a lacustrine record from lop nur xinjiang china implications for paleoclimate change during late pleistocene abstract climate variability during the late pleistocene is studied from the proxies in core ck 2 drilled from the luobei depression 91 03 e 40 47 n lop nur in the eastern tarim basin xinjiang china geophysical and geochemical properties including magnetic susceptibility granularity chroma carbonate content loss on ignition and trace elements have been determined to reconstruct the environmental evolution of the area during 32 9 ka bp the chronology is established by uranium thorium disequilibrium dating techniques our data suggest four paleoclimate stages indicating glacial variations between cold humid and warm arid environments a period of extreme humidity occurred during 31 900 19 200 yr bp is attributed the last glacial maximum lgm the period was followed by a warm arid episode during 19 200 13 500 yr bp then a cold humid interval during 13 500 12 700 yr bp may correspond to another cooling phases at high latitudes of the northern hemisphere the last stage from 12 700 to 9000 yr bp has a trend that the climate turned warm and arid the lop nur region is characterized by particularly humid stadials and arid interstadials the climate variability in lop nur was constrained by global climate change because it is correlated with dansgaard oeschger and heinrich events which were observed at the northern high latitudes the synchroneity of the palaeoclimatic events suggested that cold air activity at the northern high latitudes was the most important factor that influenced the climate evolution in the lop nur region a probable mechanism that involves the migration of westerly winds is proposed to interpret this synchroneity

building conceptual models of field scale uranium reactive transport in a dynamic vadose zone aquifer river system 1 subsurface simulation is used to build test and couple conceptual process models to better understand the persistence of uranium concentrations above federal drinking water standards in a 0 4 km by 1 0 km groundwater plume beneath the 300 area of the u s department of energy s hanford site in eastern washington state at this location the unconfined aquifer and the variably saturated lower vadose zone sediments are subject to significant variations in water levels driven by diurnal weekly and seasonal fluctuations in the columbia river stage in the near river aquifer uranium contaminated sediments in the highly transmissive hanford formation are subject to high groundwater velocities daily flow reversals and exposure to river water one and two dimensional simulations of variably saturated flow and reactive transport based on laboratory derived models of uranium sorption are used to assess the representation of uranium transport processes in the vadose zone aquifer river system the simulations show that the various frequencies of river stage fluctuation are capable of driving significant inland transport above the average water table which is in contrast to the net groundwater flow to the river inclusion of a rate limited uranium mass transfer process model is notably more important to the timescales of the river stage driven groundwater flow than for vadose zone flow driven by natural recharge spatially and temporally variable solution chemistry from the dynamic exchange of river water and groundwater in the unconfined aquifer is shown to significantly alter uranium mobility as represented by a multicomponent uranium surface complexation model

interaction between shallow groundwater saline surface water and nutrient discharge in a seasonal estuary the swan canning system the swan and canning rivers converge to form an estuary that is seasonally forced by wet winter and dry summer conditions the estuary is also tidally forced due to its contact with the indian ocean the perception that the occurrence of nuisance algal blooms has increased in frequency and severity in recent years has prompted the present investigation into the interaction of the shallow groundwater system with the swan canning estuary the extent to which this interaction contributes to nutrient delivery to the river is a focus of the work groundwater interaction with the upper reaches of the swan river is shown to occur at three length scales i the scale of the river bed sediments i e 1000 m two dimensional groundwater flow modelling in plan covering the regionally advected groundwater flow domain of the upper swan river estuary from the causeway to guildford shows that there is a net groundwater discharge to the swan river of groundwater discharge of about 80 000 m3 day or about 29 million m3 year between 1987 and 1996 the average surface tributary inflow to the swan river was about 460 million m3 year thus groundwater discharge contributed approximately 6 of the total annual river flow this percentage is clearly small in comparison to the total river flow however in the six months from november to april in summer tributary flow into the swan river declines sharply to an average total of approximately 12 million m3 groundwater discharge during this six month period is approximately 14 million m3 or about 55 of the surface tributary flow and thus groundwater is a significant component of the total inflow to the swan canning estuary during this period nutrient concentrations particularly ammonium within the sediment pore fluids underlying the river are very high relative to concentrations in the river such that groundwater discharge rates of this magnitude are capable of introducing significant nutrient loadings to the river the nitrogen load to the swan river derived from regionally advected groundwater discharge is conservatively estimated at between 30 and 60 t year this ranks groundwater as one of the highest single inputs of nitrogen to the swan canning estuary when compared to surface water flows it contributes about 10 of the total nitrogen load entering this reach of the river seasonal and tidal variations increase the complexity of the system and may act to increase the presence and availability of groundwater derived nutrients in the river and estuary system field observations and results from numerical groundwater flow modelling show that groundwater preferentially discharges into the swan river along the outside of river meanders along the inside of meanders groundwater discharge is either very low or at times the flow direction reverses such that saline river water recharges the aquifer during the late spring summer and early autumn months short term high frequency fluctuations such as wave induced displacement seawater intrusion hyporheic flux and tidal fluctuations may cause small spatial scale mixing and perturbation of the nutrient rich groundwater and sediment porewater with either the river water directly or with fresher groundwater as it discharges to the river these short term fluctuations appear to cause nutrient release from the sediment pore fluids particularly in summer low flow periods such that they are a significant contributing factor in triggering algal blooms copyright 2001 john wiley sons ltd

vegetation and climate history in arid western china during mis2 new insights from pollen and grain size data of the balikun lake eastern tien shan marine isotope stage mis 2 is mostly a cold period encompassing the last glacial maximum lgm but the regional expression of mis2 in arid areas of china is not well known in this paper we use high resolution lacustrine pollen and grain size records from balikun lake to infer vegetation lake evolution and climate in arid western china during mis2 our results suggest that 1 the regional vegetation around balikun was mainly dominated by desert and or desert steppe and balikun lake was relatively shallow and experienced high aeolian input during mis2 2 distinctive runoff from mountain glacial meltwater in the eastern parts of the balikun basin caused a high relative abundance of artemisia pollen during the lgm 26 5 19 2 cal kyr bp while simultaneously the desert areas expanded as indicated by the high abundance of desert shrubs e g elaeagnaceae rhamnaceae hippophae this cold and dry lgm climate triggered a substantial lowering of lake level 3 an extremely cold and dry climate prevailing from 17 0 to 15 2 cal kyr bp correlated with heinrich event 1 h1 would explain the low vegetation cover found then and 4 the warm and humid bolling allered interstadial ba ca 15 ca 13 cal kyr bp is clearly recorded in the balikun region by the development of wetland herb communities e g poaceae cyperaceae typha and the lake level rose due to increased runoff our results challenge the traditional view of cold and wet climatic conditions and high lake levels in arid western china during the lgm and we propose that changes in local temperature modulated by july insolation was an indispensable factor in triggering vegetation evolution in the balikun region during mis2 c 2015 elsevier ltd all rights reserved

c32 and c34 hopanoids in recent sediments of european lakes novel intermediates in the early diagenesis of biohopanoids a study of hopanoids in the sediments of five european lakes has identified bacteriohopane 32 33 34 35 tetrol 35 methoxybacteriohopane 32 33 34 triol and two new hopanoids with shorter side chains 35 norbacteriohopane 32 33 34 triol and 33 34 35 trinorbacteriohopane 31 32 diol their structures have been revealed by mass spectrometry polyfunctionalised hopanoids with shortened side chains are not often reported in sediments mainly due to the analytical procedures used their systematic investigation could shed further light upon the early diagenesis of biohopanoids

the use of overbank sediment for geochemical mapping and contamination assessment results from selected english and welsh floodplains abstract overbank sediment profiles from floodplains in england and wales contain a record of both natural geochemical patterns and those showing the influence of man s activities it has been suggested that this characteristic can be used to allow maps to be compiled which show human impact on the fluvial geochemical environment studies reviewed in this paper however show that a single overbank profile very rarely spans the period from before anthropogenic disturbance through to the industrial revolution and later significant lateral variations in metal concentrations occur also over a relatively small area in overbank sediments of the same general age these and the nature of vertical changes in chemistry make the choice of sample sites and sampling interval within a profile difficult even sediments which appear uncontaminated may record anthropogenic influences from activities such as deforestation and agriculture a means of dating the sediment and an appreciation of river erosion and sedimentation histories are shown to be essential in order to ensure that maps intended to depict natural geochemical variations are based on material deposited before disturbance of the catchment by human activity these considerations and associated costs may render overbank sediment non viable as a regional geochemical mapping medium

determining the spatial and temporal patterns of climate changes in china s western interior during the last 15 ka from lacustrine oxygen isotope records china s western interior is a climatologically complex region where climatic conditions are primarily controlled by the westerly jet stream and the asian monsoon system observations reveal that the 18o signatures of these atmospheric elements as expressed in their meteoric waters are different and these differences are reflected in the lacustrine systems that are ultimately fed by the meteoric waters empirical orthogonal function eof decomposition of 17 lacustrine 18o records from this area clearly reveals the spatial and temporal structures of climate changes during the last 15 ka the first eof mode dominated by sites in the nw sector captures the temperature effect on the variability of the 18o dataset we interpret the variations through time in the amplitude of this mode to be indicative of changes in summer air temperature the second eof mode heavily weighted by sites in the se sector reveals the amount effect on 18o and thus its amplitude time series indicates changes in the intensity of the asian summer monsoon our eof based reconstructions of regional climate are generally consistent with the 18o records of ice cores cave speleothems and marine carbonates copyright 2008 john wiley sons ltd

