Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

Journal ArticleDrylands worldwide are experiencing rapid and extensive environmental change, concomitant with the encroachment of woody vegetation into grasslands. Woody encroachment leads to changes in both the structure and function of dryland ecosystems and has been shown to result in accelerated soil erosion and loss of soil nutrients. Covering 40% of the terrestrial land surface, dryland environments are of global importance, both as a habitat and a soil carbon store. Relationships between environmental change, soil erosion, and the carbon cycle are uncertain. There is a clear need to further our understanding of dryland vegetation change and impacts on carbon dynamics. Here two grass-to-woody ecotones that occur across large areas of the southwestern United States are investigated. This study takes a multidisciplinary approach, combining ecohydrological monitoring of structure and function and a dual-proxy biogeochemical tracing approach using the unique natural biochemical signatures of the vegetation. Results show that following woody encroachment, not only do these drylands lose significantly more soil and organic carbon via erosion but that this includes significant amounts of legacy organic carbon which would previously have been stable under grass cover. Results suggest that these dryland soils may not act as a stable organic carbon pool, following encroachment and that accelerated erosion of carbon, driven by vegetation change, has important implications for carbon dynamics.University of ExeterRothamsted Research North Wyk

Intensive management in grasslands causes diffuse water pollution at the farm scale

Arable land use is generally assumed to be the largest contributor to agricultural diffuse pollution. This study adds to the growing evidence that conventional temperate intensively managed lowland grasslands contribute significantly to soil erosion and diffuse pollution rates. This is the first grassland study to monitor hydrological characteristics and multiple pollutant fluxes (suspended sediment [SS] and the macronutrients: total oxidized nitrogen-N [TONN], total phosphorus [TP], and total carbon [TC]) at high temporal resolution (monitoring up to every 15 min) over 1 yr. Monitoring was conducted across three fields (6.5-7.5 ha) on the North Wyke Farm Platform, UK. The estimated annual erosion rates (up to 527.4 kg ha-1), TP losses (up to 0.9 kg ha-1), and TC losses (up to 179 kg ha-1) were similar to or exceeded the losses reported for other grassland, mixed land-use, and arable sites. Annual yields of TONN (up to 3 kg ha-1) were less than arable land-use fluxes and earlier grassland N studies, an important result as the study site is situated within a Nitrate Vulnerable Zone. The high-resolution monitoring allowed detailed "system's functioning" understanding of hydrological processes, mobilization- transport pathways of individual pollutants, and the changes of the relative importance of diffuse pollutants through flow conditions and time. Suspended sediment and TP concentrations frequently exceeded water quality guidelines recommended by the European Freshwater Fisheries Directive (25 mg L-1) and the European Water Framework Directive (0.04 mg soluble reactive P L-1), suggesting that intensively managed grasslands pose a significant threat to receiving surface waters. Such sediment and nutrient losses from intensively managed grasslands should be acknowledged in land management guidelines and advice for future compliance with surface water quality standards.NERC-Case PhD awardUK Biotechnology and Biological Sciences Research Counci

Understanding spatial variability of soil properties: a key step in establishing field- to farm-scale agro-ecosystem experiments

PublishedNo abstract is available for this article.NERCBBSR

Long-lived excited-state dynamics of i-motif structures probed by time-resolved infrared spectroscopy

UV-generated excited states of cytosine (C) nucleobases are precursors to mutagenic photoproduct formation. The i-motif formed from C-rich sequences is known to exhibit high yields of long-lived excited states following UV absorption. Here the excited states of several i-motif structures have been characterized following 267 nm laser excitation using time-resolved infrared spectroscopy (TRIR). All structures possess a long-lived excited state of ∼300 ps and notably in some cases decays greater than 1 ns are observed. These unusually long-lived lifetimes are attributed to the interdigitated DNA structure which prevents direct base stacking overlap

Catalysis in flow: Operando study of Pd catalyst speciation and leaching

A custom-made plug flow reactor was designed and constructed to examine the behaviour of Pd catalysts during Suzuki-Miyaura cross-coupling reactions. Spatial-temporal resolution of catalyst activation, deactivation and leaching processes can be obtained by single-pass experiments. Subsequent deployment of the flow reactor in a XAS beam line revealed speciation of Pd along the catalyst bed

