The geographic distribution of small dams in Oregon using ecoregion and landform classification

Abstract

Small dams fragment river landscapes, disrupting channel connectivity and impacting water quality and quantity. Although they impound volumetrically less total water than large dams, the ubiquity of small dams suggests their cumulative impacts could be significant. Documenting the distribution and characteristics of small dams is necessary to understanding and mitigating their impacts. In this study, we compare datasets of small dams in Oregon, compile a new comprehensive dataset, and document geographic variations in small dam distributions between different ecoregions. We used Oregon Water Resources Department dam and Oregon Department of Fish and Wildlife fish passage barrier datasets to compare dam heights and contributing drainage areas between different ecoregions. Over 61% of Oregon’s land area is above one or more small dam. We highlight the location of Oregon’s small dams at valley margins, transition zones between flat plains and mountains, and areas of high population density. Given the hidden nature of small dams, evaluation of small dam impacts using public imagery is not effective. However, knowledge of small dam distributions given their association with landforms can aid in finding unrecorded dams, assessing approaches for evaluating their geomorphic impacts, and informing their management.     

Understanding interlinkages between long-term trajectory of exposure and vulnerability,path dependency and cascading impacts of disasters in Saint-Martin (Caribbean)

This empirical and interdisciplinary study investigates the contribution of deeply enrooted social-political factors to the accumulation of exposure and vulnerability and amplification of cascading impacts of disasters, with implications on the creation and reinforcement of path dependency maintaining social-ecological systems on a maladaptive trajectory. Applying the Trajectory of Exposure and Vulnerability approach to Saint-Martin (Caribbean), we more specifically highlight how the causal chain linking historical geopolitical and political-institutional drivers to legal, economic, demographic, sociocultural, planning-related and environmental drivers, created the accumulation of exposure and vulnerability over time and contributed to the propagation and amplification of the impacts of tropical cyclones Irma and José in 2017. We find that historical social-political dynamics involving unsustainable development and settlement patterns, the weakness of local institutions, population mistrust in public authorities, high social inequalities and environmental degradation maintained Saint-Martin on a maladaptive trajectory through powerful reinforcing mechanisms operating both between and during cyclonic events. This study demonstrates that long-term interdisciplinary approaches are required for a better understanding of path dependency and the identification of levers to break it in risk-prone contexts. In Saint-Martin, breaking path dependency requires the alignment of local institutional capacities with national risk reduction policies, the promotion of social justice and involvement of local communities in decision making. This study therefore confirms the relevance of backward-looking approaches to support forward-looking climate adaptation.     

Ecological quality assessment of small estuaries from the Portuguese coast based on fish assemblages indices

The importance of establishing the ecological quality of estuarine systems has been widely acknowledged and led to the development of several fish community-based multimetric indices. Nevertheless, a question rose about the accuracy of these tools when natural disturbance is acting upon the organization of the systems’ communities. Four multimetric indices were used to examine their ability to differentiate the ecological status of five small estuarine systems (southern Portugal), and also to test if they reflected the level of anthropogenic pressures. Fish assemblages from Mira, Odeceixe and Aljezur (in the Southwest coast), Gilão and Bensafrim (in the South coast) estuaries were sampled seasonally for one year, and anthropogenic sources of pressure were identified and quantified. We found that although the applied indices provided information on ecological condition differentiation among systems, they are unable to explain different classes of ecological status in systems with equivalent pressure levels.     

霍山皖33井水位与"霍山窗"小震活动关系的初步研究

分析了霍山皖33井水位变化与"霍山窗"地震活动的关系:首先采用差分法和从属函数等方法对水位数据进行处理,提取了水位的短期异常,结果表明该井水位异常对霍山以及周边地区的中小地震有较好的反映;其次,通过对该井水位与"霍山窗"小震活动性的对比研究,发现该地区小地震在水位低值时活跃.参考该地区的环境剪应力,我们认为霍山皖33井...     

青藏块体东北缘中强地震前小震频度异常研究

1980年以来青藏块体东北缘共发生26次M_S5.0以上地震,其中22次在时间和空间上相对独立。 通过系统研究这22次中强地震前其邻区小震活动的增强现象,发现有17次中强地震前存在比较明显的小震增强现象。 虽然小震增强现象在多数中强地震前存在,但是利用小震活动的增强对未来中强地震的预测比较困难。 文中结合青藏块体东北缘小震活动的特点,尝试提出根据小震活动空间格局是否改变统计小震频度的方法,并且进行了初步的应用。 结果表明: 利用新方法统计小震的频度更能突出中强地震前的小震频度异常,并且中强地震前的小震频度异常幅度受空间范围大小的影响不大,能够有效的提取青藏块体东北缘中强地震前的中短期异常指标。     