stable isotope studies on mono lake california 1 d18 in lake sediments as proxy for climatic change during the last 15 years mono lake is a hypersaline alkaline lake in the mono basin located at the eastern base of the californian sierra nevada its lake level history since 1912 has been recorded instrumentally showing the decline of lake surface elevations initiated by the 1941 artificial diversion of stream inflow we have made high resolution oxygen isotopic measurements on the total carbonate fraction of lake sediments and shown that the s o record parallels the lakelevel fluctuations rather well the measurements were carried out on sediments that had been leached with deionized water to isolate the isotopic signals of the calcium carbonate from those of pore water and water soluble carbonate salts in the sediment extending the s o record back in time we found that lake level changed markedly during the past 150 yr reflecting climatic variations and resultant runoff fluctuiitions lake levels were high around 1845 1880 and 19 15 and low around 1860 1900 and 1933 this study demonstrates that closed basin lake sediment s180 provides an effective means of probing past precipitation variations in arid to semiarid regions such as the great basin in the western united states numerous attempts have been made to reconstruct paleolake levels on the basis of geological and stable isotopic evidence from which paleohydrological conditions have been inferred studies on closed basin lakes in semiarid and tropical zones have contributed greatly to paleoclimatic research particularly for the late pleistocene and the holocene e g street perrott and harrison 1985 chivas et al 1986 gasse et al 1991 water entering closed basin lakes via rain and runoff leaves by evaporation hence fluctuations in lake level and volume should serve to indicate changes in the moisture budget associated with climatic change mono lake located in eastern california about 480 km north of los angeles fig l is the only terminal lake in the mono basin its present ratio of surface area 150 km2 to catchment area 2 072 km2 is 7 100 in contrast to the ratio of 33 100 for lake russell during the last glacial period russell 1889 lajoie 1968 mono lake committee 1981 since 1912 the levels of mono lake have been measured by the u s geological survey usgs and the los angeles department of water and power ladwp blevins et al 1987 since its historic high in 1915 the water level within the lake has fallen as a result of climatic changes the lake level fall has been exacerbated by the diversion of inflow to the lake by ladwp since 1941 and has caused a further increase in salinity and alkalinity dur

mixed convection processes below a saline disposal basin abstract saline groundwater and irrigation drainage are commonly diverted and stored in both natural and artificial depressions throughout the murray darling basin of australia the disposal basin brines that are formed are often denser than ambient groundwater under certain conditions these dense brines may become unstable causing them to mix with groundwater over distances several orders of magnitude greater than due to diffusion alone a model is developed to study the mixed convection processes below a saline disposal basin located between a recharge and discharge zone numerical simulations are performed in cross section using the 2 d density dependent model sutra saturated unsaturated transport it is shown that the salt front movement is related to both the ability of the dense saline brines to mix convectively with underlying groundwaters rayleigh convection and the strength of the regional advective velocity both homogeneous and heterogeneous aquifer systems are studied and the effects of anisotropy are considered our numerical results suggest that the behaviour of a dense brine plume overlying less dense groundwater in a homogeneous porous medium depends on the magnitude of at least two non dimensional numbers a rayleigh number and modified peclet number defined in terms of basin scale hydrogeologic parameters including dispersion it is shown that the onset of gravitational instabilities and the formation of free convective cells begins when the magnitude of a non dimensional parameter combining the rayleigh and modified peclet number exceeds a certain critical value 1997 elsevier science b v all rights reserved

late pleistocene paleoclimatic history documented by an oxygen isotope record from carbonate sediments in qarhan salt lake ne qinghai tibetan plateau late pleistocene paleoclimatic variability on the northeastern qinghai tibetan plateau ne qtp was reconstructed using a chronology based on ams 14 c and 230 th dating results and a stable oxygen isotopic record these are derived from lake carbonates in a 102 m long qarhan sediment core isl1a collected from the eastern qaidam basin previous research indicates that the d 18 o values of lacustrine carbonates are mainly controlled by the isotopic composition of lake water which in turn is a function of regional p e balance and the proportion of precipitation that is monsoon derived on the ne qtp modern isotopic observations indicate that the d 18 o values of lake carbonates in hyper arid qaidam basin are more positive during the warm and wet period due to strong evaporation and continental effect in this basin the positive d 18 o values in the arid region indicate drier climatic conditions based on this interpretation and

trace elements in streambed sediments of floodplains consequences for water management measures the occurrence of trace metals was studied at the interface between groundwater and the drainage system of a large floodplain in ne germany the oderbruch region depending on the predominant hydraulic connectivity between groundwater and the drainage channels the geochemical environment creates a high variability in the accumulation of fe mn cd zn cu and as the mobility of the trace metals depends on spatial variable redox transition zones which act as geochemical barriers between the anaerobe aquifer and the oxic surface waters in drainage ditches with high exchange flow between groundwater and surface water the transition zone is small and unstable with a low retention potential for trace metals decreasing hydraulic gradients and respectively decreasing base flow cause the change for an extensive transition zone with increasing trace metal accumulation in the channel sediments the accumulation is mainly controlled by oxidation and degassing of co2 in the streambed sediments of channels which periodically run dry an effective chemical barrier can be observed this fe dominated oxic horizon controls the accumulation of mn cu as zn cd which are mainly associated with fresh amorphous fe oxyhydroxides the chemical barriers can be instable and reversible therefore water management decisions are discussed which stabilize the barriers by controlling aquifer channel exchange rates channel oxygen content and surface water levels

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

a 94 10 ka pollen record of vegetation change in qaidam basin northeastern tibetan plateau drill core isl1a was obtained from the qarhan salt lake in central eastern qaidam basin northeastern tibetan plateau ne tp fossil pollen and the lithology of the core sediment were analyzed in conjunction with ams c 14 and th 230 dating the results indicated that artemisia and chenopodiaceae dominated the steppe desert steppe vegetation developed around the lake between 94 and 51 2 ka corresponding with the organic rich silty clay deposited in the core sediments pediastrum continuously appeared in the core sediments between 94 and 51 2 ka indicating freshwater to oligohaline conditions of the paleo qarhan lake during the late marine isotope stage mis 5 mis 4 and early mis 3 during the 51 2 to 32 5 ka period ephedra dominated shrub desert vegetation expanded in the basin while pediastrum disappeared in the core sediments the core sediments consisted of interbedded layers of halite silt and clay rich halite between 51 2 and 32 5 ka signifying a shift toward drier hydrologic conditions thus the paleo qarhan lake experienced periods of desiccation and shallow water levels artemisia and chenopodiaceae dominated steppe desert steppe vegetation appeared again from 32 5 to 253 ka with clay rich sediments in the core thereby suggesting an increase of runoff from the lake under relatively wetter climatic conditions since 253 ka however pollen concentrations declined corresponding with the amount of halite deposited in the core sediment and suggesting a cold dry climatic condition during mis2 our findings have important implications for understanding complex regional vegetation and climatic responses to large scale forcings in the qaidam basin c 2015 elsevier b v all rights reserved

us geological survey research on the environmental fate of uranium mining and milling wastes studies by the us geological survey usgs of uranium mill tailings umt have focused on characterizing the forms in which radionuclides are retained and identifying factors influencing the release of radionuclides to air and water selective extraction studies and studies of radionuclide sorption by and leaching from components of umt showed alkaline earth sulfate and hydrous ferric oxides to be important hosts of radium 226 226ra in umt extrapolating from studies of barite dissolution in anerobic lake sediments the leaching of226ra from umt by sulfate reducing bacteria was investigated a marked increase in226ra release to aqueous solution as compared to sterile controls was demonstrated a similar action of iron iii reducing bacteria was later shown ion exchangers such as clay minerals can also promote the dissolution of host phase minerals and thereby influence the fate of radionuclides such as226ra radon release studies examined particle size and ore composition as variables aggregation of umt particles was shown to mask the higher emanating fraction of finer particles studies of various ores and ore components showed that umt cannot be assumed to have the same radon release characteristics as their precursor ores nor can226ra retained by various substrates be assumed to emanate the same fraction of radon over the last decade usgs research directed at offsite mobility of radionuclides from uranium mining and milling processes has focused on six areas the midnite mine in washington ralston creek and reservoir colorado sites near canon city colorado the monument valley district of arizona and utah the cameron district of arizona and the puerco river basin of arizona and new mexico

230th dating of stem carbonate deposits from tai cuo lake western tibetan plateau china abstract the saline lake tai cuo located in western tibetan plateau china is a closed endorheic basin mainly recharged by meteoric water and groundwater carbonate sediments mainly showing stem structure are extensively developed in the first terrace of tai cuo lake area and are over 3 m thick the u series method has been applied to those carbonate deposits sieved carbonates samples smaller than 0 595 mm 30 and larger than 0 177 mm 80 were the research object for 230th dating the results indicate that the uranium contents are high up to 6 14 ppm and activity ratios of 234u 238u range from 1 533 at the top to 1 437 at the base of the succession indicating that the sedimentary environment was relatively stable during the period ages obtained with precision of 1 3 have recorded environmental evolution history in this area during the period 13 340 5200 yr bp with an error bar of only 240 89 yr and are consistent with the lithological deposition sequence and greatly improved compared to previously published 230th chronologies this chronology will be of great importance for interpreting the environmental changes in the study area

a 40 000 year record of aridity and dust activity at lop nur tarim basin northwestern china abstract the taklamakan desert is a major dust source area for northwestern china the history of aridification and sandstorm activity of the desert is recorded in the lacustrine sediments of the lop nur paleolake on the eastern margin of the desert in this study we used accelerator mass spectrometry 14c dating the ln al ca ratio and the grain size of the non biogenic fraction of sediment core ky01 taken from the center of lop nur to produce a 40 kyr record of local climate change during mid late marine isotope stage mis 3 increases in the ln al ca ratio alluvial mud content and atmospheric dust content and a decrease in the dust storm content indicate an overall wet climate during mis 2 marked decreases in the ln al ca ratio and alluvial mud content especially during the last glacial maximum and heinrich event 1 cold interval indicate lowered atmospheric temperatures as also recorded in greenland ice cores during mis 2 fluvial input to the site was reduced and almost ceased suggesting extreme aridity at lop nur very strong low altitude winds and frequent dust storms during early mis 1 the contribution of dust storms to the lake sediments fell gradually and was then relatively constant even during the younger dryas cold interval this result might be ascribed to the increased supply of meltwater from snow and ice to lop nur representing a response to the rise in atmospheric temperatures during the deglacial accompanied by strong high level winds during 9 7 kyr bp there was an increase in the input of sediment from sandstorms and hence an increase in low level wind strength possibly relating to the 8 2 kyr bp cold event from 7 0 to 1 5 kyr bp there was a decrease in sandstorm input and thus a gradual weakening of the strength of low level winds however after 1 5 kyr bp the sandstorm input increased overall we conclude that dust storm activity in the region of lop nur since 40 kyr bp has been controlled mainly by northern hemisphere cold events with atmospheric dust providing a background sedimentary component that was dominant during warm intervals our findings contribute to an improved understanding of the dynamics of dust transport and to the history of dust activity and the lacustrine sedimentary record in northwestern china

