SCREENING THE RELOCATION STRATEGIES OF WATER QUALITY MONITORING STATIONS BY COMPROMISE PROGRAMMING1

Water quality monitoring network designs historically have tended to use experience, intuition, and subjective judgment in siting monitoring stations only sporadically. Better design procedures for optimizing monitoring systems with respect to multiple criteria decision analysis had rarely been put into practice up front when the needs for intensive monitoring became critical. This paper describes a systematic relocation strategy that is organized to identify several significant planning objectives and consider a series of inherent constraints simultaneously. The planning objectives considered in this analysis are designed to enhance the detection possibility for lower compliance areas, reflect the emphasis for different attainable water uses at different locations, promote the potential detection for the lower degradation areas of pollutants, increase the protection degree of those areas with higher population density in the proximity of the river system, and strengthen the pre‐warning capability of water quality for water intakes. The constraint set contains the limitations of budget, the equity implication, and the detection sensitivity in the water environment. A case study in the Kao‐Ping River Basin, South Taiwan, demonstrates the application potential of this methodology based on a seamless integration between the optimization and the simulation models. It enables identification of the optimal locational pattern stepwise using the embedded screening and sequencing capacity in a compromise programming model. However, a well calibrated and verified water quality model is an indispensable tool in support of this multiobjective evaluation. Extra sampling procedures become necessary for the sites with sparse environmental information. Comparison of planning outcomes of compromise programming is made against previously achieved analyses by using weighted programming and fuzzy programming.     

SOURCES OF VARIABILITY IN CONDUCTING PEBBLE COUNTS: THEIR POTENTIAL INFLUENCE ON THE RESULTS OF STREAM MONITORING PROGRAMS1

Pebble counts have been used for a variety of monitoring projects and are an important component of stream evaluation efforts throughout the United States. The utility of pebble counts as a monitoring tool is, however, based on the monitoring objectives and the assumption that data are collected with sufficient precision to meet those objectives. Depending upon the objective, sources of variability that can limit the precision of pebble count data include substrate heterogeneity at a site, differences in substrate among sample locations within a stream reach, substrate variability among streams, differences in when the substrate sample is collected, differences in how and where technicians pick up substrate particles, and how consistently technicians measure the intermediate axis of a selected particle. This study found that each of these sources of variability is of sufficient magnitude to affect results of monitoring projects. Therefore, actions such as observer training, increasing the number of pebbles measured, evaluating several riffles within a reach, evaluating permanent sites, and narrowing the time window during which pebble counts are conducted should be considered in order to minimize variability. The failure to account for sources of variability associated with pebble counts within the study design may result in failing to meet monitoring objectives.     

Large Woody Debris and Land Management in California’s Hardwood-Dominated Watersheds

Although large woody debris (LWD) has been studied extensively in conifer-dominated watersheds, relatively little is known about LWD in hardwood-dominated watersheds. Field surveys of 32 hardwood-dominated stream reaches in northern coastal California revealed that levels of LWD varied with land ownership and that living trees strongly influenced debris jam formation. Almost half of the channel-spanning debris jams, which stored the most wood and were most likely to form a pool, were formed behind a key piece that was still living. These living key pieces might provide greater longevity and stability than would otherwise be expected from hardwood LWD. Compared to streams on private land, streams on public land had significantly greater LWD loading and debris-jam frequency. Land management practices that remove wood from streams might be contributing to the degradation of salmonid habitat in Californias hardwood-dominated watersheds.     

