Numerical simulation of pollutant diffusion and decay process after a water pollution incident in the Three Gorges Reservoir

We established a hydrodynamic model to simulate the pollutant transport and decay process in the case of a pollution incident in the sections of the Yangtze and the Jialing passing through the city area of Chongqing. The Boussinesq assumptions and the Navier-Stokes equations of incompressible fluid were applied to setting up the pollutant diffusion equations and the equations for the decay process. E. colt was taken as the example pollutant, and chloride dosage, light, temperature and ultraviolet intensity were considered in the equations for bacterial decay process. The calculated values of the fluid velocities in the two rivers agree well with corresponding measured results, indicating an ideal accuracy of the model. In simulation, the concentration of E. colt in water was assumed to be zero before the accident. The and 1.75 m/s for the Yangtze flow, and the downriver boundary was upriver boundary velocity was -1.35 m/s for the Jialing flow water depth set at 0. Simulation results show that the bacteria are transported downstream along the riverbank. A long and narrow pollutant belt develops at 12 h after the start of the accident ascribed to the quick longitudinal transfer. After the pollution sources are cut off, the pollutant concentration decreases slowly, mostly by advection and diffusion, suggesting inadequate self-purification ability of the rivers and the necessity of effective decontaminating measures in the case of a pollution incident, The model can be a useful tool for understanding the polluting situations of an improper discharge incident and evaluating the effects of decontaminating measures for the water body of the Three Gorges Reservoir.

Groundwater Contribution to Surface Water Contamination in a North German Low Land Catchment with Intensive Agricultural Land Use

The contribution of groundwater (GW) to the nitrate loads in surface waters (SW) was exemplarily studied for the river Augraben with a catchment area of 89.9 km2, located in north eastern Germany. The study uses available GW and SW quality data in order to develop a relationship between SW and GW in the Augraben catchment. The calculated ratio of base flow varies from 40% to 80% using various filtering methods of hydrograph separation methods (without taking into account the drainage) in comparison to a calculated GW infiltration of 5% - 7% applying Darcy’s law (upper unconfined aquifer). Drainage was estimated as the difference in base flow obtained through filtering methods of hydrograph separation and the Darcy’s law. Results on the basis of monitoring data and hydrograph separation in quick flow and base flow showed that during winter periods, high concentration in SW has been found parallel to periods of higher GW flow with a strong correlation between SW and GW concentrations. These findings also coincided with the non-vegetation period, i.e. low nitrogen uptake by plants. Overall, nitrate-nitrogen loads at the SW monitoring point (Bei Lindenberg represents the 85% area of the catchment) were 193.5, 97.72, and 122 tons for the year 2010, 2011 and 2012 respectively. Measured GW concentrations in the catchment differ strongly, depending on land use, with elevated concentrations in agricultural areas compared to monitoring points in grass land and in forest areas. In one GW monitoring station, NO3 concentrations exceed the maximum permissible limits (MPL) according to EU water quality standards (MPL = 50 mg/l NO3), up to factor two. High ammonia concentrations at another station may be due to excessive application of manure. The contribution of the different sub-catchments to nitrate load in SW can be ranked in decreasing order in Zone B, D, A and C. Drainage and interflow proved to be a major contributor with 55% - 65% of total load in SW. With the applied method a robust estimation of GW contribution to nitrate loads is feasible using typically available monitoring data of German environmental authorities.

Estimation of Pollutant Loads in Ardila Watershed Using the SWAT Model

Abstract： Excess of organic matter and nutrients in water promotes eutrophication process observed in the Ardila River. It was classified as much polluted being critical for Alqueva-Pedrogāo System. The aim of this study was to estimate the transported nutrients loads in a transboundary watershed using the SWAT （soil and water assessment tool） model and to determine the contribution of nutrients load in the entire watershed. Ardila watershed is about 3,711 km^2 extended from Spain （78%） to the eastern part of Portugal （22%）. It was discretized into 32 sub-basins using automated delineation routine, and 174 hydrologic response units. Monthly average meteorological data （from 1947 to 1998） were used to generate daily values through the weather generator Model incorporated in SWAT. Real daily precipitation （from 1931 to 2003） was introduced. The model was calibrated and verified for flow （from 1950 to 2000） and nutrients （from 1981 to 1999）. Model performance was evaluated using statistical parameters, such as NSE （Nash-Sutcliffe efficiency） and root mean square error （R2）. Calibration and verification flow results showed a satisfactory agreement between simulated and measured monthly date from 1962 to 1972 （NSE = 0.8; R^2 = 0.9）. The results showed that the most important diffuse pollution comes from the two the main tributary （Spain）. The estimated nitrogen and phosphorous loads contribution per year was respectively 72% and 59% in Spain and 28% and 41% in Portugal. The SWAT model was revealed to be a useful tool for an integrated water management approach that might be improved taking into count the WFD （water framework directive）.

