1) and Nile (0.4 tons km–2 a–1) rivers). These high chemical denudation rates indicate that the GrIS is a potential source of solute to downstream environments. Dissolved silica yields, indicative of silicate weathering rates, also varied by an order of magnitude, with upper values similar to the world mean (0.2–3.8 tons km–2 a–1, world mean = 3.53 tons km–2 a–1). Elevated chemical weathering rates in GrIS catchments are strongly influenced by the specific discharge, which drives flushing of the subglacial environment and physical erosion of the ice sheet bed. The direct relationship between specific discharge and chemical denudation rates supports the hypothesis that GrIS chemical weathering rates and solute fluxes are likely to increase with enhanced melt rates in a warming climate.

Many regions have formed subsidence lakes due to underground mining in the world. However, seasonal variations of lacustrine groundwater discharge (LGD) rate and solute fluxes in the coal mining subsidence were rarely reported. In this study, we conducted four seasonal samplings in a coal mining subsidence, during which samples for stable water (δ 18 O) and radioactive ( 222 Rn) isotopes were collected to quantify the seasonal dynamics of LGD rates. The LGD rates estimated from the 222 Rn mass balance model were 10.2 ± 8.7, 5.5 ± 3.2, 11.5 ± 7.8, and 7.8 ± 4.5 mm d -1 in summer, autumn, winter and spring, respectively. According to the 18 O mass balance model, the corresponding LGD rates were 15.1, 7.3, 15.6, and 11.3 mm d -1 in summer, autumn, winter and spring, respectively. We found a significant correlation between precipitation and LGD rates, suggesting precipitation was recognized as the main control factor for seasonal variations of LGD rates. Based on this correlation, the extrapolated LGD rates over a year ranged from 3.1 to 12.7 mm d -1 with an average of 8.8 mm d -1 . Moreover, the fluxes of dissolved silicon (DSi), iron (Fe), and manganese (Mn) from LGD in autumn were (1.6 ± 0.9) × 10 5 , (1.9 ± 1.1) × 10 4 , and (1.1 ± 0.6) × 10 4  mol a -1 , respectively. Correspondingly, in winter they were (3.5 ± 2.4) × 10 5 , (4.1 ± 2.8) × 10 3 , and (2.8 ± 1.9) × 10 3  mol a -1 , respectively. This study demonstrated significantly seasonal variations of LGD, with precipitation being the main control factor of LGD in the coal mining subsidence lake. The fluxes of dissolved substance (DSi, Fe, Mn) from LGD need to be emphasized because they may have important impacts on the ecological stability in coal mining subsidence lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The ongoing loss of biodiversity and global environmental changes severely affect the structure of coastal ecosystems. Consequences, in terms of ecosystem functioning, are, however, difficult to predict because the context dependency of the biodiversity-ecosystem function relationships within these heterogeneous seascapes is poorly understood. To assess the effects of biological and environmental factors in mediating ecosystem functioning (nutrient cycling) in different natural habitats, intact sediment cores were collected at 18 sites on a grain size gradient from coarse sand to silt, with varying organic matter content and vegetation. To assess ecosystem functioning, solute fluxes (O2, NH4+, PO43−, Si) across the sediment-water interface were measured. The macrofaunal communities changed along the grain size gradient with higher abundance, biomass and number of species in coarser sediments and in habitats with more vegetation. Across the whole gradient, the macrofauna cumulatively accounted for 25% of the variability in the multivariate solute fluxes, whereas environmental variables cumulatively accounted for 20%. Only the biomass and abundance of a few of the most dominant macrofauna species, not the number of species, appeared to contribute significantly to the nutrient recycling processes. Closer analyses of different sediment types (grouped into coarse, medium and fine sediment) showed that the macrofauna was an important predictor in all sediment types, but had the largest impact in fine and medium sediments. The results imply that even if the ecosystem functioning is similar in different sediment types, the underpinning mechanisms are different, which makes it challenging to generalize patterns of functioning across the heterogeneous shallow coastal zones. [ABSTRACT FROM AUTHOR]

