Modelling the dynamics of fecal indicators bacteria in surface waters: a review

info:eu-repo/semantics/publishe

Residence time vs influence time

The concepts of age, residence time, exposure time and influence time provide space and time dependent quantitative measures of the rate at which watermasses and pollutants enter and/or leave a control domain. To help avoid confusion between these concepts, this paper provides clear definitions of the residence time and the influence time. The similarities and differences between them are illustrated using both a simplified 1D advection–diffusion model and a realistic two-dimensional model of the Scheldt Estuary (Belgium and the Netherlands). The residence time of a water parcel in a control domain is the time taken by this parcel to leave the control domain for the first time. The influence time is the time required to replace the water in the domain of interest by renewing water. For steady flows, the influence time is numerically identical to the age of the renewing water, but the two timescales differ for unsteady flows. The residence timemeasures the influence of a hypothetical point discharge on a control domain. In environmental studies, it provides a measure of the effectiveness of hydrodynamic processes at helping a semi-enclosed basin to recover froma local pollution event. The influence time quantifies the local influence of a tracer that would be uniformly distributed in the control domain at the initial time. It is therefore a relevant diagnostic tool in impact studies focusing on the local persistence of a pollution problem

Modelling faecal contamination in the Scheldt land–sea continuum. Part I. The Scheldt drainage network

This study developed a model simulating the seasonal and spatial variations of microbiological water quality (expressed in terms of Escherichia coli concentrations) in rivers. The model (SENEQUE-EC) consists of a microbiological module appended to a hydro-ecological model describing the functioning of the entire Scheldt drainage network. The microbiological module describes the sources of E. coli, their transport and the processes responsible for the fate of E. coli once released into the natural environment (mortality, settling and resuspension). This model differentiates the dynamics of three types of E. coli: free-floating E. coli, E. coli attached to suspended solids in the water column and E. coli present in sediments. The model was verified by comparison of its results with temporal and spatial distributions of field data in different stretches of rivers of the Scheldt drainage network. It was then used to test various scenarios involving diverse modifications in wastewater management, which was shown to be the most determining factor of microbiological water quality. Due to its low temporal resolution, the SENEQUE-EC is poorly adapted to describing the microbiological quality in areas under tidal influence. Therefore, the data of the SENEQUE-EC model were used as upstream boundary conditions to run a microbiological model with a high temporal resolution devoted to the tidal Scheldt River and Estuary (the SLIM-EC2 model).info:eu-repo/semantics/publishe

Water renewal timescales in the Scheldt Estuary

TIMOTH

Modelling Escherichia coli concentrations in the tidal Scheldt River and Estuary

Recent observations in the tidal Scheldt River and Estuary revealed a poor microbiological water quality and substantial variability of this quality which can hardly be assigned to a single factor. To assess the importance of tides, river discharge, point sources, upstream concentrations, mortality and settling a new model (SLIM-EC) was built. This model was first validated by comparison with the available field measurements of Escherichia coli (E. coli, a common fecal bacterial indicator) concentrations. The model simulations agreed well with the observations, and in particular were able to reproduce the observed long-term median concentrations and variability. Next, the model was used to perform sensitivity runs in which one process/forcing was removed at a time. These simulations revealed that the tide, upstream concentrations and the mortality process are the primary factors controlling the long-term median E. coli concentrations and the observed variability. The tide is crucial to explain the increased concentrations upstream of important inputs, as well as a generally increased variability. Remarkably, the wastewater treatment plants discharging in the study domain do not seem to have a significant impact. This is due to a dilution effect, and to the fact that the concentrations coming from upstream (where large cities are located) are high. Overall, the settling process as it is presently described in the model does not significantly affect the simulated E. coli concentrations.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Modeling Si isotopic compositions and fluxes in the Southern Ocean with a box model

info:eu-repo/semantics/nonPublishe

Isotopic model of oceanic silicon cycling: The Kerguelen Plateau case study

info:eu-repo/semantics/nonPublishe

Preliminary results of a finite element model of the ecohydrodynamics of the Scheldt estuary and the adjacent Belgian/Dutch coastal zone

info:eu-repo/semantics/nonPublishe

Modelling fecal bacteria in the Scheldt river and estuary

With its population density of over 500 inhabitants per km2, its active industrial developmentand its intensive agriculture and animal farming, the Scheldt watershed representsan extreme case of surface water and groundwater pollution which in turn hasan impact on eutrophication and the ecological functioning of the receiving coastalwaters. A Belgian interuniversity collaboration (http://www.climate.be/TIMOTHY)has recently started, aiming to better understand past, present and future changes inthe quality of surface, ground and marine waters and to relate them to changing humanactivities on the watershed. Part of the originality of the new network resides inthe coupling of existing hydrodynamical and biogeochemical models to describe thetransport and transformation of nutrients and contaminants.One of these couplings consists of connecting an ecological module to the SecondgenerationLouvain-la-Neuve Ice-oceanModel (SLIM, http://www.climate.be/SLIM).The results of a first application will be shown, where the ecological module considersthe dynamics of one fecal bacteria indicator (Escherichia coli). The power of SLIMis that it solves the governing hydrodynamical equations using finite elements on anunstructured mesh. As such it is able to accurately model the different scales in thedomain, going from the Scheldt river, over the estuary (including the special featureof sand banks being periodically submerged), to the North Sea.This modelling exercise illustrates the combined effect of hydrodynamics, mortalityand sedimentation on the abundance of E. coli in the study domain - with a resolutionthat is impossible to achieve by sampling alone. However, in order to have a reliableand accurate tool, much effort was put on data gathering and the optimal incorporationof this information (e.g. for the initial and boundary conditions, for the estimation ofmodel parameters, or for validation). In addition, the first modelling results helpedto guide future sampling campaigns such that data and modelling can be optimallyadjusted and a maximum of information can be retrieved.Although the hydrodynamical model and its coupling to an ecological module may beof scientific interest on their own, it is even more attractive that their output can beinterpreted in terms of practical needs, i.e. the abundance of fecal indicators which aredirectly related to sanitary risk and standards for water quality. In this framework, themodel is also intended for assessing the effect of different scenarios for the future, andadditional pollution indicators will also be included in the ecological module.info:eu-repo/semantics/publishe