mineralogy and geochemistry of alluvium contaminated by metal mining in the rio tinto area southwest spain the rio tinto in sw spain drains cu and pyrite mines which have been in operation since at least the bronze age extensive metal mining especially from 1873 to 1954 has resulted in contamination of the rio tinto alluvium with as cu pb ag and zn x ray diffraction xrd wavelength dispersive x ray mapping scanning electron microscope petrography and x ray energy dispersive edx analysis has revealed that 4 major groups of contaminant metal and as bearing minerals including sulphides fe as oxides fe oxides hydroxides oxyhydroxides and fe oxyhydroxysulphates occur in the alluvium sulphide minerals including pyrite chalcopyrite arsenopyrite and sphalerite occur in alluvium near the mining areas iron hydroxides and oxyhydroxides such as goethite and possibly ferrihydrite occur in cements in both the mining areas and alluvium downstream and carry minor amounts of as cu and zn iron oxyhydroxysulphates including jarosite plumbojarosite and possibly schwertmannite are the most common minerals in alluvium downstream of the mining areas and are major hosts of cu pb zn and of as next to the fe as minerals this work and other field observations suggest that 1 the extreme acidity and elevated metal concentrations of the river water will probably be maintained for some time due to oxidation of pyrite and other sulphides in the alluvium and mine waste tips and from formation of secondary oxide and oxyhydroxysulphates 2 soluble fe oxyhydroxysulphates such as copiapite which form on the alluvium are a temporary store of contaminant metals but are dissolved during periods of high rainfall or flooding releasing contaminants to the aqueous system 3 relatively insoluble fe oxyhydroxysulphates and hydroxides such as jarosite and goethite may be the major long term store of alluvial contaminant metals and 4 raising river ph will probably cause precipitation of fe oxyhydroxides and oxides hydroxides oxyhydroxides and thus have a positive effect on water quality but this action may destabilise some of these contaminant metal bearing minerals releasing metals back to the aqueous system

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

distinguishing allogenic from autogenic causes of bed elevation change in late quaternary alluvial stratigraphic records abstract allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records asrs allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale climate tectonism base level land use land cover and direct human modification of channels late quaternary asrs are influenced by the greatest range of allogenic forcing variables with climate among the most important autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time transgressive autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time space envelope within which its effects are capable of operating asrs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing this formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms over late quaternary timescales 10 2 to 10 5 years in tectonically stable regions climate change is the dominant allogenic mechanism and therefore the first order control on the morphology sedimentology pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality

climate change and the episodicity of sediment flux of small california rivers abstract we studied the streamflow and sediment flux characteristics of the 20 largest streams entering the pacific ocean along the central and southern california coast extending for 750 km from monterey bay to just south of the u s mexico border drainage basins ranged in area from 120 to 10 800 km2 with headwater elevations ranging from 460 to 3770 m annual streamflow ranged from 0 to a maximum of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 1 times 10 9 end document m3 yr for the santa clara river in 1969 with a

spatial and temporal analysis of hillslope channel coupling and implications for the longitudinal profile in a dryland basin author s michaelides katerina hollings rory singer michael bliss nichols mary h nearing mark a

coupled thermal hydraulic and geochemical evolution of pyritic tailings in unsaturated column experiments the evolution of pore water and the composition of solid phases in the vadose zone of pyritic tailings was studied by means of unsaturated column experiments several columns of water saturated mine tailings were dried during 125 days under controlled laboratory conditions the columns were dismantled at four successive drying stages and the evolution of pore water mineralogy water content and temperature was characterized sulfide and aluminosilicate minerals present in the waste dissolved releasing sulfate and other solutes mainly fe zn cu al mg and ca to the pore water evaporation caused a crust of efflorescent water soluble sulfates to develop over the complete top surface of the columns and into the pores of the underlying waste material this crust which has also been identified in the field changed the hydraulic properties of the tailings and produced a decrease in the evaporation rate of the columns moreover these water soluble precipitates mainly rozenite szomolnokite halotrichite hexahydrite mirabilite and gypsum acted as temporary sinks for cd pb co and ni which could be released to the surface run off or the groundwaters during rainfall events under field conditions pore water evolution was determined not only by geochemical processes dissolution of sulfides and aluminosilicates precipitation of secondary phases but also by thermal and hydraulic processes progressive dilution was observed in the lower part of the columns dilution was caused by the thermally driven vapor flux from the top of the column to its colder bottom and subsequent condensation therein this process which may also occur in tailings under sub arid climate played a key role on the evolution of pore water with increasing drying