A negative feedback between silicate weathering rates and climate is hypothesized to play a central role in moderating atmospheric CO 2 concentrations on geologic timescales. However, uncertainty regarding the processes that regulate the operation of the negative feedback limits our ability to interpret past variations in the ocean–atmosphere carbon cycle. In particular, the mechanisms that determine the flux of weathered material for a given climatic state are still poorly understood. Here, we quantify the processes that determine catchment-scale solute fluxes for two lithologic end-members—basalt and granite—by applying a recently developed solute production model that links weathering fluxes to both discharge and the reactivity of the weathering material. We evaluate the model against long-term monitoring of concentration–discharge relationships from basaltic and granitic catchments to determine the parameters associated with solute production in each catchment. Higher weathering rates in basaltic catchments relative to granitic catchments are driven by differing responses to increases in runoff, with basaltic catchments showing less dilution with increasing runoff. In addition, results from the solute production model suggest that thermodynamic constraints on weathering reactions could explain higher concentrations in basaltic catchments at lower runoff compared to granitic catchments. To understand how the response to changing discharge controls weathering fluxes under different climatic states, we define basalt/granite weatherability as the ratio of the basalt catchment flux to the granite catchment flux. This weatherability is runoff-dependent and increases with increasing runoff. For HCO 3 − and SiO 2 (aq) fluxes, for modern global runoff, the derived mean basalt/granite weatherability is 2.2 (1.3–3.7, 2 σ ) and 1.7 (1.6–2.1, 2 σ ), respectively. Although we cannot determine the array of individual processes resulting in differences among catchments, the relative differences in certain model parameters that represent catchment-scale weathering fluxes of granitic and basaltic lithologies are robust. Our approach provides a mechanism that links runoff with the distribution of global sub-aerial silicate lithologies to understand how the basalt/granite weatherability of the Earth’s surface may have varied on geologic timescales. The relationships between basalt/granite weatherability and runoff derived in this study could be used to parameterize the silicate weathering negative feedback to model past changes in p CO 2 . [ABSTRACT FROM AUTHOR]

Headwaters are a source of fresh water and material transported to the downstream sections of river channels. In most regions of Europe, the natural environment of headwaters has been significantly transformed by human activities, which is reflected in the quality of surface waters and the rate of solute fluxes. The aim of the study was to determine the anthropogenic impact on solute fluxes in a headwater catchment in Germany. The study area (Wüstebach experimental catchment) is located in the Eifel Mountains and is part of the TERENO (Terrestrial Environmental Observatories) network. The catchment is currently subject to the following anthropogenic pressures: the use of de-icing salts on the motorway running through the catchment and the logging of 22% of the forest area in 2013 by the National Park to promote the regeneration of near-natural beech forest. We used data from almost 13 years (June 2009-April 2022) of environmental monitoring in the Wüstebach catchment to calculate monthly and annual rates of solute fluxes. The concentrations of ions in stream water and precipitation were determined: Ca2+, Mg2+, Na+, K+, Al3+, Fetot, Mn2+, NH4+, NO3−, SO4−, and Cl−. Data from the Wüstebach catchment were compared with data from the control (untreated) catchment. The average annual rate of total dissolved solids in the Wüstebach catchment was 83 t/km2/a. Only the loads of four ions performed a significant difference after deforestation (SO4−, NH4+, Al3+, Fetot). However, total dissolved solids and loads of most of the ions did not show any significant differences after deforestation, which indicates a slight impact of logging on the chemical denudation. This resulted from the limited soil erosion that followed deforestation as the soil was well protected during logging works by covering harvester lanes with branches. However, there is a significant impact of road salting on the solute fluxes in the headwater catchment. Assuming that the control catchment is not affected by using de-icing salts, the road salting inputs in the Wüstebach catchment calculated based on the precipitation share for Na+, Ca2+, Mg2+, K+, and Cl− ions were, on average, 88%, 53%, 18%, 53%, and 90%, respectively, of the original ion loads. The input with road salting was so large that elevated concentrations of Na+ and Cl− were noted throughout the study period with slight seasonal fluctuations. This proves the subsurface build-up of salt due to the long-term application of de-icing salt. Without the input of de-icing salts, the average annual rate of chemical denudation in the catchment would be about 19 t/km2/a. Thus, on average, this ion storage effect in the soil has increased the total dissolved solids rate by 62%. In summary, it can be concluded that long-term intensive road salting in winter has a greater impact on the solute fluxes than the clear-cut of 22% of the catchment area. [ABSTRACT FROM AUTHOR]

