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1.
Dye tracing field data were collected in small, steep streams in Ontario and used to calculate longitudinal dispersion coefficients for these headwater streams. A predictive equation for longitudinal dispersion coefficient is developed using combined data sets from five steeper head – water streams and 24 milder and larger rivers. The predictive equation relates the longitudinal dispersion coefficient to hydraulic and geometric parameters of the stream and has been developed using multiple regression analysis. The newly developed equation shows impressive accuracy of predictions for longitudinal dispersion coefficient (R2 = 0.86, RMSE = 25, Nash–Sutcliffe coefficient Ens = 0.86 and Index of Agreement D = 0.96) for both small, steep headwater streams as well as large, mild rivers. The Froude number has been introduced as a third key parameter to capture the effect of slope of the reach – in addition to the aspect ratio and bed material surface roughness – on the longitudinal dispersion coefficient. The pronounced improvement in the accuracy of the prediction is due to the addition of the Froude number to capture the effect of the slope of the reach on longitudinal dispersion coefficient. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
S. Grimaldi 《水文科学杂志》2013,58(6):1035-1051
Abstract A detailed investigation of the behaviour of various hydraulic parameters, using data from rivers in Greece, was conducted in order to explore the universality of features that many natural streams are believed to have in common. Analysis of vertical profiles of temporal mean of horizontal velocities (u) in the longitudinal (river flow) direction and of transverse profiles of depth-mean longitudinal velocities (U) estimated from these vertical profiles, measured at 232 cross-sections of several rivers in Greece, provided valuable information: on the distribution of local roughness coefficients (ni ) along the wetted perimeter of the cross-sections examined; on the shape of u profiles; on the ratio of maximum to mean cross-sectional velocity, Vmax/Vm , and its relation to a dimensionless entropy parameter, M; on the shape of U profiles; and on the normalized intensity, r, of the spatial departure of u velocities from Vm . The similarities among the quantities (u, U, n, Vmax/Vm , M, r) analysed in this study and in pertinent literature reveal that the rivers examined exhibit many of the basic features, of rather universal character, shown by other rivers (all over the world) having different geometric and/or other characteristics (aspect ratios, bottom roughness, flow kinematics, etc.). Corresponding differences are also described and explained. 相似文献
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Previous genetic studies on perch (Perca fluviatilis L.) in northern and southern regions of Europe have shown low heterozygosity. No such investigation has been conducted in the central part of Europe. The genetic variability ofP. fluviatilis in four Swiss lakes (Lake Constance, Lake Zürich, Lake Geneva and Lake Maggiore) was investigated. These four lakes belong to three different drainage systems (Rhine, Rhone and Po) without connections. A total of 136 fish were analysed electrophoretically. Only one locus (SOD
*) was highly polymorphic in Lake Constance among the 27 loci studied. The expected heterozygosities for each population and for the total population were higher than in the previous studies but low (H
S= 0.38–2.7%;H
T=1.22%) and Nei's genetic distances were small (0.000–0.003). However, the jack-knifed mean of the Wright'sF
STwas calculated as 0.142, which indicates modest genetic differentiation among the perch populations in Switzerland, due to the differentiated population in Lake Constance. 相似文献
