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Project manager Kari Austnes The current status of surface water acidification related to air pollution in Europe and North America has been assessed using country reports, monitoring data, critical loads and exceedance data, acid sensitivity and deposition maps, and data reported under the European Commission’s Water Framework Directive (WFD). Acidification is still observed in many countries, but the extent and severity vary. Maps of acid sensitivity and deposition suggest that surface water acidification is present in regions and countries for which no data or reports were delivered for the current assessment. Existing national monitoring varies in the ability to assess the spatial extent of acidification and the recovery responses of acidified sites. The monitoring requirements under the European Union’s National Emission Ceilings Directive are expected to reverse the recent decline in the number of monitoring sites observed in some countries. The information reported under the WFD is currently of limited value in assessing the extent of acidification of surface waters in Europe. Chemical recovery in response to reductions in acid deposition can be slow, and biological recovery can lag severely behind. Despite large and effective efforts across Europe and North America to reduce surface water acidification, air pollution still constitutes a threat to freshwater ecosystems. Norwegian Environment Agency (Miljødirektoratet) United Nations Economic Commission for Europe (UNECE)

The distance–decay relationship has been claimed to be a predictor for biological diversity because it unites several ecological phenomena such as dispersal ability and environmental structure. The effect of long-term disturbances on distance decay, however, has been widely overlooked, especially for microorganisms. We examine the effect of eutrophication on the distance–decay relationship in communities of attached diatoms in three peatland areas: mesotrophic, eutrophic and hypertrophic. The study follows a spatially explicit sampling scheme, collecting evenly spaced samples along 6-km sampling tracks. The three areas shared 24% of the total number of species, but the different nutrient levels in the three areas are reflected by the prominence of low profile and planktonic diatom species. Our study demonstrates that eutrophication can affect distance–decay relationships by decreasing turnover rates in microorganisms. Diatom communities are shown to be constrained by both environmental and spatial features, whose relative importance depends on the degree of eutrophication. Under eutrophic conditions, species are filtered from the regional species pool and community structure responds strongly to environmental factors (water chemistry variables and depth), while in mesotrophic environments, purely spatial processes play a prominent role in structuring diatom communities. These findings reveal that homogenisation of communities triggered by environmental disturbance is an ecological phenomenon of importance in the microbial world.

The relatively new inorganic scintillator LaBr(3):Ce is well suited for time-of-flight positron emission tomography (TOF-PET), since it has short scintillation decay time, high light yield and very good energy resolution. Silicion photomultipliers (SiPMs) show low noise, high gain and small transit-time jitter, and are thus well suited for fast timing applications. The work presented here focuses on the timing performance of bare LaBr(3):Ce(5%) crystals coupled to commercially available SiPMs. First, relatively small crystals coupled to single SiPMs were used to study the intrinsic timing resolution of such detectors. Special attention was paid to the optimization of digital signal processing (DSP) time-pickoff methods. A coincidence timing resolution of 101 ps FWHM was achieved. Next, a monolithic LaBr(3):Ce crystal was coupled to a 4x4 SiPM array and an intial timing performance characterization was performed. A single detector timing resolution of 225 ps FWHM was achieved. The timing delay induced by the scintillation photon transport was virtually constant over the depth-of-interaction (DOI) range of the detector.