Ebeko volcano at the northern part of Paramushir Island in the Kuril island arc produces frequent phreatic eruptions and relatively strong fumarolic activity at the summit area ~ 1000 m above sea level (asl). The fumaroles are characterized by low-temperature, HCl- and S-rich gas and numerous hyper-acid pools (pH < 1) without drains. At ~ 550 m asl, in the Yurieva stream canyon, many hot (up to 87 °C) springs discharge ultra-acidic (pH 1–2) SO 4 –Cl water into the stream and finally into the Sea of Okhotsk. During quiescent stages of degassing, these fumaroles emit 1000–2000 t/d of water vapor, < 20 t/d of SO 2 and < 5 t/d of HCl. The measurement of acidic hot Yurieva springs shows that the flux of Cl and S, 60–80 t/d each, is independent on the volcanic activity in the last two decades. Such high flux of Cl is among the highest ever measured in a volcano–hydrothermal system. Oxygen and hydrogen isotopic composition of water and Cl concentration for Yurieva springs show an excellent positive correlation, indicating a mixing between meteoric water and magmatic vapor. In contrast, volcanic gas condensates of Ebeko fumaroles do not show a simple mixing trend but rather a complicated data suggesting evaporation of the acidic brine. Temperatures calculated from gas compositions and isotope data are similar, ranging from 150 to 250 °C, which is consistent with the presence of a liquid aquifer below the Ebeko fumarolic fields. Saturation indices of non-silicate minerals suggest temperatures ranging from 150 to 200 °C for Yurieva springs. Trace elements (including REE) and Sr isotope composition suggest congruent dissolution of the Ebeko volcanic rocks by acidic waters. Waters of Yurieva springs and waters of the summit thermal fields (including volcanic gas condensates) are different in Cl/SO 4 ratios and isotopic compositions, suggesting complicated boiling–condensation–mixing processes. [ABSTRACT FROM AUTHOR]

Mineral waters were monthly sampled in selected springs from Furnas and Fogo trachytic central volcanoes (São Miguel, Azores, Portugal). Water temperatures between 15.1°C and 90.2°C, characterize poorly mineralized waters of Na–HCO3 and Na–HCO3–Cl types. According to the spring location, two watersheds were selected in each volcano to evaluate solute fluxes and chemical weathering rates (Fogo volcano: Ribeira Grande river — RRG; Furnas volcano: Ribeira Quente river — RRQ). Na, Mg, K and Ca fluxes in groundwater represented 43%, 60%, 46% and 57% of the total (subsurface plus surface fluxes) in RRG, and respectively 43%, 53%, 46% and 49% in RRQ. Average HCO3 flux is ten times higher in RRQ (130.1×106 mol/yr) compared to RRG (13.8×106 mol/yr), reflecting the volcano degassing and the lower ratio between groundwater and river water fluxes. Based on these values, total CO2-consumption by weathering ranged from 1.5×106 mol/km2/yr (RRG) to 4×106 mol/km2/yr (RRQ). TDS load varied between 3772t/yr (RRG) and 15388t/yr (RRQ), and the ratio between values in groundwater and in surface water is respectively equal to 0.72 and 2.04. The associated chemical weathering rates in groundwater were 206t/km2/yr (RRG) and 399t/km2/yr (RRQ). Coupled to river water, these values indicate that total chemical weathering rates are respectively equal to 493t/km2/yr and 594t/km2/yr. A similar approach developed for the entire archipelago showed that the chemical weathering rates due to groundwater are in the range from 33 to 321t/km2/yr, being partially controlled by the age of the islands. Results of the present study point out to the need to consider groundwater solute fluxes due to weathering when establishing geochemical budgets. [ABSTRACT FROM AUTHOR]

Hydrochemical characteristics and solute dynamics of bulk meltwater draining from Urumqi Glacier No.1 were investigated in years 2006 and 2007. The glacial meltwater was slightly alkaline with the mean pH of 7.64 and 7.61 in 2006 and 2007, respectively. In the meltwater, the dominant anions were the bicarbonate and sulphate, and the dominant cation was calcium. The concentration of major cations were varied as c(Ca) > c(Mg) > c(K) > c(Na), while the order for the cations was c(HCO) > c(SO) > c(NO) > c(Cl). The total dissolved solids (TDS) in meltwater had inverse relationships with the diurnal discharge. The major ion composition of meltwater was mainly controlled by rock weathering as inferred from the Gibbs model. Furthermore, the ion ratios and Piper diagram indicated that the main processes controlling the meltwater chemistry were carbonate weathering, pyrite weathering and feldspar weathering in rocks, and Ca and HCO were the dominant ions during the carbonate weathering process. Solute flux calculation at Glacier No.1 station suggested that chemical denudation rates were 11.46 and 13.90 ton·km·yr in 2006 and 2007, respectively. [ABSTRACT FROM AUTHOR]

