Nutrient cycling in hybrid poplar stands in Saskatchewan : implications for long-term productivity

Intensive management of short rotation hybrid poplar (HP) plantations on agriculture land has demonstrated good early yields and promise as an alternative crop for farmers selling fibre to the forest industry. However, multiple rotations of HP may impact the future productivity of plantations through nutrient removals. The objectives, therefore, of this study were to determine the nutrient stores and fluxes for two HP plantations with differing site quality, fertilizer applications and past land management practices and to construct a 20-year nutrient budget to examine impacts of harvesting short rotation HP on long-term productivity.Heights and biomass were measured by harvesting above- and below-ground and separating biomass into tree components; measurement of atmospheric deposition, mineral weathering, litterfall, litter decomposition, and leaching for HP plantations on an Alfalfa (HPA) and Pasture (HPP) sites in 2004-05. The budget was developed by averaging fluxes over 2 years and scaling up to a 20-year rotation. Unfertilized treatments in the HPA plantation showed greater tree growth than all other treatments. Fertilized and unfertilized treatments had greater biomass production and nutrient pools than treatments at the HPP plantation. The fertilizer treatments did not affect on biomass production and nutrient accumulation.Nutrient additions to the HPA were greater than the HPP plantations for leaf litterfall and leaching. Nutrient resorption from senescing leaves was greater at the HPP plantation suggesting that nutrient pools were smaller and that trees responded by keeping nutrients in the biomass. Fertilization at both plantations increased nutrient flow for inputs and outputs in 2004-05. Water leachate and leaf litterfall showed increased nutrient contents in fertilized treatments at both plantations.A high fertility plantation that used fertilizer and practiced whole-tree harvesting exported more nutrients (and fibre) than a plantation with marginal site quality practicing stem-only harvesting. Time to replenish nutrients from atmospheric deposition and mineral weathering would range from 6 to 50 years for Ca and N, respectively, suggesting that subsequent plantations would require fertilizers to replenish soil nutrient reserves.While HP plantations in Saskatchewan can produce high yields, they require large nutrient inputs and are inefficient (sequester a large amount) in nutrient use. High site quality is important to obtain high yields but conservational techniques, such as stem-only harvesting, are important in maintaining site quality over the long-term

Conrad Deep: a new northern Red Sea deep. Origin and implications for continental rifting

A previously unknown deep, here called Conrad Deep, was discovered during an extensive geophysical survey of the northern Red Sea in June, 1984. Conrad Deep is located at 27°03’N, 34°43’E, only 90 km south of the Gulf of Suez and is the most northern deep yet discovered in the Red Sea. It is located within a well developed axial depression which also contains Charcot Deep, 100 km to the south. The axial depression is associated with abundant recent deformation and is situated at the peak of a regional heat flow high extending across the rift. Conrad Deep is typical of the small northern type Red Sea Deep. It is 10 km long, 2 km wide and has a maximum depth of 1460 m. It is associated with high and variable heat flow values and large magnetic anomalies. There is no evidence of a dense brine layer. Detailed analysis of the geophysical data implies that the deep probably results from a very recent (< 40,000 years) intrusion into continental type basement. The formation of a well defined axial depression associated with very high heat flow and small deeps resulting from isolated intrusions may be the first step in the transition from continental extension to seafloor spreading

Stereoacuity in various fields of gaze

Stereoacuity in various fields of gaz

Thermal consequences of lithospheric extension: Pure and simple

Simple shear and pure shear extension of the lithosphere produce very different patterns of heat flow and topography. These differences are investigated using a numerical technique which solves for two-dimensional conductive and advective heat transport through time. Simple shear extension of the lithosphere is modeled as occurring along a straight shear zone. Two parameters define the simple shear model: the dip of the shear zone and its width. Likewise, the pure shear model is defined by two variables: the initial width of a vertical zone of pure shear extension and the rate of change of its width. These pairs of parameters are varied between calculations, as is the overall rate of extension. Each model results in distinct patterns of crustal thinning, lithospheric thermal structure, heat flow, thermal uplift, crustal subsidence, and topography. For the simple shear model, extension results in asymmetric uplift across the rift, while the total volume of uplift is limited by the total amount of extension. The peak heat flow and thermal uplift are centered over the intersection of the shear zone with the surface. Isostatic response to simple shear extension results in successive, formerly active shear zones being rotated into listric faults which sole into a sub-horizontal detachment. The pure shear results show that the surface heat flow is greater for smaller widths of the zone of extension. For the same overall extension rate, a pure shear model with a narrow zone of extension can result in pressure release melting of the mantle long before low angle simple shear models. These results are compared with topographic and heat flow data from the northern Red Sea rift, a Neogene continental rift which is close to initiating seafloor spreading. The long wavelength topographic asymmetry across the Red Sea, which has been cited as evidence for simple shear extension of the lithosphere, is not matched by any of the models. The observed high heat flow anomalies in the Red Sea require a large component of pure shear lithospheric extension centered under the region of maximum crustal extension. In contrast, at the plate separation rate of the northern Red Sea, simple shear extension of the lithosphere along a shallow ( <30° ) dip detachment is ineffective in reproducing the observed heat flow anomalies. Only a narrowing region of pure shear extension can satisfy the width of the rift, and the peak heat flow values and generate pressure release meltin

Reconstruction of Tertiary Progradation and Clinoform Development on the New Jersey Passive Margin by 2-D Backstripping

