Multiple lines of evidence to identify the sources of fecal pollution at a freshwater beach in Hamilton Harbour, Lake Ontario

Multiple microbial source-tracking methods were investigated to determine the source of elevated Escherichia coli levels at Bayfront Park Beach in Hamilton Harbour, Lake Ontario. E. coli concentrations were highest in wet foreshore sand (114,000 CFU/g dry sand) and ankle-depth water (177,000 CFU/100mL), declining rapidly in deeper waters. Many gull and geese droppings were enumerated each week on the foreshore sand within 2m of the waterline. Both antimicrobial resistance analysis and rep-PCR DNA fingerprinting of E. coli collected at the beach and nearby fecal pollution sources indicated that E. coli in sand and water samples were predominantly from bird droppings rather than from pet droppings or municipal wastewater. Both methods indicated a trend of decreasing bird contamination, and increasing wastewater contamination, moving offshore from the beach. When foreshore sand was treated as a reservoir and secondary source of E. coli, waterborne E. coli were found to be more similar to sand isolates than bird or wastewater isolates out to 150 m offshore. Multiple lines of evidence indicated the importance of bird droppings and foreshore sand as primary and secondary sources of E. coli contamination in beach water at Bayfront Park.     

Microbial source tracking using host specific FAME profiles of fecal coliforms

The objective of this study was to investigate the host-specific differences in fatty acid methyl ester (FAME) profiles of fecal coliforms (FC). A known-source library was constructed with 314 FC isolates cultured from 6 possible sources of fecal pollution; 99 isolates from sewage; 29 from bovine; 29 from poultry; 50 from swine; 46 from waterfowl; and 61 from deer. It was found that the hydroxy FAMEs 12:0 2 OH, 12:03 OH, and 14:02 OH were exclusively associated with isolates of human origin. On the other hand, 3 saturated FAMEs, 10:0, 15:0, and 18:0 were found only in isolates from non-human sources, 15:0 being associated with livestock samples only. In addition to the presence of these signature FAMEs, the mean relative masses of 16:1 omega7c and 16:1 ISO/14:03 OH were significantly different between the isolates of human and non-human origins. A linear discriminant function differentiated FC isolates of human origin from those of livestock and wildlife origin at 99% accuracy. These results strongly suggest that the FAME profiles of FC show statistically significant host specificity and may have the potential to be used as a phenotypic microbial source tracking tool.     

Comparison of the efficacy of an existing versus a locally developed metabolic fingerprint database to identify non-point sources of faecal contamination in a coastal lake

A comparison of the efficacy of an existing large metabolic fingerprint database of enterococci and Escherichia coli with a locally developed database was undertaken to identify the sources of faecal contamination in a coastal lake, in southeast Qld., Australia. The local database comprised of 776 enterococci and 780 E. coli isolates from six host groups. In all, 189 enterococci and 245 E. coli biochemical phenotypes (BPTs) were found, of which 118 and 137 BPTs were unique (UQ) to host groups. The existing database comprised of 295 enterococci UQ-BPTs and 273 E. coli UQ-BPTs from 10 host groups. The representativeness and the stability of the existing database were assessed by comparing with isolates that were external to the database. In all, 197 enterococci BPTs and 179 E. coli BPTs were found in water samples. The existing database was able to identify 62.4% of enterococci BPTs and 64.8% of E. coli BPTs as human and animal sources. The results indicated that a representative database developed from a catchment can be used to predict the sources of faecal contamination in another catchment with similar landuse features within the same geographical area. However, the representativeness and the stability of the database should be evaluated prior to its application in such investigation.     

Numerical investigation of airflow pattern and particulate matter transport in naturally ventilated multi-room buildings

This study reports on a numerical investigation of transport behavior of indoor airflow and size-dependent particulate matter (PM) in multi-room buildings. An indoor size-dependent PM transport approach, combining the Eulerian large-eddy simulation of turbulent flow with the Lagrangian particle trajectory tracking, was developed to investigate indoor airflow pattern and PM1/PM2.5/PM10 removal efficiency in naturally ventilated multi-room buildings. A displacement ventilation with a measured indoor PM10 profile in Taipei Metropolis as the initial condition was carried out to characterize spatial and temporal variations of indoor PM1/PM2.5/PM10 removal behavior. The effects of indoor airflow pattern on particle transport mechanisms, e.g., deposition, suspension, migration and escape, were analyzed. Two comparison scenarios, which considered the effects of no indoor partition and different air change rate, respectively, were also conducted. In comparison with the effectiveness of PM1/PM2.5/PM10 removal, the simulated results showed that coarse particles were easier to be removed out of the building than fine particles. Natural ventilation was not an effective way to remove fine particles such as PM1 and PM2.5 in a multi-room building. Indoor partitions can impede 12% of the mean streamwise velocities and significantly increase 30-50% turbulence intensities. However, indoor partitions increased particle deposition and decreased particle escape. As a result of the two opposite particle removal mechanisms, i.e., deposition and escape, the impact of indoor partitions on PM1/PM2.5/PM10 removal behavior was not as significant as the results of airflow velocities. PRACTICAL IMPLICATIONS: This work developed a computational fluid dynamics technique to investigate indoor airflow patterns and PM1/PM2.5/PM10 removal ability in ventilated multi-room buildings. The results of this paper can help to identify adequate PM1/PM2.5/PM10 cleaning procedure and provide useful size-dependent PM control strategy in multi-room buildings.     