Effects of Mine Drainage on Breakdown of Aspen Litter in Mountain Streams

Rates of aspen litter breakdown were measured at 40 sites in streams of the Rocky Mountains of Colorado, U.S.A. The sites encompassed a range of effects of mine drainage, from pristine (no effects) to highly stressed. The pH, concentrations of dissolved zinc, and deposition rates of metal oxides (the three main stresses from mine drainage) were measured in each stream. Rates of litter breakdown were estimated from changes in mass of aspen leaves in litterbags. The biological communities associated with litter breakdown also were evaluated by measuring the biomass of shredding invertebrates in litterbags and the rate of microbial respiration on litter. Of the stresses from mine drainage, concentration of zinc and deposition rate of metal oxides were most closely related (negatively) to rate of litter breakdown. Biomass of shredding invertebrates was also negatively related to concentration of dissolved zinc and deposition of metal oxides. Microbial respiration was negatively related to deposition rate of metal oxides and positively related to concentration of nutrients. Both shredder biomass and microbial respiration were positively related to litter breakdown rate and, together, accounted for 79% of its variation. Recovery of litter breakdown in streams affected by mine drainage requires remediation that limits both dissolved and deposited metals.     

人类面对荒漠化的问题应采取的对策

荒漠化是当今重大的全球性环境问题,困扰着人类社会的生存和发展,针对这一长期 存在的问题,提出了一些人类面对荒漠化的对策。     

AVERAGE DISCHARGE,PERENNIAL FLOW INITIATION,AND CHANNEL INITIATION ‐ SMALL SOUTHERN APPALACHIAN BASINS1

ABSTRACT: Regional average evapotranspiration estimates developed by water balance techniques are frequently used to estimate average discharge in ungaged streams. However, the lower stream size range for the validity of these techniques has not been explored. Flow records were collected and evaluated for 16 small streams in the Southern Appalachians to test whether the relationship between average discharge and drainage area in streams draining less than 200 acres was consistent with that of larger basins in the size range (> 10 square miles) typically gaged by the U.S. Geological Survey (USGS). This study was designed to evaluate predictors of average discharge in small ungaged streams for regulatory purposes, since many stream regulations, as well as recommendations for best management practices, are based on measures of stream size, including average discharge. The average discharge/drainage area relationship determined from gages on large streams held true down to the perennial flow initiation point. For the southern Appalachians, basin size corresponding to perennial flow is approximately 19 acres, ranging from 11 to 32 acres. There was a strong linear relationship (R²= 0.85) between average discharge and drainage area for all streams draining between 16 and 200 acres, and the average discharge for these streams was consistent with that predicted by the USGS Unit Area Runoff Map for Georgia. Drainage area was deemed an accurate predictor of average discharge, even in very small streams. Channel morphological features, such as active channel width, cross‐sectional area, and bankfull flow predicted from Manning's equation, were not accurate predictors of average discharge. Monthly baseflow statistics also were poor predictors of average discharge.     

EFFECTS OF ARTIFICIAL RECHARGE ON GROUND WATER QUALITY AND AQUIFER STORAGE RECOVERY1

ABSTRACT: Ground water nitrate contamination and water level decline are common concern in Nebraska. Effects of artificial recharge on ground water quality and aquifer storage recovery (ASR) were studied with spreading basins constructed in the highly agricultural region of the Central Platte, Nebraska. A total of 1.10 million m³ of Platte River water recharged the aquifer through 5000 m² of the recharge basins during 1992, 1993, and 1994. This is equivalent to the quantity needed to completely displace the ground water beneath 34 ha of the local primary aquifer with 13 m thickness and 0.25 porosity. Successful NO₃-N remediation was documented beneath and downgradient of the recharge basins, where NO₃-N declined from 20 to 2 mg L^-1. Ground water atrazine concentrations at the site decreased from 2 to 0.2 mg L^-1 due to recharge. Both NO₃-N and atrazine contamination dramatically improved from concentrations exceeding the maximum contaminant levels to those of drinking water quality. The water table at the site rose rapidly in response to recharge during the early stage then leveled off as infiltration rates declined. At the end of the 1992 recharge season, the water table 12 m downgradient from the basins was elevated 1.36 m above the preproject level; however, at the end of the 1993 recharge season, any increase in the water table from artificial recharge was masked by extremely slow infiltration rates and heavy recharge from precipitation from the wettest growing season in over 100 years. The water table rose 1.37 m during the 1994 recharge season. Resultant ground water quality and ASR improvement from the artificial recharge were measured at 1000 m downgradient and 600 m upgradient from the recharge basins. Constant infiltration rates were not sustained in any of the three years, and rates always decreased with time presumably because of clogging. Scraping the basin floor increased infiltration rates. Using a pulsed recharge to create dry and wet cycles and maintaining low standing water heads in the basins appeared to reduce microbial growth, and therefore enhanced infiltration.     

