The effect of sewage effluent on denitrification in Grasmere (English Lake District)

SUMMARY. Denitrification processes in Grasmere were studied using several techniques. Sediments were analysed for nitrate reductase activity and the accumulation of nitrogenous gases in samples incubated in the laboratory. Changes in the concentrations of inorganic nitrogen species in the water column and the release of gas bubbles into gas traps suspended above the sediment were also measured. Sewage effluent entered the lake via the main inflow and faecal bacteria were used as tracers to map the path of the river (and effluent) across the lake. The main river flow was west of the island in the centre of the lake and across the smaller of the two main basins. A preliminary study indicated that this western basin was the site of most active denitrification and this was confirmed in the following year when a seasonal survey showed that deoxygenation, nitrate reduction and ammonium accumulation was more advanced at this site. In addition, this basin was the only area where consistent discharge of nitrogen and methane from the profundal zone was observed. The nitrate reductase assay demonstrated that the sediment was the major site of denitrification, and that activity in the water column was higher in the anoxic hypolimnion than in the euphotic zone. Gas evolution from incubated sediment samples was analysed by gas liquid chromatography (GLC) and indicated that maximum denitrifying activity occurred below the mud surface in oxidized sediments. There was reasonable agreement between the enzyme assay and the GLC technique but neither predicted events in the field satisfactorily. Viable, most probable number (MPN) counts of denitrifying bacteria had similar limitations. A bimodal seasonal pattern of nitrate reductase activity was observed at four sites during thermal stratification, but this could not be explained fully. The major site of denitrification was identified and it was calculated that the nitrogen gas discharged was equivalent to c. 54% of the nitrate removed from the water column.     

The Ediacaran Period: a new addition to the geologic time scale

The International Union of Geological Sciences has approved a new addition to the geologic time scale: the Ediacaran Period. The Ediacaran is the first Proterozoic period to be recognized on the basis of chronostratigraphic criteria and the first internationally ratified, chronostratigraphically defined period of any age to be introduced in more than a century. In accordance with procedures established by the International Commission on Stratigraphy, the base of the Ediacaran Period is defined by a Global Stratotype Section and Point (GSSP) placed at the base of the Nuccaleena Formation cap carbonate directly above glacial diamictites and associated facies at Enorama Creek in the Flinders Ranges of South Australia. Its top is defined by the initial GSSP of the Cambrian Period. The new Ediacaran Period encompasses a distinctive interval of Earth history that is bounded both above and below by equally distinctive intervals. Both chemostratigraphic and biostratigraphic data indicate that the subdivision of the period into two or more series is feasible, and this should be a primary objective of continuing work by the Ediacaran Subcommission of the ICS.     

Multiscale topoedaphic heterogeneity increases resilience and resistance of a dominant grassland species to extreme drought and climate change

It is argued that the inclusion of spatially heterogeneous environments in biodiversity reserves will be an effective means of encouraging ecosystem resilience and plant community conservation under climate change. However, the resilience and resistance of plant populations to global change, the specific life‐history traits involved and the spatial scale at which environmentally driven demographic variation is expressed remains largely unknown for most plant groups. Here we address these questions by reporting an empirical investigation into the impacts of an unprecedented 3‐year drought on the demography, population growth rates (λ) and biogeographical distribution of core populations of the perennial grassland species Austrostipa aristiglumis in semiarid Australia. We use life‐history analysis and periodic matrix population models to specifically test the hypothesis that patch‐ and habitat‐scale variation in vital life‐history parameters result in spatial differences in the resilience and resistance of A. aristiglumis populations to extreme drought. We show that the development of critical soil water deficits during drought resulted in collapse of adult A. aristiglumis populations (λ?1), rapid interhabitat phytosociological change and overall contraction towards mesic refugia where populations were both more resistant and resilient to perturbation. Population models, combined with climatic niche analysis, suggest that, even in core areas, a significant reduction in size and habitat range of A. aristiglumis populations is likely under climate change expected this century. Remarkably, however, we show that even minor topographic variation (0.2–3 m) can generate significant variation in demographic parameters that confer population‐level resilience and resistance to drought. Our findings support the hypothesis that extreme climatic events have the capacity to induce rapid, landscape‐level shifts in core plant populations, but that the protection of topographically heterogeneous environments, even at small spatial scales, may play a key role in conserving biodiversity under climate change in the coming century.     

