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1.
Composition and flux of suspended organic matter in the middle and lower reaches of the Changjiang (Yangtze River) — impact of the Three Gorges Dam and the role of tributaries and channel erosion 
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下载免费PDF全文 To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ13C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ13C (?24.3‰ – ?26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC‐2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end‐member model based on δ13C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
2.
湖泊沉积有机碳同位素与环境变化的研究进展 总被引：20，自引：2，他引：20
湖泊沉积有机质稳定碳同位素（δ^13Corg)在区域气候与环境变化方面的应用近年来发展迅速，成果令人瞩目，保存在各类湖泊岩芯中的δ^13Corg记录揭示了晚更新世以来大气CO2浓度的变化、湖泊水位波动、湖区生态与植被的变迁以及气温变化等重要环境信息，由于造成δ^13Corg值变化的影响因素较多，确定个湖与环境变化有关的主导因素时常有赖于其它证据的帮助，诸如地球化学、古湖沼学、孢粉学、分子同位素地层学等等，前人通过研究来自不同类型湖泊、具不同曲线形态特征的δ^13Corg记录，提出了多种环境解释模型，本文对此作了归纳和评述。鉴别和澄清湖泊沉积有机质的源物质以及有机物源随环境变化而发生过的变化，是研究δ^13Corg记录环境意义至关重要的基础性工作，由于有机质含量、碳氮比值、氢指数、生物残留物鉴别等常能提供有关有关湖泊有机质来源、产率、成岩作用等方面的有用信息，这方面的研究结果应该尽可能一并提供，以利于恰当地应用现有的环境解释模型，或者建立个湖新模型，单体生物标志化合物鉴别通常也能为区分湖积有机质中陆生、水生、细菌生等不同碳的来源提供有用信息，特定化合物同位素分析技术近年来成功地应用于建立单体生物标志化合物碳同位素地层学，为湖积有机碳同位素在生态环境演变研究方面的应用提供了思路，我国许多湖泊的湖底沉积岩芯尚未钻取，那些对过去全球变化研究有价值的δ^13Corg记录有待我们去获取和研究。 相似文献
3.
《Continental Shelf Research》2006,26(17-18):2260-2280
On October 3, 2002 Hurricane Lili made landfall on a previously studied region of the inner Louisiana shelf as a Category 2 storm with winds over 160 km/h. A week after the hurricane, major impacts of the storm were not evident in the water column except for the lower than expected inshore salinities (∼12 psu) for this time of year, which was characterized by low river discharge. Turbidity profiles were typical of those measured during previous investigations with suspended sediment concentrations >75 mg/L at inshore stations and <50 mg/L in surface waters and offshore. The implication is that the sediments resuspended during the hurricane settled soon after the storm passage. Water column particulate organic carbon (POC) concentrations ranged from 0.1 to over 2.0 mg/L, with the highest concentrations measured near the seabed and in the inshore portions of the study area. Suspended particles were characterized by low organic matter content (%POC of 0.5–2 wt%), low chlorophyll:POC ratios (Chl:POC<4 mg/g) and moderately elevated POC:particulate nitrogen ratios (POC:PN of 10–14 mol/mol), all suggesting their source was locally resuspended seabed sediment rather than from algal biomass or land-derived vascular plant detritus.Post hurricane sediment deposition throughout the study area resulted in a storm layer that ranged from <0.5 to 20 cm in thickness. In most locations sediment accumulation ranged from 3 to 10 cm. The storm deposits were generally composed of silty clays with a coarser, somewhat sandy 1–2 cm basal layer. Surface sediments from the storm layer were characterized by relatively high mineral surface areas (SA of 30–50 m2/g) and elevated OC contents (%OC of 1.0–2.0%). The dispersal of fine sediments following the hurricane resulted in marked changes in the SA and %OC values of surface sediments from offshore locations, which prior to the storm contained coarser, organic-poor particles (SA of 5–15 m2/g and %OC of 0.2–0.6%). The OC:SA and OC:N ratios of storm layer sediments ranged from 0.4 to 0.6 mg OC/m2 and from 10 to 12 mol/mol, respectively, and were comparable to those measured in surface sediments prior to the hurricane. Such similarities in the composition of the organic matter reinforce the idea that the source of the storm deposits was the finer fraction of resuspended seabed sediments, with little evidence for inputs from local land-derived sources or autochthonous algal production. Overall, the magnitude of sediment and organic matter deposition on the seabed after the storm greatly exceeded the annual inputs from the Atchafalaya River and coastal primary production. The combined effects of hurricane-driven erosion and post-storm deposition represent a major perturbation to the benthic community of the region, which is already subject to these types of disturbances due to the combined effects of peaks in river discharge and the passage of storm fronts. 相似文献
4.
