Alteration of a Komatiite Flow from Alexo, Ontario, Canada

To investigate the ability of komatiites to preserve duringalteration a record of the geochemical and isotopic compositionof the Archean mantle, we studied the petrology and geochemistryof a komatiite flow from Alexo, Ontario. Although this flowis relatively well preserved, two main types of alteration arerecognized: (1) hydration of variable intensity throughout thewhole flow; (2) local rodingitization. In samples only slightlyaffected by hydration, the alteration was essentially isochemical;where more intense, hydration was accompanied by the mobilityof TiO₂, Zr and the light rare-earth elements (LREE). The mobilityof these reputedly immobile trace elements is influenced bytexture and secondary mineral assemblages. Rodingitization wasaccompanied by still greater mobility. An Nd isochron with anage of 272698 Ma and Nd_(T) =+ 2.5 is defined by wholerock samples.Because the spread of Sm-Nd ratios is far greater than can beexplained by magmatic processes, the age is interpreted as thatof the main alteration event during or soon after emplacement.Scattered initial Sr isotopic ratios and Nd _(T) (+ 3.6 to +0.7)provide evidence for several younger events. The Nd (T) of magnaticclinopyroxene ( plus;3.8) is higher than that of mafic tofelsicrocks and pyroxenes from the Abibiti belt (Nd _(T) +2.5). Thisresult implies: (1) the komatiites exchanged Nd with surroundingrocks during waterrock interaction; (2) the isotopic compositionof komatiites and their mantle source differed from that ofthe more common basalts of the Abitibi belt. KEY WORDS: alteration; Archean; Komatiite; trace elements; radiogenic and stable islotopes ^*Present address: Ore Genesis Research Group, VIEPS Department of Earth Science, Monash University, Clayton, Vic 3168, Australia. Telephone: (61) 3 9905-3881. Fax: (61) 3 9905–4903. e-mail: ylahaye{at}artemis.earth.monash.edu.au     

The evolution of groundwater in the Tyrrell catchment, south-central Murray Basin, Victoria, Australia

The Tyrell catchment lies on the western margin of the Riverine Province in the south-central Murray Basin, one of Australia’s most important groundwater resources. Groundwater from the shallow, unconfined Pliocene Sands aquifer and the underlying Renmark Group aquifer is saline (total dissolved solids up to 150,000 mg/L) and is Na-Cl-Mg type. There is no systematic change in salinity along hydraulic gradients implying that the aquifers are hydraulically connected and mixing during vertical flow is important. Stable isotopes (¹⁸O+²H) and Cl/Br ratios indicate that groundwater is entirely of meteoric origin and salts in this system have largely been derived by evapotranspiration of rainfall with only minor halite dissolution, rock weathering (mainly feldspar dissolution), and ion exchange between Na and Mg on clays. Similarity in chemistry of all groundwater in the catchment implies relative consistency in processes over time, independent of any climatic variation. Groundwater in both the Pliocene Sands and Renmark Group aquifers yield ages of up to 25 ka. The Tyrrell Catchment is arid to semi-arid and has low topography. This has resulted in relatively low recharge rates and hydraulic gradients that have resulted in long groundwater residence times.     

The landscape-scale relationship between lake sediment geochemistry and catchment bedrock composition from the Temagami and Gowganda areas of Northeastern Ontario,Canada