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喀斯特筑坝河流中生物碳泵效应的碳施肥及对水化学时空变化的影响——以贵州平寨水库及红枫湖为例 总被引：3，自引：0，他引：3
耦联水生光合作用的碳酸盐风化碳汇是全球碳循环的重要组成部分，而生物碳泵效应是稳定碳酸盐风化碳汇的关键机制.河流筑坝后，生物碳泵效应的变化、控制因素及对水化学影响的研究甚少.本研究对2个喀斯特筑坝河流平寨水库和红枫湖进行系统采样，以研究河流筑坝后生物碳泵效应的变化、控制因素及对水化学的影响.研究结果表明，入库河流的水化学变化不明显，而2个水库的水化学则表现出显著的季节变化特征，具体表现为水库的水温和pH均呈现出夏季高、冬季低的变化特征，而电导率（EC）、HCO3-浓度和pCO2则表现出夏季低、冬季高的季节变化特征.以叶绿素a（Chl.a）浓度和溶解氧（DO）饱和度指代的生物碳泵效应则是在夏季最强、冬季最弱.生物碳泵效应利用溶解性无机碳（DIC），形成有机质并释放出氧气，是造成夏季水库pH值和DO饱和度升高，电导率（EC）、HCO3-浓度和pCO2降低的主要因素.空间上，水库的Chl.a浓度及DO饱和度均大于河水，EC、HCO3-浓度和pCO2均小于河水，这表明河流筑坝后，由于水库的“湖泊化”导致水库的生物碳泵效应显著提高.通过对Chl.a与碳、氮和磷浓度及化学计量比的相关性分析发现，平寨水库和红枫湖的生物碳泵效应受到碳施肥的影响.平寨水库和红枫湖水库生物碳泵效应碳施肥机制的发现，表明在喀斯特地区，生物碳泵效应不仅受到氮磷元素的控制，也受到碳元素的控制，因此在富营养化湖泊治理时，也应考虑碳的影响. 相似文献
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We developed an index (MESH – Macroinvertebrates in Estonia: Score of Hydromorphology) to assess hydromorphological quality of Estonian surface waters based on macroinvertebrate taxonomic composition. The MESH is an average score based on the affinities of selected indicator taxa to flow velocity and bottom type. As both parameters were highly correlated (r = 0.65) indicator response to both parameters were combined. The list of MESH indicators includes 394 freshwater macroinvertebrate taxa derived from 3282 samples collected from rivers and lakes during 1985–2009. The indicators were selected out of 690 taxa, by applying the information-theoretical Kullback–Leibler divergence. The individual scores of macroinvertebrates range from 0 to 3, the higher scores indicating faster flow and/or solid bottom substrate. For standing waters, flow velocity was always considered zero. Among the reference waterbodies, mean MESH was the highest for small streams followed by middle streams, large streams, and lakes. In lakes with medium water hardness (the prevailing type in Estonia), the MESH decreased gradually from stony to muddy bottom. The highest MESH values for standing waters were observed in the stony surf zone of very large lakes (area > 100 km2). The lowest values occurred for small lakes with exceptional hydrochemical characteristics (soft- and darkwater, and calcareous types). Similarly, MESH indicated stream degradation by damming. Mean MESH in reservoirs with a muddy bottom was significantly lower than in reservoirs with a hard bottom, or in unregulated stream sections. 相似文献
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采用特异性引物对中华刺鳅基因组DNA进行扩增和测序,获得了江苏省5个湖泊的中华刺鳅种群线粒体cyt b基因767 bp的序列.分析表明,cyt b基因中A+T含量略高于G+C含量,144个中华刺鳅共获得cyt b基因单倍型28个,变异位点38个,其中单倍型Hap1分布最为广泛,可能为祖先型单倍型.平均单倍型多样性和平均核苷酸多样性指数分别为0.58751和0.00214,遗传多样性较低.群体间遗传分化系数为0.0356,绝大多数的遗传变异都来自群体内部,而群体间的遗传分化极小.构建的系统进化树未出现明显的以单个湖泊群体的聚簇,5个湖泊的种群间基因交流极其强烈.研究结果表明,当前5个湖泊的中华刺鳅遗传多样性水平比较低,亟待加强保护. 相似文献
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Abstract Discharge in most rivers consists mainly of baseflow exfiltrating from shallow groundwater reservoirs, while surface or other direct flows cease soon after rain storms or snowmelt. Analysis of observed baseflow recessions of two rivers in Turkey with intermittent flows and different geographical and climatic characteristics yielded nonlinear storage–outflow relationships of the highly seasonal aquifers. Baseflow separation was carried out using a nonlinear reservoir algorithm. Baseflow seasonality is related to the hydro-climatic conditions influencing groundwater recharge and evapotranspiration of groundwater. As intermittent streams generally have zero flows in the dry season, calibration of recession parameters is in many cases a complicated task. Citation Aksoy, H. & Wittenberg, H. (2011) Nonlinear baseflow recession analysis in watersheds with intermittent streamflow. Hydrol. Sci. J. 56(2), 226–237. 相似文献
13.
