Global change impacts on organic matter dynamics in stream ecosystems

1. With freshwater ecosystems worldwide at significant risk from global change, there is an urgent need to understand the processes involved and to develop adaptive responses. Riparian management might offer a means of increasing resilience to global change in headwaters, but evidence is scarce. This thesis investigates the potential effects of riparian management on the storage, processing and downstream export of resource subsidies – dominantly as terrestrial litter – that enter streams from the riparian zone. 2. In a large scale field study over four years, natural and experimental systems were used to test the hypothesis that riparian woodlands enhance stream ecosystem resilience to climatically mediated changes in flow regimes. Specific work included assessments of benthic organic matter stocks and export in contrasting catchments (broadleaf woodland, conifer plantations or sheep-grazed moorland), flow manipulations in mesocosms, and a large-scale field experiment simulating riparian broadleaved tree planting. 3. Standing stocks of particulate organic matter (POM) were influenced by flow regime, and declined following larger and longer flow-events, but event frequency had no apparent impact. Experimental data showed also that coarse fractions of POM in transport were significantly elevated in the early stages of simulated floods. 4. Despite flow effects on POM dynamics, streams bordered by broadleaves maintained consistently higher standing stocks of POM than conifer or moorland streams. Broadleaved streams also transported the highest concentrations of carbon in the form of high-quality FPOM. Leaf litter additions of stream channels did not reproduce these effects, possibly because the scale was insufficient to mimic real riparian woodlands. 5. While predicted flow changes under a warmer climate might affect the storage and flux of organic matter, riparian broadleaves are likely to mitigate these effects in stream ecosystems. This project illustrates the value of blending catchment-scale studies with field-based mesocosms to understanding complex global change processes

Identifying future research directions for biodiversity, ecosystem services and sustainability: perspectives from early-career researchers

We aimed to identify priority research questions in the field of biodiversity, ecosystem services and sustainability (BESS), based on a workshop held during the NRG BESS Conference for Early Career Researchers on BESS, and to compare these to existing horizon scanning exercises. This work highlights the need for improved data availability through collaboration and knowledge exchange, which, in turn, can support the integrated valuation and sustainable management of ecosystems in response to global change. In addition, clear connectivity among different research themes in this field further emphasizes the need to consider a wider range of topics simultaneously to ensure the sustainable management of ecosystems for human wellbeing. In contrast to other horizon scanning exercises, our focus was more interdisciplinary and more concerned with the limits of sustainability and dynamic relationships between social and ecological systems. The identified questions could provide a framework for researchers, policy makers, funding agencies and the private sector to advance knowledge in biodiversity and ES research and to develop and implement policies to enable sustainable future development

Episodic acidification affects the breakdown and invertebrate colonisation of oak litter

Summary 1. Although European streams are now recovering chemically from acidification, biological recovery is limited. One hypothesis is that continuing acid episodes restrict acid-sensitive species in recovering locations either through direct toxicity or by affecting ecological processes. Here, we test this hypothesis by assessing the effects of episodic acid exposure on the breakdown and macroinvertebrate colonisation of oak (Quercus robur) litter. 2. Over 83 days, acid episodes of 4 days’ duration were simulated by repeatedly transplanting litter bags of contrasting mesh size between replicate acidic and circumneutral streams around Llyn Brianne (Wales, U.K.). Results were compared against controls from circumneutral streams and circumneutral transplants, while invertebrates colonising litter were compared with adjacent assemblages. 3. Breakdown was retarded significantly by repeated acid exposure in comparison with circumneutral transplants, but only in litter to which invertebrates had access. Overall breakdown was also significantly slower in fine-mesh than in coarse-mesh bags. 4. Plecopteran shredders were the major invertebrate colonists of litter, along with smaller numbers of grazers and predators. However, acid exposure eliminated or suppressed acid-sensitive families, resulting in an overall composition converging on that in acid streams. 5. The rapid loss of sensitive invertebrates from acid-exposed litter supports the hypothesis that acid episodes suppress biological recovery from acidification through direct physiological effects. However, our litter breakdown data indicate that (i) some effects of acid episodes could be mediated through litter processing; and (ii) episodic acidification could disrupt litter breakdown through effects on invertebrate composition or activity. These data suggest that delayed biological recovery from acidification can reflect a combination of direct toxic and indirect ecological effects

