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1.
In 1967, the original Walker Branch Watershed (WBW) project was established to study elemental cycling and mass balances in a relatively unimpacted watershed. Over the next 50+ years, findings from additional experimental studies and long-term observations on WBW advanced understanding of catchment hydrology, biogeochemistry, and ecology and established WBW as a seminal site for catchment science. The 97.5-ha WBW is located in East Tennessee, USA, on the U.S. Department of Energy's Oak Ridge Reservation. Vegetation on the watershed is characteristic of an eastern deciduous, second-growth forest. The watershed is divided into two subcatchments: the West Fork (38.4 ha) and the East Fork (59.1 ha). Headwater streams draining these subcatchments are fed by multiple springs, and thus flow is perennial. Stream water is high in base cations due to weathering of dolomite bedrock and nutrient concentrations are low. Long-term observations of climate, hydrology, and biogeochemistry include daily (1969–2014) and 15-min (1994–2014) stream discharge and annual runoff (1969–2014); hourly, daily, and annual rainfall (1969–2012); daily climate and soil temperature (1993–2010); and weekly stream water chemistry (1989–2013). These long-term datasets are publicly available on the WBW website (https://walkerbranch.ornl.gov/long-term-data/ ). While collection of these data has ceased, related long-term measurements continue through the National Ecological Observatory Network (NEON), where WBW is the core terrestrial and aquatic site in the Appalachian and Cumberland Plateau region (NEON's Domain 7) of the United States. These long-term datasets have been and will continue to be important in evaluating the influence of climatic and environmental drivers on catchment processes. 相似文献
2.
The Shenandoah Watershed Study (established in 1979) and the Virginia Trout Stream Sensitivity Study (established in 1987) serve to increase understanding of hydrological and biogeochemical changes in western Virginia mountain streams that occur in response to acidic deposition and other ecosystem stressors. The SWAS-VTSSS program has evolved over its 40+ year history to consist of a temporally robust and spatially stratified monitoring framework. Currently stream water is sampled for water quality bi-hourly during high-flow events at three sites and weekly at four sites within Shenandoah National Park (SHEN), and quarterly at 72 sites and on an approximately decadal frequency at ~450 sites within the wider western Virginia Appalachian region. Stream water is evaluated for pH, acid neutralizing capacity (ANC), base cations (calcium, magnesium, sodium and potassium ion), acid anions (sulphate, nitrate and chloride), silica, ammonium, and conductivity with a subset of samples evaluated for monomeric aluminium and dissolved organic carbon. Hourly stream discharge (four sites) and in-situ measurements of conductivity, water and air temperature (three sites) are also measured within SHEN. Here we provide an overview and timeline of the SWAS-VTSSS stream water monitoring program, summarize the field and laboratory methods, describe the water chemistry and hydrologic data sets, and document major watershed disturbances that have occurred during the program history. Website links and instructions are provided to access the stream chemistry and time-series monitoring data in open-access federal databases. The purpose of this publication is to promote awareness of these unique, long-term data sets for wider use in catchment studies. The water chemistry and hydrologic data can be used to investigate a wide range of biogeochemical research questions and provide key inputs for models of these headwater stream ecosystems. SWAS-VTSSS is an ongoing program and quality assured data sets are uploaded to the databases annually. 相似文献
3.
Sherri L. Johnson Don Henshaw Greg Downing Steve Wondzell Mark Schulze Adam Kennedy Greg Cohn Stephanie A. Schmidt Julia A. Jones 《水文研究》2021,35(5):e14187
The H. J. Andrews Experimental Forest (HJA) encompasses the 6400 ha Lookout Creek watershed in western Oregon, USA. Hydrologic, chemistry and precipitation data have been collected, curated, and archived for up to 70 years. The HJA was established in 1948 to study the effects of harvest of old-growth conifer forest and logging-road construction on water quality, quantity and vegetation succession. Over time, research questions have expanded to include terrestrial and aquatic species, communities and ecosystem dynamics. There are nine small experimental watersheds and 10 gaging stations in the HJA, including both reference and experimentally treated watersheds. Gaged watershed areas range from 8.5 to 6242 ha. All gaging stations record stage height, water conductivity, water temperature and above-stream air temperature. At nine of the gage sites, flow-proportional water samples are collected and composited over 3-week intervals for chemical analysis. Analysis of stream and precipitation chemistry began in 1968. Analytes include dissolved and particulate species of nitrogen and phosphorus, dissolved organic carbon, pH, specific conductance, suspended sediment, alkalinity, and major cations and anions. Supporting climate measurements began in the 1950s in association with the first small watershed experiments. Over time, and following the initiation of the Long Term Ecological Research (LTER) grant in 1980, infrastructure expanded to include a set of benchmark and secondary meteorological stations located in clearings spanning the elevation range within the Lookout Creek watershed, as well as a large number of forest understory temperature stations. Extensive metadata on sensor configurations, changes in methods over time, sensor accuracy and precision, and data quality control flags are associated with the HJA data. 相似文献
4.
