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

Abstract

ABSTRACT1. Although the Don˜ana 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.

Evidence of Hydroperiod Shortening in a Preserved System of Temporary Ponds

“…Since pumping is concentrated in the more permeable layers of the lower aquifer, it is supposed to affect a large area through a small lowering of the water-table [33]. This would explain that a trend that had been already reported for some particular ponds [36] is general for the whole study area, as it was earlier predicted [76] and this study evidences. It should be noted that, along with the potential anthropogenic cause, the progressive lowering of the water-table level also has a natural origin due to slow transient evolution of the aquifer system that cannot be avoided.…”

“…We should also be aware that the accuracy of model predictions is expected to get worse towards the beginning of the time-series data, due to changes in Landsat sensors, caused by their degradation over time, i.e. radiometric drift [55], and changes in the vegetation cover in the temporary pond basin and surroundings, as detected in particular ponds [36,57].…”

“…A plausible driver of hydroperiod deterioration is groundwater exploitation [72,73], which started in the 1970s, peaking in the 1980s, and currently is more or less stable but with variable emplacements. The exploitation of the aquifer is causing a progressive lowering of the phreatic level [74] and a probably damage to ponds hydrology [36], such as a decrease in the frequency of appearance of temporary ponds [75]. Since pumping is concentrated in the more permeable layers of the lower aquifer, it is supposed to affect a large area through a small lowering of the water-table [33].…”

“…Doñana temporary ponds have no direct connection to the sea except through airborne salt deposition [35]. Serrano and Zunzunegui [36], in a study conducted in six ponds, indicated that some of them may be under threat, since their hydrologic regime may have been damaged by aquifer water extraction by a nearby tourist resort [see also 37]. Scientifically-based management of Doñana National Park requires information on historical flooding patterns, both spatially and temporally, and their relationship with natural fluctuations and anthropogenic modifications [38].…”

Ecological similarities between two Mediterranean wetlands: Sidi Boughaba (North-West Morocco) and the Doñana National Park (South-West Spain)

“…The huge dimensions of the Doñana aquifer (over 3400 km 2 and up to 100 m in depth; Llamas, 1990) ensure that the groundwater input to these ponds remains free from significant external nutrient loads and, for most of these ponds, is still largely controlled by natural hydrological processes. The exception is represented by those ponds located less than 1 km away from the tourist resort of Matalascañas, for which the length of the wet period has been significantly reduced due to groundwater abstraction over the last decade (Serrano and Zunzunegui, 2008). The Mamora aquifer (North-West Morocco) covers a few hundred km 2 and supplies water for several major cities (including Rabat and Kenitra) in a region with strong demographic and agricultural pressures (Zouhri et al, 2004).…”