We examine effects of high river particulate flux and municipal wastewater effluent on heterotrophic organic carbon cycling in coastal subtidal sediments. Heterotrophic production was a predictable (r2 = 0.95) proportion (56%) of oxidized OC flux and strongly correlated with organic/inorganic flux. Consistent growth efficiencies (36%) occurred at all stations. Organic biomass was correlated with total, OC and buried OC fluxes, but not oxidized OC flux. Near the river, production was modest and biomass high, resulting in low P/B. Outfall deposition resulted in depleted biomass and high bacterial production, resulting in the highest P/B. These patterns explain why this region is production “saturated”. The δ15N in outfall effluent, sediments and dominant taxa provided insight into where, and which types of organisms feed directly on fresh outfall particulates, on older, refractory material buried in sediments, or utilize chemosynthetic symbiotic bacteria. Results are discussed in the context of declining bottom oxygen conditions along the coast. 相似文献
5.
A sustained dynamic inflow perturbation and bar–floodplain conversion are considered crucial to dynamic meandering. Past experiments, one-dimensional modelling and linear theory have demonstrated that the initiation and persistence of dynamic meandering require a periodic transverse motion of the inflow. However, it remains unknown whether the period of the inflow perturbation affects self-formed meander dynamics. Here, we numerically study the effect of the inflow perturbation period on the development and meander dynamics of a chute-cutoff-dominated river, which requires two-dimensional modelling with vegetation forming floodplain on bars. We extended the morphodynamic model Nays2D with growth and mortality rules of vegetation to allow for meandering. We tested the effect of a transversely migrating inflow boundary by varying the perturbation period between runs over an order of magnitude around typical modelled meander periods. Following the cutoff cascade after initial meander formation from a straight channel, all runs with sufficient vegetation show series of growing meanders terminated by chute cutoffs. This generates an intricate channel belt topography with point bar complexes truncated by chutes, oxbow lakes, and scroll-bar-related vegetation age patterns. The sinuosity, braiding index and meander period, which emerge from the inherent biomorphological feedback loops, are unrelated to the inflow perturbation period, although the spin-up to dynamic equilibrium takes a longer time and distance for weak and absent inflow perturbations. This explains why, in previous experimental studies, dynamic meandering was only accomplished with a sustained upstream perturbation in flumes that were short relative to the meander wavelength. Our modelling of self-formed meander patterns is evidence that scroll-bar-dominated and chute-cutoff-dominated meanders develop from downstream convecting instabilities. This insight extends to many more fluvial, estuarine and coastal systems in morphological models and experiments, which require sustained dynamic perturbations to form complex patterns and develop natural dynamics. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
6.
The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g. chute channels), but growing evidence suggests some channels originate outside of the channel‐belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3064 km2 of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g. oxbow lakes) of chute‐channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down‐valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we compared the presence of channelization types with measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems are characterized by large floodplain‐to‐river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach‐scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo‐meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre‐existing topographic lows, such as meander cutoffs. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Irene Ylla Isis Sanpera-Calbet Isabel Muñoz Anna M. Romaní Sergi Sabater 《Aquatic Sciences - Research Across Boundaries》2011,73(4):523-535
Amino acid composition (quality) and abundance (quantity) of organic matter (OM) in an intermittent Mediterranean stream were
followed during transitions from wet to dry and dry to wet conditions. Amino acids were analyzed in benthic material (epilithic
biofilms, sand sediments, leaf material) as well as in the flowing water (dissolved organic matter, DOM). A principal component
analysis and the estimation of the amino acid degradation index (DI) elucidated differences in amino acid composition and
quality among the wet–drought–wet cycle. Amino acid content and composition were dependent on the source of OM as well as
on its diagenetic state. The highest-quality OM (high DI and high N content) occurred on epilithic biofilms and the most degraded
and lowest-quality OM occurred in sandy sediments. Differences between the pre- and post-drought periods were evident in DOM
quality; autochthonous-derived material was predominant during the pre-drought (wet period preceding drying), while allochthonous
inputs dominated during the post-drought period (wet period following drying). In contrast, benthic OM compartments were more
stable, but benthic OM quality decreased continuously throughout the drought period. This study revealed that wet–drought–wet
cycles resulted in subtle changes in benthic OM quality, and degradation of DOM was related to flow intermittency. 相似文献
8.