The International Pulsar Timing Array: First data release

International audienceThe highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such 'pulsar timing arrays' (PTAs) have been set up around the world over the past decades and collectively form the 'International' PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limit

Treatment of established osteoporosis: a systematic review and cost–utility analysis

Background and aims Osteoporosis is a systemic skeletal disease, characterised by low bone mass and microarchitectural deterioration of bone tissue with a subsequent increase in bone fragility and susceptibility to fracture. The most serious clinical consequence of osteoporosis is hip fracture, which increases in incidence exponentially with age and incurs high morbidity, mortality and healthcare expenditure. Other common fractures occur at the spine, forearm and shoulder. Osteoporosis is operationally defined by the measurement of bone mineral density (BMD) at the hip, and is diagnosed in women when BMD is 2.5 standard deviations (SDs) or more below the average for young healthy women. Established osteoporosis denotes the disease in the presence of one or more fragility fractures. A variety of agents are available for the treatment of osteoporosis. The evidence for their efficacy is examined and their cost-effectiveness is modelled in established osteoporosis. Methods Therapeutic intervention A systematic review was undertaken of all randomised controlled trials (RCTs) in which fracture was measured as an outcome. RCTs that studied fracture benefits in patients in whom osteoporosis or osteopaenia was not identified were excluded, as were epidemiological studies, although account was taken of these lower levels of evidence in the interpretation and subsequent analysis of information. The interventions reviewed were: bisphosphonates, vitamin D, 1-alpha hydroxylated derivatives of vitamin D, calcitonin, calcium, oestrogens, oestrogen-like agents, anabolic steroids, fluoride salts, thiazide diuretics, raloxifene, vitamin K2, protein supplements and exercise. Epidemiology, costs and utilities The annual risk of osteoporotic fracture was characterised for women from the UK. Fractures of the hip, spine, distal forearm and humerus were designated as being osteoporotic. Collectively, they account for approximately 70% of osteoporotic fractures in postmenopausal women and more than 70% of the morbidity. The risk of osteoporotic fractures in women at the threshold for osteoporosis was determined from a published meta-analysis of the relationship between BMD and fracture risk. The risk of such a fracture in the presence of a prior osteoporotic fracture was computed from a published metaanalysis of the relationship between the prior occurrence of fracture of each type and the risk of a future fracture of each type. The consequences of fracture on mortality were assessed for each fracture type. The annual risk of breast cancer, coronary heart disease (CHD) and mortality were reviewed so that extraskeletal risks and benefits of hormone replacement therapy (HRT) and raloxifene could be modelled. Costs and utilities were determined for osteoporosis in the UK by systematic review of the literature. Health economics model A model was developed comprising an individual patient-based approach that simulated whether or not events occurred in each subsequent year for each patient. Transition states included fracture states (hip, wrist, vertebral and proximal humerus), death from hip fracture, nursing home admission owing to the hip fracture, fatal and non-fatal CHD, fatal and non-fatal breast cancer, and death from other causes. The model simulated cohorts at fixed ages (50, 60, 70 and 80 years) with established osteoporosis. The proportions of the population with different fracture types were simulated from the known distribution of these fractures at different ages. Effectiveness was populated from the systematic review of interventions in osteoporosis. Treatments were given for 5 years using a 5-year offset time, except for calcium and calcitonin for which a 3-year offset time was used (in this context, offset time is the duration for which an effect persists after the treatment stops). The analytic framework was set at 10 years. Because of the many uncertainties, particularly for hip fracture and extra-skeletal risks and benefits, extensive sensitivity analyses were undertaken for each agent. Results The results of the systematic review of RCTs indicated that bisphosphonates, calcitonin, calcium, fluoride salts and raloxifene reduced the incidence of vertebral fracture. The bisphosphonate, alendronate, also decreased non-vertebral fracture, including hip fracture. For several agents, failure to demonstrate efficacy, particularly for hip fracture, was largely due to the lack of appropriate RCTs. Epidemiological evidence suggested that treatment with calcium, calcitonin, HRT, thiazide diuretics, etidronate and anabolic steroids decreased hip fracture risk. There was also RCT evidence that calcium plus vitamin D decreased fracture risk in patients for whom BMD was not known. The results for each agent at each age are presented as a central estimate of cost per quality-adjusted lifeyear (QALY) gained compared with no treatment. Costs were discounted