The Bear Brook Watershed in Maine: Multi-decadal whole-watershed experimental acidification     

Kaizad F. Patel  Ivan J. Fernandez  Sarah J. Nelson  Stephen A. Norton  Cheryl J. Spencer 《水文研究》2021,35(5):e14147

The Bear Brook Watershed in Maine (BBWM) is a long-term research site established to study the response of forest ecosystem function to environmental disturbances of chronic acidic deposition and ecosystem nitrogen enrichment. Starting in 1989, the West Bear (treated) watershed received bimonthly applications of ammonium sulfate [(NH₄)₂SO₄] fertilizer from above the canopy, whereas East Bear (reference) received ambient deposition. The treatments were stopped in 2016, marking the beginning of the recovery phase. Research at the site has focused on soils, streams, and vegetation. Here, we describe data collected over three decades at the BBWM—input and stream output nutrient fluxes, quantitative soil pits and soil chemistry, and soil temperature and moisture.  相似文献   

Origin of K-rich diamond-forming immiscible melts and CO2 fluid via partial melting of carbonated pelites at a depth of 180–200 km     

《Gondwana Research》2019

Melt inclusions in kimberlitic and metamorphic diamonds worldwide range in composition from potassic aluminosilicate to alkali-rich carbonatitic and their low-temperature derivative, a saline high-density fluid (HDF). The discovery of CO₂ inclusions in diamonds containing eclogitic minerals are also essential. These melts and HDFs may be responsible for diamond formation and metasomatic alteration of mantle rocks since the late Archean to Phanerozoic. Although a genetic link between these melts and fluids was suggested, their origin is still highly uncertain. Here we present experimental results on melting phase relations in a carbonated pelite at 6 GPa and 900–1500 °C. We found that just below solidus K₂O enters potassium feldspar or K₂TiSi₃O₉ wadeite coexisting with clinopyroxene, garnet, kyanite, coesite, and dolomite. The potassium phases react with dolomite to produce garnet, kyanite, coesite, and potassic dolomitic melt, 40(K_0.90Na_0.10)₂CO₃·60Ca_0.55Mg_0.24Fe_0.21CO₃ + 1.9 mol% SiO₂ + 0.7 mol% TiO₂ + 1.4 mol% Al₂O₃ at the solidus established near 1000 °C. Molecular CO₂ liberates at 1100 °C. Potassic aluminosilicate melt appears in addition to carbonatite melt at 1200 °C. This melt contains (mol/wt%): SiO₂ = 57.0/52.4, TiO₂ = 1.8/2.3, Al₂O₃ = 8.5/13.0, FeO = 1.4/1.6, MgO = 1.9/1.2, CaO = 3.8/3.2, Na₂O = 3.2/3.0, K₂O = 10.5/15.2, CO₂ = 12.0/8.0, while carbonatite melt can be approximated as 24(K_0.81Na_0.19)₂CO₃·76Ca_0.59Mg_0.21Fe_0.20CO₃ + 3.0 mol% SiO₂ + 1.6 mol% TiO₂ + 1.4 mol% Al₂O₃. Both melts remain stable to at least 1500 °C coexisting with CO₂ fluid and residual eclogite assemblage consisting of K-rich omphacite (0.4–1.5 wt% K₂O), almandine-pyrope-grossular garnet, kyanite, and coesite. The obtained immiscible alkali‑carbonatitic and potassic aluminosilicate melts resemble compositions of melt inclusions in diamonds worldwide. Thus, these melts entrapped by diamonds could be derived by partial melting of the carbonated material of the continental crust subducted down to 180–200 km depths. Given the high solubility of chlorides and water in both carbonate and aluminosilicate melts inferred in previous experiments, the saline end-member, brine, could evolve from potassic carbonatitic and/or silicic melts by fractionation of Ca-Mg carbonates/eclogitic minerals and accumulation of alkalis, chlorine and water in the residual low-temperature supercritical fluid. Direct extraction from the hydrated marine sediments under conditions of cold subduction would be another possibility for the brine formation.  相似文献   

Effects of changes in canopy interception on stream runoff response and recovery following clear-cutting of a Japanese coniferous forest in Fukuroyamasawa Experimental Watershed in Japan     

Tomoki Oda  Tomohiro Egusa  Nobuhito Ohte  Norifumi Hotta  Nobuaki Tanaka  Mark B. Green  Masakazu Suzuki 《水文研究》2021,35(5):e14177

Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest.  相似文献   

Sustainable groundwater management: How long and what will it take?     

