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   

A 2000-YEAR CONTEXT FOR MODERN CLIMATE CHANGE     

K.A. MAASCH  P.A. MAYEWSKI  E.J. ROHLING  J.C. STAGER  W. KARLEN  L.D. MEEKER  E.A. MEYERSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):7-15

ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric ¹⁴C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale.  相似文献   

Southern Hemisphere Early Cretaceous (Valanginian-Early Barremian) carbon and oxygen isotope curves from the Neuquén Basin,Argentina     

《Cretaceous Research》2008,29(1):87-99

The first carbon and oxygen isotope curves for the Valanginian to Early Barremian (Early Cretaceous) interval obtained from outcrops in the Southern Hemisphere are presented. They were obtained from well-dated (by ammonites) sediments from the Neuquén Basin, Argentina. Measurements were acquired by the innovative method of analysing fossil oyster laminae. The occurrence of the well-established mid-Valanginian positive carbon isotope excursion is documented, while less well-marked positive events may also correlate with peaks identified in the well-known successions of SE France. The mid-Valanginian positive carbon isotope event in the Neuquén Basin is possibly associated with organic-rich sediments. A similar relationship is seen in the European Alps and in oceanic cores in some areas of the world.  相似文献   

A submarine canyon conduit under typhoon conditions off Southern Taiwan     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):223-240

The function of a submarine conduit under typhoon conditions is examined. The study site is the Kao-ping river, shelf, and submarine canyon (KPRSC) system located off southern Taiwan on a wave-dominated microtidal coast. The head of the canyon is located approximately 1 km off the river mouth. Two comprehensive 1-month field experiments were carried out in 2000 and 2002 during the flood season of the river. Both experiments encountered typhoons that generated significant river discharge and wave resuspension events. Particle samples collected in 2000 by sediment-traps were analyzed for coarse fraction by the wet sieving method. Among the coarse fraction, foraminiferal species and their abundance were recorded as a tracer for biogenic particles of marine origin. Stable isotopes of carbon (δ¹³C) of organic particles of sediment-trap samples were analyzed as a tracer for particles of terrestrial origin. All the measured flow and particle concentration records were analyzed by conventional time-series analytical methods. Simultaneously observed records of suspended sediment concentration at the river mouth and the volume concentration of suspended particles near the canyon floor were compared. Instantaneous flux and cumulative transport of suspended particles near the canyon floor were estimated during the deployment period. Results show that Kao-ping Submarine Canyon is a multi-level and process-dependant two-way conduit for particles of terrestrial and marine origins. In general, terrestrial signals are stronger than the marine signals in sediment-trap samples near the head of the canyon. During typhoon events, in the early distal phase of their influence nonlithogenic and biogenic marine sources are enhanced; in the later proximal phase signals of locally generated terrestrial lithogenic sources are enhanced. An episode of momentary downcanyon flushing of suspended particles near the canyon floor is observed during one typhoon occurrence. This flushing suggests nondeposition during the typhoon at the locale of deployment despite increased input of particles to the canyon floor. It also suggests a mechanism by which turbidity currents could be triggered. Yet, this flushing phenomenon is not observed in another typhoon occurrence, suggesting it is not universal in the canyon's response to the typhoon.  相似文献   

潮汐对瞬态气候响应模拟的影响研究     

于溢  刘海龙  林鹏飞  兰健 《海洋学报(英文版)》2020,39(1):52-62

In this study, the impact of oceanic processes on the sensitivity of transient climate change is investigated using two sets of coupled experiments with and without tidal forcing, which are termed Exp_Tide and Exp_Control,respectively. After introducing tidal forcing, the transient climate response(TCR) decreases from 2.32 K to 1.90 K,and the surface air temperature warming at high latitudes decreases by 29%. Large ocean heat uptake efficiency and heat storage can explain the low TCR in Exp_Tide. Approximately 21% more heat is stored in the ocean in Exp_Tide(1.10×10~(24) J) than in Exp_Control(0.91×10~(24) J). Most of the large ocean warming occurs in the upper 1 000 m between 60°S and 60°N, primarily in the Atlantic and Southern Oceans. This ocean warming is closely related to the Atlantic Meridional Overturning Circulation(AMOC). The initial transport at mid-and high latitudes and the decline in the AMOC observed in Exp_Tide are both larger than those observed in Exp_Control. The spatial structures of AMOC are also different with and without tidal forcing in present experiments. The AMOC in Exp_Tide has a large northward extension. We also investigated the relationship between AMOC and TCR suggested by previous studies using the present experiments.  相似文献   