distributions and sources of hopanes hopanoic acids and hopanols in miocene to recent sediments from odp leg 190 nankai trough the distributions and origins of hopanes hopenes hopanoic acids and hopanols in marine sediments from sites 1175 1176 and 1178 ocean drilling program odp leg 190 nankai trough were investigated the high concentrations of hopanoic acids and anhydrobacteriohopanetetrol in the sediments correspond well with a terrestrial contribution as indicated by the abundance of higher plant derived lipids and turbidite layers suggesting that they are mainly transported from land bacteriohopanetetrol and hopanepolyols with short side chains were commonly detected down to about 400 m below sea floor diagenetic transformation from biohopanoids to geohopanoids can take place quickly after the death of bacteria the presence of intact bacteriohopanetetrol in geological sediments tends to suggest an origin from in situ living bacteria so bacteriohopanetetrol might be a potential life marker for deep sub surface bacteria

reevaluation of the lake sediment chronology in the dead sea basin israel based on new 230th u dates the dead sea is surrounded by chemical and detrital sediments that were deposited in its larger precursor lakes lake samra and lake lisan the sedimentary history of these lakes was recon structed by means of 230th234u ages of 30 samples mostly of argonite laminae from 8 columnar sections up to 110 km apart the general validity of the ages was demonstrated by subjecting them to tests of internal isotopic consistency agreement with stratigraphic order and concordance with 14c ages in the south only the part of the samra formation older than 170 000 yr is exposed while the aragonite detritus rhythmites found in the central and northern region are generally younger than 120 000 yr the lisan formation started accumulating about 63 000 yr b p with the clay and aragonite beds in the south central area reflecting a rise in water level to at least 280 m the upper part of the lisan formation the aragonite rich white cliff member started accumulating about 36 000 yr b p the lake probably reached its highest level sometime after this based on the ages of lisan sediments preserved in the southernmost reaches of the basin

biogeochemical aspects of uranium mineralization mining milling and remediation abstract natural uranium u occurs as a mixture of three radioactive isotopes 238 u 235 u and 234 u only 235 u is fissionable and makes up about 0 7 of natural u while 238 u is overwhelmingly the most abundant at greater than 99 of the total mass of u prior to the 1940s u was predominantly used as a coloring agent and u bearing ores were mined mainly for their radium ra and or vanadium v content the bulk of the u was discarded with the tailings finch et al 1972 once nuclear fission was discovered the economic importance of u increased greatly the mining and milling of u bearing ores is the first step in the nuclear fuel cycle and the contact of residual waste with natural water is a potential source of contamination of u and associated elements to the environment uranium is mined by three basic methods surface open pit underground and solution mining in situ leaching or in situ recovery depending on the deposit grade size location geology and economic considerations abdelouas 2006 solid wastes at u mill tailings umt sites can include both standard tailings i e leached ore rock residues and solids generated on site by waste treatment processes the latter can include sludge or mud from neutralization of acidic mine mill effluents containing fe and a range of coprecipitated constituents or barium sulfate precipitates that selectively remove ra e g carvalho et al 2007 in this chapter we review the hydrometallurgical processes by which u is extracted from ore the biogeochemical processes that can affect the fate and transport of u and associated elements in the environment and possible remediation strategies for site closure and aquifer restoration this paper represents the fourth in a series of review papers from the u s geological survey usgs on geochemical aspects of umt management that span more than three decades the first paper landa 1980 in this series is a primer on the nature of tailings and radionuclide mobilization from them the second paper landa 1999 includes coverage of research carried out under the u s department of energy s uranium mill tailings remedial action program umtra the third paper landa 2004 reflects the increased focus of researchers on biotic effects in umt environs this paper expands the focus to u mining milling and remedial actions and includes extensive coverage of the increasingly important alkaline in situ recovery and groundwater restoration

a holocene dust record in arid central asia inferred from lake barkol northwest china grain size distributions and detrital minerals were investigated for modern dust and for lacustrine sediment in lake barkol region northwest china characteristics of the modern dust and lacustrine sediments principle component analysis and changes of quartz contents all suggest grain size 45 138 m in the core sediment is the dust sensitive component it indicates that high dust flux climate occurred at mid holocene 5 5 4 5 cal ka bp corresponding to the high dust flux record in northwest pacific and the drought interval of deserts in northwest china during the mid holocene the strong dust activity is in contradiction with the climatic optimum recorded by the lacustrine evidence in xinjiang different responses of the dust source region and watershed to the regional climate may have led to the inconsistency between dust and climate records during the mid holocene in arid central asia

impact of land cover change on the climate of southwest western australia 1 a sudden reduction in rainfall occurred in the southwest of western australia in the mid 20th century this reduced inflows to the perth water supply by about 120 gl 42 and led to an acceleration of projects to develop new water sources at a cost of about 300 million the reduction in rainfall was coincident with warmer temperatures a major analysis of these changes indicated that the changes in temperature were likely caused by the enhanced greenhouse effect and that the changes in rainfall were likely caused by a large scale reorganization of the atmospheric circulation we explore an alternative hypothesis that large scale land cover change explains the observed changes in rainfall and temperature we use three high resolution mesoscale model configurations forced at the boundaries to simulate for each model five july climates for each of natural and current land cover we find that land cover change explains up to 50 of the observed warming following land cover change we also find in every simulation a reduction in rainfall over southwest western australia and an increase in rainfall inland that matches the observations well we show that the reduced surface roughness following land cover change largely explains the simulated changes in rainfall by increasing moisture divergence over southwest western australia and increasing moisture convergence inland increased horizontal wind magnitudes and suppressed vertical velocities over southwest western australia reduce the likelihood of precipitation inland moisture convergence and increased vertical velocities lead to an increase in rainfall our results indicate that rainfall over southwest western australia may be returned to the long term average through large scale reforestation a policy option within the control of local government such a program would also provide a century scale carbon sink to ameliorate australia s very high per capita greenhouse gas emissions index terms 1655 global change water cycles 1836 3322 meteorology and atmospheric dynamics land atmosphere interactions 3329 meteorology and atmospheric dynamics mesoscale meteorology keywords land cover change mesoscale modeling regional climate change

uranium series dating of carbonate tufa deposits associated with quaternary fluctuations of pyramid lake nevada abstract uranium series dating of dense tufa deposited in a small cave at former lake margins and in large tufa mounds clarifies the timing of lake level variation during the past 400 000 yr in the pyramid lake basin a moderate sized lake occasionally overflowed the emerson pass sill at elevation of 1207 m between ca 400 000 and 170 000 and from ca 60 000 to 20 000 yr b p as shown by230th 234u ages of the cave samples 230th excess ages of tubular tufas and average isochron plot ages of shoreline deposited tufas by comparison modern pyramid lake is 50 m below this sill there is a lack of tufa record during the intervening period from ca 170 000 to 60 000 yr b p after ca 20 000 yr pyramid lake underwent abrupt changes in level and based on previous14c ages reached its highest elevation ca 1335 m at ca 14 000 yr b p the youngest uranium series ages are comparable with previously reported14c ages

u series dating by the tims technique of land snails from paleosols in the canary islands a sequence of seven superimposed paleosols developed on eolian calcarenites and alluvium was sampled on the island of lanzarote in order to examine the possibility of dating land snail shells by the u series method using a tims technique allowing measurement of u and th isotopes in very small samples in the lower six units the fossil shells yielded d allo l isoleucine a i ratios of about 0 5 and apparent ams 14c ages ranging from 41 000 to 34 000 yr b p indicating that most paleosols formed during a relatively short mid wurm humid episode the upper unit paleosol 7 yielded more variable a i ratios ranging from 0 6 to 0 2 and a younger 14c age 27 000 yr b p most samples contained enough u to allow the calculation of u series ages after correction for the presence of a detrital component in samples containing a few tens of ppb of u paleosols 1 2 3 6 and 7 the ages are strongly dependent upon the model used for the correction in samples containing more than 300 ppb of u paleosols 4 and 5 concordant ages of 31 000 1000 yr were obtained regardless of the correction model used u uptake in these shells occurred during one single early diagenetic phase soon after burial since shells of modern snails do not contain any significant amount of u the arid conditions subsequent to the mid wurm humid episode have likely ensured since then a fair closure of the radioactive system

defining the hyporheic zone in a large tidally influenced river summary an investigation was conducted to characterize the spatial and temporal distribution of the hyporheic zone of a large tidally influenced river the field site is located on the fraser river in british columbia canada approximately 30 km from its outlet to the ocean the physical attributes of the riverbed were mapped using geophysical techniques coupled with sediment sampling the spatial and temporal distribution of groundwater composition beneath the riverbed was determined through detailed profiling contaminated fresh groundwater discharges through a narrow band of the riverbed at a distance approximately 88 105 m from the shoreline coinciding with the termination of a massive silty unit saline groundwater as part of a regional flow system dominates the riverbed sediments from 105 m beyond the shoreline towards the centre of channel three water types occur within the upper 2 m of the riverbed sediments a result of both mixing of river water contaminated fresh groundwater and saline groundwater and modification by cation exchange reactions the interaction of these waters produced distinct zones of ca hco 3 na cl and ca cl type waters the distribution of groundwater solutes indicates that during a single tidal cycle river water penetrates the riverbed to a depth of approximately 15 cm but the long term effects of tidal pumping of river water into the riverbed is observed to a depth of approximately 1 m below the river bed

influence of variable salinity conditions in a tidal creek on riparian groundwater flow and salinity dynamics while recent studies have revealed that tidal fluctuations in an estuary significantly affect groundwater flows and salt transport in the riparian zone only seawater salinity in the estuary has been considered a numerical study is conducted to investigate the influence of estuarine salinity variations on the groundwater flow and salt dynamics in the adjacent aquifer to extend our understanding of these complex and dynamic systems tidal salinity fluctuations synchronous with estuary stage were found to alter the magnitude and distribution of groundwater discharge to the estuary which subsequently impacted on groundwater salinity patterns and residence times especially in the riparian zone the effects of salinity fluctuations were not fully captured by adopting a constant time averaged estuarine salinity the modelling analysis also included an assessment of the impact of a seasonal freshwater flush in the estuary similar to that expected in tropical climates e g mean estuary level during flood significantly greater than average on adjacent groundwater flow and salinity conditions the three month freshwater flushing event temporarily disrupted the salt distribution and re circulation patterns predicted to occur under conditions of constant salinity and tidal water level fluctuations in the estuary the results indicate that the salinity variations in tidal estuaries impact significantly on estuary aquifer interaction and need to be accounted for to properly assess salinity and flow dynamics and groundwater residence times of riparian zones

