Experimental simulation of biodegradation in rivers: Oxygen, organic matter and biomass concentration changes

Dissolved oxygen (DO) and biochemical oxygen demand (BOD) concentration changes after an organic matter discharge into a river have been studied in the absence of oxygen transfer. According to these laboratory experiments, biodegradation of various organic compounds (glucose, glutamic acid, starch, ovalbumin and ethanol) in Seine river samples incubated at 15 30°C follow a biphasic behaviour. During a lag-phase of 10–20 h, DO decreases linearly (0.12 ppm h⁻¹ at 20°C), whereas BOD is constant. During a subsequent aerobic exponential phase, DO and BOD uptake are proportional and increase exponentially with time (0.13 h⁻¹ at 20°C). Using cell ATP as biomass indicator, the latter phase was shown to correspond to a cell division step. A kinetic model was developed for stimulating DO and BOD concentration changes after a waste water discharge at temperatures ranging between 15 and 30°C.     

Influence of pH and TOC concentration on Cu,Zn, Cd,and Al speciation in rivers

Dissolved ( < approximately 4 nm, dialysis in situ), colloidal ( < 0.45 microm filtered, minus dissolved) and particulate (total, minus < 0.45 microm filtered) concentrations of Cu, Zn, Cd, (Al) in eight (three) mining polluted rivers were determined by atomic absorption spectrometry (flame and graphite furnace). The metal size distribution in the rivers was compared to pH, Ca concentration, alkalinity, conductivity, and total organic carbon (TOC). Data plots based on the present and other studies also yielded information about the interrelations between TOC, pH and metal adsorption in rivers and lakes. Less than 10% of Cu, Zn, and Cd were sorbed on particles or colloids in two rivers with average pH at 3.1 and 5.1, whereas 46%, 21%, and 21% of Cu, Zn, and Cd, respectively, occurred in sorbed form in six pH neutral rivers. In three pH neutral rivers, on average 55% of Al was in colloidal form, whereas the dissolved and particulate fractions were 21% and 23%, respectively. Our data combined with data from similar studies support conclusions from other research suggesting that the percent fraction of metals adsorbed on particles rises steeply from almost zero to nearly 100% within a narrow and element specific pH range. Changes in TOC concentration seem capable of shifting the pH to % metal absorption curves in the order of one pH unit.     

Excitation-emission fluorescence matrix to study pH influence on organic matter fluorescence in the Amazon basin rivers

A study of the three-dimensional excitation-emission fluorescence matrix (EEFM) of organic matter from the Amazon basin rivers is reported in this paper. The EEFM, applied to the fractions obtained from sequential tangential ultrafiltration (STUF), give spectroscopic informations on the fluorescent properties of particulate (>0.22 microm), colloidal and dissolved (< 5 kD) organic matter. STUF process does not seem to alter the characteristic peaks position of humic material. Two characteristic excitation-emission peaks were observed in all fractions of the samples investigated, one stimulated by UV excitation (peak A) and one by visible excitation (peak C). Increasing the pH, fluorescence intensities of the fluorophores A and C, respectively, I(A) and I(C), responded in the same manner to pH, increasing with increasing pH. However, the fluorophore A seems more sensitive to this pH variation because its fluorescence intensity enhancement is always higher. Thus the chemical behaviour of the two fluorophores must be somewhat differentiated. The evolution of the I(A)/I(C) ratio with pH is studied for all samples. This investigation showed a linear relation between I(A)/I(C) and pH. Moreover, this behaviour is water type (black or white) and molecular size independent. Indeed, this linear relationship is observed for all samples and all fractions.     

