1,990 research outputs found

    Identifikation von Schadstoffeinleitungen und angepasstes Design eines Monitoringnetzwerkes in Ästuaren

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    In the last decades there have been thousands of accidental pollution spills as well as intentional illegal discharges into surface waters all over the world. The identification of pollution source parameters (e.g. the source location) has often proven difficult and heavily depends on measured pollutant concentration data collected after the incident. This thesis investigates how an adapted monitoring design can improve the identification of source parameters after a spill incident, especially in the case of estuaries. Initially, the effect of the spatial and temporal monitoring design on parameter identifiability is analyzed based on a synthetic unidirectional (river) as well as a bidirectional (estuary) test case is carried out. While the transport processes in the river could be represented by an analytical solution of the 2D advection-dispersion-reaction equation, to take into account the tidal dynamics in the estuary, a numerical transport model had to be set up with the Delft3D software suite. The results of the analysis indicate that parameter dependencies exist between different source parameters, which can weaken the identifiability of the individual parameters. However, an appropriate monitoring design can improve parameter identifiability and consequently lead to more reliable parameter estimates. To identify the source parameters after potential pollution incidents, two optimization approaches were selected in this work, which were initially applied to the synthetic bidirectional test case. Both approaches achieved very good results for both perfect and noise perturbed monitoring data. Subsequently, both optimization approaches were transferred to a real-world estuary, the Thi Vai Estuary, located in South Vietnam. To simulate pollution scenarios, a 2D hydrodynamic transport model was set up in Delft3D and calibrated based on monitoring data collected in the EWATEC-COAST research project. The synthetically generated monitoring data of an optimized monitoring network were then used to identify several theoretical spill incidents in the Thi Vai Estuary. Both optimization approaches performed generally well and could correctly identify the source parameters in 80% of the considered scenarios.In den letzten Jahrzehnten kam es weltweit immer wieder zu zahlreichen UnfĂ€llen und illegalen Einleitungen, bei denen Schadstoffe in OberflĂ€chengewĂ€sser eingeleitet wurden. Die Identifikation der Einleitungsparameter (u.a. des Ortes) stellt hierbei eine große Herausforderung dar und hĂ€ngt stark von den gesammelten Konzentrationsdaten ab, die nach dem Schadstoffeintrag erhoben wurden. Daher bestand das Hauptziel der Dissertation darin, die Identifikation der Einleitungsparameter im Falle eines Schadstoffeintrags durch ein angepasstes Monitoringdesign insbesondere in Ästuaren zu verbessern. ZunĂ€chst wurde, aufbauend auf einen synthetischen Fluss- und Ästuarabschnitt, der Einfluss des rĂ€umlichen und zeitlichen Monitoringdesigns auf die Identifizierbarkeit der Einleitungsparameter analysiert. WĂ€hrend die Transportprozesse im Fluss durch eine analytische Lösung der 2D Advektions-Dispersions-Reaktions-Gleichung abgebildet werden konnten, musste fĂŒr das Ästuar zur BerĂŒcksichtigung des Tideeinflusses ein numerisches Transportmodell mit der Software Delft3D aufgebaut werden. Die Ergebnisse der Analyse zeigen, dass zwischen bestimmten Einleitungsparametern Interaktionen bestehen, die die Identifizierbarkeit der einzelnen Parameter schwĂ€chen. Ein angepasstes Monitoringdesign kann die Identifizierbarkeit allerdings verbessern und folglich zu einer zuverlĂ€ssigeren ParameterschĂ€tzung fĂŒhren. Zur Identifikation der Einleitungsparameter nach potentiellen SchadstoffeintrĂ€gen wurden in dieser Arbeit zwei verschiedene OptimierungsansĂ€tze ausgewĂ€hlt, die zunĂ€chst auf den synthetischen Ästuarabschnitt angewandt wurden. Hier konnten durch beide AnsĂ€tze sowohl fĂŒr perfekte als auch fehlerbehaftete Messdaten sehr gute Ergebnisse erzielt werden. Anschließend wurden beide OptimierungsansĂ€tze auf einen realen Ästuar, den Thi Vai Ästuar in SĂŒdvietnam ĂŒbertragen. Zur Simulation verschiedener Einleitungsszenarien wurde ein 2D hydrodynamisches Transportmodell in Delft3D aufgebaut und mit Messdaten, die im Forschungsprojekt EWATEC-COAST erhoben wurden, kalibriert. Die synthetisch generierten Monitoringdaten eines optimalen Monitoringnetzwerkes dienten anschließend zur Identifikation mehrerer theoretischer Einleitungsszenarien. Beide OptimierungsansĂ€tze zeigten gute Ergebnisse und konnten die Einleitungsparameter in 80% der betrachteten Szenarien korrekt bestimmen