numerical modeling of subsurface release and fate of benzene and toluene in coastal aquifers subjected to tides abstract a numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach the simulations were conducted by using a numerical model biomarun which coupled a multi monod kinetic model biob to a density dependent variably saturated groundwater flow model marun the fate and transport of the contaminant plume were characterized by computing its centroid trajectory spreading area and percentage of biodegradation in beach saturated and unsaturated zone respectively key factors likely affecting this process were investigated including tide amplitude capillarity and hydraulic conductivity it was found that aerobic biodegradation was the major fate of the contaminant plume in the beach tidal action twisted the centroid of the contaminant plume during its migration in the beach which increased the residence time of the plume in the beach high tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach in contrast the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach the increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone up to 40 which is comparable to that in the saturated zone hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach higher hydraulic conductivity induced faster contaminant biodegradation in the beach

geochemical study of different aged mining dump materials in the freiberg mining district germany historical mining dumps are useful archives for the investigation of weathering processes the objective of this study was to investigate the weathering behavior of waste rock material derived from the 800 year old silver ore mining in freiberg germany for identifying time dependent weathering indices dumped material of four dumps of different ages and corresponding rock was examined regarding the geochemical composition the dumped material is characterized by high contents of heavy metal containing sulfidic ores such as pyrite arsenopyrite sphalerite and galena acid mine drainage is produced by the oxidative weathering of the sulfide minerals and causes the increased dissolving of soluble metals with increasing age of dumps as a result of these weathering processes a clear depletion of chalcophile elements in the older dump material 800 years compared to the youngest dump 100 years was observed in the soil horizons downstream the dumps high quantities of heavy metals e g up to 12 000 ppm as 3 300 ppm pb 640 ppm zn mainly adsorbed on organic matter were determined and indicate a time dependent element transfer from the dumps into their surrounding soils

last deglacial and holocene lake level variations of qinghai lake north eastern qinghai tibetan plateau qinghai lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid latitude westerlies and the low latitude asian summer monsoon asm most published lake level histories of qinghai lake are interpreted from drill core proxies here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial the results indicate that two periods of highstands occurred during the last deglacial approximate to 16 14 9 and approximate to 12 6 12 2 ka and that lake levels were 6 7 4m higher than at present lake levels dropped abruptly during the younger dryas and were generally low with frequent fluctuations during the early holocene qinghai lake reached its highest holocene level 9 1m higher than modern at approximate to 5 ka and has regressed during the past 2 ka we propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters supplemented by enhanced westerlies precipitation and decreased evaporation during heinrich event 1 approximate to 16 14 9 ka and increased asm rainfall during the bolling allerod warm period approximate to 14 12 ka lake level fluctuations during the holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland china

delineating seasonal porewater displacement on a tidal flat in the bay of bengal by thermal signature implications for submarine groundwater discharge summary submarine groundwater discharge sgd to the bay of bengal is an important groundwater discharge process to southern asia as well as to the global oceans water fluxes in these regions are not very well understood the present study demonstrates the use of sea bed porewater temperature as a tracer for delineating seasonal sgd from a shallow coastal aquifer to the bay of bengal porewater temperature mapping along with chemical profile of porewater column were used to delineate groundwater discharge zones for different seasons in a hydrologic year while the temperature profiles were used to evaluate total groundwater discharge both terrestrial and marine the salinity and total dissolved solids profiles were used to evaluate the component due to terrestrial freshwater discharge several springs and seeps were mapped to finger print the freshwater discharge zones and identify the terrestrial sourced sgd temperature windows these zones are also identified to be enriched with algal mats and hence may indicate the pathways of nutrient solute discharge that enhance the primary productivity in the marine ecosystem assuming vertical flow in the seabed simulated rates of discharged groundwater provided a good match with measured discharge rates the porewater fluxes were estimated by applying analytical solutions of the heat conduction advection equations to the observed vertical temperature profiles high resolution thermal profiles to identify t sgd signatures and chemical profiles along mapped transects reveal the nuances of 3 d seasonal hydrodynamics of groundwater seawater interactions the calculated vertical porewater fluxes through the seabed ranged from negligible to 2 45 10 2 m 3 m 2 d 1 within a zone extending from high tide line to 40 m offshore and represent the vertical porewater velocity and the average vertical porewater velocity is found as 8 2 10 3 m 3 m 2 d 1 approximations suggest that in present day condition total average annual sgd to bay of bengal is about 1 16 10 7 m 3 y seasonal estimates suggest that the averages sgd during pre monsoon and post monsoon seasons are ranges 0 6 0 8 10 7 m 3 y for pre monsoon and 0 8 1 5 10 7 m 3 y for post monsoon respectively the findings suggest that monsoonal activity result in a significant porewater displacement from tidal flat sediments by increased groundwater discharge

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

an experimental and numerical investigation of saltwater movement in coupled saturated partially saturated systems 1 a combined experimental and numerical analysis is used to examine the movement and interaction of saltwater and freshwater in unconfined porous media particular emphasis is placed on flow phenomena in the partially saturated region above the water table and along the interface between the saturated and partially saturated regions while some numerical models are apparently capable of simulating these phenomena there is still a significant lack of experimental data with which to verify the models here a series of laboratory scale experiments is considered to evaluate density dependent saltwater freshwater flow patterns in both the saturated and partially saturated zones the laboratory experiments demonstrate clearly that significant lateral flows and coupled density driven flow effects may take place in the partially saturated region above the water table and at the interface between the saturated and partially saturated zones in parallel a finite element numerical model is developed the model reproduces effectively the observed flow behaviors the quality of the results suggests that the numerical model has the capacity to provide realistic predictions

a high resolution record of holocene environmental and climatic changes from lake balikun xinjiang china implications for central asia a high resolution record of holocene environmental and climatic change in the balikun area was reconstructed from a sediment core from the lake balikun multiproxy data show that the climate was extremely arid during the early holocene before 8 6 cal ka bp moisture began to increase after 8 6 cal ka bp and the climate was humid between 7 9 and 4 3 cal ka bp a significant dry event occurred around 4 3 3 8 cal ka bp the climate became generally wet during the late holocene after 3 8 cal ka bp the holocene pollen and geophysical records do not indicate a wet early holocene making it evident that there was no early holocene humid period associated with peak asian monsoon strength regional comparisons indicate that this region has a different pattern of holocene environmental and climatic change from the asian monsoonal area and south siberia

u series chronology of lacustrine deposits in death valley california uranium series dating on a 186 m core dv93 1 drilled from badwater basin in death valley california and on calcareous tufas from nearby strandlines shows that lake manly the lake that periodically flooded death valley during the late pleistocene experienced large fluctuations in depth and chemistry over the last 200 000 yr death valley has been occupied by a long standing deep lake perennial shallow saline lakes and a desiccated salt pan similar to the modern valley floor the average sedimentation rate of about 1 mm yr for core dv93 1 was punctuated by episodes of more rapid accumulation of halite arid conditions similar to the modern conditions prevailed during the entire holocene and between 120 000 and 60 000 yr b p from 35 000 yr b p to the beginning of the holocene a perennial saline lake existed over 70 m at its deepest a much deeper and longer lasting perennial lake manly existed from about 185 000 to 128 000 yr b p with water depths reaching about 175 m if not 330 m this lake had two significant dry excursions of 102 103yr duration about 166 000 and 146 000 yr b p and it began to shrink to the point of halite precipitation between 128 000 and 120 000 yr b p the two perennial lake periods correspond to marine oxygen isotopic stages ois 2 and 6 based on the shoreline tufa ages we do not rule out the possible existence 200 000 yr ago of yet a third perennial lake comparable in size to the ois 6 lake the234u 238u data suggest that u in tufa owes its origin mainly to ca rich springs fed by groundwater that emanated along lake shorelines in southern death valley and that an increase of this spring water input relative to the river water input apparently occurred during ois 6

chemical remobilization of contaminant metals within floodplain sediments in an incising river system implications for dating and chemostratigraphy metals such as pb zn cd and cu from historical mining activity have been used as stratigraphic markers for dating and provenancing vertically accreted fine grained floodplain overbank deposits this study presents evidence for chemical remobilization of these metals within overbank sediments in the tyne basin uk the evidence includes breakdown of metal bearing minerals sulphides carbonates iron and manganese oxyhydroxides shifts of chemical fractions within zones of relatively low ph towards more soluble and reactive phases and accumulation of secondary iron and manganese oxyhydroxides at levels related to fluctuating water table levels or to the breakdown of organic matter all of this suggests that fine centimetre scale chemostratigraphy using metal concentrations and ratios is unlikely to provide reliable data in river systems that have experienced or are experiencing major changes in water table levels or pedogenesis coarse tens of centimetre to metre scale chemostratigraphy when applied with caution may still provide a means of delineating contaminated units

redox zonation and oscillation in the hyporheic zone of the ganges brahmaputra meghna delta implications for the fate of groundwater arsenic during discharge abstract riverbank sediment cores and pore waters shallow well waters seepage waters and river waters were collected along the meghna riverbank in gazaria upazila bangladesh in jan 2006 and oct nov 2007 to investigate hydrogeochemical processes controlling the fate of groundwater as during discharge redox transition zones from suboxic 0 2 m depth to reducing 2 5 m depth then suboxic conditions 5 7 m depth exist at sites with sandy surficial deposits as evidenced by depth profiles of pore water n 7 and sediment n 11 diffuse reflectance fe iii fe ratios and fe iii concentrations the sediment as enrichment zone up to 700 mg kg 1 is associated with the suboxic zones mostly between 0 and 2 m depth and less frequently between 5 and 7 m depth the as enriched zones consist of several 5 10 cm thick dispersed layers and span a length of 5 15 m horizontally from the river shore depth profiles of riverbank pore water deployed along a 32 m transect perpendicular to the river shore show elevated levels of dissolved fe 11 6 11 7 mg l 1 and as 118 91 g l 1 mostly as arsenite between 2 and 5 m depth but lower concentrations between 0 and 2 m depth 0 13 0 19 mg l 1 fe 1 1 g l 1 as and between 5 and 6 m depth 1 14 0 45 mg l 1 fe 28 17 g l 1 as because it would take more than a few hundred years of steady groundwater discharge 10 m yr 1 to accumulate hundreds of mg kg 1 of as in the riverbank sediment it is concluded that groundwater as must have been naturally elevated prior to anthropogenic pumping of the aquifer since the 1970s not only does this lend unequivocal support to the argument that as occurrence in the ganges brahmaputra meghna delta groundwater is of geogenic origin it also calls attention to the fate of this as enriched sediment as it may recycle as into the aquifer

