Long-term hydrology and aquatic biogeochemistry data from H. J. Andrews Experimental Forest,Cascade Mountains,Oregon     

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   

Forest operations,tree species composition and decline in rainfall explain runoff changes in the Nacimiento experimental catchments,south central Chile     

Andrés Iroumé  Julia Jones  James C. Bathurst 《水文研究》2021,35(6):e14257

Few long-term studies have explored how intensively managed short rotation forest plantations interact with climate variability. We examine how prolonged severe drought and forest operations affect runoff in 11 experimental catchments on private corporate forest land near Nacimiento in south central Chile over the period 2008–2019. The catchments (7.7–414 ha) contain forest plantations of exotic fast-growing species (Pinus radiata, Eucalyptus spp.) at various stages of growth in a Mediterranean climate (mean long-term annual rainfall = 1381 mm). Since 2010, a drought, unprecedented in recent history, has reduced rainfall at Nacimiento by 20%, relative to the long-term mean. Pre-drought runoff ratios were <0.2 under 8-year-old Eucalyptus; >0.4 under 21-year-old Radiata pine and >0.8 where herbicide treatments had controlled vegetation for 2 years in 38% of the catchment area. Early in the study period, clearcutting of Radiata pine (85%–95% of catchment area) increased streamflow by 150 mm as compared with the year before harvest, while clearcutting and partial cuts of Eucalyptus did not increase streamflow. During 2008–2019, the combination of emerging drought and forestry treatments (replanting with Eucalyptus after clearcutting of Radiata pine and Eucalyptus) reduced streamflow by 400–500 mm, and regeneration of previously herbicide-treated vegetation combined with growth of Eucalyptus plantations reduced streamflow by 1125 mm (87% of mean annual precipitation 2010–2019). These results from one of the most comprehensive forest catchment studies in the world on private industrial forest land indicate that multiple decades of forest management have reduced deep soil moisture reservoirs. This effect has been exacerbated by drought and conversion from Radiata pine to Eucalyptus, apparently largely eliminating subsurface supply to streamflow. The findings reveal tradeoffs between wood production and water supply, provide lessons for adapting forest management to the projected future drier climate in Chile, and underscore the need for continued experimental work in managed forest plantations.  相似文献   

Geography Deserts: State and Regional Variation in the Formal Opportunity to Learn Geography in the United States, 2005–2015     

Mark C. Jones  Marcos Luna 《The Journal of geography》2019,118(2):88-100

The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG.  相似文献   

Forests and floods: Using field evidence to reconcile analysis methods     

James C. Bathurst  Barry Fahey  Andrés Iroumé  Julia Jones 《水文研究》2020,34(15):3295-3310

The extent to which forests, relative to shorter vegetation, mitigate flood peak discharges remains controversial and relatively poorly researched, with only a few significant field studies. Considering the effect purely of change of vegetation cover, peak flow magnitude comparisons for paired catchments have suggested that forests do not mitigate large floods, whereas flood frequency comparisons have shown that forests mitigate frequencies over all magnitudes of flood. This study investigates the apparent inconsistency using field-based evidence from four contrasting field programmes at scales of 0.34–3.1 km². Repeated patterns are identified that provide strong evidence of real effects with physical explanations. Magnitude and frequency comparisons are both relevant to the impact of forests on peak discharges but address different questions. Both can show a convergence of response between forested and grassland/logged states at the highest recorded flows but the associated return periods may be quite variable and are subject to estimation uncertainty. For low to moderate events, the forested catchments have a lower peak magnitude for a given frequency than the grassland/logged catchments. Depending on antecedent soil saturation, a given storm may nevertheless generate peak discharges of the same magnitude for both catchment states but these peaks will have different return periods. The effect purely of change in vegetation cover may be modified by additional forestry interventions, such as road networks and drainage ditches which, by effectively increasing the drainage density, may increase peak flows for all event magnitudes. For all the sites, forest cover substantially reduces annual runoff.  相似文献   