Organic litter dynamics in headwater streams draining contrasting land uses

Climate change could alter fluxes of organic matter and macronutrients through freshwater ecosystems potentially affecting stream organisms. However, riparian controls on litter dynamics offer an opportunity to adapt headwaters to climate change by protecting or restoring riparian vegetation. We assessed how riparian land cover and climatic variability affected the supply, retention and downstream transport of particulate organic matter (POM) in headwaters—the most extensive small water bodies in temperate landscapes. Leaf litter inputs, benthic stocks and suspended organic matter were measured nominally monthly in second–third-order streams draining broadleaf woodland, conifer, acid moorland and circumneutral moorland over four years with varying discharge. Streams draining broadleaf woodland received more leaf litter from the riparian zone than conifer and moorland and transported higher concentrations of CPOM and FPOM at base flows. Broadleaf sites had higher CPOM stocks, even after hydrological events that reduced CPOM in conifer and moorland sites. In contrast, FPOM dynamics reflected hydrological conditions irrespective of land cover. These results show how some organic matter fractions in streams are sensitive to hydrological conditions, illustrating how wetter climates will influence FPOM exports. Nevertheless, riparian broadleaves have the potential to offset climatic effects on organic matter processing in headwaters through the replenishment and retention of CPOM

Temperature Dependence of the Structural Relaxation Time in Equilibrium below the NominalTg: Results from Freestanding Polymer Films

When the thickness is reduced to nanometer scale, freestanding high molecular weight polymer thin films undergo large reduction of degree of cooperativity and coupling parameter n in the Coupling Model (CM). The finite-size effect together with the surfaces with high mobility make the α-relaxation time of the polymer in nanoconfinement, tau_alphanano(T), much shorter than tau_alphabulk(T) in the bulk. The consequence is avoidance of vitrification at and below the bulk glass transition temperature, Tg_bulk, on cooling, and the freestanding polymer thin film remains at thermodynamic equilibrium at temperatures below Tg_bulk. Molecular dynamics simulations have shown that the specific volume of the freestanding film is the same as the bulk glass-former at equilibrium at the same temperatures. Extreme nanoconfinement renders total or almost total removal of cooperativity of the alpha-relaxation, and tau_alphanano(T) becomes the same or almost the same as the JG beta-relaxation time tau_betabulk(T) of the bulk glass-former at equilibrium and at temperatures below Tg_bulk. Taking advantage of being able to obtain tau_betabulk(T) at equilibrium density below Tg_bulk by extreme nanoconfinement of the freestanding films, and using the CM relation between tau_alphabulk(T) and tau_betabulk(T), we conclude that the Vogel−Fulcher−Tammann−Hesse (VFTH) dependence of tau_alphabulk(T) cannot hold for glass-formers in equilibrium at temperatures significantly below Tg_bulk. In addition, tau_alphabulk(T) does not diverge at the Vogel temperature, T0, as suggested by the VFTH-dependence and predicted by some theories of glass transition. Instead, tau_alphabulk(T) of the glass-former at equilibrium has a much weaker temperature dependence than the VFTHdependence at temperature below Tg_bulk and even below T0. This conclusion from our analysis is consistent with the temperature dependence of tau_alphabulk(T) found experimentally in polymers aged long enough time to attain the equilibrium state at various temperatures below Tg_bulk

The Ubiquitin–Proteasome System and Cardiovascular Disease

Over the past decade, the role of the ubiquitin–proteasome system (UPS) has been the subject of numerous studies to elucidate its role in cardiovascular physiology and pathophysiology. There have been many advances in this field including the use of proteomics to achieve a better understanding of how the cardiac proteasome is regulated. Moreover, improved methods for the assessment of UPS function and the development of genetic models to study the role of the UPS have led to the realization that often the function of this system deviates from the norm in many cardiovascular pathologies. Hence, dysfunction has been described in atherosclerosis, familial cardiac proteinopathies, idiopathic dilated cardiomyopathies, and myocardial ischemia. This has led to numerous studies of the ubiquitin protein (E3) ligases and their roles in cardiac physiology and pathophysiology. This has also led to the controversial proposition of treating atherosclerosis, cardiac hypertrophy, and myocardial ischemia with proteasome inhibitors. Furthering our knowledge of this system may help in the development of new UPS-based therapeutic modalities for mitigation of cardiovascular disease