Timescales of carbon turnover in soils with mixed crystalline mineralogies

Organic matter–mineral associations stabilize much of the carbon (C) stored globally in soils. Metastable short-range-order (SRO) minerals such as allophane and ferrihydrite provide one mechanism for long-term stabilization of organic matter in young soil. However, in soils with few SRO minerals and a predominance of crystalline aluminosilicate or Fe (and Al) oxyhydroxide, C turnover should be governed by chemisorption with those minerals. Here, we correlate mineral composition from soils containing small amounts of SRO minerals with mean turnover time (TT) of C estimated from radiocarbon (¹⁴C) in bulk soil, free light fraction and mineral-associated organic matter. We varied the mineral amount and composition by sampling ancient soils formed on different lithologies in arid to subhumid climates in Kruger National Park (KNP), South Africa. Mineral contents in bulk soils were assessed using chemical extractions to quantify Fe oxyhydroxides and SRO minerals. Because of our interest in the role of silicate clay mineralogy, particularly smectite (2 : 1) and kaolinite (1 : 1), we separately quantified the mineralogy of the clay-sized fraction using X-ray diffraction (XRD) and measured ¹⁴C on the same fraction. <br><br> Density separation demonstrated that mineral associated C accounted for 40–70 % of bulk soil organic C in A and B1 horizons for granite, nephelinite and arid-zone gabbro soils, and &gt; 80 % in other soils. Organic matter strongly associated with the isolated clay-sized fraction represented only 9–47 % of the bulk soil C. The mean TT of C strongly associated with the clay-sized fraction increased with the amount of smectite (2 : 1 clays); in samples with &gt; 40 % smectite it averaged 1020 ± 460 years. The C not strongly associated with clay-sized minerals, including a combination of low-density C, the C associated with minerals of sizes between 2 µm and 2 cm (including Fe oxyhydroxides as coatings), and C removed from clay-sized material by 2 % hydrogen peroxide had TTs averaging 190 ± 190 years in surface horizons. Summed over the bulk soil profile, we found that smectite content correlated with the mean TT of bulk soil C across varied lithologies. The SRO mineral content in KNP soils was generally very low, except for the soils developed on gabbros under more humid climate that also had very high Fe and C contents with a surprisingly short, mean C TTs. In younger landscapes, SRO minerals are metastable and sequester C for long timescales. We hypothesize that in the KNP, SRO minerals represent a transient stage of mineral evolution and therefore lock up C for a shorter time. <br><br> Overall, we found crystalline Fe-oxyhydroxides (determined as the difference between Fe in dithionate citrate and oxalate extractions) to be the strongest predictor for soil C content, while the mean TT of soil C was best predicted from the amount of smectite, which was also related to more easily measured bulk properties such as cation exchange capacity or pH. Combined with previous research on C turnover times in 2 : 1 vs. 1 : 1 clays, our results hold promise for predicting C inventory and persistence based on intrinsic timescales of specific carbon–mineral interactions

Do Farm Subsidies Affect Crop Diversification?

The United States spends $20 billion each year on farm subsidies. Farmers face increased risk and income variation when their crop portfolio is less diversified. It’s possible for farm subsidies to decrease diversification if they are focused on specific crops. Utilizing state level subsidy and agricultural data from the Environmental Working Group, I used econometric analysis to estimate the effect of farm subsidies on crop diversification. I used the number of acres planted from the 15 top most subsidized and grown crops in the United States to derive my dependent variable, the Herfindahl-Hirschman index (HHI). The HHI is a market concentration index; I used it as my measure of crop diversification. I tested to see if changes in subsidy values had an impact on the index. I found that crop specific subsidies had a statistically significant effect on diversification. Some crop subsidies increase overall crop diversification while others lead to less diversification. Research suggests that decreases in crop diversification has negative consequences for farmers and society in general

How Changes in Plant Community Structure Affect Ant Communities

We investigated how change in plant community composition and vegetative structure brought about by annual grass-specific herbicide application affects terrestrial arthropod communities, with special emphasis on the potential of the endangered Fender’s blue butterfly, Plebejus icarioides fenderi (Family: Lycaenidae). Larvae of this species form facultative protective mutualisms with ants, who chase away potential predators of the larvae. We used pitfall trapping to compare ant community structure between control and herbicide-treated plots through time. The extent to which major changes in plant community composition affect the mutualistic ant community may have relevance for management decisions if the focus of the conservation effort has strong ecological interactions with greatly affected non-target species