Lake sediments are integrators of watershed wide environmental information that includes bedrock geology, glacial overburden, vegetation, hydrology and land use. Lake sediments were collected from an area covering approximately 13,600 km² from the Gowganda and Temagami regions to determine the geochemical background conditions representing different bedrock types. For the entire dataset, the median value for arsenic in lake sediment was 2.6 mg/kg, well within the prescribed limits indicating that the Canadian national objective for arsenic in sediments for the protection of aquatic life (17 mg/kg). Overall, the vast majority of lake sediment samples (97.2%) were below the 17 mg/kg Canadian objective for the protection of aquatic life, however, catchments with Nipissing Diabase had the highest background levels for arsenic (10 mg/kg) with some lakes ranging up to 30 mg/kg. The major geological controls influencing changes in lake sediment geochemistry were determined using random forest classification and principal component analysis (PCA). Random forest classification was able to identify which geological province the samples were derived from and the dominant rock types in the sample catchment with respectable accuracy. PCA revealed strong spatial relationships between lake sediment geochemistry and bedrock geology, particularly a strong relationship between Nipissing Diabase in the watershed of the lake and the cobalt-type mineralization indicator elements in the lake sediment including naturally higher levels of arsenic. Within the samples that exceeded regulatory standards, over half the samples that exceeded the regulatory objectives were located in watersheds that contained Nipissing Diabase in their catchment. This study demonstrates that unique geochemical assemblages can be associated with specific geological areas which is of interest to exploration geologists, for target generation and prospecting, and to environmental policy makers, for site-specific restoration targets.     

地下水中高锰酸盐指数和硝酸根铵根稳定性研究

高锰酸盐指数(CODMn)、硝酸根(NO-3)、铵根(NH+4)是判断水体是否受到三氮污染的重要指标。对于测定这三个指标的水样保存方式和时间,地质行业标准和国内外主要国家标准间存在明显差异。地质行业标准规定地下水样品原水室温保存,CODMn和NH+4在3天内测定;NO-3在20天内测定;国家标准和美国标准推荐样品硫酸酸化,避光或冷藏保存,在2~7天内完成CODMn和NO-3和1~7天内完成NH+4测试。为了分析各类标准在样品保存要求上的差异对检测结果的影响,确保检测数据能真实地反映水体污染状况,找寻简便的保存方式,本文在广州地区采集地下水,按照地质行业标准与国家标准进行处理和保存,并在不同时间段对三个指标进行测试。分析验证结果表明:地质行业标准与国家和美国标准关于水样的保存方法均非常可靠。地质行业标准主要针对静态地下水,保存方法相对宽松;国家标准和美国标准适用范围除了地下水,还包括动态的地表水和废水,采样对象成分更为复杂,更不稳定,更容易受外界影响发生变化,故保存条件高于地质标准。在广州地区,采用原水室温避光保存水样,CODMn、NH+4保存时间可为5天,NO-3保存时间可为30天;采用酸化水室温保存水样,CODMn、NO-3和NH+4保存时间可长达30天。这两种方式均比地质行业标准和国家标准推荐的有效时间长,且原水和酸化水室温保存方式相对于冷藏保存方式更为方便。本文提出,如果采集的水样能方便、快速送达实验室,可采用原水保存;如果不能在短时间内送达实验室检测,可采用硫酸酸化保存。     

A S-isotope approach to determine the relative contribution of redox processes to net SO4 export from upland, and wetland-dominated catchments

Reoxidation of S stored in lowlands after summer droughts has been reported to be responsible for the excess SO₄ export observed in many catchments in south central Ontario. Stable S isotopes can be used to identify the source of SO₄ export in stream water, and are particularly well suited to evaluating zones of dissimilatory SO₄ reduction (DSR) and the contribution of oxidation of reduced S species to stream SO₄. The Plastic Lake-1 (PC1) stream drains an upland coniferous forest and then passes through a Sphagnum-dominated swamp before discharging to Plastic Lake. Measurements of SO₄ fluxes and isotope ratios were used to determine the source of net SO₄ export and the contribution of redox processes to S retention and export in the upland and wetland, respectively. Mass balance budgets for the years 1999/00 and 2000/01, which had comparatively wet summers, indicated that the upland part of the catchment consistently exported SO₄ in excess of bulk deposition inputs. In contrast, mass budget calculations for the swamp indicated a net retention of 3 and 2 g S-SO₄/m² of wetland area, in 1999/00 and 2000/01 respectively. Higher δ³⁴SO₄ ratios and lower SO₄ concentrations in the swamp outflow (average +8.6 ± 2.6‰; 1.5 ± 0.6 mg S-SO₄/L) compared to the inflow draining the upland (+5.4 ± 0.7‰; 2.4 ± 0.3 mg S-SO₄/L) indicated that DSR was at least partly responsible for net SO₄ retention in the swamp. Isotope values in upland stream water (+5.7 ± 0.7‰) were only slightly higher than values in bulk deposition (average +5.1 ± 0.6‰) and soil leachate (+4.4 ± 0.4‰) over the 2-year period of study. Similar δ³⁴SO₄ values in upland stream water compared to deposition and soil leachate, despite substantial variations in water table height in the streambed (92 cm), suggest that reoxidation of reduced sulphides is not an important contributor to SO₄ export from the upland. Rather, net SO₄ export from the upland subcatchment is likely due to net release from upland soil, and slight differences in δ³⁴SO₄ between bulk deposition and soil leachate are consistent with SO₄ release from organic S forms.     

