Three-component Mixing Model Research Articles

Pacific waters in the East Siberian Sea: identification by δ13С(DIC) and [DIC

The estimates of the scale and distribution of Bering Sea waters in the Pacific sector of the Arctic Ocean were made using the high-precision data on the isotopic composition and concentration of dissolved inorganic carbon. Despite the fact that δ13С(DIC) and [DIC] are not classic conservative tracers, in the East Siberian Sea, which is a zone of active interaction of river runoff with sea waters, these parameters can indicate the presence of sea waters not only of Atlantic, but also of Pacific origin, similar to the waters of the Bering Sea. Using a three-component mixing model, the spatial distribution of Pacific, Atlantic and river waters along two sections of the East Siberian Sea was estimated. The Pacific component extends from east to west to approximately 160 degrees east longitude, and possibly further west, skirting Wrangel Island not only from the north, but also possibly from the south. In the East Siberian Sea, waters similar to the open sea Bering summer surface waters are found, which are carried to the northern shelf by the circular Bering Sea Current, and upper intermediate waters, which can enter the zone of the northern shelf of the sea due to upwelling or active mixing.

Constraining seasonal and spatial ambient and urban groundwater contributions to streamflow across a mixed land-use regional-scale Precambrian Shield watershed

Groundwater-surface water (GW-SW) interactions are complex phenomena that vary naturally over space and time and are being influenced by environmental change. The Whitson River watershed is a mixed land-use Precambrian shield watershed located in Northeastern Ontario, Canada in which groundwater is a source of municipal water supply and in which groundwater and surface waters are at risk of potential impacts from urban runoff, ongoing municipal drainage projects, periodic flooding, and climate change. This study used watershed-scale synoptic surveys of stable isotopes (δ18O and δ2H) and geochemistry, and corresponding mixing-model approaches (two-component and three-component) to quantify the seasonal and spatial variation in surface water, ambient, and urban groundwater contributions to streamflow. Multiple mixing models were generated based on isotope and geochemical source water identification, and the performance of these models was compared. Mixing-model analyses showed that groundwater contributes a critical, sustaining source to streamflow (> 50 % or more) during summer baseflow conditions, dropping to ∼ 15 % in fall when connection to shield lakes and wetlands dominate. Three-component mixing models showed similar results to the two-component models, refining groundwater contributions into ambient and urban groundwater sources. Estimated urban groundwater contributed 30 % or more to summer baseflow, dropping to ∼ 4 % in the fall. Baseflow estimates derived from graphical hydrograph separation were similar to mixing model groundwater estimates in the summer but suggest this approach overestimates groundwater contributions during the fall. These results demonstrate the complexity of source water contributions to streamflow and the challenges in their determination in mixed-land-use Precambrian Shield landscapes where communities are largely located. Assessment of source water contributions to streamflow across the Whitson River sub-watershed has generated a region-specific conceptualization (e.g. urban versus ambient groundwater) of a basin that is experiencing increased urban development, providing information that will be of value for long term management.

Ore–forming potential of the Wubaduolai monzogranite porphyry, western Gangdese copper belt, Tibet: Insights from geochronology and petrogeochemistry