We have reconstructed the Oligocene to Middle Miocene paleobathymetry and stratigraphy of the New Jersey margin using a modified backstripping technique. By analyzing the geometry of the margin through time, we investigate its response to fluctuating sea level, changing climate, and variable sediment supply during the Tertiary. The reconstructions reveal a change in the margin morphology from a more steeply dipping (1 : 300 to 1 : 500) carbonate ramp in the Eocene to a flatter shelf with a sharp shelf edge at present. This was accomplished by an increase in the terrigenous sediment supply that filled available accommodation and caused progradation across the margin. We link the increase in sediment flux with climatic cooling rather than tectonic processes. The progradation is evidenced by a series of clinoforms whose formation was modulated by sea level and which extend over 100 km across the shelf. The height and dip of the clinoforms increased as they extended onto the deeper parts of the earlier ramp. The Miocene clinoform rollovers at the New Jersey margin had water depths of ∼60–130 m and are interpreted as the edge of a new continental shelf built over the older ramp. Sea-level fall was probably insufficient to drive the Miocene shorelines past the shelf breaks. Thus, measurements of sea-level amplitude based upon `coastal' onlap over the clinoforms are not reliable

Active deformation and shallow structure of the Wagner, Consag, and Delfín Basins, northern Gulf of California, Mexico

Oblique rifting began synchronously along the length of the Gulf of California at 6 Ma, yet there is no evidence for the existence of oceanic crust or a spreading transform fault system in the northern Gulf. Instead, multichannel seismic data show a broad shallow depression, ∼70 × 200 km, marked by active distributed deformation and six ∼10-km-wide segmented basins lacking well-defined transform faults. We present detailed images of faulting and magmatism based on the high resolution and quality of these data. The northern Gulf crust contains a dense (up to 18 faults in 5 km) complex network of mainly oblique-normal faults, with small offsets, dips of 60–80° and strikes of N-N30°E. Faults with seafloor offsets of tens of meters bound the Lower and two Upper Delfín Basins. These subparallel basins developed along splays from a transtensional zone at the NW end of the Ballenas Transform Fault. Twelve volcanic knolls were identified and are associated with the strands or horsetails from this zone. A structural connection between the two Upper Delfín Basins is evident in the switching of the center of extension along axis. Sonobuoy refraction data suggest that the basement consists of mixed igneous sedimentary material, atypical of mid-ocean ridges. On the basis of the near-surface manifestations of active faulting and magmatism, seafloor spreading will likely first occur in the Lower Delfín Basin. We suggest the transition to seafloor spreading is delayed by the lack of strain-partitioned and focused deformation as a consequence of shear in a broad zone beneath a thick sediment cover

Vulnerability of low-arsenic aquifers to municipal pumping in Bangladesh

Sandy aquifers deposited >12,000 years ago, some as shallow as 30 m, have provided a reliable supply of low-arsenic (As) drinking water in rural Bangladesh. This study concerns the potential risk of contaminating these aquifers in areas surrounding the city of Dhaka where hydraulic heads in aquifers >150 m deep have dropped by 70 m in a few decades due to municipal pumping. Water levels measured continuously from 2012 to 2014 in 12 deep (>150 m), 3 intermediate (90-150 m) and 6 shallow (<90 m) community wells, 1 shallow private well, and 1 river piezometer show that the resulting drawdown cone extends 15-35 km east of Dhaka. Water levels in 4 low-As community wells within the 62-147 m depth range closest to Dhaka were inaccessible by suction for up to a third of the year. Lateral hydraulic gradients in the deep aquifer system ranged from 1.7 × 10-4 to 3.7 × 10-4 indicating flow towards Dhaka throughout 2012-2014. Vertical recharge on the edge of the drawdown cone was estimated at 0.21 ± 0.06 m/yr. The data suggest that continued municipal pumping in Dhaka could eventually contaminate some relatively shallow community wells

PEERS - an open science “Platform for the Exchange of Experimental Research Standards” in biomedicine

Funding The PEERS Consortium is currently funded by Cohen Veterans Bioscience Ltd and grants COH-0011 from Steven A. Cohen. Acknowledgements We would like to thank IJsbrand Jan Aalbersberg, Natasja de Bruin, Philippe Chamiot-Clerc, Anja Gilis, Lieve Heylen, Martine Hofmann, Patricia Kabitzke, Isabel Lefevre, Janko Samardzic, Susanne Schiffmann and Guido Steiner for their valuable input and discussions during the conceptualization of PEERS and the initial phase of the project.Peer reviewedPublisher PD

Locked and loading megathrust linked to active subduction beneath the Indo-Burman Ranges

The Indo-Burman mountain rangesmarkthe boundary between the Indian and Eurasian plates, north of the Sumatra–Andaman subduction zone. Whether subduction still occurs along this subaerial section of the plate boundary, with 46mm/yr of highly oblique motion, is contentious. About 21mm/yr of shear motion is taken up along the Sagaing Fault, on the eastern margin of the deformation zone. It has been suggested that the remainder of the relative motion is taken up largely or entirely by horizontal strike-slip faulting and that subduction has stopped. Here we present GPS measurements of plate motions in Bangladesh, combined with measurements from Myanmar and northeast India, taking advantage of a more than 300 km subaerial accretionary prism spanning the Indo-Burman Ranges to the Ganges–Brahmaputra Delta. They reveal 13–17mm/yr of plate convergence on an active, shallowly dipping and locked megathrust fault. Most of the strike-slip motion occurs on a few steep faults, consistent with patterns of strain partitioning in subduction zones. Our results strongly suggest that subduction in this region is active, despite the highly oblique plate motion and thick sediments. We suggest that the presence of a locked megathrust plate boundary represents an underappreciated hazard in one of the most densely populated regions of the world