The stability of a remediated bed in Hamilton Harbour,Lake Ontario,Canada

ABSTRACT In situ measurements of lakebed sediment erodibility were made on three sites in Hamilton Harbour, Lake Ontario, using the benthic flume Sea Carousel. Three methods of estimating the surface erosion threshold (τ_c(0)) from a Carousel time series were evaluated: the first method fits measures of bed strength to eroded depth (the failure envelope) and evaluates threshold as the surface intercept; the second method regresses mean erosion rate (E_m) with bed shear stress and solves for the floc erosion rate (E_f) to derive the threshold for E_m = E_f = 1 × 10^?5 kg m^?2 s^?1; the third method extrapolates a regression of suspended sediment concentration (S) and fluid transmitted bed shear stress (τ₀) to ambient concentrations. The first field site was undisturbed (C) and acted as a control; the second (W) was disturbed through ploughing and water injection as part of lakebed treatment, whereas the third site (OIP) was disturbed and injected with an oxidant used for remediation of contaminated sediment. The main objectives of this study were: (1) to evaluate the three different methods of deriving erosion threshold; (2) to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts; and (3) to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability. Five deployments of Sea Carousel were carried out at the control site. Mean erosion thresholds for the three methods were: τ_c(0) = 0·5 (±0·06), 0·27 (±0·01) and 0·34 (±0·03) Pa respectively. Method 1 overpredicted bed strength as it was insensitive to effects in the surface 1–2 mm, and the fit of the failure envelope was also highly subjective. Method 2 exhibited a wide scatter in the data (low correlation coefficients), and definition of the baseline erosion rate (E_f) is largely arbitrary in the literature. Method 3 yielded stable (high correlation coefficients), reproducible and objective results and is thus recommended for evaluation of the erosion threshold. The results of this method correlated well with sediment bulk density and followed the same trend as marine counterparts from widely varying sites. Mass settling rates, expressed as a decay constant, k, of S(t), were strongly related to the maximum turbidity at the onset of settling (S_max) and were also in continuity with marine counterparts. Thus, it appears that differences in salinity had little effect on mass settling rates in the examples presented, and that biological activity dominated any effects normally attributable to changes in salinity. Bedload transport of eroded aggregates (2–4 mm in diameter) took place by rolling below a mean tangential flow velocity (U_y) of 0·32 ms^?1 and by saltation at higher velocities. Mass transport as bedload was a maximum at U_y = 0·4 ms^?1, although bedload never exceeded 1% of the suspended load. The proportion of material moving as bedload was greatest at the onset of erosion but decreased as flow competence increased. Given the low bulk density and strength of the lakebed sediment, the presence of a bedload component is notable. Bedload transport over eroding cohesive substrates should be greater in estuaries, where both sediment density and strength are usually higher. Significant differences between the ploughed and control sites were apparent in both the erosion rate and the friction coefficient (φ), and suggest that bed recovery after disruption is rapid (< 24 h). τ_c(0) increased linearly with time after ploughing and recovered to the control mean value within 3 days. The friction coefficient was reduced to zero by ploughing (diagnostic of fluidization), but increased linearly with time, regaining control values within 6 days. No long‐term reduction in bed strength due to remediation was apparent.     

