Methane and oxygen dynamics in a shallow floodplain lake: the significance of periodic stratification

Temperature, dissolved oxygen and dissolved methane profiles were measured during autumn and summer, in a shallow floodplain lake in south-eastern Australia to determine the effects of water-column stability on methane and oxygen dynamics. The water column was well mixed in autumn. Strong thermal stratification developed in the late afternoon in summer, with top-to-bottom temperature differences of up to 6 °C. Methane concentrations in surface waters varied over a daily cycle by an 18-fold range in summer, but only by a 2-fold range in autumn. The implication of short-term temporal variation is that static chambers deployed on the water surface for short times (less than a day) in summer will significantly underestimate the diffusive component of methane emissions across the water–atmosphere interface. There was a marked diel variation in dissolved oxygen concentrations in summer, with the highest oxygen values (commonly 5–8 mg l^–1) occurring in the surface waters in late afternoon; the bottom waters were then devoid of oxygen (< 0.2 mg l^–1). Because of high respiratory demands, even the surface water layers could be nearly anoxic by morning in summer. The concentration of dissolved oxygen in the surface waters was always less than the equilibrium value. When the water column became thermally stratified in summer, the dissolved oxygen and methane maxima were spatially separated, and planktonic methanotrophy would be limited to a moving zone, at variable depth, in the water column. In summer the whole-wetland rates of oxygen production and respiration, calculated from long-term (5 h) shifts in dissolved oxygen concentrations over a diel period, were approximately 6–10 and 3–6 mmol m^–3 h^–1, respectively. These values correspond to net and gross primary production rates of 0.7–1.2 and 1.0–1.9 g C m^–3 day^–1, respectively.     

Distribution of bacteria in the sediment of an oxbow tropical lake (Lagoa do Infernão,SP, Brazil)

The temporal distribution of bacteria on the surface sediment of the oxbow lake Lagoa do Infernão was studied over a period of one year using different techniques for bacterial counts. Several bacterial groups were differentiated, such a total bacteria and filamentous, heterotrophic, amylolytic, and lipolytic bacteria. The best defined temporal distribution pattern was obtained by total-AO bacterial counts, with a variation of 1.26 × 10¹⁰ to 8.58 × 10¹⁰ bacteria (g dw)^–1 during the dry and rainy seasons, respectively. The electrode potential (Eh) of the surface sediment ranged from – 148 mV during the rainy season to + 371 mV during the dry season. The variations detected on the surface sediment suggest a greater allochthonous contribution of material and bacteria resulting in high decomposing activity during the rainy season.     

Fishes of floodplain habitats of the Fly River system, Papua New Guinea, and changes associated with El Niño droughts and algal blooms

Biological monitoring of the Fly River system in Papua New Guinea has shown that floodplain habitats (oxbow lakes, blocked valley lakes and seasonally inundated grassed floodplain) support diverse and abundant populations of freshwater fishes. Since monitoring first commenced in the early 1980's, a total of 66 fish species representing 33 families has been sampled, with gillnets and rotenone, from a range of sites located on the floodplains of the Fly and Strickland rivers. The fish fauna was dominated by catfishes in the families Ariidae (11 species) and Plotosidae (7 species), with aquatic invertivores being the dominant feeding group. Herring species (Nematalosa spp.) were often very abundant in the oxbow lakes, forming 66% of the total catch in all the floodplain habitats. The fish communities in the oxbow lakes and blocked valley lakes were distinctly different, with several of the smaller fish species being more abundant in the blocked valley lakes, while the oxbow lakes supported more of the larger predatory species. Catches in the oxbow lakes were also generally higher and more diverse than the blocked valley lakes or grassed floodplain sites. Since the commencement of monitoring, catches from the floodplain sites have varied considerably, both spatially and temporally. Reduced catches seen at some sites are probably associated with natural climatic factors, particularly El Niño-induced droughts and algal blooms. Introduced species and increased commercial and artisanal fishing may also be affecting stocks of native fish. Fish populations were shown to recover only slowly in lakes affected by severe drought conditions, with extensive mats of floating grasses hindering fish recolonisation. Fish stocks in a lake affected by an algal bloom recovered more quickly than stocks in lakes affected by drought.     

Spatial Distribution and Temporal Variance of Fish Communities in the Channelized and Regulated Vltava River (Central Europe)

Spatial distribution and temporal variations of fish communities in a channelized portion of the Vltava River (Central Europe) were investigated from May to October 1992. Fish abundance and species number were collected monthly during diel samples in the main channel and a large oxbow. To determine differences in fish communities we chose the low-flow period when maximal differences in physical environment between habitats are expected. Fish community patterns from the main channel and oxbow differed only in abundance of ecological groups; the main channel had higher abundance of rheophilic species, whereas eurytopic species were more abundant in the oxbow. However, our analysis revealed significant differences in temporal variations between habitats. Fish abundance usually varied unpredictably over day-night periods in the main channel, whereas in the oxbow we observed a pronounced peak in fish abundance from morning to mid-afternoon. Diel changes in fish abundance in the oxbow corresponded to occurrence of low dissolved oxygen during afternoon and night-time periods. The effect of oxygen depletion induced by strong organic pollution limited the oxbow suitability for fishes. Similar habitats are usually occupied by limnophilic and phytophilic species that were absent in our samples. Our results suggested that man-induced high variability of physical environment decreased variability in fish community.     