The Wubaduolai deposit is a newly discovered porphyry copper deposit in the Zhunuo-Beimulang ore-concentrated area of the Gangdese belt. The monzogranite porphyry is the causative intrusion in the deposit with a zircon U-Pb age of ∼16 Ma. Monzogranites have high Sr (332–673 ppm) and Sr/Y ratios (35–69), typical of adakite affinity. They have initial 87Sr/86Sr ratios of 0.7083–0.7093 and εNd(t) values between −9.2 and −7.1. The zircon εHf(t) values range from −6.45 to −2.09 and zircon δ18O values have a narrow range of 7.4 to 8.1 ‰ for the porphyry. These geochemical characteristics indicate that the parental magma was derived from juvenile Tibetan lower crust, with contributions from Indian plate-released fluids and metasomatized mantle-derived mafic magmas. The porphyry shows high values of log w(Fe2O3/FeO) (>0) and V/Sc (mostly > 12) in whole rock and high values of △FMQ (4.13–5.79), 10000 × (δEu)/Y(>4), and low Dy/Yb (<0.3) in zircons, suggesting that the magma was oxidized and hydrous. The oxidized and hydrous parental magma is consistent with those evaluated for the Zhunuo and Beimulang deposits. The three-component mixing model result shows that compared with the ore-related porphyries in the Zhunuo and Beimulang deposits, the Wubaduolai intrusion has higher proportion of Indian plate-released fluids and mafic magmas and lower proportion of juvenile Tibetan lower crust. Therefore, we suggest that although the causative intrusions have similar oxygen fugacity and water content, the source has more Indian continental crust and mantle-derived materials and fewer juvenile Tibetan lower crust materials at Wubaduolai, implying that the Wubaduolai monzogranite porphyry has lower potential for mineralization.

Influence of Pleistocene glacial deposits on the transport of agricultural nitrate in the river Wensum catchment, UK

Mitigating NO3− pollution requires an understanding of the hydrological processes controlling contaminant mobilisation and transport, particularly in agricultural catchments underlain by Pleistocene glacial deposits. Focusing on the Wensum catchment in East Anglia, UK, precipitation (n = 20), stream water (n = 50), field drainage (n = 22) and groundwater (n = 84) samples collected between February–March 2011 and April–September 2012 were variously analysed for water stable isotopes (δ2HH2O and δ18OH2O), the dual-isotopes of NO3− (δ15NNO3 and δ18ONO3), groundwater residence time indicators (CFCs and SF6) and hydrochemical parameters. The residence time indicators suggested a component of modern (post-1960) groundwater throughout the sequence of glacial deposits that corresponds with the penetration of agricultural NO3−. Denitrification and lower NO3− concentrations (<8 mg L−1) are observed in the glacial tills, compared with higher NO3− concentrations (<90 mg L−1) observed under more oxidising conditions in the glacial sands and gravels. Storm hydrograph separation for two storms in April and September 2012 using two- and three-component mixing models showed a faster response with field drainage (36–38 %) and baseflow (5–37 %) contributing to the total stream discharge in areas of clay loam soils over glacial tills. In these areas, the dual stable isotopes of NO3− (δ15NNO3 = +11.8 ‰ and δ18ONO3 = +7.1 ‰) indicated a denitrified source of nitrogen from field drainage and groundwater. In comparison, a dampened response and a higher percentage of baseflow (29–80 %) was observed in areas of sandy clay loam soils over glacial sands and gravels. In these areas, mean NO3− isotopic signatures (δ15NNO3 = +7.8 ‰ and δ18ONO3 = +5.0 ‰) indicated a source of nitrified NH4+. In conclusion, understanding hydrological processes in catchments underlain by variable glacial deposits can inform nutrient management plans and cultivation practices to reduce the risk of agricultural NO3− contamination.

Trace Element and Isotope Systematics in Vent Fluids and Sulphides From Maka Volcano, North Eastern Lau Spreading Centre: Insights Into Three-Component Fluid Mixing