The isotope geochemistry of fracture calcites from the Chalk River area,Ontario, Canada

Calcite is a common fracture inflilling mineral in the Grenville gneisses of the Chalk River area, Ontario, Canada. It exhibits a variety of occurrences and textures which suggests calcite has precipitated under different hydrogeochemical conditions that may be identified through a detailed chemical and isotopic investigation of the calcite and associated infilling minerals.The δ¹⁸O of these calcites range over 20%. but the δ¹³C varies over a narrow range of 5%.. None of the calcites analyzed is in isotopic equilibrium with both the δ¹⁸O and δ¹³C of the present day ground water. The lightest δ¹⁸O calcites (near 0%. SMOW) are present in sealed fractures and are sometimes associated with laumontite. This suggests that these light calcites formed from hydrothermal solutions (at temperatures less than about 300°C) shortly after the period of metamorphism that formed the gneisses. This interpretation is supported by relatively unradiogenic⁸⁷Sr/⁸⁶Sr ratios near 0.709 and δ¹³C values of −5 to −6%..Most of the Chalk River calcites, however, are considerably heavier in¹⁸O and lighter in¹³C than the hydrothermal end member. This may be the result of low temperature recrystallization of the hydrothermal calcites by meteoric waters under variable water/rock ratios. The¹³C contents and⁸⁷Sr/⁸⁶Sr ratios of these younger, low temperature calcites appear to be partially buffered by the isotopic composition of the original hydrothermal calcite.Pyrite is often associated with the fracture calcites. These pyrites display a wide range in δ³⁴S values of about 70%., which suggests that sulphide precipitation occurred under semi-closed conditions. These data indicate that fracture permeability has been a major control on the isotopic composition of fracture minerals since formation of the gneiss.     

硝酸盐中15N和18O测试新技术

最近40年,硝酸盐(NO-3)已成为最常见的地下水污染源之一.本文介绍了用CaO除去CO2与H2O的测定氮同位素比值的燃烧管方法和用AeNO3+C(石墨)生成CO2的测定NO-3中氧同位素比值的燃烧法,它们是1995年以后发展起来的最新测试技术.     

福建厦门市硝酸型地下水特征、成因及其治理措施建议

地下水硝酸盐污染是世界性水环境问题。地下水硝酸盐绝对含量的增加，引起水质恶化，而其相对含量的增加，改变了地下水的水化学特征。在某些地区NO₃^-成为地下水中的主要阴离子之一，用"硝酸型水"命名这种新的地下水化学类型，目前正在逐渐被学者所接受。本研究通过分析厦门市平原区地下水中硝酸型水分布特征和影响因素，探讨了硝酸型水的水化学指示意义。结果表明，厦门市地下水已受到硝酸盐氮污染。在全区采集的87组地下水样品中，硝酸型水占比36.8%，主要分布于风化残积平原区，东部翔安区和同安区已形成较大面状分布，西部集美区和海沧区分布较少，且呈点状或局部小面积分布。硝酸型水主要存在于氧化沉积环境，具有低pH、低TDS和低硬度特征。风化残坡积含水层的酸性土壤、地下水径流缓慢和浅层地下水埋深浅等特征为地下水NO₃^-富集提供了有利的环境条件。人类生活污水、垃圾渗滤液下渗、农业施肥等是地下水硝酸盐污染的主要来源。建议开展地下水硝酸盐污染源识别研究，针对不同污染来源采取完善污染管网建设、农村改厕、科学施肥等措施，从源头上防治污染。     

