Spatial variations in sedimentary organic matter in surficial lake sediments of Nyanza Gulf (Lake Victoria,Kenya) after invasion of water hyacinth

No detailed studies have been conducted on the spatial distribution of sediment characteristics within Nyanza Gulf of Lake Victoria, especially after the invasion of water hyacinth. Accordingly, a rapid, inexpensive method was used to determine the spatial sediment organic matter variations, expressed as loss on ignition (LOI). Surficial sediments were collected during different survey periods from about thirty‐two sampling sites between 1994 and 2012, in order to characterize the sediments. Although the deeper (>40 m) depositional areas are located in the open lake, visual observations indicate that most of the offshore sediments consist of muddy deposits, plus significant shell remains, with a more sandy type of sediments located in some areas off the inflowing river mouths. The surficial sediments were characterized by a relatively high water content, with over 89% of the samples containing water contents greater than 75%. The sediment organic matter contents from the 2012 survey were more variable, ranging from 1.90% to 33.47%. The sediment organic carbon contents varied spatially, although there were no significant variations between the different sampling periods. Evaluating the SOM at different heating durations at a constant temperature (550 °C) and a very high temperatures (950 °C) did not identify any significant differences. High primary production and greater settling in the deeper areas contribute to the nature of sediments deposited, also being reflected in the relatively high OC contents. Spatially, it is thought that detritus from water hyacinth and terrestrial external loads are important sources of organic matter deposited on the lake bottom within the gulf and may support its growth because of enrichment of nutrient elements. The importance of sediments in adsorption of contaminant substances and influencing geochemical processes within the lake is also emphasized.     

An Investigation of the Impacts of Agricultural Runoff on the Water Quality and Aquatic Organisms in a Lowveld Sand River System in Southeast Zimbabwe

In this research we examined the hypothesis that agricultural pollution is a key determinant of variability in nutrients concentrations and benthic fauna in a semi-arid tropical lowveld region of southeast Zimbabwe. Water quality was monitored in the river water column and river bottom sediments at a time when dissolved oxygen concentration was thought to be very low during the winter period in the rivers passing through low input agricultural sections and intensive commercial agricultural sections. The surveys used established chemical methods and biological methods. Benthic fauna assemblages were used to complement chemical cases of nutrient loading at localities chosen for sampling. Unpolluted control sites were not significantly different (t test, p < 0.05) from polluted sites in levels in mean values of dissolved oxygen, conductivity, total dissolved solids and mean density (no.m²) of benthic invertebrates in May. Significant differences (t test, p < 0.05) were not found in mean values of calcium, magnesium, potassium, total nitrogen, nitrate nitrogen, ammonia nitrogen and total phosphorous in river bottom sediments in May and August. These data certainly do not support the notion that the Runde River is severely polluted by the upstream agricultural activities and the hypothesis that agricultural runoff is a key determinant of water quality is rejected. As the data suggests the Runde River may be receiving moderate nutrient pollution. The positive effects of moderate eutrophication on fish catch and the trade-off in pollution implied here needs to be addressed by appropriate agricultural and environmental policies that relate to water pollution and land use.     

Fish community alterations due to pollution and damming in Tietê and Paranapanema rivers (Brazil)

