Environmental controls, composition, structure, and typology of microbial mats in temporary salt lakes of the mancha húmeda biosphere reserve (central Spain)

Temporary shallow lakes (lagunas) of the Mancha Húmeda Biosphere Reserve are unbeatable natural labs for the study of microbial mats. Different types of these communities have been observed in them; besides, microbial mats are the dominant communities in some lagunas. The aim of this study is to quantify the factors involved in the formation of microbial mats in inland salt lakes under variable environmental conditions (i.e. substrate, hydroperiod, water ionic concentration and composition, and available nutrients). Special focus is made on the analyisis of correspondences between microorganisms? assemblages and specific combination of environmental conditions. Studied communities are located in 10 fluctuating lagunas of the Mancha Húmeda Biosphere Reserve. Twelve sampling campaigns were done along a hydrological year; environmental factors studied were temperature, water level, turbidity, conductivity, pH, major ions, soluble reactive phosphorus, nitrate, ammonium, and sediment granulometry. Microbial mat thickness, structure, and within-site spatial distribution were recorded in situ. Dominant components of the mat and the relative frequency of the different morphological patterns were determined after observation with an Olympus BH-2 optical microscope of samples previously collected. Multivariate techniques were used to identify the most informative variables in terms of the type, function, and development of microbial mats, and relationships between hydrochemistry and sediment descriptors which are most relevant for microbial mat communities. Nitrate concentration in water discriminated best between different types of microbial mats. Nitrate concentration was highest in lagunas with thin and weak mats, ranging from 0.37-18.49 mg L-1, which correspond to hypereutrophic lagunas. Undetectable to 0.54 mg NO3- L-1 was found in lagunas with compact mats and in lagunas without mats. No significant differences in salinity were found between lagunas with different types of microbial mats, but magnesium-sulphate ionic composition predominates in compact-mats lagunas, whereas sodium-chloride waters are associated to weak and thin mats