Case Study of Atmospheric Pollutant Diffusion Data Based on Gaussian Model

Air pollution as one of the major environmental issues in modern society,has already brought severe impact to human life and production,thus it is an urgent task for studying environmental and ecological science to solve this issue that has bothered human society for the last centuries.Scientists have endeavored to figure out the laws of atmospheric pollutant diffusion using various mathematical models and statistical models,and drawn some precious conclusions.This paper explored the basic model of atmospheric diffusion—modeling and solution of Gaussian Diffusion Model,clarify its principles and operation forms,then applied the model into the PM_(2.5) atmospheric diffusion cases,make the program planning base on the results of model calculation,and get the final conclusion.

High-precision parallel computing model of solute transport based on GPU acceleration

The scenario simulation analysis of water environmental emergencies is very important for risk prevention and control,and emergency response.To quickly and accurately simulate the transport and diffusion process of high-intensity pollutants during sudden environmental water pollution events,in this study,a high-precision pollution transport and diffusion model for unstructured grids based on Compute Unified Device Architecture(CUDA)is proposed.The finite volume method of a total variation diminishing limiter with the Kong proposed r-factor is used to reduce numerical diffusion and oscillation errors in the simulation of pollutants under sharp concentration conditions,and graphics processing unit acceleration technology is used to improve computational efficiency.The advection diffusion process of the model is verified numerically using two benchmark cases,and the efficiency of the model is evaluated using an engineering example.The results demonstrate that the model perform well in the simulation of material transport in the presence of sharp concentration.Additionally,it has high computational efficiency.The acceleration ratio is 46 times the single-thread acceleration effect of the original model.The efficiency of the accelerated model meet the requirements of an engineering application,and the rapid early warning and assessment of water pollution accidents is achieved.

Diffuse pollution: A hidden threat to the water environment of the developing world

This Special Section collects eight articles from the 16th IWA International Conference on Diffuse Pollution and Eutrophication （16th DIPCON）, which was held in Beijing on 18 to 23 August, 2013. These articles focus on the diffuse pollution problems encountered in the development process.

Ecotoxicological assessment of diffuse pollution using biomonitoring tool for sustainable land use in Thailand

As a developing country, Thailand has a significant issue with diffuse pollution of the soil ecosystem due to an indiscriminate use of agrichemicals and poorly regulated disposal of a wide variety of hazardous wastes. Practical risk assessment tools based on locallyoccurring species are needed to assess the effects of diffuse pollutants on the soil ecosystem in Thailand because reliance on soil criteria developed for overseas conditions may provide inadequate protection. Native soil organisms in Thailand may be more or less sensitive to contaminants compared to overseas test species. This article described a biological indicator approach for ecological risk assessment of diffuse pollution in the soil ecosystem of Thailand from pesticide application with the aim of developing standardized protocols using native species and locally generated data to better evaluate the ecological risks of non-point source soil pollution. It was found that ecotoxicological assessment provided a better understanding of the ecological impacts that diffuse pollution induced on Thai environmental conditions. Thai soil biota species were more sensitive to soil contaminants than similar species overseas. Soil series also had an influence on the ecotoxicology of contaminants to soil biota. Collembolan, Cyphoderus sp., was demonstrated as a useful alternative test species to Folsomia candida （international test species） for terrestrial ecotoxicological testing of Thai soils. In addition, the soil biota activities such as soil respiration and earthworm avoidance including soil biodiversity and the litter bag decomposition technique are also good tools to assess the effects of diffuse pollution by pesticides on the soil ecosystem of Thailand.

Suitability of common models to estimate hydrology and diffuse water pollution in North-eastern German lowland catchments with intensive agricultural land use