The Tietê River crosses the metropolitan region of São Paulo (Brazil) and receives a large amount of pollution, in contrast to Paranapanema River which runs in a less populated area. In the inferior portions of the basins of these rivers, a series of reservoirs has been built for hydroelectric energy generation which improve the water quality due to the decantation of suspended soils and aeration in the water spills. Twenty‐nine sampling sites were established along the two rivers and in each sampling site, two groups of eight gillnets were used with standardized sizes in two seasons: winter (dry season: June–September 1994) and summer (rainy season: December–March 1995). The fishes were measured and weighed. Twenty‐five parameters related to the water were recorded. PCA and cluster analysis helped to identify two groups of sampling sites. The first one corresponds to the rainy season samples, while the second corresponds to the dry season samples, so evidencing strong seasonal environmental variation. However, the dry season group is still divided into polluted and non‐polluted sites, showing that during drought there are larger effects of pollutant concentration due to the decreased flow. A total of 415 kg of fish were caught, corresponding to 8324 individuals belonging to 64 different species, in 22 families and four orders of Teleostei. The largest catches occurred in the middle Tietê River. The catches in the reservoirs of the Tietê River during the rainy season are superior to those of the dry season. On the other hand, sampling sites located in running water presented an inverse pattern with the largest catches in the dry season. In river Paranapanema, catches are lower than in the Tietê River, except in Rosana Reservoir during the rainy season. Fish diversity was shown to be a good indicator of environmental stress. In Tietê River an expressive fall in species richness was detected in the polluted stretches, with dominance of one or two species. In the intermediary stretches, the presence of rapids increases the amount of dissolved oxygen, allowing the development of the most abundant and diverse fish community of the river. Fish communities in the reservoirs of the inferior stretch of Tietê River are more diverse. On the other hand, the damming of the superior reaches of Paranapanema River provoked a decrease in diversity. O the whole, types of local fish communities detected, showing different compositions and specific abundances, revealed different ecological situations. A discriminant analysis revealed that the parameters of the water influencing the fish community were: dissolved oxygen, conductivity, nitrogen (nitrate, ammoniacal and albuminoid), phosphate, alkalinity, hardness and iron. Copyright © 2003 John Wiley & Sons, Ltd.     

Ecological implications of the analysis of the redox system of organic matter in the streams of vizcaya (Northern Spain)

Eleven physicochemical variables (pH, temperature, oxygen, percentage of oxygen saturation, orthophosphate, nitrite, nitrate, ammonium, orthosilicate, organic matter and organic matter in sediment) have been analysed in 175 sampling sites during four seasons in 1985. A principal component analysis has been applied after standardization of the density function of the variables, according to skewness and kurtosis. Four main groups of sites have been differentiated. These groups represent different degrees in the redox process of organic matter. (A) Very oxygenated sites with high pH values indicating that the mineralization process prevails. Organic matter appears in low concentrations and a reduced state. (B) Sites nutrient enrichment where elements with high oxidation number prevail (nitrite, nitrate, and orthophosphate). (C) Sites supporting high organic pollution. (D) Sites subjected to heavy urban and/or industrial dumping.     

The distribution and turnover of benthic organic matter in a lowland river: influence of hydrology,seston load and impoundment

The standing stocks of benthic organic matter (BOM) and some of its biochemical compounds (particulate organic carbon, particulate nitrogen, protein, and chlorophyll a) were investigated in the upper 12 cm of the sediments at several sampling sites in a free‐flowing and in an impounded river section of the lowland River Spree (Germany). Several environmental variables were recorded, in order to determine their potential influence on the organic matter content in the sediments. It was shown that the organic matter content in the upper sediment layers was mainly determined by the local hydrological regime, which was best reflected by the particle size distribution at the sampling sites. For the deepest investigated sediment strata, no influencing factors could be determined. The amount and quality of suspended matter was of minor importance to sediment composition. Also seasonal effects could not be detected. The impounded river section exhibited less seasonal variation in organic matter storage, as well as shorter carbon turnover lengths, longer carbon turnover times and lower rates of annual organic matter recycling than the free‐flowing river section, which indicates that changes in river hydraulics result in alterations to the organic matter budget. These alterations could be related to the changed mesohabitat composition and to the higher standing stocks of organic matter in the impounded river reach. We conclude that both morphological and hydrological alterations affect the structure and function of running water ecosystems because of their negative effect on the organic matter cycling. Copyright © 2002 John Wiley & Sons, Ltd.     

Responses of consumers and food resources to a high magnitude,unpredicted flood in the upper Mississippi River basin

The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25 232 m³/s on the upper Mississippi and 21 240 m³/s on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river–floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately for each river, indicated there were few interannual differences in δ¹³C and δ¹⁵N of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between‐year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years, with fine and ultra‐fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in δ¹³C and δ¹⁵N between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright © 2001 John Wiley & Sons, Ltd.     

