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。     

LONG-TERM CHANGES IN LOW-FLOW CHANNEL WIDTHS WITHIN THE SOUTH UMPQUA WATERSHED,OREGON1

ABSTRACT: Recent stream survey data (1989–1993) from 31 stream segments of 21 streams within the upper South Umpqua Watershed Oregon were compared to 1937 stream survey data collected from these same stream segments. Current low-flow wetted stream widths of 22 of the 31 surveyed stream segments were significantly different than in 1937; 19 stream segments were significantly wider while the remaining three stream segments were significantly narrower. In only 1 of 8 tributaries to the South Umpqua River which had headwaters within land designated wilderness area did low-flow stream channel width increase since 1937. Conversely, 13 of the 14 tributaries to the South Umpqua River which originated from lands designated as timber emphasis were significantly wider than in 1937. The observed change in stream width was linearly related to timber harvest (r²= 0.44), road density (r²= 0.45), and the amount of large organic debris remaining within the active stream channel (r²= 0.43). These findings suggest that timber harvest and road construction may have resulted in changes in channel characteristics. These channel changes may also be a factor in the observed decline of three of the four populations of anadromous salmonids within the basin.     

STATUS AND PROSPECTS OF KAREZ IRRIGATION1

ABSTRACT: The karez is a traditional irrigation water source, consisting of hand-dug horizontal wells, that is still used in parts of South Asia, the Middle East, and North Africa. This paper describes the construction, management, and current problems of karez irrigation systems based on investigations conducted in Baluchistan Province, Pakistan. While karezes have served irrigation needs well in the past, they are now threatened by high costs of labor for construction and maintenance, and by the encroachment of tubewells which lower the water tables on which the karez systems depend. Possible methods for improving karez performance and needs for research are discussed.     

A PROGRAM TO CALCULATE CHANNEL SCOUR AND FILL1

ABSTRACT: A computer program written in BASIC calculates net changes in stream channel cross-sections. Calculations are based on dividing the channel cross-section into discrete regions of scour and fill. Internal boundaries of these regions (along the x-axis of the cross-section) are determined by the location of vertical depth measurements taken at two distinct times. The right and left boundaries of the cross-section can be specified so that scour or fill can be calculated for any portion of the profile desired.     

狭长通道内风幕挡烟效果的数值分析

研究利用风幕阻挡通道内烟气蔓延的可能性及其效果,结合一小型狭长通道,采用数值模拟计算方法进行了初步分析.重点考察了风幕前倾角、风幕出口风速和回风口位置三个主要因素对风幕在狭长通道内挡烟效果的影响.结果表明,适当增大风幕前倾角、逐渐提高出口风速、适当前移回风口位置均有助于加强风幕在狭长通道内的挡烟效果.而当火源功率较大而风幕出口风速过小时,将不能很好地阻挡烟气的蔓延.数值分析结果表明,综合考虑上述三种因素,就可以使用风幕有效地阻挡烟气在狭长通道内的蔓延.     

TIMBER HARVEST IMPACTS ON SMALL HEADWATER STREAM CHANNELS IN THE COAST RANGES OF WASHINGTON1

ABSTRACT: We evaluated changes in channel habitat distributions, particle‐size distributions of bed material, and stream temperatures in a total of 15 first‐or second‐order streams within and nearby four planned commercial timber harvest units prior to and following timber harvest. Four of the 15 stream basins were not harvested, and these streams served as references. Three streams were cut with unthinned riparian buffers; one was cut with a partial buffer; one was cut with a buffer of non‐merchantable trees; and the remaining six basins were clearcut to the channel edge. In the clearcut streams, logging debris covered or buried 98 percent of the channel length to an average depth of 0.94 meters. The slash trapped fine sediment in the channel by inhibiting fluvial transport, and the average percentage of fines increased from 12 percent to 44 percent. The trees along buffered streams served as a fence to keep out logging debris during the first summer following timber harvest. Particle size distributions and habitat distributions in the buffered and reference streams were largely unchanged from the pre‐harvest to post‐harvest surveys. The debris that buried the clearcut streams effectively shaded most of these streams and protected them from temperature increases. These surveys have documented immediate channel changes due to timber harvest, but channel conditions will evolve over time as the slash decays and becomes redistributed and as new vegetation develops on the channel margins.     

CHANGING NEAR‐STREAM LAND USE AND RWER CHANNEL MORPHOLOGY IN THE VENEZUELAN ANDES1

ABSTRACT: The shape of a river channel is linked to surrounding land use through interacting hydrologic and geologic processes. This study analyzes the relationship between the change in near‐stream land use and the shape of the adjacent river channel over time. Three watersheds in the foothills of the Venezuelan Andes that have experienced differing degrees of development were studied to determine river channel width, sinuosity, and position relative to surrounding land use. Change in land use over time was obtained from multiple‐date aerial photographs (1946 and 1980) referenced to 1996 Landsat Thematic Mapper (TM) satellite imagery, and verified by field inspection. Measurements of land‐use type and amount and river channel morphology from the two dates were made using geographic information system (GIS) methods. The three watersheds differed in the extent of deforestation, the location of remaining forested land, and how much land‐use change had already occurred by 1946. Change in river channel morphology was greatest at the most deforested sites. Valley shape and channel constraint also had a discernible effect on change in channel morphology. This study introduces a method for analyzing change in coupled terrestrial‐aquatic systems based on multiple‐date, remotely sensed data and GIS analysis of spatial properties. The results document human impacts on river channels through a comparison of multiple watersheds over a 35‐year time interval.     

河道生态环境分区需水量的计算方法与实例分析

为真实反映流域各区间的河道生态环境需水量差异 ,同时解决流域上下游河道生态环境需水量的重复计算问题 ,提出了河道生态环境分区需水量的概念 ,对流域分区、河道功能确定和河道生态环境分区需水量计算方法进行了研究 .以黄河流域为例进行了实证分析 .结果表明 ,黄河流域的河道需水分区需水量差异显著 ,黄河下游区间的河道分区需水量最大 ,为 14 8 93× 10 8m3·a- 1 ,上游兰州—河口干流区间最小 ,为-5 0 12× 10 8m3·a- 1 ,龙羊峡—兰州干流区间和黄河下游区间河道分区需水量超过区间的自产水资源量 ,需要其它区间的水量补充 ,才能维持其河道的生态环境功能 .黄河流域的河道分区需水量之和为 2 3 0 6× 10 8m3·a- 1 ,约为流域地表水资源量的 3 9% ,说明黄河流域地表水资源的最大利用率应低于 61% .