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101.
M. C. Ramos 《Theoretical and Applied Climatology》2001,69(3-4):163-170
Summary
In dry farming areas, where rainfall is the only source of water for crops, changes in both quantity and distribution of rainfall
during the year could affect the economy of an area. Inter-annual variability makes it difficult to assess rainfall variability,
especially in areas with Mediterranean climate. In this paper, interannual rainfall variations in the Alt Penedès region were
evaluated using 24-h rainfall records at Vilafranca del Penedès (1889–1999) and at Sant Sadurni d’Anoia (1960–1999). The distribution
patterns during the year and their changes over the time were also analysed. Rainfall data were normalised and the values
corresponding to the percentiles 0.1, 0.25, 0.5, 0.75 and 0.9 were calculated to analyse whether they were very dry, dry,
normal, wet and very wet periods. Annual rainfall and the rainfall recorded during the main rainfall periods during the year
and its trend were analysed. Annual rainfall did not show a clear tendency, although during the last decade reduced interannual
variability occurred. The percentage of dry years did not increase but the percentage of wet and very wet years decreased.
During the last decade, an increase of dry spring seasons andwet autumn seasons was observed, even in normal or wetyears.
These changes could affect the timing of whencrops receive water and could therefore affect their yields.
Received May 31, 2000/Revised February 26, 2001 相似文献
102.
Channel avulsion occurred on the Thomson River in Victoria, Australia, in 1952 along a 12 km length of the valley. A comparison of the old and new channels reveals considerable differences in channel characteristics. The old channel was perched above the floodplain on an alluvial ridge such that when bankfull capacity was exceeded, floodwaters concentrated on the lowest part of the floodplain some distance away. This is where the new channel formed. It is an incised channel with larger capacity and longer meander wavelength than the old channel and is also shorter and steeper. The new channel is subject to larger floodflows and a more variable flood regime than the old course because of the differences in the channel/floodplain relationship and channel capacity. The resulting concentration of stream power along the new course is responsible for the contrast in channel characteristics and for the more rapid meander migration. This example shows that river metamorphosis can occur without major environmental changes. Measures of channel geometry such as gradient, sinuosity, and meander wavelength therefore cannot be used in palaeohydrological work to infer climatic or other environmental changes without independent supporting evidence. Differences in channel geometry can arise simply from changes in the relationship between the channel and its loodplain. 相似文献
103.
104.
Balanced Sediment Fluxes in Southern California’s Mediterranean-Climate Zone Salt Marshes 总被引:1,自引:0,他引:1
Jordan A. Rosencranz Neil K. Ganju Richard F. Ambrose Sandra M. Brosnahan Patrick J. Dickhudt Glenn R. Guntenspergen Glen M. MacDonald John Y. Takekawa Karen M. Thorne 《Estuaries and Coasts》2016,39(4):1035-1049
Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Niño storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km2 salt marsh (Seal Beach) and a less modified 1-km2 marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits. 相似文献
105.
106.
Alicia Daniela Robles Paula Polizzi María Belén Romero Leila Natalia Chiodi Boudet Sandra Medici Agustín Costas Marcela Gerpe 《Environmental Earth Sciences》2016,75(23):1479
The presence of arsenic (As) in surface water constitutes an important environmental risk, where mobility and adsorption processes are responsible for its behavior in the sediment–water interface. Therefore, the assessment of adsorption, mobility and water availability of arsenic in freshwater sediments, with agricultural, livestock and urban soil uses was performed. Arsenic concentrations in sediments ranged from 5.4 to 15.9 mg kg?1 (total) and 2.8 to 6.5 mg kg?1 (labile), and those of iron and manganese were 11,563–23,500 and 140.6–662.1 mg kg?1, respectively. The As levels in water were significantly lower than those of sediments. Results would suggest that As co-precipitation and adsorption on Fe oxides are probably the major route of immobilization, determining its low lability. Manganese did not present an outstanding contribution to the retention, and cation-exchange capacity, pH and organic matter of sediments did not show an influence on the mobility of As. 相似文献
107.
Submerged vegetation complexity modifies benthic infauna communities: the hidden role of the belowground system 下载免费PDF全文
Vanessa González‐Ortiz Luis Gonzalo Egea Rocio Jiménez‐Ramos Francisco Moreno‐Marín José Lucas Pérez‐Lloréns Tjeerd Bouma Fernando Brun 《Marine Ecology》2016,37(3):543-552
Marine plants provide a variety of functions with high economic and ecological values in ecosystems. The above‐ (AG) and below‐ground (BG) systems increase the structural complexity of plants, which also enhance faunal abundance and diversity. The ecological role of the AG compartment in structuring inter‐tidal macrobenthic communities has been widely studied; however, this is not the case for the BG compartment. This study addressed the effects of variation in vegetation complexity (in both AG and BG systems) on associated macrobenthic infauna with respect to abundance, species richness, composition, weight and body type. To achieve this aim, a field experiment using artificial vegetation mimics was carried out using replicated treatments with different AG‐BG complexity ratios. We found a significant increase in the density and the number of taxa of macrobenthic infaunal species in plots with vegetation mimics compared with unvegetated areas, regardless of either AG or BG complexity. This effect was found even when AG parts were not present (i.e. when only BG parts were used). Furthermore, a positive relationship between structural complexity and diversity was recorded. Variation in one or both plant compartments was strongly related to diversity changes in the associated macrobenthic infauna. In conclusion, our experimental set‐up provides the first evidence that the BG compartment is at least as important as the AG compartment in controlling diversity in inter‐tidal vegetated areas because it was able to strongly affect community structure even when the AG system was totally absent. 相似文献
108.
109.
Interest in obtaining a more accurate snapshot of irrigation management from a geographical perspective is increasingly relevant. This proposal is based on existing qualitative approaches in combination with an alternative method (the territorial irrigation management model) to identify and present key stakeholders attitudes and perceptions in the Segarra-Garrigues irrigation system in Spain. Advantages are (1) the focus on interrelations and context, (2) the applicability and extrapolation of the irrigation system, and (3) the irrigator-driven rather than researcher-driven perspective. Results revealed that there are conceptual and practical heterogeneities between the preferences of stakeholders' groups regarding water resources management, environmental protection, and agricultural challenges. 相似文献
110.