The relevance of preserving temporary ponds during drought: hydrological and vegetation changes over a 16-year period in the Donana National Park (south-west Spain)

1. Although the Donana National Park is given the highest degree of environmental protection in Spain, it is likely that groundwater discharge to several ponds within the Biological Reserve has been damaged by abstraction to a tourist resort located less than 1 km away. 2. Hydrological changes were monitored over 16 years (1 October 1989 to 30 September 2005) by recording the shallow water table of six temporary ponds at 1-8-week intervals, and the duration of pond wet phase (or hydroperiod) during each hydrological cycle. 3. The average rainfall for the study period was 563.2 mm, and included 6 wet, 5 moderate, and 5 dry years in a seemingly random sequence. The average rainy season extended from October until the end of March, while the dry season occupied the rest of the year. 4. The water table generally oscillated following this alternation of rainy and dry seasons, but this fluctuation was minimal during dry years, and even failed to occur at some ponds. 5. Since 1998/99, the average hydroperiod has shortened by 3 months at Charco del Toro pond, and by almost 2 months at Brezo pond, while the rest of the ponds exhibited a reduction of less than 1 month. 6. Vegetation changed in the ponds between May 1990 and 2005. Total plant cover increased (range of increase: 16-65%), and species richness decreased in all ponds (range of species loss: 4-18). 7. The reduction in the hydroperiod probably enhanced the growth of a few woody plants to the detriment of flooding-dependent species as the cover of Pinus pinea increased nearly fourfold at Brezo pond, while that of Scirpus lacustris was halved at Charco del Toro pond. 8. The pumping area for the nearby tourist resort should be relocated, and a specific management strategy should be developed in order to prevent further damage to the ponds. Copyright (C) 2007 Joint Wiley & Sons, Ltd.