INTERREGIONAL COMPARISON OF ALLUVIAL STREAM CHANNEL MORPHOLOGY: GREAT PLAINS VERSUS CENTRAL LOWLANDS1

ABSTRACT: Stream channel development is a complicated process involving many factors. A major goal of research in fluvial geomorphology is to develop an understanding of the relations between channel form, water discharge, and sediment discharge characteristics. The concept of thresholds has been introduced as an element in fluvial processes, with the implication that the factors involved in a process might change in some way as threshold boundaries are passed. This study is focused on the extent to which a particular regional boundary represents a threshold in the process of stream channel development. Twenty-four alluvial stream channels from the Great Plains region and 24 from the Central Lowlands region are compared with regard to the distributional form, central tendency and dispersion characteristics, and correlation structure of ten variables, including indicators of discharge, channel sediment, and channel morphology. The results suggest that these aspects of the data are very similar between the regions, except for certain differences in central tendency characteristics, which are assumed to reflect underlying differences between the regions in geology and climate. In general, the results support the idea that this regional boundary is not an effective threshold with respect to the stream channel development process, and that, therefore, stream channels develop in these environmentally distinct regions by way of a similar process.     

DIAGNOSTIC APPROACH TO STREAM CHANNEL ASSESSMENT AND MONITORING1

ABSTRACT: We suggest that a diagnostic procedure, not unlike that followed in medical practice, provides a logical basis for stream channel assessment and monitoring. Our argument is based on the observation that a particular indicator or measurement of stream channel condition can mean different things depending upon the local geomorphic context and history of the channel in question. This paper offers a conceptual framework for diagnosing channel condition, evaluating channel response, and developing channel monitoring programs. The proposed diagnostic framework assesses reach‐level channel conditions as a function of location in the channel network, regional and local biogeomorphic context, controlling influences such as sediment supply and transport capacity, riparian vegetation, the supply of in‐channel flow obstructions, and disturbance history. Field assessments of key valley bottom and active channel characteristics are needed to formulate an accurate diagnosis of channel conditions. A similar approach and level of understanding is needed to design effective monitoring programs, as stream type and channel state greatly affect the type and magnitude of channel response to changes in discharge and sediment loads. General predictions are made for five channel types with respect to the response of various stream characteristics to an increase in coarse sediment inputs, fine sediment inputs, and the size and frequency of peak flows, respectively. These predictions provide general hypotheses and guidance for channel assessment and monitoring. However, the formulation of specific diagnostic criteria and monitoring protocols must be tailored to specific geographic areas because of the variability in the controls on channel condition within river basins and between regions. The diagnostic approach to channel assessment and monitoring requires a relatively high level of training and experience, but proper application should result in useful interpretation of channel conditions and response potential.     

三亚电厂码头航道泥沙洄淤预测

本文从波浪掀沙和潮流输沙问题入手，对三亚电厂码头二种拟建方案的航道泥沙洄淤进行了预测。预测结果表明：航道的淤积强度呈自北向南递增的趋势，航道的南段淤积最重。在航道的北段，长山村方案淤积较重；在航道的南段，梅村方案的淤积较重。总体上看，二种方案均不属严重淤积。如果根据两种方案的洄淤分布特征对航道走向做适当调整，可望进一步改善航道的防淤效果。     

航道疏浚对珠江口附近海洋生态环境影响及预防措施

广州港航道疏浚工程中开挖和处理底泥会产生大量悬浮物，悬浮物及其含有的各种污染物将影响珠江口近海洋生态和渔业。本文主要介绍污染情况以及预防措施。通过扩散实验认为与航道疏浚工程有一定的污染，但是影响不大。通过施工前及施工期间监测结果相对照，认为航道疏浚工程对珠江口附近海洋生态环境基本没有产生大的影响，疏浚工程所采取的环保措施是极为有效的。     

一体化氧化沟固液分离和回流机理探讨

论述了一体化氧化沟中固液分离和污泥回流的基本原理，提出了固液分离器的表面负荷ＳＯＲ与污泥层厚度、回流污泥浓度等有关，计算模型为ＳＯＲ＝１１＋Ｒ·ＨｗＴ·ＣｕＣ０．固液分离器与二沉池的功效显著不同，所需面积远低于二沉池，在固液分离器内不发生污泥压缩、回流及时，不易受污泥沉降性能影响，是值得推荐的一体化氧化沟固液分离方式．     

Aggression and fighting ability are correlated in the swordtail fish Xiphophorus cortezi: the advantage of being barless

Males of the swordtail fish Xiphophorus cortezi are polymorphic for the pigment pattern vertical bars. Previous studies indicate that barred males exhibit higher levels of aggression towards males with bars than those without, while barless males fail to exhibit differential levels of aggression to either morph. In this study I matched barred and barless males for size and paired them in dyadic contests in order to determine if either morph was more dominant and if so, if dominance was the result of higher aggression levels. I found that barless males had higher bite frequencies and were able to win a majority of the contests while barred males consistently escalated to biting first, even though in most cases they were ultimately the losers. In order to determine whether the observed aggression levels and fighting abilities were inherent to being barless or a consequence of responses to the bars themselves, the dyads were re-paired once after barless males were given temporary bars and once after barred males had their bars removed. Thus, each morph encountered his opponent in both a barred and barless state. Regardless of bar state, naturally barless males continued to be more aggressive and more dominant than their barred counterparts. In addition, naturally barred males only won contests in which they bit more. These results indicate that for this species, aggression is an important component of winning contests when opponents are roughly the same size. As a result, naturally barless males as a whole appear to have higher resource holding potential (RHP) than naturally barred males of the same size because of their greater aggression levels.     

Turbulence-Based Models for Gas Transfer Analysis with Channel Shape Factor Influence

Gas transfer through surface water of streams is an effective process for the environmental quality of the aquatic ecosystem. Several theoretical approaches have been proposed to estimate gas transfer rate. This paper is devoted to present a turbulence-based model and to compare it with other 3 turbulence-based modeling frameworks that provide an estimation of gas-transfer coefficient K_L at the air-water interface. These models were derived for the reaeration process. In this paper, they have been verified both for reaeration and volatilization using experimental data collected in a laboratory rectangular flume and in a circular sewer reach. These data refer to oxygen absorption and cyclohexane volatilization, respectively. Comparison of results for oxygen shows that the tested models exhibit an average absolute difference between their results and the experimental data ranging from 12.5% and 25.6%. Also, the scaling analysis of the experimental data support both small-eddy based models and the model proposed by the authors. Moreover, volatilization results show that the process is also affected by a channel shape factor, which was, finally, quantified.     

上澳塘水体微型动物的变化及指示作用

作为水生生态系统中重要的生物组分之一,微型动物的存在与水环境状况密切相关。在以美国Probiotic Solutions公司开发的促生产品Bio-Energizer对上澳塘进行生物修复试验的过程中,发现水体中的微型动物具有从少到多,从低等到高等的变化趋势,而上澳塘水体已基本消除黑臭。