Dividing rivers into homogeneous reaches is key for river processes and watershed management. In contrast to downstream fluvially dominated rivers, upstream debris-flow dominated torrents have steeper channel slopes and smaller valley width/depth ratios. Investigating transition reaches between torrents and fluvially dominated rivers, not only explores the structure of the landscape, but also contributes to hazard management. This study proposed a valley morphology index combining two variables, channel slope and valley width/depth ratio, to determine transition reaches between torrents and rivers. The methodology was applied to 41 mountain streams in Taiwan using a Geographic Information System (GIS)-based topographic analysis. Plots of valley width/depth ratio versus channel slope were used to determine boundary values of the valley morphology index (Iv) separating torrents from rivers. The plots showed that about 80% of the river basins present “L-shaped” curves, which indicate sharp decreases in slope for upstream sections and dramatic increases of valley width/depth ratio for downstream sections. Results further demonstrated an average value of Iv 0.0047 across the study sites. Spatial comparison between geographic regions indicated that transition reaches in eastern rivers tend to occur lower in the drainage basin due, in part, to higher terrain. Local factors, such as tributary confluences and landslides promote the transition from torrents to fluvially dominated rivers. Satellite images verified that the approach correctly identified transition reaches, suggesting that it may provide a useful reference for river management. 相似文献
14.
Abiotic effects of UV on planktonic P kinetics 总被引：1，自引：0，他引：1
Jeff M. Sereda Jeff J. Hudson William D. Taylor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):127-134
15.
Victor U. Chukwuma 《Acta Geophysica》2007,55(4):469-489
A study of the geomagnetic storm of July 13–14, 1982, and its ionospheric response is presented using the low-latitude magnetic
index, Dst, and interpreted using solar wind interplanetary data: proton number density, solar wind flow speed, interplanetary magnetic
field southward component B
Z
, and solar wind dynamic pressure. The F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storm from a network of various ionosonde stations. Our results appear to show simultaneous abrupt
depletion of foF2 that occurred at all latitudes in both the East Asian and African/European longitudinal zone during the period: 18:00–19:00
UT on July 13 and is as result of an abrupt increase in the dynamic pressure between 16:00 and 17:00 UT. The dynamic pressure
increased from 3.21 to 28.07 nPa within an hour. The aforementioned abrupt depletion of foF2 simultaneously resulted in an intense negative storm with peak depletion of foF2 at about 19:00 at all the stations in the East Asian longitudinal zone. In the African/European longitudinal zone, this simultaneous
abrupt depletion of foF2 resulted in intense negative storm that occurred simultaneously at the low latitude stations with peak depletion at about
20:00 UT on July 13, while the resulting negative storm at the mid latitude stations recorded peak depletion of foF2 simultaneously at about 2:00 UT on July 14. The present results indicate that most of the stations in the three longitudinal
zones showed some level of simultaneity in the depletion of foF2 between 18:00 UT on July 13 and 2:00 UT on July 14. The depletion of foF2 during the main phase of the storm was especially strongly dependent on the solar wind dynamic pressure. 相似文献
16.
In many streams, microbial growth largely relies on terrigenous organic carbon that has been initially stored in soils and
that is generally believed to be recalcitrant to microbial metabolism. The various mechanisms that underlie the availability
of terrigenous organic carbon as it enters streams remain poorly understood. One possible mechanism can be photodegradation
of terrigenous dissolved organic carbon (DOC) upon exposure to sunlight in streamwater. To explore this, we experimentally
exposed streamwater, shallow groundwater and soil water from a clear-water Alpine headwater stream, and both soil and algal
extracts, to UV-radiation and studied the effects on DOC optical properties and implications for microbial growth. Our results
on the apparent quantum yield suggest that DOC from groundwater and soil water is more resistant to photodegradation than
DOC in the streamwater itself. This would highlight the relevance of the exposure history of DOC to sunlight. Overall, UV-radiation
decreased the aromaticity (as SUVA254) of the DOC and reduced its molecular weight as indicated by the slope ratio, S
R (S
275–295/S
350–400). UV-treatment significantly increased bacterial growth rate and bacterial growth efficiency in the streamwater, soil water,
groundwater and soil extract but not in algal extract. Our findings suggest photodegradation as one mechanism that contributes
to the microbial utilisation of terrigenous DOC even in clear-water streams. 相似文献
17.
