Fragmentation of an Intermittent Stream During Seasonal Drought: Intra‐annual and Interannual Patterns and Biological Consequences

Intermittent streams lose surface flow during some portion of the year and can be important breeding and rearing habitats for stream biota. However, habitat contraction and deteriorating water quality across the summer can result in harsh conditions and mortality. We explored patterns of drying in a small intermittent stream across the summer in Mediterranean‐climate California, including across 4 years that differed in antecedent precipitation. Wet–dry mapping revealed earlier stream fragmentation following dry winters and that entire sections of the stream varied in their propensity to dry suggesting an important influence of geomorphology on drying. Within two ‘slow‐drying’ reaches, initial riffle volumes were higher following wetter winters, but the rate of riffle drying was higher following wet years, presumably because higher initial volumes resulted in greater drying capacity. Initial pool volumes were similar across years, but the rate of pool drying was faster following dry versus wet winters (pool half‐life ranged from 9.7 weeks in the driest year to 26.3 weeks in the wettest year). Stream temperature differed among years, but differences were slight, and temperatures rarely exceeded optimal conditions for trout growth. We observed limited movement of trout during drier years and found that movement was negatively associated with pool depth, riffle length and date, and positively associated with riffle volume. Overall, we found that antecedent rainfall influenced variability in pool drying more than riffle drying, that entire sections of the creek varied in their propensity to dry and that biological fragmentation preceded physical fragmentation by 3 to 7 weeks. Copyright © 2015 John Wiley & Sons, Ltd.     

城市河流生态修复技术研究

城市河流作为城市环境要素的一部分,在城市发展中发挥着不可替代的作用,但由于过去粗放式的发展模式,引发了一系列生态环境问题,导致河流生态环境受损,河流部分功能丧失,影响了城市的未来发展。本文通过对当前城市河流普遍存在的问题进行分析总结,梳理了城市河流生态修复的发展历程。在此基础上,展望了未来的研究重点,可为我国的城市河流治理提供理论借鉴。     

内河交汇处沉管隧道基槽回淤厚度研究

基槽回淤对沉管隧道平顺度影响较大,对其防水性能产生威胁。为研究两河交汇处沉管隧道基槽的回淤特性,依托如意坊沉管隧道,构建数值计算模型,对比实际监测值以验证模型的适用性,进而揭示内河交汇处沉管隧道基槽回淤规律。研究结果表明:模型中河流流速与实际监测数据误差较小,验证了模型的适用性;内河交汇处基槽淤积厚度整体呈中间大两端小、上游大下游小的规律;回淤分布受空间影响较大,基槽底脚淤积显著,且坡顶淤积厚度显著小于坡底;回淤量随时间的延长其敏感性逐渐下降;基槽开挖后,回淤均值为10 cm,将影响沉管隧道的施作,现场须采取清淤措施进行处置。研究成果为两河交汇处沉管隧道基槽回淤分析与治理提供了指导。     

宽浅河道瞬时源源项反问题及反演精度主要影响因子分析

根据宽浅河道的水动力特性和可溶性污染物在河道内的迁移转化特征,建立了宽浅河道内突发性瞬时源污染物排放位置及污染物排放量的数学反问题;采用微分进化算法,给出了反问题的数学求解方法;构造典型案例,利用瞬时源污染物浓度平面分布的理论解,对反问题求解方法进行了验证;并采用情景分析方法,进一步分析了事故应急监测点位、监测频次对污染源反演精度的影响。结果表明,反演精度依赖于监测点位的数量、监测频次等影响因子,基于一定观测数据、观测精度的污染源的数学反演,可以为瞬时源强、发生位置的确定提供技术佐证。     

福建省域河流生态流量监管与控制目标核定

通过梳理福建省河流水系基本特征及提炼总结生态流量控制断面选取原则,筛选出不同控制目标需求的4个类别44处生态流量控制断面;综合河流生态保护需求与工作基础条件,采用水文学方法分析,确定各断面生态流量控制目标。对控制断面分布密度进行检验,以及根据水资源配置格局与工程调度能力对生态流量控制目标合理性进行检验,结果表明,断面设置与生态流量控制目标成果合理有效,可以满足福建省作为国家生态文明试验区的有关生态流量监管要求。     