the climatic signature of incised river meanders climate controls landscape evolution but quantitative signatures of climatic drivers have yet to be found in topography on a broad scale here we describe how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the western north pacific spatially averaged river sinuosity generated from digital elevation data peaks in the typhoon dominated subtropics where extreme rainfall and flood events are common and decreases toward the equatorial tropics and mid latitudes where such extremes are rare once climatic trends are removed the primary control on sinuosity is rock weakness our results indicate that the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers

environmental controls of the seasonal variation in oxygen uptake in sulfidic tailings deposited in a permafrost affected area oxygen consumption sulfide oxidation and acid mine drainage amd of pyritic mine tailings were investigated at nanisivik mine which is located in an area with continuous permafrost on baffin island in northern canada tailings of varying age and water content have been deposited under alkaline conditions one area consisting of tailings deposited on land in 1992 was selected for detailed measurements of in situ oxygen uptake rates at the tailing surface in the summers 1998 and 1999 and periodically during autumn and winter in 1998 measurements included oxygen gas water content and temperature in profiles as well as chemical analyses of pore solution and solids additional oxygen consumption rates were measured under controlled temperature conditions on columns filled with partly oxidized tailings on the basis of temperature dependency of pyrite oxidation observed in the laboratory an arrhenius diffusion equation with soil temperature as input was used to simulate the observed temporal variation in oxygen uptake field data reveal that the ongoing sulfide oxidation of well drained tailings primarily takes place in the upper 30 cm and that oxidation has resulted in a depletion of pyrite carbonates and metals from this reaction zone the model provides a reasonable fit to the observed trend in oxygen consumption and documents that oxidation of sulfide minerals in tailings is not reduced to neglectable levels at o c the amd generation rate has been quantified based on the changes in concentration of oxidation products in the pore water and oxidation rates based on in situ measurements of oxygen consumption the two rate descriptions provide comparable estimates of seasonal amd generation and provide detailed information on weather related controls of amd generation i e ground temperature freezing water content and snow cover these environmental controls are crucial for the design of frozen cover schemes in permafrost regions where the aim is to force the frost table to the top of the tailings maintaining tailings at subzero temperatures year round and thereby controlling the amd generation

acid mine drainage in the iberian pyrite belt odiel river watershed huelva sw spain geochemistry mineralogy and environmental implications abstract this work reports the physical properties and water chemistry of 64 amd discharges from 25 different mines in the ipb draining to the odiel river watershed which have been investigated during the hydrologic year 2003 2004 these amd solutions vary largely in flow rate and chemical composition both spatially between the different mine sites suggesting a strong geologic control on amd chemistry and seasonally due to marked hydrologic variations and include cases with very low ph mostly in the range 1 4 4 and extreme sulphate up to 44 g l so 4 2 and metal content e g up to 7 7 g l fe 2 6 g l al or 1 4 g l zn different hydrogeochemical facies of amd namely fe ii anoxic fe iii suboxic and aluminous oxic are recognized in the field as a response to the continuous oxidation and hydrolysis of dissolved fe relevant geochemical aspects of these amd environments are discussed including i the redox chemistry of the fe ii fe iii couple ii the reaction rates for bacterially catalyzed oxidation of fe ii and hydrolysis of fe iii iii the role played by dissolved fe and al in the acidity and chemical buffering of the amd systems and iv the solubility and trace metal retention capacity of the fe oxyhydroxysulphate and hydrated sulphate minerals commonly associated with amd in addition the mineralogy and chemistry of the fe precipitates schwertmannite jarosite goethite ferrihydrite al phases e g basaluminite and mg fe al efflorescent so4 salts e g epsomite hexahydrite copiapite halotrichite rozenite coquimbite present in the amd generating mine sites have also been studied the mineralogy of the fe precipitates is well correlated with the water ph with jarosite at ph 2 schwertmannite at ph 2 4 basaluminite at ph 4 5 and ferrihydrite at ph 6 schwertmannite appears to be the most important mineral phase both in controlling the fe solubility at ph 2 4 and as sorbent of trace elements as cu zn which favours natural attenuation finally a basin scale environmental perspective is given in order to evaluate the impact of amd on the water quality including calculation of metal loadings transported by amd from the most important mine districts in the province