Dating of the near-surface layer of a peatland in northwestern Ontario, Canada

The near-surface layer of the dominant microhabitat types on a peatland in the Rainy River area, northwestern Ontario, Canada was dated using a number of previously published methods. No single method was found to be appropriate in all microhabitat types, and discrepancies of up to 15 yr over a time-scale of 80 yr were encountered. The results suggested that the post-depositional mobility of ²¹⁰Pb, and possibly its atmospheric supply, are affected by microhabitat type. ²¹⁰Pb dates consistently underestimated independently derived dates in the uppermost sections of the cores. Ages derived by measuring the length of annual increments on moss stems were in general agreement with the ²¹⁰Pb dates, but were subject to bias where the moss remains were poorly preserved. ¹⁴C analyses on material from the base to the near-surface horizon confirmed the modern (post-AD 1950) origin suggested by the ²¹⁰Pb and moss increment dates. Increased ash content at the base of the near-surface layer was correlated with the dustbowl of the 1930s, but assignment of dates to other stratigraphic markers (charcoal, Ambrosia pollen, and Larix needles) was less certain. The ash peak (55 yr before AD 1990) was used as datum for relative dating methods based on assumptions of a constant rate of peat accumulation (constant bulk density method) and constant rate of pollen accumulation (pollen density method). The constant bulk density method provided quick, inexpensive estimates of maximum age, but could not be extrapolated beyond datum, nor applied to cores showing marked stratigraphic changes. The pollen density method was a valuable but time-consuming alternative for dating peatland depressions, which lack annual moss increments and are subject to ²¹⁰Pb leaching.     

AMS 14C测年揭示的临夏盆地巴谢河流域典型滑坡的四次滑动

正1研究目的(Objective)自1983年3月7日甘肃省东乡族自治县发生导致237人死亡的洒勒山滑坡灾害以来,巴谢河流域吸引了国内外大量学者在此开展滑坡研究。这一地区灾难性滑坡多具有多期次活动的特征,但对滑坡历史的认识,尚缺乏年代学数据支持。本研究以本地区典型滑坡——上正滑坡为例,通过滑坡年代学研究,重建滑坡的滑动历史。     

The combined RUSLE/SDR approach integrated with GIS and geostatistics to estimate annual sediment flux rates in the semi-arid catchment,Turkey

Quantitative evaluation of the spatial distribution of the erosion risk in any watershed or ecosystem is one of the most important tools for environmentalists, conservationists and engineers to plan natural resource management for the sustainable environment in a long term. This study was performed in the semi-arid catchment of the Saraykoy II Irrigation Dam, Cankiri, located in the transition zone between the Central Anatolia Steppe and the Black Sea Forests of Turkey. The total area of the catchment is 262.31 ha. The principal objectives were to quantify both potential and actual soil erosion risks by the Revised Universal Soil Loss Equation (RUSLE) and to estimate the amount of sediments to be delivered from the hillslope of the catchment to the reservoir of the dam using the sediment delivery ratio (SDR) in combination with the RUSLE model. All factor and sub-factor calculations required for solving the RUSLE model and SDR in the catchment were made spatially using DEM, GIS and Geostatistics. As the main catchment was divided into twenty-five sub-catchments, the predicted actual soil loss (by the model) was 146,657.52 m³ year^?1 and the weighted average of SDR estimated by areal distribution (%) of the sub-watersheds was 0.344 for whole catchment, resulted in 50,450.19 m³ year^?1 sediment arriving to the reservoir. Since the Dam has a total storage capacity of 509 × 10³ m³, the life expectancy of the Dam is estimated as 10.09 year. This estimation indicated that the dam has a relatively short economic life and there is a need for water-catchment management and soil conservation measures to reduce erosion.     

