Evolution of wetland functions and services in the Camargue
Lead Author: Brigitte Poulin (TdV)
Hydrology is a prime factor influencing wetland functions, biodiversity and services (Coops and Hosper, 2002; Janssen et al., 2005). In semi-permanent and brackish environments, seasonal variations in water levels are particularly crucial for the maintenance of emerged and submerged macrophytes and their associated fauna (Bolduc and Afton, 2004; Osland et al., 2011). As a result of urban and agricultural development, palustrine wetlands (shallow lakes, marshes, ponds) are often disconnected from most of their catchment area, requiring active water management to maintain or enhance their functions (Tamisier and Grillas, 1994; Janssen et al., 2005). Further reduction in freshwater availability and quality either due to changes in land use, water allocation, or climate is increasingly threatening the functions, biodiversity and human uses of wetlands (Lyons et al., 2008). Preserving wetlands functions and services is a priority of the European Water Framework Directive, with management of water scarcity being recognized as a major future challenge in southern Europe (European Commission, 2010).
The Camargue Biosphere Reserve in the Rhône delta covers 193 000 ha, including natural habitats such as lagoons, brackish/freshwater marshes with emergent or aquatic vegetation, as well as halophilous scrubs and steppes. These ecosystems are intermingled with agro-systems dominated by rice, an irrigated crop. Through a complex network of irrigation and drainage channels, 730 millions of cubic meters of water are pumped from the Rhône on average each year to compensate for river embankment, to avoid soil salinization, enhance primary production (overcome summer drought) and create suitable breeding habitat for waterbirds either for sustaining commercial hunting activity or conversely enhancement of bird populations for conservation. Half of this water is returned to the Rhône through drainage channels, the other half being evacuated to the Vaccarès lagoon. This water, primarily pumped for rice farming, is also used for flooding marshes used for nature conservation, wildfowl hunting and reed harvest, as well as for irrigation of pasture meadows. Pesticides used for rice farming have been shown to affect biodiversity (Mesléard et al. 2005, 2016), but management options to reduce pesticide use (organic farming, dry sowing, winter flooding) with positive impacts on wildlife are gaining in popularity (Pernollet et al. 2015, Delmotte et al. 2016).
Wetland ecosystems of the Camargue are important for a range of regulating ecosystem services such as climate regulation, flood mitigation, water purification and nutrient cycling. They also provide important provisioning and cultural services through agriculture, fishing, cattle grazing, wildfowl hunting and bird watching. Each ecosystem type has a different dependency on water management, and resilience to fluctuations in water levels and salinity. External factors influencing agricultural land use (eg., CAP reform, global market evolution for rice or biofuels) or hydrological conditions (increased salinity in the Rhône estuary, reduced rainfall due to climate change) will affect the functions, biodiversity and services of these ecosystems, with potential tradeoffs among provisioning, regulating and cultural services. For instance, wetland management for wildfowl hunting has resulted in the imposition of hydrological conditions opposed to natural cycles. This affects the native Mediterranean flora and fauna adapted to seasonal brackish wetlands, and increases vulnerability to invasive plant species. Flooding of hunting marshes and pasture meadows in summer further increases mosquito abundance with deleterious effects on ecotourism. Inadequate grazing pressure can lead to proliferation of unpalatable species, but also to habitat shift when in combination with hydrological management (Mesléard et al. 1999).
This storyline aims at making the best use of remote-sensing tools to document the evolution in the state of wetlands and the services they can deliver within a context of global changes, integrating feedback processes occurring at local scale through stakeholder management.
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