Conserving dynamic wetlands under combined global, regional and local stressors
Lead Author: Javier Bustamante (CSIC)
Contributors: Luis Santamaría (CSIC), Guyonne Janss (CSIC), Andy Green(CSIC), Coralie Beltrame (TdV), Brigitte Poulin (TdV), Cristian Mihai Adamescu (UB), Constantin Cazacu (UB)
Wetlands are a diverse array of dynamic ecosystems formed in the contact of land and water. They have long been considered unproductive and unhealthy and transformed into farmlands, afforestations, rice paddies, aquaculture farms, or transportation channels. Only recently it has been realized the importance of wetlands for the conservation of biodiversity, and for the ecosystem services they provide. For example, Doñana National Park was created in the 1960's for the protection of waterbirds after two thirds of its original extension were drained for agriculture 
Fresh water is and will be under increasing demand. While wetland drainage and transformation has slowed down in Europe, underground water extraction, surface water diversion, modification of hydrological regimes, pollution, overgrazing, and the introduction of exotic species are still important and growing threats. Many wetlands are nowadays protected, yet they are dependent on catchment areas or aquifers much larger than the protected area and thus subjected to anthropogenic degradation.
In addition, climate change will affect the hydrology of most wetlands. In many areas, the combined effects of decreased rainfall and increased evapotranspiration will reduce water levels, changing permanent into temporary wetlands or making them disappear. Reduced flows and water levels will exacerbate the impact of anthropogenic pollution, the concentration of contaminants will increase and this will decreases the capacity of wetlands to purify water. Climate change will also cause sea-level rise, aggravating the increase in coastal erosion. The reduction in river flow and sediment transport by rivers (due to water diversion for human use, sediment trapping by dams and catchment reforestation) may not compensate wetland reduction by the increase in coastal erosion due to marine currents. High herbivore densities (wild and domestic) can cause a reduction in water quality and biodiversity through their treading, faecal inputs and overgrazing.
Shallow lakes and ponds have well-documented “tipping points” leading to a loss of biodiversity and ecosystem services – caused e.g. by excessive nutrient loading leading to dominance by microalgae or cyanobacteria (cultural eutrophication). Some cyanobacteria produce toxins that threaten wildlife, cattle and drinking water supply. Similarly, overgrazing causes erosion, siltation and bioturbation that may lead to turbid-water systems with low biodiversity and poor water quality. In summary, global (climate change), regional (water extraction, eutrophication) and local (modification of hydrological and grazing regimes) stressors could act in synergy and can push the ecosystem to these undesirable states. Park management can act on local stressors (water management, livestock density, control of alien species) while regional authorities and policies may act on regional ones (water extraction, urban waste water treatment, pesticide/fertilizer regulation). To compensate for the effect of climate change, it may be necessary to maintain local and regional stressors under safe limits (creating a “safe operating space”). Such limits should be stricter in protected areas, to ensure the preservation of the values for which they were designated and the ecosystem services they provide including those provided by waterbirds.
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