Advanced Security Infrastructures for Grid Education

This paper describes the research conducted into advanced authorization infrastructures at the National e-Science Centre (NeSC) at the University of Glasgow and their application to support a teaching environment as part of the Dynamic Virtual Organisations in e-Science Education (DyVOSE) project. We outline the lessons learnt in teaching Grid computing and rolling out the associated security authorisation infrastructures, and describe our plans for a future, extended security infrastructure for dynamic establishment of inter-institutional virtual organisations (VO) in the education domain

Offshore CO2 storage: Sleipner natural gas field beneath the North Sea

Sleipner is the world's longest-running industrial-scale storage project and the first example of underground CO2 storage arising as a direct response to environmental legislation. It began in 1996, injecting around one million tonnes (1 Mt) of CO2 per year into the Utsira Sand, a relatively shallow saline aquifer. By late 2011 over 13 Mt of CO2 had been securely stored. A comprehensive research-focused monitoring programme was carried out with multiple time-lapse surveys; predominantly 3D seismic but also 2D seismic, gravimetry and controlled-source electromagnetics (CSEM). The time-lapse seismic data image the CO2 plume clearly in the reservoir with very high detection capability and show no evidence of CO2 migration from the storage reservoir. Although not specifically designed for this purpose, the monitoring programme fulfils most of the requirements of the recently developed European regulatory framework for CO2 underground storage

Saline aquifer CO2 storage : a demonstration project at the Sleipner Field : Work Area 5 (Geophysics) : gravity modelling of the CO2 bubble

A principal aim of the SACS project is to monitor the injected CO2 by geophysical methods and to develop a robust and repeatable monitoring and verification methodology for future CO2 sequestration operations. This report evaluates the applicability of microgravity surveys as a means of monitoring the future subsurface distribution and migration of the Sleipner CO2 bubble. Time-lapse seismic data acquired in 1999, after 2.3 MT of CO2 injection, show an exceptionally clear image of the CO2 bubble, characterised by very high reflection amplitudes. The outer envelope of the amplitude anomaly roughly defines an elliptical cylindrical ‘bubble envelope’, ~ 225 m high, with a major axis of ~ 1500 m oriented NNE and a minor axis of ~ 600 m. Gravity modelling was based on a number of scenarios. Two ‘in situ’ scenarios assume that the CO2 is entirely contained within the bubble envelope. The 1999 and 2001 in situ models assume respectively that 2.3 MT and 4MT of CO2 are contained within the envelope. Two migration scenarios are also modelled. The first assumes that 2.3MT of CO2 migrate vertically upwards into the overlying caprock succession to between depths of 375 and 600 m. The second migration model looks further ahead to the situation where 3 x 107 m3 (~ 10.5 – 21.0 MT depending on the density) of CO2 have been injected, and migrate laterally beneath the caprock at the top of the reservoir. Results depend strongly on the assumed density of the injected CO2 at reservoir conditions, which is subject to significant uncertainty. Only one, poorly-constrained, reservoir temperature measurement of 37 ° C is available. A density-depth profile based on this suggests that the density of CO2 in the reservoir is ~ 700 kgm-3. However the possibility of significantly lower densities cannot be discounted and modelling also includes a lower density case of 350 kgm-3. The 1999 and 2001 in situ cases produce anomalies which would be barely detectable if the higher density of CO2 is assumed. With the lower density however anomalies should be readily detectable with a modern seabed gravimeter. The vertical migration scenario indicates that large-scale vertical migration into the caprock, to depths where densities would be unequivocally lower, would be readily detected. The lateral migration scenario, whereby a single thin layer of CO2 migrates beneath the top reservoir seal, produces small anomalies which may be locally detectable but with insufficient resolution to enable effective migration mapping. However if lateral migration is via several layers, beneath intra-reservoir shales, then anomalies should be more usefully measurable. Obtaining time-lapse gravimeter readings directly above the bubble would appear to offer the best chance of obtaining useful information. Coupled with geometric information provided by the time-lapse seismic data, the gravity should be able to discriminate between the low and high CO2 density scenarios. This would provide important constraints on future reservoir modelling and also the volume estimates based on the seismic velocity pushdown effect. Related to this, gravity data would offer the potential to provide independent verification of the amount of CO2 sequestered. In addition gravimetric surveys above the bubble could provide an effective ‘early warning’ of major caprock breaching

