Abstract
Long-term assessment of ecosystem restoration projects is complex because of ecological processes such as succession, particularly in highly dynamic ecosystems such as estuaries. Restoration of intertidal flats and marshes on formerly embanked land, often called managed coastal realignment (MR), became popular in estuarine management. In our study, biophysical and monetary data were collected to calculate the value of 15 (sub)ecosystem services (ES) delivered by a large tidal marsh restoration project in the Schelde estuary in Belgium and the Netherlands. We hypothesized that ES delivery changes over time due to ecological succession and hence the long-term benefits are subject to this phenomenon and need to be taken into consideration. A marsh sediment accretion model (MARSED) was used to simulate potential marsh succession scenarios. In this way, the temporal evolution of ES delivery caused by ecological succession could be evaluated. Our study shows that benefits during successional marsh stages could actually be higher than for marshes in equilibrium. This finding does not suggest that ecosystems in transition always have a higher value than systems in equilibrium, but emphasizes the need to consider long-term ecological dynamics, such as succession, in a benefit assessment for restoration projects.
Highlights
Ever increasing human activity means that many ecosystems are being damaged or lost, which in turn causes a loss of ecosystem service (ES) delivery with a negative impact on human well-being (MEA 2005, The Economics of Ecosystems and Biodiversity (TEEB) 2010)
For scenarios s1.1 and s1.5, the high marsh (HM) and the mudflat (F") scenarios, respectively, does elevation increase at a rate that is almost parallel to mean high water level (MHWL) rise, meaning that succession will probably not occur
The increase in MHWL has a clear influence on the speed of marsh succession: when MHWL does not increase, high marsh is already reached within 100 years, but when MHWL increases faster, the high marsh equilibrium stage is not reached within 200 years (Fig. 2)
Summary
Ever increasing human activity means that many ecosystems are being damaged or lost, which in turn causes a loss of ecosystem service (ES) delivery with a negative impact on human well-being (MEA 2005, TEEB 2010). The building of embankments over the last centuries, plus sea-level rise, has caused tidal marshes, together with the many ES they provide (e.g., flood protection, water quality improvement, and fisheries production), to be lost (Barbier et al 2011). Climate regulation has been given an individual monetary value in some of the studies (e.g., Shepherd et al 2007). Other important functions, such as flood protection, are not given an explicit value in these studies. Flood protection is given a monetary value in some more general studies about existing coastal wetlands and salt marshes, i.e., no studies on marsh restoration (King and Lester 1995, Mangi et al 2011). It should be acknowledged that, in general, for all ES assessments, only services that are currently known and that could be quantified and valued are included
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