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1.
The reduction of pollution in the river Elbe since 1990 has resulted in changes in the processes taking place in the river. The heterotrophic degradation which dominated until 1990 was accompanied by a lack of oxygen, floating masses of sewage fungi, and sludge formation in the areas of still water. Since the early 1990s, autotrophic processes have come to dominate, with an increase in pH fluctuations and the oxygen production potential, but evidently not the chlorophyll level during the growing season. The degradable organic pollution of the Elbe is determined by algae production. The high levels of ammonium previously encountered in the Elbe were attributable to not only dischargers but also in particular the lack of oxygen in the water. Via heterotrophic nitrate assimilation, nitrate served as an oxygen reserve, resulting in high levels of nitrite. At present, when the oxygen contents are sufficient, the concentration reductions of nitrate and nitrite along the reach of the Elbe are approximately parallel, which in view of the lack of ammonium indicates the denitrification of microzones low in oxygen. The relative proportion of structurally bound substance turnover will become increasingly important for the Elbeπs material budget.  相似文献   

2.
Tidal straining effect on sediment transport dynamics in the Huanghe (Yellow River) estuary was studied by field observations and numerical simulations. The measurement of salinity, suspended sediment concentration, and current velocity was conducted during a flood season in 1995 at the Huanghe river mouth with six fishing boats moored at six stations for 25-h hourly time series observations. Based on the measurements, the intra-tidal variations of sediment transport in the highly turbid river mouth was observed and the tidal straining effect occurred. Our study showed that tidal straining of longitudinal sediment concentration gradients can contribute to intra-tidal variability in sediment stratification and to asymmetries in sediment distribution within a tidal cycle. In particular, the tidal straining effect in the Huanghe River estuary strengthened the sediment-induced stratification at the flood tide, thus producing a higher bottom sediment concentration than that during the ebb. A sediment transport model that is capable of simulating sediment-induced stratification effect on the hydrodynamics in the bottom boundary layers and associated density currents was applied to an idealized estuary to demonstrate the processes and to discuss the mechanism. The model-predicted sediment processes resembled the observed characteristics in the Huanghe River estuary. We concluded that tidal straining effect is an important but poorly understood mechanism in the transport dynamics of cohesive sediments in turbid estuaries and coastal seas.  相似文献   

3.
《国际泥沙研究》2020,35(2):146-156
Many of the dams built in estuaries in the last century have difficulty with water quality management.Numerous factors have affected the estuary lake water,most importantly external loadings,tidal currents,and increases in the phosphorus(P) release from sediment,so that most water quality characteristics in the estuary are highly interactive and dynamic.In the current study,water quality measurements were made in the laboratory and field,and a series of phosphorus release experiments was done to understand the behavior of P in an estuary lake.The concentrations of chemical oxygen demand(COD),chlorophyll-a(Chl-a),and total P(TP) showed an increasing trend when the pollutant loading of the influent stream water was high.The measurements showed increasing trends,which indicates the constituents are produced in the internal environment of the lake.When a large amount of freshwater flowed in from the upper watershed,density stratification was observed,which forms strongly because of the salinity of seawater.During the period of stratification,a hypoxic layer formed,which can accelerate P release.Comparing the open and dosed conditions of the release experiments,the P release rate was much higher under the closed condition than under the open condition.The maximum P release rates from the sediment collected from the five main sites of the lake were more than 2.5 times the P loading from the inflowing streams in April.Spatially,the release rate was higher mid-reservoir than down-reservoir where a halocline was evident The pollutant load discharged from the tributary watershed was deposited on the bottom mid-reservoir,whereas it was washed out downreservoir because of the density stratification and strong tide in that area.To sustainably manage water quality and decrease lake eutrophication in brackish environments formed by freshwater from streams mixing with seawater entering through sluice dikes,different measures than those applied in strictly freshwater environments are required.Considering the spatial characteristics of an estuary lake,these measures include 1) blocking settleable particles discharged from the rivers upstream,2) controlling hypoxia to avoid P release from the sediment and inhibiting algae growth mid-reservoir,and 3)decreasing stratification caused by the halocline down-reservoir.  相似文献   