An ecosystem approach to planning for groundwater: The case of Waterloo Region, Ontario, Canada

Sustaining the human-ecological benefits of groundwater requires carefully planned strategies for reducing the cumulative risks posed by diverse human actions. Municipal governments in Ontario, Canada, play a key role in developing solutions to groundwater management and protection. The responsibility to provide drinking water and sewage works, regulate the use of private land, and protect public health provides the mandate and authority to take action. Waterloo Region, in the province of Ontario, contains the single largest population in Canada that uses groundwater as its primary source of drinking water. The region's Water Resources Protection Strategy provides a model of planning for groundwater at a regional scale. The ecosystem approach offers a comprehensive basis for designing community-based groundwater strategies, within a regional context. This approach is defined by the following key components: ecosystem boundaries, objectives, functions, and cumulative effects; and is integrated, adaptable, coordinated, and catalytic. Waterloo's groundwater strategy is distinguished by the degree to which it embodies many elements of the ecosystem approach. Future priorities include embracing a comprehensive vision; enumerating essential ecological functions; integrating a full set of regulatory, voluntary, and economic instruments; and accelerating partnerships with key stakeholders for implementation. Résumé Le fait de tirer des eaux souterraines des bénéfices écologiques pour l'homme exige des stratégies soigneusement préparées pour réduire les risques cumulatifs posés par les diverses actions humaines. Les municipalités de l'Ontario, au Canada, jouent un rôle clé en développant des solutions de gestion et de protection des eaux souterraines. La responsabilité de fournir des réseaux d'eau potable et d'eaux usées, de réguler l'usage des territoires privés et de protéger la santé publique donne le mandat et l'autorité pour agir. La région de Waterloo, dans la province d'Ontario, possède la plus grande communauté qui, au Canada, utilise l'eau souterraine comme unique ressource primaire d'eau potable. La stratégie de protection des ressources en eau de la région fournit un modèle d'organisation pour l'eau souterraine à l'échelle régionale. L'approche de l'écosystème fournit une base d'ensemble pour définir des stratégies basées sur la communauté pour les eaux souterraines, dans un contexte régional. Cette approche est définie par les composantes clés suivantesu: frontières de l'écosystème, objectifs, fonctions, effets cumulatifsu elle est intégrée, adaptable, coordonnée et catalytique. La stratégie de Waterloo pour les eaux souterraines se distingue par le degré par lequel elle rassemble de nombreux éléments de l'approche écosystémique. Les futures priorités prévoient de prendre en compte une vision d'ensemble, de lister les fonctions écologiques essentielles, d'intégrer un ensemble complet d'instruments économiques, spontanés et de régulation, et d'accélérer les partenariats avec les acteurs clés pour la mise en muvre du dispositif. Resumen Para mantener los beneficios ecológicos del agua subterránea se requiere una estrategia para reducir los riesgos asociados a las diversas acciones antrópicas. En la Provincia de Ontario, Canadá, los gobiernos municipales son los encargados de gestionar y proteger las aguas subterráneas. En concreto, estos organismos tienen competencia sobre la gestión del abastecimiento y saneamiento, la regulación de usos del suelo y la protección de la salud pública. La región de Waterloo, en la Provincia de Ontario, contiene la mayor población de Canadá que es abastecida primordialmente por aguas subterráneas. La Water Resources Protection Strategy (Estrategia de Protección de los Recursos de Agua) de la región supone un modelo de planificación de aguas subterráneas a escala regional. La denominada metodología de ecosistema, que ofrece una base global para el diseño de las estrategias a escala de comunidad, engloba las siguientes componentes: contornos del ecosistema, objetivos, funciones, y efectos acumulativos, y es una metodología integrada, adaptable, coordinada y catalítica. La estrategia utilizada en Waterloo se distingue por el grado de aplicación de varios de los elementos correspondientes a esta metodología. Las prioridades futuras incluyen una visión globalizadora, enumerando las funciones ecológicas esenciales, integrando una serie de instrumentos reguladores, voluntarios y económicos, y acelerando la implantación de asociaciones de usuarios.     

Comparative 210Pb, 137Cs,and pollen geochronologies of sediments from Lakes Ontario and Erie

The distribution of ²¹⁰Pb, ¹³⁷Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with ²¹⁰Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with ¹³⁷Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of ¹³⁷Cs and ²¹⁰Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on ²¹⁰Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of ²¹⁰Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both ²¹⁰Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated.     