Do Malaysian Myrmarachne associate with particular species of ant?

Ant-mimicry has evolved in numerous families of spiders. Although some mimics resemble ants very precisely in their morphology and behaviour, others have only a superficial resemblance to ants. In the present study, each of at least seven (and probably ten) out of 11 species of Myrmarachne from peninsular Malaysia associates with one particular species or genus of ant that it specifically resembles; these are therefore 'good' or 'specific' mimics. Myrmarachne malayana lives in the foraging ranges of a variety of ants and shows no specific resemblance to any one genus of ant, and it is best considered as a 'poor' or 'general' mimic. A species of Castianeira (Corinnidae) with a much less precise similarity to ants (a 'poor' mimic) was associated with Polyrhachis ants. It had previously been suggested that Orsima ichneumon (Salticidae) is an ant or insect mimic in reverse; in the present study, it was associated with Polyrhachis ants but is not considered to be an ant-mimic. Two recent theoretical models show how a poor ant-mimic may be better protected than a good mimic under certain circumstances. These data provide some support for the multimodel hypothesis, although not for Sherratt's hypothesis. However, a realistic test of these hypotheses requires more information than that provided here on both mimics and models.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 645–653.     

Assessment of Physical and Chemical Attributes of Sub-Tropical Soil to Predict Long Term Effluent Treatment Potential

On-site wastewater treatment systems aim to assimilate domestic effluent into the environment. Unfortunately failure of such systems is common and inadequate effluent treatment can have serious environmental implications. A research project was undertaken to determine the role of physical and chemical soil properties in the treatment performance of subsurface effluent disposal areas. Monitoring changes in these properties permits improved prediction of the treatment potential of a soil. The changes within soil properties of the disposal area due to effluent application were found to be directly related to the subsurface drainage characteristics, including permeability, clay content and clay type. The major controlling soil physical and chemical attributes were found to be moderate drainage, significant soil cation exchange capacity and dominance of exchangeable Ca or exchangeable Mg over exchangeable Na, low exchangeable Na, clay type and a minimum depth of 0.4 m of potential unsaturated soil before encountering a restrictive horizon. The study confirmed that both the physical properties and chemistry of the soil can be valuable predictive tools for evaluating the long term operation of sewage effluent disposal systems.     

Sex, diet and feeding method-related differences in body condition in the Oystercatcher Haematopus ostralegus

Measurements were made of Oystercatcher corpses to find the most reliable measure of body condition in live birds. Total body weight was as accurate as muscle thickness in assessing the weight of the pectoral muscles, a major store of protein reserves. Total body weight was also a good indicator of fat reserves. Wing‐length was the most reliable measure of body size. Body condition in live birds was measured as an individual's residual weight derived from a general linear model of (loge) body weight against age, month, (loge) wing‐length and time since capture. On the Exe estuary in autumn, there was no significant difference in body condition between same‐age Oystercatchers of different diets and feeding methods. In the winter months, however, body condition differed significantly between mussel feeders using different feeding methods, and between mussel feeders and birds that fed on worms and clams. Differences between diet/feeding methods were not the same for each age group. Birds with the highest mean body condition index in adults were mussel hammerers, in immatures mussel stabbers and in juveniles, worm/clam feeders. No significant difference in body condition was found between the sexes in any age group in autumn. In winter, when birds with the same diet/feeding method were considered, females were significantly heavier than males. However, when birds of all diets and feeding methods were combined, weight differences between the sexes were not apparent. We examine reasons why birds with certain diets and feeding methods may be heavier than others in winter, and why females are sometimes heavier than males. We conclude that, in most cases, it is due to differences between birds in their ability to achieve a common target weight. However, we conclude that adult females try to achieve a higher target weight than males, probably as a premigratory and prebreeding strategy. In the light of this, we consider the consequences for adult females, in terms of reproductive success and survival, of specializing in diets and feeding methods associated with lower body weights in winter.     

