Journal of Environmental Management 271 (2020) 110976 Available online 24 June 2020 0301-4797/© 2020 Elsevier Ltd. All rights reserved. Research article Nutrient mitigation under the impact of climate and land-use changes: A hydro-economic approach to participatory catchment management Johannes Friedrich Carolus a, b, * , Alena Bartosova c , Søren Bøye Olsen a , Seifeddine Jomaa d , Art � urs Veinbergs e , Andis Z � ıl� ans f , Søren Marcus Pedersen a , Gerald Schwarz b , Michael Rode d , Karin Tonderski g a Department of Food and Resource Economics, University of Copenhagen, Rolighedsvej 25, 1958, Frederiksberg C, Denmark b Thuenen Institute of Farm Economics, Bundesallee 63, 38116, Braunschweig, Germany c Swedish Meteorological and Hydrological Institute (SMHI), 60176, Norrk€ oping, Sweden d Department of Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research, Brückstraße 3a, 39114, Magdeburg, Germany e Latvia University of Life Sciences and Technologies, 19 Akademijas Street, Jelgava, LV-3001, Latvia f Faculty of Geography and Earth Sciences, University of Latvia, Jelgavas iela 1, R � ıga, LV-1004, Latvia g IFM Biology, Link€ oping University, SE 581 83, Link€ oping, Sweden A R T I C L E INFO Keywords: Nutrient mitigation Baltic sea region Water quality Cost-effectiveness HYPE Catchment model Participatory approach ABSTRACT Excessive nutrient loadings into rivers are a well-known ecological problem. Implemented mitigation measures should ideally be cost-effective, but perfectly ranking alternative nutrient mitigation measures according to cost- effectiveness is a diffcult methodological challenge. Furthermore, a particularly practical challenge is that cost- effective measures are not necessarily favoured by local stakeholders, and this may impede their successful implementation in practice. The objective of this study was to evaluate the cost-effectiveness of mitigation measures using a methodology that includes a participatory process and social learning to ensure their successful implementation. By combining cost data, hydrological modelling and a bottom-up approach for three different European catchment areas (the Latvian Berze, the Swedish Helge and the German Selke rivers), the cost- effectiveness of 16 nutrient mitigation measures were analysed under current conditions as well as under selected scenarios for future climate and land-use changes. Fertiliser reduction, wetlands, contour ploughing and municipal wastewater treatment plants are the measures that remove nutrients with the highest cost- effectiveness in the respective case study context. However, the results suggest that the cost-effectiveness of measures not only depends on their design, specifc location and the conditions of the surrounding area, but is also affected by the future changes the area may be exposed to. Climate and land-use changes do not only affect the cost-effectiveness of measures, but also shape the overall nutrient loads and potential target levels in a catchment. 1. Introduction Eutrophication is mainly caused by anthropogenic nutrient inputs, namely nitrogen (N) and phosphorus (P). It represents a major problem for the water quality and ecology of streams, rivers and the Baltic and North Seas (Artioli et al., 2008; Kiedrzy� nska et al., 2014; Reusch et al., 2018; Saux Picart et al., 2015). Nutrient enrichment beyond the natural intake capacities of aquatic ecosystems increases algal growth, turbidity and oxygen depletion, and leads to a loss in aquatic biodiversity (EEA, 2018; HELCOM, 2014). This adversely affects a range of ecosystem services that generate welfare to people. Consequences are, among others, negative impacts on human health, fshing opportunities, tourism, or the availability of drinking water (EEA, 2018; Le Moal et al., 2019, and the references therein). Many studies deal with the benefts of water quality improvements in various contexts (e.g. Hanley and Black, 2006; Hyyti€ ainen et al., 2015; Hyyti€ ainen et al., 2013; Martin-Ortega et al., 2015). For example, the gain in societal welfare of a reduced eutrophication in the Baltic Sea was estimated to be worth almost four billion euros annually (Ahtiainen et al., 2014). Despite years of mitigation efforts, only half of the European water * Corresponding author. Department of Food and Resource Economics, University of Copenhagen, Rolighedsvej 25, 1958, Frederiksberg C, Denmark. E-mail address: johannes.carolus@thuenen.de (J.F. Carolus). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman https://doi.org/10.1016/j.jenvman.2020.110976 Received 28 February 2020; Received in revised form 5 June 2020; Accepted 14 June 2020