It has been proposed that in the absence of blood supply, the ocular lens operates an internal microcirculation system that delivers nutrients to internalized fiber cells faster and more efficiently than would occur by passive diffusion alone. To visualize the extracellular space solute fluxes potentially generated by this system, bovine lenses were organ cultured in artificial aqueous humor (AAH) for 4 h in the presence or absence of two gadolinium-based contrast agents, ionic Gd3+, or a chelated form of Gd3+, Gd-diethylenetriamine penta-acetic acid (Gd- DTPA; mol mass = 590 Da). Contrast reagent penetration into the lens core was monitored in real time using inversion recovery-spin echo (IR-SE) magnetic resonance imaging (MRI), while steady-state accumulation of [Gd-DTPA]-2 was also determined by calculating T1 values. After incubation, lenses were fixed and cryosectioned, and sections were labeled with the membrane marker wheat germ agglutinin (WGA). Sections were imaged by confocal microscopy using standard and reflectance imaging modalities to visualize the fluorescent WGA label and gadolinium reagents, respectively. Real-time IR-SE MRI showed rapid penetration of Gd3+ into the outer cortex of the lens and a subsequent bloom of signal in the core. These two areas of signal were separated by an area in the inner cortex that limited entry of Gd3+. Similar results were obtained for Gd-DTPA, but the penetration of the larger negatively charged molecule into the core could only be detected by calculating T1 values. The presence of Gd-DTPA in the extracellular space of the outer cortex and core, but its apparent absence from the inner cortex was confirmed using reflectance imaging of equatorial sections. In axial sections, Gd-DTPA was associated with the sutures, suggesting these structures provide a pathway from the surface, across the inner cortex barrier to the lens core. Our studies have revealed inner and outer boundaries of a zone within which a narrowing of the extracellular space restricts solute diffusion and acts to direct fluxes into the lens core via the sutures. [ABSTRACT FROM AUTHOR]

The southwestern coast of India is drained by many small rivers with lengths less than 250 km and catchment areas less than 6,500 km. These rivers are perennial and are also the major drinking water sources in the region. But, the fast pace of urbanization, industrialization, fertilizer intensive agricultural activities and rise in pilgrim tourism in the past four to five decades have imposed marked changes in water quality and solute fluxes of many of these rivers. The problems have aggravated further due to leaching of ionic constituents from the organic-rich (peaty) impervious sub-surface layers that are exposed due to channel incision resulting from indiscriminate instream mining for construction-grade sand and gravel. In this context, an attempt has been made here to evaluate the water quality and the net nutrient flux of one of the important rivers in the southwestern coast of India, the Manimala river which has a length of about 90 km and catchment area of 847 km. The river exhibits seasonal variation in most of the water quality parameters (pH, electrical conductivity, dissolved oxygen, total dissolved solids, Ca, Mg, Na, K, Fe, HCO, NO-N, NO-N, P $_{\rm \text{-}inorg}$, P $_{\rm \text{-}tot}$, chloride, SO, and SiO). Except for NO-N and SiO, all the other parameters are generally enriched in non-monsoon (December-May) samples than that of monsoon (June-November). The flux estimation reveals that the Manimala river transports an amount of 2,308 t y of dissolved inorganic nitrogen, 87 t y dissolved inorganic phosphorus, and 9246 t y of SO, and 1984 t y K into the receiving coastal waters. These together constitute about 23% of the total dissolved fluxes transported by the Manimala river. Based on the study, a set of mitigation measures are also suggested to improve the overall water quality of small catchment rivers of the densely populated tropics in general and the south western coast in particular. [ABSTRACT FROM AUTHOR]