Various process-based models are extensively being used to analyze and forecast catchment hydrology and water quality. However, it is always important to select the appropriate hydrological and water quality modeling tools to predict and analyze the watershed and also consider their strengths and weaknesses. Different factors such as data availability, hydrological, hydraulic, and water quality processes and their desired level of complexity are crucial for selecting a plausible modeling tool. This review is focused on suitable model selection with a focus on desired hydrological, hydraulic and water quality processes(nitrogen fate and transport in surface, subsurface and groundwater bodies) by keeping in view the typical lowland catchments with intensive agricultural land use,higher groundwater tables, and decreased retention times due to the provision of artificial drainage. In this study, four different physically based, partially and fully distributed integrated water modeling tools, SWAT(soil and water assessment tool), SWIM(soil and water integrated model),HSPF(hydrological simulation program– FORTRAN) and a combination of tools from DHI(MIKE SHE coupled with MIKE 11 and ECO Lab), have been reviewed particularly for the Tollense River catchment located in North-eastern Germany. DHI combined tools and SWAT were more suitable for simulating the desired hydrological processes, but in the case of river hydraulics and water quality, the DHI family of tools has an edge due to their integrated coupling between MIKE SHE, MIKE 11 and ECO Lab. In case of SWAT, it needs to be coupled with another tool to model the hydraulics in the Tollense River as SWAT does not include backwater effects and provision of control structures. However, both SWAT and DHI tools are more data demanding in comparison to SWIM and HSPF. For studying nitrogen fate and transport in unsaturated, saturated, and river zone, HSPF was a better model to simulate the desired nitrogen transformation and transport processes. However, for nitrogen dynamics and transformations in shallow streams, ECO Lab had an edge due its flexibility for inclusion of user-desired water quality parameters and processes. In the case of SWIM, most of the input data and governing equations are similar to SWAT but it does not include water bodies(ponds and lakes), wetlands and drainage systems. In this review, only the processes that were needed to simulate the Tollense River catchment were considered, however the resulted model selection criteria can be generalized to other lowland catchments in Australia, North-western Europe and North America with similar complexity.

Fully integrated approach： an alternative solution of coupling a GIS and diffuse pollution models

As a tool for management, query, visualization and analysis of spatially referred information, GIS has been recognized as a method to aid the modeling of diffuse pollution and visualize the results in a spatial context. A common question in integrating diffuse pollution models and GIS is to choose a suitable coupling approach, in which the feature of diffuse pollution models should be taken into account. In this paper, we report on our experience in coupling a distributed diffuse pollution model with a GIS. A prototype of fully integrated system is developed in this paper. This system has high flexibility, extendibility and great data management efficiency. Differences in applicability of loose coupling, tight coupling and fully integrated approaches are addressed. It is concluded that the fully integrated approach can avoid tanglesome data exchange and routine execution and more robust than loose and tight coupling approaches and is suitable for distributed diffuse pollution modes.

Forecasting the effects of EU policy measures on the nitrate pollution of groundwater and surface waters

We used the interdisciplinary model network REGFLUD to predict the actual mean nitrate concentration in percolation water at the scale of the Weser river basin （Germany） using an area differentiated （100 m × 100 m） approach. REGFLUD combines the agro-economic model RAUMIS for estimating nitrogen surpluses and the hydrological models GROWA/DENUZ for assessing the nitrate leaching from the soil. For areas showing predicted nitrate concentrations in percolation water above the European Union （EU） groundwater quality standard of 50 mg NO3-N/L, effective agri-environmental reduction measures need to be derived and implemented to improve groundwater and surface water quality by 2015. The effects of already implemented agricultural policy are quantified by a baseline scenario projecting the N-surpluses from agricultural sector to 2015. The REGFLUD model is used to estimate the effects of this scenario concerning groundwater and surface water pollution by nitrate. From the results of the model analysis the needs for additional measures can be derived in terms of required additional N-surplus reduction and in terms of regional prioritization of measures. Research work will therefore directly support the implementation of the Water Framework Directive of the European Union in the Weser basin.

Classification of different sustainable flood retention basin types

Using a revised version of a previously published expert classification system, a database of potential Sustainable Flood Retention Basins has been developed for Scotland. The research shows that the majority of small and former （often old） drinking water reservoirs are kept full and their spillways are continuously in operation. Utilising some of the available capacity to contribute to flood control could significantly reduce the costs of complying with the European Union Flood Directive. Furthermore, the application of a previously developed classification model for Baden in Germany for the Scottish data set showed a lower diversity for basins in Scotland due to less developed infrastructure. The classification system appears to be robust and has the potential, with minor modifications, to be applied across Europe. The principle value of this approach is a clear and unambiguous categorisation, based on standard variables, which can help to promote communication and understanding between stakeholders.

Experimental study of water and dissolved pollutant runoffs on impervious surfaces

The water and dissolved pollutant runoffs on impervious surfaces are the essential factor to be considered in design methods to minimize the impacts of the diffuse water pollution. In this paper, experiments are conducted to study the water and dissolved pollutant runoffs on impervious surfaces for different rainfall intensities and surface roughnesses. It is shown that a larger rainfall intensity and a smaller surface roughness reduce the time of concentration and increase the pollutant transport rate. Most of the pollutant runoffs take place at the initial stage of the rainfall. The pollutant transport rate rapidly reaches a peak and then gradually drops to zero.