Abstract
In this study, we explored how a targeted land use change in a Danish catchment (River Odense) may provide multi-functional benefits through nitrogen (N)-load reductions to obtain good ecological quality in Odense estuary, protection of N-vulnerable groundwater aquifers, protection of Natura2000 sites and carbon sequestration. An N-load model linked to GIS thematic layers of known protected areas (Natura2000 sites and N-vulnerable groundwater aquifers) was utilised targeting high N-load areas to locate set-aside land. The achieved multi-functional benefits within the catchment and estuary were assessed and cost–benefit assessment was performed by dividing the total welfare costs of the set-aside by the total multi-functional benefits gained from each strategy. The results show that obtaining multi-functional benefits at the lowest cost requires a targeted shift of set-aside from the traditional hot-spot N-load areas to designated protected areas.
Highlights
Many aquatic action plans aimed at reducing the level of nitrogen (N)-loads from non-point sources have been implemented in Denmark since the late 1980s (Kronvang et al 2008) and resulted in an almost 50% reduction of N-leaching from the mid-1980s to 2003 (Naturstyrelsen 2014)
We investigated the outcomes of different strategies for targeted set-aside using a map-based N-load model in a sub-catchment of Odense Fjord, followed by a cost–benefit assessment performed by dividing the total cost by the total multi-functional benefits gained from each strategy
5% set-aside resulted in 19% fulfilment for good ecological status (GES) (% of N-load reduction target for the catchment), whereas fulfilment for nature (% of targeted set-aside located within the Natura2000 border), groundwater (% of targeted setaside located within the border of N-vulnerable groundwater aquifers) and climate (% of Danish climate goals) amounted to 8%, 3% and 11%, respectively (Fig. 4). 40% set-aside resulted in 100%, 40%, 72% and 28% fulfilment for GES, nature, climate and groundwater, respectively
Summary
Many aquatic action plans aimed at reducing the level of nitrogen (N)-loads from non-point sources have been implemented in Denmark since the late 1980s (Kronvang et al 2008) and resulted in an almost 50% reduction of N-leaching from the mid-1980s to 2003 (Naturstyrelsen 2014). N-leaching is still a major concern for meeting the requirements for good ecological status in groundwater and coastal waters (Kronvang et al 2005). The Food and Agriculture Package implemented by the Danish Parliament in 2016 introduced new spatially targeted measures for N-load reductions that include specific N-load reduction targets for all coastal water catchments. The present focus in Denmark for enacting a new policy of differentiated agricultural N-mitigation is based on the spatial variation in groundwater N-reduction (i.e. the redox reaction where nitrate is reduced to N2, primarily under anaerobic conditions), a result of geological heterogeneity in the subsurface geology. The Paris Agreement in 2016 entails a focus on carbon sequestration and with regard to this, Denmark is obliged to meet a 30% CO2 reduction target for agricultural emissions by 2030. The EU Habitats Directive and the Rio Agreement require protection of biodiversity
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