4.
An integrated hydro-environmental model has been developed for predicting the distribution of nutrients in estuarine and coastal waters. This paper also reports on an application of the model to the Loughor Estuary in the UK, which has a high tidal range. The horizontal two-dimensional model considers the hydrodynamic, sediment transport, dissolved oxygen and nutrient cycling processes. In particular, the effect of sediment suspension and deposition on the nutrient distribution in the water column has been included in the model. A TVD-MacCormack scheme has been adopted to numerically solve the coupled partial differential equations. Field surveys and laboratory experiments in connection with the Loughor Estuary were conducted to obtain measured data for model calibration and verification. It was found that the linear isotherm model gave a good approximation of the adsorption/desorption processes over the range of nitrogen and phosphorus concentrations measured in the natural estuary. Through experiments on the collected soil samples, the salinity-dependent partition ratios between the adsorbed and dissolved nutrients were determined. The results of the established model showed good agreement with the measured data. Finally, the model was used to examine the implications of changing the sewage effluent discharge scheme on the nutrient distributions in the estuary.  相似文献   

5.
Large parts of the tidal estuary of river Elbe (Germany) are characterized by regular patterns of sand dunes. They evolve due to complex sand transport mechanisms and show multi-faceted migration patterns, which are influenced by hydrodynamic boundary conditions such as runoff and tidal forces. This study aims at increasing the understanding of the way hydrodynamic boundary conditions influence dune behavior. This is the basis of an effective sediment management as well as an important requirement for planning offshore structures. From a unique data set of up to six annual bathymetrical multibeam soundings between 1995 and 2010, bedform characteristics and migration rates were processed and analyzed with a set of automated methods. The influence of river runoff, water levels, current velocities, tidal range, and river depth on characteristics and migration were tested statistically. The results show that migration is mainly dominated by the incoming flood tide while rates and directions depend on the amount of runoff originating from the inland catchment.  相似文献   

6.
The Guadalquivir estuary was impacted by the accidental release of 5 million cubic meters of acid waste from the processing of pyrite ore (25 April 1998). The waste entered ecologically sensitive and protected areas such as the National Park of Doñana. Here are presented the results obtained from a time sequence of different sampling sites in the estuary and in the surrounding areas from May to September 1998. Water, suspended solids and sediments were analysed for six different metals (Fe, Mn, Zn, Cd, Pb, Cu). Also, the concentration of the metals in the different geochemical sediment fractions was determined as a means of assessing bioavailability. The results obtained during the first weeks after the incident show high concentrations of Zn. At the end of June a 10 000 m3 temporary water-treatment plant was constructed on site for depuration of the toxic waters. The results obtained in August and September show a decrease in the metal concentrations measured in the estuary. Only concentrations of Zn were higher than sediment quality values proposed by various authors.  相似文献   

7.
《国际泥沙研究》2019,34(6):591-599
Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macaé River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armação dos Búzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.  相似文献   

8.
In this article, we describe the dynamics of pH, O2 and H2S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment. In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms, as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this way create specific niches for various types of microorganisms.  相似文献   

9.
The response of the Yalu River Estuary to human activities was investigated.Changes of sediment dynamics during the past 10 years were explored through hydrodynamic calculation,as well as heavy mineral...  相似文献   

10.
Tidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

11.
Mercury in sediments of Ulhas estuary   总被引：5，自引：0，他引：5  
Hg levels in water, suspended particulate matter and sediment of the Ulhas estuary are under considerable environmental stress due to the indiscriminate release of effluents from a variety of industries including chlor-alkali plants. Concentration ranges of dissolved (0.04-0.61 micro gl(-1)) and particulate (1.13-6.43 micro gg(-1)) Hg reveal a definite enhancement of levels in the estuary. The Hg burden in sediment upstream of the weir that limits the tidal influence is low (0.08-0.19 micro gg(-1)) with low C(org) content (1.8-2.9%). The high Hg content of the sediment just below the weir varies seasonally (highest concentration recorded being 38.45 micro gg(-1)) due to incremental accretion of sediment as the fresh water flow over the weir progressively decreases. The 30 km segment of the estuary sustains markedly high levels of Hg in the sediment with an exponential decrease in the seaward direction from the weir. Higher concentrations than the expected background prevail in all the estuarine cores up to the bottom, though the overall concentration decreases from about 20 micro gg(-1) in core 7 (inner estuary) to 1 micro gg(-1) in core 31 (outer estuary). The Hg in sediment is associated with C(org), while its correlation with Al, Fe and Mn is poor. The Hg profiles in cores from the Arabian Sea (stations 34, 35 and 37) have a distinct horizon of enhanced concentration in the 5-60 cm segment. Based on 210Pb dating of core 37, the sediment at the bottom of this core is inferred to have been deposited in the year 1949, roughly two year prior to the establishment of the first chlor-alkali plant and represents the background (0.06-0.10 micro gg(-1)). The Hg profiles in the offshore cores indicate a marked increase in transfer of Hg to sediment subsequent to 1980, with a peak around 1990-1992. Based on the index of geoaccumulation it is considered that the estuarine segment between stations 4 and 23 is extremely polluted, while the sediment from the open coast is moderately polluted in the top 25-30 cm with respect to Hg. The enrichment factor of Hg in the sediment is 350-700 for core 4 and decreases to 0-7 for the open-shore cores.  相似文献   