Back-arc spreading centres and related volcanic structures are known for their intense hydrothermal activity. The axial volcanic edifice of Maka at the North Eastern Lau Spreading Centre is such an example, where fluids of distinct composition are emitted at the Maka hydrothermal field (HF) and at Maka South in 1,525–1,543 m water depth. At Maka HF black smoker-type fluids are actively discharged at temperatures of 329°C and are characterized by low pH values (2.79–3.03) and a depletion in Mg (5.5 mmol/kg) and SO4 (0.5 mmol/L) relative to seawater. High metal (e.g., Fe up to ∼6 mmol/kg) and rare Earth element (REE) contents in the fluids, are indicative for a rock-buffered hydrothermal system at low water/rock ratios (2–3). At Maka South, venting of white smoke with temperatures up to 301°C occurs at chimneys and flanges. Measured pH values range from 4.53 to 5.42 and Mg (31.0 mmol/kg), SO4 (8.2 mmol/L), Cl (309 mmol/kg), Br (0.50 mmol/kg) and Na (230 mmol/kg) are depleted compared to seawater, whereas metals like Li and Mn are typically enriched together with H2S. We propose a three-component mixing model with respect to the fluid composition at Maka South including seawater, a boiling-induced low-Cl vapour and a black smoker-type fluid similar to that of Maka HF, which is also preserved by the trace element signature of hydrothermal pyrite. At Maka South, high As/Co (&amp;gt;10–100) and Sb/Pb (&amp;gt;0.1) in pyrite are suggested to be related to a boiling-induced element fractionation between vapour (As, Sb) and liquid (Co, Pb). By contrast, lower As/Co (&amp;lt;100) and a tendency to higher Co/Ni values in pyrite from Maka HF likely reflect the black smoker-type fluid. The Se/Ge ratio in pyrite provides evidence for fluid-seawater mixing, where lower values (&amp;lt;10) are the result of a seawater contribution at the seafloor or during fluid upflow. Sulphur and Pb isotopes in hydrothermal sulphides indicate a common metal (loid) source at the two vent sites by host rock leaching in the reaction zone, as also reflected by the REE patterns in the vent fluids.

Sr-Nd-Pb-Ca Isotopes of Holocene Basalts from Jingpohu, NE China: Implications for the Origin of Their Enriched Mantle Signatures

The geochemistry on Holocene lavas from the Jingpohu volcanic field in NE China are compared with other Cenozoic lavas from across the back-arc rift of NE China, in order to constrain their enriched mantle sources. Holocene lavas within Jingpohu volcanic field comprise two separate “Crater Forest” (CF) and “Frog Pool” (FP) volcanic areas. FP lavas have lower MgO, CaO, and heavy rare earth elements and higher Al2O3, Na2O, K2O, and large-ion lithophile elements than CF lavas. Yet, both CF and FP lavas share similar isotopic signatures, with depleted Sr and Nd isotopes (87Sr/86Sr = 0.703915–0.704556, 143Nd/144Nd = 0.512656–0.512849) and unradiogenic Pb isotopes (208Pb/204Pb = 37.79–38.06, 207Pb/204Pb = 15.45–15.54, 206Pb/204Pb = 17.49–18.15), similar to oceanic island basalts. An important new constraint for the Jingpohu lavas lies in their Ca isotopes of δ44/40Ca from 0.63‰ to 0.77‰, which are lower than that of the bulk silicate earth (0.94 ± 0.05‰). By comparing the isotopic signatures of sodic lavas with that of the potassic lavas across NE China, we propose a three-component mixing model as the source for the sodic lavas. In consistence with geophysical results, we propose that subducting Pacific plate induces asthenospheric mantle upwelling of an upper depleted mantle (DM), including subducted ancient sediments (EM I), which partially melted upon ascent. These primary melts further interacted with the lithospheric mantle (EM II), before differentiating within crustal magma chambers and erupting.

A Stable Isotope Approach for Estimating the Contribution of Recycled Moisture to Precipitation in Lanzhou City, China

The proportional contribution of recycled moisture to local precipitation is a geographically dependent parameter that cannot be ignored in water budgets. Stable hydrogen and oxygen isotopes are sensitive to environmental changes and can be applied to investigate the modern water cycle. In this study, a three-component mixing model is used to calculate the contribution of different water vapors (advection, evaporation and transpiration) to summer precipitation in Lanzhou city, Northwest China. The results show that for all sampling sites in Lanzhou, the contribution of advection vapor to precipitation is the largest, followed by the plant transpiration vapor, and the contribution of surface evaporation water vapor is usually the least, with the average values of 87.96%, 9.1% and 2.9%, respectively. The spatial differences of plant transpiration vapor are generally larger than those of advection vapor and surface evaporation vapor, and the high values appear in Yongdeng, Daheng and Gaolan.

