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1.
Wetland hydroperiod classification in the western prairies using multitemporal synthetic aperture radar 下载免费PDF全文
Joshua S. Montgomery Chris Hopkinson Brian Brisco Shane Patterson Stewart B. Rood 《水文研究》2018,32(10):1476-1490
Wetlands represent one of the world's most biodiverse and threatened ecosystem types and were diminished globally by about two‐thirds in the 20th century. There is continuing decline in wetland quantity and function due to infilling and other human activities. In addition, with climate change, warmer temperatures and changes in precipitation and evapotranspiration are reducing wetland surface and groundwater supplies, further altering wetland hydrology and vegetation. There is a need to automate inventory and monitoring of wetlands, and as a study system, we investigated the Shepard Slough wetlands complex, which includes numerous wetlands in urban, suburban, and agricultural zones in the prairie pothole region of southern Alberta, Canada. Here, wetlands are generally confined to depressions in the undulating terrain, challenging wetlands inventory and monitoring. This study applied threshold and frequency analysis routines for high‐resolution, single‐polarization (HH) RADARSAT‐2, synthetic aperture radar mapping. This enabled a growing season surface water extent hyroperiod‐based wetland classification, which can support water and wetland resource monitoring. This 3‐year study demonstrated synthetic aperture radar‐derived multitemporal open‐water masks provided an effective index of wetland permanence class, with overall accuracies of 89% to 95% compared with optical validation data, and RMSE between 0.2 and 0.7 m between model and field validation data. This allowed for characterizing the distribution and dynamics of 4 marsh wetlands hydroperiod classes, temporary, seasonal, semipermanent, and permanent, and mapping of the sequential vegetation bands that included emergent, obligate wetland, facultative wetland, and upland plant communities. Hydroperiod variation and surface water extent were found to be influenced by short‐term rainfall events in both wet and dry years. Seasonal hydroperiods in wetlands were particularly variable if there was a decrease in the temporary or semipermanent hydroperiod classes. In years with extreme rain events, the temporary wetlands especially increased relative to longer lasting wetlands (84% in 2015 with significant rainfall events, compared with 42% otherwise). 相似文献
2.
生态水文学是20世纪90年代兴起的一门研究生态过程和生态格局水文机制的新学科。湖泊湿地作为中国5大类天然湿地类型之一,湖泊湿地生态水文学的研究业已成为生态水文学的研究的一个重要对象和分支,其核心在于研究湖泊湿地生态系统中多时空尺度的水文与生物格局、过程的耦合特征及其相互作用。论文首先概述了湖泊湿地生态水文学的研究进展,包括其基本理论,内涵、外延及其主要研究内容;凝练了湖泊湿地生态水文学研究的方法体系、思路及框架;针对目前湖泊湿地生态水文学研究中存在的问题及薄弱环节,提出了湖泊湿地生态水文学未来研究的发展趋势和亟需加强研究的重点方向。在此基础上,以长江中游的典型通江湖泊湿地——鄱阳湖湿地为例,通过开展的湖泊湿地生态水文过程与模拟研究的典型案例,阐述了鄱阳湖湖泊湿地生态水文过程的变化及其植被响应研究的最新进展和研究成果。论文对于构建涵盖湖泊湿地水资源、湖泊湿地生态景观格局与流域管理、湖泊湿地生物多样性保育以及湿地资源可持续利用与生态管理等方向在内的战略研究体系,完善湿地生态水文研究与流域生态与管理的技术支撑体系具有重要的指导意义和实践价值。 相似文献
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《Sedimentology》2018,65(6):2055-2087
This study, conducted in the Catalan Coastal Ranges, north‐east Spain, describes the Upper Devonian Kellwasser event in a shallowing‐upward sequence of black shales, siltstones and quartz arenites. This sequence was deposited in a progradational and regressive coastal system where the sedimentary environment evolved from the inner shelf to a lagoonal pond located landward of the shoreline. Three anomalous succeeding steps have been identified by geochemical analysis. The first one, detected on the inner shelf, was characterized by oxygen depletion and high organic productivity. The second, detected in the nearshore, was caused by hydrothermal activity occurring under normal oxic conditions. The third and most intense step was identified in the muds of the lagoonal pond and has been linked to strong anoxic conditions, elevated clastic input derived from changes in the weathering regime at the source area and moderate hydrothermal activity. The Kellwasser event is thus defined in the study area as stepwise and multi‐causal. This is the first time that the Kellwasser event has been identified in a sedimentary environment behind the shoreline. It is also the first time that it has been reported in the Catalan Coastal Ranges. 相似文献
6.