《Global Environmental Change》2019

Groundwater depletion is arguably one of humanity's greatest sustainability challenges of the 21st century. With Sustainable Development Goals only a decade away, water authorities around the world are in the urgent need for concrete and targeted measures to ensure that communities adhere to groundwater management policies as rapidly and as effectively as possible. In this paper, we combine computational social science, groundwater modelling and empirical data from the World Values Survey to generate future ensembles of hydro-social trajectories under alternative courses of management and social action or inaction. Our simulations shed new light on the role that cultural values can play in shaping the societal trajectories and norms that emerge when resources are either allocated or not sufficiently allocated to monitor compliance, issue fines, engage community leaders, and deter rule-breakers. This study presents a new approach to explore and evaluate the capacity of existing and future management actions to steer groundwater systems towards sustainable trajectories, to forecast the celerity and timing of social transformations at the inter-decadal scale, and to help nations identify the most pertinent management options under institutional, political, social, and/or cultural constraints. The methods presented here are broadly applicable to support strategic decisions that rely on the monitoring, enforcement, and compliance of environmental regulations.  相似文献   

Deep-water sediment transport patterns and basin floor topography in early rift basins: Plio-Pleistocene syn-rift of the Corinth Rift,Greece     

Martin Muravchik  Gijs A. Henstra  Gauti T. Eliassen  Rob L. Gawthorpe  Mike Leeder  Haralambos Kranis  Emmanuel Skourtsos  Julian Andrews 《Basin Research》2020,32(5):1184-1212

Our current understanding on sedimentary deep-water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio-Pleistocene deep-water sedimentary system (Rethi-Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep-water syn-rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast-count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone-dominated sheets, B—conglomerate-dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone-dominated broad shallow lobes, F—sandstone-dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland-fed Mavro delta, with minor contributions from a transverse system of conglomerate-dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep-water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin-floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large-scale subaqueous landslides and eventual uplift of the whole fault block.  相似文献   

Assessment of alternative adsorption models and global sensitivity analysis to characterize hexavalent chromium loss from soil to surface runoff          下载免费PDF全文

Chuan‐An Xia  Juxiu Tong  Bill X. Hu  Xiujie Wu  Alberto Guadagnini 《水文研究》2018,32(20):3140-3157

We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, that is, the Langmuir, Freundlich, Temkin, and linear models, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes are associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through maximum likelihood model calibration and four model identification criteria (i.e., the Akaike information criteria [AIC and AIC_C] and the Bayesian and Kashyap information criteria). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within subregions of the parameter space. In this context, the modelling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skilful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component.  相似文献   

Magmatic expression of tectonic transition from oceanic subduction to continental collision: Insights from the Middle Triassic rhyolites of the North Qiangtang Block     

《Gondwana Research》2020

The tectonic transition from subduction to collision is a fundamental process during orogenesis, yet the magmatic expression of this transition and related deep geodynamic processes remain unclear. This study focuses on a newly identified volcanic belt within the Moyun–Zaduo–Sulu area of the North Qiangtang Block and presents new zircon U-Pb data that indicate that this belt formed during the Middle Triassic (247–241 Ma), a time characterized by a regional transition from subduction to collisional tectonism. The volcanic belt is located to the south of a Permian to Early Triassic arc and is dominated by high-K calc-alkaline and peraluminous rhyolites. These rhyolites have low Mg^#, Nb/Ta, and δEu values, contain low contents of Sr, have high Rb/Sr and whole-rock ε_Nd(t) values, and show positive zircon ε_Hf(t) values, all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material. The migration of Middle Triassic volcanism in this region was most likely caused by rollback of the subducting Longmucuo–Shuanghu Tethyan oceanic slab. Combining our new data with previously published results of numerical modeling of subduction–collisional processes and regional data from north-central Tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision. This combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction, the transition from subduction to collision, and collisional tectonism.  相似文献   

A near-inertial current event in the homogeneous deep layer of the northern Sea of Japan during winter     

Michio Watanabe  Toshiyuki Hibiya 《Journal of Oceanography》2018,74(2):209-218

Under strong surface wind forcing during winter, direct current observations in the northern Sea of Japan show the existence of strong near-inertial currents in the deep water that is characterized by the extremely homogeneous vertical structures of temperature and salinity. However, the mechanism generating internal waves in the deep water of the northern Sea of Japan has not been well understood. In this study, to clarify the dynamical link between the surface wind forcing and near-inertial currents in the deep water of the northern Sea of Japan, we drive a general circulation model taking into account realistic wind stress, ocean bottom and land topography. In the northern Sea of Japan, the numerical results show that vertically coherent horizontal currents with a speed of ~ 0.05 m s^?1 are excited throughout the homogeneous deep water. A two-layer model successfully reproduces the pattern of the horizontal current velocities shown by the general circulation model, indicating that internal waves emanate westward from the northwestern coast of Japan through coastal adjustment to the strong wind forcing event and, while propagating into the ocean interior, they excite evanescent near-inertial response throughout the lower layer below the interface.  相似文献   