A River-wide Survey of Polychlorinated Biphenyls (PCBs), Polycylic Aromatic Hydrocarbons (PAHs), and Selected Organochlorine Pesticide Residues in Sediments of the Detroit River—1999

The spatial distribution of hydrophobic organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and octachlorostyrene (OCS) in sediments of the Detroit River was established using data from a 1999 river-wide survey. The survey employed a stratified random sampling design that divided the river into six geostatistical zones consisting of upper, middle, and lower U.S. and equivalent Canadian river reaches. Organic carbon normalized OCS sediment concentrations demonstrated no significant differences between U.S. or Canadian sediments or upstream/downstream gradients suggesting that OCS is derived primarily from sources upstream of the Detroit River. In contrast, sum PCBs and sum PAHs were significantly elevated at U.S. as compared to Canadian stations and demonstrated significant increasing upstream/downstream gradients in organic carbon normalized sediment contamination. The upper and middle U.S. river reaches contained a number of near-shore stations with high localized PCB and PAH sediment concentrations suggesting multiple inputs along the upper U.S. portion of the river. Consistent with past surveys, wide-spread sediment contamination of PCBs and PAHs continues to be observed in the highly industrialized Trenton Channel and downstream of Grosse Isle. Threshold effect level (TEL) sediment quality guidelines for PAHs and PCBs were exceeded in 92.6 and 77.8%, respectively, of stations in Trenton Channel and downstream of Grosse Isle. This large reservoir of degraded sediments in the lower U.S. river reach has the potential to enter Lake Erie during sediment disturbance events and likely contributes to gentoxic stress and increased bioaccumulation of PCBs in resident benthos, fish, and wildlife.     

Organic carbon biodegradability and heterotrophic bacteria along a combined sewer catchment during rain events

The aim of this study was the evaluation of fluxes of organic carbon and biodegradability of waste waters during rain events in order to better predict the impacts of combined sewer overflows (CSO). The combined sewer system studied was located in a densely populated urban catchment adjacent to Paris. Five subcatchments of different size, have been monitored during several rain events for suspended solids, conductivity, ammonium, chemical and biological oxygen demand. In addition, two of these subcathments have been evaluated for dissolved and particulate organic carbon, their biodegradable fractions, and the total bacterial biomass. Several indexes, indicate a lower degradability of waste water during dry weather at the downstream stations, accompanied by an increase of bacterial size and bacterial biomass. A further decrease of biodegradable organic carbon related to rain intensity can be seen at all stations. Our results show a higher proportion of refractory organic carbon during rain events than during dry weather with a possible contribution of the in-sewer sediments to the bacterial wet weather flux.     

Water quality assessment of a recently refilled reservoir: The case of Bütgenbach Reservoir, Belgium

Bütgenbach Reservoir is situated in the High Ardennes plateau in eastern Belgium (50°25′N; 6°13′E). It is used principally for flood control and for production of hydroelectric energy. It has been subjected to a previous series of studies because of its eutrophication problems and their impacts on the local economy. Bütgenbach Reservoir was emptied during spring 2004 for dam restoration, being refilled in mid‐September of the same year. Selected physicochemical and biological parameters (temperature, dissolved oxygen, pH, inorganic and organic nutrients, chlorophyll‐a) were measured fortnightly during the lake's productive season (mid‐April to mid‐October 2005) at three sampling sites throughout the water column. The water quality conditions after refilling of the lake were compared to previous studies accomplished at the same sampling sites (prior to emptying the lake). The actual trophic status was mesotrophic to eutrophic, based on the combination of total phosphorous and chlorophyll‐a concentrations, as well as water transparency. Bütgenbach Reservoir generally exhibits good water quality, based on the French water quality system SEQ‐eau. A longitudinal decrease in water quality was observed from upstream to downstream, because mainly of the differences in lake bottom morphology and water residence time, and their impacts on nutrient distribution in the lake.     