    Optimizing the design of an estuarine water quality monitoring network by optimal control techniques

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    In this work, we propose a novel methodology in order to automatically optimize the location of the sampling points for a water quality monitoring network in an estuary, in such a way that any unknown pollution source can be identified (both in intensity and location) from the data supplied by those sampling points. In the central part of the article, after a rigorous mathematical formulation of the environmental problem, the full details of its numerical implementation are given. Finally, we present and analyze the results when applying the above proposed technique to study a real case in RĂ­a of Vigo (northwestern Spain).Agencia Estatal de InvestigaciĂłn | Ref. TED2021-129324B-I00Universidade de Vigo/CISU

    Solving inverse problems of unknown contaminant source in groundwater-river integrated systems using a surrogate transport model based optimization

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    The paper presents a new approach to identify the unknown characteristics (release history and location) of contaminant sources in groundwater, starting from a few concentration observations at monitoring points. An inverse method that combines the forward model and an optimization algorithm is presented. To speed up the computation, the transfer function theory is applied to create a surrogate transport forward model. The performance of the developed approach is evaluated on two case studies (literature and a new one) under different scenarios and measurement error conditions. The literature case study regards a heterogeneous confined aquifer, while the proposed case study was never investigated before, it involves an aquifer-river integrated flow and transport system. In this case, the groundwater contaminant originated from a damaged tank, migrates to a river through the aquifer. The approach, starting from few concentration observations monitored at a downstream river cross-section, accurately estimates the release history at a groundwater contaminant source, even in presence of noise on observations. Moreover, the results show that the methodology is very fast, and can solve the inverse problem in much less computation time in comparison with other existing approaches

    Integrated Assessment of Heavy Metal Contamination in Sediments from a Coastal Industrial Basin, NE China

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    The purpose of this study is to investigate the current status of metal pollution of the sediments from urban-stream, estuary and Jinzhou Bay of the coastal industrial city, NE China. Forty surface sediment samples from river, estuary and bay and one sediment core from Jinzhou bay were collected and analyzed for heavy metal concentrations of Cu, Zn, Pb, Cd, Ni and Mn. The data reveals that there was a remarkable change in the contents of heavy metals among the sampling sediments, and all the mean values of heavy metal concentration were higher than the national guideline values of marine sediment quality of China (GB 18668-2002). This is one of the most polluted of the world’s impacted coastal systems. Both the correlation analyses and geostatistical analyses showed that Cu, Zn, Pb and Cd have a very similar spatial pattern and come from the industrial activities, and the concentration of Mn mainly caused by natural factors. The estuary is the most polluted area with extremely high potential ecological risk; however the contamination decreased with distance seaward of the river estuary. This study clearly highlights the urgent need to make great efforts to control the industrial emission and the exceptionally severe heavy metal pollution in the coastal area, and the immediate measures should be carried out to minimize the rate of contamination, and extent of future pollution problems

