Transport of mercury by the Katun river,West Siberia

Some results of a 2-year study of mercury pollution of the Katun river (Siberia) are summarised. Measurements of water flow, sediment transport and mercury concentrations were made and used to calculate the amount of mercury transported by the river. The distribution of transport between water phase and suspended material is calculated. It is concluded that suspended sediments play the main role in this process. The significance of different fractions of suspended sediment is also discussed.     

Hydrological problems of the vistula river valley near Płock

The Vistula river valley near the city of Plock is characterized by the presence of a cascade of terraces, determining the circulation of water and matter. The relationship between the surface water of the Vistula river and the alluvial groundwater is discussed.     

The Vistula river and its riparian zones

Vistula, the main Polish river, runs from the very south to the very north of Poland, draining 54% of its area. It serves as a source of water and at the same time as recipient of sewage. The pollution of the river is high in its upper reaches, where the country is heavily populated and industrialized. The pollution along the river fluctuates with the distribution of urban agglomerations and industry, but decreases towards the Baltic Sea, due to dilution and selfpurification. However, the load of nitrogen and phosphorus to the sea about 20% of the load from all Baltic countries is very high. Up to 50% of this load comes from dispersed sources. Despite of the heavy pollution, life in the river and its valley is thriving. The river, the many old river beds and rich vegetation in this valley are an ecological corridor along the whole country which is important for nature protection (including migrations of birds) and for recreation. A landscape park should be organized in the mist valuable middle course and upper part of low course of the Vistula. The river urgently needs measures to improve its purity: sewage purification plants, protective zones along most tributaries (such a zone along the Vistula itself is essentially sufficient), and improvement of the landscape management (especially agrotechnics) to decrease the load of substances to the Vistula and the Baltic Sea.     

Variation in material transport and water chemistry along a large ephemeral river in the Namib Desert

• 1 The chemical characteristics of floodwaters in ephemeral rivers are little known, particularly with regard to their organic loads. These rivers typically exhibit a pronounced downstream hydrological decay but few studies have documented its effect on chemical characteristics and material transport. To develop a better understanding of the dynamics of floods and associated material transport in large ephemeral rivers, floods of the ephemeral Kuiseb River in south‐western Africa were tracked and repeatedly sampled at multiple points along the river's lower 220 km.
• 2 We quantified the composition and transport of solute and sediment loads in relation to longitudinal hydrological patterns associated with downstream hydrological decay. Source and sink areas for transported materials were identified, and the composition and transport dynamics of the organic matter load were compared to those described from more mesic systems.
• 3 Concentrations of sediments and solutes transported by floods in the Kuiseb River tended to increase downstream in association with pronounced hydrological decay. The contribution of particulate organic matter to total organic load is among the highest recorded, despite our observation of unusually high levels of dissolved organic matter. Hydrological decay resulted in deposition of all transported material within the lower Kuiseb River, with no discharge of water or materials to the Atlantic Ocean.
• 4 Our results suggest that longitudinal variation in surface flow and associated patterns of material transport renders the lower Kuiseb River a sink for materials transported from upstream. The downstream transport and deposition of large amounts of labile organic matter provides an important carbon supplement to heterotrophic communities within the river's lower reaches.

     

Variability and transport of suspended sediment,particulate and dissolved organic carbon in the tidal freshwater Hudson River

Measurements of suspended matter, particulate organic carbon and dissolved organic carbon were made over a three year period at stations spanning 150 km of the tidal freshwater Hudson River. Suspended matter concentrations varied from year-to-year and were not related to freshwater discharge. The increase in suspended matter with depth in vertical profiles suggests that, during medium to low flow conditions, resuspension of bottom sediments was as important a source of sediment as loadings from tributaries. Particulate organic carbon showed significant variability among stations, and both autochthonous primary production and detrital organic matter are contributing to POC standing stocks. Dissolved organic carbon represented over half of the total organic carbon in the water column and showed little variation among stations.Examining downstream changes in transport showed that there was significant production of both suspended matter and POC within the study reach during the ice-free season. Tributary loadings within the study reach do not appear to be the cause of these increases in downstream transport. Dissolved organic carbon behaved conservatively in that there was no evidence for net production or net consumption within the river.The spatial/temporal patterns and analyses of transport suggest that suspended matter and POC, but not DOC, were controlled to a significant extent by processes occurring within the river and were not simply related to loadings from outside.     

Sediment transport in an inland river in North Queensland

Rivers in northern Queensland are ephemeral and carry water mainly as a direct response to heavy rainfall. Sediment is transported downstream with the runoff and sediment deposition may be a major problem in many proposed reservoirs. Hence information about sediment transport, particularly under high flow conditions, is required for planning and design of water storage reservoirs. In this region, bed material samples can be obtained during low flow periods and suspended sediment sampling during floods is possible but only with difficulty. Little reliable data is available.This paper outlines a possible approach to predicting sediment loads in such rivers. Suspended sediment samples have been analysed to give both particulate concentrations and their grain size distributions. The latter have been compared with bed material size distributions, and the concentrations of suspended bed material and wash load components have been estimated.After investigations of a number of methods for predicting bed material transport, those which treat bed load and suspended load independently have been selected. Field data have been used to determine the wash load and the suspended bed material load. The bed load was then computed so that the total sediment load could be determined.This approach has been applied to the Flinders River at Glendower, based on field data obtained by the Queensland Water Resources Commission in 1982/83.     