imprint of climate and climate change in alluvial riverbeds continental united states 1950 2011 alluvial riverbed elevation responds to the balance between sediment supply and transport capacity which is largely dependent on climate and its translation into fl uvial discharge we examine these relations using u s geological survey streamfl ow and channel measurements in conjunction with basin characteristics for 915 reference least disturbed measurement stations across the conterminous united states for the period a d 1950 2011 we fi that 1 68 of stations have bed elevation change bec trends p 0 05 with median values of 0 5 cm yr for aggradation and 0 6 cm yr for degradation with no obvious relation to drainage basin structure physiography or lithology 2 bec correlates with drainage basin area 3 high fl ow variability q 90 q 50 where q is discharge and 90 and 50 are annual fl ow percentiles translates directly into the magnitude though not the direction of bec after accounting for the scale dependence 4 q 90 q 50 declines systematically from dry to wet climates producing disproportionately high rates of bec in drier regions and 5 marked increases in precipitation and streamfl ow occurred disproportionately at dry sites while streamfl ow declined disproportionately at wet sites climatic shifts in streamfl ow have the potential to increase decrease sediment fl ux and thus affect riverbed elevation by altering fl ood frequency these unforeseen responses of bed elevation to climate and climate change have important implications for sediment budgets longitudinal profi les ecology and river management

modelling and field measurements of water percolation through an experimental soil cover on mine tailings a composite soil cover constructed on acid producing tailings was evaluated for its ability to retain a high degree of water saturation and low hydraulic conductivity the cover consisted of a 60 c

release transport and attenuation of metals from an old tailings impoundment abstract the oxidation of sulfide minerals from mine wastes results in the release of oxidation products to groundwater and surface water the abandoned high sulfide camp tailings impoundment at sherridon manitoba wherein the tailings have undergone oxidation for more than 70 a was investigated by hydrogeological geochemical and mineralogical techniques mineralogical analysis indicates that the unoxidized tailings contain nearly equal proportions of pyrite and pyrrhotite which make up to 60 wt of the total tailings and which are accompanied by minor amounts of chalcopyrite and sphalerite and minute amounts of galena and arsenopyrite extensive oxidation in the upper 50 cm of the tailings has resulted in extremely high concentrations of dissolved so4 and metals and as in the tailings pore water ph 1 m thick geochemical modeling and mineralogical analysis indicate that the hardpan layer consists of secondary melanterite rozenite gypsum jarosite and goethite the minerals indicated mainly control the dissolved concentrations of so4 fe ca and k the highest concentrations of dissolved metals are observed directly above and within the massive hardpan layer near the water table at a depth of 4 m most metals and so4 sharply decline in concentration although dissolved concentrations of metals and so4 decrease below the water table these concentrations remain elevated throughout the tailings with up to 60 600 mg l 1 fe and 91 600 mg l 1 so4 observed in the deeper groundwater during precipitation events surface seeps develop along the flanks of the impoundment and discharge pore water with a geochemical composition that is similar to the composition of water directly above the hardpan these results suggest that shallow lateral flow of water from a transient perched water table is resulting in higher contaminant loadings than would be predicted if it were assumed that discharge is derived solely from the deeper primary water table the abundance of residual sulfide minerals the depletion of aluminosilicate minerals in the upper meter of the tailings and the presence of a significant mass of residual sulfide minerals in this zone after 70 a of oxidation suggest that sulfide oxidation will continue to release acid metals and so4 to the environment for decades to centuries