Snowmelt Simulation

The rapid growth in recent years of a variety of demands upon available water resources has lead to an increasing interest in more fundamental approaches to the science of hydrology. Accompanying this growth has been a need for an increased understanding of the snowmelt process. A completely adequate description of the entire physical process of snowmelt under all conditions is not yet available. The complex interrelated and variable nature of the snowmelt processes that occur simultaneously complicate the problem. A preliminary mathematical model of the snowmelt process has been developed in which processes such as pack settlement rates and energy flow in the pack by means of both conduction and liquid movement are considered. Factors such as an temperature, surface albedo, and degree and direction of slope are also included. A temperature criterion is applied to predict the form of precipitation input (snow or rain) to the model. Equations of the various processes are synthesized into a dynamic model of the total system by means of an electronic analog computer. This computer was utilized primarily because of its ability to (1) perform repetitive operations at very high speeds and (2) solve directly the several time-dependent partial differential equations included in the model. Field data from snow laboraties operated by the Corps of Engineers and highly instrumented watersheds of the Agricultural Research Service are being used to test and verify the model. Inital results have indicated close agreement between observed and computed results. Sensitivity studies have been conducted, and work is continuing to further test and improve the model

History of Popular Music 2 (1960-today)

A syllabus designed for a course covering the history of popular music (country, rock, hip hop, R&B, etc.) from 1960 to today

Drug resistance outcomes of long-term ART with tenofovir disoproxil fumarate in the absence of virological monitoring

Objectives: The resistance profiles of patients receiving long-term ART in sub-Saharan Africa have been poorly described. This study obtained a sensitive assessment of the resistance patterns associated with long-term tenofovir-based ART in a programmatic setting where virological monitoring is yet to become part of routine care. Methods: We studied subjects who, after a median of 4.2 years of ART, replaced zidovudine or stavudine with tenofovir disoproxil fumarate while continuing lamivudine and an NNRTI. Using deep sequencing, resistance-associated mutations (RAMs) were detected in stored samples collected at tenofovir introduction (T0) and after a median of 4.0 years (T1). Results: At T0, 19/87 (21.8%) subjects showed a detectable viral load and 8/87 (9.2%) had one or more major NNRTI RAMs, whereas 82/87 (94.3%) retained full tenofovir susceptibility. At T1, 79/87 (90.8%) subjects remained on NNRTI-based ART, 5/87 (5.7%) had introduced lopinavir/ritonavir due to immunological failure, and 3/87 (3.4%) had interrupted ART. Whilst 68/87 (78.2%) subjects maintained or achieved virological suppression between T0 and T1, a detectable viral load with NNRTI RAMs at T0 predicted lack of virological suppression at T1. Each treatment interruption, usually reflecting unavailability of the dispensary, doubled the risk of T1 viraemia. Tenofovir, lamivudine and efavirenz selected for K65R, K70E/T, L74I/V and Y115F, alongside M184V and multiple NNRTI RAMs; this resistance profile was accompanied by high viral loads and low CD4 cell counts. Conclusions: Viraemia on tenofovir, lamivudine and efavirenz led to complex resistance patterns with implications for continued drug activity and risk of onward transmission

Renal health after long-term exposure to tenofovir disoproxil fumarate (TDF) in HIV/HBV positive adults in Ghana

Objectives: The study assessed markers of renal health in HIV/HBV co-infected patients receiving TDF- containing antiretroviral therapy in Ghana. Methods: Urinary protein-to-creatinine ratio (uPCR) and albumin-to-protein ratio (uAPR) were measured cross-sectionally after a median of four years of TDF. At this time, alongside extensive laboratory testing, patients underwent evaluation of liver stiffness and blood pressure. The estimated glomerular filtration rate (eGFR) was measured longitudinally before and during TDF therapy. Results: Among 101 participants (66% women, median age 44 years, median CD4 count 572 cells/mm 3 ) 21% and 17% had detectable HIV-1 RNA and HBV DNA, respectively. Overall 35% showed hypertension, 6% diabetes, 7% liver stiffness indicative of cirrhosis, and 18% urinary excretion of Schistosoma antigen. Tubular proteinuria occurred in 16% of patients and was independently predicted by female gender and hypertension. The eGFR declined by median 1.8 ml/min/year during TDF exposure (IQR −4.4, −0.0); more pronounced declines ( ≥5 ml/min/year) occurred in 22% of patients and were associated with receiv-ing ritonavir-boosted lopinavir rather than efavirenz. HBV DNA, HBeAg, transaminases, and liver stiffness were not predictive of renal function abnormalities. Conclusions: The findings mandate improved diagnosis and management of hypertension and suggest targeted laboratory monitoring of patients receiving TDF alongside a booster in sub-Saharan Africa