以DO、ORP、pH控制SBR法的脱氮过程

为实现SBR法脱氮在线模糊控制,以啤酒废水为研究对象,通过不同进水混合液氨氮浓度的试验,详细地研究了SBR法在去除有机物和硝化、反砂化过程中DO、ORP、pH的变化规律。试验表明,DO、ORP、pH的特征点和平台的重现性很好,可以作为SBR法去除有机物、砂化、反硝化的过程控制参数。     

Immediate and delayed oxygen depletion in rivers

It is important to distinguish between those processes that remove organic matter from the water phase of a river with an immediate oxygen consumption, as opposed to those processes that remove the organic matter by fixation at the bottom where it will be degraded with delayed consumption. An investigation of a steady-state discharge shows the importance of this distinction, but a theoretical analysis shows this to be of far greater importance during and after an abrupt discharge. It is particularly true in case of storm overflows from combined sewers—as demonstrated experimentally in this and the following paper.     

Pollution levels in some nigerian rivers

Surveys of five rivers in a hot-humid zone of a tropical country (Nigeria) were carried out over 3 years by obtaining samples for physical, chemical and bacteriological analyses. The main characteristics monitored were temperature, turbidity, total, dissolved and suspended solids, pH, dissolved oxygen, BOD, ammonia-nitrogen and the coliform counts. In addition, the main characteristics of the liquid waste being discharged into the rivers were determined.During the dry season, the highest mean temperature is 29°C with a range of 5°C and the lowest is 26°C with a range of 3°C. In the wet season, the highest mean temperature is 27.3°C with a range of 2°C while the lowest is 24.5°C with a range of 1°C. The other characteristics vary more widely with seasons. The high temperature in these rivers all the year round encourages pollution by human activities. During the dry season, pollution causes prolific algae boom, which causes oxygen supersaturation during periods of high temperature and abundant sunlight. The physical, chemical and biological characteristics of the rivers deteriorate sharply as they flow through towns and other human communities.     

Heavy metals in rivers of Latvia

Total heavy metal concentrations in waters and sediments (HNO3 digestible Pb, Cu, Co, Ni, Mn, Zn) and their speciation forms in sediments (exchangeable, carbonate bound, iron-manganese oxide bound, organic matter bound and residual) in major and common small watercourses (31 sampling stations) along their flow in Latvia were determined. The metal loads entering the Baltic Sea from Latvia were calculated. Increased metal concentrations were found only in lower reaches of the largest rivers and locally around known industrial pollution sources. Differences in metal concentrations and loads in rivers from different regions of Latvia were related to natural geochemical processes. Metal speciation analysis showed that the dominant metal species are residual metals and those bound to organic matter. Residual and carbonate-bound metal dominated only in rhitral regions of rivers. The concentrations of exchangeable metals increased below pollution sources.     

Methylmercury in rivers draining cultivated watersheds

Total mercury (THg) concentrations in streams draining cultivated watersheds in Minnesota, USA are strongly correlated with total suspended sediment (TSS) concentrations, varying widely in response to precipitation-driven inputs of soil-derived suspended sediments. Methylmercury (MeHg) concentrations in these waterways have not been studied, and little is known about mercury uptake mechanisms in resident fish populations. To begin to identify factors influencing MeHg concentrations and loadings in these streams, we measured THg and MeHg concentrations in unfiltered whole water samples from the Minnesota River and two of its major tributaries, the Blue Earth and Le Sueur Rivers. Land use in the watersheds of these rivers is over 90% row-crop agriculture, and extensive artificial drainage systems deliver runoff and associated solids quickly to local streams and rivers. THg concentrations were elevated (>10 ng/l) during much of Spring 2000 and part of the summer when runoff from precipitation events increased stream discharge and carried soil materials into the streams. Reduced precipitation resulted in low flow conditions from August through October, and THg concentrations decreased to <4.0 ng/l in all three rivers. MeHg concentrations in the Le Sueur River ranged from 0.07 to 0.42 ng/l between June and December. Higher MeHg concentrations (>0.2 ng/l) were measured during summer months when THg and TSS concentrations were high after precipitation events. Elevated MeHg concentrations were also observed in late October after leaf litter inputs. Conditions on the Blue Earth River were different, with elevated MeHg concentrations (>0.5 ng/l) observed during low flow in August and September. These higher concentrations coincided with a period of enhanced microbial growth stimulated by high late-summer temperatures. A late-October increase in MeHg concentration attributed to leaf litter inputs was also observed in this river. MeHg concentration trends in the Minnesota River were similar to those in the Blue Earth River. Indicators of biological productivity (chlorophyll a, volatile suspended solids, and total Kjeldahl nitrogen) were higher in the Blue Earth and Minnesota Rivers compared to the Le Sueur River, which may signal a connection between higher biological activity and increased MeHg concentrations.     

