The importance of worm identity and life history in determining the vertical distribution of tubificids (Oligochaeta) in a riverine mud

The vertical distribution of Tubifex tubifex, Limnodrilus hoffmeisteri and L. udekemianus, in a riverine mud was studied over a year. Distribution was dependent upon species identity, season and locality. The size structure of the population, and hence species life history, was of fundamental importance in determining temporal patterns of vertical distribution. A positive correlation between worm length and depth of penetration was clearly demonstrated for all three species. However, the mid-stream populations of the three species were closer to the mud surface during the summer and autumn than were the near-bank populations, although the size structures of the populations were not significantly different. Thus, another factor, possibly the distribution of food, also influenced the vertical distribution of the worms. Cocoon distribution was similar to that of the adult worms. Cocoons of the larger species, L. udekemianus, occurred deeper in the mud than those of T. tubifex. A comparison between the vertical distributions of tubificids in cores sectioned in situ, on the stream bank, and 30 mins later, showed there to be no significant change in distribution with time.     

Comparison of chemical analyses of boat and helicopter-collected water samples

Helicopters can be used to collect water samples from many lakes over a wide geographic area within a relatively short time period. Here we report the results from an experiment in which sequential water samples from a lake were collected first from a nonmotorized boat and then immediately afterward from a helicopter. No significant differences were found between the means of the measurement of 20 chemical parameters for the two methods of collection. When compared to obtaining samples from a boat, collection of samples from a helicopter platform had no effect on the content of the water samples.     

Assessing the impact of episodic pollution

The increased tightening of controls on industrial and municipal wastewater discharges has resulted in steady improvements in the quality of many important rivers over recent years. However, episodic pollution, particularly from farm wastes and combined sewer overflows continues to pose a major problem, and is one of the main causes of poor quality rivers today. Despite our acknowledgement of this continuing problem, very little is known of the mechanistic basis of responses and recovery of aquatic organisms and communities exposed to intermittent pulses of common pollutants. The majority of ecotoxicological studies to date have been concerned with the effects of continuous exposure. Although such studies may provide a means of predicting the impact of episodic pollution events, a more appropriate test design would be to assess toxicity under pulsed and fluctuating exposure. Studies should also include a post-exposure observation period and should consider recovery of individuals and communities. This paper reviews the results of reported studies relevant to the investigation of episodic pollution and pays particular attention to the effects of magnitude, duration and frequency of exposure. Results of field investigations using an in situ bioassay technique are also presented to emphasize the importance of field validation of proposed water quality criteria for intermittent pollution events.     

Geographical distribution,morphology and water quality of caldera lakes: a review

The geographical distribution, morphometry and water quality of lakes within large calderas (> 2 km in diameter) were evaluated through a review of the literature and maps. Eighty-eight lakes in 75 calderas were located in 31 volcanic subregions. As a group, the lakes varied greatly in elevation, surface area, maximum depth, and shoreline development. The average surface area was 16.9 km², surface elevation 873 m, depth 151.1 m, and shoreline development 1.35. Water quality ranged from ultraoligotrophic to highly eutrophic. None of the lakes had an inlet that originated outside the calderas. Most lakes did not have a surface outlet, were circular or subcircular in shape, and covered only parts of the caldera basins. Water clarity in some lakes was among the highest recorded for freshwater systems, but there are indications of possible declining clarity in some cases. Secondary volcanic activity, such as primary (hydrothermal) water and eruptions, has been associated with deteriorated water quality conditions in some lakes.     

Algal epilithon and water quality of a stream receiving oil refinery effluent

Changes in epilithic algal communities colonizing introduced substrata were determined in a stream polluted with oil refinery effluent at Digboi (Assam, India). The number of algal taxa was reduced but the growth of blue-green algae, particularly two species ofOscillatoria, was encouraged. Epilithic biomass (as chlorophylla) also declined at polluted stations. The algal community of the upstream station was markedly different from the community occurring just after the confluence of effluent; however, the differences were gradually reduced downstream, indicating improvement in water quality. Of the various criteria tested for possible relationships with the level of pollutants, species richness, Shannon diversity and biomass showed significant relationships. The study demonstrates the usefulness of algal criteria for monitoring oil pollution in running waters.     

Neuropeptide gene expression and neural activity: Assessing a working hypothesis in nucleus caudalis and dorsal horn neurons expressing preproenkephalin and preprodynorphin

1. The working hypothesis that neuropeptide gene expression in a neuron is an indicator of that neuron's physiological activity is discussed. 2. Representative examples from the literature are presented to support the hypothesis. 3. Further, we discuss the regulation of expression of two opioid peptides, preproenkephalin and preprodynorphin, in laminae I and II of the spinal cord and in nucleus caudalis of the trigeminal nuclear complex, where they may play a role in pain modulation. 4. The expression of the opioid peptide genes can be induced by both painful and nonnoxious stimuli in neurons in time-dependent and sensory-specific fashions.     

Molecular cloning and expression of a proteinase gene from Lactococcus lactis subsp. cremoris H2 and construction of a new lactococcal vector pFX1

The 6.5 kb HindIII DNA fragment of the Lactococcus lactis subsp. cremoris H2 plasmid pDI21 was cloned into Escherichia coli POP13 with NM1149, and also directly into Lactococcus lactis subsp. lactis 4125 using a newly-constructed broad host-range vector pFX1. Proteinase was experessed in both transformed organisms. The proteinase resembles a PI type since it preferentially degraded -casein. The restriction map of the 6.5 kb proteinase gene fragment has minor differences from those of published plamid proteinase genes. High-efficiency electroporation with pFX1 provides a direct approach for gene cloning in lactococci.Abbreviations cfu colony forming units - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] Dedicated to Prof. Dr. G. Drews on the occasion of his 65th birthday     

Intercellular structure in a many-celled magnetotactic prokaryote

A many-called magnetotactic prokaryote obtained from brackish water was observed to possess intercellular connections at points of contact between the outer membranes of constituent cells. Each aggregate organism consisted of 10 to 30 individual Gram-negative cells containing material with the appearance of poly--hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outwards surfaces of each cell, showed motility indicative of co-ordination between individual component cells. These results suggest that this organism could be a multicellular prokaryote.     

Ischemic flow threshold for striatal dopamine release in rats

To determine the level of cerebral blood flow reduction which causes striatal dopamine release, extracellular dopamine and cerebral blood flow was simultaneously determined using in vivo brain dialysis and a hydrogen clearance method, respectively, in the striatum of spontaneously hypertensive rats, before and during experimental cerebral ischemia. The ischemic flow threshold for neurotransmitter dopamine release was found to be 20% of the resting value or 8–10 ml/100g/min of cerebral blood flow, being similar to those for energy and membrane failures.     

麦田冠层气孔导度的分层研究

小麦灌浆期和乳熟期冠层各层叶片上、下表面的气孔导度之间呈正相关关系;冠层不同层的叶片气孔导度从早到傍晚有平行变化的趋势,数值上存在较大的差异,一般从冠层上到下递减。经分析,这主要与冠层叶片接受的光强自上而下递减有关,且这时所对应的叶片水势自冠层上到下递增的幅度大。测算结果表明,冠层气孔导度白天亦呈明显的日变化,灌浆期的值大于乳熟期的值。