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

investigation of early eocene water vapor transport and paleoelevation using oxygen isotope data from geographically widespread mammal remains the oxygen isotope composition 18 o of apatite from mammalian tooth enamel can be used to infer the 18 o value of ingested water which is in turn related to that of precipitation stored in surface reservoirs therefore the 18 o value of phosphate from fossil tooth enamel can be used to infer the 18 o value of these reservoirs in the past in this paper tooth enamel from a semiaquatic mammal taxon coryphodon collected from five early eocene localities in north america is used to construct patterns in 18 o values of river water for this time period at all localities the 18 o value of river water 18 o r is estimated to have been higher during the early eocene relative to present day north american rivers although the 18 o vs latitude gradient was shallower during the eocene higher 18 o r values are consistent with warmer eocene air masses being able to hold more water vapor and with an increase in the poleward transport of both moisture and latent heat the regular decrease in 18 o r with latitude indicates that global atmospheric circulation patterns and hydrological transport were not much different from those of the present although the shallower 18 o vs latitude gradient during the eocene may reflect regional differences in precipitation evaporation and river recharge at a more regional scale the 18 o value of river water can provide insight into topographic relief during the early eocene in the case of intermontane basins of wyoming differences in average 18 o r values between basins indicate that laramide mountain relief was on the order of 475 m it is suggested that anomalously low 18 o r values reported previously do not provide unambiguous evidence for permanent snow at higher elevations and may instead reflect brief episodes of cooler winters and or altered atmospheric circulation patterns

geochemical evolution of inactive pyritic tailings in the elliot lake uranium district geochemical data obtained between 1979 and 1983 from a network of piezometer nests and cores from three inactive uranium tailings impoundments in the elliot lake district indicate that oxidation of pyrite taking place in the shallow part of the zone above the water table is causing the chemistry of the pore water above and below the water table to change a two layer hydrochemical zonation has developed in which infiltration water from rain and snow has resulted in an upper zone of low ph water with high concentrations of so4 fe and heavy metals this zone is gradually expanding downward at rates generally between 0 2 and 2 m year causing displacement of the original mill process water which has neutral ph and low concentrations of heavy metals high concentrations of fe iii at shallow depth in the zone above the water table indicate that ferric iron is an important oxidizer of pyrite in the presence of free oxygen the pe of the groundwaters is controlled by the ferric ferrous redox couple and trend

multiphase flow and reactive transport model in vadose tailings weathering processes affecting pyritic wastes may generate huge amounts of acid waters with high concentrations of potentially toxic contaminants acid mine drainage acid mine drainage is mainly produced in the vadose zone in the present study a coupled non isothermal multiphase flow and reactive transport model of the vadose zone of sulfide mine tailings was developed the geochemical model included kinetically controlled reactions for fe ii oxidation and for the dissolution of sulfide and aluminosilicate phases and the pitzer ion interaction model to describe the behavior of the pore water solutions model results were compared with experimental observations in unsaturated column experiments under strongly evaporative conditions similar to arid or semiarid climates evolution trends for temperature water saturation evaporation rates pore water hydrochemistry and mineral phases observed during the drying experiment were adequately reproduced the coupled model reproduced the increase of solute concentrations in the column top and the precipitation of a crust of secondary mineral phases this crust became a barrier for water vapour diffusion to the atmosphere and modified the thermohydraulic behavior of the tailings enhanced downward migration of water vapour and its condensation in this colder end of the column were correctly taken into account by the model which reproduced the dilution observed in the lower part of the column during the experiments

combined effects of dissolution kinetics secondary mineral precipitation and preferential flow on copper leaching from mining waste rock a probabilistic lagrangian approach to reactive subsurface transport is used to investigate possible processes that may explain reported discrepancies between modelled and observed copper concentrations at the aitik waste rock heaps in northern sweden and to quantify the implications of these processes for the long term dynamics of copper leaching the presented lagrangian transport system couples two different types of primary dissolution kinetics with flow heterogeneity and ph dependent equilibrium precipitation dissolution of secondary copper bearing minerals of the investigated processes which we chose to study based on previous geochemical studies of the site only flow heterogeneity in the form of preferential flow paths can provide a possible explanation for the low drainage water concentrations of copper currently measured in the field the investigated ph dependent precipitation dissolution of secondary copper bearing minerals provides an explanation for even lower copper concentrations observed in laboratory column experiments in fresh waste rock these experiments correspond to the initial part of the weathering phase in the field if both preferential flow and secondary copper precipitation dissolution occur at the aitik site the assumed prevailing type of primary dissolution kinetics does not influence the modelled expected long term copper leaching nearly as much as it does under homogeneous flow conditions without formation of secondary minerals the present sensitivity analysis does not provide a comprehensive prediction model for the aitik site since not all possible hydrological and chemical processes have been included in the investigation this study rather exemplifies the application of the probabilistic lagrangian approach as an investigation methodology for field scale geochemical problems by using and extending results of detailed geochemical modelling

