Abstract
In this paper, we investigate the potential gains in cost-effectiveness from changing the spatial scale at which nutrient reduction targets are set for the Baltic Sea, with particular focus on nutrient loadings from agriculture. The costs of achieving loading reductions are compared across five levels of spatial scale, namely the entire Baltic Sea; the marine basin level; the country level; the watershed level; and the grid square level. A novel highly-disaggregated model, which represents decreases in agricultural profits, changes in root zone N concentrations and transport to the Baltic Sea is used. The model includes 14 Baltic Sea marine basins, 14 countries, 117 watersheds and 19,023 10-by-10 km grid squares. The main result which emerges is that there is a large variation in the total cost of the program depending on the spatial scale of targeting: for example, for a 40% reduction in loads, the costs of a Baltic Sea-wide target is nearly three times lower than targets set at the smallest level of spatial scale (grid square). These results have important implications for both domestic and international policy design for achieving water quality improvements where non-point pollution is a key stressor of water quality.
Highlights
Non-point nutrient inputs from agriculture constitute one of the main sources of total nutrient inputs to the Baltic Sea, and are one of the main determinants of eutrophication (HELCOM, 2011; Reusch et al, 2018)
We compare the scenarios with N reduction targets specified at the following spatial scales: (1) Baltic Sea drainage basin as a whole, (2) separate targets for each of the 14 sea basins, (3) separate targets for each of 14 countries in the Baltic drainage basin, (4) separate targets for each of 117 watersheds or (5) separate targets for each of the 19,023 grid squares
For each reduction target the minimized total cost of abatement is calculated, given the constraints imposed by satisfying the target for the Baltic Sea as a whole (Overall), for each sea basin separately (Basin), for each country (Ctr), each watershed (Wts) and each grid square (Grid)
Summary
Non-point nutrient inputs from agriculture constitute one of the main sources of total nutrient inputs to the Baltic Sea, and are one of the main determinants of eutrophication (HELCOM, 2011; Reusch et al, 2018). A neglected yet vital aspect of this environmental management problem is the role that the choice of spatial scale plays for the analysis and management of large-scale eutrophication. This choice is important due to spatial heterogeneity in control costs as well as in the impact of emissions. A policy which sets a reduction target at the largest area of spatial aggregation – in this case, the drainage basin for the entire Baltic Sea – would be more cost-effective than a policy which imposes targets at lower levels of spatial disaggregation, since this would provide greater opportunities to take advantage of potential measures where agricultural nutrient loading into the Baltic can be reduced at a relatively low cost. Policy instruments are often uniformly applied at country or regional level, which limits the possibilities to make use of the most cost-effective mitigation strategies across the Baltic Sea catchment
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