Identifying DOC gains and losses during a 20-year record in the Trout Beck catchment,Moor House,UK

The turnover of organic carbon in rivers could represent a large source of greenhouse gases to the atmosphere and studies have suggested that of the order of 70% of the dissolved organic carbon exported from soils could be lost in rivers before it flows to continental seas. The Environmental Change Network (ECN) monitoring of the dominantly peat-covered Trout Beck catchment within the Moor House site enabled the amount of dissolved organic carbon (DOC) lost within a stream over a 20-year period to be estimated. The study compared DOC concentrations of precipitation, shallow and deep soil waters with those at the catchment outlet. The mass balance between source and outlet was reconstructed by two methods: a single conservative tracer; and based upon a principal component analysis (PCA) using multiple tracers. The study showed the two methods had different outcomes, with the PCA showing a DOC gain and the single tracer showing a DOC loss. The DOC gain was attributed to an unmeasured groundwater contribution that dominates when the river discharge is lower. The DOC loss was related to the in-stream residence time, the soil temperature and month of the year, with longer in-stream residence times, warmer soils and summer months having larger DOC losses. The single tracer study suggested a 10 year average loss of 8.77 g C m⁻² year⁻¹, which is 33.1 g CO_2eq m⁻² year⁻¹, or 29% of the DOC flux from the source over a mean in-stream residence time of 4.33 h.     

On Explicit Congestion Notification for Stream Control Transmission Protocol in Lossy Networks

As a congestion avoidance mechanism, Explicit Congestion Notification (ECN) is designed to inform a data source to react to potential congestion early. Currently, the new transport protocol, Stream Control Transmission Protocol (SCTP), is not ECN-capable. An ECN-capable SCTP is proposed in this paper, which is bandwidth-efficient and robust to non-congestion losses. An SCTP source needs to adjust its congestion window when receiving ECN messages. We find the optimal value of the congestion window for an SCTP source in response to ECN messages, and develop a simple and practical method to achieve this optimal congestion window. Both simulation results and analysis are provided to support the effectiveness of the proposed ECN mechanism for SCTP. The simplified method in achieving the optimal congestion window is attractive because the total goodput performance of SCTP associations or the bottleneck link utilization is not sensitive to the window reduction policies when the network load is heavy. Using complicated methods to fine-tune SCTP or TCPs congestion window in response to congestion indications may not be worth the increase in complexity of the protocol.Prepared through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.Guanhua Ye received the B.E. degree in Information & Electronic Technology from Zhejiang University, China, in 1997 and M.E. degree in Communication & Information Systems from China Academy of Telecommunications Technology in 2000. He is currently working toward the Ph.D. degree in Electrical Engineering at City College and Graduate Center of City University of New York.His research interests are in computer networks, congestion control, ad hoc networks, voice over IP and multimedia communications.Tarek N. Saadawi received the B.Sc. and the M.Sc. from Cairo University Egypt and the Ph.D from the University of Maryland, College Park (all in Electrical Engineering). Since 1980 he has been with the Electrical Engineering Department, The City University of New York, City College. His current research interests are telecommunications network, high-speed networks, multimedia networks, AD-HOC networks and packet radio networks. He has published extensively in the area of telecommunications networks. He is a Co-author of the book, Fundamentals of Telecommunication Networks, John Wiley & Sons, 1994. He is also the lead author of Egypt Telecommunications Infrastructure Master Plan covering the fiber network, IP/ATM, DSL and the wireless local loop. Dr. Saadawi is a Former Chairman of IEEE Computer Society of New York City (1986–87). He has received IEEE Region 1 Award, 1987, and the Nippon Telegraph and Telephone (NTT) of America for research on Broadband Telecommunication Networks.Dr. Myung Jong Lee received the B.S from Seoul National University in Korea and M.S and Ph.D degrees in electrical engineering from Columbia University, 1986 and 1990 respectively. He joined the Department of Electrical Engineering, City College and Graduate Center of City University of New York, where he is currently an associate professor.His recent researches focus on various aspects of wireless ad hoc networks, sensor networks, and personal area networks. He has published over 50 refereed journal and conference papers. He is the Director of Samsung-CUNY Joint Laboratory on Sensor Networks. Dr. Lee received CUNYs Excellence Performance Award in 1999. Dr. Lee is a senior member of IEEE, and served many IEEE and other conferences as program committee member and session chair, and also actively participates in ZigBee Alliance and IEEE1451 Smart Sensor WG.     

