Microbial decomposition of reed (Phragmites communis) leaves in a saline lake

Microbial colonization and its relation to the decomposition of reed (Phragmites communis) leaf litter were studied in the littoral area of a saline lake from autumn to summer using litter bag method. There was considerable fungal population on the leaves at the beginning of submergence. These fungi were probably terrestrial in origin. The fungal population rapidly disappeared few days after submergence, when bacteria, including cellulolytic and xylanolytic types, proliferated. Associated with this rapid colonization of bacteria, decomposition rates of cellulose and xylan increased. The rates declined from day 39 to day 100 with decreasing water temperature, though cellulolytic and xylanolytic bacteria maintained a sizeable population until day 150. A community of cellulolytic and xylanolytic fungi increased steeply after day 150. It coincided with a second increase in decomposition rate. These results suggest that the principal decomposers of reed leaf litter were bacteria in the initial phase and fungi in the later phase of the experiment.     

Litho- and palynostratigraphy at Lobsigensee: Evidences for trophic changes during the Holocene

In the pond of Lobsigensee (2 ha, on the Swiss Plateau) lithostratigraphic and palynostratigraphic units for the Late-glacial and the Holocene have been described. During the Late-Glacial the sediment types are mainly controlled by climate (the end of clay deposition coincides with the end of the Oldest Dryas, i.e. with reforestation at the beginning of Bölling) or by facies (lake marl in the littoral, gyttja in the profundal during Bölling and Alleröd). During the Holocene the facies and the changes in the trophic status, partly combined with water level changes, seem to determine the types of sediment. Two phases of natural eutrophication are deduced from laminated sections during the Boreal and the early Older Atlantic. Towards the end of the Younger Atlantic an early example of a probably anthropogenic eutrophication is found in the layers contemporaneous with the neolithic settlement of the Cortaillod culture. Since the Roman colonization the amount of erosional input has markedly increased.     

Decomposition of Acer Rubrum Leaves at three depths in a eutrophic Ohio lake

Decomposition of terrestrial litterfall, that could enter a lake, was investigated at three depths within the lake in question using leaves of red maple (Acer rubrum). Sixty litter bags each containing 10 g dry weight of maple leaves were anchored at 1 m, 4 m and 12 m in East Twin Lake. At monthly intervals five bags were harvested at each level and dry weight changes noted. Results indicate little difference in decomposition between depths over the winter months. Beginning in May, however, significant differences were noted between 1 m and all other depths for the remainder of the experimental period. Maples lost 100% of weight at 1 m, 54% at 4 m, and 55% at 12 m over the experimental period. The rate of decomposition over the total experiment period was approximately .03 g da^–1 at 1 m and .015 g da^–1 at the 4 and 12 m depths. These results are discussed in terms of regulation of decomposition, position of decomposition and contribution to lake metabolism.     

A new bathymetric map based on echo-sounding and morphometrical characterization of the Lake of Banyoles (NE-Spain)

A new bathymetric map of the Lake of Banyoles (NE-Spain) is presented. Echo-sounding transects identified new bathymetric features. The map locates the 13 bottom springs that are presently known and shows a configuration of the lake in six basins. A morphometrical study based on the new bathymetry is also presented.     

The phosphorus status of sediments in a hypertrophic impoundment (Hartbeespoort Dam): implications for eutrophication management

The phosphorus status and distribution of sediments in a hypertrophic water supply reservoir (Hartbeespoort Dam) were investigated, with a view to assessing the role of sediments in counteracting the effects of reduced external phosphorus loading as a restoration measure. In comparison with similar water bodies in South Africa, the sediments in Hartbeespoort Dam contained high levels of both total and potentially mobile phosphorus. The potentially mobile fraction constituted about 60% of the total phosphorus content of the sediments, compared with about 11% in other reservoirs. The excessive eutrophication of Hartbeespoort Dam is clearly reflected in the phosphorus status of the sediments. Sediment distribution in the impoundment was found to be extremely heterogeneous, due to the combined influences of morphometry, hydrology and an imbalance in the nutrient loads entering via rivers at remote points in the water body. It is concluded that sufficient mobile phosphorus has accumulated in the sediments to prolong the response time of the impoundment to phosphorus load reductions. Since phosphorus release from sediments is dependent on dynamic processes not addressed in this study, the extent of the delays in trophic response to load reduction cannot be estimated.     