Lateral variations of 134Cs and 228Ra concentrations in surface waters in the western North Pacific and its marginal sea (2018–2019): Implications for basin-scale and local current circulations

Lateral variations in 134Cs, 137Cs, and 228Ra concentrations (activities) in surface waters off the northeastern coast of Japan, including the subarctic Oyashio Current, subtropical Kuroshio Current, East Sakhalin Current (ESC), and Soya Warm Current (SWC), were examined from July to October in 2018 and 2019. The 134Cs concentrations in the surface seawater samples, decay-corrected to the date of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, were in the range of 0.2–0.9 mBq/L, whereas those transported to the study area with basin-scale currents varied between 0.2 and 1.3 mBq/L; this included the East Kamchatka Current (EKC) for 8 years following the FDNPP accident. Combined with the 228Ra (0.1–1.4 mBq/L) and 137Cs (1.0–1.7 mBq/L) concentrations and the salinity (32.4–34.6), the distribution of 134Cs concentrations indicated that FDNPP-derived radiocesium in this study area was partially transported with the EKC from the northeastern North Pacific. Based on a simple three-component (SWC, ESC, and EKC) mixing model that uses the salinity and 134Cs concentration, the fractions of the EKC showed a maximum value of ~ 0.4 off the southeastern Hokkaido, Japan.

Geochemistry and mantle source characteristics of the Itasy volcanic field: Implications for the petrogenesis of basaltic magmas in intra-continental-rifts

We present new major and trace element and Sr, Nd, Pb, Hf, and Os isotope data for Quaternary basaltic lavas and tephra from the Itasy volcanic field, in order to assess the origin and sources of recent volcanism in the central highlands of Madagascar. Our age determinations provide further evidence for Pleistocene volcanism on the island, with ages between ∼31 and 104 ka. Mafic magmas from Itasy exhibit significant geochemical heterogeneity, and they are chemically distinct from those of the neighboring Ankaratra volcanic complex. Trace element signatures of the Itasy volcanic field are very similar to those of ocean island basalts (OIB), with significant enrichment in high field strength elements (e.g. Nb and Ta) and depletion in large ion lithophile elements (e.g. Rb, Cs, and K), and relatively high Nb/U (>45) and Ce/Pb (>25) ratios. Significant intra-volcanic field isotopic heterogeneity is observed, with well-defined negative correlations of 87Sr/86Sr with 206Pb/204Pb and 143Nd/144Nd. These correlations, along with highly radiogenic Os isotopic signatures in many Itasy samples, could be attributed to assimilation of the Precambrian basement. However, with the exception of Os, the elemental and isotopic characteristics of the Itasy magmas are inconsistent with significant crustal assimilation, and instead are interpreted to represent features of their mantle sources. The Itasy ΔεHf and Δ7/4 values fall within the range of MORB and OIB, and indicate derivation primarily from an asthenospheric mantle source. The absence of significantly negative ΔεHf in the Itasy magmas argues against the involvement of ancient recycled oceanic crust or stranded lower crust in their sources, but the presence of a low µ (LOMU) component in some Itasy magmas can be attributed to pollution of the asthenosphere by delaminated subcontinental lithospheric mantle. A simple two-stage, three-component mixing model indicates that a mixture of mantle containing 90% depleted asthenosphere (DMM) and 10% foundered SCLM, which is further mixed with 30 to 50% of a plume-type mantle component, can reproduce the isotopic compositions of the Itasy magmas. Based on our model, it is possible that easily fusible superplume materials might be widely distributed in the upper mantle underneath the EARS, from the Indian Ocean to the Red Sea-Gulf of Aden, and mixed with shallow asthenosphere that has itself incorporated eroded SCLM. These components are heterogeneously distributed at a small spatial scale, similar to that observed recently in other mafic monogenetic volcanic fields in both intraplate and subduction settings.

