Invertebrate biodiversity in cold groundwater fissures in Iceland

Iceland has an abundance of fissures that are parallel to the Mid‐Atlantic Ridge where bedrock cracks as a result of continental rifting. Some fissures penetrate the aquifer and expose the groundwater within the bedrock, becoming springs. As such, groundwater fissures have uniform and constant physical and chemical environment but they can differ greatly in morphology. In addition, there is often great variation in depth within fissures and substrate types contrast between vertical rock wall and more heterogenous horizontal bottom. The variation in morphological environment may create dissimilar habitats with unique characteristics and/or influence distribution of resources. Our objective was to study macrozoobenthos communities in cold groundwater fissures in Iceland in relation to physical habitat by comparing invertebrate diversity and density both between fissures with different morphological characteristics as well as between substrate types and depths within fissures. Samples were collected in two fissures in SW Iceland, Silfra and Flosagjá. Assemblages were similar between fissures except for higher densities of cladocerans in Flosagjá fissure. Within fissures, there was significant difference in Shannon diversity between substrate types in Flosagjá, and ostracods were found in significantly higher densities on the bottom. The distribution of all other taxa groups was homogenous in both fissures regardless of depth gradient and substrate. Invertebrates were found to be living within and around a biofilm that covered the entire substrate. These biofilm mats are made from Cyanobacteria and benthic diatoms, which are successful under low light conditions and may minimize any effect of the heterogeneous habitat creating a uniform and suitable microhabitat for invertebrates regardless of depth and substrate type.     

The macroinvertebrate fauna and hydrogeology of springs in central Sweden

The macroinvertebrate fauna of 23 springs in central Sweden was sampled. A total of 79 taxa was recorded, including three crenobiont, nine crenophilic, 33 lotic, 11 lentic and 21 ubiquitous taxa. Only eight were non-insect taxa. Geological and hydrogeological maps were used to categorize each spring, resulting in eight glaciofluvial, 11 moraine and four limestone springs. Faunal composition and environmental factors showed an overall similarity among spring types, except for geographic position, the almost exclusive occurrence of crenobionts in glaciofluvial springs, and factors associated with high concentrations of calcium carbonate in limestone springs. Canonical correspondence analysis showed that the crenobiont caddisflies Parachiona picicornis(Pictet), Crunoecia irrorataCurtis were associated with high discharge and high summer temperature. Lotic taxa, including the stonefly nymph Isoperla grammatica(Poda), the caddis larvae Halesussp. and the mayfly nymph Baetis bundyaeLehmkuhl, were associated with high discharge and low summer temperature, while many lentic and ubiquitous taxa, e.g. dytiscids, were characteristic of small springs. It is suggested that the dominance of insect taxa, and the restricted occurrence of crenophilic and crenobiont taxa, are consequences of the glacial history and/or the hydrogeological setting of springs. Also, the possible influence of `diffusive rarity' of C. irrorataand P. picicornis, is discussed.     

Variation in the Diet of Ducks During Spring Migration

Because management practices that promote the production of plant foods may differ from management practices that promote the production of aquatic invertebrates, a thorough understanding of the diet is needed to develop management strategies for various stages of the annual cycle for dabbling and diving ducks. Diet of dabbling (tribe Anatini) and diving (tribe Aythyini) ducks during breeding, autumn migration, and winter has been documented. Our goal was to estimate and compare the diet of blue-winged teal (Spatula discors), gadwall (Mareca strepera), mallard (Anas platyrhyncos), lesser scaup (Aythya affinis), and ring-necked duck (Aythya collaris) during spring migration in the Mississippi Flyway in the United States and evaluate variation among species. We collected 919 ducks for diet analysis from multiple wetlands at 6 sites across 4 states during the spring migration of 2006 and 2007. We collected ≥10 individuals of each species at each of the 6 study sites except we collected only 1 gadwall at the Scioto River site and 2 lesser scaup at the Cache River site. We detected that the proportion of plant and animal material in foods of each spring migrating duck species was in general intermediate of that found in wintering and breeding birds. Furthermore, the proportion of plant and animal material in the diet of species varied even among closely related species, indicating species are partitioning food sources along a protein-carbohydrate gradient during spring migration. We recommend that resources for ducks be managed to provide diverse wetlands to support the varied diets of even closely related species. © 2021 The Wildlife Society.     

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10^-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.     

