Sensitivity of coastal waters to anthropogenic trace metal emissions

Trace metal concentrations in the waters of the Gulf of St. Lawrence and the Scotian Shelf and their sensitivity to changes in the composition of the major contributor of fresh water, the St. Lawrence River, are assessed. Comparison of the levels of trace metals in eastern Canadian coastal waters with those in other coastal waters of the world reveals that the former area generally has lower trace metal concentrations and is, therefore, probably less contaminated than elsewhere. The increased anthropogenic activity in the St. Lawrence drainage basin required to increase the levels of trace metals in receiving coastal waters by detectable amounts is discussed. We demonstrate that faster and more reliable warning of changes due to anthropogenic activity will be revealed through river monitoring than through monitoring of coastal waters. Changes in the marine environment can then be assessed through a thorough understanding of the geochemical behaviour of trace metals in nearshore waters.     

Effect of basin physical characteristics on solute fluxes in nine alpine/subalpine basins,Colorado, USA

Alpine/subalpine basins may exhibit substantial variability in solute fluxes despite many apparent similarities in basin characteristics. An evaluation of controls on spatial patterns in solute fluxes may allow development of predictive tools for assessing basin sensitivity to outside perturbations such as climate change or deposition of atmospheric pollutants. Relationships between basin physical characteristics, determined from geographical information system (GIS) tools, and solute fluxes and mineral weathering rates were explored for nine alpine/subalpine basins in Rocky Mountain National Park, Colorado, using correlation analyses for 1993 and 1994 data. Stream‐water nitrate fluxes were correlated positively with basin characteristics associated with the talus environment; i.e., the fractional amounts of steep slopes (≥ 30°), unvegetated terrain and young debris (primarily Holocene till) in the basins, and were correlated negatively with fractional amounts of subalpine meadow terrain. Correlations with nitrate indicate the importance of the talus environment in promoting nitrate flux and the mitigating effect of areas with established vegetation, such as subalpine meadows. Total mineral weathering rates for the basins ranged from about 300 to 600 mol ha^?1 year^?1. Oligoclase weathering accounted for 30 to 73% of the total mineral weathering flux, and was positively correlated with the amount of old debris (primarily Pleistocene glacial till) in the basins. Although calcite is found in trace amounts in bedrock, calcite weathering accounted for up to 44% of the total mineral weathering flux. Calcite was strongly correlated with steep slope, unvegetated terrain, and young debris—probably because physical weathering in steep‐gradient areas exposes fresh mineral surfaces that contain calcite for chemical weathering. Oligoclase and calcite weathering are the dominant sources of alkalinity in the basins. However, atmospherically deposited acids consume much of the alkalinity generated by weathering of calcite and other minerals in the talus environment. Published in 2001 by John Wiley & Sons, Ltd.     

After the peak water: the increasing influence of rock glaciers on alpine river systems

Human‐accelerated climate change is quickly leading to glacier‐free mountains, with consequences for the ecology and hydrology of alpine river systems. Water origin (i.e., glacier, snowmelt, precipitation, and groundwater) is a key control on multiple facets of alpine stream ecosystems, because it drives the physico‐chemical template of the habitat in which ecological communities reside and interact and ecosystem processes occur. Accordingly, distinct alpine stream types and associated communities have been identified. However, unlike streams fed by glaciers (i.e., kryal), groundwater (i.e., krenal), and snowmelt/precipitation (i.e., rhithral), those fed by rock glaciers are still poorly documented. We characterized the physical and chemical features of these streams and investigated the influence of rock glaciers on the habitat template of alpine river networks. We analysed two subcatchments in a deglaciating area of the Central European Alps, where rock glacier‐fed, groundwater‐fed, and glacier‐fed streams are all present. We monitored the spatial, seasonal, and diel variability of physical conditions (i.e., water temperature, turbidity, channel stability, and discharge) and chemical variables (electrical conductivity, major ions, and trace element concentrations) during the snowmelt, glacier ablation, and flow recession periods of two consecutive years. We observed distinct physical and chemical conditions and seasonal responses for the different stream types. Rock glacial streams were characterized by very low and constant water temperatures, stable channels, clear waters, and high concentrations of ions and trace elements that increased as summer progressed. Furthermore, one rock glacier strongly influenced the habitat template of downstream waters due to high solute export, especially in late summer under increased permafrost thaw. Given their unique set of environmental conditions, we suggest that streams fed by thawing rock glaciers are distinct river habitats that differ from those normally classified for alpine streams. Rock glaciers may become increasingly important in shaping the hydroecology of alpine river systems under continued deglaciation.     

Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia

The crater lake of Kawah Ijen volcano contains extremely low pH (<0.4) waters with high SO₄ (70000 mg/kg), Cl (21000 mg/kg), F (1500 mg/kg), Al (5000 mg/kg), Fe (2000 mg/kg) and trace metal (Cu 0.5, Zn 4, Pb 3 mg/kg) contents. These brines seep outward through the western crater rim and reappear on the other side as streamlets, which form the headwaters of the Banyupahit stream. The Banyupahit first mixes with fresh rivers and thermal springs in the Ijen caldera and then irrigates a coastal agricultural plain which is 30 km from the summit crater.We discuss the downstream composition changes affecting the Banyupahit waters by using stable isotope, chemical and mineralogical data collected from sites along the stream length. The saturation of the stream waters with respect to minerals was evaluated with SOLVEQ and WATEQ4F and compared with the geochemical observations. An aluminous mineralogy (alunogen, pickeringite, tamarugite and kalinite) develops in the upper part of the Banyupahit due to concentration of the headwaters by evaporation. Downstream attenuation of dissolved element concentrations results principally from dilution and from mineral precipitation. The stream pH changes from 0 at the source to >4 close to the mouth. The δD and δ¹⁸O values and the relative SO₄–Cl–F contents of the Banyupahit waters indicate that the tributaries are mostly meteoric. Dissolved SO₄ in the acidic stream come only from the crater lake seepages and are not involved later in microbially mediated reactions, as shown by their δ³⁴S and δ¹⁸O values. Re-equilibration of the stream SO₄ oxygen-isotope composition with H₂O from tributaries does not occur.Calcium, SiO₂, Al, Fe, K and SO₄ behave non-conservatively in the stream waters. Gypsum, silica (amorphous or poorly ordered), a basic aluminum hydroxysulfate (basaluminite?), K-jarosite and amorphous ferric hydroxide may exert a solubility control on these elements along the entire stream length, or in certain stream sections, consistent with the thermochemical model results. Downstream concentration trends and mineral saturation levels suggest that precipitation of Sr-, Pb-rich barite and celestite consume Ba, Sr and Pb, whereas dissolved Cu, Pb and Zn may adsorb onto solid particles, especially after the junctions of the acidic stream with non-acidic rivers. We calculated that significant fluxes of SO₄, F, Cl, Al, SiO₂, Ti, Mn and Cu may reach the irrigation system, possibly causing serious environmental impacts such as soil acidification and induration.     

Temporal and spatial variability of cation and silica export in an alpine watershed,Emerald Lake,California