小旋转椭球粒子群的微波衰减系数与雷达反射率因子之间的关系

通过模拟及取样导出了小旋转椭球粒子群旋转轴呈 3种不同取向 ,而入射电磁波分别为水平发射水平偏振波及水平发射垂直偏振波时的衰减系数与雷达反射率因子之间的关系 ,获得 3种波长的具体表达式 ,并对结果作了物理分析。所得结果可直接用于雷达定量测量降水时的衰减订正。     

小当量激发的远距离信号检测研究

为了研究利用小当量震源进行远距离探测的可能性,通过现场试验进行了研究.野外实验采用1次大当量激发和16次小当量激发,研究结果表明：①有可能利用数十公斤当量的炸药实现200km距离的探测;②在激发条件相同（或相近）时,不同当量的激发波形滤波后存在一定的相似性;③依据人工震源可重复性采用以下的激发组合方式和处理方法能够有效提高信噪比：针对大当量激发与小当量激发波形的相似性,利用大当量激发的波形作模板与小当量激发的波形作相关,可判断台站是否接受到小当量激发的信号并检测其震相到时信息.针对小当量激发波形的相似性,采用小当量多次激发的方式,通过N次根加权叠加方法,能有效提高记录的信噪比和震相识别精度.     

1997～1998年伽师强震群小地震震源机制解系统聚类分析

用P、S波最大振幅比法计算1997~1998年伽师强震群MS2.5~3.7小地震震源机制解,对小地震震源机制解进行系统聚类分析。结果表明,伽师小地震主要以走滑和正断层为主,与该时段发生的伽师6级强震具有相似的断错性质。1997年伽师小地震主压应力P轴方位为北东或近南北向,与1997~1998年6级强震主压应力P轴方位一致。1997年4月6日6.4级和1998年8月2日6.1级两次6级正断层地震前出现地震空段现象。     

金沙江支流黑水河松新电站短须裂腹鱼（Schizothorax wangchiachii）过坝后上溯行为

鱼类过坝后的上溯行为对鱼类寻找适宜的产卵、索饵等功能性栖息地至关重要。现阶段我国大多数研究聚焦于鱼类上溯通过鱼道的游泳行为量化,而过坝后的上溯行为分析鲜有报道。本研究在金沙江下游支流黑水河松新坝址处利用PIT(passive integrated transponder)遥测技术对松新电站过鱼对象短须裂腹鱼(Schizothorax wangchiachii)过坝后的上溯行为开展监测,考虑监测过程中水文情势变化对过坝后上溯行为的影响,采用生存分析方法,构建了耦合多因素(流量、水温、河道涨落水率、昼夜节律、肥满度等)的Cox风险比例回归模型,利用AIC模型准则筛选出最优模型参数,识别了影响鱼类过坝后上溯成功率的关键因素。结果表明:(1)短须裂腹鱼在松新鱼道的上溯效果显著优于河道;(2)水温及河道涨落率是影响短须裂腹鱼过坝后上溯效果的关键因素;(3)水温与短须裂腹鱼过坝后河道上溯成功率呈负相关,当水温超过短须裂腹鱼最适温度后,河道上溯成功率随着温度的上升呈递减趋势;河道涨落水率与短须裂腹鱼过坝后河道上溯成功率呈正相关,其中涨水情势下短须裂腹鱼河道成功上溯的概率高于落水,河道上溯成功率随着涨...     

小白洋淀水-沉积物系统多环芳烃的分布、来源与生态风险

以端村小白洋淀为研究对象,利用GC-MS测定了6个样点水、悬浮物和沉积物中15种优控多环芳烃(PAHs)的含量,分析了其组成与来源特征,探讨了不同多环芳烃单体的生态风险,结果表明:(1)15种优控多环芳烃的总含量(PAH15),水相为40.1-74.0ng/L,算术均值51.0ng/L;悬浮物为2438.0-5927.0ng/g,算术均值4528ng/g;沉积物为466.9-1366.4ng/g,算术均值为755.6ng/g;与国内外有关研究相比,污染较轻,(2)三相中均以2、3环PAHs为主,其比例均高于80%;并且,从水相、悬浮物相到沉积物相,2环PAHs依次降低,3环、4环依次升高,高环检出率和含量也依次升高,(3)沉积物中多环芳烃的来源以生物质燃料(秸秆、薪材)和煤的燃烧为主,以液体化石燃料(汽油、柴油和原油)的燃烧为辅,(4)沉积物中的芴(FLO)、菲(PHE)含量在潜在生态风险效应区间低值(ERL)与中值(ERM)之间,其生态风险几率介于10%-50%之间;其他PAHs单体的含量均低于ERL,其生态风险几率均低于10%.