Nitrification in rivers in the trent basin

The presence of autotrophic nitrifying bacteria in the waters and sediments of both the River Trent and its polluted tributary the River Tame was established and their concentrations determined. Nitrification was shown to occur mainly in the sediments, where it was estimated that at least 80 per cent of the oxidation of ammonia occurred.     

Fate of herbicide CNP in rivers and agricultural drainages

The occurrence and fate of a herbicide CNP (2,4,6-trichlorophenyl-4′-nitrophenylether) in rivers and agricultural drainages was investigated. CNP residues in water samples were extracted by adsorption on a macroreticular XAD-2 resin column and subjected to gas chromatographic analysis using an electron capture detection after desorption from the column and concentration. The minimum detectable amount was 0.04 ng and a positive identification of CNP residue in water samples was obtained with a combined gas chromatography-mass spectrometry-computer system when 500 ng of CNP was injected. CNP residues were detected in water samples taken in June to September, and these levels were between 0.01 and 16.67 μg l⁻¹. The maximum level was found in a sample taken on 13th July, 1977, about a month after beginning rice seedling transplantation, and the minimum level was detected on August 29th, 1977. However CNP residue levels were increased again in September because flooded water on the paddy fields was excluded. CNP was more persistent in the aquatic environment than a herbicide benthiocarb.     

129I in Swedish rivers: distribution and sources

We analyzed the concentration of 129I in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4 x 10(9) atoms l(-1)), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The 129I concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the 129I in the studied rivers is atmospheric fallout of 129I emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the 129I concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue.     

Analysis of thermal impact in tidal rivers and estuaries

The paper presents a far field mathematical model for numerical simulation of transient one- or two-dimensional thermal distributions in regions with severe reversing flow conditions. The Eulerian formulation employs the integral form of the conservation principles for mass and thermal energy. The two-dimensional (2D) solution area is spanned by discrete elements of variable size and shape. The three-dimensional geometry of the flow region is accounted for by spatially integrating over the enclosure surfaces of the discrete element. The derivation of the two-dimensional depth-averaged temperature equations includes the contributions of the vertical variations of velocity and temperature. Surface heat transfer as well as turbulent effects are taken into account.Important mathematical and computational features of the model are summarized. There is a discussion of the four main algorithms, necessary to treat flow regions with complex shoreline geometries, viz. (i) specification of the boundary (ii) determination of all discrete element midpoints lying within the (possibly multiconnected) solution area (iii) construction of discrete elements of irregular geometry exactly matching the (curved) boundary, (iv) treatment of boundary conditions and numerical solution of the resulting mathematical system of weakly coupled, ordinary differential equations derived from the conservation principles.Preliminary results of a computer simulation are compared with the available data for a section of the Lower Elbe river. The calculation of the two-dimensional temperature distribution includes existing power plants and industrial sites. It is noted that the programs developed for this study are more widely applicable, potentially to solving the Poisson equation, in constructing the ion trajectories of an ion extraction system, or in calculating 1D and 2D flow fields.     

