Abstract. The turbidity variation in time and space is investigated in the downstream stretch of the river GötaÄlv in Sweden. The river is heavily regulated and carries the discharge from the largest fresh water lake in Sweden, Lake Vänern, to the outflow point in Göteborg Harbour on the Swedish west coast. The river is an important waterway and serves as a fresh-water supply for 700 000 users. Turbidity is utilised as a water quality indicator to ensure sufficient quality of the intake water to the treatment plant. The overall objective of the study was to investigate the influence of rainfall, surface runoff, and river water flow on the temporal and spatial variability of the turbidity in the regulated river system by employing statistical analysis of an extensive data set. A six year long time series of daily mean values on precipitation, discharge, and turbidity from six stations along the river were examined primarily through linear correlation and regression analysis, combined with nonparametric tests and analysis of variance. The analyses were performed on annual, monthly, and daily bases, establishing temporal patterns and dependences, including; seasonal changes, impacts from extreme events, influences from tributaries, and the spatial variation along the river. The results showed that there is no simple relationship between discharge, precipitation, and turbidity, mainly due to the complexity of the runoff process, the regulation of the river, and the effects of Lake Vänern and its large catchment area. For the river GötaÄlv, significant, positive correlations between turbidity, discharge, and precipitation could only be found during periods with high flow combined with heavy rainfall. Local precipitation does not seem to have any significant impact on the discharge in the main river, which is primarily governed by precipitation at catchment scale. The discharge from Lake Vänern determines the base level for the turbidity in the river, whereas local surface runoff and tributary discharge induced by rainfall govern the temporal variability in turbidity. Autocorrelation analysis indicates a temporal persistence in turbidity of about 10 days. The results also show that erosion along the main river, from the river bed and banks, is not a dominant contributor to the suspended sediment transport in the river under normal conditions. Further studies on the correlation between turbidity and suspended sediment transport and its relation to erosion processes are suggested.
Background, aim, and scope The aim of this paper is to highlight a not yet recognized hazard for mass failure (landslides) of contaminated soils into rivers and to provide an understanding of important interactions of such events. A first effort to investigate the problem is made focusing on the south eastern part of the Göta Älv river valley, in Sweden, by combining geographical information on potentially contaminated sites with slope stability levels on maps. The objectives of this study were to: (1) Review current Swedish risk assessment methodologies for contaminated areas and landslides, and analyze their capability to quantify the risk of contaminated areas being subject to landslides. (2) Investigate the presence of contaminated areas at landslide risk along the Göta Älv river valley. (3) Provide an overview of the national methods for landslide risk analysis and for environmental risk classification, followed by a comparison between the methods and the results from the superposition of the two methods for the study site. (4) Make a first attempt to conceptualize the release and transport mechanisms. Materials and methods Environmental risk assessment data of the study site was combined with data on slope stability levels. Conceptual issues of the release and transport scenario were identified and a first conceptual model was created. ResultsOf 31 potentially contaminated sites, eight had moderate to high probability for landslide, and of these eight sites, five were classified as having a high or very high environmental risk. These findings had not been revealed when the data had only been considered separately. The 'actual' risk could hence be even higher than the highest environmental risk class actually suggests. By visualizing results from the landslide risk analysis with the results from the environmental risk classification of contaminated sites, a better understanding of the potential hazard involved is obtained. Discussion The release mechanisms as a result of a landslide into surface water were conceptualized using two time scales: the instantaneous and the long-term release. It is clear that the Swedish method for landslide risk assessment and for environmental risk assessment of contaminated soil considers hazard events that are characterized by different time scales. The method for landslide risk assessment addresses events that are rapid (occurring over minutes) with instantaneous impact and consequences. Measurements are made within a short time after the event (days to months). The environmental risk assessment is done with respect to events that are slowly evolving (over years or decades) and any possible consequence materializes after a long period of time. Conclusions The combined data provided a more solid basis for decisions; however, inherent difficulties when combining data based on different methods were revealed. Separate assessment methodologies executed by different authorities may lead to incorrect assessments and inappropriate protective measures.Recommendations and perspective...
