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The South Pennines, an area of acid-sensitive geology at the center of a major industrial region, have undergone perhaps the most severe historic exposure to sulphur and nitrogen deposition in the UK. This study addresses a lack of existing research on the region by presenting the findings of a survey of 62 surface waters sampled during a 1-week period in April 1998. Results indicate that acidification in the region is acute; 27 of the sampled surface waters had a negative acidneutralizing capacity (ANC) and 28 had a pH below 5.0. Minimum recorded pH values were below 4.0. Non-marine sulphate levels were extremely high (median 222 mueq/1), and widespread high nitrate concentrations (median 41 mueq/1) suggest that soils in the region as a whole maybe at an advanced stage of nitrogen saturation. A consistent relationship was identified between site acidity and the balance between themajor weathering-derived cations, calcium and magnesium, and sulphate. This could in turn be linked to catchment soil type and land use, with the most acidic conditions occurring in peat-dominated catchments, where weathering is minimal and the influence of atmospheric deposition most pronounced. Percentage of peat in each catchment was the single best predictor of surface water acidity. Nitrate concentrations, although not a dominant control on acidity, varied significantly according to land use. Elevated concentrations were observed in catchments containing forestry, due to enhanced deposition inputs, and in catchments containing improved land, linked to fertilizer use. Ammoniumconcentrations, although low at most catchments, were a significant component of the inorganic nitrogen total in a number of surface waters draining waterlogged peat catchments. [ABSTRACT FROM AUTHOR]

Lakes in mountainous areas are of special interest in environmentalstudies because such takes are generally particularly sensitive to inputs of atmospheric pollution and to changes in climate. Mountain lakes provide, therefore, an early warning of more widespread environmental changes. Surveys of lake-water chemistry in mountain areas in Norway, and mountain areas elsewhere in Europe which have crystalline bedrock, clearly show that such lakes are generally very dilute with low concentrations of base cations, alkalinity and SO42-. Mountain lakes also have low concentrations of total-P and TOC. The low concentrations of inorganic and organic ions are due to several factors of which low weathering rates, thin soils, high water fluxes and sparse vegetation in the catchment are of major importance. N03- concentrations on the other hand, are often higher in mountain lakes relative to low elevation lakes in the same area, due to the lower retention capacity of atmosphericallydeposited N in mountain catchments. [ABSTRACT FROM AUTHOR]

During the last three decades the experimental manipulations of whole ecosystems have been a useful and widely-used tool for investigation of the effects of air pollution, air pollution reduction strategiesand management practices on the health and productivity of forests and the acidification of catchments and fresh waters. NITREX and EXMANprojects involve whole-ecosystem manipulations of forest ecosystems in Europe. The aims of these ecosystem experiments have been to investigate the impact of a continued or increased load of air pollutants on the ecosystems, and the possibilities of reversing the acidifying effects by soil amelioration, addition of buffer-acting substances orby removal of the air pollutants. Along with the field experiments, models have been used to predict future effects and dynamics in the ecosystems under different air pollution scenarios. The major findingsfrom those projects have been used in political decisions on reduction of sulphur emission in Europe via the sulphur protocol signed in 1994. Today work is going on to formulate a NOx protocol. NITREX and EXMAN results contribute to the scientific information basefor these protocols. Large-scale ecosystem manipulation projects have increased our understanding of ecosystem function and response to external change and created scientific evidence for political environmental decisions and legislation. In the future, controlled-ecosystem experiments clearly play an important role in new research on ecological effects of changes in the global atmosphere and climate. [ABSTRACT FROM AUTHOR]

European concern over the cause and consequences of forest decline, acidification of soils and surface waters, and the nutrient enrichment of terrestrial and aquatic ecosystems, led to the establishment of the NITREX (Nitrogen saturation experiments) and EXMAN (Experimental Manipulation of Forest Ecosystems in Europe) projects, two research networks of large-scale manipulation experiments under the auspices ofthe EU Commission of European Communities. NITREX comprises 10 experiments at 8 sites in 7 countries at which nitrogen is either added toor removed from ambient atmospheric deposition to simulate major changes in nitrogen deposition. EXMAN comprises experiments at 6 sites in 4 countries at which ambient atmospheric deposition is experimentally altered in chemical composition and/or quantity. The ultimate goalof this research is to contribute to the scientific basis required for the refinement of EU policy on atmospheric quality, and the legislation which will emanate from that policy. [ABSTRACT FROM AUTHOR]

The NITREX project entails large-scale manipulation of nitrogen deposition to whole, forested ecosystems at eight sites in Europe. Nitrogen is added at sites with low-to-intermediate ambient N deposition and removed at sites with high deposition. Changes in outputs of dissolved constituents reflect the integrated effects on ecosystem processes and changes in storage. At sites exhibiting clear symptoms of nitrogen saturation prior to treatment, the nitrate flux in leachate and runoff responded rapidly to changes in deposition. Reduced deposition gave immediate improvement in water quality. At sites with low nitrogen losses prior to treatment, the response to increased deposition was small and delayed. Together the results point to significant hysteresis in output response related to the nitrogen status of the ecosystem. The input--output budgets indicate that forest ecosystems requiremany years to adjust to changes in nitrogen deposition. [ABSTRACT FROM AUTHOR]

The deposition of nitrogen from the atmosphere to coniferous forestsposes the risk of N saturation and disruption of the N cycle. Beginning in April 1991, we have conducted a whole-ecosystem manipulation of N deposition at a mature coniferous forested-catchment at Gardsjon,SW Sweden. We have added in weekly portions of about 40 kg NH4NO3-N ha-1 yr-1 in 5% extra water to the ambient 11 kg NH4NO3-N ha-1 yr-1 in throughfall. The Gardsjon experiment is part of the European NITREX project (Nitrogen saturation experiments). Both the annual mean concentrations and peak concentrations of nitrate in runoff increased dramatically in response to the chronic additions of N. The seasonal pattern and yearly amount of N loss changed during the 5 years of treatment. During the first years of treatment, concentrations of NO3- were low during the growing season and high during the winter; during the fourth and fifth years, elevated concentrations were present also during the summer. Ammonium concentrations, although generally much lower than NO3-, followed the same seasonal pattern. The inorganic N lost during the 5 years of treatment was 0.6%, 1.1%, 5.0%, 5.7% and 4.5% respectively, of the annual inorganic N input. In the fifth year, drought and generally very low runoff led to moderate N loss despite the highNO3- and NH4+ concentrations. Sulphate, inorganic Aln+, H+ and Na+ concentrations were significantly lower during the treatment period relative to the untreated control catchment while NO3-, NH4+, K+ and Ca2+ concentrations increased. The N concentrations in the runoff indicate incipient N saturation at the manipulated catchment. But theexperimental dramatic increase in N deposition occurred so rapidly that [ABSTRACT FROM AUTHOR]