Robert R. Twilley 《Estuarine, Coastal and Shelf Science》1985,20(5):543-557
The magnitude and seasonality of organic carbon exchange was estimated for two basin mangrove forests in Rookery Bay, Florida. Runoff and tidal inundation in the forests were seasonal with half the annual total of each occurring from August to October. In each forest there were 152 tides yr?1 with a cumulative depth of about 12 m. Total organic carbon increased in bay waters exporting from the mangroves following a flood tide and peak concentrations were associated with export due to rainfall. The amount of net export from each basin forest was similar, although the concentration of organic carbon in each were different. Monthly net organic carbon export was proportional to the cumulative tidal amplitude within the forest. Total organic carbon export was 64 gC m?2 yr?1 and DOC was 75% of the total. A comparison of organic carbon export among riverine, fringe and basin mangroves suggests that tidal hydrology influences the proportion of litter fall that is exported from mangroves; and the magnitude of this organic carbon export from mangroves is related to the cumulative tidal amplitude within the forests. 相似文献
7.
Verónica Oliveros Gilbert Féraud Luis Aguirre Luis Ramírez Michel Fornari Carlos Palacios Miguel Parada 《Mineralium Deposita》2008,43(3):281-293
The 40Ar/39Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district
in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic
Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed
mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting
a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit.
Because of the superposition of several magmatic and hydrothermal events, the obtained 40Ar/39Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories
of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate
volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting
the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal
stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma.
Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is
the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in
the metallogenic belt of the Coastal Cordillera of northern Chile.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications
Kusala Rajendran C.P. Rajendran Anil Earnest G.V. Ravi Prasad K. Dutta D.K. Ray R. Anu 《Tectonophysics》2008,455(1-4):53-60
The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr− 1 in the Little Andaman to 2.80 mm yr− 1 in South Andaman and 2.45 mm yr− 1 in the North Andaman. Our radiocarbon dates converge on 600 yr and 1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region. 相似文献
9.
The shallow water wave simulation model-SWAN incorporated with a simple fine sediment erosion model is applied to Hangzhou
Bay, China, to model the horizontal distribution of the maximum bottom orbital velocity and corresponding fine sediment erosion
rates induced by: (1) southeasterly steady winds (5, 20 and 30 m/s), (2) southwesterly steady winds (5 and 20 m/s); (3) northwesterly
steady winds (5 and 20 m/s); (4) east-southeasterly steady winds (5 and 20 m/s); (5) easterly steady winds (5 and 20 m/s)
under closed and unclosed boundaries; and (6) unsteady winds during the slack water periods. Results suggest: (1) the steady
wind wave-induced maximum bottom orbital velocities and corresponding fine sediment erosion rates generally increased with
the increasing steady winds; (2) closed and unclosed boundary conditions had more significant influences on modeled fine sediment
erosion rates under 5 m/s easterly steady winds than 20 m/s; and (3) steady and unsteady wind wave-induced maximum bottom
currents could be significant in eroding fine sediment bed in Hangzhou Bay. The results show implications for geomorphology,
sedimentology, coastal erosion, and environmental pollution mitigation in Hangzhou Bay. 相似文献
10.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献