Development of a physically-based model for transport of Cryptosporidium parvum in overland flow

Surface runoff from animal production facilities contains numerous microbial pathogens which pose a direct health hazard to both humans and animals. In order to preserve safe water resources and sustainable agriculture by reducing runoff-mediated contamination of agricultural watersheds, microbial transport processes need to be properly understood and quantified. Cryptosporidium parvum is a protozoan parasite responsible for the largest outbreak of waterborne disease ever recorded in US history. Infected mammals can pass as many as 10 billion Cryptosporidium oocysts per gram of faeces, hence only a few infected animals can potentially contaminate a large watershed. Little information is available on the environmental or physicochemical factors governing the transport of microbial pathogen in surface and near-surface runoff, in particular the zoonotic pathogen Cryptosporidium. The objective of this study is to develop a physically-based model for simulating transport of C. parvum oocysts in overland flow, and to compare the model results with experimental observations. Transport of oocysts in overland flow can be simulated mathematically by including terms for the concentration of the oocysts in the liquid phase (in suspension or free-floating) and the solid phase (adsorbed to the fine solid particles like clay and silt). Oocysts adsorption and decay processes are considered. These processes are solved using numerical techniques to predict spatial and temporal changes in oocyst concentrations in solid and liquid phases. The model results are also compared with experimental results to validate the model. The model output reproduced the recovery kinetics satisfactorily, but under-predicted the total recovery in a few cases when multiple peaks were observed during experiments. Similarly, the calibrated model produced a good agreement between observed and modeled total oocysts recovery. With future modification, this model may provide a promising tool for developing effective management practices for controlling microbial pathogens in surface runoff.     

An automatic segmentation method for moving objects based on the spatial-temporal information of video

The new MPEG-4 video coding standard enables content-based functions. In order to support the new standard, frames should be decomposed into Video Object Planes （VOP）, each VOP representing a moving object. This paper proposes an image segmentation method to separate moving objects from image sequences. The proposed method utilizes the spatial-temporal information. Spatial segmentation is applied to divide each image into connected areas and to find pre~：ise object boundaries of moving objects. To locate moving objects in image sequences, two consecutive image frames in the temporal direction are examined and a hypothesis testing is performed with Neyman-Pearson criterion. Spatial segmentation produces a spatial segmentation mask, and temporal segmentation yields a change detection mask that indicates moving objects and the background. Then spatial-temporal merging can be used to get the final results. This method has been tested on several images. Experimental results show that this segmentation method is efficient.     

High-Frequency Diel Dissolved Oxygen Stream Data Modeled for Variable Temperature and Scale

Diel dissolved oxygen (DO) concentrations and temperature were sensed at high-frequency and modeled in an eastern Iowan stream, Clear Creek, in an agricultural setting. The magnitude of the diel changes in DO and temperature were largest at the upstream (headwater) station. Inclusion of temperature change factors increased the accuracy of modeling results and yielded estimates of the reaeration rate constant, primary production rate, and respiration rate. The DO modeling of the high-frequency measurements (15-min intervals) revealed a temperature-driven nonlinear reaeration process that led to increases in nighttime DO concentrations. The DO modeling results from three sensing stations in the watershed revealed decreasing trends in primary productivity, respiration, and the reaeration rate constant with increasing drainage area. Light extinction from suspended solids was the main factor limiting net primary production. As a result, the P/R ratio also decreased with increasing drainage area. High-frequency sensor data and DO modeling revealed the effects of temperature and watershed scale on the primary factors that dictate diel DO dynamics in a stream setting.     

Integrated Two-Dimensional Surface and Three-Dimensional Subsurface Contaminant Transport Model Considering Soil Erosion and Sorption

To investigate the complex hydrological, morphodynamic, and environmental processes in watersheds, a physically-based integrated two-dimensional (2D) surface and three-dimensional (3D) subsurface model for flow, soil erosion and transport, and contaminant transport in the surface-subsurface system is presented in this paper. The model simulates the rainfall-induced surface flow by solving the depth-averaged 2D diffusion wave equation and the variably-saturated subsurface flow by solving the 3D mixed-form Richards equation. The surface and subsurface flow equations are coupled using the continuity conditions of pressure and exchange flux at the ground surface. The model uses the concept of nonequilibrium in the depth-averaged 2D simulation of nonuniform total-load sediment transport in upland fields, considering detachments by rainsplash and hydraulic erosion driven by surface flow. The integrated 2D surface and 3D subsurface contaminant transport model takes into account the contaminant changes due to sediment sorption and desorption, as well as exchanges between surface and subsurface domains due to infiltration, diffusion, and bed change. The model applies the same set of surface equations of flow, sediment, and contaminant transport for describing both upland areas and streams, so that no special treatments are required at their interface. The established model has been evaluated by comparisons with published experimental, numerical, and analytical data and then applied in an agricultural watershed. The model is suitable for wetland areas and agricultural watersheds in which streams are not very narrow and deep, and meanwhile a relatively fine mesh that can distinguish the streams is preferred.     