at 6% and QALYs at 1.5% in base-case scenarios. The estimate was bounded by a 90% confidence interval representing the range of cost–utility that was incurred by 90% of the combinations of relative risks (RRs) for efficacy. Cost-effectiveness was graded A–D from the range of cost-effectiveness ratios using a threshold value of £30,000/QALY gained to denote good cost-effectiveness. Only those agents that RCT data showed to have significant effectiveness for at least one fracture outcome were tested – raloxifene, HRT, calcium (with and without vitamin D), calcitonin, alendronate, other bisphosphonates, fluoride and alfacalcidol. It was not cost-effective to treat established osteoporosis with raloxifene in the time frame modelled. If cardiovascular benefits were assumed, treatment was only cost-effective compared with no intervention at ages of at least 70 years. HRT was not cost-effective except below the age of 60 years. However, treatment became costeffective from the age of 50 years if the effects on appendicular fractures reported in epidemiological studies were included. Additional benefits from reductions in CHD, with additional risks from an increased incidence of breast cancer, did not markedly change the conclusions on cost-effectiveness. Treatment with calcium alone was cost-effective compared with no intervention from age 60 years, assuming an effect only on vertebral fracture risk. Treatment was cost-effective at all ages if effects on appendicular fractures were included, as shown by the RCT data for calcium with vitamin D. Treatment with calcitonin was not cost-effective at any age largely because of its high costs. Treatment with alendronate was only cost-effective from age 70 years onwards. Since no difference in efficacy between the bisphosphonates could be shown, a pooled analysis was undertaken using the cost of intervention equivalent to etidronate. ‘Bisphosphonate’ treatment was cost-effective from age 60 years solely because its therapeutic cost was lower than that for alendronate. Using the meta-analysis of RCTs, treatment with fluoride was not cost-effective, largely because of a high point estimate for hip fracture risk (RR = 1.78). If no adverse effect on hip fracture was assumed, then treatment became cost-effective from age 60 years. Compared with no treatment, it was not costeffective to treat established osteoporosis with alfacalcidol except at ages of 70 years or more. Further sensitivity analyses were undertaken, focussing on those agents with cost-effectiveness grades A or B. Age and cost of intervention were important determinants of cost-effectiveness. Cost-effectiveness ratios were sensitive to changes in discount rates for benefits and in the assumption relating to offset of effect (offset time). Cost-effectiveness was markedly improved when women with T-scores under –2.5 SD were selected. The results were not markedly affected by the threshold used for cost-effectiveness, poor compliance, variations in the assumptions about mortality after hip fracture, duration of treatment and duration of analysis. The inclusion of costs for added years of life had little effect in the elderly but improved cost-effectiveness in women aged up to 60 years. In contrast, the inclusion of all vertebral fractures (in addition to clinically overt fractures) had a marked effect on improving cost-effectiveness. Conclusions Cost-effective scenarios for several interventions in the management of established osteoporosis were identified. Cost-effectiveness ratios decrease with age. At age 50 years, only HRT and calcium plus vitamin D were cost-effective (assuming that the agent would decrease the risk of appendicular fractures at this age). At age 80 years, HRT, calcium with or without vitamin D, alfacalcidol, alendronate and bisphosphonate were all cost-effective. The conclusions derived are conservative, mainly because of the assumptions made in the absence of sufficient data. The conservative assumptions included the following: (i) not all osteoporotic fractures are included (ii) not all vertebral fractures are included (iii) base-case scenarios are modelled at the threshold for osteoporosis (iv) risks of re-fracture in the few years after a fracture are likely to be underestimated (v) vertebral fracture incurs no reversible mortality (vi) long-term effects of osteoporotic fractures on utilities are ignored. Thus conclusions that treatments are costeffective are reasonably secure. In contrast, scenarios shown to be cost-ineffective are less secure. As information in these areas becomes available, the implications on cost-effectiveness of interventions should be reappraised. Recommendations for research Intervention thresholds differ substantially from diagnostic thresholds, and should be based on the absolute fracture probability that depends not only on the T-score but also on other independent risk factors. Health economics assessment based on probability of fracture is an important area for further research. Other areas for further research arise from gaps in empirical knowledge on utilities and side-effects that are amenable to primary research. Further secondary research should be undertaken to more closely evaluate the impact of vertebral deformities (rather than clinically overt vertebral fractures) on cost-effectiveness