The Geul River, located in the south‐eastern part of The Netherlands, is a meandering river with a planform shape characterized by large loops consisting of multiple bends. We evaluate the effect(s) of groundwater flow on the shapes of meanders as a possible explanation for the multi‐bend loops, using a combined meandering–groundwater computer model. In the model seeping groundwater enhances bank erodibility. Based on the simulation results, we present a conceptual, generalized model for groundwater–meandering interaction, based on wavelength selection and fixation effects. Wavelength selection occurs because of the positive feedback between growing meander bends and groundwater flow patterns and velocities. The promoted wavelengths have the same spatial scale as the groundwater flow system in the aquifer underlying the floodplain. In the case of the Geul River these wavelengths are of the order of 100 m. Since groundwater flow velocities are largest close to the recharging hill‐slopes, the seepage‐enhanced bank erodibilities are at a maximum near the floodplain limits. At these locations the difference in erodibility between banks facing the floodplain and those facing the hill slopes is large, so it is difficult for the river to migrate away from the floodplain limits. This causes long stretches of the river to be aligned along the floodplain limits, which we term a fixation effect. This mechanism best explains the multi‐bend loops of the Geul River. The general interaction between groundwater flow and meandering is site specific since it depends on climatic, fluvial and hydrogeological parameters. The Geul is characterized by a wide floodplain and steep hill‐slopes, and it is underlain by coarse‐grained deposits with good aquifer properties, favoring an important groundwater system. Since this kind of river frequently occurs, our results could apply to many other river systems. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
三峡库区拥有目前世界上规模最大的水利枢纽工程，自投入使用以来，为长江流域提供了丰富的水源及电力，促进了经济的发展，但同时也对该区域的生态环境造成了严重的冲击。澎溪河流域作为三峡库区长江流域干流的典型回水区和消落带，是众多学者研究三峡库区生态环境变化的重点区域。为探究不同时空尺度下土地利用对河流溶解性有机质（DOM）的影响，以澎溪河流域为研究对象，基于紫外-可见光谱分析和三维荧光光谱矩阵-平行因子分析，结合河段缓冲区、河岸带缓冲区及子流域3种空间尺度的二级土地利用类型，解析了旱雨季水体DOM的组成及来源特征，并采用相关分析和冗余分析方法探讨了3种空间尺度下土地利用方式对旱雨季水体DOM的多时空尺度影响。结果表明：（1）旱季水体DOM荧光组分以陆源类腐殖质所占比例更大，雨季水体DOM荧光组分以富里酸贡献为主。（2）流域内陆源输入和内源产生对水体DOM丰度均有贡献，雨季较旱季水体DOM的陆源性更强，自生源特征较弱。（3）土地利用在雨季和子流域尺度下对水体DOM的影响更显著，其中，雨季子流域尺度下，土地利用指数对水体DOM参数的解释率为90.35%。（4）不同土地利用方式对水体DOM产生的影响... 相似文献
10.
在不同季节,采集太湖梅梁湾和贡湖湾沉积物柱状样,研究沉积物Eh、pH、总氮、总磷以及有机质四季垂向剖面分布变化特征.研究结果表明,在表层下(0-3 cm),Eh随沉积物深度的增加迅速下降,很快进入还原状态.沉积物剖面上pH变化幅度不大,在6.4-7.8之间,冬季沉积物pH均有所降低.太湖沉积物中含有丰富的营养盐,总氮和总磷最高浓度分别为2.68和0.864 mg/g,其剖面分布特征表明,沉积物表层总氮和总磷含量远高于底层,其含量随深度增加而降低,但四季变化趋势不明显.沉积物中有机质含量在10 cm以上变化幅度较大,随着沉积物深度的增加,有机质含量明显减少,季节变化幅度不大.比较不同采样点发现,位于梅梁湾生态系统试验区内的S1位点沉积物氮磷内源负荷最大. 相似文献
11.