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

novel polyfunctionalised geohopanoids in a recent lacustrine sediment priest pot uk abstract the sediment of a highly productive lake priest pot uk contains the biosynthesised hopanoid bacteriohopanetetrol bht and a series of hopanediols and triols these polyols represent intermediate stages in the conversion of biologically produced hopanoids to the diagenetic products hopanes two of these geohopanoids assigned as trishomohopane 32 33 diol and bishomohopane 30 31 32 triol have not been previously reported in recent sediments and their identification in addition to that of tetrakishomohopane 32 33 34 triol and a bishomohopanediol gives valuable information on the original composition and subsequent diagenesis of bacteriohopanepolyols within recent sediments

u series chronology of sediments associated with late quaternary fluctuations balikun lake northwestern china abstract the u series dating method was used to date the sediment core b194 from balikun lake xinjiang northwestern china the samples were extracted with acids of different concentrations and 230th 232th and 234u 232th ratios of each sample were measured contamination with non radiogenic 230th can be overcome in most instances using an isochron correction scheme for a sequential acid leach procedure the method can provide the most reliable dates from samples in lake of the arid semiarid regions where carbonate is assumed close to uranium and thorium after deposition where three known ages of palaeomagnetic reversals have already been obtained in the same core the u series ages appear to compare reasonably well with palaeomagnetic event ages based on the u series chronology and stable isotope records lake level history was reconstructed which suggests that balikun has been a shallow saline lake since 150 ka bp and its level frequently changed in response to climate changes arid climates occurred between 129 71 ka bp and at 62 25 ka bp corresponding to marine oxygen isotopic stages ois 5 and 3 during which times balikun lake approached playa conditions after 13 ka bp the lake shrank and became a saline field and mudflat with a water table at or below the lake bed three major high lake stands were identified at about ca 138 132 69 65 and 25 18 ka bp and the three high stand periods correspond to ois 6 4 and 2 rising lake levels during the penultimate glaciation and both stades of the last glaciation might have resulted from the location of the lake in an arid region where the climate was controlled mainly by the westerly winds

preservation and diagenesis of hopanoids in recent lacustrine sediments of priest pot england abstract absolute concentrations of various bio and geohopanoids have been determined in a 24 cm long core from anoxic recent sediments of priest pot a small highly productive lake in the english lake district samples were soxtherm extracted derivatised by methods targeted at specific hopanoid groups and quantified by gc ms periodic acid sodium borohydride treatment was used to cleave the side chains of highly functionalised hopanoids producing products more amenable to our detection methods biohopanoids are extremely abundant totalling up to 3000 g g dry sediment particularly those with composite or highly penta and hexa functionalised side chains suggesting that these are important precursors to sedimentary hopanoids in priest pot downcore biohopanoid abundance profiles show a general diagenetic decline with a marked dip at 5 8 cm which we interpret as a change in bacterial input since this is most marked in the composite hopanoids rather than bacteriohopanetetrol we suggest that these two hopanoid groups have at least partly different sources and may thus have potential as environmental markers the geohopanoids are also abundant totalling up to 1700 g g dry sediment being dominated by the and bishomohopanoic acids and bishomohopanol and hop 17 21 ene downcore plots show no apparent conversion of free bio to geohopanoids with depth which suggests that incorporation into kerogen may be commencing at an early diagenetic stage in the sediments

contrasting early holocene temperature variations between monsoonal east asia and westerly dominated central asia abstract numerous studies have demonstrated that there are major differences in the timing of maximum holocene precipitation between the monsoonal east asia and westerly dominated central asia but it is unclear if the moisture differences are also associated with corresponding temperature contrasts here we present the first alkenone based paleotemperature reconstructions for the past 21 kyr from lake balikun central asia we show unlike the initiation of holocene warm conditions at 11 kyr bp in the monsoon regions the arid central asia remained in a glacial like cold condition prior to 8 kyr bp and experienced abrupt warming of 9 c after the collapse of the laurentide ice sheet comparison with pollen and other geochemical data indicates the abrupt warming is closely associated with major increase in the moisture supply to the region together our multiproxy data indicate 2 thousand years delay of temperature and moisture optimum relative to local summer insolation maximum suggesting major influence of the laurentide ice sheet and other high latitude ice sheet forcings on the regional atmospheric circulation in addition our data reveal a temperature drop by 4 c around 4 kyr bp lasting multiple centuries coinciding with severe increases in aridity previously reported based on multiproxy data in contrast model simulations display a much less pronounced delay in the initiation of holocene warm conditions raising unresolved questions about the relative importance of local radiative forcing and high latitude ice on temperature in this region

hypoaigic influences on groundwater flux to a seasonally saline river hypoaigic zones are aquifer volumes close to and beneath the shores of saline surface water bodies and are characterized by the presence of time dependent natural convection and chemical stratification when transient and cyclic processes are involved there is significant potential for complex flow and reaction in the near shore aquifer presenting a unique challenge to pollutant risk assessment methodologies this work considers the nature of some hypoaigic processes generated by the seasonally saline canning river of western australia near a site contaminated by petroleum hydrocarbons a dissolved hydrocarbon plume migrates within the shallow superficial aquifer to the nearby bank of the canning river beneath the river bank a zone of complex fluid mixing is established by seasonal and tidal influences understanding this complexity and the subsequent ramifications for local biogeochemical conditions is critical to inferring the potential for degradation of advecting contaminants a range of modelling approaches throws light on the overall topographic controls of discharge to the river on the saline convection processes operating under the river bank on the potential for fluid mixing and on the various important time scales in the system saline distributions simulated within the aquifer hypoaigic zone are in at least qualitative agreement with previous field measurements at the site and are strongly affected by seasonal influences groundwater seepage velocities at the shoreline are found to be positively correlated with river salinity calculations of fluid age distributions throughout the system show sensitivity to dispersivity values however maximum fluid ages under the river appear to be diffusion limited to a few decades the saline convection cell in the aquifer defines a zone of strong dispersive dilution of aged many decades deep aquifer fluids with relatively young several months riverine fluids seasonal recharge and river salinity cycles induce regular perturbations to the convection cell yielding intra annual variations of 50 in seepage velocity and almost 30 in wedge penetration distance at the plume location

the significance of groundwater stream interactions and fluctuating stream chemistry on waterborne uranium contamination of streams a case study from a gold mining site in south africa through seepage dissolved uranium and other heavy metals migrate from tailings deposits of gold mines via groundwater into adjacent fluvial systems the extent of associated stream contamination is determined inter alia by the retardation of dissolved contaminants along the pathway and the rate in which polluted groundwater enters the stream channel comparing several sediment water systems of the aqueous pathway significantly higher immobilisation of u was found in fast flowing surface water systems such as the stream than in slow moving alluvial groundwater of the floodplain mainly triggered by redox initiated co precipitation bottom sediments in streams act as geochemical barrier and long term sink for u and other heavy metals from polluted groundwater real time in situ measurements of hydraulic interactions between contaminated groundwater and streamwater suggest a highly dynamic water exchange between both water bodies including daily inversions of the direction of flow in certain times of the year this results in distinct diurnal differences of the associated stream contamination the extent of subsequent downstream transport of u within the fluvial system is largely determined by pronounced diurnal oscillations of ph and redox potential in the stream affecting u speciation as well as adsorption and precipitation rates in addition event triggered fluctuations of both parameter impact on the fluvial transport of u

a raised ois 3 sea level recorded in coastal sediments southern changjiang delta plain china abstract the distribution of marine influenced oxygen isotope stage ois 5 to ois 1 sediments was examined in several late quaternary boreholes from the southern changjiang yangtze delta plain china using different dating methods including osl u series ams 14c and paleomagnetism results demonstrate that coastal and estuarine deposition during ois 5 and ois 3 occurred throughout the study area however holocene transgressive sediments were absent on the taihu block the burial depth of intertidal to subtidal sediment deposited during ois 5e records 30 80 m subsidence caused by sediment compaction and tectonic movement since that time however coastal sediments formed during the late phase of ois 3 were buried to a depth of ca 6 15 m in the taihu lake area while the burial depth increased eastward to ca 45 60 m on the coastal plain this phenomenon combined with the distribution of holocene marine strata indicates at least 25 30 m uplift of the taihu block since the end of ois 3 we suggest that this uplift was mainly caused by the differential subsidence due to substantial amount of post glacial deposition by the changjiang and huanghe rivers on the continental shelf of east china marginal sea

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

saline water intrusion adjacent to the fraser river richmond british columbia during periods of average to low flow in the fraser river seawater from georgia strait migrates with a rising tide up the river channel reaching distances up to 16 km from the river s outlet to the ocean this relatively dense water infiltrates through the river bed and circulates as a stable wedge of saline water within permeable deltaic deposits adjacent to the river at the kidd2 site in richmond the wedge extends approximately 500 m inland from the river the top of the transition zone between fresh and saline water is 10 m below ground surface the bottom of the saline wedge is located at the contact with underlying low permeability delta slope deposits resulting in a wedge with a vertical extent of approximately 10 m maximum salinity values observed in the wedge 16 17 parts per thousand reflect the time averaged response to density driven flow under a complex sequence of daily and seasonal variations in salinity within the fraser river and mixing with fresh river water that may enter the aqui

water quality assessment and the investigation of the relationship between the river delice and the aquifer systems in the vicinity of yerkoy yozgat turkey the aim of this study was to investigate the pollution parameters relating to surface and groundwaters and to establish an interaction between these for the area near yerkoy three characteristic facies were determined based on the results of hydrochemical analyses 1 na cl facies were greater the deeper the aquifer 2 na so42 facies were the greater portion of the shallow alluvium aquifer and 3 na hco3 so42 facies represented the western portion of the shallow alluvium aquifer based on field and laboratory observations it was found that the water of the river delice is suitable for irrigation and domestic use whereas the water from the shallow aquifer is extremely saline and considered to have been polluted by local lithological units active groundwater circulation and dilution between the alluvium aquifer and the river delice was observed because of the short residence time of the groundwater in this area the hydrogeochemical concentration and the salinity were found to be low the other portions of the alluvium aquifer bear higher concentrations of soluble ions

u series isochron dating a generalized method employing total sample dissolution the age of a sedimentary deposit can be determined by measuring 238u 234u 232th and 230th in two or more samples of the deposit with the requirement that these samples have different u th ratios but an identical 230th232th ratio when deposited this paper presents the theoretical and experimental aspects of the dating method the latter involves techniques for securing samples of varied u th ratios from the same deposit plotting isochrons of the radiochemical data obtained on totally dissolved samples for age analysis and estimating the errors involved although applications to impure carbonates and lacustrine evaporite sediments are given as examples in this paper the method potentially can be generalized for dating a variety of authigenic deposits such as rock varnish peat opal sulfate minerals and marine phosphorites