Water quality before and after dam building on a heavily polluted river in semi‐arid Algeria

The impact of the construction and management of a reservoir on a polluted stream in a semi‐arid region has been highlighted using physico‐chemical indicators. The Tafna river (Algeria) collects heavily polluted wastewater from the town of Maghnia and from several factories. Organic pollution comes from domestic sewage and from food industries. Ore treatment industries discharge very acidic wastewater. Temperature, pH, conductivity, chloride, dissolved oxygen, biological oxygen demand (BOD), and nitrogen compounds have been surveyed between 1996 and 2001, before and after the construction of the dam. The change in each parameter is compared between sites located upstream and downstream from the dam. The spatio‐temporal evolution of the organic pollution indicators was highlighted by ANOVA and principal component analysis. By enhancing sedimentation of the organic matter, the reservoir makes possible a significant decline in the BOD downstream of the dam, but increases NH₄ concentration at the downstream sites. The pollution is diluted during high flows and dam releases. Conversely, during low flow periods, mineralization of organic matter is higher in the lower Tafna. Copyright © 2004 John Wiley & Sons, Ltd.     

Phosphorus and nitrogen in the waters of the El-Kabir River watershed in Syria and Lebanon

In order to assess the quality of the waters of the El‐Kabir River, which forms the border between Lebanon and Syria, water samples were collected for phosphorus (P) and nitrogen analyses at 39 sample stations in the river watershed (18 in Syria, 21 in Lebanon). These samples were collected on the main stem and three major tributaries (Nahr al‐Arous and Nahr Nasrive in Syria, Chadra River in Lebanon). Three major springs also were sampled. The sampling was carried out in September 2001, and January, April and August 2002. Nutrient analyses were carried out on samples taken in September 2001, January and April 2002 in Syria, and in September 2001 and August 2002 in Lebanon. The P concentrations were extremely high throughout the watershed, as were the ammonia‐nitrogen and nitrate‐nitrogen concentrations, indicating extensive pollution. Although the nitrite‐nitrogen concentration was relatively low, it is at the upper end of what might be considered normal, thereby perhaps being indicative of some anthropogenic sources. The spring waters were found to be polluted by nutrients. The nutrient sources contributing to the river pollution were mainly from piped, direct sewage discharges from the many settlements throughout the basin. These were supplemented by diffuse sources directly from agricultural fertilizer use and from the indiscriminate disposal of solid wastes into the river and on the stream banks and lands adjacent to the roads of the watershed.     

Trend analysis of water quality in some rivers with different degrees of development within the São Paulo State,Brazil

Time series of dissolved oxygen (DO), biochemical oxygen demand (BOD), nitrate, total phosphorus, chloride, ammonia and faecal coliforms (FC), monitored by CETESB (‘Companhia de Tecnologia de Saneamento Ambiental’), in the period from 1979 to 2001, were analysed in seven river basins located in the São Paulo State, one of the most developed regions in Brazil. The selected rivers, Piracicaba, Mogi‐Guaçu, Turvo Grande, Peixe, Aguapeí, São José dos Dourados and Alto Paranapanema have different degrees of development concerning industrial, agricultural and population growth. Trend analysis methodology was based on graphical exploratory analysis followed by confirmation through statistical tests. Results showed impoverishment of the water quality conditions in most of the studied basins, represented by the positive trends of the parameters (BOD, nitrogens, total phosphorus, clorate and FC) and negative trend of the parameter (DO). Among the analysed basins, the Piracicaba River is the most severely affected with higher variations in the magnitude followed by the basins of the Mogi‐Guaçu, Turvo Grande, Peixe and Aguapeí Rivers. On the other hand, the Alto Paranapanema and São José dos Dourados basins are the least affected. Copyright © 2008 John Wiley & Sons, Ltd.     