A close negative correlation was found to exist between oxygen concentration in winter and the latitude in rivers in the basins
of the Ob and Volga. This can be explained by an increase in the duration of the freeze-up period (during which oxygen is
consumed for oxidation of organic matter (OM) in water and bottom sediments) in the direction from the south to the north,
while the input from oxygen from the atmosphere and photosynthesis is practically zero. No inverse relationship was found
to exist between dissolved oxygen and the latitude, because in rivers of mountain and semimountain types, typical of this
basin, organic matter (OM) does not accumulate in bottom sediments and the conditions of atmospheric circulation are better
than in lowland rivers. The magnitude of seasonal variations in oxygen in lowland rivers is greater than in mountain ones
because of an abrupt drop in oxygen concentration in slowly flowing rivers in winter and the saturation of their water by
oxygen from photosynthesis in summer. 相似文献
12.
Water samples from the Yamuna and its tributaries, one of the major river systems draining the Himalaya, have been analysed for their stable oxygen and hydrogen isotopes during three seasons (summer, monsoon and post‐monsoon). The data show clear seasonal and altitudinal variations; waters from higher altitudes and those collected during monsoon season are characterized by relatively depleted isotopic composition. Regression analysis of δD–δ18O data of samples collected during summer and monsoon seasons shows that the slope of the best‐fit lines are nearly identical to those of precipitation at New Delhi for the same period. The similarity in their slopes suggests that the isotopic composition of precipitation contributing water to these rivers are reasonably well preserved in both monsoon and non‐monsoon seasons, however, during the non‐monsoon period both rainfall and river waters carry signatures of evaporation. The ‘deuterium excess’ in river waters during the three seasons though overlap with each other, the values during October are higher. This can be understood in terms of recycled moisture contributions to precipitation. The ‘altitude effect’ for δ18O in these waters is determined to be 0·11‰ per 100 m, a factor of about two less than that reported for the Ganga source waters from similar altitudinal range. The variability in altitude effects in rivers draining the Himalaya seems to be controlled by the ‘amount effect’ associated with the monsoon. The significant spatial variability in altitude effect in these river basins, which are a few hundred kilometers apart, suggests that reconstruction of palaeoelevation in the Himalaya, based on δ18O‐altitude gradients, would depend critically on its proper assessment in the region. This study has established a relationship between total cation abundance and δ18O in waters of the Yamuna mainstream; total cations (corrected for cyclic components) double for a 1·4 km decrease in altitude as the Yamuna flows downstream. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
Continuous monitoring of dissolved organic matter (DOM) character and concentration at hourly resolution is rare, despite the importance of analysing organic matter variability at high‐temporal resolution to evaluate river carbon budgeting, river water health by detecting episodic pollution and to determine short‐term variations in chemical and ecological function. The authors report a 2‐week experiment performed on DOM sampled from Bournbrook, Birmingham, UK, an urban river for which spectrophotometric (fluorescence, absorbance), physiochemical (dissolved organic carbon [DOC], electrical conductivity, pH) and isotopic (D/H) parameters have been measured at hourly frequency. Our results show that the river had sub‐daily variations in both organic matter concentration and characteristics. In particular, after relatively high‐magnitude precipitation events, organic carbon concentration increased, with an associated increase in intensity of both humic‐like and tryptophan‐like fluorescence. D/H isotopic ratio demonstrates different hydrological responses to different rainfall events, and organic matter character reflects this difference. Events with precipitation < 2 mm typically yielded isotopically heavy water with relatively hydrophilic DOM and relatively low specific absorbance. Events with precipitation > 2 mm had isotopically lighter water with higher specific absorbance and a decrease in the proportion of microbially derived to humic‐like fluorescence. In our heavily urbanized catchment, we interpret these signals as one where riverine DOM is dominated by storm sewer‐derived ‘old’ organic matter at low‐rainfall amounts and a mixed signal at high‐precipitation amounts where ‘event’ surface runoff‐derived organic matter dominate during storm sewer and combined sewer overflow routed DOM. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
14.