12.
Estuarine environments are influenced by both river flows and oceanic tidal movement of water, sediment, and nutrients, often forming ecosystems that are rich in resources and biodiversity. The Yellow River once carried the world’s largest sediment load, but artificial structures have transformed its hydrodynamic processes. An annual Water-Sediment Regulation Scheme(WSRS) was introduced to flush accumulated sediment from the Xiaolangdi Reservoir, which provides flood control and water storage.Ho...  相似文献   

13.
The formation and dynamics of turbidity maxima (TM) in the Pearl River estuary (PRE) are not well understood but the existence of TM in the estuary have great potential engineering and environmental impacts. Based on the measurements of two large-scale field surveys conducted in the wet season of 1978 (July of 1978) and the dry season of 1979 (March of 1979), the existence and seasonal variations of TM in the PRE focusing on the two major natural navigation channels have been studied. The sediment transport fluxes over two consecutive tidal cycles have been analyzed in detail. The analysis results reveal that the formation mechanisms of TM in the estuary are rather complex. In general, gravitational circulation, tidal trapping, and sediment resuspension and deposition processes are the primary TM formation mechanisms in the PRE. The clockwise back flow pattern around Lingding Island also leads to the formation of TM in the West channel of the PRE. The occurrence of TM far upstream of the salt water wedge is the result of the complex hydrodynamic and sediment transport processes generated by the runoff of the major rivers.  相似文献   

14.
鄱阳湖不同湖区营养盐状态及藻类种群对比   总被引：4，自引：1，他引：3  
在平水期、丰水期和枯水期对鄱阳湖典型天然碟形湖、人控湖汊和主湖区进行了水质、藻类和蓝藻毒素等对比调查,结果表明鄱阳湖各个湖区的水质与藻类种群等差异较大,蓝藻毒素浓度和底泥中铁含量的分布具有一定关联性.在各水文季节蓝藻均为人控湖汊藻类的主要优势种之一.平水期鄱阳湖藻类生物量(叶绿素a浓度)与水体的pH呈正相关关系,与采样点的水深呈负相关关系,碟形湖区水体营养盐浓度和藻类细胞密度均较其他湖区水体低.丰水期各湖区的水质差异相对较小,碟形湖藻类细胞密度仍低于其他湖区,但蓝藻已成为各湖区的优势种,该时期藻类生物量与水体总磷浓度及浊度呈正相关关系.枯水季鄱阳湖各水体藻类生物量与水体总氮浓度、铵态氮浓度及电导率呈正相关关系,碟形湖与主湖区发生了完全分离,水体流动性差,暴发蓝藻水华的风险较高.高温丰枯季节鄱阳湖水体蓝藻毒素浓度与底泥铁含量呈现一定的相关分布关系,底泥铁含量高的地方,其水体蓝藻毒素浓度通常比较高,应警惕鄱阳湖流域富铁红壤流失带来的湖区蓝藻水华风险加剧后果.上述研究结果将为鄱阳湖水环境的预警和污染控制提供科学指导.  相似文献   