    Weight of evidence to assess sediment quality

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    Estuaries are perhaps the most threatened environments in the coastal fringe; the coincidence of high natural value and attractiveness for human use has led to conflicts between conservation and development. These conflicts occur in the Sado Estuary since its location is near the industrialised zone of Peninsula of SetĂșbal and at the same time, a great part of the Estuary is classified as a Natural Reserve due to its high biodiversity. These facts led us to the need of implementing a model of environmental management and quality assessment, based on methodologies that enable the assessment of the Sado Estuary quality and evaluation of the human pressures in the estuary. These methodologies are based on indicators that can better depict the state of the environment and not necessarily all that could be measured or analysed. Sediments have always been considered as an important temporary source of some compounds or a sink for other type of materials or an interface where a great diversity of biogeochemical transformations occur. For all this they are of great importance in the formulation of coastal management system. Many authors have been using sediments to monitor aquatic contamination, showing great advantages when compared to the sampling of the traditional water column. The main objective of this thesis was to develop an estuary environmental management framework applied to Sado Estuary using the DPSIR Model (EMMSado), including data collection, data processing and data analysis. The support infrastructure of EMMSado were a set of spatially contiguous and homogeneous regions of sediment structure (management units). The environmental quality of the estuary was assessed through the sediment quality assessment and integrated in a preliminary stage with the human pressure for development. Besides the earlier explained advantages, studying the quality of the estuary mainly based on the indicators and indexes of the sediment compartment also turns this methodology easier, faster and human and financial resource saving. These are essential factors to an efficient environmental management of coastal areas. Data management, visualization, processing and analysis was obtained through the combined use of indicators and indices, sampling optimization techniques, Geographical Information Systems, remote sensing, statistics for spatial data, Global Positioning Systems and best expert judgments. As a global conclusion, from the nineteen management units delineated and analyzed three showed no ecological risk (18.5 % of the study area). The areas of more concern (5.6 % of the study area) are located in the North Channel and are under strong human pressure mainly due to industrial activities. These areas have also low hydrodynamics and are, thus associated with high levels of deposition. In particular the areas near Lisnave and Eurominas industries can also accumulate the contamination coming from Águas de Moura Channel, since particles coming from that channel can settle down in that area due to residual flow. In these areas the contaminants of concern, from those analyzed, are the heavy metals and metalloids (Cd, Cu, Zn and As exceeded the PEL guidelines) and the pesticides BHC isomers, heptachlor, isodrin, DDT and metabolits, endosulfan and endrin. In the remain management units (76 % of the study area) there is a moderate impact potential of occurrence of adverse ecological effects and in some of these areas no stress agents could be identified. This emphasizes the need for further research, since unmeasured chemicals may be causing or contributing to these adverse effects. Special attention must be taken to the units with moderate impact potential of occurrence of adverse ecological effects, located inside the natural reserve. Non-point source pollution coming from agriculture and aquaculture activities also seem to contribute with important pollution load into the estuary entering from Águas de Moura Channel. This pressure is expressed in a moderate impact potential for ecological risk existent in the areas near the entrance of this Channel. Pressures may also came from AlcĂĄcer Channel although they were not quantified in this study. The management framework presented here, including all the methodological tools may be applied and tested in other estuarine ecosystems, which will also allow a comparison between estuarine ecosystems in other parts of the globe

    The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations

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    Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 Όg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water

    Development of watershed-based modeling approach to pollution source identification

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    Identification of unknown pollution sources is essential to environmental protection and emergency response. A review of recent publications in source identification revealed that there are very limited numbers of research in modeling methods for rivers. What’s more, the majority of these attempts were to find the source strength and release time, while only a few of them discussed how to identify source locations. Comparisons of these works indicated that a combination of biological, mathematical and geographical method could effectively identify unknown source area(s), which was a more practical trial in a watershed. This thesis presents a watershed-based modeling approach to identification of critical source area. The new approach involves (1) identification of pollution source in rivers using a moment-based method and (2) identification of critical source area in a watershed using a hydrograph-based method and high-resolution radar rainfall data. In terms of the moment-based method, the first two moment equations are derived through the Laplace transform of the Variable Residence Time (VART) model. The first moment is used to determine the source location, while the second moment can be employed to estimate the total mass of released pollutant. The two moment equations are tested using conservative tracer injection data collected from 23 reaches of five rivers in Louisiana, USA, ranging from about 3km to 300 km. Results showed that the first moment equation is able to predict the pollution source location with a percent error of less than 18% in general. The predicted total mass has a larger percent error, but a correction could be added to reduce the error significantly. Additionally, the moment-based method can be applied to identify the source location of reactive pollutants, provided that the special and temporal concentrations are recorded in downstream stations. In terms of the hydrograph-based method, observed hydrographs corresponding to pollution events can be utilized to identify the critical source area in a watershed. The time of concentration could provide a unique fingerprint for each subbasin in the watershed. The observation of abnormally high bacterial levels along with high resolution radar rainfall data can be used to match the most possible storm events and thus the critical source area

    Improved Estimates of the Spatial Distribution and Temporal Trends of Water Quality Parameters Using Geostatistical Data Fusion Methods.

