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31.
Geotectonics - Study of morphometric parameters such as stream length (Lu) and stream length ratios (Rl), bifurcation ratio (Rb), drainage density (D), form factor (Rf), circularity ratio (Rc),... 相似文献
32.
Judit Rubio-Delgado Susanne Schnabel Álvaro Gómez-Gutiérrez Joaquín Francisco Lavado-Contador 《地球表面变化过程与地形》2019,44(11):2141-2155
Changes in land use are common in Mediterranean areas and are reported as having produced changes in the intensity of soil erosion. Dehesas are rangelands with a disperse tree cover, widespread in the south-western part of the Iberian Peninsula and similar ecosystems are also common in other areas with a Mediterranean climate. The aim of the present study is to analyse temporal and spatial variations of soil erosion rates estimated along three hillsides, located in two farms (Buitrera and Parapuños) in southwest Spain. To understand the temporal variation, soil erosion rates were studied in light of land use-management changes that took place during the last few centuries. Results indicate very low erosion rates prior to the 18th century in both farms. In Buitrera, a first increase of soil loss rates was identified during the period 1831-1897, amounting to 7.4 t ha-1 y-1. A further increase took place during the 20th century, reaching a mean erosion rate of 29.1 t ha-1 y-1. In Parapuños, data points to a significant increase from 1881 onwards, with an estimated mean erosion rate of 18.5 t ha-1 y-1. Those increases were presumably connected with an intensification of land use, such as cultivation and excessive livestock populations. Regarding spatial variation, the bare surface and the erosive power of run-off along the hillsides accounts for 76% of the soil erosion rates dispersion. At a local scale, the variability of erosion rates could not be explained, because of (i) uncertainty related to the micromorphology of the past soil surface and (ii) the role of tillage erosion in the past. However, the results obtained offer valuable data on the temporal and spatial variation of erosion rates in dehesas at the hillslope scale and a similar approach could be used for other rangelands with a disperse tree cover. © 2019 John Wiley & Sons, Ltd. 相似文献
33.
Water Resources - The size structure of zooplankton in Kolsay Lakes was characterized with the use of the values of Clarke W-statistic, ?-Shannon–Weaver, and the average individual mass... 相似文献
34.
Water Resources - The results of hydrochemical analysis of water in Lake Itkul, which is a natural monument of Chelyabinsk oblast and an important recreation and tourist object for the population... 相似文献
35.
Miquel Poyatos‐Mor George D. Jones Rufus L. Brunt Daniel E. Tek David M. Hodgson Stephen S. Flint 《Basin Research》2019,31(5):920-947
Exhumed basin margin‐scale clinothems provide important archives for understanding process interactions and reconstructing the physiography of sedimentary basins. However, studies of coeval shelf through slope to basin‐floor deposits are rarely documented, mainly due to outcrop or subsurface dataset limitations. Unit G from the Laingsburg depocentre (Karoo Basin, South Africa) is a rare example of a complete basin margin scale clinothem (>60 km long, 200 m‐high), with >10 km of depositional strike control, which allows a quasi‐3D study of a preserved shelf‐slope‐basin floor transition over a ca. 1,200 km2 area. Sand‐prone, wave‐influenced topset deposits close to the shelf‐edge rollover zone can be physically mapped down dip for ca. 10 km as they thicken and transition into heterolithic foreset/slope deposits. These deposits progressively fine and thin over tens of km farther down dip into sand‐starved bottomset/basin‐floor deposits. Only a few km along strike, the coeval foreset/slope deposits are bypass‐dominated with incisional features interpreted as minor slope conduits/gullies. The margin here is steeper, more channelized and records a stepped profile with evidence of sand‐filled intraslope topography, a preserved base‐of‐slope transition zone and sand‐rich bottomset/basin‐floor deposits. Unit G is interpreted as part of a composite depositional sequence that records a change in basin margin style from an underlying incised slope with large sand‐rich basin‐floor fans to an overlying accretion‐dominated shelf with limited sand supply to the slope and basin floor. The change in margin style is accompanied with decreased clinoform height/slope and increased shelf width. This is interpreted to reflect a transition in subsidence style from regional sag, driven by dynamic topography/inherited basement configuration, to early foreland basin flexural loading. Results of this study caution against reconstructing basin margin successions from partial datasets without accounting for temporal and spatial physiographic changes, with potential implications on predictive basin evolution models. 相似文献
36.
Birgita D. Hansen Peter G. Dahlhaus Robert G. Milne Andrew D. MacLeod Chris Pitfield 《社会与自然资源》2019,32(6):709-719
Natural Resource Management (NRM) is often conducted as a partnership between government and citizens. In Australia, government agencies formulate policy and fund implementation that may be delivered on-ground by community groups (such as Landcare). Since the late 1980s, over AUS$8b of Commonwealth investment has been made in NRM. However, quantitative evidence of environmental improvements is lacking. The NRM Planning Portal has been developed to (1) provide an online spatial information system for sharing Landcare and agency data; and (2) to facilitate NRM priority setting at local and regional planning scales. While the project successfully federates Landcare NRM activity data, challenges included (1) unstructured, non-standardized data, meaning that quantitative reporting against strategic objectives is not currently possible, and (2) a lack of common understanding about the value proposition for adopting the portal approach. Demonstrating the benefit of technology adoption is a key lesson for digital NRM planning. 相似文献
37.
Water Resources - The study is focused on the step-by-step development of the modern system of legal rules and principles used at the international level to regulate the use of transboundary... 相似文献
38.
Geomagnetism and Aeronomy - It is possible that the radially independent, spatial-spectral components of the energy and power of the potential part of the main geomagnetic field were determined and... 相似文献
39.
Geomagnetism and Aeronomy - The data from observation of the geomagnetic field variations at the Midlatitude Mikhnevo Geophysical Observatory of Institute of Geosphere Dynamics of the Russian... 相似文献
40.
Vasil’ev G. I. Konstantinov A. N. Kudryavtsev I. V. Ogurtsov M. G. Ostryakov V. M. Pavlov A. K. Frolov D. A. 《Geomagnetism and Aeronomy》2019,59(8):1075-1080
Geomagnetism and Aeronomy - The causes of a sharp increase in the radiocarbon content in the Earth’s atmosphere for periods with abnormally low solar modulation of galactic cosmic rays (GCRs)... 相似文献