Deep CO2 release revealed by stable isotope and diffuse degassing surveys at Vulcano (Aeolian Islands) in 2015–2018

The partitioning of carbon dioxide (CO2) released by soils at Vulcano Island (Aeolian Islands, Italy) was performed by combining the CO2 flux and the carbon isotope measurements. Based on this method, the amount of CO2 of volcanic origin was quantified six times during the period 2015–2018. The data analysis allowed us to establish the correlation between CO2 soil degassing and changes in the contribution of volcanic fluids. Carbon isotope determinations were performed in situ to enhance the coverage of data collection in space and time. These data were combined with both the CO2 contents in the ground gases and the soil CO2 flux. The amount of volcanic CO2 was distinguished from that of biogenic origin by implementing a three-component mixing model. The results of this study indicate that the increase in CO2 output in September 2018 reflects the increase in volcanic gas emissions. The measurement method and analysis presented in this work are sufficiently general to be applicable to the monitoring programs of active volcanoes.

Recycled moisture in an enclosed basin, Guanzhong Basin of Northern China, in the summer: Contribution to precipitation based on a stable isotope approach

Recycled moisture, mainly originated from evapotranspiration (surface evaporation and transpiration), is the main sources of precipitation. Influenced on the different regional/local environments, the contributions of recycled moisture to precipitation present as different proportions. Recycled moisture has an important impact on the hydrological cycle, further occurred a series of environmental effect for regional/local. Aimed to estimate the contribution of recycled moisture to precipitation in an enclosed basin, Guanzhong Basin of northern China, precipitation and lake/reservoir samples were collected. The isotope ratio analysis was done for the summer season, and a three-component mixing model based on the stable hydrogen and oxygen isotopes was applied. The results indicated that the averaged contribution of recycled moisture to precipitation was 17.44% in Guanzhong Basin of northern China, while the mean proportions of surface evaporation moisture and transpiration moisture were found to be 0.38% and 16.97%, respectively. Comparatively, most of the recycled moisture mainly comes from transpiration moisture rather than evaporation moisture, suggesting that transpiration moisture from cropland, vegetation, and plants instead of evaporation is dominant in moisture recycling of the Guanzhong Basin.

A new perspective of probing the level of pollution in the megacity Delhi affected by crop residue burning using the triple oxygen isotope technique in atmospheric CO2

Air quality in the megacity Delhi is affected not only by local emissions but also by pollutants from crop residue burning in the surrounding areas of the city, particularly the rice straw burning in the post monsoon season. As a major burning product, gaseous CO2, which is rather inert in the polluted atmosphere, provides an alternative solution to characterize the impact of biomass burning from a new perspective that other common tracers such as particulate matters are limited because of their physical and chemical reactiveness. Here, we report conventional ([CO2], δ13C, and δ18O) and unconventional (Δ17O) isotope data for CO2 collected at Connaught Place (CP), a core area in the megacity Delhi, and two surrounding remote regions during a field campaign in October 18–20, 2017. We also measured the isotopic ratios near a rice straw burning site in Taiwan to constrain their end member isotopic compositions. Rice straw burning produces CO2 with δ13C, δ18O, and Δ17O values of −29.02 ± 0.65, 19.63 ± 1.16, and 0.05 ± 0.02‰, respectively. The first two isotopic tracers are less distinguishable from those emitted by fossil fuel combustion but the last one is significantly different. We then utilize these end member isotopic ratios, with emphasis on Δ17O for the reason given above, for partitioning sources that affect the CO2 level in Delhi. Anthropogenic fraction of CO2 at CP ranges from 4 to 40%. Further analysis done by employing a three-component (background, rice straw burning, and fuel combustion) mixing model with constraints from the Δ17O values yields that rice straw burning contributes as much as ∼70% of the total anthropogenic CO2, which is more than double of the fossil fuel contribution (∼30%), during the study days.

