Nitrogen flows from European watersheds to coastal marine waters

Nitrogen flows from European watersheds to coastal marine waters Executive summary Nature of the problem • Most regional watersheds in Europe constitute managed human territories importing large amounts of new reactive nitrogen. • As a consequence, groundwater, surface freshwater and coastal seawater are undergoing severe nitrogen contamination and/or eutrophication problems. Approaches • A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fixation,fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fluxes delivered at the basin outlets has been assembled. • A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems. Key findings/state of knowledge • Throughout Europe, NANI represents 3700 kgN/km2/yr (range, 0–8400 depending on the watershed), i.e. five times the background rate of natural N2 fixation. • A mean of approximately 78% of NANI does not reach the basin outlet, but instead is stored (in soils, sediments or ground water) or eliminated to the atmosphere as reactive N forms or as N2. • N delivery to the European marine coastal zone totals 810 kgN/km2/yr (range, 200–4000 depending on the watershed), about four times the natural background. In areas of limited availability of silica, these inputs cause harmful algal blooms. Major uncertainties/challenges • The exact dimension of anthropogenic N inputs to watersheds is still imperfectly known and requires pursuing monitoring programmes and data integration at the international level. • The exact nature of ‘retention’ processes, which potentially represent a major management lever for reducing N contamination of water resources, is still poorly understood. • Coastal marine eutrophication depends to a large degree on local morphological and hydrographic conditions as well as on estuarine processes, which are also imperfectly known. Recommendations • Better control and management of the nitrogen cascade at the watershed scale is required to reduce N contamination of ground- and surface water, as well as coastal eutrophication. • In spite of the potential of these management measures, there is no choice at the European scale but to reduce the primary inputs of reactive nitrogen to watersheds, through changes in agriculture, human diet and other N flows related to human activity

Potential impacts of a future Nordic bioeconomy on surface water quality

Nordic water bodies face multiple stressors due to human activities, generating diffuse loading and climate change. The ‘green shift’ towards a bio-based economy poses new demands and increased pressure on the environment. Bioeconomy-related pressures consist primarily of more intensive land management to maximise production of biomass. These activities can add considerable nutrient and sediment loads to receiving waters, posing a threat to ecosystem services and good ecological status of surface waters. The potential threats of climate change and the ‘green shift’ highlight the need for improved understanding of catchment-scale water and element fluxes. Here, we assess possible bioeconomy-induced pressures on Nordic catchments and associated impacts on water quality. We suggest measures to protect water quality under the ‘green shift’ and propose ‘road maps’ towards sustainable catchment management. We also identify knowledge gaps and highlight the importance of long-term monitoring data and good models to evaluate changes in water quality, improve understanding of bioeconomy-related impacts, support mitigation measures and maintain ecosystem services

Interaction of Climate Change and Acid Deposition

Projections of the synergistic effects of acid deposition and climate change on freshwater ecosystems are inherently fraught with the uncertainty that such projections are for climatic conditions not currently experienced. For many of the climate scenarios, the projected mean temperature in the future will be well above that observed even in extreme years during the period of observation (maximum 30 years for most ecosystems). The ecosystem responses are probably not linear; thus, extrapolation from observations, even those spanning several decades, entails going outside the range of observations. It is acid deposition that is responsible for the widespread acidification of surface waters in sensitive areas of Europe, eastern North America and elsewhere in the world. This means that measures to reduce acidification problems can continue to be focussed on reducing emissions of S and N compounds to the atmosphere. Although reductions in emissions of S and N compounds have led to dramatic improvements and recovery in water quality in acidified freshwater ecosystems, biological recovery has lagged and the problem will remain in many areas for decades to come. Further reductions are required if the goal is to permit recovery of all impacted ecosystems. Climate change is a confounding factor in that it can exacerbate or ameliorate the rate and degree of acidification and recovery, both with respect to chemical as well as biological effects. The absence of recovery following reduction in acid deposition, therefore, may simply be the result of the confounding influence of climatic variations. The time-scales of recovery from acid deposition are in many respects similar to those of chronic changes in climate, in part because both drivers act by affecting large pools of S, N, C and base cations in catchment soil. But extreme climatic events, such as droughts, cause extreme responses that set back the biological recovery process and slow down progress towards a stable ecosystem. The interactions are complicated and manifold, and thus the outcomes on ecosystems are difficult to predict and generalize. Both acid deposition and climate change are caused by emissions of gases to the atmosphere and are largely due to the same types of human activities – burning of fossil fuels and other industrial processes. Clearly, there are substantial ‘co-benefits’ to be gained: for example, reductions in emissions of CO2 by a switch to renewable energy sources will also bring about a reduction in S and N emissions. At the policy level, much might be gained by coordinating future emission controls, now dealt with separately under the United Nations Economic Council for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution (LRTAP) and the UN Framework Convention on Climate Change. Society will take measures to ameliorate or mitigate the effects of climate change. Some of these measures may indirectly affect the acidification of sensitive freshwaters. For example, as illustrated by the modelling example from Finland (Fig. 7.15), more intensive use of forests for biofuel may entail release of N now stored in the soil to surface waters in the form of NO3 accompanied by acidic cations. More research is needed on the effects of adaptation and mitigation. The mechanisms of the interactions between climate effects and acidification effects are still, however, poorly understood. Experiments, continued monitoring and analysis of long-term data series and modelling are complementary approaches that lead to new insights and knowledge on possible interactions. Research is particularly challenging in this field because the goal is to make projections for the future under climatic conditions that for many ecosystems have never been experienced previously. It is certain that climate change will have an increasing impact on freshwaters in the foreseeable future and there will certainly be effects not yet identified. Current assessments of total impact on freshwaters are probably underestimated