Abstract: The role of fluid residence time and catchment length scales in controlling the chemical composition of rivers is evaluated by comparing numerical simulations and scaling arguments to concentration–discharge data from small catchments. The analysis suggests that poorly-crystalline aluminosilicates are an important control on the composition of stream waters and therefore chemical equilibrium between the dissolving and precipitating phases determines the maximum concentration and the maximum silicate weathering flux. The modeling results suggest that the residence time of fluid relative to the residence time required to approach chemical equilibrium can be used to assess the controls on solute fluxes in small catchments, and possibly larger rivers. Catchments that show little variability in concentration with discharge (or “chemostatic behavior”) likely have average fluid residence times that exceed the time required to reach chemical equilibrium. Conversely, decreases in concentration with increasing discharge are explained by average residence times shorter than required to approach chemical equilibrium, resulting in dilution. Solute fluxes are also strongly impacted by the distribution of fluid residence times in a basin. The fluid residence time model provides an alternative framework for assessing both the relationship between discharge and concentration observed for individual catchments, and controls on the solute fluxes of rivers. If fluid residence times are a dominant control on weathering fluxes, the chemistry of different rivers could vary entirely as a function of the nature subsurface flow paths and the composition of the system at equilibrium, which is complex to predict and strongly coupled to biological processes, temperature and the composition of the system. As a result of thermodynamic and hydrologic restrictions on the amount of weathering, global solute fluxes may depend more strongly on the geometry, relief, runoff and permeability of basins then on temperature and rates of erosion. [Copyright &y& Elsevier]

Abstract: The effects of short term hypoxia on bioturbation activity and inherent solute fluxes are scarcely investigated even if increasing number of coastal areas are subjected to transient oxygen deficits. In this work dark fluxes of oxygen (O2), dissolved inorganic carbon (TCO2) and nutrients across the sediment–water interface, as well as rates of denitrification (isotope pairing), were measured in intact sediment cores collected from the dystrophic pond of Sali e Pauli (Sardinia, Italy). Sediments were incubated at 100, 70, 40 and 10% of O2 saturation in the overlying water, with both natural benthic communities, dominated by the polychaete Polydora ciliata (11.100±2.500 ind.m−2), and after the addition of individuals of the deep-burrower polychaete Hediste diversicolor. Below an uppermost oxic layer of ~1mm, sediments were highly reduced, with up to 6mM of S2− in the 5mm layer. Flux of S2− and O2 calculated from pore water gradients were 8.61±1.12 and −2.27±0.56mmolm−2 h−1, respectively. However, sediment oxygen demand (SOD) calculated from core incubation was −10.52±0.33mmolm−2 h−1, suggesting a major contribution of P. ciliata to O2-mediated sulphide oxidation. P. ciliata also strongly stimulated NH4 + and PO4 3− fluxes, with rates ~15 and ~30 folds higher, respectively, than those estimated from pore water gradients. P. ciliata activity was significantly reduced at 10% O2 saturation, coupled to decreased rates of solutes transfer. The addition of H. diversicolor further stimulated SOD, NH4 + efflux and SiO2 mobilisation. Similarly to P. ciliata, the degree of stimulation of SOD and NH4 + flux by H. diversicolor depended on the level of oxygen saturation. TCO2 regeneration, respiratory quotients, PO4 3− fluxes and denitrification of added 15NO3 − were not affected by the addition of H. diversicolor, but depended upon the O2 levels in the water column. Denitrification rates supported by water column 14NO3 − and sedimentary nitrification were both negligible (<0.5µmolm−2 h−1). They were not significantly affected by oxygen saturation nor by bioturbation, probably due to the limited availability of NO3 − in the water column (<3µM) and O2 in the sediments. This study demonstrates for the first time the integrated short term effect of transient hypoxia and bioturbation on solute fluxes across the sediment–water interface within a simplified lagoonal benthic community. [Copyright &y& Elsevier]

Summary: Solute fluxes and transient carbon dioxide drawdown in a small glacierized basin investigated on Svalbard in 2002 are presented. It was a sample year within a period of significant climate warming in the Arctic. Discharge was recorded in the Scottbreen Basin (10.1km2), Bellsund Fjord, between July 8 and September 10, 2002. Specific runoff for this period was 0.784m, 22% more than the mean for 1986–2001. The runoff for all of 2002 (i.e. the hydrologic year) was estimated by comparison with Bayelva, the only glacial river with longer records on Svalbard. The specific runoff for 2002 was ∼1.228m, yielding crustal solute fluxes of 69.4tkm−2 yr−1 (25.8m3 km−2 yr−1). This rate is the highest chemical denudation rate reported from glacierized basins on Svalbard, and it may be underestimated because higher solute fluxes at the beginning of the melt season were not taken into account. Crustal fluxes in the fall may also have been higher because it is probable that crustal ion concentrations were increasing after recording stopped in September. The cation denudation rate was 1213∑meq+ m−2 yr−1 and the mean annual crustal ion concentration derived from it amounted to 981μeqL−1. Transient CO2 drawdown in 2002 was 5242kgCkm−2 yr−1. Most of the carbon dioxide was removed in the summer ablation waters, estimated CO2 drawdown in the fall being only 13% of the total. Comparison with crustal solute fluxes (CSF) computed from specific conductivity in the 1980s and 1990s suggests that earlier fluxes may have been overestimated by around 19%. Comparing earlier data with the 2002 rates may confirm the influence of climate warming on increasing chemical denudation rates. It was also found that a globally derived equation relating specific conductivity to concentrations of dissolved limestone in water gave estimates of the crustal solute fluxes that were only 1.1% less than those obtained via comprehensive chemical analyses of waters and ion partitioning procedures. [Copyright &y& Elsevier]