Using Water Stable Isotopes for Identifying Groundwater Recharge Sources of the Unconfined Alluvial Zagreb Aquifer (Croatia)

The main purpose of this study was to understand the interactions between precipitation, surface water, and groundwater in the Zagreb aquifer system using water stable isotopes. The Zagreb aquifer is of the unconfined type and strongly hydraulically connected to the Sava River. As the groundwater is the main source of drinking water for one million inhabitants, it is essential to investigate each detail of the recharge processes of the aquifer to ensure adequate protection of the groundwater. Measuring the content of water stable isotopes in surface waters and groundwater enabled the creation of two- and three-component mixing models based on the isotopic mass balance for the purpose of the quantification of each recharge component. The mixing models gave ambiguous results. Observation wells equally distant from the Sava River did not have the same recharge component ratio. This indicated that there were more factors (in addition to the distance from the river) that were affecting groundwater recharge, and the properties of the unsaturated zone and surface cover data were therefore also taken into consideration. The thickness of the unsaturated zone and the characteristics of different soil types were identified as important factors in the recharge of the Zagreb aquifer. The areas with high thickness of the unsaturated zone and well-permeable soil had a very similar recharge component ratio to the areas with small thickness of the unsaturated zone but low-permeable soil.

Using multiple tracers (F−, B, δ11B, and optical brighteners) to distinguish between municipal drinking water and wastewater inputs to urban streams

Releases of municipal waters, including drinking water and wastewater, can considerably alter urban stream chemistry. However, the relative contributions of drinking water versus wastewater to streams have not been quantified previously and are therefore the focus of this study. We sampled streams along a land use gradient that included watersheds with impervious surface areas (ISA) ranging from 1.6 to 62.6%. Samples were analyzed for F−, total B, δ11B, and optical brighteners to determine municipal water inputs to streams. We observed low F− (75 ± 20 μg/L), B (29 ± 6 μg/L), and optical brightener (3.66 ± 0.76 RFU) levels in rural streams, but their concentrations increased with urbanization (up to 475 μg/L, 227 μg/L, and 22.09 RFU, respectively). The δ11B values for drinking waters (16.52 ± 0.39‰) and wastewaters (untreated = 6.06 ± 0.88‰ and treated = 6.46 ± 0.93‰) were distinct, but there was poor correlation between δ11B and ISA for the streams (R2 = 1 × 10−5; p = 0.99), likely due to variable lithology in the study area. We used inverse and three-component mixing models to quantify municipal water inputs to the streams. In densely urbanized watersheds, drinking water and wastewater can respectively contribute up to 54% and 16% of the total streamflow. In addition to our spatial sampling, we collected weekly samples at a suburban stream to test the effects of discharge and seasonality on municipal water tracer behavior. We found that tracer levels did not change significantly (p ≥ 0.28) with discharge or season, suggesting that municipal water inputs are fairly constant. Understanding the relative proportions of differing municipal water types to streams is crucial in guiding infrastructure improvements to conserve drinking water and reduce harmful wastewater releases. The unique chemical signatures of municipal waters aid in the widespread applicability of our multi-tracer method for identifying water sourcing to urban streams.

Modification of Laptev sea freshened shelf waters based on isotope and salinity relations

This paper is dedicated to the estimation of the river runoff contribution to the Arctic shelf waters, where freezing and melting of desalinated waters are intensively proceeding. A mixing-modification model is offered. The model takes into account the sea ice formation from desalinated waters on the shelf. The model was used to explain the data obtained from 63 and 69 cruises of the research vessel “Akademik Mstislav Keldysh” (2015 and 2017). Two sources of water masses — the Atlantic waters and the Lena river were established for the studied area of Laptev Sea. The waters in this zone are modified, i.e. they have a higher salinity than the one that corresponds to the two components mixing. The presence of modified waters generated at the Laptev Sea shelf is traced in the continental slope zone. Desalination in the continental slope zone reaches 15–27% and affects depths no more than 20 m, at more than 50 m depths it is practically disappeared. A mixing-modification model was proposed to calculate river water input in the modified waters. The data obtained for the Laptev Sea shelf were used to calculate the fraction of river waters according to both the proposed model and the conventional three-component mixing model of Ostlund and Hut, 1984. A comparison of the estimates obtained by both models has shown that the application of the three-component mixing model to modified waters leads to an overestimation of the river water contribution, which can reach 20%.&#x0D; Each sample of shelf waters can be processed using either a mixture-modification model or a three-component mixing model. To choose the appropriate model the special criterion is proposed. Using this criterion, the calculations of river water and melted ice contribution will be free from the unrealistic or negative values.