The turbidity variation in time and space is investigated in the downstream stretch of the river Göta Älv in Sweden. The river is heavily regulated and carries the discharge from the largest fresh water lake in Sweden, lake Vänern, to the outflow point in Göteborg Harbour on the Swedish west coast. The river is an important waterway and serves as fresh-water supply for 700 000 users. Turbidity is utilised as an indicator to ensure sufficient quality of the intake water to the treatment plant. The overall objective of the study was to investigate the influence of rainfall, surface runoff, and river water flow on the temporal and spatial variability of the turbidity in the regulated river system by employing statistical analysis of an extensive data set. Six-year long time series of daily mean values on precipitation, discharge, and turbidity from six stations along the river were examined primarily through linear correlation and regression analysis, combined with nonparametric tests and analysis of variance. The analyses were performed on annual, monthly, and daily basis, establishing temporal patterns and dependences, including seasonal changes, impacts from extreme events, influences from tributaries, and the spatial variation along the river. The results showed that there is no simple relationship between discharge, precipitation, and turbidity, mainly due to the complexity of the runoff process, the regulation of the river, and the effects of lake Vänern and its large catchment area. For the river Göta Älv, significant, positive correlations between turbidity, discharge, and precipitation could only be found during periods with high flow combined with heavy rainfall. Local precipitation does not seem to have any significant impact on the discharge in the main river, which is primarily governed by the precipitation at catchment scale. The discharge from the lake Vänern determines the base level for the turbidity in the river, whereas local surface runoff and tributary discharge induced by rainfall govern the temporal variability in turbidity. Autocorrelation analysis indicates a temporal persistence in turbidity of about 10 days. The results also show that erosion in the main river, from the river bed and banks, is not a dominant contributor to the suspended sediment transport in the river. Further studies on the correlation between turbidity and suspended sediment transport and in relation to erosion processes are suggested
Purpose Numerous sites contaminated with fiber emissions from pulp and paper industries are found in coastal areas of the Baltic Sea, but there is limited knowledge about the magnitude of dispersal of persistent organic pollutants (POPs) from these anthropogenic, organic-rich sediments called fiberbanks. The aim of this study was to quantify and compare different POP dispersal pathways from such fiberbanks. Dispersal mechanisms studied included abiotic and biotic routes (dissolved in water, particle-bound, and bioaccumulation). Materials and methods Contaminated fibrous sediments located in Ångermanälven River estuary in north-eastern Sweden were studied in sediment types representing different fiber content (i.e., fiberbanks, fiber-rich sediments, and less fiber impacted sediments). Sediment-to-water fluxes of dissolved contaminants (polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), and dichlorodiphenyltrichloroethane (DDT)) were measured in situ using benthic flux chambers. Particle resuspension was measured by sampling bottom water, before and after disturbing the sediment surface. Benthic biota was collected to determine the body burden of contaminants and to determine biota-pore water accumulation factors (BAFPW) and biota-sediment accumulation factors (BSAFs). In addition, concentrations of dissolved POPs in the water column were measured in field using passive samplers. Instrumental analysis was performed using gas chromatography coupled to a triple quadrupole mass spectrometer (GC-MS/MS). Results and discussion The flux of dissolved Σ20PCBs was approximately two times higher from one of the investigated fiberbanks (3.4 ng m− 2 day− 1) compared to the other. The average particle burden of PCBs was also higher at this fiberbank after artificial disturbance (15 ng g−1 particle), which indicates that larger amounts of contaminants are likely to disperse via particle resuspension from this site compared to the other fiberbank (4.8 ng g− 1 particle). The difference might be associated with a layer of recently settled minerogenic material that covers one of the fiberbanks, which probably functions as a protective barrier. The lack of benthic biota implies that contaminant release by bioturbation is negligible in the studied fiberbanks. However, benthic biota from fiber-rich sediment showed bioaccumulation and biomagnification of contaminants. Conclusions The importance of diffusive flux from fiberbanks under undisturbed conditions became apparent when the different dispersal pathways were quantified. However, no dispersal pathway could be judged as irrelevant, since even under undisturbed conditions, advective particle transport was significant. Additionally, the uptake by biota and trophic transfer can be considerable. Quantification of dispersal routes and understanding of the relative importance of various pathways is critical for proper risk assessment and management of contaminated sediments.
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