Sediment Fingerprinting: Review of the Method and Future Improvements for Allocating Nonpoint Source Pollution

Sediment fingerprinting has been developed by researchers over the past three decades for watershed sediment transport research. Sediment fingerprinting is a method to allocate sediment nonpoint source pollutants in a watershed through the use of natural tracer technology with a combination of field data collection, laboratory analyses of sediments, and statistical modeling techniques. The method offers a valuable tool for total maximum daily load assessment to aid in developing efficient remediation strategies for pollution in watersheds. We review the methodological steps of sediment fingerprinting including classification of sediment sources in a watershed, identification of unique tracers for each sediment source, representation of sediment sources and sinks using field sampling, accounting for sediment and tracer fate during transport from source to sink, and utilization of an unmixing model to allocate sediment sources. This review places additional emphasis upon tracers used to discriminate sediment sources during past studies performed on different continents and across different physiogeographic regions. Review and analysis of tracer dependence upon watershed variables provides an additional resource for tracer selection to the community. Finally, future improvements needed for sediment fingerprinting are discussed in order to practically apply the technology for sediment nonpoint source pollution allocation within the context of total maximum daily load assessments.     

基于自适应预处理的图像分割方法

为了防止分水岭算法过分割问题,该文提出了一种基于自适应预处理的图像分割算法。该方法在分水岭算法的基础上,首先结合像素点亮度特征和空间分布特性应用自适应方法对梯度图像进行预处理。通过考察各像素点邻域中像素分类后的分布情况,来判断考察点是处于区域中心还是处于边界,并据此对考察点的梯度值进行调节。然后在预处理后的梯度图像上选定标记,将预处理后的梯度图像中大于200个像素的连通区域标定为标记。最后用分水岭分割方法对带标记的参考图像进行分割。试验结果表明,该分割方法具有良好的分割效果。     

Real-Time Watershed Delineation System Using Web-GIS

A Web-based geographic information system (GIS) that can delineate watersheds in real time was developed for use in hydrologic analysis and to support hydrologic model operation on the Internet. The system integrates a watershed delineation (WD) engine, common gateway interfaces, a Web-GIS user interface, and supports digital spatial data including vector and grid formats. The WD program utilizes a double-seed array-replacement algorithm to obtain a watershed boundary from point coordinates. The system provides a user interface for the selection of an outlet point from a map display in the Web browser using MapServer Web-GIS capability. The WD and data extraction system has been implemented for all of Indiana, with extensive verification conducted in the 2,082.7 km2 Wildcat Creek watershed in Indiana. The time to obtain results and the quality of results are acceptable for use as a real-time system for WD via the Web.     

Synthesis of water networks considering the sustainability of the surrounding watershed

This paper presents a new mathematical programming model for the optimal synthesis of recycle and reuse networks considering simultaneously the integration of the water network system and the surrounding watershed to satisfy process and environmental constraints. The model considers the optimal location of the new industrial facility to integrate its wastewater discharge to the environment with the surrounding watershed through a disjunctive formulation. The pollutants discharged for the new plant are tracked simultaneously with the other discharges to the watershed (i.e., residential, sanitary, industrial and extractions), and the natural phenomena that affect the composition of the watershed (i.e., evaporation, filtration, etc.), in addition to the chemical reactions that are carried out in the rivers. The objective function consists in minimizing the total annual cost that is constituted by the installation of the new plant cost (including the transportation for raw materials, products and services, as well as the land cost), the wastewater treatment costs (including the piping cost) and the fresh sources cost. Two example problems were used to show the applicability of the proposed methodology.     

Corrosion Deterioration in Consumer Battery Litter

Recent studies have shown that the annual rates of consumer battery litter on urban pavements can be as high as 215 batteries per hectare of pavement and 0.4 batteries per meter of curb. As littered batteries deteriorate, they release components (Ag, Ba, Cd, Cr, Cu, Hg, Li, Mn, Na, Ni, Pb, Ti, and Zn) that can be significant sources of storm-water contamination. Results of ambient environmental and laboratory-accelerated corrosion studies are presented to quantify the mechanisms that yield chemical deterioration of littered batteries. The analysis concentrates on AA size alkaline and zinc chloride/zinc carbon (ZnCl/ZnC) cells since these are the most commonly littered batteries. Results indicate that littered batteries exposed to ambient well-drained environmental conditions for more than two months will develop surface corrosion over most of their surface but fewer than 10% will be ruptured by corrosion within the first 6 months. This agrees well with field observations. Exposure under poorly drained conditions yields more rapid deterioration but it requires exposure to more aggressive conditions such as those produced by road salts to reproduce the high degree of deterioration observed in some battery litter.