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21.
22.
E. González-Ortegón M.D. Subida J.A. Cuesta A.M. Arias C. Fernández-Delgado P. Drake 《Estuarine, Coastal and Shelf Science》2010
Estuaries are used as nursery grounds by numerous marine species despite being usually subject to strong anthropogenic disturbances. Abundances of marine recruits (fish and crustacean decapods) and their main prey (mysids) were monitored by monthly sampling, from June 1997 to February 2009, in the lower reaches of the Guadalquivir estuary (SW Spain). During that period, unusually high and persistent turbidity events (HPTEs) were observed twice. Both HPTEs started with strong and sudden freshwater discharges after relatively long periods of very low freshwater inflow. Data from this time-series were used to test the hypothesis that HPTEs may negatively impact the nursery function of estuaries either by decreasing prey availability or by decreasing survival/arrival of marine recruits. During HPTEs, the commonest mysid (Mesopodopsis slabberi), a key species in the estuarine food web, showed a significant decrease in abundance. Likewise, some marine recruits that prey on M. slabberi and whose peaks of abundance within the estuary occur in summer–autumn (Engraulis encrasicolus and Pomadasys incisus) were less abundant during HPTEs. It is also suggested that HPTEs might have triggered a shift in the distribution of the most euryhaline prey (Neomysis integer) and predator (Dicentrarchus punctatus and Crangon crangon) species, towards more saline waters. This could have contributed to an increase in the inter-specific competition (for food/habitat) within the estuarine nursery area. The results discussed in this study call attention to the need to reduce as much as possible the anthropogenic pressures that may stimulate the occurrence of high and persistent turbidity events (HPTEs) in order to preserve the nursery function of temperate estuaries. 相似文献
23.
Ghulam Jeelani Rouf Ahmad Shah Rajendrakumar D. Deshpande Ashok P. Dimri Suraj Mal Anupam Sharma 《水文研究》2021,35(11):e14406
Western disturbances (WDs) and Indian summer monsoon (ISM) led precipitation play a central role in the Himalayan water budget. Estimating their contributions to water resource is although a challenging but essential for hydrologic understanding and effective water resource management. In this study, we used stable water isotope data of precipitation and surface waters to estimate the contribution of ISM and WDs to the water resources in three mountainous river basins - Indus, Bhagirathi and Teesta river basins of western, central and Eastern Himalayas. The study reveals distinct seasonality in isotope characteristics of precipitation and surface waters in each river basin is due to changes in moisture source, hydrometeorology and relief. Despite steady spatial variance in the slope and intercept of regression lines from the Teesta to Indus and the Bhagirathi river basins, the slope and intercept are close to the global meteoric water line and reported local meteoric water line of other regions in the Himalayas and the Tibetan Plateau. The two-component end-member mixing method using d-excess as tracer were used to estimate the contribution from ISM and WD led precipitation to surface water in aforementioned river basins. The results suggest that the influence of the ISM on the water resources is high (>72% to annual river flow) in Teesta river basin (eastern Himalayas), while as the WDs led precipitation is dominantly contributing (>70% average annual river flow) to the surface waters in the Indus river basin (western Himalayas). The contribution of ISM and WD led precipitation in Bhagirathi river basin is 60% and 40%, respectively. The findings demonstrate that the unusual changes in the ISM and WD moisture dynamics have the potential to affect the economy and food security of the region, which is dependent on the availability of water resources. The obtained results are of assistance to policy makers/mangers to make use of the information for better understanding hydrologic response amid unusual behaviour of the dual monsoon system over the region. 相似文献
24.
Abstract Ecohydrology is the science that studies the mutual interaction between the hydrological cycle and ecosystems. Such an interaction is especially intense in water-controlled ecosystems, where water may be a limiting factor, not only because of its scarcity, but also because of its intermittent and unpredictable appearance. Soil moisture is the key variable modulating the complex dynamics of the climate-soil-vegetation system and controlling the spatial and temporal patterns of vegetation. In this note the authors' perspective to the field is discussed and some open questions are outlined. 相似文献
25.
Wen-Yao Xu 《Pure and Applied Geophysics》1989,131(3):371-393
Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence. 相似文献
26.
W. Swider 《Pure and Applied Geophysics》1988,127(2-3):403-414
The most meaningful way to compare observations of the daytimeD-region under all ionization conditions, for the purpose of improving our understanding of this region, would appear to be through use of the effective electron recombination coefficient, =q/[e]2, whereq is the ionization production rate, and where [e] is the electron concentration. This ratio apparently increases monotonically with decreasing altitude, and is much less variable than its componentsq and [e]. This parameter appears eminently suitable as a best first order solution to [e] after determiningq. For nighttime conditions, is more sensitive toq. However, an accurate but simple formula exists for the calculation of electron concentrations. 相似文献
27.
Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73°E longitude) at Bhopal from January
1990 to December 1990 have been used to study the characteristic variations of scintillation activity. It is found that scintillation
occurrence is essentially a night-time phenomenon and day-time scintillations are very rare. Annual average nocturnal variation
of percentage occurrence of scintillations shows maximum at around 2100–2200 hours LT. Seasonally, scintillations are most
prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations
in the pre-midnight period. 相似文献
28.
29.
The paper deals with the application of the telluric method and of magnetotelluric soundings including experimental and model
data on the localization of tectonic disturbances in connection with the selection of appropriate sites for nuclear plants. 相似文献
30.
斜压半地转模式中的非频散周期解 总被引:2,自引:0,他引:2
给出了3个通量矢量,从而将非线性平流项表示为3个通量矢量的旋度和散度,它们分别对纬向风和经向风的低频加速产生贡献。经过卷积运算,还建立了低频变化的动力学模型。给出了通量矢量E.、G1.、G2.等的空间分布及其相应的流函数与势函数的水平分布和时间演变,从而指出,瞬变扰动间的相互作用对流动具有低频加速作用。 相似文献