A reaction set of possible mineral weathering reactions is proposed to explain observed cation and silica export for the Emerald Lake watershed, a small Sierra Nevada, California catchment. The reaction set was calculated through a stoichiometric mole‐balance method, using a multiyear record of stream flow and snowpack chemical analyses and site‐specific mineral compositions. Reaction‐set calculations were intended to explore how the processes controlling stream cation and silica export depend on differing bedrock mineralogy across the catchment as snowmelt and runoff patterns change over the year. Different regions within the watershed can be differentiated by lake inflow subdrainages, each exhibiting different stream‐flow chemistry and calculated weathering stoichiometry, indicating that different silica and cation generation processes are dominant in wet steep portions of the catchment. Short‐term differences in stream concentrations were assumed to reflect ion exchange equilibria and rapid biological processes, whereas long‐term persistent stream concentration differences in different areas of the catchment were assumed to reflect spatial variability in mineral weathering stoichiometry. Mineralogical analyses of rock samples from the watershed provided site‐specific chemical compositions of major mineral species for reaction calculations. Reaction sets were evaluated by linear regression of calculated versus observed differences between snowmelt and stream‐flow chemistry and by a combined measure. Initially, single weathering reactions were balanced and evaluated to determine the reactions that best explained observed stream chemical export. Next, reactions were combined, using mineral compositions from different rock types to estimate the dependence of ion fluxes on lithology. The seasonal variability of major solute calculated fluxes is low, approximately one order of magnitude, relative to the observed three orders of magnitude variability in basin discharge. Reaction sets using basin‐averaged lithology and Aplite lithologies gave superior explanations of stream chemical composition. Copyright © 2004 John Wiley & Sons, Ltd.     

Diel stream geochemistry,Taylor Valley,Antarctica

Unlike temperate and polythermal proglacial streams, the proglacial streams in Taylor Valley (TV), Antarctica, are derived primarily from glacier surface melt with no subglacial or groundwater additions. Solute responses to flow reflect only the interaction of glacial meltwater with the valley floor surrounding the stream channel. We have investigated the major, minor and trace element 24‐h variations of two proglacial melt streams, Andersen Creek and Canada Stream, originating from the Canada Glacier in TV, Antarctica. Both streams exhibited diel mid‐austral summer diurnal flow variation, with maximum flow being more than 50 times the minimum flow. Dissolved (< 0.4 µm) major, minor and trace solute behaviors through diel periods were strongly controlled by the availability of readily solubilized material on the valley floor and hyporheic‐biological exchanges. Anderson Creek had generally greater solute concentrations than Canada Stream because of its greater receipt of eolian sediment. Andersen Creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb because of dissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic‐biological exchange. Conversely, Canada Stream had less available eolian sediment, but a greater hyporheic‐biological exchange, which preferentially removed trace and major solutes in the rising limb and released them in the falling limb. Given the dynamic nature of discharge, eolian, and hyporheic‐biological processes, solute loads in TV streams are difficult to predict. Copyright © 2012 John Wiley & Sons, Ltd.     

Heavy metals in particulate and colloidal matter from atmospheric deposition of urban Guangzhou,South China

Suspended particulate matter (SPM) and colloidal matter (COM) in annual dry and wet deposition samples in urban Guangzhou were for the first time collected, and their trace metals were investigated by using inductively coupled plasma mass spectrometry (ICP-MS). The deposition flux of SPM and of metal elements varied largely among the investigated seasons, and reached the maximum in spring. The correlation analysis indicated that significant correlations existed among some of the metal elements in the deposition samples. The enrichment factors (EF) of metals in COM in the deposition ranging from 79.66 to 130,000 were much higher than those of SPM ranging from 1.65 to 286.48, indicating the important role of COM. The factor analysis showed that emissions from street dust, non-ferrous metal production, and heavy fuel oil were major sources of the trace metals. Positive matrix factorization (PMF) model was used to quantitatively estimate anthropogenic source.     

Role of sediment in solute acquisition in the Himalayan glacier meltwater stream,Gangotri glacier,Uttarakhand, India