长江天鹅洲故道江豚的集群规模及其时空分布

2 0 0 1年 5月至 2 0 0 2年 4月 ,选择使用岸上定点观察、流动观察和水上流动观察 3种观察方式 ,对长江天鹅洲故道内约 2 0头江豚的集群状况进行了一个周年的监测 ,共观察到江豚集群 5 88次。结果表明 :天鹅洲故道内江豚以集群的方式迁移和活动 ,集群规模从 2— 2 0头不等 ,一般分成 2个 9— 11头规模的亚群体 ,2个亚群体活动范围相对独立 ,其活动主要为D区和H区。每个亚群体又常分成规模较小的核心群体 ,其中 3头集群最多。一年中春、秋和冬季江豚集群状况基本相同 ,而夏季有所差别。天鹅洲故道江豚集群在白天期间有 3个高峰期 ,主要发生在9:0 0— 11:30 ;12 :30— 16 :15和 17:15— 18:0 0 ;正午时间 ,江豚的集群活动处于相对低谷。江豚集群相对集中在天鹅洲故道D、E、F、G和H区域 ,占 70 % ,江豚在上下区域集群相对较少。根据江豚集群规模在天鹅洲故道的时空分布规律 ,作者对长江天鹅洲保护区江豚群体的保护与管理提出了科学的合理化建议。     

湖北天鹅洲故道试养江豚生活习性的初步观察

为抢救濒危水生兽类白暨豚,建立保护区无疑是最有效的途径,１９９０年３月到１９９３年１０月,我们对引进白暨豚保护区湖北天鹅洲故道中试养的１１头江豚的生活状况和对环境的适应性,进行了较为详细的研究,力求在引入白暨豚前,对此地江豚的生活情况及白暨豚保护区的建区工作做进一步的生态评价。结果表明,江豚非常适应故道环境,它们能在其中正常生活,完成妊娠过程,顺利分娩,抚幼,幼体也能正常发育和成长。此外,故道还存     

The Stratification of Pools in the Alluvium of the River Lužnice

The stratification of two shallow and small pools, situated in a floodplain ecosystem, was investigated. A new methodological approach was applied. The parameter called summarized chemical and biological stratification (SCB), was derived from basic limnological parameters in order to evaluate the global intensity of chemical and biological stratification and to compare it with a thermal one. Three situations were described when the seasonal courses of thermal and SCB stratification were compared: 1. Both SCB and thermal stratification are present. 2. The water column is homogeneous — there is no stratification in the pool. 3. SCB stratification is present, but the water is homoiothermic. The thermal stratification is very unstable because of the small volume of the pools and frequent floods. The SCB stratification is of higher stability and it may persist in a homoiothermic water column. In comparison with temperate deep lakes, the thermal stratification does not play such an important role in initiating the chemical and biological stratification. The surface/volume ratio and the depth in the pools are lower, which cause the “bottom-initiated” quick renovation of stratification even in homoiothermic water. The differences in oxygen regime, volume and localization of both investigated pools cause the differences in stratification patterns. Frequent oxygen depletions in one of the pools increase the intensity of stratification and influence its character. The anaerobic conditions lead to steeper gradients of basic nutrients, pH, alkalinity and water color. The occurrence of a unique phytoplankton community (Cryptophyceae) is probably closely related to the described stratification patterns.     

Fish assemblage changes relative to environmental factors and time in the Warta River, Poland, and its oxbow lakes

Four oxbow lakes and two neighbouring sections of their parent Warta River (Odra River system, Poland) were sampled to investigate differences in fish assemblages between habitats in 1999–2000. Additional comparisons were made with 12 other oxbow lakes in this section of the river that were sampled 30–40 years ago. Downstream of a man‐made reservoir, higher species number, diversity and evenness were recorded in oxbow lakes than in the river channel. Upstream of the reservoir, differences in these variables from both habitats were insignificant. Fluvial and stagnant water samples were clearly separated in the multivariate space of a detrended correspondence analysis (DCA). For two oxbow lakes and two neighbouring sections of the Warta River, 12 abiotic and biotic environmental variables were available, and only velocity, water temperature and conductivity were significantly correlated with canonical correspondence analysis (CCA) axes. Fish assemblages of four recently investigated oxbow lakes were clearly separated in the multivariate space of DCA from other neighbouring oxbows sampled 30–40 years ago. Species previously subdominant were becoming rare. Oxbow lakes that are continuously or at least periodically connected with the channel are indispensable for maintaining high biodiversity and a sustainable fishery in the river system.     

Isolation,Identification and Efficacy of Inorganic Phosphate-Solubilizing Bacteria from Oxbow Lakes of West Bengal,India

Microbial mobilization of sediment calcium-bound P constitutes an important process of P cycling in aquatic environments. The present study was conducted to identify the bacterial community responsible for inorganic phosphate solubilization in tropical oxbow lakes. Fifty eight phosphate-solubilizing bacteria were isolated from bottom soil, water, and fish gut and examined for solubilization of tricalcium phosphate. Results revealed aquatic PSB to be low-to-moderately capable in P solubilization (mean: 33.5 mg P L^?1; range: 6.3–68.8 mg P L^?1), and bacteria from wetland sediment and water were more effective than those from fish gut. The PSB were identified to belong to diverse genera, viz. Bacillus, Brevibacillus, Enterobacter, Agrobacterium, Pseudomonas, Acinetobacter, Microbacterium, Curtobacterium, Stenotrophomonas and Novosphingobium. The findings help in understanding the microbial role in inorganic P solubilization and identifying important P solubilizers in freshwater environments.     

老江河故道四大家鱼天然资源库研究

扼要介绍了老江河故道四大家鱼天然资源库的结构,并根据老江河故道水域生态系统的结构和功能特点,提出了四大家鱼的放养量应在重视种质质量的基础上,合理调控其放养结构和密度,此外文中还就保护和合理利用长江四大家鱼种质资源的有效途径以及维持老江河四大家鱼天然资源库健康运行的关键进行了分析探讨。