Valley-bottom wetland selection for water-quality preservation: How to deal with the absence of quantification of water-quality benefits?

We combine soil science and economics to provide an integrated framework of Valley-Bottom Wetland (VBW) selection criteria for surface water-quality preservation at the headwater watershed scale when there is no reliable method for quantifying water-quality benefits. We focus on a French agricultural landscape and more particularly on wet meadows. We implement a method of VBW identification based on topographic indices which use threshold values that are calibrated using field measurements. This identification criterion allows us to accurately identify both downstream and upstream VBWs. We then look for criteria with which to prioritize the VBWs identified for conservation purposes. We concentrate on budget-constrained cases and provide a procedure for estimating the cost of conservation for the VBWs. We finally show that it is very important (i) to simultaneously consider hydrogeomorphic and cost criteria for the selection in a budget constrained context and (ii) to go beyond the mean per hectare cost of conservation.