A new device for collection of interstitial water from wetland sediments

A sampler for collection of interstitial water from wetland sediments is described. It differs from other sampling devices because it does not have to be filled with solution to facilitate diffusion, it does not have to be removed from the wetland to collect samples, and it can be used to draw repeated samples over time from identical locations. The device facilitates in situ measurement of a wide range of abiotic parameters such as electrical conductivity, redox potential, and pH in wetland sediments. The device has application in ecological investigations of sediment-borne wildlife diseases, studies of benthic invertebrates, measurement of nutrient exchange, and other aspects of wetland ecology.     

The choice between desiccation of wetlands or the spread of Rhine water over The Netherlands

The dry summer of 1976 triggered a wholesale installation of sprinkler systems for agriculture. This dry summer also revealed areas in The Netherlands most susceptible to drought, namely sandy regions and the coastal fringe. This resulted in distribution of Rhine water to new areas, and in quantities hitherto unknown. The Second National Water Management Plan (1982) consequently focussed on enlarging the capacity of water distribution works. This distribution has led to a multitude of ecological effects, such as changes in salinity and nutrient concentration, as well as the spreading of contaminants. Consequently, the Third National Water Management Plan (1990) includes fewer distribution works because of the adverse environmental effects and the reduced feasibility due to increasing costs and decreasing agricultural benefits.A climatic change as predicted may result in climatic conditions in The Netherlands resembling those of France or the Mediterranean, implying drier summers and more precipitation in winter. An increased frequency of dry summers will no doubt revive water distribution plans now shelved and may even bring new ones to the drawing board. An increase in Rhine water distribution will have serious consequences for many aquatic and terrestrial ecosystems, as will a lowering of the groundwater table. In this paper we will discuss the dilemma of choosing between allowing increased desiccation of wetlands as the climate becomes drier or increasing the distribution of Rhinewater and the potential ecological effects of these choices. Alternative strategies to water management also are discussed.This article is largely based on Duel et al. 1989.     

Partition coefficients of plant cuticles for monoterpenes

Summary Cuticle/water partition coefficients (K_c/w) for d-limonene, -pinene and -pinene were determined by an extrapolation and a desorption method. The sorption experiments were carried out with isolated angiosperm and gymnosperm cuticles and with [¹⁴C]-labelled monoterpenes, which were obtained biosynthetically. Both methods were suitable for the determination of the K_c/w of volatile hydrophobic compounds. For the angiosperm cuticles the partition coefficients are of the order of 10⁴, which indicates a high accumulation of monoterpenes in the cuticle. The values of the conifer cuticles of Picea abies (L.) Karst. and Abies alba Mill., however, are lower due to their high lignin content. This is proved by the increase of the partition coefficients after removal of polar and phenolic components. The K_c/w can be estimated with good accuracy from the octanol/water partition coefficient, which was determined experimentally.     

A bacteriological survey of an oyster-growing area: The Oualidia Lagoon,Morocco

A 3-year bacteriological survey of an oyster-growing area in Morocco, where the Japanese oyster (Crassostrea gigas) is grown, showed that the contamination of this lagunar ecosystem was not continuous but intermittent and that animal manure and human recreational activities were important sources of pollution. The major source of contamination was of animal origin, except during the summer, when human contamination prevailed.     

The influence of habitat use and foraging on the replacement of one introduced wasp species by another in New Zealand

Abstract.

• 1 New Zealand was colonized by the German wasp, Vespula germanica (F.), in the 1940s and it subsequently became established throughout the country. The common wasp, V.vulgaris (L), colonized in the late 1970s and is still spreading.
• 2 The common wasp has replaced the German wasp in some habitats in New Zealand. Samples from a nationwide postal survey indicate that the common wasp is now the more abundant species in honeydew beech forests (Nothofagus spp.), and to a lesser extent in other native forests. The German wasp is still the more abundant wasp in rural areas (excluding forest). The two species are at present co-dominant in urban areas, although this may be a transient phase.
• 3 In honeydew beech forest the two species show different foraging patterns that provide the potential for local coexistence. Although both species are generalist feeders, the German wasp is more commonly found foraging for protein amongst the forest litter, whereas the common wasp forages more on shrubs and tree saplings. Despite this difference, the common wasp can still replace the German wasp in honeydew beech forest within a few years of invasion.
• 4 In honeydew beech forests in which the German wasp is the more abundant species it dominates honeydew trunks (sugar resource), whereas the common wasp dominates honeydew trunks in areas where it is the more abundant species. The change from German to common wasp domination of honeydew trunks is more rapid than the change in dominance in other microhabitats. Aggressive interactions may be taking place on this high quality, potentially defensible sugar resource.