James E. Pizzuto 《地球表面变化过程与地形》1984,9(3):199-207
Cross-sections of 16 straight sandbed streams in Minnesota, Iowa, and Nebraska were surveyed. Two stratigraphic horizons were found in the banks at each site, an upper cohesive unit usually composed of silt and clay and a lower unit composed of sand. Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by beam or cantilever failure. As upper bank failure is a direct result of undercutting, the stability and rate of retreat of the bank are largely determined by erosion of the sandy part of the bank. The cohesive layer has little influence on bank retreat and width adjustment on the rivers studied here. A quantitative lateral sediment transport model developed by Parker (1978a) is used to calculate the steady-state geometry of the sandy part of the bank. Results are obtained for the shape, length, and height of the sandy part of the bank. The model predicts the length of the bank fairly well, and the theoretical equation for the height of the bank is of the correct form. The model, however, overestimates the slope of the bank. The height of the sandy part of the bank (Db) is approximately equal to the depth of the mean annual flow. Since Db is determined by the lateral sediment transport model, the width (W) may be obtained from the equation of continuity (Q = WDbV), published flow (Q) data, and a resistance equation for the mean velocity, V. The calculated widths are similar to those measured in the field. 相似文献
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The magnitude (M
w) 7.9 Wenchuan earthquake occurred on 12 May 2008 in the Longmen Shan region of China, the transition zone between the Tibetan
Plateau and the Sichuan Basin, resulting in widespread damage throughout central and western China. The steep, high-relief
eastern margin of the Tibetan Plateau has undergone rapid Cenozoic uplift and denudation accompanied by folding and thrusting,
yet no large thrust earthquakes are known prior to the 2008 M
w 7.9 Wenchuan earthquake. Field and excavation investigations reveal that a great historical earthquake occurred in the Sichuan
region that ruptured a >200-km-long thrust fault within the Longmen Shan Thrust Belt, China, which also triggered the 2008
M
w 7.9 Wenchuan earthquake. The average co-seismic slip amount produced by this historical earthquake is estimated to be 2–3 m,
comparable with that caused by the 2008 Wenchuan earthquake. Paleoseismic and archaeological evidence and radiocarbon dating
results show that the penultimate great earthquake occurred in the Sichuan region during the late Tang-Song Dynasty, between
AD 800 and 1000, suggesting a recurrence interval of ~1,000–1,200 years for Wenchuan-magnitude (M = ~8) earthquakes in the late Holocene within the Longmen Shan Thrust Belt. This finding is in contrast with previous estimates
of 2,000–10,000 years for the recurrence interval of large earthquakes within the Longmen Shan Thrust Belt, as obtained from
long-term slip rates based on the Global Positioning System and geological data, thereby necessitating substantial modifications
to existing seismic-hazard models for the densely populated region at the eastern marginal zone of the Tibetan Plateau. 相似文献
20.
Effect of reservoir construction on suspended sediment load in a large river system: thresholds and complex response 总被引：2，自引：0，他引：2
Dam construction greatly alters the channel boundary of rivers, making the dammed river system a human‐controlled system. Based on hydrometric data in the upper Changjiang River basin, the change in behaviour of sediment transport of some dammed rivers was studied. As a result, some phenomena of threshold and complex response were found. When the coefficient (Cr,a) of actual runoff regulation by reservoirs, defined as the ratio of total capacity of reservoirs to annual runoff input, is smaller than 10%, suspended sediment load at Yichang station, the control station of the Changjiang River, shows a mild decreasing trend. When this coefficient becomes larger than 10%, suspended sediment load decreases sharply. The coefficient of 10% can be regarded as a threshold. The Cr,a of 10% is also a threshold, when the variation of suspended sediment concentration (SSC) with Cr,a at Yichang station is considered. The impacts of reservoir construction can be divided into several stages, including road construction, dam building and closure, water storage and sediment trapping. During these stages, some complex response was identified. At the station below the dam, SSC increases and reaches a maximum, and then declines sharply. This phenomenon was found on the main‐stem and several major tributaries of the upper Changjiang River. In the Minjiang River, where a series of dams were built successively, the response of SSC is more complicated. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献