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

mixed convection and density dependent seawater circulation in coastal aquifers 1 density dependent circulation of seawater in coastal aquifers results in submarine groundwater discharge sgd across the seabed that is a mixture of terrestrial groundwater and former marine water in this study the controls of the relative amount of seawater to freshwater in sgd were investigated numerically using the feflow and sutra codes it was found that the key controls could be expressed in the form of a single nondimensional recirculation number that incorporates the combined effects of free convection forced convection and hydrodynamic dispersion on convective overturn within the coastal salt wedge anisotropy effects were incorporated into the recirculation number with limited success based on the principle of equivalent isotropic hydraulic conductivity the type of boundary condition employed along the seabed was shown to be important convective overturn was substantially increased if backward dispersion of salt into the aquifer from along the outflowing portion of the seabed boundary was prevented overall the results demonstrated a strong dependence of convective overturn on the aquifer dispersivities suggesting that results from numerical simulations are problematic to apply to real aquifer systems that typically exhibit uncertain scale dependent dispersion properties

waste rock dump investigation at rosia montană gold mine romania a geostatistical approach rosia montan the largest european gold mine could be re opened environmental problems led to severe pollution of the rosia and abrud rivers the two main potentially toxic element pte sources in mine sites are in general the abandoned underground workings and the piles of waste rock since the composition of waste rocks is often heterogeneous this study faces the problem of estimating their mineralogical and chemical features starting from a set of sampling point twenty five samples were collected on the main waste dump of the rosia montan mine following a virtual squared grid knots distance about 25 m grain size color bulk chemistry mineralogy acid mine drainage potential and a set of selected pte ag as cu ni pb and zn concentrations were determined on each sample in a first approximation two main waste rock groups were identified wr1 bulk composition is dacite dominated while wr2 is andesite dominated in both of them the concentrations of ptes are below the regulatory limits for soils with the exception of as in terms of acid mine drainage wr1 has a net acid producing potential while wr2 has a net neutralizing potential the anisotropy of wr properties were analysed by means of semi variograms and displayed with contour maps application of positive matrix factorization for the analysis of all the data relative to waste rocks allowed defining in a semi quantitative way the factors controlling pollution and their spatial distribution the processing of score matrix g factor associated with the geostatistical elaboration promises to be a powerful tool to discern the composition of mine dumps and support the exploitation and remediation phases

the mobility of radium 226 and trace metals in pre oxidized subaqueous uranium mill tailings the exchange of 226ra and trace metals across the tailings water interface and the mechanisms governing their mobility were assessed via sub centimetre resolution profiling of dissolved constituents across the tailings water interface in cell 14 of the quirke waste management area at rio algom s quirke mine near elliot lake ontario canada shallow zones 2 m water depth fosters stagnant bottom waters and permits the development of anoxia above the benthic boundary these anoxic tailings are characterized by substantial remobilization of 226ra resulting in a relatively large flux of 226ra from the tailings to the water column the strong correlation between the porewater profiles of 226ra and ba r2 0 99 as well as solubility calculations indicate that the mobility of ra is controlled by saturation with respect to a poorly ordered and or impure barite phase ra ba so4 in the anoxic zones severe undersaturation with respect to barite is sustained by microbial so4 reduction flux calculations suggest that the increase in 226ra activity in the water cover since 1995 from 0 5 to 2 5 bq l 1 can be attributed to an increase in the spatial distribution of anoxic bottom waters caused by increased density of benthic flora the anoxic vegetated areas also exhibit minor remobilization with respect to dissolved as ni and zn the removal of trace metals in the anoxic bottom waters appears to be limited by the availability of free sulphide collectively the data demonstrate that while the water cover over the u mill tailings minimizes sulphide oxidation and metal mobility anoxic conditions which have developed in deeper areas have led to increased mobility of 226ra

groundwater hydrochemistry and soil pollution in a catchment affected by an abandoned lead zinc mine functioning of a diffuse pollution source the importance of polluted alluvial soils as a potential diffuse source of heavy metals was investigated in a catchment of the matylda stream affected by an abandoned lead and zinc ore mine in upper silesia southern poland this was attempted by means of standard groundwater analyses performed together with measurements of cd pb zn fe and mn concentrations in soil and groundwater the matylda stream receiving mine water was converted in the 20th century into a straight channel directed in its middle reach over the valley bottom this changed the drainage direction of the matylda stream water during mining operations groundwater seepage combined with surface drainage by shallow ditches caused pollution of sandy soils exceeding over 100 mg kg of cd 24 of zn and 4 of pb at surface or subsurface soil horizons and reaching at least 60 cm in depth after mine closure in the 1970s the network of ditches appears to be a source of ca mg chlorides carbonates and nitrates as indicated by the more or less regular increase of these major ion concentrations in groundwater down ditches whereas the ditches are a sink rather than a source of zinc cadmium and lead in permanently dry reaches or transition zones in reaches with surface water flowing periodically the metal concentrations and distribution in soil and groundwater suggest the slow mobilization of heavy metals stored in the valley bottom and the minor importance of soil as a diffuse source for surface water pollution

early diagenesis of bacteriohopanoids in recent sediments of lake pollen norway abstract the distribution of free bio and geohopanoids were studied in a short 46 cm core from recent sediments of lake pollen norway bacteriohopanepolyols are abundant components of the sediments totalling up to 321 g g dry sediment 7485 g g toc being dominated by c 32 33 34 35 tetrafunctionalised hopanoids significantly bacteriohopanetetrol only accounts for between 7 to 62 of these 24 on average indicating that composite bacteriohopanoids are more abundant sedimentary constituents and thus more important precursors of geohopanoids than previously recognised downcore profiles of bio and geohopanoid abundance show maxima at ca 25 to 30 cm with a marked decrease in abundance above this depth which coincides with a well documented change in environment from fjord to isolated lake a second maximum in biohopanoid abundance occurs at ca 5 to 12 cm depth specific biohopanoids were affected to different extents by the change in environment suggesting that they have at least partly different sources our data thus indicate that biohopanoids and their geohopanoid products may be sensitive to changes in depositional environment and that they have potential to act as markers for environmental conditions

230th 234u and 36cl dating of evaporite deposits from the western qaidam basin china implications for glacial period dust export from central asia the western qaidam basin contains numerous hydrologically closed lakes and playas we have measured uranium thorium and chlorine radioisotopes in sediments from drill cores at two of these gasikule lake and dalangtan dry playa in order to date cycles of high and low lake level the sediment chronologies from the two sub basins are generally concordant and the u th ages indicate transitions from high to low lake levels at 302 56 ka at 138 6 ka and at 16 3 2 2 ka these ages indicate that high lake stands in the qaidam basin were terminated at the end of continental glacial maxima this result is unexpected because previously the large eolian dust fluxes out of central asia during glacial maxima have been considered to be associated with increased aridity in the region not increased humidity the lacustrine evidence combined with previous data from ice cores suggests instead that the persistence of strong winds may have played a more important role in enhanced dust fluxes than did variations in dust availability due to changes in aridity

interaction between shallow groundwater saline surface water and contaminant discharge at a seasonally and tidally forced estuarine boundary this paper presents findings from a 2 year field investigation of a dissolved hydrocarbon groundwater plume flowing towards a tidally and seasonally forced estuarine river system in perth western australia samples collected from transects of multiport wells along the riverbank and into the river enabled mapping of the fine scale 0 5 m vertical definition of the hydrocarbon plume and its longitudinal extent spear probing beneath the river sediments and water table and transient monitoring of multiport wells electrical conductivity was also carried out to define the zone of mixing between river water and groundwater the hyporheic zone and its variability the results showed that groundwater seepage into the estuarine surface sediments occurred in a zone less than 10 m from the high tide mark and that this distance and the hyporheic transition zone were influenced by tidal fluctuations and infiltration of river water into the sediments the dissolved btexn benzene toluene ethylbenzene the xylene isomers and naphthalene distributions indicated the behaviour of the hydrocarbon plume at the groundwater surface water transition zone to be strongly influenced by edge focussed discharge monitoring programs and risk assessment studies at similar contaminated sites should therefore focus efforts within the intertidal zone where contaminants are likely to impact the surface water and shallow sediment environments

quantifying hyporheic exchange in a tidal river using temperature time series 1 an investigation into groundwater surface water interaction gswi beneath a large tidally influenced river was conducted to determine the effect of tides on the development of a hyporheic zone hz and to quantify mixing of river water and groundwater temperature measurements coupled with independent hydraulic head measurements were used to detect groundwater flow within the riverbed gwsi under tidal forcing produced a 1 m deep hz time averaged riverbed temperature profiles displayed a distinct compressed convex pattern clear evidence of net groundwater discharge however the instantaneous time series data indicate that riverbed temperatures were affected by tidal forcing to a depth of 1 m heat transport modeling revealed that instantaneous velocities within the shallow sediments of the riverbed are rather high creating a zone of vigorous exchange during either a flooding or ebbing tide furthermore the magnitude of the tidal pressure gradient was found to be significantly greater than the pressure gradient expected across 0 8 m high dunes evidence that bed form driven exchange under these conditions and this scale of observation did not contribute to the development of the hz conditions for exchange induced by shear and current bed form are favorable during ebbing tidal conditions only flow paths are therefore limited in depth exchange flow paths in an estuary setting are complex they are limited in duration and space and dominated by tidal pumping

