456 research outputs found
Investigating periphyton biofilm response to changing phosphorus concentrations in UK rivers using within-river flumes
Get PDFThe excessive growth of benthic algal biofilms in UK rivers is a widespread problem, resulting in loss of plant communities and wider ecological damage. Elevated nutrient concentrations (particularly phosphorus) are often implicated, as P is usually considered the limiting nutrient in most rivers. Phosphorus loadings to rivers in the UK have rapidly decreased in the last decade,due to improvements in sewage treatment and changes to agricultural practises. However, in many cases, these improvements in water quality have not resulted in a reduction in nuisance algal growth. It is therefore vital that catchment managers know what phosphorus concentrations need to be achieved, in order to meet the UKās obligations to attain good ecological status, under the EUās Water Framework Directive. This study has developed a novel methodology, using within river mesocosms, which allows P concentrations of river water to be either increased or decreased, and the effect on biofilm accrual rate is quantified. These experiments identify the phosphorus
concentrations at which algae becomes P-limited, which can be used to determine knowledge-based P targets for rivers. The ability to reduce P concentrations in river water enables algaeānutrient limitation to be studied in nutrient-enriched rivers for the first time
Formative evaluation of the National Scholarship Programme : report to HEFCE by CFE and the Widening Participation Research Centre, Edge Hill University
Get PDFCollaborative systems for enhancing the analysis of social surveys: the grid enabled specialist data environments
Get PDFThis paper describes a group of online services which are designed to support social
survey research and the production of statistical results. The 'Grid Enabled Specialist
Data Environment' (GESDE) services constitute three related systems which offer
facilities to search for, extract and exploit supplementary data and metadata concerned
with the measurement and operationalisation of survey variables. The services also offer
users the opportunity to deposit and distribute their own supplementary data resources for
the benefit of dissemination and replication of the details of their own analysis.
The GESDE services focus upon three application areas: specialist data relating to the
measurement of occupations; educational qualifications; and ethnicity (including
nationality, language, religion, national identity). They identify information resources
related to the operationalisation of variables which seek to measure each of these
concepts - examples include coding frames, crosswalk and translation files, and
standardisation and harmonisation recommendations. These resources constitute
important supplementary data which can be usefully exploited in the analysis of survey
data. The GESDE services work by collecting together as much of this supplementary
data as possible, and making it searchable and retrievable to others. This paper discusses
the current features of the GESDE services (which have been designed as part of a wider
programme of āe-Scienceā research in the UK), and considers ongoing challenges in
providing effective support for variable-oriented statistical analysis in the social sciences
Plasma diagnosis of reactive high power impulse magnetron sputtering (HiPIMS) discharges
Get PDFReactive HiPIMS discharges have been investigated by employing a selection of plasma diagnostic techniques. Plasma dynamics in a reactive HiPIMS discharge were studied by means of a single Langmuir probe which revealed electron and positive ion densities of the order of 10^17 to 10^18 m^-3 in typical substrate positions, the temporal evolutions of which exhibited a dual-peak structure attributed to the propagation of an ion acoustic wave or the compression and subsequent rarefaction of the process gas caused by the intense 'sputter wind'. The compression phase is also thought to be the cause of the quenching of the effective electron temperature observed during the on-time with the rarefaction phase being responsible for the increase in the effective electron temperature toward the end of the voltage pulse. Negative ion dynamics in the afterglow of a reactive HiPIMS discharge were also studied by means of a Langmuir probe for a range of oxygen partial pressures. The extended afterglow was found to be highly electronegative with the negative ion-to-electron ratio (alpha) at 3 milliseconds after the pulse termination reaching values of almost 400 for the highest oxygen partial pressures. By comparing results to a simple plasma-chemical model, it is speculated that increased negative ion formation occurs for higher oxygen partial pressures due to the increased availability of oxygen metastables that are formed in the active phase. Despite exhibiting a strong correlation, a comparison to the alpha values determined by photodetachment revealed an overestimation by a factor of 8-15 when employing the Langmuir probe method. Furthermore, from photodetachment measurements the O- ion density was observed to peak in the early afterglow at values of the order of 10^17 m^-3. It was also concluded that a negative ion flux of approximately 10^17-10^18 m^-2 s^-1 could be expected at the chamber walls and substrate surface once the plasma afterglow transitions into an ion-ion