Variation in acoustic signals within and among leafhopper species of the genus Alebra (Homoptera, Gicadellidae)

Acoustic behaviour was studied in the four species of Alebra Fieber leafhoppers found in Britain, which are morphologically the closest in the genus: A. wahlbergi (Boheman), A. coryli Le Quesne, A. albostriella (Fallen) and A. viridis Rey. One male call, of a diagnostic structure and produced in all behavioural contexts observed, was recorded for each species. No female acoustic signals were identified. Using male call pattern the three species of Alebra coexisting on Castanea sativa Miller in Kastanitsa, southern Greece, were identified as A. wahlbergi, A. albostriella and A. viridis. Individuals of A. viridis from Kastanitsa had more pronounced external pigmentation than those from Cardiff, South Wales. Discriminant and principal component analysis on variables of the male call of A. viridis distinguished the populations from Cardiff and Kastanitsa, but could not differentiate populations from the two British host plants, Quercus petraea and Q. cerris , in Cardiff. The British and Greek populations differed in the covariation as well as the duration of call components.
Castanea sativa was also recognized as a host plant of A. viridis in Cardiff. Individuals collected from C. saliva had external patterning in the same range of variation as that found for individuals from species of Quercus.
Present evidence strongly suggests that divergence in the acoustic species recognition signals of Alebra is occurring among geographic rather than sympatric host plant-associated populations.     

Nucellar Senescence and Ethylene Production as they Relate to Avocado Fruitlet Abscission

Events preliminary to avocado (Persea americana Mill) fruitletabscission include senescence of the nucellus and seed coat.The dynamics of nucellar deterioration and ethylene productionleading to seed abortion and abscission in avocado was examined.Excised branches bearing clusters of fruit from 1.0–2.5cm diameter were placed in humid chambers to reduce transpirationalwater loss. Fruitlets synchronously began nucellar and seedcoat deterioration 27–33 h after excision and rapidlyprogressed through stages of increasing degradation culminatingin abscission approximately 2 days later. The nucellus-seedcoat produced a temporary burst of ethylene at the first visiblesign of nucellar senescence followed by less ethylene productionin the mesocarp approximately 12 h later. All fruit underwentnucellar degradation prior to abscission. Exogenously appliedethylene accelerated fruitlet abscission with concentrationsas low as 1.0µ 1^–1 and with maximum response at100µl^–1 or greater. Maximal response took 2 days.Aminoethoxyvinyl-glycine (AVG) at 30 µ M inhibited ethyleneproduction and fruitlet abscission. The senescence process,however, was not af fected in any way by ethylene or AVG treatments.Observations of attached fruit suggest that nucellar-seed coatsenescence, concomitant ethylene production, and resulting abscissiontake place in a manner and within a time period similar to thatobserved on detached branches. It is concluded that nucellarand seed coat senescence is prerequisite to avocado fruitletabscission, and the time required from the first indicationof nucellar breakdown to abscission of that fruitlet appearsto be approximately 2 days. The senescence process is responsiblefor a large, transient rate increase in ethylene productionby the nucellus and perhaps seed coat. Ethylene is consideredto be the result rather than the cause of nucellar-seed coatsenescence. The ethylene thus produced induces fruit abscission.     

Opisthobranchiate Mollusca from Ghana: Chromodorididae

Nine species of the opisthobranch family Chromodorididae are described from Ghana: Cadlina evelinae Marcus; C. rumia Marcus; C. dubia sp. nov.; Chromodoris ghanensis (Edmunds); C. kpone sp. nov.; C. luleorosea (Rapp); Hypselodoris tana sp. nov.; H. bilineata (Pruvot-Fol) and Mexichromis tricolor (Cantraine). The small number of species found belonging to this warm-water family is attributed to the cold water of the Benguela current.     

Euryhalinity of Palaeozoic articulate brachiopods

OMonotypic and very low diversity virgianid shell beds from the Upper Ordovician to Lower Silurian dolomites of North Greenland were formed in marginal marine quiet-water hypersaline environments. In the light of this evidence the salinity tolerances of other Palaeozoic articulate brachiopods is evaluated. There are only a small number of species apparently invading hypersaline or brackish environments, but it is significant considering that previously all articulate brachiopods were thought to be fully marine. Two types of occurrence are noted, those species specifically related to marginally marine environments, disappearing with the introduction of fully marine faunas, and the majority of species which extend their normal marine range into marginal conditions. No brachiopod species appears to have invaded very hypersaline or truly brackish conditions. No single group of articulate brachiopods specifically specialised in colonising marginal marine environments, apart from possibly the virgianid pentamerids. Palaeozoic, Upper Ordovician, Lower Silurian, Brachiopoda. Pentamerida, Virgianidae, Greenland, palaeoecology. hypersaline environments, brackish environments .