Chlorophyll-a in the rivers of eastern England

Chlorophyll-a concentration variations are described for two major river basins in England, the Humber and the Thames and related to catchment characteristics and nutrient concentrations across a range of rural, agricultural and urban/industrial settings. For all the rivers there are strong seasonal variations, with concentrations peaking in the spring and summer time when biological activity is at its highest. However, there are large variations in the magnitude of the seasonal effects across the rivers. For the spring-summer low-flow periods, average concentrations of chlorophyll-a correlate with soluble reactive phosphorus (SRP). Chlorophyll-a is also correlated with particulate nitrogen (PN), organic carbon (POC) and suspended sediments. However, the strongest relationships are with catchment area and flow, where two straight line relationships are observed. The results indicate the importance of residence times for determining planktonic growth within the rivers. This is also indicated by the lack of chlorophyll-a response to lowering of SRP concentrations in several of the rivers in the area due to phosphorus stripping of effluents at major sewage treatment works. A key control on chlorophyll-a concentration may be the input of canal and reservoir waters during the growing period: this too relates to issues of residence times. However, there may well be a complex series of factors influencing residence time across the catchments due to features such as inhomogeneous flow within the catchments, a fractal distribution of stream channels that leads to a distribution of residence times and differences in planktonic inoculation sources. Industrial pollution on the Aire and Calder seems to have affected the relationship of chlorophyll-a with PN and POC. The results are discussed in relation to the Water Framework Directive.     

浅谈山水城市与建筑文化

论述了山水城市的理念，并结合各种理念发展演变过程，阐述了山水城市的相对优越性。阐明了建筑作为文化的载体，有着深刻的文化印迹和浓厚的人文精神要素，指出只有体现中国文化特性与民族特色的中国山水城市及其建筑，才会有它的艺术魅力和文化价值。     

Sediment nutrient characteristics and aquatic macrophytes in lowland English rivers

Aquatic macrophytes play an important role in the nutrient dynamics of streams. As a result, there is much interest in their use as trophic indicators. However, the relationship between aquatic macrophytes and the trophic status of rivers is a complex one, partly because of the effects of a wide range of environmental variables and partly because submerged, rooted macrophytes can absorb nutrients from the river sediments and/or the water column. Experiments which have tried to establish the relative importance of sediments or water as sources of nutrients are inconclusive and further work is needed to establish how sediment nutrient characteristics vary within and among rivers (spatially and temporally) and the inter-relationships between sediment nutrients, water column chemistry and macrophytes. This paper presents the initial findings from a study of 17 lowland rivers in southern England which is exploring the spatial variability of sediment characteristics (total and inorganic phosphorus, total nitrogen, organic carbon, silt-clay fraction and organic matter content) and the relationship with aquatic macrophytes. The preliminary analysis indicates that although sediment characteristics are highly variable within 100-m river reaches, the variability across the 17 rivers is even greater; this is despite the limited geographic and trophic range of the study sites. The results presented in this paper also give some indication of the sediment characteristics associated with five macrophyte species but it is too early to ascribe sediment preferences for particular species.     

Delivery and cycling of phosphorus in rivers: a review

Phosphorus (P) supply (concentration and flux) is an important driver for biological activity in flowing waters and needs to be managed to avoid eutrophication impacts associated with urbanisation and agricultural intensification. This paper examines the role of in-stream retention and cycling in regulating river P concentrations in order to better understand the links between P sources and their ecological impacts. In terms of their composition (solubility and concentration), patterns of delivery (mode and timing) and therefore ecological relevance, P sources entering rivers are best grouped into wastewater discharges > runoff from impervious surfaces (roads, farmyards) > runoff from pervious surfaces (forestry, cultivated land and pasture). The localized impacts of soluble P discharges during ecologically sensitive periods can be distinguished from the downstream impacts associated with particulate P discharges under high flows due to the different processes by which these sources are retained, transformed and assimilated within the river channel. The range of physico-chemical processes involved in P cycling and the variable importance of these processes in different river environments according to stream size, stream geomorphology and anthropogenic pressures are summarised. It is concluded that the capacity to retain (process) P within the river channel, and hence regulate the downstream delivery of P without stressing the aquatic communities present, is considerable, especially in headwaters. To help achieve good water quality, there is scope to better manage this ecosystem service through regulation of P supply whilst optimising in-stream P retention according to subsidy-stress theory. Further research is needed to develop in-stream management options for maximising P subsidies and to demonstrate that regulation of downstream P delivery will reduce the incidence of eutrophication in connected waterbodies.     