Abstract: In a small mountain stream (Erlenbach, Alptal, central Switzerland), water samples were taken during 15 years by two different methods: weekly-bulked, discharge-proportional sampling and fortnightly grab (instantaneous) sampling. Compared with continuous, in-stream measurements of the electrical conductivity, the discharge-proportional sampling proved to give very accurate and precise estimates of solute fluxes. Relatively to discharge-proportional samples, integration methods based on the grab samples resulted in more or less biased fluxes of: Ca, Mg, K, Na , Cl−, and electrical conductivity. Unweighted means were all positively biased due to concentrations decreasing with the discharge. Means weighted by discharges averaged fortnightly were less positively biased. On the other hand, weighing by the instantaneous discharge gave negative biases. Fluxes calculated from regressions of concentrations against discharge were also negatively biased, but the accuracy could partly be improved by including further factors into the regressions, especially the seasonality. If both grab and discharge-proportional samples are taken in parallel for some time, it is possible to calibrate the fluxes calculated from the first against the second. Calibration periods of 1–7 years were tested and found to improve the accuracy in 8 other years used for validation. Five years were sufficient to achieve unbiased regression estimates and a precision better than 10%. Replacing a less accurate grab sampling scheme by a discharge-proportional sampling should thus be done with a transition period during which both methods are run in parallel, 5 years being advisable for most solutes and for small streams. [Copyright &y& Elsevier]

Because of their fast response to hydrological events, small catchments show strong quantitative and qualitative variations in their water runoff. Fluxes of solutes or suspended material can be estimated from water samples only if an appropriate sampling scheme is used. We used continuous in‐stream measurements of the electrical conductivity of the runoff in a small subalpine catchment (64 ha) in central Switzerland and in a very small (0·16 ha) subcatchment. Different sampling and flux integration methods were simulated for weekly water analyses. Fluxes calculated directly from grab samples are strongly biased towards high conductivities observed at low discharges. Several regressions and weighted averages have been proposed to correct for this bias. Their accuracy and precision are better, but none of these integration methods gives a consistently low bias and a low residual error. Different methods of peak sampling were also tested. Like regressions, they produce important residual errors and their bias is variable. This variability (both between methods and between catchments) does not allow one to tell a priori which sampling scheme and integration method would be more accurate. Only discharge‐proportional sampling methods were found to give essentially unbiased flux estimates. Programmed samplers with a fraction collector allow for a proportional pooling and are appropriate for short‐term studies. For long‐term monitoring or experiments, sampling at a frequency proportional to the discharge appears to be the best way to obtain accurate and precise flux estimates. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACTOrobanche species are holoparasites which are very efficient sinks for host-derived solutes. Here, we report the use of direct measurements of xylem sap solute concentrations and water fluxes, together with a modelling procedure to calculate element fluxes within an association between Orobanche cernua and its tobacco host. Infection of tobacco by the parasite markedly influenced carbon acquisition and partitioning; net fixation of carbon was 20% higher in infected tobacco compared with controls. Orobanche cernua caused a 84% increase in net carbon flux moving downward from the tobacco shoot and 73% of this carbon was intercepted by the parasite, almost entirely through the phloem (>99%). Further, the parasite also exerted a large impact on the nitrogen relations of the plant, notably nitrate uptake was stimulated and the amino acid content of xylem sap was lower. The parasite also relied heavily on host phloem for the supply of other resources, with only 5 to 15% of N, and 16% of K, 23% of Na, 63% of Mg and 13% of S being derived from the xylem. Thus, we provide quantitative information on the phloem dependency of the parasite and show that host carbon and nitrogen metabolism is stimulated as a consequence of infection. [ABSTRACT FROM AUTHOR]