     

Water hyacinth productivity and detritus accumulation

Water hyacinth [Eichhornia crassipes (Mart) Solms] productivity and detritus accumulation were evaluated in eutrophic lake water with and without added nutrients (fertilized and control reservoirs, respectively). Seasonal changes in plant productivity and detritus accumulation were determined at monthly intervals for one year. Significant differences were observed in plant productivity between seasons and nutrient additions. Seasonal plant productivity ranged from 1.9 to 23.1 mg (dry wt) ha⁻¹ for the fertilized reservoir and −0.2 to 10.2 mg ha⁻¹ for the control reservoir. Detritus accumulation was not significantly different between seasons or nutrient additions. Seasonal N assimilation by plants ranged from 34 to 242 kg N ha⁻¹ for plants in the fertilized reservoir and < 0 to 104 kg N ha⁻¹ for plants in the control reservoir. Annual net N recovered in detritus represented 21 and 28% of the total N removed by plants in the fertilized and control reservoirs, respectively. Net N loading to the reservoirs from detritus was 92 to 148 kg N ha⁻¹ yr⁻¹.     

Population differences in larval hostplant use in the checkerspot butterfly, Euphydryas chalcedona

Larvae from two populations of Euphydryas chalcedona Doubleday & Hewitson (Nymphalidae) were reared on their own hostplant and that of the other population, in both pre-diapause and post-diapause instars. One population, Chico, uses Penstemon breviflorus Lindl. (Scrophulariaceae), and the other, Echo Lake, uses P. newberryi Gray. Growth rate and survival were determined for pre-diapause and post-diapause larvae from both populations on both plant species; and digestive efficiencies were calculated during the prediapause instars. The results showed that larvae from the two populations differed in their responses to the two plant species. Pre-diapause larvae from Chico performed equally well on both plant species—survival and digestive indices were not significantly different for two Penstemon species. In contrast, pre-diapause larvae from Echo Lake performed significantly worse on the non-hostplant—growth and survival were significantly lower on the non-host, P. breviflorus. In addition, comparison of digestive efficiencies for the two plants showed that larvae from Echo Lake digested P. breviflorus better than P. newberryi, but were significantly less able to convert P. breviflorus to body mass. In the post-diapause instars, larvae from Chico grew faster on the host than on the non-host. Larvae from Echo Lake grew quite slowly on both plant species and significantly more of the Echo Lake larvae returned to diapause instead of completing development.

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Résumé Des chenilles de deux populations d'E. chalcedona ont été élevées sur leur propre plante-hôte et sur celle de l'autre population, aux stades avant et après diapause. Les deux populations s'alimentent sur différentes espèces de Penstemon (Scrophulariaceae), et une population—Echo Lake—est monophage sur P. newberry, tandis que l'autre—Chico—utilise d'abord P. breviflorus, mais les chenilles après diapause sont trouvées sur au moins deux autres espèces de plantes. Les taux de croissance et de survie ont été déterminés pour des chenilles avant et après diapause pour les deux populations sur les deux plantes; les efficacités digestives ont été calculées sur les chenilles avant diapause.Les résultats ont montré que les chenilles des deux populations différaient par leur degré de spécialisation digestive sur leur plante hôte normale: les chenilles de Chico ont utilisé aussi bien les deux plantes, tandis que celles d'Echo Lake le faisaient significativement moins bien sur la plante non-hôte, par suite de l'inaptitude à la digérer. Ainsi la population oligophage est alimentairement moins spécialisée et plus capable de se débrouiller avec une plante non-hôte. Après diapause, les chenilles de Chico s'alimentaient significativement mieux sur plante hôte que non-hôte, ce qui était le cas aussi pour la population monophage. Dans l'ensemble, les chenilles de la population monophage semblaient moins capables de se débrouiller dans des conditions défavorables ou moins avantageuses.

     

Techniques for encapsulating bioactive agents into liposomes

As a prerequisite for the use of liposomes for delivery of biologically active agents, techniques are required for the efficient and rapid entrapment of such agents in liposomes. Here we review the variety of procedures available for trapping hydrophilic and hydrophobic compounds. Considerations which are addressed include factors influencing the choice of a particular liposomal system and techniques for the passive entrapment of drugs in multilamellar vesicles and unilamellar vesicles. Attention is also paid to active trapping procedures relying on the presence of (negatively) charged lipid or transmembrane ion gradients. Such gradients are particularly useful for concentrating lipophilic cationic drugs inside liposomes, allowing trapping efficiencies approaching 100%.     

Morphology,physics, chemistry and biology of Lake Rara in West Nepal

A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and maximum depth is 167 m. The surface area covers 9.8 km², and the lake contains 0.98 km³ volume of water. Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient was 8.3 × 10⁻². The concentration of Chl.-a was in the range of 0.06–0.46 mg m⁻³, and total nitrogen was 18–30 μg 1⁻¹. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity, and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely low. The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species of Copepoda. The zooplankton density range was 6200–16200 individuals m⁻³. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983.