Sediment Features, Primary Producers and Food Web Structure in Two Shallow Temporary Lakes (Monegros, Spain)

The aim of this study is to describe general features of sediment, primary producers and both benthic and planktonic consumers in two shallow saline lakes (Salada de La Muerte andSalada de Piñol) in order to detect main factors influencing food web structure. The lakes are located in Los Monegros district, in the central area of the Ebro River catchment, NE Spain. Both lakes are temporary with salinity well above 30 g L⁴. Although they are situated close to each other (distance: 300 m), their communities of primary producers differ dramatically. One lake (La Muerte) is dominated by microbial mats and seems to function through the benthic pathway. The other (Piñol) has some macrophytes but phytoplankton is the main source of primary production. Two cycles (1994/95 and 1995/1996), quite different in their hydrological characteristics, have been studied. PCA demonstrated the major influence of hydrologic features (e.g. water level) over biotic and abiotic parameters. The presence of microbial mats in La Muerte played a key role in stabilizing the sediments. A comparison of food web structure and dynamics in both lakes has been performed and the influence of sediment features is discussed.