state, which could have implications for many plasma processing methods. Time-averaged energy distributions of oxygen negative ions obtained using energy-resolved mass spectrometry during reactive HiPIMS of Ti in an Ar/O2 gas mixture revealed three distinct populations of O- ions at varying energies. The peak of the high-energy population was found to correspond to the value of average applied target potential during the pulse on-time. Comparison to a Thompson energy distribution of sputtered particles suggested that O- ions are sputtered from the target surface before undergoing acceleration in the cathode sheath. A study of the attenuation of the high-energy O- ion population as a function of the pressure-distance product yielded an effective total cross section of 2 x 10^-19 m^2 for O- interacting with the background Ar/O2 gas mixture for both Ti and Nb targets. During reactive HiPIMS of different target materials, a correlation between O- emission and the ion-induced secondary electron emission coefficient was found. In addition, large differences in the high-energy O- yield were also observed when employing different inert gases mixed with O2, which was also attributed to changes in the ion-induced secondary electron emission coefficient. The deposition rates in reactive HiPIMS of TiO2 using different inert gases were measured by means of a quartz crystal microbalance. In contrast to the trends predicted by SRIM as well as those measured in DCMS, the power normalized deposition rate, D_n, was found to increase with the mass of inert gas in both metallic and reactive modes, with the exception of the Xe/O2 gas mixture. The observed increase of D_n with the mass of inert gas was partially attributed to a decreased return effect in the heavier gases. For the case of Kr/O2, the normalized deposition rate measured in HiPIMS was found to be 87% of that measured in equivalent DCMS operation despite no attempt at optimization
Improved procedures for valuation of the contribution of recreation to national economic development
Get PDFImproved procedures are presented for evaluating the contribution of recreation to national economic development. These procedures are to replace those outlined in the Principles and Standards for Planning Water and Related Land Resources. Desirable criteria for valuation procedures are specified. Variation procedures currently used by federal agencies make almost exclusive use of the āinterim unit day value approach,ā sometimes augmented by point systems. This approach has little theoretical or empirical justification and does not encourage efficient allocation of resources. Revision and modification of the āinterim unit day value approachā and the use of point systems is not a useful method of developing improved procedures. Rather, it is recommended that models be developed to predict individual willingness-to-pay for many types of recreation as functions of site characteristics, the characteristics of the individual user (including the history of the previous use), the availability of substitute activities and sites, and the location of the individual in relation to the resources under study. The total value of the resource would then be a function of these variables, the number of users, and the distribution of users within the market area. These functions may be derived from regional travel cost demand functions (which would also provide estimates of use) or could be explicit willingness-to-pay functions derived from the survey method (which must be supplemented by a use estimate). Examples of the desired models are provided along with guidelines for their development and use. Needs for further research are identified.U.S. Department of the InteriorU.S. Geological SurveyOpe
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Using high-frequency water quality data to assess sampling strategies for the EU Water Framework Directive
Get PDFThe EU Water Framework Directive (WFD) requires that the ecological and chemical status of water bodies in Europe should be assessed, and action taken where possible to ensure that at least "good" quality is attained in each case by 2015. This paper is concerned with the accuracy and precision with which chemical status in rivers can be measured given certain sampling strategies, and how this can be improved. High-frequency (hourly) chemical data from four rivers in southern England were subsampled to simulate different sampling strategies for four parameters used for WFD classification: dissolved phosphorus, dissolved oxygen, pH and water temperature. These data sub-sets were then used to calculate the WFD classification for each site. Monthly sampling was less precise than weekly sampling, but the effect on WFD classification depended on the closeness of the range of concentrations to the class boundaries. In some cases, monthly sampling for a year could result in the same water body being assigned to three or four of the WFD classes with 95% confidence, due to random sampling effects, whereas with weekly sampling this was one or two classes for the same cases. In the most extreme case, the same water body could have been assigned to any of the five WFD quality classes. Weekly sampling considerably reduces the uncertainties compared to monthly sampling. The width of the weekly sampled confidence intervals was about 33% that of the monthly for P species and pH, about 50% for dissolved oxygen, and