The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a midwestern agricultural watershed

Defining the control that hydrology exerts on organic carbon (OC) export at the watershed scale is important for understanding how the source and quantity of OC in streams and rivers is influenced by climate change or by landscape drainage. To this end, molecular (lignin phenol), stable carbon isotope, and dissolved organic carbon (DOC) data were collected over a range of flow conditions to examine the influence of hydrology on annual OC export from an 850 km² Midwestern United States agricultural watershed located in west central Indiana. In years 2002 and 2003, modeled annual DOC loads were 19.5 and 14.1 kg ha⁻¹yr⁻¹, while 71% and 85%, respectively, of the total annual OC was exported in flow events occurring during less than 20% of that time. These results highlight the importance of short-duration, high-discharge events (common in smaller watersheds) in controlling annual OC export. Based on reported increases in annual stream discharge coupled with current estimates of DOC export, annual DOC loads in this watershed may have increased by up to 40% over the past 50 years. Molecular (lignin phenol) characterization of quantity and relative degradation state of terrestrial OC shows as much temporal variability of lignin parameters (in high molecular weight dissolved organic carbon) in this one watershed as that demonstrated in previously published studies of dissolved organic matter in the Mississippi and Amazon Rivers. These results suggest that hydrologic variability is at least as important in determining the nature and extent of OC export as geographic variability. Moreover, molecular and bulk stable carbon isotope data from high molecular weight dissolved organic carbon and colloidal organic carbon showed that increased stream flow from the study watershed was responsible for increased export of agriculturally derived OC. When considered in the context of results from other studies that show the importance of flood events and in-stream processing of terrestrial organic carbon, our results show how hydrologic variability in smaller watersheds can reflect landscape-scale carbon dynamics in ways that cannot necessarily be measured at the outlets of large rivers due to multiple source signals and attenuated hydrology.     

岩溶洞穴系统SO42-、NO3-来源及其对水岩作用的影响

为揭示洞穴系统中SO₄2-和NO₃-离子来源及其对洞穴碳酸盐溶解的影响,通过对麻黄洞6个水点自2018年8月至2019年7月进行为期一个完整水文年的系统监测,对于监测结果进行综合分析.结果表明:（1）麻黄洞洞穴水水化学类型为HCO₃-Ca·Mg以及HCO₃·SO₄-Ca·Mg型;（2）通过实地调查与元素比值法综合分析可知,麻黄洞NO₃-与SO₄2-各水点来源存在一定差异,其中麻黄洞NO₃-主要源于农业活动和大气N沉降,而SO₄2-主要以农业活动、石膏溶解为主要来源,SO₄2-和NO₃-均参与了岩溶作用,加速了基岩的溶蚀,这一过程主要受离子浓度、径流大小以及补给模式影响;（3）基于水化学计量法和稳定同位素技术估算可知,SO₄2-和NO₃-洞穴水DIC的贡献为0.05~0.61,释放DIC的同时改变了水中离子浓度,对于岩溶作用形成扰动,总体呈现出旱季>雨季、滴水>裂隙水的特征.同样,由于岩溶区的复杂和不可知,在对其进行系统研究时应当注重多种方法的结合与比较,提高研究精度与可信度.      

The impact of vegetation on REE fractionation in stream waters of a small forested catchment (the Strengbach case)

Previous studies on waters of a streamlet in the Vosges Mountains (Eastern France) have shown that strontium and rare earth elements (REE) mainly originate from preferential dissolution of apatite during weathering. However, stream water REE patterns normalized to apatite are still depleted in the light REE (LREE, La-Sm) pointing to the presence of an additional LREE depleting process. Vegetation samples are strongly enriched in LREE compared to stream water and their Sr and Nd isotopic compositions are comparable with those of apatite and stream water. Thus, the preferential LREE uptake by vegetation might lead to an additional LREE depletion of surface runoff in the forested catchment. Mass balance calculations indicate, that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling LREE depletion in river water. This is underlined by the observation that rivers from arctic and boreal regions with sparse vegetation appear to be less depleted in LREE than rivers from tropical environments or boreal environments with a dense vegetation cover.     

