Factors affecting the survival of E. coli in a river

The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T₉₀ (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T₉₀, there is an indirect effect of temperature upon T₉₀ through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively.     

Steady state terrestrial ecosystems and the global carbon cycle

The assumption that landscapes dominated by mature vegetation are presently in carbon steady state with the atmosphere is challenged. Evidence suggests that the vegetation and soils of these landscapes are frequently disturbed and over short time periods (<300 yr) slowly sequester atmospheric carbon. The critical consideration in this argument is the time interval used to evaluate a steady state. Current models of carbon flux through the terrestrial biota limit their time considerations to 120 yr, a short and inadequate time interval for realistic assumptions about steady state in the carbon cycle of vegetation.Research performed under subcontract 19B-07762C with S. Brown and 19X-43326C with the Center for Energy and Environment Research of the University of Puerto Rico (A. E. Lugo) under Martin Marietta Energy Systems, Inc., contract DE-AC05-840R21400 with the U.S. Department of Energy.     

金沙江河谷苏铁天然植物群落的研究

近年在金沙江干热河谷及其邻近地区陆续发现的苏铁天然植物群落,为本属植物在欧亚大陆内陆分布的最北边缘。其中,面积最大和保存较好的是渡口市攀枝花苏铁(Cycas panzhihuaensis)植物群落。本文研究了这个群落的分布与生境、生长状况、外貌、种类组成以及群落的综合特征等。认为具有稀树草原的特点,而这里的稀树草原是次生性质的,苏铁群落是其中幸存的残遗植被类型。这对研究我国植物地理有着重要意义。     

Age and growth of a colonizing minnow,Barbus anoplus,in a man-made lake in South Africa

Synopsis Aspects of the life history of Barbus anoplus were studied in Lake le Roux, a turbid man-made lake on the Orange River, South Africa. This minnow underwent a population explosion and successfully colonized the shoreline of the newly-formed lake during the early phases of reservoir filling. Male and female B. anoplus reach sexual maturity in one year at about 40 mm fork length. They have a multiple spawning habit with the first spawning in November–January and the second in February–March. The growth of the two resulting cohorts is discussed. It is proposed that the offspring from the second spawning not only acts as a ‘back-up’ but is capable of prolonging the life of that year-class into an additional reproductive season. Most of the minnows die after their second summer, but more offspring from the second spawning, especially females, live into a third summer. Females attain a larger maximum size (73 mm FL) and age (3–4 years) than males (60 mm FL, 2–3 years). B. anoplus is small and short-lived with a high seasonal reproductive potential, which is in contrast to the larger Barbus species in the Orange River system. These life-history traits enable the species to colonize and successfully inhabit unstable environments and probably account for its widespread distribution.     

图们江流域林区居民点鸟类群落的研究

居民点鸟类与人类关系极为密切,在居民点生态系统中起着不可忽视的作用,因此对其生态学的研究具有一定意义。杜恒勤(1958、1959)、周昌乔等(1959)、钱国桢(1964)、郑光美(1965、1982),赵正阶(1981)等,对麻雀、家燕、金腰燕等居民点鸟类进行过大量种群生态学研究。居民点鸟类群落研究和数量统计,尚未见有报道。     

珠江三角洲高畦深沟农田生态系统的结构及功能研究

前言自然和社会经济条件不同,农田生态系统的类型也不同。研究农田生态系统的结构与功能,可了解特定系统对当地环境条件的适应性。近年来,国内外很多学者,都从能流物流和经济效益方面对各类型结构农田生态系统结构与功能作了研究。高畦深沟结构农田生态系统,是珠江三角洲平原区人民为在当地地下水位较高的条件下,进行旱作而发展的一种农田生态系统类型。它的特点是,以一定的比例挖深沟,利用挖沟的泥土起高畦,沟中长期保持有水层,畦面进行旱作,沟里进行种植、养殖或其它利用,结构多年不变,是一种相对稳定的农田生态系统。     

Habitat alteration and its effects on native fishes in the upper Tennessee River system, east-central U.S.A.

The upper Tennessee River drainage, which includes portions of the States of Virginia, North Carolina, and Tennessee, supports an exceptionally diverse fish fauna. Recent reductions in abundance and geographic ranges of several freshwater fishes have promulgated the imposition of protective measures for about 115 species among the three states, with nearly half of those species occurring in the upper Tennessee River. Most protected species are darters (Percidae: Etheostomatinae) or minnows (Cyprinidae), and are typically small, benthic invertivores. Major impacts on the fish fauna have resulted from dams, introduced species, toxic spills, mining and agriculture. An important cumulative effect of these impacts is fragmentation of the watershed; nearly 40% of the riverine habitat in major tributaries is either impounded or altered by tailwater discharges. The isolation and stress imposed on tributaries of the river have caused and will continue to cause extirpations of fishes, mussels and other aquatic fauna. Numerous federal, state, and private organizations are co-operating in efforts to protect rare species and habitats, improve agricultural and coal-producing practices, and enforce regulations for industrial and municipal effluents.     

The habitat diversity and fish reproductive function of floodplain ecosystems

Synopsis Fish reproduction in floodplain ecosystems, based on relative abundance and total biomass of 0+ juveniles, was studied using the synchronic approach to typological analysis in conjunction with Point Abundance Sampling by modified electrofishing. In 3 different flood plains of the Upper Rhône River, 1015 point samples yielding 4573 juveniles (0+) from 21 species were collected from 48 ecosystems of various geomorphological origin. The results demonstrate the lotic-to-lentic succession of floodplain ecosystems to be a series of non-sequential reproductive zones, with spawning conditions being reflected by the specific composition and guild structure of the YOY fish assemblages. The habitat diversity and the fish reproductive potential of floodplain ecosystems are strongly influenced by geomorphological origin and by past and present hydrological conditions. The YOY assemblages of autogenically driven ecosystems (usually of anastomose or meander origin) tend to differ both in composition and in quantity from those found in allogenically driven ecosystems (generally of braided origin). Ecosystems of intermediate character, and fish reproduction thereof, occur as the result of either ecosystem rejuvenation or senescence: autogenically driven ecosystems by allogenic mechanisms, or allogenically driven ecosystems by anthropic and/or autogenic mechanisms, respectively. Because of co-occurrence of ecosystems at similar and at different successional status, the flood plain as an entity is seen as stable with respect to fish reproduction.     

长江中游鱼类寄生棘头虫区系的研究

经过3年10次调查,剖检湖北省宜都、黄冈两处江段所产72种鱼类,共计766尾。收集棘头虫10种,其中包括2新种和1新组合,即蛇鮈新棘吻虫(新种)Neoechinorhynchus saurogobi sp.nov.,长江丽棘虫(新种)Brentisentis yangtzensis sp.nov.(Illiosontidae),鲤丽棘虫(新组合)B.cyprini comb.nov.。对长江中游鱼类寄生棘头虫区系的特点进行了分析和探讨。     

湘南山区农业生态系统能量分析

一、引言由于农业系统的复杂性和存在较多的随机因素,对农业系统实行全面定量研究是比较困难的,仅从定性的描述和一些经济指标来判定系统的优劣及系统的特征是不理想的。而从能量观点对农业生态系统加以分析则是一个全面且能定量的方法,并且具有较强的客观性,能够反映农业生态系统最基本、最本质的关系。