Sequence- or Position-Specific Mutations in the Carboxyl-Terminal FL Motif of the Kidney Sodium Bicarbonate Cotransporter (NBC1) Disrupt Its Basolateral Targeting and α-Helical Structure

The sodium-bicarbonate cotransporter NBC1 is targeted exclusively at the basolateral membrane. Mutagenesis of a dihydrophobic FL motif (residues 1013–1014) in the C-terminal domain disrupts the targeting of NBC1. In the present study, we determined the precise constraints of the FL motif required for basolateral targeting of NBC1 by expressing epitope-tagged wild-type and mutant NBC1 in MDCK cells and RNA-injected Xenopus oocytes and examining their subcellular localization. We assayed the functional activity of the mutants by measuring bicarbonate-induced currents in oocytes. Wild-type NBC1 (containing PFLS) was expressed exclusively on the basolateral membrane in MDCK cells. Reversal of the FL motif (PLFS) had no effect on basolateral targeting or activity. Shifting the FL motif one residue upstream (FLPS) resulted in mistargeting of the apical membrane but the FLPS mutant retained its functional activity in oocytes. Shifting the FL motif one residue downstream resulted in a mutant (PSFL) that did not efficiently translocate to the plasma membrane and was instead colocalized with the ER marker, protein disulfide isomerase (PDI). Analysis of circular dichroism (CD) revealed that a short peptide, 20 amino acid residues, of wild-type NBC1 contained a significant α-helical structure, whereas peptides in which the FL motif was reversed or C-terminally shifted were disordered. We therefore propose that the specific orientation and the precise location of the FL motif in the primary sequence of NBC1 are strict requirements for the α-helical structure of the C-terminal cytoplasmic domain and for targeting of NBC1 to the basolateral membrane.     

黄河三角洲盐沼湿地乡土植物恢复配置对潮流的调控作用模拟

黄河三角洲互花米草治理之后使得大面积盐沼湿地裸露,面临侵蚀和湿地面积退化的风险,因此亟需开展乡土植物恢复工作,从而稳定生态系统结构。针对此状况,研究运用 Delft3D 模型,设置光滩、碱蓬、碱蓬+芦苇三种情景,结合实地监测数据,分析不同植物配置模式对潮流水深及流速的调控作用。结果显示,模型对水深和流速模拟准确性较高,但流速增加时模拟结果残差略有增加。本土植物恢复对水淹深度的调控作用不明显,但能够有效减缓潮流流速。不同情境下水淹深度几乎没有变化,小潮期间各情景下模拟点平均水深 0.95-0.97m,风暴潮期间 1.71-2.02m。对流速而言,在植物种植区中,碱蓬和碱蓬+芦苇情景在小潮和风暴潮期间都能够显著降低潮流流速,而种植区后方原始流速在10-60 cm/s 之间的潮流也会被显著减缓。综合模拟结果,碱蓬+芦苇的种植模式较单一碱蓬种植模式在调控潮流方面具有更显著的效果,建议黄河三角洲管理部门在互花米草治理工程结束后尽快开展乡土植物恢复工作,从而减少湿地遭受侵蚀的风险。     

Development and ecological importance of phytoplankton in a large lowland river (River Meuse,Belgium)

The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river.Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R>1, whereas they are assumed to be heterotrophic (P:R<1) in the River Continuum concept.The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the importation hypothesis for explaining maintenance of potamoplankton in the downstream reaches.     

Oligotrophic bacteria: Seasonal fluctuations and correlations with environmental variables (Middle Paraná River,Argentina)

Numbers of oligotrophic bacteria (on ‘Microcosm-agar’, a low nutrient medium) fluctuated between 4.4 and 88.103 cfu · ml⁻¹ during 1977–1979. The measured environmental variables (water level, suspended solids, temperature, conductivity, pH and phosphate), explained 79% of this variability. The epipsammic, free-living, mesophilic (35 °C), oligotrophic and psychotrophic bacteria (3 °C) were also quantified. The partial correlation analysis showed that the main factor influencing the epipsammic population was one directly linked to rainfall: the suspended solids concentration (r = 0.826, p < 0.001). This suggests that these oligotrophs are predominantly terrestrial in origin and that the river would mainly represent a means of transport. The presence of free-living was more closely related to the nutritional charateristics of the environment, thus allowing to consider them as ‘autochtonous’ oligotrophic bacteria. The significant correlations between oligotrophs and some other ecological-trophic groups (hyper- and mesotrophic) suggest that their presence is controlled by common environmental factors.     

