Predicting Water Quality Impaired Stream Segments using Landscape-Scale Data and a Regional Geostatistical Model: A Case Study in Maryland

In the United States, probability-based water quality surveys are typically used to meet the requirements of Section 305(b) of the Clean Water Act. The survey design allows an inference to be generated concerning regional stream condition, but it cannot be used to identify water quality impaired stream segments. Therefore, a rapid and cost-efficient method is needed to locate potentially impaired stream segments throughout large areas. We fit a set of geostatistical models to 312 samples of dissolved organic carbon (DOC) collected in 1996 for the Maryland Biological Stream Survey using coarse-scale watershed characteristics. The models were developed using two distance measures, straight-line distance (SLD) and weighted asymmetric hydrologic distance (WAHD). We used the Corrected Spatial Akaike Information Criterion and the mean square prediction error to compare models. The SLD models predicted more variability in DOC than models based on WAHD for every autocovariance model except the spherical model. The SLD model based on the Mariah autocovariance model showed the best fit (r² = 0.72). DOC demonstrated a positive relationship with the watershed attributes percent water, percent wetlands, and mean minimum temperature, but was negatively correlated to percent felsic rock type. We used universal kriging to generate predictions and prediction variances for 3083 stream segments throughout Maryland. The model predicted that 90.2% of stream kilometers had DOC values less than 5 mg/l, 6.7% were between 5 and 8 mg/l, and 3.1% of streams produced values greater than 8 mg/l. The geostatistical model generated more accurate DOC predictions than previous models, but did not fit the data equally well throughout the state. Consequently, it may be necessary to develop more than one geostatistical model to predict stream DOC throughout Maryland. Our methodology is an improvement over previous methods because additional field sampling is not necessary, inferences about regional stream condition can be made, and it can be used to locate potentially impaired stream segments. Further, the model results can be displayed visually, which allows results to be presented to a wide variety of audiences easily.     

A red water occurrence in drinking water distribution systems caused by changes in water source in Beijing,China: mechanism analysis and control measures

A red water phenomenon occurred in several communities few days after the change of water source in Beijing, China in 2008. In this study, the origin of this problem, the mechanism of iron release and various control measures were investigated. The results indicated that a significant increase in sulphate concentration as a result of the new water source was the cause of the red water phenomenon. The mechanism of iron release was found that the high-concentration sulphate in the new water source disrupted the stable shell of scale on the inner pipe and led to the release of iron compounds. Experiments showed that the iron release rate in the new source water within pipe section was over 11-fold higher than that occurring within the local source water. The recovery of tap water quality lasted several months despite ameliora- tive measures being implemented, including adding phosphate, reducing the overall proportion of the new water source, elevating the pH and alkalinity, and utilizing free chlorine as a disinfectant instead of chloramine. Adding phosphate was more effective and more practical than the other measures. The iron release rate was decreased after the addition of 1.5 mg. L-1 orthophosphate- P, tripolyphosphate-P and hexametaphosphate-P by 68%, 83% and 87%, respectively. Elevating the pH and alkalinity also reduced the iron release rate by 50%. However, the iron release rate did not decreased after replacing chloramine by 0.5-0.8 mg. L-1 of free chlorine as disinfectant.     

感潮河流的排污规划与管理模型研究

根据河流水质的差分模型,推导出一个感潮河流的排污规划与管理模型,它表现了河段上各排口允排量Ｐｊ与各排口单独排放时的允排量Ｙｊ的关系：ΣＰｊ／Ｙｊ＝１。文中用实例阐述了该模型的应用与验证情况,结果显示：该模型结构简单,容易计算,能方便地用于排污规划、管理与实时控制工作中。     

2007年京杭大运河扬州市区段和里下河段水质变化比较及对策的研究

通过对京杭大运河扬州市区段和里下河段pH、COD、DO、BOD、氨氮及石油类指标监测,分析2007年水质变化及主要污染物。得出京杭大运河扬州段主要为有机污染,里下河水质优于市区。大运河春秋季水质相对较差,夏、冬季相对好转。市区比里下河pH低0．5左右,COD含量高0．5～0．3mg·L^-1,DO含量高0．8mg·L^-1,春季BOD,含量高2．3mg·L^-1,氨氮含量高0．44mg·L^-1。因此,市区段春、秋季应重点针对削减BOD5、COD、氨氮进行水污染治理。里下河段春季针对降低COD进行治理,秋季针对降低COD、BOD5氨氮进行水污染治理。两区在夏季重点应针对提高水体中DO含量进行治理。提出的植物治理技术及管理对策措施,不仅为扬州到2010年建成生态市不断改善水环境质量,提供技术支撑和决策依据,也为如何提高具有跨流域、区域和内城河多重功能的水体水质提供启示。     

天津汉沽生物稳定塘藻类群落变化与污水净化

汉沽生物稳定塘建成后的藻类调查结果表明，随污水的净化，藻类的群落结构发生了明显变化；从入水口至生态塘出口，藻类的种类数，种类多样性指数ｄ值不断上升，出水口平均达２６．８种，累积达５６种；ｄ平均为１．４２；优势种由耐污种逐渐变为中污种；藻类的数量随污染物浓度的下降而上升，平均为４１１５５．６×１０＾４个／Ｌ。水中的ＳＳ，ＢＯＤ５，ＣＯＤ，ＮＨ３－Ｎ，ＰＯ４－Ｐ等的浓度与藻类的种类数呈直线相关，与藻类