15.
Spatiotemporal variations of P species and adsorption behavior in water column, interstitial water, and sediments were investigated in the large shallow eutrophic Lake Chaohu. Ortho-phosphate (Ortho-P) and total phosphorus (TP) concentrations were significantly higher in the western part than in the eastern part of the lake, due to different nutrient inputs from the surrounding rivers. Moreover, paniculate phosphorus (PP) concentration was in a similar spatial pattern to Ortho-P and TP concentrations, and also showed significantly positive correlation with the biomass of Microcystis, indicating more uptake and store of phosphorus by Microcystis than by other algae. Increase of pH and intensive utilization of P by phytoplankton were the main factors promoting P (especially Fe-P) release from the sediment to interstitial water during the cyanobacterial blooms in Lake Chaohu. Spatial dynamics in TP concentration, P species and adsorption behavior of the sediment, coupled with the statistical analyses, suggested that the spatial heterogeneity of P contents in the sediment was influenced by various factors, e.g. human activities, soil geochemistry and mineral composition. In spite of similar TP contents in the sediments, increase in proportion of Fe-P concentration in the sediment may result in a high risk of P release.  相似文献   

16.
Numerical modelling of morphodynamics—Vilaine Estuary   总被引：1，自引：0，他引：1  
The main objective of this paper is to develop a method to simulate long-term morphodynamics of estuaries dominated by fine sediments, which are subject to both tidal flow and meteorologically induced variations in freshwater run-off and wave conditions. The method is tested on the Vilaine Estuary located in South Brittany, France. The estuary is subject to a meso–macrotidal regime. The semi-diurnal tidal range varies from around 2.5 to 5 m at neap and spring, respectively. The freshwater input is controlled by a dam located approximately 8 km from the mouth of the estuary. Sediments are characterised as mostly fines, but more sandy areas are also found. The morphology of the estuary is highly influenced by the dam. It is very dynamic and changes in a complicated manner with the run-off from the dam, the tide and the wave forcing at the mouth of the estuary. Extensive hydrodynamic and sediment field data have been collected in the past and provide a solid scientific basis for studying the estuary. Based on a conceptual understanding of the morphodynamics, a numerical morphological model with coupled hydrodynamic, surface wave and sediment transport models is formulated. The numerical models are calibrated to reproduce sediment concentrations, tidal flat altimetry and overall sediment fluxes. Scaling factors are applied to a reference year to form quasi-realistic hydrodynamic forcing and river run-off, which allow for the simulations to be extended to other years. The simulation results are compared with observed bathymetric changes in the estuary during the period 1998–2005. The models and scaling factors are applied to predict the morphological development over a time scale of up to 10 years. The influence of the initial conditions and the sequence of external hydrodynamic forcing, with respect to the morphodynamic response of the estuary, are discussed.  相似文献   

17.
The formation and evolution of tidal platforms are controlled by the feedbacks between hydrodynamics, geomorphology, vegetation, and sediment transport. Previous work mainly addresses dynamics at the scale of individual marsh platforms. Here, we develop a process-based model to investigate salt marsh depositional/erosional dynamics and resilience to environmental change at the scale of tidal basins. We evaluate how inputs of water and sediment from river and ocean sources interact, how losses of sediment to the ocean depend on this interaction, and how erosional/depositional dynamics are coupled to these exchanges. Model experiments consider a wide range of watershed, basin, and oceanic characteristics, represented by river discharge and suspended sediment concentration, basin dimensions, tidal range, and ocean sediment concentration. In some scenarios, the vertical accretion of a tidal flat can be greater than the rate of sea level rise. Under these conditions, vertical depositional dynamics can lead to transitions between tidal flat and salt marsh equilibrium states. This type of transition occurs much more rapidly than transitions occurring through horizontal marsh expansion or retreat. In addition, our analyses reveal that river inputs can affect the existence and extent of marsh/tidal flat equilibria by both directly providing suspended sediment (favoring marshes) and by modulating water exchanges with the ocean, thereby indirectly affecting the ocean sediment input to the system (favoring either marshes or tidal flats depending on the ratio of the river and ocean water inputs and their sediment concentrations). The model proposed has the goal of clarifying the roles of the main dynamic processes at play, rather than of predicting the evolution of a particular tidal system. Our model results most directly reflect micro- and meso-tidal environments but also have implications for macro-tidal settings. The model-based analyses presented extend our theoretical understanding of marsh dynamics to a greater range of intertidal environments. © 2020 John Wiley & Sons, Ltd.  相似文献   