Changes in monthly baseflow across the U.S. Midwest   总被引：1，自引：0，他引：1  

Jessica R. Ayers  Gabriele Villarini  Christopher Jones  Keith Schilling 《水文研究》2019,33(5):748-758

Characterizing streamflow changes in the agricultural U.S. Midwest is critical for effective planning and management of water resources throughout the region. The objective of this study is to determine if and how baseflow has responded to land alteration and climate changes across the study area during the 50‐year study period by exploring hydrologic variations based on long‐term stream gage data. This study evaluates monthly contributions to annual baseflow along with possible trends over the 1966–2016 period for 458 U.S. Geological Survey streamflow gages within 12 different Midwestern states. It also examines the influence of climate and land use factors on the observed baseflow trends. Monthly contribution breakdowns demonstrate how the majority of baseflow is discharged into streams during the spring months (March, April, and May) and is overall more substantial throughout the spring (especially in April) and summer (June, July, and August). Baseflow has not remained constant over the study period, and the results of the trend detection from the Mann–Kendall test reveal that baseflows have increased and are the strongest from May to September. This analysis is confirmed by quantile regression, which suggests that for most of the year, the largest changes are detected in the central part of the distribution. Although increasing baseflow trends are widespread throughout the region, decreasing trends are few and limited to Kansas and Nebraska. Further analysis reveals that baseflow changes are being driven by both climate and land use change across the region. Increasing trends in baseflow are linked to increases in precipitation throughout the year and are most prominent during May and June. Changes in agricultural intensity (in terms of harvested corn and soybean acreage) are linked to increasing trends in the central and western Midwest, whereas increasing temperatures may lead to decreasing baseflow trends in spring and summer in northern Wisconsin, Kansas, and Nebraska.  相似文献   

Traces of volcanic ash from the Mediterranean,Iceland and North America in a Holocene record from south Wales,UK     

Gwydion Jones  Siwan M. Davies  Richard A. Staff  Neil J. Loader  Sarah J. Davies  Michael J. C. Walker 《第四纪科学杂志》2020,35(1-2):163-174

A tephra record is presented for a sediment core from Llyn Llech Owain, south Wales, spanning the early- to mid-Holocene. Seven cryptotephra deposits are discovered with three thought to correlate with known eruptions and the remaining four considered to represent previously undocumented events. One deposit is suggested to correlate with the ~6.9 cal ka bp Lairg A tephra from Iceland, whereas more distant sources are proposed as the origin for two of the tephra deposits. A peak of colourless shards in early-Holocene sediments is thought to tentatively correlate with the ~9.6 cal ka bp Fondi di Baia tephra (Campi Flegrei) and a second cryptotephra is tentatively correlated with the ~3.6 cal ka bp Aniakchak (CFE) II tephra (Alaska). The Fondi di Baia tephra has never been recorded beyond proximal sites and its discovery in south Wales significantly extends the geographical distribution of ash from this eruption. The remaining four cryptotephra deposits are yet to be correlated with known eruptions, demonstrating that our current understanding of widespread tephra deposits is incomplete. This new tephra record highlights the potential for sites at more southerly and westerly locations in northwest Europe to act as repositories for ash from several volcanic regions.  相似文献   

Fluid flow and pore pressure development throughout the evolution of a trough mouth fan,western Barents Sea     

Jaume Llopart  Roger Urgeles  Carl Fredrik Forsberg  Angelo Camerlenghi  Maarten Vanneste  Michele Rebesco  Renata Giulia Lucchi  Denise Christina Rüther  Hendrik Lantzsch 《Basin Research》2019,31(3):487-513

Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure.  相似文献   

Refining the ice flow chronology and subglacial dynamics across the migrating Labrador Divide of the Laurentide Ice Sheet with age constraints on deglaciation     

