Regional climate changes drive increased scaled-chrysophyte abundance in lakes downwind of Athabasca Oil Sands nitrogen emissions

Several limnological and paleolimnological investigations have linked enhanced atmospheric nitrogen (N) deposition to nutrient enrichment and increased primary production. The Athabasca Oil Sands Region (AOSR) in northeast Alberta, Canada is a significant source of N emissions, particularly since development intensified during the 1990s, and recent paleolimnological investigations provide evidence of increased lake production in adjacent areas subject to enhanced N deposition. The AOSR, however, has also experienced atmospheric warming since ca. AD 1900, and therefore the relative effects of nutrient deposition and climate changes on lake production remain unclear. We undertook a factorial-design paleolimnological assessment of 16 lakes in northwest Saskatchewan to quantify changes in abundance and species composition of scaled chrysophytes over the past 100 years. Study sites included both N-limited and P-limited lakes within control regions, as well as lakes that receive enhanced N deposition from the AOSR. We hypothesized that a change in algal communities within N-limited AOSR-impacted lakes, without concurrent changes in the other lake groups, would suggest AOSR-derived N as a driver of enhanced primary production. Instead, marked increases in concentrations of scaled chrysophytes, mainly Mallomonas crassisquama, occurred in the recent sediments in cores from all four lake groups (N-limited vs. P-limited, impacted vs. control), suggesting that regional climate change rather than N deposition was the paramount process enhancing chrysophyte production. Because chrysophyte abundances tended to be higher in deep, lower-pH lakes, and chrysophyte time series were fit best by lake-specific generalized additive models, we infer that climate effects may have been mediated by additional catchment and/or lake-specific processes.     

The use of geophysical images in subsurface investigations of the Solway Basin,England

This paper focuses on the use of low-cost geophysical data sets in raster format for structural analysis of a small onshore basin in NW England. Gravity and aeromagnetic data are expressed as images enhanced by a variety of image-processing methods, aimed at expressing the data in a form most readily appreciated by human vision. This involves side-illumination of the data using directional first derivative filters, and pseudo-colouring based on look-up table techniques. The principal data handling method was trend-surface analysis and calculation ofnth-order residual images. Most of the known structural attributes of the basin are resolved, together with previously unknown features affecting the basin's deep architecture.     

Modelling stream acidification in afforested catchments: An assessment of the relative effects of acid deposition and afforestation

A model of the combined long-term effects of acidic deposition and forest growth has been developed and calibrated for an upland site in Scotland. The model is used to perform a series of simulation experiments to assess the relative effects of afforestation and acidic deposition on soil and surface water chemistry. The experiments compare and contrast: (a) the simulated historical effects of increased acidic deposition and forest growth, both individually and in combination; (b) the simulated future effects of various levels of reduction of deposition in combination with the forestry strategies of harvesting with and without replanting. Results indicate that historical acidification of surface waters in areas receiving high levels of acidic deposition has been exacerbated by afforestation practices. Afforestation in the absence of acidic deposition, however, has had a lesser effect on surface water acidification even though the nutrient demands of forest growth have caused significant soil acidification. Comparisons of future forest management strategies in conjunction with likely deposition reductions indicate that, in sensitive areas, replanting of a felled forest without treatment of the soil by addition of base cations, should not be undertaken even if significant deposition reductions are realised.     

Ion microprobe study of intragrain micropermeability in alkali feldspars

Alkali feldspar cleavage fragments from the Klokken layered syenite, South Greenland, were heated to 700°C at 0.1 GPa in 99% H₂ ¹⁸O for 75 h. These samples were then polished and imaged by ion microprobe for ¹⁸O. The feldspars were known to contain areas of pristine, braid micro-perthite which were not turbid and areas of deuteric patch perthite which were turbid. Turbidity is related to the presence of micropores in the feldspars. On imaging the grain, it was found that the ¹⁸O had penetrated into the parts of the grain which were microporous and not into the pristine areas. Micropores are therefore responsible for rendering the feldspars permeable as well as porous. The implications of micropermeable feldspars in several areas of geology are discussed.     

Climatic forcing of carbon-oxygen isotopic covariance in temperate-region marl lakes

Carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern Michigan marl lake display linear covariance over a range of 4.0% Peedee belemnite (PDB) in oxygen and 3.9% (PDB) in carbon. Mechanisms of delta 13 C-delta 18 O coupling conventionally attributed to lake closure in arid-region basins are inapplicable to hydrologically open lake systems. Thus, an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required. We propose that isotopic covariance is a direct record of change in regional climate. In short-residence-time temperate-region lake basins, summer meteoric precipitation is enriched in 18O relative to winter values, and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13C. Thus, climate change toward longer summers and/or shorter winters could result in greater proportions of warm-month meteoric precipitation, longer durations of warm-month productivity, and net long-term enrichment in carbonate 18O and 13C. Isotopic covariance observed in the Michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature, a shift toward greater proportions of seasonal summer precipitation, a shortening of the winter season, or some combination of these three factors.     

The formation of circular littoral cones from tube-fed pāhoehoe: Mauna Loa,Hawai'i

Pyroclastic cones along the southwest coast of Mauna Loa volcano, Hawai'i, have a common structure: (a) an early formed circular outer rim 200–400 m in diameter composed mostly of scoria and lapilli, and (b) one or more later-formed inner rims composed almost exclusively of dense spatter. The spatter activity locally fed short lava flows that ponded within the outer rims. Based on various lines of evidence, these cones are littoral in origin: relationships between the cones and associated flows; the degassed nature of the pyroclasts; and (although not unequivocal) the position of the cones relative to known eruptive vent locations on Mauna Loa. Additional support for the littoral interpretation comes from their similarity to (smaller) littoral cones that have been observed forming during the ongoing Kilauea eruption. The structure of these Mauna Loa cones, however, contrasts with that of standard Hawaiian littoral cones in that there is (or once was) a complete circle of pyroclastic deposits. Furthermore, they are large even though associated with tubefed phoehoe flows instead of 'a'. The following origin is proposed: An initial flow of tube-fed phoehoe into the ocean built a lava delta with a base of hyaloclastite. Collapse of an inland portion of the active tube into the underlying wet hyaloclastites or a water-filled void allowed sufficient mixing of water and liquid lava to generate strong explosions. These explosions broke through the top of the flow and built up the outer scoria/lapilli rims on the solid carapace of the lava delta. Eventually, the supply of water diminished, the explosions declined in intensity to spattering, and the initial rim was filled with spatter and lava.     

Follow-up observations of β-pic-like stars

Following the discovery, by IRAS, of the dust disc around Vega and three other main sequence stars, searches have been made for other candidates. The-Pic-like candidates have 12µm excesses and 100µm fluxes (unlike the Vega-like candidates), so they can be further investigated using ground-based techniques. Data are presented here, comprising 10µm spectroscopy and sub-mm observations, for several candidates from the Walker & Wolstencroft list, showing that the stars have silicate dust, and optically thick dust discs even at 1300µm.     

Mobile Learning in a Human Geography Field Course

This article reports on reusable mobile digital learning resources designed to assist human geography undergraduate students in exploring the geographies of life in Dublin. Developing active learning that goes beyond data collection to encourage observation and thinking in the field is important. Achieving this in the context of large class sizes presents several challenges. Combining in situ learning with spatially accurate historical and contemporary multimedia, a set of location-aware digital mobile tools, or mediascapes, was developed. How scaffolding can be achieved in such a context, focusing on the development of students’ observational, enquiry, and thinking skills in the field was explored.