Low temperature in-stream solute acquisition in a glacial environment with very high suspended sediment is critical for downstream evolution of water chemistry. Present work is carried out on 18 km headwater reach from Gomukh (snout of the Gangotri glacier) to Gangotri along River Bhagirathi, India for understanding the hydrological processes controlling the solute acquisition in the glacial environment. This is the first attempt to conduct dissolution experiments with river bed sediments and meltwater considering different operating variables namely; contact time, seasonality, different sediment particle sizes, different sediment dose, effect of pH, wetting and crushing of bed sediments of the glacial stream. The role of sediment in low temperature solute acquisition process is characterized by sudden release of ions from the sediment in initial few seconds. Equilibrium time was observed to be 600 s (10 min). Further progressive increase in EC was observed from Gomukh to Gangotri, suggesting change in sediment surface characteristics/or source. Higher dissolution was observed from the bed sediments collected in June. It is found that the dissolution increases with increase in sediment doses but decreases with an increase in sediment particle size fraction. Higher solute acquisition was observed from crushed sediment because of an abundance of very fine particles having fresh, aggressive/reactive mineral surfaces which are capable of dissolution. The solute released from wetted sediment is significantly lower than the fresh sediment, which may be attributed to the destruction of microparticles adhering to mineral grains, the removal of fresh reactive surface sites, dissolution of rapidly weathered minerals such as calcite and evolution towards to equilibrium of the solution. Further, higher dissolution was observed with decrease in pH, which may be attributed to the availability of more hydrogen ion concentration of the solution, which favours more solute acquisition from sediment into meltwater.     

Contribution to the study of thermal waters in Greece: chemical patterns and origin of thermal water in the thermal springs of Lesvos

The occurrence of thermal/spa waters on Lesvos Island is related to the presence of a major faulting system. Thermal waters are the result of mixing of meteoric and infiltrating seawater at great depth, and their total salinity depends on the percentage of seawater in their composition. According to the diagrams of main elements, trace elements and environmental isotopes, most of the components that determine the chemical composition of thermal waters such as sodium, chloride and sulphates originate from seawaters. On the other hand, the concentration of calcium, magnesium, boron, lithium, etc., was affected by water–rock interaction under high temperature conditions. Moving towards the surface, thermal waters may become polluted by influx of recent seawater, allowing their chemical composition to become similar to that of seawater. The thermal waters of Lesvos Island present relatively high concentrations of ammonia and redox sensitive metals because they are hosted in a reducing environment. They also exhibit low nitrate concentrations due to their mixture with recent fresh water. Finally, they show increased radon concentrations, ranging from 20 to 60 kBq m^?3 in the eastern and southern parts of the island, and about 230 kBq m^?3 in the north, in the area of Eftalou–Argenos. Copyright © 2007 John Wiley & Sons, Ltd.     

Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.     

Evaluating the hydrological and hydrochemical responses of a High Arctic catchment during an exceptionally warm summer

The Arctic has experienced substantial warming during the past century with models projecting continued warming accompanied by increases in summer precipitation for most regions. A key impact of increasing air surface temperatures is the deepening of the active layer, which is expected to alter hydrological processes and pathways. The aim of this study was to determine how one of the warmest and wettest summers in the past decade at a High Arctic watershed impacted water infiltration and storage in deeply thawed soil and solute concentrations in stream runoff during the thaw period. In June and July 2012 at the Cape Bounty Watershed Observatory, we combined active layer measurements with major ion concentrations and stable isotopes in surface waters to characterize the movement of different runoff sources: snowmelt, rainfall, and soil water. Results indicate that deep ground thaw enhanced the storage of infiltrated water following rainfall. Soil water from infiltrated rainfall flowed through the thawed transient layer and upper permafrost, which likely solubilized ions previously stored at depth. Subsequent rainfall events acted as a hydrological flushing mechanism, mobilizing solutes from the subsurface to the surface. This solute flushing substantially increased ion concentrations in stream runoff throughout mid to late July. Results further suggest the importance of rainfall and soil water as sources of runoff in a High Arctic catchment during mid to late summer as infiltrated snowmelt is drained from soil following baseflow. Although there was some evaporation of surface water, our study indicates that flushing from solute stores in the transient layer was the primary driver of increased ion concentrations in stream runoff and not evaporative concentration of surface water. With warmer and wetter summers projected for the Arctic, ion concentrations in runoff (especially in the late thaw season), will likely increase due to the deep storage and subsurface flow of infiltrated water and subsequent flushing of previously frozen solutes to the surface.     

