Study area
The present study was performed on 22 permanent and temporary ponds
located in a lowland area (900 m. a. s. l.) area (ca. 230
km2) in the northwest part of Spain (Figure
1). The study sites were characterized by a marked variability in
environmental conditions, such us morphometry, nutrient content and
mineralization (Table 1). The predominant land uses in the
study area are arable land and pasture. The climate is Mediterranean dry
moderate with mean temperatures in summer and winter of 18
°C and 3.2 °C,
respectively, and a mean precipitation in summer and winter of 84.5 mm
and 173 mm, respectively (1976-2015; data provided by the Spanish Met
Agency-AEMET; http://www.aemet.es). The majority of ponds are shallow
(0.2-1.5 m), are fed by groundwater and rainfall, and they experience a
high reduction in water volume during summer.