T.R. Gireeshkumar P.M. Deepulal N. Chandramohanakumar 《Marine pollution bulletin》2013,66(1-2):239-245
Surface sediments samples were collected from 9 stations of the Cochin estuary during the monsoon, post-monsoon and pre-monsoon seasons and were analyzed for grain size, total organic carbon (OC), total nitrogen (TN) and stable isotopic ratios of carbon (δ13C) and nitrogen (δ15N) to identify major sources of organic matter in surface sediments. Sediment grain size is found to be the key factor influencing the organic matter accumulation in surface sediments. The δ13C values ranges from ?27.5‰ to ?21.7‰ in surface sediments with a gradual increase from inner part of the estuary to the seaward side that suggest an increasing contribution of marine autogenous organic matter towards the seaward side. The δ15N value varies between 3.1‰ and 6.7‰ and it exhibits complex spatial and seasonal distributions in the study area. It is found that the dynamic cycling of nitrogen through various biogeochemical and organic matter degradation processes modifies the OC/TN ratios and δ15N to a considerable degree. The fraction of terrestrial organic matter in the total organic matter pool ranges from 13% to 74% in the surface sediments as estimated by δ13C based two end member mixing model. 相似文献
15.
We develop a new method for analysis of meandering channels based on planform sinuosity. This analysis objectively identifies three channel‐reach lengths based on sinuosity measured at those lengths: the length of typical, simple bends; the length of long, often compound bends; and the length of several bends in sequence that often evolve from compound bends to form multibend loops. These lengths, when normalized by channel width, tend to fall into distinct and clustered ranges for different natural channels. Mean sinuosity at these lengths also falls into distinct ranges. That range is largest for the third and greatest length, indicating that, for some streams, multibend loops are important for planform sinuosity, whereas for other streams, multibend loops are less important. The role of multibend loops is seldom addressed in the literature, and they are not well predicted by previous modelling efforts. Also neglected by previous modelling efforts is bank–flow interaction and its role in meander evolution. We introduce a simple river meandering model based on topographic steering that has more in common with cellular approaches to channel braiding and landscape evolution modelling than to rigorous, physics‐based analyses of river meandering. The model is sufficient to produce reasonable meandering channel evolution and predicts compound bend and multibend loop formation similar to that observed in nature, in both mechanism and importance for planform sinuosity. In the model, the tendency to form compound bends is sensitive to the relative magnitudes of two lengths governing meander evolution: (i) the distance between the bend cross‐over and the zone of maximum bank shear stress, and (ii) the bank shear stress dissipation length related to bank roughness. In our simple model, the two lengths are independent. This sensitivity implies that the tendency for natural channels to form compound bends may be greater when the banks are smoother. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
16.
采用高通量测序技术,研究了内蒙古岱海流域入湖河流、湖水及沉积物细菌多样性及群落组成.结果显示,细菌多样性从高到低依次为：沉积物>河流>湖泊.聚类分析表明入湖河流、湖水和沉积物细菌群落可分为明显不同的3支,说明这3种生境中细菌群落结构有较大差异.物种注释结果表明,河流中优势细菌菌群为髌骨细菌（Patescibacteria）、变形菌门（Proteobacteria）、拟杆菌门（Bacteroidetes）和放线菌门（Actinobacteria）;湖水中优势细菌菌群为放线菌门（Actinobacteria）;而沉积物中优势细菌菌群为变形菌门和绿弯菌门（Chloroflexi）.典范对应分析及Monte Carlo检验表明,电导率和悬浮物含量对水体中（河流与湖泊）细菌群落影响显著,二者共解释了细菌群落变化的86.5%;而冗余分析及Monte Carlo检验表明,泥深、磁化率和总有机碳对沉积物中细菌群落影响显著,三者共解释了细菌群落变化的47.9%.近30年来,岱海地区气候变化和人类活动导致湖水咸化,沉积物碳氮指标显著增长.岱海水体及沉积物细菌多样性及群落组成的差异及其主要驱动因子,反映了细菌对这种气候变化和人类活动共同作用的响应. 相似文献
17.
Sedimentary architecture of abandoned channel fills 总被引：1，自引：0，他引：1
18.