REGIONAL CHARACTERISTICS OF NUTRIENT CONCENTRATIONS IN STREAMS AND THEIR APPLICATION TO NUTRIENT CRITERIA DEVELOPMENT1

ABSTRACT: In order to establish meaningful nutrient criteria, consideration must be given to the spatial variations in geographic phenomena that cause or reflect differences in nutrient concentrations in streams. Regional differences in stream nutrient concentrations were illustrated using stream data collected from 928 nonpoint‐source watersheds distributed throughout the country and sampled as part of the U.S. EPA National Eutrophication Survey (NES). Spatial patterns in the differences were compared and found to correspond with an a priori regional classification system based on regional patterns in landscape attributes associated with variation in nutrient concentrations. The classification consists of 14 regions composed of aggregations of the 84 U.S. EPA Level III Ecoregions. The primary distinguishing characteristics of each region and the factors associated with variability in water quality characteristics are presented. The use of the NES and many other extant monitoring data sets to develop regional reference conditions for nutrient concentrations in streams is discouraged on the basis of sample representation. The necessity that all sites used in such an effort be regionally representative and consistently screened for least possible impact is emphasized. These sampling issues are rigorously addressed by the U.S. EPA Environmental Monitoring and Assessment Program (EMAP). A case‐study, using EMAP data collected from the Central and Eastern Forested Uplands, demonstrates how regional reference conditions and draft nutrient criteria could be developed.     

家用小型汽车室内多溴联苯醚(PBDEs)的检测

为了研究家用小型汽车室内多溴联苯醚(PBDEs)的存在状态,对上海市7辆使用2 a以上的不同型号家用轿车进行了调查。采集形成于车窗玻璃内表面的有机膜,采用气相色谱-质谱联用仪(GCMS)对有机模样品进行了定性及定量分析,并根据表面膜-空气分配模型计算汽车室内空气中PBDEs的质量浓度。结果表明:13种待测多溴联苯醚(PBDEs)目标化合物均被检出;在车窗玻璃内表面有机膜中,Σ13PBDEs含量为19.63~26.13 ng/m2;家用小型汽车室内空气中Σ13PBDEs质量浓度为376.61~961.24 pg/m3;由于PBDEs的正辛醇-空气分配系数KOA与PBDEs的溴代度正相关,高溴代PBDEs在有机膜中的含量较高(实测BDE-209是其最主要的污染物),而低溴代PBDEs在空气中的含量较高(BDE-28是其最主要的污染物);与家庭、办公场所、公共场所等室内环境相比,家用小型汽车室内空气中PBDEs质量浓度处于较高水平。     

风量调节方式对室内污染物浓度的影响分析

针对不同室外空气质量条件,利用MATLAB/Simulink分别对新回风比例不变、新风量不变改变回风量、回风量不变改变新风量的变风量空调系统室内PM_(2.5)质量浓度和CO2体积分数进行了模拟分析。模拟结果表明:对于新回风比例不变的系统,室内PM_(2.5)稳定质量浓度与室外PM_(2.5)质量浓度有关,而与回风量和额定回风量的比值R1无关;但室内PM_(2.5)质量浓度下降速度与R1有关。对于新风量不变改变回风量的系统,室内PM_(2.5)质量浓度主要受回风量影响。对于回风量不变改变新风量的系统,室外PM_(2.5)质量浓度和新风量是影响室内PM_(2.5)质量浓度的主要因素。