From on high: Geochemistry of alpine springs,Niwot Ridge,Colorado Front Range,USA

Snowmelt‐fed springs and small (0.5 km²) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca²⁺, Na⁺, and HCO₃^?, locally SO₄^2?. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na⁺ and Si. Concentrations of Ca²⁺ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca²⁺ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m^?2·s^?1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments.     

Chemistry of streams draining grassland and forest catchments at Plynlimon,mid-Wales

Abstract

The chemistry of streamwater, bulk precipitation, throughfall and soil waters has been studied for three years in two plantation forest and two moorland catchments in mid-Wales. Na and CI are the major ions in streamwater reflecting the maritime influence on atmospheric inputs. In all streams, baseflow is characterised by high pH waters enriched in Ca, Mg, Si and HCO³. Differences in baseflow chemistry between streams reflect the varying extent of calcite and base metal sulphide mineralization within the catchments. Except for K, mean stream solute concentrations are higher in the unmineralized and mineralized forest catchments compared with their respective grassland counterparts. In the forest streams, storm flow concentrations of H⁺ are approximately 1.5 times and Al four times higher than in the moorland streams. Annual catchment losses of Na, Cl, SO⁴, NO³, Al and Si are greatest in the forest streams. In both grassland and forest systems, variations in stream chemistry be explained by mixing waters from different parts of the catchment, although NO³ concentrations may additionally be controlled by N transformations occurring between soils and streams. Differences in stream chemistry and solute budgets between forest and moorland catchments are related to greater atmospheric scavenging by the trees and changes in catchment hydrology consequent on afforestation. Mineral veins within the catchment bedrock can significantly modify the stream chemical response to afforestation.     

Dissolved trace metals in the surface waters of Puget Sound

Employing clean and quantitative techniques, a marine monitoring programme succeeded in detecting large surface elevations in the concentrations of dissolved Cu, Zn and Pb in the marine surface waters of Puget Sound adjacent to Seattle and Tacoma, Washington. Physical mixing with cleaner waters was the controlling factor in reducing the dissolved concentrations of Cu downstream of these contaminated regions. Comparisons between Puget Sound waters and coastal waters adjacent to Puget Sound suggest that a portion of this Cu, Zn and Pb pollution is being advected out of Puget Sound. The low Ni and Cd concentrations found in this study indicate that these trace metals are not a significant pollution problem in the main basin of Puget Sound.     

Concentration–discharge relationships reflect chemostatic characteristics of US catchments

Concentration–discharge relationships have been widely used as clues to the hydrochemical processes that control runoff chemistry. Here we examine concentration–discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments. We show that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude. Similar patterns are observed at the inter‐annual time scale. This behaviour implies that solute concentrations in stream water are not determined by simple dilution of a fixed solute flux by a variable flux of water, and that rates of solute production and/or mobilization must be nearly proportional to water fluxes, both on storm and inter‐annual timescales. We compared these catchments' concentration–discharge relationships to the predictions of several simple hydrological and geochemical models. Most of these models can be forced to approximately fit the observed concentration–discharge relationships, but often only by assuming unrealistic or internally inconsistent parameter values. We propose a new model that also fits the data and may be more robust. We suggest possible tests of the new model for future studies. The relative stability of concentration under widely varying discharge may help make aquatic environments habitable. It also implies that fluxes of weathering solutes in streams, and thus fluxes of alkalinity to the oceans, are determined primarily by water fluxes. Thus, hydrology may be a major driver of the ocean‐alkalinity feedback regulating climate change. Copyright © 2009 John Wiley & Sons, Ltd.     