Using Pb isotope ratios of particulate matter and epiphytic lichens from the Athabasca Oil Sands Region in Alberta, Canada to quantify local, regional, and global Pb source contributions

Ambient air particulate matter (PM) was collected at the Wood Buffalo Environmental Association Bertha Ganter Fort McKay monitoring station in the Athabasca Oil Sand Region (AOSR) in Alberta, Canada from February 2010 to July 2011 as part of an air quality source assessment study. Daily 24-hour duration fine (PM2.5) and coarse (PM10–2.5) PM was collected using a sequential dichotomous sampler. 100 pairs of PM2.5 and PM10–2.5 were selected for lead (Pb) concentration and isotope analysis. Pb isotope and concentration results from 250 epiphytic lichen samples collected as far as 160 km from surface mining operations in 2008, 2011, and 2014 were analyzed to examine longer term spatial variations in Pb source contributions. A key finding was recognition of thorogenic 208Pb from eastern Asia in the springtime in the PM2.5 in 2010 and 2011. 206Pb/207Pb and 208Pb/207Pb isotope ratios were used in a three-component mixing model to quantify local, regional, and global Pb sources in the PM and lichen data sets. 47 ± 3% of the Pb in the PM2.5 at AMS-1 was attributed to sources from eastern Asia. Combined results from PM10–2.5 and PM2.5 indicate PM2.5 Pb contributions from eastern Asia (34%) exceed local AOSR sources of PM2.5 Pb (20%), western Canada sources of PM2.5 Pb (19%), and PM10–2.5 Pb from fugitive dust including oil sands (14%), tailings (10%), and haul roads (3%). The lichen analysis indicates regional sources contribute 46% of the Pb, local sources 32%, and global sources 22% over the 2008–2014 timeframe. Local sources dominate atmospheric Pb deposition to lichens at near field sites (0–30 km from mining operations) whereas regional Pb sources are prevalent at distal sites (30–160 km). The Pb isotope methodology successfully quantified trans-Pacific transport of Pb to the AOSR superimposed over the aerosol footprint of the world's largest concentration of bitumen mining and upgrading facilities.

The Moyjil site, south-west Victoria, Australia: chronology

An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) opercula (the dominant shellfish present) and optically stimulated luminescence (OSL) of the host calcarenite. AAR dating of the shell bed and four Last Interglacial (LIG) beach deposits at Moyjil and Goose Lagoon, 30 km to the west, confirmed a LIG age. OSL analysis of the host sand revealed a complex mixing history, with a significant fraction (47%) of grains giving an early LIG age (120–125 ka) using a three-component mixing model. Shell deposition following the LIG sea-level maximum at 120–125 ka is consistent with stratigraphic evidence. A sand layer immediately below the shell deposit gave an age of ~240 ka (i.e. MIS 7) and appears to have been a source of older sand incorporated into the shell deposit. Younger ages (~60–80 ka) are due to bioturbation before calcrete finally sealed the deposit. Uranium/thorium methods were not applicable to L. undulata opercula or an otolith of the fish Argyrosomus hololepidotus because they failed to act as closed systems. A U–Th age of 103 ka for a calcrete sheet within the 240 ka sand indicates a later period of carbonate deposition. Calcium carbonate dripstone from a LIG wave-cut notch gave a U–Th age of 11–14 ka suggesting sediment cover created a cave-like environment at the notch at this time. The three dating techniques have collectively built a chronology spanning the periods before and after deposition of the shell bed, which occurred just after the LIG sea-level maximum (120–125 ka).