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

thermo hydraulic behaviour of the vadose zone in sulphide tailings at iberian pyrite belt waste characterization monitoring and modelling abstract unsaturated conditions favour the oxidation of sulphide minerals from mine wastes which results in the release of contaminant products into groundwater an abandoned high sulphide impoundment in the iberia pyritic belt wherein tailings have undergone oxidation for more than 28 years was investigated for hydrological purposes the objective was to understand the interactions between those mining tailings and the atmosphere under natural semiarid conditions wet and dry seasons short intensive rain events and strong daily temperature differences during the dry season after the deposition the sequence of waste textures that results from the sedimentation process is strongly dependent on the distance to discharge point the spatial continuity of the sedimentation layers was studied by means of small scale dynamic penetration tests the thermo hydraulic characterization of the waste includes the determination of the water retention curve saturated and unsaturated permeability pore size distribution and thermal properties for the different textures atmospheric and waste physical measures from 2002 to 2006 were performed using different techniques the important changes in the salinity of the waste avoided the use of a single calibration for the electromagnetic sensors a valid alternative was the evaluation of the water content from thermal conductivity estimations finally a numerical model using the hydrus 1d software is presented model results reasonably fit the in situ measures of soil moisture soil temperature soil water potential and soil heat flux in the vadose zone of tailings impoundment moreover they provide information for energy and water balance determinations

the human role in changing river channels abstract direct consequences of the human role where human activity affects river channels through engineering works including channelization dam construction diversion and culverting have been long recognised marsh 1864 thomas 1956 the less obvious indirect effects of point and reach changes occurring downstream and throughout the basin however are much more recently appreciated dating from key contributions by strahler strahler a n 1956 the nature of induced erosion and aggradation in w l thomas ed man s role in changing the face of the earth university of chicago press chicago 621 638 wolman wolman m g 1967 a cycle of sedimentation and erosion in urban river channels geografiska annaler 49a 385 95 schumm schumm s a 1969 river metamorphosis proceedings american society of civil engineers journal hydraulics division 95 255 73 and graf graf w l 1977 the rate law in fluvial geomorphology american journal of science 277 178 191 these are complemented by effects of alterations of land use such as deforestation intensive agriculture and incidence of fire with the most extreme effects produced by building activity and urbanisation changing river channels are most evident in the channel cross section where changes of size shape and composition are now well established with up to tenfold increases or decreases illustrated by results from more than 200 world studies in addition the overall channel planform the network and the ecology have changed specific terms have become associated with changing river channels including enlargement shrinkage and metamorphosis although the scope of adjustment has been established it has not always been possible to predict what will happen in a particular location because of complex response and contingency the ways in which changes in cross section relate to reach and network changes are less clear despite investigations showing the distribution of changes along segmented channels when considering the human role in relation to changing river channels at least five challenges persist first because prediction of the nature and amount of likely change at a particular location is not certain and because the contrasting responses of humid and arid systems needs to be considered modelling is required to reduce uncertainty as was first emphasised by burkham burkham d e 1981 uncertainties resulting from changes in river form american society civil engineers proceedings journal hydraulics division 107 593 610 second feedback effects incorporated within the relationship between changes at channel reach and network scales can have considerable implications especially because changes now evident may have occurred or have been initiated under different environmental conditions third consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions fourth channel design involving geomorphology should now be an integral part of restoration procedures this requires fifthly greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes

the formation and potential importance of cemented layers in inactive sulfide mine tailings abstract investigations of inactive sulfide rich tailings impoundments at the heath steele new brunswick and waite amulet quebec minesites have revealed two distinct types of cemented layers or hardpans that at heath steele is 10 15 cm thick occurs 20 30 cm below the depth of active oxidation is continuous throughout the tailings impoundment and is characterized by cementation of tailings by gypsum and fe ii solid phases principally melanterite hardpan at the waite amulet site is only 1 5 cm thick is laterally discontinuous 10 100 cm occurs at the depth of active oxidation and is characterized by cementation of tailings by fe iii minerals principally goethite lepidocrocite ferrihydrite and jarosite at heath steele an accumulation of gas phase co2 of up to 60 of the pore gas occurs below the hardpan the calculated diffusivity of the hardpan layer is only about 1 100 that of the overlying uncemented tailings the pore water chemistry at heath steele has changed little over a 10 year period suggesting that the cemented layer restricts the movement of dissolved metals through the tailings and also acts as a zone of metal accumulation generation of a cemented layer therefore has significant environmental and economic implications it is likely that in sulfide rich tailings impoundments the addition of carbonate rich buffering material during the late stages of tailings deposition would enhance the formation of hardpan layers

modelling the effect of chemical heterogeneity on acidification and solute leaching in overburden mine spoils abstract the generation of acid mine drainage from overburden spoil piles at open pit lignite mines is impacting the quality of groundwater and surface water bodies in large parts of the lusatian mining area in germany values of ph as low as 1 have been observed in the groundwater after decommissioning mine pits are generally converted to lakes which may also be acidic owing to the acidic groundwater discharge the acidic effluent is generated by sulphide oxidation in the unsaturated zone of the spoil pile which generally extends to large depths as a result of dewatering the long term evolution of the acidification is still largely unknown our research focuses on the effects of physical and chemical heterogeneity caused by mixing of soil materials that may have already been oxidized to different degrees during the deposition of the spoil pile processes considered include variably saturated groundwater flow oxygen diffusion in the soil gas kinetic pyrite oxidation and acidic effluent generation advective dispersive transport of the aqueous components equilibrium geochemical reactions between the chemical components and the soil minerals and possible buffering and acid neutralization several existing numerical codes were coupled to represent the complete set of processes simulations were carried out in one and two dimensions using representative characteristics of mine spoil piles with the two dimensional representation being based on spatially heterogeneous random fields of hydraulic conductivity and sulphide mineral fractions results show the long term evolution of the oxidation front the mass flux of oxidation products and the effects of system heterogeneity under conditions of constant flow the system is found to return to neutral conditions over a time period on the order of several decades further work including sensitivity analyses with respect to the controlling parameters and model calibration using site specific field data will be necessary to obtain a full understanding of the complex interacting mechanisms the simulation approach shows promise as a potentially useful tool for predicting the effects of sulphide oxidation on the water quality of pit lakes

the pore water geochemistry and the mineralogy of the vadose zone of sulfide tailings waite amulet quebec canada low ph waters requiring treatment because of high concentrations of dissolved metals are being discharged from a decommissioned tailings impoundment at the former waite amulet zncu mine in northeastern quebec canada a detailed study of the vadose zone of the tailings comparing mineralogical and geochemical analyses of the tailings solids with geochemical analysis of the tailings pore water and pore gas indicates the presence of three zones within the tailings these zones include an upper sulfide depleted zone in which the sulfides have been extensively removed and oxidation is largely complete an intermediate zone where sulfide oxidation and acid neutralization reactions are occurring and an unoxidized zone below the depth of oxygen penetration where sulfides are unoxidized high aqueous concentrations of dissolved solids are being displaced downward from the sulfide depleted zone through the unoxidized zone toward the water table sulfide oxidation and acid neutralization reactions have generated concentrations of dissolved solids high enough to lead to the precipitation of a series of secondary solid phases precipitation dissolution reactions involving these solid phases control the concentrations of the major ions in the tailings pore water concentrations of dissolved metals are controlled by precipitation dissolution crystal structural replacement and adsorption coprecipitation reactions predictions based on the observed data and numerical simulations suggest that in the absence of an effective remedial program sulfide oxidation and h production will continue for several centuries