The effect of rhizoctonia root disease and applied nitrogen on growth,nitrogen uptake and nutrient concentrations in spring wheat

Root disease caused by Rhizoctonia solani is a common problem of spring wheat in South Australia. There are reports that nitrogen applications can reduce the incidence and severity of the disease. A glasshouse trail in pots examined the effects of disease and of applied nitrogen on wheat growth, and evaluated the utility of the basal stem nitrate concentration in diagnosing deficiency in plants with and without root disease. Plants were harvested at the mid-tillering stage. Shoot growth was increased by applied nitrogen until a maximum yield was attained, after which additional N had no effect on shoot yield. Root growth, however, responded positively only to low levels of applied N, after which it declined, and in the highest N treatment root mass was less than in the plants without applied N. Root disease caused severe reductions in plant growth, and both root and shoot mass were affected similarly. Even though growth of diseased plants responded positively to applied nitrogen the response was less than that of disease-free plants. The critical concentration of basal stem nitrate-N did not appear to be affected by root disease, and was estimated at 1200 mg kg^-1, consistent with other glasshouse data. The basal stem nitrate-N concentration, either in fresh or dried tissue, appeared a better diagnostic tool of N stress than did total shoot N concentration or content, because of sharper definition of critical concentrations. Concentrations of other nutrients in shoot tissue were affected differentially by both applied nitrogen and root disease, but generally did not reach critical levels, although phosphorus and magnesium appeared deficient in very disease-stressed plants.     

Ecology of a cyanobacterial mat community in a Korean thermal wastewater stream

Cyanobacterial mats along a small stream receiving thermal wastewater from an artificial hot spring in the mid-upper part of the Mankyeong River system, Korea, were studied during the winter of 1995-1996. In the cyanobacterium, Oscillatoria terebriformiscomprised >95% of total biomass. Ash-free dry-weight (AFDW) and chlorophyll a in the cyanobacterial mats decreased significantly (r²= 0.78 and 0.83, respectively) with distance downstream from the thermal water outlet, while primary productivity increased slightly. The concentrations of the majority of ions sharply decreased with distance downstream, although they were not markedly related with spatial changes in AFDW, Chl a and primary productivity. O. terebriformis appeared to have a tremendous potential in wastewater treatment because of its marked ability to glean ions.     

Radiation of crenobiontic gastropods on an ancient continental island: the Hemistomia-clade in New Caledonia (Gastropoda: Hydrobiidae)

A vast radiation of hydrobiid spring snails endemic to New Caledonia, a continental island in the Southwest Pacific known for its unique flora and fauna, is described. This radiation comprises a total of 54 named species of which 50 are new. The majority of the species belong to the most basal genus, Hemistomia, which happens to be the first one described from New Caledonia. The remaining species are attributed to four genera, Kanakyella, Pidaconomus, Caledoconcha, and Leiorhagium, which are all introduced in this paper. The radiation as a whole is characterized by the formation of the digestive gland, the stomach with an additional, ciliated proximal chamber, and the subdivision of the pallial oviduct. Whether or not a denticle situated behind the outer lip is a synapomorphy of the whole group cannot be stated with certainty. The genera are distinguished mainly by features of the genital system. For the cladistic analysis, which resulted in 419 equally parsimonious trees, only five characters could be used, and even those were not free of homoplasy. The genera Hemistomia and Pidaconomus are paraphyletic according to this analysis. In contrast to the widely accepted principles of phylogenetic systematics we retain these paraphyletic genera, because otherwise the diversification, i.e. the evolution, which has taken place within the clade could not be expressed in the classification. The majority of the species occur in very restricted areas. Twenty-six (48%) species were found in a single locality and only six species (11%) in ten or more places. The hydrobiid diversity of west coast drainages is much higher than that of river systems draining to the east. This is, at least partly, explained by the differing precipitation regimes and geological conditions of the regions considered. The west coast receives much less rainfall so that in continuous periods of drought the area of a species would be fragmented by drying up of springs and consequently gene flow between the remaining populations reduced, enhancing speciation. In addition, the west is geologically more heterogenous. Unfavourable, insular ultramafic mountains represent barriers for the dispersal along the west coast. Many of the taxa are highly threatened to become extinct in the closer future as a consequence of human activities, such as deforestation, agriculture, surface mining, or uncontrolled fires. The conservation of the unique New Caledonian radiation of crenobiontic gastropods requires a transformation of land management practices on privately-owned sites, and a more global reappraisal of the impact of fire and deforestation on water resources. This revised version was published online in July 2006 with corrections to the Cover Date.