《Limnologica》2020
Riparian land use is a key driver of stream ecosystem processes but its effects on water quality are still a matter of debate when proposing measures to improve freshwater quality. The aim of this study was to examine the influence of riparian land use on stream habitat and water chemistry, and to assess in what extent stream habitat also affects water quality. To that end, we selected eight reaches in the Ave River basin (northwestern Portugal) and compared longitudinal variations in water chemistry and stream habitat between reaches with different land use (urban, agricultural and natural), and between reaches with natural riparian areas and different habitats. Stream habitat was assessed using the Fluvial Functional Index, the HABSCORE, and the Riparian Forest Quality Index. Longitudinal variations in water chemistry were determined measuring differences in concentrations of ammonium, nitrate, phosphate and oxygen, and conductivity, pH and temperature between the downstream and the upstream ends of each reach. Nitrate concentration tended to decrease along reaches with more natural riparian areas and to increase along reaches with more urban and agricultural land uses. Longitudinal variations in water chemistry also differed between reaches with natural riparian areas, suggesting that water quality also depends on stream habitat. Moreover, longitudinal variation in water chemistry was proven a simple, useful and low-cost approach to assess the influence of land cover and stream habitat on water quality. Overall results demonstrated that both riparian land use and stream habitat influence water quality and that riparian forests are essential to reduce nutrient export to downstream ecosystems. 相似文献
5.
6.
富Al球粒是原始球粒陨石中一种矿物岩石学特征介于富钙铝包体(CAIs)和镁铁质硅酸盐球粒之间的特殊集合体,所以常常认为富Al球粒在认识CAIs和镁铁质硅酸盐球粒形成演化过程中的相互联系具有特殊意义。然而,对富Al球粒的初始物质组成以及形成演化过程一直存在较多争议,而氧同位素组成研究能够对球粒演化和早期星云环境等提供重要的信息。在本文中我们报导了来自Kainsaz(1937年降落于俄罗斯,CO3型)碳质球粒陨石中的2个富Al球粒(编号K1-CH1和K2-CH2)的矿物岩石学和氧同位素组成特征。K1-CH1的矿物组成主要为橄榄石、低钙辉石和富钙长石,K2-CH2为橄榄石和富钙长石。2个球粒中的矿物均具有贫~(16)O同位素组成特征。K1-CH1中矿物的△~(17)O组成基本上位于2个区间:-11.1‰~-8.7‰和-3.9‰~0.4‰;而K2-CH2的△~(17)O介于-6.6‰~-0.6‰之间,且具有从中部至边部升高的趋势。矿物岩石学和氧同位素特征表明,这2个富Al球粒的初始物质组成为富CAIs和镁铁质硅酸盐。在球粒熔融结晶过程中,与贫~(16)O同位素组成(△~(17)O:-8.7‰~-7.8‰)的星云发生了氧同位素交换。球粒形成后,发生迁移进入陨石母体,在相对更贫~(16)O同位素组成(△~(17)O:-0.6‰~0.4‰)的母体中(流体参与)发生变质作用,并再次发生了氧同位素交换。 相似文献
7.
This study is focused on a plagioclase‐bearing spinel lherzolite from Chah Loqeh area in the Neo‐Tethyan Ashin ophiolite. It is exposed along the west of left‐lateral strike‐slip Dorouneh Fault in the northwest of Central‐East Iranian Microcontinent. Mineral chemistry (Mg#olivine < ~ 90, Cr#clinopyroxene < ~ 0.2, Cr#spinel < ~ 0.5, Al2O3orthopyroxene > ~ 2.5 wt%, Al2O3clinopyroxene > ~ 4.5 wt%, Al2O3spinel > ~ 41.5 wt%, Na2Oclinopyroxene > ~ 0.11 wt%, and TiO2clinopyroxene > ~ 0.04 wt%) confirms Ashin lherzolite was originally a mid‐oceanic ridge peridotite with low degrees of partial melting at spinel‐peridotite facies in a lithospheric mantle level. However, some Ashin lherzolites record mantle upwelling and tectonic exhumation at plagioclase‐peridotite facies during oceanic extension and diapiric motion of mantle along Nain‐Baft suture zone. This mantle upwelling is evidenced by some modifications in the modal composition (i.e. subsolidus recrystallization of plagioclase and olivine between pyroxene and spinel) and mineral chemistry (e.g. increase in TiO2 and Na2O of clinopyroxene, and TiO2 and Cr# of spinel and decrease in Mg# of olivine), as a consequence of decompression during a progressive upwelling of mantle. Previous geochronological and geochemical data and increasing the depth of subsolidus plagioclase formation at plagioclase‐peridotite facies from Nain ophiolite (~ 16 km) to Ashin ophiolite (~ 35 km) suggest a south to north closure for the Nain‐Baft oceanic crust in the northwest of Central‐East Iranian Microcontinent. 相似文献
8.
