Hydrological functioning and anthropogenic influence in four shalllow ponds by means of daily water balances. Doñana National Park, southern Spain (years 2016-17 and 2017-18)

Daily hydrological balances were made in four shallow ponds of Doñana National Park (southern Spain). Results indicates that Santa Olalla pond is the one receiving a major contribution of groundwater discharge and Zahíllo is the one with a lesser contribution. Nevertheless, all the ponds could be classified as through-flow ponds. Distance to a touristic resort and altitude of the pond's floor have found to be relevant parameters regarding groundwater discharge. In that sense, the ponds located near the resort and higher in altitude receive a minor proportion of groundwater discharge and vice versa. Furthermore, differences in the water balance among year 2016-17 and 2017-18 have also been found in the ponds. Regarding the evolution of the water level and the hydroperiod, the Santa Olalla pond has remained flooded during the entire study period. Zahíllo pond has remained 157 days flooded (43% of the year). Taraje pond was flooded 236 days (64% of the year). Finally, Sopetón pond was flooded 231 days a year (63% of the time). In the case of Sopetón, the water is lost in addition to evaporation and recharge also through an overflow.