Trace element composition of Pistia stratiotes L. in a polluted lake in Nigeria

Pistia stratiotes L. in a Nigerian lake receiving organic and laboratory chemical wastes, accumulated trace elements from the lake water. Its possible use in the treatment of specific industrial wastes or in selective enrichment of specific elements is discussed.     

Observations on the zooplankton and littoral macroinvertebrates of Nyumba ya Mungu reservoir, Tanzania

Eight species of Crustacea and 28 species of Rotifera were identified in zooplankton samples from Nyumba ya Mungu reservoir. In all localities the dominant organism was the copepod Thermocyclops hyalinus. Cladocerans and rotifers made a variable contribution. Insects, among which the Chironomidae were pre-eminent, formed the major component of littoral macroinvertebrate communities. Oligochaetes, crustaceans and gastropods, including vectors of Schistosomiasis, were rare or restricted in distribution. In contrast to the deep end of the lake, where submerged trees were the poorest substrate, those at the shallow end supported a high biomass of invertebrates, since prolonged exposure had accelerated rotting and facilitated colonisation by the burrowing nymphs of Povilla. The variety of invertebrates on stony and muddy shores was increased when rooted emergent plants were present. The richest benthic community was found in submerged beds of Ceratophyltum. It is suggested that drawdown and the restricted development and movement of floating vegetation, have limited the spread of gastropods in the lake. Zooplankton, chironomid larvae and pupae, and ephemeropteran nymphs were shown to be important in the diet of small carnivorous and omnivorous fish species.     

湖光岩玛珥湖可培养浮游细菌的BOX-PCR图谱及生物多样性分析

玛珥湖是一类具有独特地质构造特征的火山口湖泊, 目前国内外对玛珥湖内微生物多样性的研究还鲜有报道。为了解具有典型玛珥特征的湖光岩湖泊中可培养浮游细菌的种群资源特征, 采用盒式PCR (BOX-PCR) 筛选技术, 通过通用贫营养和原位湖水培养基研究在冬夏两季各水层内获得的可培养细菌种群的差异。结果表明: 不同培养基在不同水层上表现的细菌数量的变化相一致, 为夏季的5 m>1 m>13 m, 冬季的1 m>5 m>13 m, 变形菌占据优势地位, 其它为放线菌、厚壁菌和拟杆菌; 两类培养基上所获培养菌BOX-PCR图谱的多样性相似, 但菌群结构不同; 而细菌多样性在季节上的变化表现为冬季高于夏季, 这与相关湖泊内细菌微生物多样性在夏季会发生减少的特点相似; 相同季节同一水层上不同培养基上获得的培养菌门类不同, 表明此类通用性培养基在培养该环境微生物中的局限。研究的结果为探讨此类型湖泊微生物多样性与环境的关系及分离该环境下特定微生物菌株提供参考。     

Characterization of a Chromobacterium haemolyticum population from a natural tropical lake

Aim: To study genetic diversity of Chromobacterium haemolyticum isolates recovered from a natural tropical lake. Methods and Results: A set of 31 isolates were recovered from a bacterial freshwater community by conventional plating methods and subjected to genetic and phenotypic characterization. The 16S ribosomal RNA (rRNA) gene phylogeny revealed that the isolates were related most closely with C. haemolyticum. In addition to the molecular data, our isolates exhibited strong β‐haemolytic activity, were nonviolacein producers and utilized i‐inositol, d ‐mannitol and d ‐sorbitol in contrast with the other known chromobacteria. Evaluation of the genetic diversity in the 16S rRNA gene, tRNA intergenic spacers (tDNA) and 16S‐23S internal transcribed spacers (ITS) unveiled different levels of genetic heterogeneity in the population, which were also observed with repetitive extragenic palindromic (rep)‐PCR genomic fingerprinting using the BOX‐AR1 primer. tDNA‐ and ITS‐PCR analyses were partially congruent with the 16S rRNA gene phylogeny. The isolates exhibited high resistance to β‐lactamic antibiotics. Conclusion: The population genetic heterogeneity was revealed by 16S rRNA gene sequence, ITS and BOX‐PCR analysis. Significance and Impact of the Study: This study provides for the first time an insight into the genetic diversity of phylogenetically close isolates to C. haemolyticum species.