Pond basin colonization by terrestrial vegetation indicates wetland deterioration

Abstract

Efforts to conserve the pond network in the Doñana National Park are being threatened by groundwater overexploitation. The dramatic expansion of farming and tourism in nearby areas has caused a severe lowering of the water table, reducing pond hydroperiod length or even instigating pond desiccation. It is important to document the link between groundwater abstraction and pond deterioration with a view to decreasing human pressures on the park and preserving the pond network's singular biodiversity. Here, the gradual deterioration of one of the network's main ponds is described in detail by characterizing vegetation patterns within the pond's basin using orthophotos taken between 1956 and 2019. In the earliest images, the pond contained a wide central area of bare soil during its dry phase. This area was surrounded by reeds and had a line of Tamarix canariensis trees along its southern edge. Starting in 2000, the orthophotos showed the pond's gradual colonization by terrestrial vegetation. In tandem, pond hydroperiod decreased, as did the length of time the pond retained certain depths of water. In recent years, Tamarix trees finally fully invaded the pond's central area, which is surrounded by reeds and has scattered terrestrial bushes and pines. This invasion resulted from the pond's sparse inundation over recent decades, being the cover of trees related to the depth of groundwater, and is a clear sign of pond deterioration. More broadly, colonization by terrestrial vegetation has been observed in approximately 60% of the network's ponds. Colonization of temporary pond basins by terrestrial vegetation can be used as an indicator of deterioration and highlights the need for active restoration and management.

Pond area and availability safeguard amphibian genetic diversity across Iberia's largest protected wetland

“…Climate change and aquifer overexploitation are jointly drying up ponds in Doñana, reducing the extent and hydroperiod even of permanent or semipermanent ponds (Bustamante et al., 2016; Camacho et al., 2022; de Felipe et al., 2023; Gómez‐Rodríguez, Bustamante, et al., 2010). Large areas that used to become flooded every year are drying up (de Felipe et al., 2023; Díaz‐Paniagua & Aragonés, 2015), to the point that terrestrial vegetation (e.g., pines, heath, rockroses) is colonising what used to be pond basins just a few years ago (de Felipe et al., 2023; Díaz‐Paniagua et al., 2023). Indeed, some of the breeding sites sampled in the present study have already lost considerable amounts of flooding area in the 6–11 years following our tissue sampling.…”