Two generations of Variscan garnet: Implications from a petrochronological study of a high-grade Avalonia-derived paragneiss from the Drosendorf unit,Bohemian Massif     

《Gondwana Research》2020

Garnets in metapelitic paragneisses from the southern Drosendorf unit in the Austrian part of the Bohemian Massif exhibit two episodes of growth during the Variscan orogeny, which can be distinguished on textural and chemical grounds. The first garnet (grt1) records evidence of high-grade metamorphism in the Late Devonian (Frasnian–Famennian), while the second garnet (grt2) formed by a second high-grade event in the Early Carboniferous (Visean). Both garnet generations contain abundant inclusions, of which monazite, rutile and crystallised melt droplets are particularly useful for reconstructing P–T–t conditions. The Late Devonian age (373 ± 9 Ma) for the first episode of garnet growth was obtained from chemical dating of monazite inclusions in grt1. Metamorphic conditions during the first episode of garnet growth are estimated to have been between 0.7 and 0.8 GPa at 680–700 °C and 0.95–1.10 GPa at 745–785 °C. There followed a phase of cooling and exhumation, after which the second garnet (grt2) were formed beginning under amphibolite facies conditions and continuing prograde to peak conditions of 0.95–1.10 GPa and 745–785 °C, which are similar to those of the first garnet forming event. Subsequently, the rocks experienced near isothermal decompression to 0.5–0.8 GPa. Chemical dating of both monazite inclusions in grt2 and the matrix provide a Visean age (343 ± 3 Ma).A study of detrital zircons in these paragneisses revealed zircon forming events at around 1.2, 1.5 and 1.8 Ga, suggesting an Avalonian provenance. The lack of zircons younger than 1 Ga and the presence of Cadomian metamorphic monazite relics (652 ± 15 Ma) indicates an Early Neoproterozoic deposition age for the sedimentary protolith likely. Our documentation of a Late Devonian high-grade metamorphic event in rocks derived from Avalonian corroborates tectonic models which assume that frontal parts of the Armorican terrane had already docked with Avalonia by this time.  相似文献   

Evaluating techniques for mapping island vegetation from unmanned aerial vehicle (UAV) images: Pixel classification,visual interpretation and machine learning approaches     

《International Journal of Applied Earth Observation and Geoinformation》2020

We evaluate three approaches to mapping vegetation using images collected by an unmanned aerial vehicle (UAV) to monitor rehabilitation activities in the Five Islands Nature Reserve, Wollongong (Australia). Between April 2017 and July 2018, four aerial surveys of Big Island were undertaken to map changes to island vegetation following helicopter herbicide sprays to eradicate weeds, including the creeper Coastal Morning Glory (Ipomoea cairica) and Kikuyu Grass (Cenchrus clandestinus). The spraying was followed by a large scale planting campaign to introduce native plants, such as tussocks of Spiny-headed Mat-rush (Lomandra longifolia). Three approaches to mapping vegetation were evaluated, including: (i) a pixel-based image classification algorithm applied to the composite spectral wavebands of the images collected, (ii) manual digitisation of vegetation directly from images based on visual interpretation, and (iii) the application of a machine learning algorithm, LeNet, based on a deep learning convolutional neural network (CNN) for detecting planted Lomandra tussocks. The uncertainty of each approach was assessed via comparison against an independently collected field dataset. Each of the vegetation mapping approaches had a comparable accuracy; for a selected weed management and planting area, the overall accuracies were 82 %, 91 % and 85 % respectively for the pixel based image classification, the visual interpretation / digitisation and the CNN machine learning algorithm. At the scale of the whole island, statistically significant differences in the performance of the three approaches to mapping Lomandra plants were detected via ANOVA. The manual digitisation took a longer time to perform than others. The three approaches resulted in markedly different vegetation maps characterised by different digital data formats, which offered fundamentally different types of information on vegetation character. We draw attention to the need to consider how different digital map products will be used for vegetation management (e.g. monitoring the health individual species or a broader profile of the community). Where individual plants are to be monitored over time, a feature-based approach that represents plants as vector points is appropriate. The CNN approach emerged as a promising technique in this regard as it leveraged spatial information from the UAV images within the architecture of the learning framework by enforcing a local connectivity pattern between neurons of adjacent layers to incorporate the spatial relationships between features that comprised the shape of the Lomandra tussocks detected.  相似文献