This study focuses on the assessment of relationships between flow and macrozoobenthos structure that was performed in a reconnected oxbow lake located in the S?upia River floodplain (northern Poland). The lake was created during river straightening at the beginning of 20th century by cutting off the right‐bank meander. The oxbow restoration was performed to enhance the ecological viability of this water body and restore riverine wetland. In July 2000 the oxbow was connected with the river channel through PVC pipes which enabled free water movement. Macrozoobenthos sampling, as well as chemical analyses of water and hydrological measurements, took place both before and after the oxbow reconnection. Before the oxbow reconnection, the dominant species was Asellus aquaticus, whereas after the reconnection the structure of benthic species changed significantly. During the first year it was replaced by bivalves and Chironomidae larvae and then A. aquaticus. After the reconnection, macrozoobenthos mean density was 5‐fold higher and the mean wet biomass was 77‐fold higher than before the reconnection. The number of taxa increased from 4 before the oxbow reconnection to 17 during the first year after the performed works and 20 in the next year. We stated that the revitalization process of the reconnected oxbow lake has long‐term consequences for the benthic communities. The most significant feature of the oxbow reconnection is the qualitative and quantitative recolonization by riverine macrozoobenthos species. The performed restoration significantly improved ecological status of the oxbow lake by the increase in biodiversity and water quality. 相似文献
19.
Roberto V. Santos Francis Sondag Gérard Cochonneau Cristelle Lagane Pierre Brunet Karina Hattingh Jeane G. S. Chaves 《水文研究》2015,29(2):187-197
We report the results of a detailed study of dissolved Sr isotopes in the Solimões and Beni‐Madeira Rivers of the Amazon basin. This study developed data collected over 8 years indicating large spatial and temporal variations in dissolved Sr isotopes among the rivers of the Amazon basin. The large 87Sr/86Sr variations were found to be correlated with the geology of the source areas of the suspended sediments. The Beni‐Madeira River displays a high average 87Sr/86Sr ratio and large 87Sr/86Sr fluctuations during the hydrological cycle. This large average value and fluctuations were related to the presence of Precambrian rocks and Ordovician sediments in the source area of the suspended sediment of the river. In contrast, the Solimões River displays a narrow range of Sr isotope ratio variations and an average value close to 0.709. This river drains mostly Phanerozoic rocks of northern Peru and Ecuador that are characterized by low Sr isotope ratios. The isotopic fluctuations in the Beni‐Madeira River were observed to propagate downstream at least as far as Óbidos. This signal is characterized by an inverse relationship between the concentration of elemental Sr and its isotopic ratios. We further demonstrate that the Sr isotopic composition and content in the Beni‐Madeira River is controlled by suspended sediments derived from the Andes. Despite draining areas underlain by Precambrian rocks and having high 87Sr/86Sr ratios, such rivers as the Negro and Tapajós play a minor role in the total Sr budget of the Amazon basin. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
20.
Distribution and ecological relevance of fine sediments in organic-enriched lagoons: the case study of the Cabras lagoon (Sardinia, Italy) 总被引：2，自引：0，他引：2
Magni P De Falco G Como S Casu D Floris A Petrov AN Castelli A Perilli A 《Marine pollution bulletin》2008,56(3):549-564
In organic-enriched sedimentary systems, like many Mediterranean coastal lagoons, a detailed analysis of sediment grain size composition and partitioning within the muds is crucial to investigate sedimentological trends related to both hydrodynamic energy and basin morphology. In these systems, sediment dynamics are particularly important because the partitioning and transport of fine sediments can strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution of benthic assemblages and the trophic status and functioning of a lagoon. Nevertheless, studies on benthic-sediment relationships have been based mainly on a rather coarse analysis of sediment grain size features. In muddy systems, however, this approach may impede a proper evaluation of the relationships and effects of the distribution of fine sediment and organic matter on the biotic benthic components. Here we show that the distribution of sedimentary organic matter (OM) and total organic carbon (TOC) in the Cabras lagoon (Sardinia, Italy) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of the cohesive fraction of sediments (< or = 8 microm grain size particles) and that this fraction strongly influences the structure, composition and distribution of macrobenthic assemblages. Even in such a homogeneously muddy system, characterized by "naturally" occurring impoverished communities, impaired benthic assemblages were found at < or = 8 microm, OM, TOC contents of about 77%, 11% and 3.5%, respectively. A review of studies conducted in Mediterranean coastal lagoons highlighted a lack of direct integrated analysis of sediment features and the biotic components. We suggest that, especially in organic-enriched coastal lagoons, monitoring programs should primarily investigate and consider the cohesive fraction of sediments in order to allow a better assessment of benthic-sediment relationships and ecological quality of the system. 相似文献