Transport of major solutes and the relationship between solute concentrations and discharge in the Apure River,Venezuela

The Apure River is a major white-water tributary of the Orinoco River in Venezuela. The Apure is rich in solutes; its contribution to dissolved inorganic solids in the Orinoco (24%) is proportionately much greater than its contribution to discharge (6%). About 40% of the calcium and bicarbonate at the mouth of the Orinoco originate in the Apure drainage. The relationship between discharge and the concentrations of major solutes in the Apure was characterized with a two-compartment hyperbolic mixing model. Previous applications of the two-compartment model have been based on separate determinations of the model parameter , which is a constant describing watershed hydrology, for each solute from data on concentrations. The use of a weighted mean for all solutes is proposed as a means of assessing the importance of processes other than mixing. The model, when used on the Apure data, shows that a strong dilution effect prevails for sodium, calcium, magnesium, sulfate, and bicarbonate, and that a strong purging effect (increase of concentration with increasing discharge) is characteristic of soluble silicon. Biological immobilization of soluble silicon by diatoms during the season of low discharge is sufficiently large to account for the positive relationship between discharge and the concentration of soluble silicon. Specific transport rates of solutes from the basin are generally higher than global averages. In contrast, specific transport of chloride is low. Atmospheric sources control chloride transport in the Apure watershed; the low transport rates of chloride are probably explained by the great distance between the Apure watershed and the oceanic sources of atmospheric chloride.     

Aspects of modelling sediment transport and night conditions in Lake Marken

In lake Marken (Markermeer), a shallow lake in the Netherlands, sediment transport and suspended solids concentration are dominated by wind induced resuspension of sediment. The suspended solids concentration in the lake determines the attenuation of light. A 2-dimensional sediment transport model, STRESS-2d, was used to estimate the special distribution of the silt content for periods with different wind conditions. The model was calibrated using measured values of the fall velocity distributions of sediment, freshly deposited material and suspended solids. The specific light attenuation coefficient of the various sediment classes was also measured and used in the light attenuation model, CLEAR, together with simulation results from the STRESS-2d model, to simulate the light attenuation variations in time and space. By comparison of the simulation results for different scenarios, the influence of regional planning features on the sediment balance and the light attenuation can quantified. A provisional example of this method is presented.     

Entrainment,deposition, and transport of fine-grained sediments in lakes

Recent work on the settling, diffusion, entrainment, and deposition of fine-grained sediments in fresh water is reviewed and synthesized. Particular attention is given to the dependence of these processes on sediment properties such as particle size. The application of this knowledge to the analysis and numerical modeling of sediment transport is also discussed. Much of the work is concerned with the Great Lakes and, more specifically, with the Western Basin of Lake Erie.     

The Lens Circulation

The lens is the largest organ in the body that lacks a vasculature. The reason is simple: blood vessels scatter and absorb light while the physiological role of the lens is to be transparent so it can assist the cornea in focusing light on the retina. We hypothesize this lack of blood supply has led the lens to evolve an internal circulation of ions that is coupled to fluid movement, thus creating an internal micro-circulatory system, which makes up for the lack of vasculature. This review covers the membrane transport systems that are believed to generate and direct this internal circulatory system.     

Physical and chemical post-dam alterations in the Jamari River, a hydroelectric-developed river of the Brazilian Amazon

The regulation of the Jamari River advanced peak floods by 1–2 months and increased dry-season discharges from 60 to 200 m³ s^–1, resulting in water levels approximately 1 m above those recorded before regulation. Daily variation in water level associated with fluctuations in electricity production by the dam propagated to the lower reaches of the tributary Candeias River. Dissolved oxygen (DO), temperature, pH, and conductivity measured over 1.5 years on three locations along the regulated and two free-flowing rivers indicated important alterations in the case of oxygen concentrations. DO levels shifted from saturated (7–8 mg l^–1) during the flood season (when the spillways were open releasing epilimnetic water) to hypoxic (1.5–3 mg l^–1) during the dry season (when the floodgates were closed and only hypolimnetic water used to run the turbines was feeding the river). Fluctuations in water level and variation in dissolved oxygen tended to be greater at the site closest to the dam, gradually attenuating downstream. Mitigation of the downstream effects of river regulation would require modifications in the operation of the dam.     

Is genus or species identification of periphytic diatoms required to determine the impacts of river regulation?

As periphytic diatoms are widely used for biological assessment of rivers, a comparison was made of the use of information at genus or species levels to test the effects of river regulation in eastern Australia. 74 species from 30 genera were recorded from 10 regulated and 13 unregulated sites. The interpretation of the effects of eight dams and weirs on the periphytic diatom assemblages gave broadly similar results whichever taxonomic level was used. The similarity of the efficiency of using data at either taxonomic level is probably related to the fact that the majority of genera have few species. It is suggested that the small number of species within each genus effectively reduces the chances of differing species responses to environmental disturbance negating the response at the genus level. This revised version was published online in July 2006 with corrections to the Cover Date.