Past and future changes to acidified eastern Canadian lakes: A geochemical modeling approach

As SO₂ emissions are being reduced in North America, it has become important to know how rapidly the surface water chemistry of aquatic systems will recover. The authors applied the model of acidification of groundwater in catchments (MAGIC) to 410 acid-sensitive lakes located in a 3000 km east–west gradient in eastern Canada. The goal was to estimate the water chemistry from pre-acidification times, under worst case conditions (mid 1970s) and what it should be in the year 2030 after proposed acid emission reduction levels agreed-to or planned by Canada and the United States are in place. In eastern Canada, large decreases in pH and ANC are shown between pre-acidification and 1975, the year of greatest historical deposition. Current-day conditions are much improved from 1975. Under the most likely future acid deposition reduction scenarios, an improvement of pH and ANC is shown in all the regions from current-day levels, but not to pre-acidification levels. Dissolved Ca levels were considerably higher at the height of acidification than under pristine conditions, but will return to pre-acidification levels at most of the sites by the year 2030. The results also show that under proposed control programs, a large number of sites in eastern Canada will not return to ANC values >40 μeq L⁻¹, thought to be suitable for healthy aquatic communities.     

Depth zonation of epibenthos on sublittoral hard substrates off Deer Island,Bay of Fundy,Canada

Three locations were selected for detailed study of the epibenthos of sublittoral hard substrates in the Deer Island region of the Bay of Fundy. A total of 10 transects, using photographic and quadrat methods, yielded data on percentage coverage, density and diversity of biota in relation to depth.A cluster analysis, using the Jaccard Coefficient of Association, produced five major clusters, representing three depth zones. The shallow and mid-depth zones lie within the infralittoral, the deep zone within the circalittoral.The shallow zone extends from mean low water (MLW) to a mean depth of 5 m below MLW and consists of two clusters representing minor biological differences. It is characterized by crustose coralline algae and Petrocelis middendorfii which together cover over 70% of the primary substrate. Other macro-algae are rare, as are bryozoans, while sponges are absent. The sea urchin Stronglyocentrotus droebachiensis, the limpet Acmaea testudinalis and chitons belonging to Tonicella are very common and may exert a significant influence on the community structure in terms of grazing pressure.The mid-depth zone has a mean depth of 10 m and consists of two clusters, one representing well-illuminated upward-facing surfaces, the other representing shaded steeply-inclined cliff faces. The zone is characterized by higher species richness (relative to the shallow zone); greater coverage of sponges, bryozoans and hydroids; lower densities of sea urchins and limpets; and less areal coverage by encrusting algae. The cliff-face cluster is characterized by enrichment of bryozoans, anemones, sponges and brachiopods.The deep zone has a mean depth of 18 m, and is animal-dominated, supporting the greatest species richness, with sponges, hydroids, anemones, brachiopods and tunicates common, but algal coverage much reduced.Organisms colonizing the upward-facing surfaces in the shallow and mid-depth zones are here regarded as belonging to the encrusting algae-urchin community, while biota of the shaded cliff faces of the mid-depth zone, together with the biota of the deep zone, are regarded as belonging to the Terebratulina septentrionalis community of previous authors.     

A New Mapping Protocol for Laser Ablation (with Fast-Funnel) Coupled to a Time-of-Flight Mass Spectrometer (LA-FF-ICP-ToF-MS) for the Rapid,Simultaneous Quantification of Multiple Minerals

Although in situ analysis by LA-ICP-MS is considered a rapid technique with minimal sample preparation and data reduction, mapping areas of millimetres in size using a small beam (< 15 μm) can be time consuming (several hours) when a quadrupole ICP-MS is used. In addition, fully quantitative imaging using internal standardisation by LA-ICP-MS is challenging in samples with more than one mineral phase present due to varying ablation rates. A new protocol for the quantification of multiple coexisting phases, mapped at a rate of about 12 mm² h^-1 and a resolution of 12 μm × 12 μm per pixel, is presented. The protocol allows mapping of most atomic masses, ranging from ²³Na to ²³⁸U, using a time-of-flight mass spectrometer (ICP-ToF-MS, TOFWERK) connected to a 193 nm excimer laser. A fast-funnel device was successfully used to increase the aerosol transport speed, reducing the time usually required for mapping by a factor of about ten compared with a quadrupole ICP-MS. The lower limits of detection for mid and heavy masses are in the range 0.1–10 μg g^-1, allowing determination of trace to ultra-trace elements. The presented protocol is intended to be a routine analytical tool that can provide greater access to the spatial distribution of major and trace elements in geological materials.     

Triploporella ? edgelli n. sp., a new Dasycladalean alga from the Lower Cretaceous of Lebanon

The Dasycladalean assemblage of the Jezzinian strata (uppermost Barremian–lowermost Aptian) of Lebanon consists of two organo‐genera and eight genera with eleven species, including eight Triploporellaceae. Although Triploporella marsicana (Praturlon, 1964) was reported by Saint‐Marc from the same interval, it is not found in our material. However, a lookalike, which is herein described as Triploporella ? edgelli n. sp., is identified. This new species has cyst‐containers within the primary segments of its laterals but, because it lacks calcified secondary segments, it is left in open nomenclature.     

The effects of longitudinal variations in valley geometry and wood load on flood response

We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m³ ha⁻¹. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m³ ha⁻¹. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd.     