18.
藻源性湖泛发生过程CDOM变化对水色的影响   总被引：1，自引：1，他引：0  
利用Y-型沉积物再悬浮发生装置模拟湖泛发生过程,分析其中有色可溶性有机物(CDOM)的变化特征及其对水色的影响.结果表明,藻类死亡过程消耗大量的氧气,水中溶解氧在短时间内消失殆尽,形成厌氧环境;并同时分解产生大量CDOM,使得水中CDOM显著增多.前期阶段,CDOM浓度随时间一直升高,第6 d时CDOM浓度达到峰值,CDOM在443 nm处的吸收系数ag(443)为4.48 m-1.水体黑度值(Fe S浓度)呈先增大后减小的趋势,最大值0.35 mmol/L同样出现在第6 d,整个过程中,CDOM浓度和黑度值变化趋势一致,ag(443)与水体黑度呈显著正相关.利用Hydrolight和CIE颜色匹配函数模拟不同梯度的CDOM对水色的影响,发现随ag(443)增大,水体颜色也逐渐由绿色转为棕色,整体向长波方向移动,水色逐渐变暗.因此,可以认为CDOM浓度变化是引起湖泛水体发黑的重要原因之一,可作为定量监测湖泛强度的指示性参数.  相似文献   

19.
藻源性湖泛发生过程CDOM变化对水色的影响   总被引：1，自引：0，他引：1  
利用Y-型沉积物再悬浮发生装置模拟湖泛发生过程,分析其中有色可溶性有机物(CDOM)的变化特征及其对水色的影响.结果表明,藻类死亡过程消耗大量的氧气,水中溶解氧在短时间内消失殆尽,形成厌氧环境;并同时分解产生大量CDOM,使得水中CDOM显著增多.前期阶段,CDOM浓度随时间一直升高,第6 d时CDOM浓度达到峰值,CDOM在443 nm处的吸收系数ag(443)为4.48 m-1.水体黑度值(FeS浓度)呈先增大后减小的趋势,最大值0.35mmol/L同样出现在第6 d,整个过程中,CDOM浓度和黑度值变化趋势一致,ag(443)与水体黑度呈显著正相关.利用Hydrolight和CIE颜色匹配函数模拟不同梯度的CDOM对水色的影响,发现随ag(443)增大,水体颜色也逐渐由绿色转为棕色,整体向长波方向移动,水色逐渐变暗.因此,可以认为CDOM浓度变化是引起湖泛水体发黑的重要原因之一,可作为定量监测湖泛强度的指示性参数.  相似文献   

20.
Anthropogenic mercury pollution was studied in Kastela Bay (Croatia), 10 years after chloralkaline plant (PVC) stopped production. The concentration of total mercury determined in sediments which are composed mainly of calcite and quartz, are in the range 14,280-30,400 ng/g. The values are higher than reported in the literature for Elbe and Seine estuaries and also above 25,000 ng/g used for criterion in remediation project in Minamata Bay. The concentration of methylmercury 6.05-36.74 ng/g are typical for slightly to highly contaminated estuarine sediments. The low ratio of methylmercury to total mercury found in sediments of Kastela Bay is in the range 0.04-0.18%. It can be explained that in this region predominate conditions which do not promote in-situ methylation. Sediments were found to be highly anoxic. Concentrations of total mercury in unfiltered surface waters are in the range 69-145 ng/l and in unfiltered bottom waters in the range 230-1,418 ngl(-1). High concentrations found in bottom waters suggest that either resuspension or partial dissolution of sediments takes place. An experiment performed on filtered and unfiltered waters showed that about 85% of total mercury in surface water and almost 100% in bottom water was retained on 45 microm filters. To demonstrate contrasts, two pristine estuaries from norths and south Europe were studied. Silicious sediments of Ore estuary (Sweden) and calcareous sediments of Krka estuary (Croatia) have total mercury concentrations close to accepted background level. The ratio of methylmercury to total mercury is < or = 1% in all samples with one exception. The highest observed ratio (2.70%) was in the surface sediment from E2 station in Krka estuary measured in March 2000. This location is suitable for studying methylmercury formation in pristine environment.  相似文献   

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