金岭岩体是鲁西地区代表性的中生代侵入杂岩体,与金岭矽卡岩型铁矿的成因密切相关。为了解石英闪长岩的成因及与矽卡岩铁矿成矿关系,本次研究对金岭杂岩体中的石英闪长岩进行了年代学、地球化学及锆石Lu—Hf同位素和角闪石矿物微区成分的系统研究。LA-ICP-MS锆石U-Pb年代学显示石英闪长岩加权平均年龄为(128±1) Ma,侵位时代为早白垩世;样品具有较低的w(SiO_2)(58.34%~65.22%),和高的w(Al_2O_3)(14.95%~15.72%),w(Na_2O)为4.44%~5.16%,w(K_2O)为2.26%~5.17%,w(CaO)为3.39%~6.30%,w(Fe_2O_3~T),w(MgO)含量变化范围较大,分别为2.21%~6.86%和2.32%~5.21%,此外,样品具有较高的Sr含量(682~834×10-6)、Ba含量(1 130~1 595×10-6),表现出高Ba, Sr花岗岩的岩石地球化学特征。石英闪长岩中角闪石为岩浆成因角闪石,具有壳源岩浆成因角闪石的特征,其结晶时的氧逸度为△NNO+0.83~△NNO+1.87,温压条件为849~1 092℃和89~279 MPa。石英闪长岩含有较高的Ni含量、Co含量、Cr含量以及Mg~#,其Nb/Ta, Zr/Hf, Rb/Sr和Ba/Rb比值接近原始地幔平均值。样品含有~2.5Ga的捕获锆石,所有锆石的εHf(t)值为负值。锆石Hf同位素和岩石地球化学特征表明石英闪长岩侵位深度为3.9~10.3 km,岩浆源区为岩石圈地幔并受到地壳物质的混染。 相似文献
9.
Gang Yang Aaron Zimmerman Nicole C. Hurtig Svetoslav V. Georgiev Vineet Goswami Judith L. Hannah Holly J. Stein 《Geostandards and Geoanalytical Research》2020,44(2):231-242
Rhenium–osmium geochronometry for samples with low Re and complex matrices requires improved Re extraction methods. Here, we investigate plausible controls on efficiency and efficacy of Re extraction during our anion resin bead purification. Four different protocols are compared, each isolating a single variable to test. Rhenium concentrations for solutions at each step of each protocol document differences in chemical recovery/yield. The negative‐thermal ionisation mass spectrometry (N‐TIMS) signal intensity serves as a proxy for Re yield and purity. These data document correlations between the N‐TIMS signal intensity and (a) the duration of anion resin bead conditioning prior to loading with Re‐bearing solution, and (b) both duration and strength of nitric acid used during rinsing of the Re‐loaded anion resin bead. The optimal protocol improved Re signal intensity around fourteen times compared with our current Re extraction protocol, an aggregate of 2.4 times improvement in chemical recovery (yield) and 5.8 times improvement in emission efficiency (purity). Repeated N‐TIMS isotopic measurements on our in‐house Re standard solution (1407) verify that our optimal protocol‐3 does not fractionate Re isotopes. The improved anion resin bead method considerably lowers the Re detection limit and allows Re‐Os isotopic analysis of picogram‐level Re hosted in geological samples with complex matrices. 相似文献
10.
Marius G. Floriancic Benjamin M. C. Fischer Peter Molnar James W. Kirchner Ilja H.J. van Meerveld 《水文研究》2019,33(22):2847-2866
Catchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods, and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in 11 catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km2), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: Neighboring sampling locations could differ significantly in their specific discharge, isotopic composition, and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analysed could explain the spatial variability in specific discharge or streamwater chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow. 相似文献