Land-use transition for bioenergy and climate stabilization: model comparison of drivers,impacts and interactions with other land use based mitigation options

In this article, we evaluate and compare results from three integrated assessment models (GCAM, IMAGE, and ReMIND/MAgPIE) regarding the drivers and impacts of bioenergy production on the global land system. The considered model frameworks employ linked energy, economy, climate and land use modules. By the help of these linkages the direct competition of bioenergy with other energy technology options for greenhouse gas (GHG) mitigation, based on economic costs and GHG emissions from bioenergy production, has been taken into account. Our results indicate that dedicated bioenergy crops and biomass residues form a potentially important and cost-effective input into the energy system. At the same time, however, the results differ strongly in terms of deployment rates, feedstock composition and land-use and greenhouse gas implications. The current paper adds to earlier work by specific looking into model differences with respect to the land-use component that could contribute to the noted differences in results, including land cover allocation, land use constraints, energy crop yields, and non-bioenergy land mitigation options modeled. In scenarios without climate change mitigation, bioenergy cropland represents 10–18 % of total cropland by 2100 across the different models, and boosts cropland expansion at the expense of carbon richer ecosystems. Therefore, associated emissions from land-use change and agricultural intensification as a result of bio-energy use range from 14 and 113 Gt CO2-eq cumulatively through 2100. Under climate policy, bioenergy cropland increases to 24–36 % of total cropland by 2100.     

Response of U‐Pb Zircon and Rb‐Sr total‐rock and mineral systems to low‐grade regional metamorphism in proterozoic igneous rocks,mount Isa,Australia

A detailed Rb‐Sr total‐rock and mineral and U‐Pb zircon study has been made on suites of Proterozoic silicic volcanic rocks and granitic intrusions, from near Mt Isa, northwest Queensland. Stratigraphically consistent U‐Pb zircon ages within the basement igneous succession show that the oldest recognized crustal development was the outpouring of acid volcanics (Leichhardt Metamorphics) 1865 ± 3 m.y. ago, which are intruded by coeval, epizonal granites and granodiorites (Kalkadoon Granite) whose pooled U‐Pb age is 1862 ⁺²⁷ _‐21 m.y. A younger rhyolitic suite (Argylla Formation) within the basement succession has an age of 1777 ± 7 m.y., and a third acid volcanic unit (Carters Bore Rhyolite), much higher again in the sequence, crystallized 1678 ± 1 m.y. ago.

All of these rocks are altered in various degrees by low‐grade metamorphic events, and in at least one area, these events were accompanied by, and can be partly related to, emplacement of a syntectonic, foliated granitic batholith (Wonga Granite) between 1670 and 1625 m.y. ago. Rocks that significantly predate this earliest recognized metamorphism, have had their primary Rb‐Sr total‐rock systematics profoundly disturbed, as evidenced by 10 to 15% lowering of most Rb‐Sr isochron ages, and a general grouping of many of the lowered ages (some of which are in conflict with unequivocal geological relationships) within the 1600–1700 m.y. interval. Such isochrons possess anomalously high initial ⁸⁷Sr/⁸⁶Sr ratios, and some have a slightly curved array of isotopic data points. Disturbance of the Rb‐Sr total‐rock ages is attributed primarily to mild hydrothermal leaching, which resulted in the loss of Sr (relatively enriched in ⁸⁷Sr in the Sr‐poor (high Rb/Sr) rocks as compared with the Sr‐rich rocks).     

Pressure-Temperature-Time Constraints for the Seve Nappe of the Singis-Tjuoltajaure area Central Norrbotten Caledonides,Sweden : Implications for Early Caledonian Marginal Baltica

Abstract

This study provides some of the first integrated P-T-t constraints for the evolution of the Finnmarkian tectonothermal event within the northern Scandinavian Caledonides. Samples from units within the Seve Nappe of the Singis-Tjuoltajaure region contain assemblages which allow the application of well calibrateted thermoharometers. New results include : I ) Eclogite grade rocks of the Aurek Assemblage yield temperatures and pressures in excess of 12 kb and 730° С. 2) Temperatures and pressures obtained for seven samples from the Savotjåkka Assemblage range from 571766” С and 8.9-13.6 kb. These pressures correspond to burial depths of approximately 30-45 km during the Finn-markian (190 Ma) for the outer margin of Baltica. when combined with ⁴⁰Ar/³⁹Ar data, uplift rates of .2-.4 mm/yr during the early Finnmarkian arc obtained, and 3) Within the Vidja Assemblage a pressure and temperature of 7.3 ± 1.7 kb and 616 ± 60° is obtained. These conditions are consistent with the interpretation of a late Finnmarkian (450 Ma) Intra-Seve juxtaposition of the Vidja and Aurek Assemblages after approximately 20-30 km of slow uplift from peak pressures recorded during the early Finnmarkian.

This study provides new constraints which need to be considered in future tectonic models. These constraints include : I ) The Savopakte Assemblage records high pressures and high temperatures during the Finnmarkian and 2) Finnmarkian uplift rates of .2-.4 mm/yr were likely for marginal Baltica after peak metamorphism. Rates of this magnitude may be accounted for solely by slow erosion and do not require (but do not preclude) more complex tectonic interpretations. A tectonic model provided by the Late Cenozoic thrust belts of the Apennine system of the mediterranean region, may lead to new insights into the Early Paleozoic evolution of the Scandinavian Caledonides.     

The structure of separated flow past a circular cylinder in a rotating frame

Abstract

This paper examines the detailed E ^1/4-layer structure of separated flow past a circular cylinder in a low-Rossby-number rotating fluid as the Ekman number E tends to zero. This structure is based on an initial proposal by Page (1987) but with some modifications in response to further evidence, outlined both in this paper and elsewhere, on the behaviour of E ^1/4-layer flows in this context. Numerical calculations for flow in an E ^1/4 shear layer along the separated free streamline are described and the mass flux from this layer is then used to calculate the higher-order flow within the separation bubble. The flow structure is found to have two forms, depending on the value of the O(1) parameter λ, and these are compared with results from published “Navier-Stokes” type calculations for the flow at small but finite values of E.