Nitrogen isotopic composition of sinking particles from the southern Bay of Bengal: Evidence for variable nitrogen sources     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(10):1658-1676

An 8-year record of N fluxes and δ¹⁵N of sinking particles from the deep southern Bay of Bengal, northern Indian Ocean, is presented. Fluxes and δ¹⁵N vary between ∼0.1 and 3 mg m⁻² day⁻¹ and ∼2‰ and 8‰, respectively. The seasonal variation is determined mainly by oceanographic processes coupled to the Indian monsoon system. The annual pattern of δ¹⁵N is characterized by minima during spring intermonsoon (∼March–May), when nutrient inputs to the euphotic zone should be low because of stratification, and lighter nitrate/particulate matter is expected to be advected from the central Bay. Highest δ¹⁵N are associated with peak fluxes during southwest monsoon (∼June–September), when the southern Bay comes under the influence of the SW monsoon current, which appears to advect particulate matter with distinctly higher δ¹⁵N. The impact of this process, however, varies interannually under the influence of factors such as ENSO and the Indian Dipole Mode. Weakened advection leads to relatively low N fluxes and reduced δ¹⁵N. The data highlight the necessity of multi-annual studies to comprehend the natural variability of a system.  相似文献   

Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence     

《Applied Geochemistry》2006,21(5):813-819

An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.  相似文献   

Behaviour of boron and strontium isotopes in groundwater–aquifer interactions in the Cornia Plain (Tuscany,Italy)     

《Applied Geochemistry》2006,21(7):1169-1183

The Cornia Plain alluvial aquifer, in Tuscany, is exploited intensely to meet the demand for domestic, irrigation and industrial water supplies. The B concentration of groundwater, however, is often above the European limit of 1 mg L⁻¹, with the result that exploitation of these water resources requires careful management. Boron and Sr isotopes have been used as part of a study on the origin and distribution of B dissolved in groundwater, and indirectly as a contribution to the development of appropriate water management strategies.The geochemistry of the Cornia Plain groundwater changes from a HCO₃ facies in the inland areas to a Cl facies along the coastal belt, where seawater intrusion takes place. The B concentration of groundwater increases towards the coastal areas, while the ¹¹B/¹⁰B ratio decreases. This indicates that there is an increasing interaction between dissolved B and the sediments forming the aquifer matrix, whose B content is in the order of 100 mg kg⁻¹. Adsorption–desorption exchanges take place between water and the sediment fine fraction rich in clay minerals, with a net release of B from the matrix into the groundwater, and a consequent δ¹¹B shift from positive to negative values. The aquifer matrix sediments therefore seem to be the major source of B dissolved in the groundwater.The groundwater–matrix interactions triggered by the ionic strength increase caused by seawater intrusion can also be detected in the Ca–Na ion exchanges. Dissolved Sr follows a trend similar to that of Ca, while the ⁸⁷Sr/⁸⁶Sr ratio is equal to that of the exchangeable Sr of the aquifer matrix and therefore does not change significantly.These results have helped to define a new strategy for groundwater exploitation, with the final objective of reducing B concentration in the water extracted from the aquifer.  相似文献   

The taphonomy of mammoth localities in southeastern Wisconsin (USA)     

《Quaternary International》2006

Four southeastern Wisconsin mammoth localities located within a glacial landscape had well-preserved remains found in inter-morainal depressions filled with lacustrine clays covered with peat. Numerous radiocarbon ages dated the mammoths to the late Pleistocene. The taphonomic analysis focused on determining the agency or agencies involved in site formation and the agency or agencies involved in modification to the bones. Statistical approaches to bone orientation data underscored that water transport was not a factor in the formation of the bone beds nor was water movement a disturbance factor. The bone modification profile of the overall assemblage was dominated by chemical weathering, followed by other chemical and microbiological processes. Root etching was the most common biological modification, and the most frequent modifications are involved with the microenvironments of the surface to burial substrate. Potentially cultural modification accounted for only a small portion of the cortical damage to the bones. This general profile indicated an assemblage far more influenced by the immediate environment than by passing animals or people.  相似文献   

Climate change impacts on U.S. Coastal and Marine Ecosystems   总被引：1，自引：0，他引：1  

Donald Scavia  John C. Field  Donald F. Boesch  Robert W. Buddemeier  Virginia Burkett  Daniel R. Cayan  Michael Fogarty  Mark A. Harwell  Robert W. Howarth  Curt Mason  Denise J. Reed  Thomas C. Royer  Asbury H. Sallenger  James G. Titus 《Estuaries and Coasts》2002,25(2):149-164

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO₂. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO₂ levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.  相似文献