Magnitude of σ1, σ2, and σ3 at mid-crustal levels in an orogenic belt: Microboudin method applied to an impure metachert from Turkey

We revised an equation for estimating palaeostress magnitude using the microboudin technique by incorporating the influence of time on the fracture strength of minerals. The equation was used to estimate triaxial palaeostresses from a rare sample of metachert from Turkey that contains microboudinaged, columnar tourmaline grains in a wide range of orientations within the foliation plane. The estimated principal palaeostresses are σ₁ = 605 MPa, σ₂ = 598 MPa, and σ₃ = 597 MPa. As the microboudinage is considered to have occurred immediately before the rock encountered the brittle-plastic transition during exhumation, these stress values correspond to conditions at approximately 18 km depth and 300 °C within a Cretaceous orogenic belt.     

Geostatistical mapping of leakance in a regional aquitard, Oak Ridges Moraine area, Ontario, Canada

The Newmarket Till forms a regionally extensive aquitard separating two major aquifer systems in the Greater Toronto area, Canada. The till is incised, and sometimes eroded entirely, by a network of sand- and gravel-filled channels forming productive aquifers and, locally, high-conductivity windows between aquifer systems. Leakage through the till may also be substantial in places. This study investigates the spatial variability of aquitard leakance in order to assess the relative importance of recharge processes to the lower aquifers. With a large database derived from water-well records and containing both hard and soft information, the Sequential Indicator Simulation method is used to generate maps of aquitard thickness and window probability. These can be used for targeting channel aquifers and for identifying potential areas of recharge to the lower aquifers. Conductivities are modeled from sparse data assuming that their correlation range is much smaller than the grid spacing. Block-scale leakances are obtained by upscaling nodal values based on simulated conductivity and thickness fields. Under the "aquifer-flow' assumption, upscaling is performed by arithmetic spatial averaging. Histograms and maps of upscaled leakances show that heterogeneities associated with aquitard windows have the largest effect on regional groundwater flow patterns. Electronic Publication     

The drainage of Lake Ojibway in glaciolacustrine sediments of northern Ontario and Quebec,Canada

Physical evidence for the drainage of glacial lakes remains relatively rare in depositional records, giving rise to much debate on the location of outlets and discharge pathways, as well as on the climate impact of the attendant meltwater forcing. Lake Ojibway developed following the withdrawal of the Laurentide Ice Sheet in northern Ontario and Quebec, Canada. The late‐stage evolution of this large ice‐dammed lake was influenced by the complex dynamics of the retreating ice margin, which highly complicates the identification of the termination of Lake Ojibway in glaciolacustrine sediment records. Here, we document the composition of sections of rhythmites that contain in their upper part an anomalously thick and whitish bed (10–15 cm) that is in turn overlain by ～1 m of faintly bedded rhythmites. Grain‐size analyses showed that the thick whitish bed consists primarily of fine to coarse silt (2–63 μm), contrasting with the lower and upper rhythmites that are largely dominated by clay (<2 μm). The detrital carbonate content of the thick silt bed is characterized by consistently high values (2.5 to 2.8%), whereas the bounding rhythmites show lower and highly variable values. Oxygen isotope measurements further show a marked change going from typical glacial meltwater values (～ ?29.6 to ?27.7‰; VSMOW) for the lower rhythmites and the silt bed to modern‐like meteoric values (?18.4 to ?14.6‰) for the uppermost rhythmites. These data suggest that this marker bed may be associated with a major drawdown event that possibly corresponds to the final drainage of Lake Ojibway. AMS radiocarbon dating of ostracods extracted from the drainage bed also documents an important hardwater effect within the Ojibway basin.