Jessey M. Rice  Martin Ross  Roger C. Paulen  Samuel E. Kelley  Jason P. Briner  Christina M. Neudorf  Olav B. Lian 《第四纪科学杂志》2019,34(7):519-535

The Laurentide Ice Sheet was characterized by a dynamic polythermal base. However, important data and knowledge gaps have led to contrasting reconstructions in areas such as the Labrador Ice Divide. In this study, detailed fieldwork was conducted at the southeastern edge of a major landform boundary to resolve the relative ice flow chronology and constrain the evolution of the subglacial dynamics, including the migration and collapse of the Labrador Ice Divide. Surficial mapping and analysis of 94 outcrop‐scale ice flow indicators were used to develop a relative ice flow chronology. ¹⁰Be exposure ages were used with optical ages to confine the timing of deglaciation within the study area. Four phases of ice flow were identified. Flow 1 was a northeasterly ice flow preserved under non‐erosive subglacial conditions associated with the development of an ice divide. Flow 2 was a northwest ice flow, which we correlate to the Ungava Bay Ice Stream and led to a westward migration of the ice divide, preserving Flow 2 features and resulting in Flow 3's eastward‐trending indicators. Flow 4 is limited to sparse fine striations within and around the regional uplands. The new optical ages and ¹⁰Be exposure ages add to the regional geochronology dataset, which further constrains the timing of ice margin retreat in the area to around 8.0 ka. Copyright © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.  相似文献   

The Upper Oligocene of Antigua: the volcanic to limestone transition in a limestone Caribbee     

Stephen K. Donovan  Trevor A. Jackson  David A.T. Harper  Roger W. Portell  Willem Renema 《Geology Today》2014,30(4):151-158

Antigua is a small island at the northern end of the Lesser Antilles chain. Its geology is largely limited to the Upper Oligocene and it records with unusual fidelity the transition from island arc volcanism to quiescence and limestone deposition. Despite the apparent limitation of a rock record confined to a short stratigraphical interval, Antigua has a geodiversity that ranges from thick andesites through silicified logs and freshwater snails in cherts to limestones that include both shallow and deeper water facies, and fine karstic features.  相似文献   

Exsolution and shock microstructures of igneous pyroxene clasts in the Northwest Africa 7533 Martian meteorite          下载免费PDF全文

Hugues Leroux  Damien Jacob  Maya Marinova  Roger H. Hewins  Brigitte Zanda  Sylvain Pont  Jean‐Pierre Lorand  Munir Humayun 《Meteoritics & planetary science》2016,51(5):932-945

Northwest Africa (NWA) 7533 is a Martian regolith breccia. This meteorite (and its pairings) offers a good opportunity to study (near‐) surface processes that occurred on early Mars. Here, we have conducted a transmission electron microscope study of medium‐ and coarse‐grained (a few tens to hundreds of micrometers) Ca‐rich pyroxene clasts in order to define their thermal and shock histories. The pyroxene grains have a high‐temperature (magmatic) origin as revealed by the well‐developed pigeonite–augite exsolution microstructure. Exsolution lamella characteristics (composition, thickness, and spacing) indicate a moderately slow cooling. Some of the pyroxene clasts display evidence for local decomposition into magnetite and silica at the submicron scale. This phase decomposition may have occurred at high temperature and occurred at high oxygen fugacity at least 2–3 log units above the QFM buffer, after the formation of the exsolution lamellae. This corresponds to oxidizing conditions well above typical Martian magmatic conditions. These oxidizing conditions seem to have prevailed early and throughout most of the history of NWA 7533. The shock microstructure consists of (100) mechanical twins which have accommodated plastic deformation. Other pyroxene shock indicators are absent. Compared with SNC meteorites that all suffered significant shock metamorphism, NWA 7533 appears only mildly shocked. The twin microstructure is similar from one clast to another, suggesting that the impact which generated the (100) twins involved the compacted breccia and that the pyroxene clasts were unshocked when they were incorporated into the NWA 7533 breccia.  相似文献