Quo vadis source tracking? Towards a strategic framework for environmental monitoring of fecal pollution

Advances in microbial source tracking (MST) have largely been driven by the need to comply with water quality standards based on traditional indicator bacteria. Recently, a number of culture-independent, and library-independent methods based on polymerase chain reaction (PCR) have been gaining popularity among source trackers. However, only a limited number of these methods have been successfully used in field applications, primarily due to the fact that many of them are still being developed. In this critical outlook, we examine different viewpoints associated with the practical use of MST to identify critical research gaps, propose a priority-based timeline to address them, and outline emerging technologies that will likely impact the future of source tracking. We propose that it is necessary to consider each of these aspects in order to advance towards a unifying framework in source identification, so that fecal pollution monitoring can be reliably used for comprehensive environmental microbial monitoring, to develop risk assessment models, and to implement and validate adequate management practices.     

水力压裂中多孔岩体的等效弹性常数应用

水力压裂调研结果认为，地下岩体中所含随机分布孔隙能够影响水力压裂的造缝过程。将多孔岩石的孔隙简化成规则排列的球形孔洞，采用渐近均匀化方法建立了等效弹性常数随孔隙比变化的关系；与基于Budiallsky自治理论得到的有效弹性常数进行比较，两曲线能较好地吻合；为水力压裂法准确地预测出水力压裂的造缝结果提供了可行方案。     

沥青混凝土路面车辙的成因分析与防治

分析了沥青混凝土路面车辙的形成原因和产生车辙的主要因素，从沥青类型、用量、矿料级配、空隙率等方面介绍了车辙的施工预防措施，提出了避免产生车辙的方法，以供工程实践选用。     

车辙的成因及控制指标

介绍了车辙的种类，分析了发生车辙的原因，阐述了车辙控制指标的计算以及车辙深度的控制标准，从而为公路建设者提供理论指导。     

Relationships between Bacteroides 16S rRNA genetic markers and presence of bacterial enteric pathogens and conventional fecal indicators

Occurrence and prevalence of different bacterial enteric pathogens as well as their relationships with conventional (total and fecal coliforms) and alternative fecal indicators (host-specific Bacteroides 16S rRNA genetic markers) were investigated for various water samples taken from different sites with different degrees of fecal contamination. The results showed that a wide range of bacterial pathogens could be detected in both municipal wastewater treatment plant samples and in surface water samples. Logistic regression analysis revealed that total and human-specific Bacteroides 16S rRNA genetic markers showed significant predictive values for the presence of Escheriachia coli O-157, Salmonella, heat-labile enterotoxin (LT) of enterotoxigenic E. coli (ETEC), and heat-stable enterotoxin for human (STh) of ETEC. The probability of occurrence of these pathogenic bacteria became significantly high when the concentrations of human-specific and total Bacteroides 16S rRNA genetic markers exceeded 10(3) and 10(4) copies/100 mL. In contrast, Clostridium perfringens was detected at high frequency regardless of sampling sites and levels of Bacteroides 16S rRNA genetic markers. No genes related to Shigella spp., Staphylococcus aureus and Vibrio cholerae were detected in any samples analyzed in this study. Conventional indicator microorganisms had low levels of correlation with the presence of pathogens as compared with the alternative fecal indicators. These results suggested that real-time PCR-based measurement of alternative Bacteroides 16S rRNA genetic markers was a rapid and sensitive tool to identify host-specific fecal pollution and probably associated bacterial pathogens. However, since one fecal indicator might not represent the relative abundance of all pathogenic bacteria, viruses and protozoa, combined application of alternative indicators with conventional ones could provide more comprehensive pictures of fecal contamination, its source and association with pathogenic microorganisms.     

一类时滞四种群捕食被捕食系统的全局稳定性

对四种群的捕食-被捕食模型,利用解的存在性定理、正性定理、上下解方法和相应的单调迭代序列,研究了一类具有时滞的非线性反应扩散系统的牛曼初边值问题,得到了解的存在性和平衡态方程正解的全局渐近稳定性的充分条件.这个结果隐含着捕食-被捕食系统的共存是持久的,平凡解和所有半平凡解是不稳定的.