Solvation structures of sodium halides in dimethyl sulfoxide (DMSO)–methanol (MeOH) mixtures

A constrained molecular dynamics technique has been used to study the structures and dynamics of the solvation shells of three sodium halides, namely sodium chloride (Na⁺–Cl^?), sodium bromide (Na⁺–Br^?) and sodium iodide (Na⁺–I^?) in DMSO–MeOH mixtures. In the case of Na⁺–Cl^? and Na⁺–Br^?, Na⁺ is preferentially solvated by DMSO and Cl^? and Br^? are preferentially solvated by methanol in the contact ion pair (CIP) state. In the solvent-assisted ion pair (SAIP) configuration, Na⁺ ions of Na⁺–Cl^? and Na⁺–Br^? are preferentially solvated by methanol and Cl^? and Br^? also show preferential solvation by methanol over DMSO. In the case of Na⁺–I^?, the only preferential solvation is in the SAIP state for I^? ion by methanol. These observations are supported by the calculated excess coordination numbers and spatial density maps. The heights of the transition states barriers for CIPs and SAIPs/solvent-shared ion pairs (SSHIPs) are significantly affected when the mole fraction of methanol (x_MeOH) changes from 0.0 to 0.25 because of a significant increase in the methanol density around halides. From the analysis of angular distribution functions of DMSO and methanol around the cations and anions, it is seen that DMSO and methanol molecules are present in parallel dipolar orientations (with respect to cation–solvent vector) in the first coordination shell of these three ion pairs at the CIP and SAIP states. Methanol molecules are nearly in an antiparallel (with respect to ion–solvent vector) orientation around the three halide ions.     

Trends and variability in weather and atmospheric deposition at UK Environmental Change Network sites (1993–2012)

We characterised temporal trends and variability in key indicators of climate and atmospheric deposition chemistry at the twelve terrestrial UK Environmental Change Network (ECN) sites over the first two decades of ECN monitoring (1993–2012) using various statistical approaches. Mean air temperatures for the monitoring period were approximately 0.7 °C higher than those modelled for 1961–1990, but there was little evidence for significant change in air temperature over either the full monthly records or within individual seasons. Some upland ECN sites, however, warmed significantly over the first decade before cooling in the second. Summers at most sites became progressively wetter, and extremes in daily rainfall increased in magnitude. Average wind speeds in winter and spring declined at the majority of sites. Directional trends in summer precipitation could be linked to an atypically prolonged negative deviation in the summer North Atlantic Oscillation (NAO) Index. Several aspects of air quality improved markedly. Concentrations and fluxes of sulphate in precipitation declined significantly and substantially across the network, particularly during the earlier years and at the most polluted sites in the south and east. Precipitation concentrations of nitrate and ammonium, and atmospheric concentrations of nitrogen dioxide also decreased at most sites. There was less evidence for reductions in the loads of wet deposited nitrogen species, while trends in atmospheric ammonia concentration varied in direction and strength between sites. Reductions in acid deposition are likely to account for widespread gradual increases in the pH of soil water at ECN sites, representing partial recovery from acidification. Overall, therefore, ECN sites have experienced marked changes in atmospheric chemistry and weather regimes over the last two decades that might be expected to have exerted detectable effects on ecosystem structure and function. While the downward trend in acid deposition is unlikely to be reversed, it is too early to conclude whether the trend towards wetter summers simply represents a phase in a multi-decadal cycle, or is indicative of a more directional shift in climate. Conversely, the first two decades of ECN now provide a relatively stable long-term baseline with respect to air temperature, against which effects of anticipated future warming on these ecosystems should be able to be assessed robustly.     