Using water stable isotopes for tracing surface and groundwater flow systems in the Barlow-Ojibway Clay Belt, Quebec, Canada

This study aims to improve the understanding of surface and groundwater flow systems based on water stable isotope data in a 19,549 km2 region of the Barlow-Ojibway Clay Belt, in western Quebec, Canada. The available geochemical database contains 645 samples including precipitation, snow cores, surface waters, groundwater and springs. All samples were analyzed for water stable isotopes (δ2H-δ18O) and complementary tritium analyses were conducted on 98 groundwater and spring samples. Precipitations depict a clear temperature-dependent seasonal pattern and define a local meteoric water line (LMWL) without a latitudinal trend in δ2H-δ18O. Samples collected from the snowpack plot on the LMWL, suggesting that the bulk snowpack preserves the isotopic composition of precipitation throughout the frozen period, prior to the spring snowmelt. Surface water samples define a local evaporation line (LEL), and evaporation over inflow (E/I) ratios range between 0 and 36%. Groundwater and spring samples are evenly distributed around the LMWL, suggesting that evaporation processes are limited prior to infiltration and that surface waters do not significantly contribute to groundwater recharge. Shallow unconfined aquifers present a greater variability in δ2H-δ18O compared to confined aquifers located farther down gradient, suggesting the mixing of varied recharge waters along the regional groundwater flow system. A three-component mixing model based on isotopic and specific electrical conductivity data allows the quantification of such mixing processes. The interpretation of isotopic data constrains a regional-scale conceptual model of groundwater flow systems and describes processes related to the timing of recharge, evaporation, mixing and discharge.

Run-off analyses using isotopes and hydrochemistry in Yushugou River basin, eastern Tianshan Mountains

Yushugou River basin of East Tianshan Mountains receives water from melting glaciers. In recent years, the glaciers retreated strongly due to global warming which intensified the water cycle in the river basin. For this reason, the relation of water bodies based on hydrochemistry and isotope in the summer flood was carried out. Hydrochemistry research showed that there was frequent hydraulic interaction between river water and groundwater. Studying the isotopes and $$\hbox {Cl}^{-}$$ of river water, glacier meltwater, groundwater and precipitation, indicated that Yushugou River was recharged by the glacier meltwater, groundwater and precipitation during the summer flood period. The analysis result based on the three-component mixing model showed that Yushugou River was recharged by 54.9% of glacier meltwater, 37.6% of the run-off came from groundwater, while less than 8% was contributed by precipitation. The study suggests that the role of glacier meltwater and groundwater, especially glacier meltwater, should be specially concerned in water resource protection and reasonable utilization, and the injection of glacier meltwater is the main reason for run-off variation in this alpine basin during the summer flood period.

Organic matter sources, transport, degradation and preservation on a narrow rifted continental margin: Shoalhaven, southeast Australia

The continental delivery of fine grained siliciclastic sediment, together with the composition of exported terrigenous organic matter (OM), has a strong impact on the content and composition of sedimentary OM accumulating on contemporary oxic continental shelf sediments. The composition of terrigenous OM appears to be, in turn, largely related to the geodynamic setting of the drained margin.This study provides results from a comprehensive source-to-sink investigation along the Shoalhaven River (New South Wales) and its associated non-deltaic deposits on the SE Australian continental margin, a margin whose dimensions and morphology differ from those of standard passive margins.The OM content of 23 surface sediment samples collected along the river course, estuary and adjacent continental shelf was investigated by integrating bulk OM measurements, such as total organic carbon content (TOC), TOC/total N (C/N), carbon stable isotope (δ13CTOC) and radiocarbon content of TOC (Δ14CTOC), with lipid biomarker analysis. Geochemical data were coupled with sediment particle size analysis. The TOC content correlated strongly with the clay+silt content in all the environments, confirming the importance of fine grained particles – OM association as an influential preservation factor.A three-component mixing model was used to show that OM in continental shelf sediments consisted of 15–20% terrigenous biospheric OM (mostly modern plants), 15–25% fossil C, and marine OM. While such bimodal terrigenous input (modern plants and fossil C) is typical of active margins, this study reinforces the paradigm that OM residence times within major bioactive reservoirs during transfer (in turn related to geomorphic characteristics) strongly influence the composition of exported OM.