INCORPORATING NATURAL VARIABILITY,UNCERTAINTY, AND RISK INTO WATER QUALITY EVALUATIONS USING DURATION CURVES1

ABSTRACT: Quantifying natural variability, uncertainty, and risk with minimal data is one of the greatest challenges facing those engaged in water quality evaluations, such as development of total maximum daily loads (TMDL), because of regulatory, natural, and analytical constraints. Quantification of uncertainty and variability in natural systems is illustrated using duration curves (DCs), plots that illustrate the percent of time that a particular flow rate (FDC), concentration (CDC), or load rate (LDC; “TMDL”) is exceeded, and are constructed using simple derived distributions. Duration curves require different construction methods and interpretations, depending on whether there is a statistically significant correlation between concentration (C) and flow (Q), and on the sign of the C‐Q regression slope (positive or negative). Flow DCs computed from annual runoff data vary compared with an FDC developed using all data. Percent exceedance for DCs can correspond to risk; however, DCs are not composed of independent quantities. Confidence intervals of data about a regression line can be used to develop confidence limits for the CDC and LDC. An alternate expression to a fixed TMDL is suggested as the risk of a load rate being exceeded and lying between confidence limits. Averages over partial ranges of DCs are also suggested as an alternative expression of TMDLs. DCs can be used to quantify watershed response in terms of changes in exceedances, concentrations, and load rates after implementation of best management practices.     

渭河流域生态环境对野鸭数量分布的影响

环境是动物生存的基础，人类的活动对环境所造成的影响，直接导致动物种群数量的变动。通过渭河咸阳段气候、水质、水域面积、植物等环境因素的改变对野鸭数量分布影响的调查，表明环境的恶化导致了动物的生存受到威胁，数量减少，分布区域缩小。随着环境保护意识的增强，渭河流域的水土流失，水质污染、退耕还草等环境问题逐渐得到解决，动物的生活环境不断得到改善，其种群数量、分布范围随之增加。     

长江铜陵段表层水中重金属含量及存在形态分布研究

通过测定长江铜陵段枯、丰水期江水中cu、Pb、Zn和cd不同形态的含量,分析了4种金属在江水中的存在形态分布,不同水期含量变化,水中悬浮物对金属吸附能力大小,以及近20年来含量的变化情况。结果表明,长江铜陵段江水中各重金属总量丰水期时大于枯水期,重金属各形态含量之间均有差异:丰水期时,各金属会被悬浮物以不同的方式携带进入水体中,cu、zn、Pb以活跃态和稳定态为主,Cd以活跃态为主;枯水期时,Zn主要以溶解态和稳定态为主,Pb以稳定态方式被携带,而80％的Cu、Cd是以溶解态形式存于水中。悬浮物(丰水期)对重金属的吸附能力大小顺序为Pb>Cu>Zn>Cd。与近20年江水中的重金属背景值比较,长江铜陵段重金属含量有普遍升高的趋势。     

四川省珙县地质灾害特征及其防治措施分析

本文从珙县地质灾害的分布特征、影响因素、防治措施等方面作了较为深入的分析和探讨，以期对地质灾害区划和防治有所借鉴和参考。     

黄冈市矿业经济布局研究

文章针对黄冈市矿业经济发展的需要，在充分考虑黄冈市地区经济发展，矿产资源分布，矿业经济合理布局的必要性的基础上，对黄冈市矿业经济布局作了详细深入研究，提出了“一个中心，四个矿业规划区，五类开发矿种，十个矿业基地”的布局构架，为该市矿业经济发展提供了明确的发展思路，并指出了发展重点，也为政府宏观调控和矿政管理提供了依据。     

Methods of Assessing and Achieving Normality Applied to Environmental Data

2 and particle concentrations. Results show that the analyzed transformations work well and are very useful to achieve normal distributions.     

PROFILE: Hungry Water: Effects of Dams and Gravel Mining on River Channels

/ Rivers transport sediment from eroding uplands to depositional areas near sea level. If the continuity of sediment transport is interrupted by dams or removal of sediment from the channel by gravel mining, the flow may become sediment-starved (hungry water) and prone to erode the channel bed and banks, producing channel incision (downcutting), coarsening of bed material, and loss of spawning gravels for salmon and trout (as smaller gravels are transported without replacement from upstream). Gravel is artificially added to the River Rhine to prevent further incision and to many other rivers in attempts to restore spawning habitat. It is possible to pass incoming sediment through some small reservoirs, thereby maintaining the continuity of sediment transport through the system. Damming and mining have reduced sediment delivery from rivers to many coastal areas, leading to accelerated beach erosion. Sand and gravel are mined for construction aggregate from river channel and floodplains. In-channel mining commonly causes incision, which may propagate up- and downstream of the mine, undermining bridges, inducing channel instability, and lowering alluvial water tables. Floodplain gravel pits have the potential to become wildlife habitat upon reclamation, but may be captured by the active channel and thereby become instream pits. Management of sand and gravel in rivers must be done on a regional basis, restoring the continuity of sediment transport where possible and encouraging alternatives to river-derived aggregate sources.KEY WORDS: Dams; Aquatic habitat; Sediment transport; Erosion; Sedimentation; Gravel mining     

四川花卉业的产业化发展

本文分析了四川发展花卉业的优势和存在的问题，提出了四川花卉产业化发展的指导思想与基本原则、区域布局以及应采取的对策．