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What controls subduction megathrust seismogenesis downdip of the mantle wedge corner (MWC)? We propose that, in the region of the 2010 Mw=8.8 Maule, Chile, earthquake, serpentine minerals derived from the base of the hydrated mantle wedge exert a dominant control. Based on modeling, we predict that the megathrust fault zone near the MWC contains abundant lizardite/chrysotile‐rich serpentinite that transforms to antigorite‐rich serpentinite at greater depths. From the MWC at 32–40 km depth to at least 55 km, the predominantly velocity‐strengthening megathrust accommodated dynamic propagation of the 2010 rupture but with small slip and negative stress drop. The downdip distribution of interplate aftershocks exhibits a gap around the MWC that can be explained by the velocity‐strengthening behavior of lizardite/chrysotile. Interspersed velocity‐weakening and dynamic weakening antigorite‐rich patches farther downdip may be responsible for increased abundance of aftershocks and possibly for some of the high‐frequency energy radiation during the 2010 rupture.

The effects of increased tropospheric ozone (O3) pollution levels on methane (CH4) emissions from peatlands, and their underlying mechanisms, remain unclear. In this study, we exposed peatland mesocosms from a temperate wet heath dominated by the sedge Schoenus nigricans and Sphagnum papillosum to four O3 treatments in open-top chambers for 2.5 years, to investigate the O3 impacts on CH4 emissions and the processes that underpin these responses. Summer CH4 emissions, were significantly reduced, by 27% over the experiment, due to summer daytime (8 h day− 1) O3 exposure to non-filtered air (NFA) plus 35 ppb O3, but were not significantly affected by year-round, 24 h day− 1, exposure to NFA plus 10 ppb or NFA plus 25 ppb O3. There was no evidence that the reduced CH4 emissions in response to elevated summer O3 exposure were caused by reduced plant-derived carbon availability below-ground, because we found no significant effect of high summer O3 exposure on root biomass, pore water dissolved organic carbon concentrations or the contribution of recent photosynthate to CH4 emissions. Our CH4 production potential and CH4 oxidation potential measurements in the different O3 treatments could also not explain the observed CH4 emission responses to O3. However, pore water ammonium concentrations at 20 cm depth were consistently reduced during the experiment by elevated summer O3 exposure, and strong positive correlations were observed between CH4 emission and pore water ammonium concentration at three peat depths over the 2.5-year study. Our results therefore imply that elevated regional O3 exposures in summer, but not the small increases in northern hemisphere annual mean background O3 concentrations predicted over this century, may lead to reduced CH4 emissions from temperate peatlands as a consequence of reductions in soil inorganic nitrogen affecting methanogenic and/or methanotrophic activity.

In this study we have demonstrated that rising background ozone has the potential to reduce grassland forage quality and explored the implications for livestock production. We analysed pasture samples from seven ozone exposure experiments comprising mesotrophic, calcareous, haymeadow and sanddune unimproved grasslands conducted in open-top chambers, solardomes and a field release system. Across all grassland types, there were significant increases in acid detergent fibre, crude fibre and lignin content with increasing ozone concentration, resulting in decreased pasture quality in terms of the metabolisable energy content of the vegetation. We derived a dose-response function for metabolisable energy of the grassland with ozone concentration, applicable to a range of grassland types, and used this to predict effects on pasture quality of UK vegetation at 1km resolution using modelled ozone data for 2007 and for predicted higher average ozone concentrations in 2020. This showed a potential total reduction in lamb production in the UK of approximately 4% in 2020 compared to 2007. The largest impacts were in geographical areas of modest ozone increases between the two years, but where large numbers of lambs were present. For an individual farmer working to a very small cost margin this could represent a large reduction in profit, both in regions where the impacts per lamb and those where the impacts per km2 of grazing land are largest. In the short term farmers could adapt their lamb management in response to changed forage quality by additional supplementary feed of high metabolisable energy content. Nationally this increase in annual additional feed in 2020 compared to 2007 would be 2,166 tonnes (an increase of 0.7%). Of added concern are the longer-term consequences of continual deterioration of pasture quality and the implications for changes in farming practices to compensate for potential reductions in livestock production capacity.

Northern hemispheric background concentrations of ozone are increasing, but few studies have assessed the ecological significance of these changes for grasslands of high conservation value under field conditions. We carried out a 3-year field experiment in which ozone was released at a controlled rate over three experimental transects to produce concentration gradients over the field site, an upland mesotrophic grassland located in the UK. We measured individual species biomass in an annual hay cut in plots receiving ambient ozone, and ambient ozone elevated by mean concentrations of approximately 4 ppb and 10 ppb in the growing seasons of 2008 and 2009. There was a significant negative effect of ozone exposure on herb biomass, but not total grass or legume biomass, in 2008 and 2009. Within the herb fraction, ozone exposure significantly decreased the biomass of Ranunculus species and that of the hemi-parasitic species Rhinanthus minor. Multivariate analysis of species composition, taking into account spatial variation in soil conditions and ozone exposure, showed no significant ozone effect on the grass component. In contrast, by 2009, ozone had become the dominant factor influencing species composition within the combined herb and legume component. Our results suggest that elevated ozone concentrations may be a significant barrier to achieving increased species diversity in managed grasslands.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981., Microfiche copy available in Archives and Science., Bibliography: leaves 95-99., by Simon Muir Peacock., M.S.

This project is an ‘Umbrella’ for CEH Edinburgh, CEH Bangor, and the universities of Newcastle, York and Lancaster. This report covers the period from autumn 2006 to spring 2007.

This report presents progress during the first year of the contract and consolidates and expands the reports presented in SID4 format in December 2006 and March 2007.

Parasitic plants are one of the most ubiquitous groups of generalist parasites in both natural and managed ecosystems, with over 3,000 known species worldwide1, 2, 3. Although much is known about how parasitic plants influence host peformance1, 2, 3, 4, their role as drivers of community- and ecosystem-level properties remains largely unexplored5. Parasitic plants have the potential to influence directly the productivity and structure of plant communities because they cause harm to particular host plants, indirectly increasing the competitive status of non-host species6, 7, 8, 9, 10. Such parasite-driven above-ground effects might also have important indirect consequences through altering the quantity and quality of resources that enter soil, thereby affecting the activity of decomposer organisms3, 11, 12, 13. Here we show in model grassland communities that the parasitic plant Rhinanthus minor, which occurs widely throughout Europe and North America14, has strong direct effects on above-ground community properties, increasing plant diversity and reducing productivity. We also show that these direct effects of R. minor on the plant community have marked indirect effects on below-ground properties, ultimately increasing rates of nitrogen cycling. Our study provides evidence that parasitic plants act as a major driver of both above-ground and below-ground properties of grassland ecosystems.