纯氧曝气在污水处理和河道复氧中的应用

由于纯氧的压力高于空气中氧的分压,纯氧曝气可显著提高氧的转移速率。德国梅塞尔（ＭＥＳＳＥＲ）集团开发的微气泡纯氧曝气技术（ＢＩＯＸ工艺）,将微孔曝气和纯氧曝气的优点结合起来,采用微孔软管曝气垫,在水深５ｍ处的氧利用率高达８０％。该工艺应用于敞开曝气...     

Elevated methylmercury concentrations and loadings during flooding in Minnesota rivers

Previous studies have identified flooded landscapes (e.g., wetlands, impoundments) as sites of elevated methylmercury (MeHg) production. Here we report MeHg and total Hg (THg) concentrations and mass loadings in rivers in Minnesota during major flooding episodes in the summer of 2002. Frequent intense precipitation events throughout the summer resulted in extraordinarily wet conditions in east-central and northwestern Minnesota. Streamflow remained at record-setting high levels in many rivers and streams in these regions for several weeks. We observed high concentrations of MeHg (>1.4 ng/L) accompanied by high MeHg/THg ratios (0.39 to 0.50) in the Roseau River in northwestern Minnesota and in the Elk and Rum Rivers in east-central Minnesota. Very high MeHg mass loadings were observed in the Mississippi River just upstream of Minneapolis on July 17 (51 g MeHg/day) and July 23 (42 g MeHg/day), when MeHg concentrations at this site were 0.89 and 0.99 ng/L, respectively. The elevated MeHg concentrations in the Roseau River were associated with low dissolved oxygen and high dissolved reactive phosphorus concentrations, both of which are characteristic of anoxic waters. These rivers drain landscapes containing varying amounts of wetlands, and some of the MeHg discharged is thought to have been flushed from anoxic wetland soils. In addition, the flooding of vast areas of normally dry land surfaces probably also resulted in increased MeHg production, adding to the quantities of MeHg exported from these watersheds. Changing climate patterns are expected to result in more frequent heavy precipitation and flooding events in Minnesota. Our results suggest that as flooding and wet conditions in this region increase, the production of MeHg and its export from terrestrial areas to surface waters will increase also.     

Air entrainment and turbulent fluctuations in hydraulic jumps

A hydraulic jump is the sudden transition from a high-velocity impinging flow into a turbulent roller in an open channel. Substantial amounts of air are entrapped at the impingement point, and significant free-surface fluctuations take place above the roller. In the present study, some physical modelling was conducted in a relatively large sized facility. The flow conditions included a wide ranges of inflow Froude numbers and Reynolds numbers (3.8 < Fr₁ < 10.0, 2.1 × 10⁴ < Re < 1.6 × 10⁵). The fluctuating features of free-surface and roller position were investigated non-intrusively with a series of acoustic displacement meters. The characteristic frequencies of the fluctuating motions were documented, and some major roller surface deformation patterns were revealed. The air-water flow properties were investigated with an intrusive phase-detection probe. The void fraction and bubble count rate data were documented in the jump roller, together with the interfacial velocity distributions. The rate of air entrainment was estimated based upon the void fraction and interfacial velocity distribution data. Some simultaneous measurements of instantaneous void fraction and free-surface fluctuations as well as longitudinal jump front oscillations were conducted. The relationship between the rate of air entrainment and turbulent fluctuations is discussed. Both the turbulent fluctuation and aeration properties are basic design parameters in urban water systems in which a hydraulic jump may take place. The present work provides relevant information for water systems including covered channels and partially-filled pipes.     

城市内河整治规划策略探讨

从宏观、中观、微观三个层面对城市内河及其两岸滨河空间的规划进行了综合思考,提出了在不同层面下,内河整治存在的问题及解决的策略,以期促进城市内河整治规划研究。