A burst from the direction of UZ Fornacis with XMM-Newton

The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ksec exposure with the EPIC cameras, suggesting that the accretion rate either decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ For during the observation. Spectral fits favour optically thin, kT = 4.4 keV thermal emission. Detection of the burst by the on-board Optical Monitor indicates that this was most probably an accretion event. The 0.1-10 keV luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from high state polars and would result from the potential energy release of ~ 10^16 g of gas. There is no significant soft excess due to reprocessing in the white dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres

Issues of diffuse pollution model complexity arising from performance benchmarking

Flow and nitrate dynamics were simulated in two catchments, the River Aire in northern England and the River Ythan in north-east Scotland. In the case of the Aire, a diffuse pollution model was coupled with a river quality model (CASCADE-QUESTOR); in the study of the Ythan, an integrated model (SWAT) was used. In each study, model performance was evaluated for differing levels of spatial representation in input data sets (rainfall, soils and land use). In respect of nitrate concentrations, the performance of the models was compared with that of a regression model based on proportions of land cover. The overall objective was to assess the merits of spatially distributed input data sets. In both catchments, specific measures of quantitative performance showed that models using the most detailed available input data contributed, at best, only a marginal improvement over simpler implementations. Hence, the level of complexity used in input data sets has to be determined, not only on multiple criteria of quantitative performance but also on qualitative assessments, reflecting the specific context of the model application and the current and likely future needs of end-users

Assemblage grouping of European benthic diatoms as indicators of trophic status of rivers

River benthic diatoms are routinely used to monitor water quality in rivers throughout Europe. Many diatom indices have been developed to monitor a single water quality variable such as phosphorus concentration, or organic pollution, and there is a need to develop diatom monitoring methods for the Water Framework Directive (WFD) which can monitor and quantify a range of environmental variables. The identification of benthic diatom assemblages, or biotypes, is an alternative method that may allow monitoring of ecological status throughout European rivers. Multivariate analysis showed that diatom species composition corresponded most strongly to altitude, temperature, pH and conductivity, while nutrient variables were of secondary importance. To assess the use of biotypes as indicators of eutrophic status benthic diatom samples collected from five European countries were grouped on the basis of their species composition using TWINSPAN. Eight diatom biotypes, some with two subgroups, were identified. Canonical Correspondence Analysis was used to investigate the relationship between these diatom groupings and nutrient concentrations, with and without the effects related to altitude and pH. A number of communities which may act as indicators of eutrophication were identified, though issues arose concerning the identification of these communities and the lack of sample sites from a range of altitudes, pH and conductivities. Finally the use of such diatom based methods to set river quality boundaries and monitor trophic status for the WFD is considered in light of their predictive strength, practicability in application and international differences in river monitoring standards

Integrated assessment of water framework directive nitrate reduction measures

The paper develops a spatially explicit method for integrated assessment of alternative measures to reduce nitrate leaching into rivers and lakes from farms, a key objective of the European Union Water Framework Directive (WFD). This approach combines regression models, based on Farm Business Survey and June Agricultural Census data, for predicting the economic costs to agriculture of nitrate reduction measures with a hydrological model encompassing both diffuse and point source pollution to estimate the water quality changes arising from such instruments. A case study of the agriculturally diverse Yorkshire Derwent catchment in the north of England illustrates the overall approach. We consider three measures previously proposed to the UK Department for Environment, Food and Rural Affairs (Defra) for tackling diffuse agricultural pollution: (i) reducing inorganic fertilizer application, (ii) reducing livestock stocking rates and (iii) converting arable land to un-grazed grassland. The results reveal marked variability in the economic impacts and nitrate leaching reductions, with the cost effectiveness of these measures varying by up to a factor of three. Furthermore, the analysis suggests that WFD implementation may entail major land use changes resulting in substantial economic impacts. The spatially explicit aspect of our approach permits assessment of the optimal targeting of policy implementation to areas of particular environmental interest

How do river nitrate concentrations respond to changes in land-use? A modelling case-study of headwaters in the River Derwent catchment, North Yorkshire, UK

A combined semi-distributed hydrological model (CASCADE/QUESTOR) is used to evaluate the steady-state that may be achieved after changes in land-use or management and to explore what additional factors need to be considered in representing catchment processes. Two rural headwater catchments of the River Derwent (North Yorkshire, UK) were studied where significant change in land-use occurred in the 1990s and the early 2000s. Much larger increases in mean nitrate concentration (55%) were observed in the catchment with significant groundwater influence (Pickering Beck) compared with the surface water-dominated catchment (13% increase). The increases in Pickering Beck were considerably greater than could be explained by the model in terms of land-use change. Consequently, the study serves to focus attention on the long-term increases in nitrate concentration reported in major UK aquifers and the ongoing and chronic impact this trend is likely to be having on surface water concentrations. For river environments, where groundwater is a source, such trends will mask the impact of measures proposed to reduce the risk of nitrate leaching from agricultural land. Model estimates of within-channel losses account for 15–40% of nitrate entering rivers