Metallogenesis along a fossil oceanic fracture zone: Arakapas fault belt,Troodos Massif,Cyprus

The Arakapas fault belt, southern Troodos Massif, which is interpreted as a fossil oceanic fracture zone, contains a sedimentary and volcanic “fill” including basaltic lava breccias, volcaniclastic sandstones, intercalated Fe-rich mudstones, and minor Cu sulphide mineralisation. The volcaniclastic sedimentary rocks were produced by submarine weathering and gravity redeposition of basalt within the transform zone. In contrast, the Fe-mudstones predominantly originated as chemical precipitates from hydrothermal solutions generated by hydrothermal leaching of basalt by seawater. The rare earth elements, and some trace metals, including Co, Ni, Pb, V and Zr, are thought to have been incorporated from seawater into the ferruginous precipitates. Unusually high Fe/Mn ratios of the Fe-mudstones relative to most modern ocean-ridge sediments may reflect deposition in relatively oxygen-depleted waters on the floor of a major bathymetric depression created by the transform faulting; release of acidic thermal waters would have further suppressed Mn precipitation. Contrary to recent suggestions of metallogenesis along oceanic fracture zones, none of the major Cyprus cupriferous sulphide bodies lie along the fossil Arakapas transform zone.     

A comparison of solute fluxes and sources from glacial and non‐glacial catchments over contrasting melt seasons

Solute and runoff fluxes from two adjacent alpine streams (one glacial and one non‐glacial) were investigated to determine how the inorganic solute chemistry of runoff responded to seasonal and interannual changes in runoff sources and volume, and to differences in physical catchment properties. Intercatchment differences in solute composition were primarily controlled by differences in catchment geology and the presence of soils, whereas differences in total solute fluxes were largely dependent on specific discharge. The glacial stream catchment had higher chemical denudation rates due to the high rates of flushing (higher specific discharge). The non‐glacial Bow River had higher overall concentrations of solutes despite the greater prevalence of more resistant lithologies in this catchment. This is likely the result of both longer average water–rock contact times, and a greater supply of protons from organic soils and/or pyrite oxidation. Increases in snowpack depth/snowmelt runoff reduced the retention of nitrate in the Bow River catchment (i.e. increased nitrate export), probably by reducing net biological uptake, or by reducing the proportion of runoff that had contact with biologically active soil horizons that tend to remove nitrate. The two streams exhibited opposite solute flux responses to climate perturbations over three melt seasons (1998, 1999, and 2000). The 1998 El Niño event resulted in an unusually thin winter snowpack, and increased runoff and solute fluxes from the glacial catchment, but decreased fluxes from the Bow River catchment. Solute fluxes in the Bow River increased proportionally to discharge, indicating that increased snowmelt runoff in this catchment resulted in a proportional increase in weathering rates. In contrast, the proportional variation in solute flux in the glacial stream was only ∼70–80% of the variation in water flux. This suggests that increased ablation of glacier ice and the development of subglacial channels during the 1998 El Niño year apparently reduced the average water–rock contact time in the glacial catchment relative to seasons when the subglacial drainage system was primarily distributed in character. Copyright © 2005 John Wiley & Sons, Ltd.     

Trace metals and radium in the Gulf of Mexico: An evaluation of river and continental shelf sources

Several studies have provided evidence for the enrichment of trace elements in coastal waters, particularly for copper. These enrichments have been attributed to diffusion from continental shelf sediments and to an influx of river water. We attempted to resolve between these sources by undertaking an extensive suite of measurements of trace metals (Cu, Ni, Cd), ²²⁶Ra and ²²⁸Ra in the surface waters of the Gulf of Mexico, along with trace metal profiles at 6 stations (April 1981 and December 1982). These data establish that enrichments of copper, nickel and cadmium occur in the shallow waters of the Gulf of Mexico. On the Mississippi continental shelf, high trace element concentrations (Cu, Ni: ～ 9 nmol/kg; Cd: ～ 200 pmol/kg) in lower-salinity waters (26‰) are similar to those observed in the Mississippi plume at the same salinity. This evidence suggests a river water source. On the other hand, trace element enrichments are also observed in the northern Gulf (Cu: +0.4 nmol/kg; Ni: +0.5 nmol/kg; Cd: +20 pmol/kg) which coincide with an increase in ²²⁸Ra but are not accompanied by decreased salinity. The excess of evaporation over precipitation in this region makes it possible that this water could be evaporated estuarine water; therefore, hydrographic observations cannot distinguish readily between river and shelf sources. A regional flux balance shows that most of the excess copper in the surface waters of the Florida Current can be supplied by the river-borne dissolved copper flux. Within the uncertainties of such calculations, the continental shelf copper flux must be less than or equal to the river flux.     