Biological monitoring and pollution assessment of the Mukuvisi River,Harare, Zimbabwe

The ecological health and biodiversity of the Mukuvisi River system were investigated during this brief study to assess the functioning of the natural river system, utilizing biological monitoring. The study covered a period of 5 weeks from 15 September to 12 October 2005, during which a weekly sampling routine was conducted, and the effects of pollution on the river were investigated. The pH, dissolved oxygen concentration, temperature and electrical conductivity, as well as the two major nutrients in the water (phosphorus; nitrogen) were measured at four sites along the Mukuvisi River. Macroinvertebrate species also were identified and enumerated at each site, using the South African Scoring System version 4 (SASS4) to assess the biological diversity and to evaluate pollution levels at each site. Site 2 was the most polluted, while site 4 was the cleanest site. It was concluded that, although the river receives pollutants along its course, it also has a self‐purification capacity that can be enhanced by remedial measures against pollution. Possible remedial actions are discussed as recommendations in this study.     

A Comparison of Main and Side Channel Physical and Water Quality Metrics and Habitat Complexity in the Middle Mississippi River

Worldwide large rivers have been severely modified by human intervention. Many modifications result in disconnection of the river from floodplain and off‐channel habitats generally characterized by lower velocities and Copyright © 2016 John Wiley & Sons, Ltd. shallower depths relative to the main channel, conditions vital to many organisms. Extensive levees on the Middle Mississippi River (MMR) have cut off backwater systems and disconnected the river from 80% of its floodplain. However, the system is characterized by large side channels associated with islands. We examined a long term data set for differences in physical (e.g. depth and velocity) and water quality metrics (e.g. temperature, suspended solids, dissolved oxygen, chlorophyll, % organic matter) between the main and side channels of a 128‐km reach of the MMR. We compared variability between main and side channels using the coefficient of variation (COV). All metrics differed between habitats. Side channels were shallower with lower velocities and had greater mean and COV of % organic matter and more variable dissolved oxygen concentrations. Velocity, temperature, and suspended solids were similar in the spring. COVs were lowest in both habitats during the spring for all metrics except temperature and DO. Resource management in the MMR tends to focus on maintaining existing side channels because of the difficulty of working in the heavily used navigation channel. This study shows that these actions protect areas that function differently than the main channel for most of the year. However, our results also highlight the need for restoration activities aimed at restoring floodplain connectivity, especially during the spring. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of River Water Quality in Northwestern Greece

The effect of land use patterns on river water quality was studied in three different river basins located in Epirus, Northwestern Greece. Studies were conducted from October 2000 to {September} 2001. During this period, the parameters chemical oxygen demand (COD), biological oxygen demand (BOD), NO_2–, NO_3–, NH₄₊ and PO_43– were measured, employing standard methods of analysis. The results were subjected to principal component analysis (PCA) for the estimation of the underlying variable correlations and were further explored by means of cluster analysis. The values of the above parameters were also compared with those awkward in the Fresh Water Fisheries Directive (78/659/EEC). It was found that the phosphate content was much higher than the upper limiting criteria for eutrophication for salmonid waters, whereas nitrate levels were lower than the permissible criteria according to the Nitrates Directive 91/676/EEC for drinking water. The inorganic nutrient load was mostly attributed to sites that drain agricultural areas, especially during winter and spring. The organic matter was due to urban activities during autumn.     

Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24‐h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below‐dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south‐east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso‐eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m³ s^?1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo‐mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m³ s^?1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above‐dam site) zones of the reservoirs, as well as in the downstream river stretches (below‐dam site). In both cases, the sampling was carried out at 4‐h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below‐dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L^?1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high‐amplitude/low‐frequency variations could negatively affect the downstream river biota.     