Cyclic perturbation of lowland river channels and ecological response

Certain lowland streams have experienced prehistorical and historical cycles of aggradation, occlusion, degradation, headward incision, and renewed aggradation. Historical cycles appear to be related to human activities. A case study is presented of the Yalobusha River in Mississippi with emphasis on the effects of blockage and removal on aquatic habitats and fish. The adjacent Skuna River, which was channelized and unblocked, was used in space for time substitution to infer effects of blockage removal on the Yalobusha. Variables describing physical aquatic habitat and fish were sampled from three groups of river reaches: unblocked channelized, channelized and blocked, and naturally sinuous. Fish collections were used to compute six indicators of ecological integrity. At baseflow, mean water depths were an order of magnitude lower in the unblocked channelized stream than for the others. In‐channel aquatic habitat volume per unit valley length was 5, 85, and 283 m³/m for the channelized, blocked channelized, and natural reaches, respectively. Mean values for all six ecological indicators were lowest for the channelized group. Species richness was greatest for the channelized blocked reach. The ecological indicators displayed gradients in response to the range of observed physical conditions. Management of corridors susceptible to the cycle described above should involve a blend of measures designed to conserve higher quality habitats.     

A new approach to estimate concentrations of alcohol ethoxylate in rivers in Japan for screening-level risk assessment

Alcohol ethoxylate (AE) is a widely used household detergent that is ubiquitous in aquatic environments. To assess and manage the risk of AE, its environmental exposure concentrations must be evaluated in rivers nationwide; however, very few AE monitoring data are currently available. Furthermore, developing a rigorous exposure model that would cover rivers nationwide would require a great deal of time, human resources, and money. We developed a new approach to estimate AE concentrations in rivers throughout Japan for screening-level risk assessment. In this approach, five-day biochemical oxygen demand (BOD₅) data were used as a surrogate indicator of the AE concentration in river water. The Tama and Nikko Rivers were ranked according to their BOD₅ data, and the AE concentrations of the Nikko River were then estimated using the Standardized Hydrology-based Assessment tool for chemical Exposure Load (AIST-SHANEL) model. For each river, the concentrations of AE in its waters were projected based on that river’s reported BOD₅ values, its ranking, the approximation formula for AE and BOD₅, and estimated AE concentrations in water of the Nikko River from the model. The accuracy of the projected values was validated by comparing the projected AE concentrations in water from the Tama River with its monitoring data. There are various technical uncertainties associated with this approach; however, our results suggest that this new approach can be applied in screening-level exposure assessment of other chemical substances that have properties similar to AE.     

Effects of variation in streamflow and channel structure on smallmouth bass habitat in an alluvial stream

We evaluated the effects of streamflow‐related changes in channel shape and morphology on the quality, quantity, availability and spatial distribution of young‐of‐year and adult smallmouth bass Micropterus dolomieu habitat in an alluvial stream, the Baron Fork of the Illinois River, Oklahoma. We developed Habitat Suitability Criteria (HSC) for young‐of‐year and adult smallmouth bass to assess changes in available smallmouth bass habitat between years, and compare predicted smallmouth bass Weighted Usable Area (WUA) with observed WUA measured the following year. Following flood events between 1999 and 2000, including a record flood, changes in transect cross‐sectional area ranged from 62.5% to 93.5% and channel mesohabitat overlap ranged from 29.5% to 67.0% in study three study reaches. Using Physical HABitat SIMulation (PHABSIM) system analysis, we found that both young‐of‐year and adult smallmouth bass habitat were differentially affected by intra‐ and inter‐annual streamflow fluctuations. Maximum WUA for young‐of‐year and adults occurred at streamflows of 1.8 and 2.3 m³ s^?1, respectively, and WUA declined sharply for both groups at lower streamflows. For most microhabitat variables, habitat availability was similar between years. Habitat suitability criteria developed in 1999 corresponded well with observed fish locations in 2000 for adult smallmouth bass but not for young‐of‐year fish. Our findings suggest that annual variation in habitat availability affects the predictive ability of habitat models for young‐of‐year smallmouth bass more than for adult smallmouth bass. Furthermore, our results showed that despite the dynamic nature of the gravel‐dominated, alluvial Baron Fork, HSC for smallmouth bass were consistent and transferable between years. Published in 2008 by John Wiley & Sons, Ltd.     

广东省典型中小河流水电站浮游植物组成与特征分析

对广东省典型中小河流的引水式和坝式水电站浮游植物的群落结构和种类组成进行了调查,结果表明,坝式电站浮游植物的种类、密度、生物量及多样性要大于引水式电站;电站坝上、坝下河段的浮游植物的物种组成和优势类群差别不大,浮游植物类群未发生明显分化,浮游植物群落内部都能够稳定发展,达到平衡状态。