Transport of adsorbing metal ions between stream water and sediment bed in a laboratory flume

The transport of adsorbing metal ions (copper, zinc, calcium and magnesium) between the water column and the sand bed in a 5 meter long recirculating laboratory flume with bottom bedforms has been investigated. A non-adsorbing tracer, lithium, was used simultaneously to observe the exchange of water between bed and water column. The presence of bedforms and associated pumping increases the exchange rate by several orders of magnitude over molecular processes. The concentrations of initially added metal ions were monitored both in the circulating overlying water and in the pore-water of the sediment bed. The sand used for the bed was composed of over 99% silica, with geometric means of 500 [microns] and 195 [microns]. Before each run, the sand was acid-washed at pH 3.5 to provide reproducible experimental conditions. The chemical composition of the recirculating water was controlled and steady flow conditions were maintained in the experiments. Batch experiments were performed to investigate the chemical partitioning of the selected metal ions to the sand grain surfaces. The adsorption of zinc onto silica was modeled in detail and binding constants were determined. The observed adsorption of the metal ions in the flume experiments compared well with batch adsorption data. The transfer of metal ions into and out of a bed covered with stationary bedforms is dominated by advective pumping caused by pressure fluctuations over the bed. A residence-time model based on pressure-driven advective flow and linear equilibrium partitioning of the pollutant to the sediment was developed and describes the observed metal ion exchange between sediment and water column well. Increased partitioning of the metal ion onto the sediment leads to an increase of the amount of tracer stored within the sediment bed. Furthermore, the concentrations of metal ions released from the bed after passing of an initial pulse in the overlying water will be lower, but longer lasting for stronger partitioning, leading to tailing in the water column for long times. For a bed with moving bedforms, the main mechanism for mass exchange is the trapping and release of overlying water by the traveling bedform. The transport of metal ions can be approximately described for the initial phase of the experiment, but large deviations from the model occur for long times. The models do not require calibration since the parameters for transport into and out of the bed can be derived from flow conditions, sediment parameters, bedform dimensions and adsorption characteristics of the tracer on the sand. Criteria for the applicability of the models and appropriate scaling variables are identified. The experimental results are presented in nondimensional form

Uncertainty study of data-based models of pollutant transport in rivers

River engineeringTransport and fate of pollutants in river

Evaluating River Water Quality Modelling Uncertainties at Multiple Time and Space Scales

Maintaining healthy river ecosystems is crucial for sustaining human needs and biodiversity. Therefore, accurately assessing the ecological status of river systems and their response to short and long-term pollution events is paramount. Water quality modelling is a useful tool for gaining a better understanding of the river system and for simulating conditions that may not be obtained by field monitoring. Environmental models can be highly unreliable due to our limited knowledge of environmental systems, the difficulty of mathematically and physically representing these systems, and limitations to the data used to develop, calibrate and run these models. The extensive range of physical, biochemical and ecological processes within river systems is represented by a wide variety of models: from simpler one-dimensional advection dispersion equation (1D ADE) models to complex eutrophication models. Gaining an understanding of uncertainties within catchment water quality models across different spatial and temporal scales for the evaluation and regulation of water compliance is still required. Thus, this thesis work 1) evaluates the impact of parameter uncertainty from the longitudinal dispersion coefficient on the one-dimensional advection-dispersion model and water quality compliance at the reach scale and sub-hourly scale, 2) evaluates the impact of input data uncertainty and the representation of ecological processes on an integrated catchment water quality model, and 3) evaluates the impact of one-dimensional model structures on water quality regulation. Findings from this thesis stress the importance of longitudinal mixing specifically in the sub daily time scales and in-between 10s of meters to 100s of meters. After the sub daily time scale, other biological and ecological processes become more important than longitudinal mixing for representing the seasonal dynamics of dissolved oxygen (DO). The thorough representation of the dominant ecological processes assists in obtaining accurate seasonal patterns even under input data variability. Furthermore, the use of incorrect model structures for water quality evaluation and regulation leads to considerable sources of uncertainty when applying duration over threshold regulation within the first 100s of meters and sub hourly time scale

Identifikation von Schadstoffeinleitungen und angepasstes Design eines Monitoringnetzwerkes in Ästuaren