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

tidal influence on behaviour of a coastal aquifer adjacent to a low relief estuary the tidal influence on groundwater hydrodynamics salt water intrusion and submarine groundwater discharge from coastal estuarine aquifers is poorly quantified for systems with a mildly sloping beach in contrast to the case where a vertical beach face is assumed we investigated the effect of beach slope for a coastal aquifer adjacent to a low relief estuary where industrial waste was emplaced over the aquifer the waste was suspected to discharge leachate towards the estuary field observations at various locations showed that tidally induced groundwater head fluctuations were skewed temporally frequency analysis suggested that the fluctuation amplitudes decreased exponentially and the phase lags increased linearly for the primary tidal signals as they propagated inland salinisation zones were observed in the bottom part of the estuary and near the beach surface flow and transport processes in a cross section perpendicular to the estuary were simulated using seawat 2000 which is capable of depicting density dependent flow and multi species transport the simulations showed that the modelled water table fluctuations were in good agreement with the monitored data further simulations were conducted to gain insight into the effects of beach slope in particular the limiting case of a vertical beach face was considered the simulations showed that density difference and tidal forcing drive a more complex hydrodynamic pattern for the mildly sloping beach than the vertical beach as well as a profound asymmetry in tidally induced water table fluctuations and enhanced salt water intrusion the simulation results also indicated that contaminant transport from the aquifer to the estuary was affected by the tide where for the mildly sloping beach the tide tended to intensify the vertical mass exchange in the vicinity of the shoreline

the hydrology of the upper swan river estuary with focus on an artificial destratification trial a trial to artificially destratify part of the water column of the swan canning estuary took place over four weeks in 1997 destratification was attempted with bubble plumes created by pumping compressed air through a porous pipe near the bed at a location in the upper estuary the purpose of the trial was to determine whether the resultant bubble curtain could mix the water column thereby altering the extent of upstream and downstream mixing and the vertical structures of salinity temperature dissolved oxygen and turbidity the destratification trial was monitored using three techniques vertical profiles taken on several days at selected stations along the estuary fine scale profiles in the vicinity of the bubble curtain on one day and continuous water column profiles taken 1 km upstream of the curtain the seasonal upstream propagation of brackish water underneath a residual freshwater discharge was affected by the magnitude of freshwater discharge and tidal elevations superimposed upon diurnal and semi diurnal tides were non tidal water level changes induced mostly by variations in barometric pressure these caused large changes in the salt wedge position destratification by the bubble curtain was compromised by these large oscillations which limited the exposure of the salt wedge region to the mixing action of the bubble curtain complete vertical mixing of the water column was observed up to 30 m either side of the curtain on 30 october disruptions to the density stratification were not evident beyond 350 m of the curtain in the immediate vicinity 30 m of the curtain deficits of dissolved oxygen in bottom waters were generally reduced or obliterated and a naturally turbid plume of water near the bottom of the estuary was mixed through the water column the effects of the bubble curtain on dissolved oxygen turbidity and temperature were however similar to those for salinity with mixing confined to around 30 m from the curtain and no effect observed further than 350 m away the upper swan river estuary although relatively narrow and strongly vertically stratified is unsuited to destratification using bubble plumes cycling of spring and neap tides and non tidal water level changes together with freshwater inflows to the estuary strongly limit the longitudinal extent of mixing by bubble curtains copyright 2001 john wiley sons ltd

structural characterization of an island aquifer via tidal methods 1 a set of water level time series collected along a transect through a sedimentary island aquifer was used to test the utility of various simple models of ocean tidal propagation in bounded one dimensional aquifers fourier spectra were calculated for the ocean tidal modes and compared with spectra measured in wells along the island transect other sources of fluctuation could be neglected an observed spatial bias in the well responses attenuations and lags could not be modeled by a homogeneous aquifer theory a theory involving composite heterogeneity accounted well for the spatial bias yielding estimates of aquifer transmissivities and storage coefficients indicating a fivefold difference in hydraulic diffusivity along the transect a lack of well locations toward one end of the transect reduced the statistical significance of this result with correlations between regression parameters evident at the same time a second bias was seen involving the ratio of signal amplitude and lag with penetration distance into the aquifer as observed in prior tidal studies a brief set of numerical experiments showed that horizontal layering in aquifer properties was the most probable cause of this propagation bias application of these results to the island data set supported a conceptual stratigraphic model of a highly conductive sloping stratum underlying a less conductive superficial sand layer this model is inconsistent with well logs along the island transect but is supported by additional off transect well logs it was concluded that one dimensional tidal propagation models may be useful in inverse characterization of aquifers with macroscale hydrogeological structures and that the analysis of measured propagation bias has the potential to yield extra information on aquifer properties in the vertical direction

environmental influence on the biohopanoid composition of recent sediments abstract bacteriohopanepolyols are the biological precursors of extended hopane biomarkers which are ubiquitous in the geosphere the abundance and composition of these biohopanoids were determined for modern sediments from eight depositional environments by gc ms analysis of hopanols derived from a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols we report quantitative data for bacteriohopanetetrol bht composite tetrafunctionalised biohopanoids pentafunctionalised biohopanoids and hexafunctionalised biohopanoids bht was found in concentrations higher than previously reported up to ca 1500 g g toc but comprised only a relatively small proportion 0 26 of the total biohopanoids in all except one sample composite tetrafunctionalised biohopanoids were the dominant group of bacteriohopanepolyols in all other sediments and are likely to be a major source of the geologically occurring extended hopanes hexafunctionalised biohopanoids were most abundant in lake sediments particularly two small highly productive stratified lakes where they comprised 20 40 of total biohopanoids this feature is interpreted to be due to greater contribution to the organic matter of these sediments from type i methanotrophic bacteria which produce dominantly hexafunctionalised biohopanoids consistent with the environmental settings in the marine environments where sulphate reduction is dominant hexafunctionalised biohopanoids are relatively minor constituents 2 6 of total biohopanoids these data comprise the first clear demonstration that bacteriohopanepolyols vary in composition between depositional environments and have the potential to preserve specific bacterial source information in sedimentary organic matter

uranium series chronology for sediments of lake hovsgol mongolia and the 1 ma records of uranium and thorium isotopes from the hdp 04 drill core abstract uranium and thorium isotopes in an 81 m long sediment core hdp 04 of lake hovsgol mongolia were measured to investigate their downcore distributions and to explore potential linkage to paleoenvironmental changes three dimensional isochron techniques using isotope ratio diagrams in 238u 234u 230th 232th system presented by ludwig and titterington were applied to age date the lake sediments at the depths of 11 42 14 71 and 14 83 m in the hdp 04 section the estimated ages of these horizons are 66 8 122 11 and 128 22 ka respectively the 238u concentration throughout the entire section fluctuated by a factor of 12 ranging from 19 9 to 232 1 mbq g with anomalously high 238u peak at 23 8 m in depth while the 232th concentration varied only by a factor of about two between 24 3 and 54 0 mbq g the discrimination of the bulk 238u into authigenic and terrigenous 238u fractions was attempted based on the measured 232th as a correction index for terrigenous materials in the upper 24 m corresponding to the last 250 ka the authigenic 238u was higher in interglacials and lower in glacials this depth profile of authigenic 238u contents was almost identical pattern with that found in a sediment core ver98 1 6 from the academician ridge lake baikal further this profile can be correlated well with that of photosynthetic pigment contents one of proxies of paleoproductivity suggesting that the variation of authigenic 238u contents were associated with the environmental change around lake hovsgol

surface water groundwater interaction near shallow circular lakes flow geometry in three dimensions steady flow regimes for three dimensional lake aquifer systems are studied via idealized mathematical models that are extensions of earlier simplified vertical section models of interaction between shallow lakes and underlying aquifers the present models apply to a shallow circular lake at the surface of a rectangular aquifer of finite depth yielding a truly three dimensional representation of the resulting flow system flux boundary conditions are applied at the ends of the aquifer with net vertical recharge or evapotranspiration at the water table the lake is defined by a region with constant head by determining and visualizing solutions to the discretized saturated flow equations a range of possible flow regimes is identified and their topological properties are studied tools for analyzing flow regimes are described including a method for locating and mapping three dimensional dividing surfaces within steady flow fields results show strong similarities between two and three dimensional systems including a large number of flow through recharge and discharge regimes and reverse flow cells flow lines calculated on a vertical plane through the middle of a lake resemble but are not identical to two dimensional streamlines for a range of aquifer flow and recharge conditions estimates of the widths and depths of capture and release zones for various lake aquifer geometries are asymptotic to earlier results for two dimensional systems numerical predictions are compared with analytical results for certain limiting flow regimes

an assessment and comparison of 230th and ams 14c ages for lacustrine sediments from qarhan salt lake area in arid western china the age framework of qarhan salt lake in arid western china is still controversial due in part to 1 age discrepancy between conventional 14c and 230th dating results and 2 no ams 14c ages of organic carbon from drilling cores in qarhan salt lake were reported until now in order to discuss these chronological problems upper 54 50 m lacustrine sediments from a drilling core isl1a recovered from qarhan salt lake were dated based on 230th and ams 14c dating techniques results show that 1 ams 14c ages of total organic carbon toc from 4 65 to 30 29 m are almost in stratigraphic order and consistent with 230th ages of halite in the corresponding layers 2 ams 14c ages of toc from 30 29 to 54 50 m are younger with increasing depth this phenomenon was also found in shell bar in the study area suggesting that ams 14c ages from upper 30 29 m are more reliable while those from lower 24 21 m in isl1a may be underestimated 3 230th ages of halite from lower 24 m lacustrine sediments are obviously older than ams 14c ages of toc in the corresponding layers which results into different age framework of salt lake sediments in qarhan salt lake 4 if extrapolating these reliable ams 14c ages in isl1a similar age framework with 230th ages in this core confirms that 230th ages are much close to the true ages of these sediments which suggests that the forming timing of the bottom salt layer is 50 ka