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    Strategies aimed at reducing the degradation of water quality and predicting future changes in surface waters resulting from natural and anthropogenic forcing rely on the ability to track water quality changes, and to accurately quantify the distribution of water quality attributes. The three components of this dissertation focus on developing geostatistical data fusion methods that make optimal use of the available monitoring data in the Passaic River, Lake Erie, and the Chesapeake Bay, respectively. The first component presents a method for accurately estimating the spatial distribution of the total organic carbon in the sediments of the Passaic River using a dataset with non-uniform resolution. Estimating the spatial distribution of water sediment attributes at a uniform spatial resolution is often required for site characterizations and the design of appropriate risk-based remediation alternatives. Using a pseudodata example, a noval geostatisitical downscaling approach is shown to yield better estimates with a more accurate assessment of uncertainties, relative to traditional kriging methods. When applied to the estimation of the distribution of total organic carbon, geostatistical downscaling shows that the uncertainty associated with the spatial distribution of attribute is higher than would have been assumed if a kriging approach had been applied. The second and third components explore the degradation of water quality in time and space. Specifically, hypoxia (low dissolved oxygen) has been observed in Lake Erie and Chesapeake Bay since the early 1900s, leading to negative impacts such as ecosystem habitat degradation, altered migration patterns, and decreased fishery production. The interannual variability in hypoxic extent since mid-1980s in these two systems is quantified by combining spatially explicit auxiliary data with in situ dissolved oxygen measurements. The significance of nutrient loading, weather patterns, and stratification in explaining hypoxia in these systems is also explored. This research points to strong meteorological controls on hypoxia, through impacts on stratification and nutrient loading, in addition to the impact of anthropogenic activities. Overall, the developed geostatistical data fusion methods are shown to provide a means for producing reliable estimates of water quality attributes along with their associated uncertainties.PHDEnvironmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98069/1/ytzhou_1.pd

    Estuarine suspended aggregate dynamics and characteristics

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    The research presented in this study is motivated by the need to improve prediction of sediment transport in estuaries. A novel application of the Acoustic Doppler Velocimeter (ADV) in the lower Chesapeake Bay is shown to estimate in-situ particle fall velocity at a single point without affecting the ambient turbulence. Acoustic backscatter from the ADV proved to be the best estimator of mass concentrations due to its apparent insensitivity to the size or density of muddy aggregates. Fall velocities are estimated analytically from a balance of settling and diffusive flux gradients using two methods, one employing Reynolds concentration flux, and the other estimating eddy diffusivity using the von-Karman Prandtl equation. Single elevation estimates of fall velocity using the ADV to estimate Reynolds concentration flux produced the best estimates of fall velocity, which are on the order of 1 mm/s. A novel method is presented to measure TKE production using a profiling ADV instrument that has been contaminated by boat motion. The relative importance of physical processes that determine particle size distributions differs in three mid-Atlantic U.S.A. estuaries (York R., Elizabeth R., Chesapeake Bay) with different hydrodynamics and benthic characteristics as well as in different depth regimes within each estuary. Surface particle size dynamics in all of the estuaries are affected by irregular advection events. Middepth regions in the energetic estuaries are controlled tidally by the combined processes of TKE production decreasing particle size and differential settling increasing particle size. Middepth regions in the low energy estuary are controlled by irregular resuspension and trapping at the pycnocline of large low density particles. Bottom regions in all estuaries are most strongly influenced by resuspension, tidally in the energetic estuaries and irregularly in the low energy estuary. The interrelationships between metal concentrations, particle size, percent fixed solids (PFS), chlorophyll a, and molar Carbon to Nitrogen (C/N) ratios of suspended sediment are investigated in a heavily industrialized and polluted estuary, the Elizabeth R., VA. The relationship between PFS, C/N and aggregate size are also investigated in a relatively energetic, high concentration, and undisturbed estuary, the York. R., VA. Standard paradigms of contaminant concentration relationships with particle size and particle constituents were not supported in the low energy, low concentration suspended sediments of the Elizabeth R. (Abstract shortened by UMI.)

    Tide-influenced contaminant transport in coastal aquifers

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    Coastal aquifers are distinguished from other aquifers because of tidal effects which cause complicated groundwater flow and contaminant transport phenomena in regions immediately adjacent to the coast. This study is designed to address the significance of tidal influence on contaminant transport by focusing on one-dimensional homogeneous coastal aquifers. This study formulates a conceptual model and corresponding flow and transport equations, analyzes coastal boundary conditions, solves numerically the transport equation, and uses experiments to verify the numerical results. Results of numerical and experimental studies conclude that tides can have a significant impact on contaminant transport, especially when under unconfined conditions, subject to moderate to high tidal amplitude, with low flow velocity, and within areas adjacent to the coastal boundary. Quantitatively, under these favorable conditions, contaminant discharge can be enhanced by tides by a factor of two or three during early stages of discharge, and the enhanced discharge can still be substantial during later stages by an order of 30 to 50 percent. When the groundwater flow is close to stagnant, as demonstrated in the case study, the tidal impact is most apparent, resulting in significant discharge tens of years ahead of the case without tides
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