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Extreme hydrological and thermal regimes characterize the Mediterranean zone and can influence the phenology of greenhouse gas (GHG) emissions in reservoirs. Our study examined the seasonal changes in GHG emissions of a shallow, eutrophic, hardwater reservoir in Spain. We observed distinctive seasonal patterns for each gas. CH4 emissions substantially increased during stratification, influenced predominantly by the increase in water temperature, net ecosystem production, and the decline in reservoir mean depth. N2O emissions mirrored CH4's seasonal trend, significantly correlating to water temperature, wind speed, and gross primary production. Conversely, CO2 emissions decreased during stratification and displayed a quadratic, rather than a linear relationship with water temperature—an unexpected deviation from CH4 and N2O emission patterns—likely associated with photosynthetic uptake of bicarbonate and formation of intracellular calcite that might be exported to sediments. This investigation highlights the imperative of integrating these idiosyncratic patterns into GHG emissions models, enhancing their predictive power. [ABSTRACT FROM AUTHOR]

With the advent of DNA-based molecular technologies, microbial ecologists now have the tools to test whether general ecological patterns apply to microorganisms. In this study, we selected ii high-mountain lakes from Sierra Nevada (Spain) to test the predictions of island-biogeography theory in relation to ecosystem size and isolation, and to assess the influence of other factors (i.e., ecosystem productivity, resource richness, and biotic interactions) on bacterial community structure. Bacterial operational taxonomic units (OTUs), generated by denaturing-gradient gel electrophoresis of polymerase chain-reaction- amplified 16S rRNA genes, were used as a surrogate of predominant "biodiversity units." OTU composition among lakes was heterogeneous, and the number of site-specific OTUs was near 50%. Lake remoteness did not affect the number of bacterial OTUs although the spatial distribution of the lakes significantly influenced bacterial composition. Lakes that were closer together had more similar bacterial fingerprints. We found a consistent positive association between bacterial OTU richness and lake area. The slope of this relationship (0.161 ± 0.026, including literature data) was similar to slopes obtained for organisms with high dispersion rates. [ABSTRACT FROM AUTHOR]

Sunlight reacts with dissolved organic matter (DOM) modifying its availability as bacterial substrate. We assessed the impact of DOM photoproducts and mineral nutrient supply on bacterial growth in seven inland waters from the South of Spain, where DOM is characterized by low chromophoric content and long residence time. Factorial experiments were performed with presence vs absence of DOM photoproducts and mineral nutrient supply. In six of the seven experiments, we found a significant and negative effect of DOM photoproducts on bacterial growth and a significant and positive effect of mineral nutrient supply. The interaction of these two factors leaded to a compensation of negative effects of photoproducts by availability of mineral nutrients. Dissolved organic matter diagenetic status and the ionic environment where organic carbon is dissolved can be influencing bacterial DOM processing.