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

clay mineralogical and geochemical constraints on late pleistocene weathering processes of the qaidam basin northern tibetan plateau abstract at the qarhan salt lake qsl on the central eastern qaidam basin northern tibetan plateau quaternary lacustrine sediments have a thickness of over 3000 m and mainly composed of organic rich clay and silty clay with some silt halite and halite in this study a 102 m long sediment core isl1a was obtained from the qsl combining with ams 14c and 230th dating clay minerals and major element concentrations of isl1a were used to reconstruct the weathering process and trend of the qsl since late pleistocene the results reveal that the clay mineral from

uranium series age estimates and paleoclimatic significance of pleistocene tufas from the lahontan basin california and nevada abstract an extended chronology of lahontan basin lake levels based on uranium series age estimates correlates with the global ice volume record lake highstands occur at or shortly after times of maximum ice sheet size moderate size lakes occur when the global ice volume is about 80 of its maximum the data indicate that lake levels rise and fall relative to the proximity of the mean position of the jetstream when the continental ice sheet is above some threshold size or shape it appears that the large scale circulation and climatic conditions are right for producing lakes of moderate to large size within the lahontan basin

u th dating of lake sediments lessons from the 700 ka sediment record of lake junin peru abstract deep sediment cores from long lived lake basins are fundamental records of paleoenvironmental history but the power of these reconstructions has been often limited by poor age control uranium thorium u th dating has the potential to fill a gap in current geochronological tools available for such sediment archives we present our systematic approach to u th date carbonate rich sediments from the 100 m drill core from lake junin peru the results form the foundation of an age depth model spanning 700 kyrs high uranium concentrations 0 3 4 ppm of these sediments allow us to date smaller amounts of material giving us the opportunity to improve sample selection by avoiding detrital contamination the greatest factor limiting the success of previous u th dating efforts in other lake basins despite this advantage the dates from 174 analyses on 55 bulk carbonate samples reveal significant scatter that cannot be resolved with traditional isochrons suggesting that at least some of the sediments have not remained closed systems to understand the source of noise in the geochronological data we first apply threshold criteria that screen samples by their u th ratio reproducibility and 234 uinitial value we then compare these results with facies types trace element concentrations carbonate and total organic carbon content color reflectance mineralogy and ostracode shell color to investigate the causes of open system behavior alongside simulations of the isotopic evolution of our samples we find that the greatest impediment to u th dating of these sediments is not detrital contamination but rather post depositional remobilization of uranium examining u th data in these contexts we identify samples that have likely experienced the least amount of alteration and use dates from those samples as constraints for the age depth model our work has several lessons for future attempts to u th date lake sediments namely that geologic context is equally as important as the accuracy and precision of analytical measurements in addition we caution that significant geologic scatter may remain undetected if not for labor intensive tests of reproducibility achieved through replication as a result of this work the deep sediment core from lake junin is the only continuous record in the tropical andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates

an isotopic study on water system of lake barkol and its implication for holocene climate dynamics in arid central asia mechanism of arid central asia climate dynamics is still an open question even it has been studied for a long time interpreting climatic proxy data properly is crucial for better understanding the paleoclimate in such a sensitive area and its role in the earth system according to the analysis of water stable isotope 18o and d lake barkol catchment obeys the typical isotopic model of a hydrologically closed lake lake input water inherits the feature of the weighted mean annual isotopes in precipitation and lake water isotopes move along the local evaporation line from the start point of input water isotopes modulated by the regional effective moisture based on the modern water isotopes and its relation to the climate sediment carbonate oxygen isotope 18ocarb record re interpretation suggests that the asian monsoon incursion to arid central asia area alone is unlikely the reason for the early holocene 18ocarb negative as the calculated extreme summer rainfall 18o change to compensate the more negative 18ocarb in the early holocene is far beyond our knowledge of precipitation isotopes in the real world besides a 40 of winter precipitation increase could explain the 18o negative change in the early holocene which does more importantly reconcile the contradiction between the pollen aretemisia chenopodiaceae effective moisture and 18o records

an assessment of the importance of some parameters for seawater intrusion in aquifers and a comparison of dispersive and sharp interface modelling approaches abstract the problem considered is that of determining the location and shape of the steady interface in a coastal aquifer discharging fresh water to the sea for homogeneous isotropic aquifers the location of the interface is obtained by the boundary integral method for an abrupt interface model these results are compared with the distribution of salt in the dispersion zone where the two fluids meet as determined by a finite difference solution of the flow and convective dispersion equations considerations are restricted to a rectangular section of isotropic homogeneous aquifer and examples are limited to those showing the effects of different convection to dispersion ratios including anisotropic dispersion different fresh water flow gradients and different relative densities of seawater these examples give an indication of the relative accuracy of the abrupt interface model for different ratios of convection to dispersion and enable the influence of various parameters on the shape and extent of the dispersion zone to be studied

mid holocene climate change in the eastern xinjiang region indicated by the grain size and stable isotope record from lake barkol northwest china a sediment core from lake barkol located in the eastern xinjiang autonomous region northwest china provided a high resolution record of environmental change covering the last 8 6 cal ka bp three major climate stages 8 6 7 1 7 1 2 0 and from 2 0 cal ka bp to the present were divided by grain size and the authigenic carbonate stable isotope of the lake sediment climatic drought during the period 7 1 4 5 cal ka bp deduced from lake barkol prevailed in the mid holocene climate in northern xinjiang and northwest mongolia in contrast it was wet in central xinjiang northwest india and the middle east during the same period the climatic difference between northern and southern arid central asia demonstrates the southward shifting of the westerlies which indicates the potential contribution of the siberian high in the mid holocene

climate variability in east central california during the past 1000 years reflected by high resolution geochemical and isotopic records from owens lake sediments abstract core ol 97a retrieved from the depocenter of owens lake represents a depositional history spanning the past 1000 yr among the 17 elements analyzed in the acid leachable fractions of 315 salt free samples at 3 yr sample mg and li which come chiefly from authigenic mg hydroxy silicates were found to have concentration variations reflecting lake salinity and climatic changes during the past a total of 231 isotopic measurements on carbonates from the same samples in the upper 181 cm show that 18 o and 13 c values range from 5 66 to 0 12 pdb and 1 38 to 4 28 pdb respectively the rate of change with time in 18 o records the rate of change in lake s volume due to climate fluctuations whereas variations in 13 c reflect mainly variations in biological productivity nutrient supply and dissolved carbonate in the lake results indicate an effectively dry climate between a d 950 and 1220 corresponding to the medieval climatic anomaly a warm period in northern europe during which owens lake approached playa conditions wet climates prevailed during a d 1220 1480 producing relatively large and deep lakes beginning about a d 1550 the regional climate turned colder but had frequently oscillating precipitation six wet dry cycles with 50 yr duration occurred between a d 1480 and 1760 during the later half of which owens lake became a playa since a d 1880 the lake level has steadily dropped from its historic high stand under strong impact of human activity

the transport and fate of fe mn cu zn cd pb and so4 in a groundwater plume and in downstream surface waters in the coeur d alene mining district idaho u s a abstract the controls on metal concentrations in a plume of acidic ph 3 29 5 55 groundwater in the moon creek watershed in idaho u s a were investigated with the use of property property plots a plot of ca vs s demonstrated that a plume of contaminated groundwater was being diluted by infiltration of rain and creek water at shallow depths and by ambient groundwater near bedrock the small amount of dissolved fe 2 1 mg l was removed while dissolved pb was added reaching a maximum concentration of 0 37 mg l the other metals zn 16 al 6 2 cu 2 1 and cd 0 077 mg l in the shallow groundwater were essentially conserved until they emerged as a seep along the creek bank upon mixing with the creek water groundwater was diluted by factors between 11 and 50 and the ph of the mixture became neutral metals originating from the contaminated groundwater were removed in the creek in the following order fe al pb cu mn zn cd pb and cu continued to be removed from solution even as the creek passed adjacent to a tailings pile in contrast zn concentrations in the creek increased adjacent to the tailings area presumably as a result of the reemergence of the upgradient plume as the creek lost elevation below the tailings dam contaminated creek water 400 800 g zn l was diluted by both smaller side streams and a creek of equal flow the presence of 3 distinctive water masses required the use of two tracers dissolved si and s to distinguish between mixing and geochemical reactions the removal of metals was greater during low flow conditions pb was removed to the greatest extent falling below detection limits 0 5 l at the first sampling location copper and mn were removed to a lesser extent during low flow conditions and approached conservative behavior during high flow conditions during a 5 km journey through two hydrological regimes less than 10 of the dissolved zn and cd was lost

impact of amd on water quality in critical watershed in the hudson river drainage basin phillips mine hudson highlands new york a sulfur and trace element enriched u th laced tailings pile at the abandoned phillips mine in garrison new york releases acid mine drainage amd generally ph 3 minimum ph 1 78 into the first order copper mine brook cmb that drains into the hudson river the pyrrhotite rich phillips mine is located in the highlands region a critical water source for the new york metro area a conceptual model for derivation dissolution sequestration transport and dilution of contaminants is proposed the acidic water interacts with the tailings leaching and dissolving the trace metals amd evaporation during dry periods concentrates solid phase trace metals and sulfate forming melanterite feso4 7h2o on sulfide rich tailings surfaces wet periods dissolve these concentrates precipitates releasing stored acidity and trace metals into the cmb sediments along cmb are enriched in iron hydroxides which act as sinks for metals indicating progressive sequestration that correlates with dilution and sharp rise in ph when mine water mixes with tributaries seasonal variations in metal concentrations were partly attributable to dissolution of the efflorescent salts with their sorbed metals and additional metals from surging acidic seepage induced by precipitation

the impact of the october november 2000 floods on contaminant metal dispersal in the river swale catchment north yorkshire uk during the autumn of 2000 large areas of england and wales were affected by severe flooding which caused widespread disruption and significant damage to property this study attempts to determine the impact of these flood events on contaminated sediment dispersal and deposition in the river swale catchment yorkshire uk where lead and zinc were extracted and processed in large quantities during the nineteenth century seventy samples of overbank and channel edge sediments were collected at 35 sites along the river swale inductively coupled plasma mass spectrometry was used to measure contaminant metal concentrations in the 2000 63 m sand and 63 m silt and clay size fractions in both the channel edge and overbank sediments collected from the upper and middle reaches of the river swale concentrations of lead zinc and cadmium were found to exceed maff guidelines highest concentrations correspond to the input of contaminated material from intensively mined tributaries and elevated levels can be observed 5 10 km downstream of these inputs this indicates that the remobilization of contaminated material during major flood events is potentially a serious problem for activities such as agriculture that utilize the swale floodplain copyright 2003 john wiley sons ltd