Functional interaction of low-homology FRPs from different cyanobacteria with Synechocystis OCP

Photosynthesis requires a balance between efficient light harvesting and protection against photodamage. The cyanobacterial photoprotection system uniquely relies on the functioning of the photoactive orange carotenoid protein (OCP) that under intense illumination provides fluorescence quenching of the light-harvesting antenna complexes, phycobilisomes. The recently identified fluorescence recovery protein (FRP) binds to the photoactivated OCP and accelerates its relaxation into the basal form, completing the regulatory circle. The molecular mechanism of FRP functioning is largely controversial. Moreover, since the available knowledge has mainly been gained from studying Synechocystis proteins, the cross-species conservation of the FRP mechanism remains unexplored. Besides phylogenetic analysis, we performed a detailed structural-functional analysis of two selected low-homology FRPs by comparing them with Synechocystis FRP (SynFRP). While adopting similar dimeric conformations in solution and preserving binding preferences of SynFRP towards various OCP variants, the low-homology FRPs demonstrated distinct binding stoichiometries and differentially accentuated features of this functional interaction. By providing clues to understand the FRP mechanism universally, our results also establish foundations for upcoming structural investigations necessary to elucidate the FRP-dependent regulatory mechanism.     

The purple Trp288Ala mutant of Synechocystis OCP persistently quenches phycobilisome fluorescence and tightly interacts with FRP

In Cyanobacteria, the Orange Carotenoid Protein (OCP) and Fluorescence Recovery Protein (FRP) are central to the photoprotective mechanism consisting in regulated quenching of phycobilisome (PBs) fluorescence. Due to a transient and flexible nature of the light-activated red quenching form, OCP^R, which is obtained from the stable dark-adapted orange form, OCP^O, by photoconversion, the detailed mechanism of photoprotection remains unclear. Here we demonstrate that our recently described W288A mutant of the Synechocystis OCP (hereinafter called OCP^W288A) is a fully functional analogue of the OCP^R form which is capable of constitutive PBs fluorescence quenching in vitro with no need of photoactivation. This PBs quenching effect is abolished in the presence of FRP, which interacts with OCP^W288A with micromolar affinity and an apparent stoichiometry of 1:1, unexpectedly, implying dissociation of the FRP dimers. This establishes OCP^W288A as a robust model system providing novel insights into the interplay between OCP and FRP to regulate photoprotection in cyanobacteria.     

The UK Environmental Change Network after twenty years of integrated ecosystem assessment: Key findings and future perspectives

The UK Environmental Change Network (ECN), the UK's Long-Term Ecosystem Research (LTER) network, has now been operating for over twenty years. It was established in 1992 as a set of terrestrial sites at which sustained observations relevant to a range of ecological indicators and environmental parameters could be made. An additional ECN freshwater network was launched in 1994. In this paper we provide a brief history of the network, and describe its current structure and role within a complementary wider range of UK environmental monitoring and observation programmes that are either more focussed on specific parameters or habitats, or operate at different temporal and spatial scales. We then provide a review of the other papers within this Special Issue, which exemplifies the broad range of environmental concerns that ECN data and sites are helping to address. These include network-wide summaries of environmental and biological trends over the first two decades of monitoring, more site-specific assessment of the ecological impacts of local pressures resulting from changes in management, biological and ecosystem service indicator development, and the testing of new monitoring technologies. We go on to consider: (i) future directions of network development and adaptation in light of recently emerging environmental concerns, dwindling financial resources and the consequent need for greater efficiency; (ii) the desire for tighter integration with other monitoring and observation programmes both nationally internationally; (iii) opportunities raised by recent technological developments; and (iv) the need to process and make available data more rapidly to increase the capacity of ECN sites as early warning systems. In its first two decades of operation the ECN has accumulated a robust set of baseline data that describe environmental and biological variability across a range of habitats in unprecedented detail. With appropriate, informed development, these should prove invaluable in discerning the causes and consequences of environmental change for decades to come.