Turbidity and dissolved organic matter as significant predictors of spatio‐temporal dynamics of phosphorus in a large river‐floodplain system

Phosphorus (P) inputs are increasing in river‐floodplain systems, but the factors which influence the dynamics of this nutrient are not clear. To assess P dynamics in this kind of river, the main channel of the Middle Paraná River, 3 anabranches, 9 secondary channels, and 20 lakes (7 permanently connected and 13 temporarily connected to the fluvial system) were sampled. Multiple linear regressions were applied to explain spatio‐temporal patterns of P through commonly measured limnological variables. Particulate P increased during the sediment peak (evaluated through turbidity). Soluble reactive P (SRP) was positively associated with dissolved organic matter (DOM, mainly the chromophoric fraction), which increased during high waters in the fluvial system but was highly variable in each kind of aquatic environment. In temporarily connected lakes, vegetated zones dominated by emergent macrophytes displayed the highest SRP and chromophoric DOM concentrations. The flood and sediment peak positively affected P load in the river due to the increase in dissolved and particulate fractions, respectively. In addition, particle‐bound alkaline phosphatase activity was positively associated with SRP concentration and load. These results suggest that the sediment peak incorporates particulate P in the system while the floodplain is a P source during floods through exportation of the dissolved fraction. Dissolved P could be largely exported associated with DOM, which stimulates phosphatase biosynthesis by decreasing P bioavailability. The effect of aquatic macrophytes on P dynamics seems to be influenced by DOM exudation. According to these considerations, DOM should be taken into account to analyse P dynamics in river‐floodplain systems.     

A physicochemical characterization of the waters of the El-Kabir River and major tributaries in Syria and Lebanon

Thirty‐nine sampling sites were selected in the El‐Kabir River watershed, including 18 in Syria and 21 in Lebanon. Three major tributaries, the Nahr al‐Arous and the Nahr Nasrive in Syria, and the Chadra River in Lebanon, were included in the site selection, together with Wadi el‐Aatchane and Wadi Khaled. Instrumental measurements for temperature, specific conductivity (Sp. Cond.), dissolved oxygen (DO) and pH were taken directly in the water at each site visit. Measurements were taken in both countries in May 2001, January, April and August 2002, and there was an additional sampling in Lebanon during September 2001. The interpretation of the data led to some specific conclusions on the conditions in the watershed. The waters of the El‐Kabir River are derived almost exclusively from ground water, with many significant springs functioning throughout the year. The water that flows rapidly through the system is well‐mixed and consistent in its major characteristics. The DO concentration > 5 mg L^?1, averaging 8.53 mg L^?1 (three DO values < 5 mg L^?1 were observed, all at the same spring). Some variability in water character was observed for Sp. Cond.; these differences could be related to the spring‐source waters originating in limestone or basaltic terrain. Furthermore, an increase in Sp. Cond. in the lower reaches of the river might be related to salinization, resulting from surface water and near‐surface ground water withdrawals for anthropogenic use, particularly irrigation.     

大型水库热分层的水质响应特征与成因分析

为研究大型水库热分层期间水质的响应特征及成因,于2018年4月-2018年12月对大黑汀水库坝前水体的水温及溶解氧等理化指标进行了连续性垂向监测,在此基础上分析了大黑汀水库季节性热分层变化规律以及各水质指标的响应特征.结果表明:(1)大黑汀水库水体呈典型的单循环混合模式,热分层期间,溶解氧在垂向分布同样表现出季节性变化...     

Sediment dynamics and pollutant mobility in rivers: An interdisciplinary approach

Characteristic dynamic features of sediment‐related processes in rivers include dramatic effects of stormwater events on particle transport, rapid and far‐reaching effects of sulphide oxidation during resuspension, and biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result of the stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine‐grained sediments and suspended matter as these materials exhibit large surface areas and high sorption capacities. Organic materials are highly reactive. Degradation of organic matter will induce oxygen depletion and might enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. Major questions relate to the potential reduction of sorption sites on minerals and degradation of organic carrier materials. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modelling the overall effects of pollutants on the water body and aquatic ecosystems. With respect to handling and remediation of contaminated river sediments, either in‐place or excavated, a chemical and biological characterization of the material, of the (disposal) site and of the long‐term processes is crucial. Passive techniques (e.g. in situ stabilization, subaqueous capping) provide economic advantages as there are no operation costs following their installation. However, the success of these ecological and geochemical engineering approaches is mainly based on an in‐depth knowledge of the underlying processes.