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 Unfällen und illegalen Einleitungen, bei denen Schadstoffe in Oberflächengewässer eingeleitet wurden. Die Identifikation der Einleitungsparameter (u.a. des Ortes) stellt hierbei eine große Herausforderung dar und hängt 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. Zunächst wurde, aufbauend auf einen synthetischen Fluss- und Ästuarabschnitt, der Einfluss des räumlichen und zeitlichen Monitoringdesigns auf die Identifizierbarkeit der Einleitungsparameter analysiert. Während die Transportprozesse im Fluss durch eine analytische Lösung der 2D Advektions-Dispersions-Reaktions-Gleichung abgebildet werden konnten, musste für das Ästuar zur Berücksichtigung 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 schwächen. Ein angepasstes Monitoringdesign kann die Identifizierbarkeit allerdings verbessern und folglich zu einer zuverlässigeren Parameterschätzung führen. Zur Identifikation der Einleitungsparameter nach potentiellen Schadstoffeinträgen wurden in dieser Arbeit zwei verschiedene Optimierungsansätze ausgewählt, die zunächst auf den synthetischen Ästuarabschnitt angewandt wurden. Hier konnten durch beide Ansätze sowohl für perfekte als auch fehlerbehaftete Messdaten sehr gute Ergebnisse erzielt werden. Anschließend wurden beide Optimierungsansätze auf einen realen Ästuar, den Thi Vai Ästuar in Südvietnam übertragen. 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 Optimierungsansätze zeigten gute Ergebnisse und konnten die Einleitungsparameter in 80% der betrachteten Szenarien korrekt bestimmen

Continuous measurement of nitrate concentration in a highly event-responsive agricultural catchment in south-west of France: is the gain of information useful?

A nitrate sensor has been set up to measure every 10 min the nitrate signal in a stream draining a small agricultural catchment dominated by fertilized crops during a 2-year study period (2006–2008) in the south-west of France. An in situ sampling protocol using automatic sampler to monitor flood events have been used to assume a point-to-point calibration of the sensor values. The nitrate concentration exhibits nonsystematic concentration and dilution effects during flood events. We demonstrate that the calibrated nitrate sensor signal gathered from the outlet is considered to be a continuous signal using the Nyquist–Shannon sampling theorem. The objectives of this study are to quantify the errors generated by a typical infrequent sampling protocol and to design appropriate sampling strategy according to the sampling objectives. Nitrate concentration signal and flow data are numerically sampled to simulate common sampling frequencies. The total fluxes calculated from the simulated samples are compared with the reference value computed on the continuous signal. Uncertainties are increasing as sampling intervals increase; the method that is not using continuous discharge to compute nitrate fluxes bring larger uncertainty. The dispersion and bias computed for each sampling interval are used to evaluate the uncertainty during each hydrological period. High underestimation is made during flood periods when high-concentration period is overlooked. On the contrary, high sampling frequencies (from 3 h to 1 day) lead to a systematic overestimation (bias around 3%): highest concentrations are overweighted by the interpolation of the concentration in such case. The in situ sampling protocol generates less than 1% of load estimation error and sample highest concentration peaks. We consider useful such newly emerging field technologies to assess short-term variations of water quality parameters, to minimize the number of samples to be analysed and to assess the quality state of the stream at any time

An approach to mathematical models as a tool for water and air quality management

Interactions between mathematical and biological sciences have been increasing rapidly in recent years. The use of system analysis and mathematical model for formulation and solving the environmental pollution is of relatively recent vintage and has been used widely since last three decades. These models can be used to conduct numerical experiments, test hypothesis and help to understand the response of environmental pollution. A mathematical model acts as a bridge between study of mathematics and application of mathematics in environmentand other fields. Modeling is an abstraction of reality and its ultimate objective is to explore the complexity of functions and structure of the system under study. Today, a wide variety of models belonging to different nature and category are available to understand the processes of the environment around us. Various models such as WASP, CE-QUAL-ICM, QUAL W2, AQUATOX, QUAL2K, IITAQ, PEARL, GRAM, UGEM, and IITLT etc. related to water and air quality are developed so far along with their principles, intended use and applications. These models generally simulate the basic physical, chemical and biological processes. In the present study, an attempt has been made to evaluate the concept and utilization of mathematical models in air and water quality management

Application of Computational Fluid Dynamics (CFD) for Simulation of Acid Mine Drainage Generation and Subsequent Pollutants Transportation through Groundwater Flow Systems and Rivers

Many environmental problems associated with the mining industry involve the understanding and analysis of fluid or gas flow. Typical examples include groundwater flow, transport of contaminants, heat transfer, explosions, fire development and dust movements. Both experimental work and numerical models can provide the necessary information for solution of any particular problem. The long-term pyrite oxidation, acid mine drainage generation and transportation of the oxidation products are noted to be the most important problems that can be modelled in order to predict the transport of thecontaminants through groundwater and rivers flow systems, to interpret the geochemistry and achieve a better understanding of the processes involved

MIXING OF POLLUTANTS IN RIVERS

Mixing is understood as a basically physical process which is controlled by the properties of the substances involved in it. The various mixing processes in nature can broadly be grouped according to the substances (solid, fluid, gaseous). As a consequence of human activities growing quantities of pollutants can be observed which alerted international organizations. The investigation of the mixing on physical models is rather complicated due to the fact that similarity can only be achieved by using undistorted models. Reliable dispersion coefficients can be expected from the field studies. Methodology and results are demonstrated by measurements over a long Danube reach and within a city. Importance of field studies and the need of further investigations are underlined and the expected results of potential field surveys are summarized. Suggestions for international coilaborations are submitted