about 67% for water temperature. For water temperature, which is assessed as the 98th percentile in the UK, monthly sampling biases the mean downwards by about 1 Ā°C compared to the true value, due to problems of assessing high percentiles with limited data. Low-frequency measurements will generally be unsuitable for assessing standards expressed as high percentiles. Confining sampling to the working week compared to all 7 days made little difference, but a modest improvement in precision could be obtained by sampling at the same time of day within a 3 h time window, and this is recommended. For parameters with a strong diel variation, such as dissolved oxygen, the value obtained, and thus possibly the WFD classification, can depend markedly on when in the cycle the sample was taken. Specifying this in the sampling regime would be a straightforward way to improve precision, but there needs to be agreement about how best to characterise risk in different types of river. These results suggest that in some cases it will be difficult to assign accurate WFD chemical classes or to detect likely trends using current sampling regimes, even for these largely groundwater-fed rivers. A more critical approach to sampling is needed to ensure that management actions are appropriate and supported by data
Mapping eutrophication risk from climate change: future phosphorus concentrations in English rivers
Get PDFClimate change is expected to increase eutrophication risk in rivers yet few studies identify the timescale or spatial extent of such impacts. Phosphorus concentration, considered the primary driver of eutrophication risk in English rivers, may increase through reduced dilution particularly if river flows are lower in summer. Detailed models can indicate change in catchment phosphorus concentrations but targeted support for mitigation measures requires a national scale evaluation of risk.
In this study, a load apportionment model is used to describe the current relationship between flow and total reactive phosphorus (TRP) at 115 river sites across England. These relationships are used to estimate TRP concentrations for the 2050s under 11 climate change driven scenarios of future river flows and under scenarios of both current and higher levels of sewage treatment.
National maps of change indicate a small but inconsistent increase in annual average TRP concentrations with a greater change in summer. Reducing the TRP concentration of final sewage effluent to 0.5 mg/L P for all upstream sewage treatment works was inadequate to meet existing P standards required through the EU Water Framework Directive, indicating that more needs to be done, including efforts to reduce diffuse pollution
Establishing the baseline in groundwater chemistry in connection with shale-gas exploration: Vale of Pickering, UK
Get PDFThe baseline chemistry of groundwater from two aquifers in the Vale of Pickering, North Yorkshire, has been investigated ahead of a proposal to explore for shale gas, planning permission for which has recently been granted. Groundwater in a shallow aquifer including Quaternary and/or Jurassic Kimmeridge Clay deposits shows compositions distinct from a Corallian (Jurassic) Limestone aquifer, reflecting different lithologies and hydrogeological conditions. Corallian groundwaters along the margins of the vale are controlled by reaction with carbonate, with redox conditions varying according to degree of aquifer confinement. Superficial aquifer groundwaters are confined and strongly reducing, with some observed high concentrations of dissolved CH4 (up to 37 mg/L; Feb 2016 data). This appears to be of mixed biogenic-thermogenic origin but further work is needed to determine whether the source includes a deeper hydrocarbon reservoir contributing via fractures, or a shallower source in the Quaternary or Kimmeridge sediments. The data show a shallow aquifer with a high-CH4 baseline which pre-dates any shale-gas activity
16S rRNA assessment of the influence of shading on early-successional biofilms in experimental streams
Get PDFElevated nutrient levels can lead to excessive biofilm growth, but reducing nutrient pollution is often challenging. There is therefore interest in developing control measures for biofilm growth in nutrient-rich rivers that could act as complement to direct reductions in nutrient load. Shading of rivers is one option that can mitigate blooms, but few studies have experimentally examined the differences in biofilm communities grown under shaded and unshaded conditions. We investigated the assembly and diversity of biofilm communities using in situ mesocosms within the River Thames (UK). Biofilm composition was surveyed by 454 sequencing of 16S amplicons (ā¼400 bp length covering regions V6/V7). The results confirm the importance of sunlight for biofilm community assembly; a resource that was utilized by a relatively small number of dominant taxa, leading to significantly less diversity than in shaded communities. These differences between unshaded and shaded treatments were either because of differences in resource utilization or loss of diatom-structures as habitats for bacteria. We observed more co-occurrence patterns and network interactions in the shaded communities. This lends further support to the proposal that increased river shading can help mitigate the effects from macronutrient pollution in rivers
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