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Human diet is responsible for a number of environmental problems. It is a driving force for water and land requirements for food production. This contribution investigates the relationships between diet and agricultural production, the resulting mass flows of nitrogen and phosphorus, their impact on the aquatic environment, the agricultural area requirements and emissions of nitrogen to the atmosphere in a clearly defined region. The combination of material flow analysis, nutrient emission model and statistical input data determines the reference state. By changing some input data (changing diet) several independent processes change. Thus the impacts of changing nutrition patterns can be investigated for a well-defined region. According to diet recommendations a scenario was developed and impacts on resources and environment drawn. Application of the method to Austria shows a 30% reduction of agricultural land requirements for food production by changing nutritional habits to a healthy balanced diet. Nitrogen export via rivers would be decreased by 11%. The diet change would also result in a reduced fertilizer input by 6% to agriculture, which is relevant especially for the limited resource phosphorus.

There is increasing evidence of water temperature being a key controlling factor of stream ecosystem metabolism. Although the focus of research currently lies on carbon emissions from fluvial networks and their potential role as positive climate feedback, it is also important to estimate the risk of eutrophication streams will be exposed to in the future. In this work, a methodological approach is developed to create a scientific basis for such assessment and is applied to two Austrian lowland rivers with significantly different characteristics. Gross primary productivity (GPP) is determined through the open diel oxygen method and its temperature dependence is quantified based on the metabolic theory of ecology. This relationship is combined with the outcomes of a climate change scenario obtained through a novel integrated modelling framework. Results indicate that in both rivers, a 1.5°C warming would provoke an increase of GPP of 7-9% and that such an increase would not be limited by nutrient availability. The results further suggest that the situation for the relatively shallow river might be more critical, given that its GPP values in summer are five times higher than in the deeper murky river.