Using stable isotopes to identify major flow pathways in a permafrost influenced alpine meadow hillslope during summer rainfall period

Global warming has leaded to permafrost degradation, with potential impacts on the runoff generation processes of permafrost influenced alpine meadow hillslope. Stable isotopes have the potential to trace the complex runoff generation processes. In this study, precipitation, hillslope surface and subsurface runoff, stream water, and mobile soil water (MSW) at different hillslope positions and depths were collected during the summer rainfall period to analyse the major flow pathway based on stable isotopic signatures. The results indicated that (a) compared with precipitation, the δ²H values of MSW showed little temporal variation but strong heterogeneity with enriched isotopic ratios at lower hillslope positions and in deeper soil layers. (b) The δ²H values of middle-slope surface runoff and shallow subsurface flow were similar to those of precipitation and MSW of the same soil layer, respectively. (c) Middle-slope shallow subsurface flow was the major flow pathway of the permafrost influenced alpine meadow hillslope, which turned into surface runoff at the riparian zone before contributing to the streamflow. (d) The slight variation of δ²H values in stream water was shown to be related to mixing processes of new water (precipitation, 2%) and old water (middle-slope shallow subsurface flow, 98%) in the highly transmissive shallow thawed soil layers. It was inferred that supra-permafrost water levels would be lowered to a less conductive, deeper soil layer under further warming and thawing permafrost, which would result in a declined streamflow and delayed runoff peak. This study explained the “rapid mobilization of old water” paradox in permafrost influenced alpine meadow hillslope and improved our understanding of permafrost hillslope hydrology in alpine regions.     

Hydroclimatic controls on dissolved organic matter (DOM) characteristics and implications for trace metal transport in Hwangryong River Watershed,Korea, during a summer monsoon period

Frequent heavy rainfalls during the East Asian summer monsoon drastically increase water flow and chemical loadings to surface waters. A solid understanding of hydroclimatic controls on watershed biogeochemical processes is crucial for water quality control during the monsoon period. We investigated spatio‐temporal variations in the concentrations and spectroscopic properties of dissolved organic matter (DOM) and the concentrations of trace metals in Hwangryong River, Korea, during a summer period from the relatively dry month of June through the following months with heavy rainfall. DOM and its spectroscopic properties differed spatially along the river, and also depended on storm and flow characteristics around each sampling time. At a headwater stream draining a forested watershed, the concentrations (measured as dissolved organic carbon (DOC)), aromaticity (measured as specific UV absorbance at 254 nm), and fulvic acid‐ and protein‐like fluorescence of DOM were higher in stormflow than in baseflow waters. DOC concentrations and fluorescence intensities increased along the downstream rural and urban sites, in which DOC and fluorescence were not higher in stormflow waters, except for the ‘first flush’ at the urban site. The response of DOM in reservoir waters to monsoon rainfalls differed from that of stream and river waters, as illustrated by storm‐induced increases in DOM aromaticity and fulvic‐like fluorescence, and no significant changes in protein‐like fluorescence. The results suggest that surface water DOM and its spectroscopic properties differentially respond to changes in hydroclimatic conditions, depending on watershed characteristics and the influence of anthropogenic organic matter loadings. DOC concentrations and intensities of spectroscopic parameters were positively correlated with some of the measured trace metals (As, Co, and Fe). Further research will be needed to obtain a better understanding of climate effects on the interaction between DOM and trace metals. Copyright © 2006 John Wiley & Sons, Ltd.