Limnetica 35

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Planktonic metabolism in a Mediterranean reservoir during a near-surface cyanobacterial bloom

Enrique Moreno-Ostos, Roberto L. Palomino-Torres, C. Escot and J. Ma Blanco
2016
35
1
117-130
DOI: 
10.23818/limn.35.10
Citation: 

Summer blooms of large, filamentous, nitrogen-fixing and potentially toxic cyanobacteria are characteristic of many productive, warm monomictic reservoirs in the Mediterranean region, where they constitute stable assemblages. The accumulation of positively buoyant cyanobacteria at the surface layers of the water column favours – among others – the interception of light, inorganic carbon and nitrogen fluxes from the atmosphere, giving these prokaryotes a competitive advantage over other phytoplankton groups. Cyanobacterial blooms can cause deleterious effects to water quality and reservoir ecosystem services. Although the structure of the plankton community in reservoirs during cyanobacterial blooms is a well-known limnological issue, few studies have been undertaken on its functional characteristics. In this study, we used a high-resolution autonomous monitoring system to investigate the short-term changes in gross primary production (GPP), net ecosystem production (NEP) and community respiration (R) in the near-surface waters of a Mediterranean reservoir during a dense summer cyanobacterial bloom. Our results demonstrate that during the bloom, the surface waters of the reservoir showed a well-balanced planktonic metabolism, with a mean GPP:R ratio not significantly different than 1 and therefore close positive correlations between GPP and R. Additionally, we found a positive correlation between the daily integrated incident light and the NEP:GPP ratio, while the mixed-layer depth and NEP:GPP ratio were negatively correlated, suggesting a central role for physical processes in the control of community metabolism and the persistence of the cyanobacterial bloom. The implications for the bloom stability and relevance for reservoir water quality management are noted.

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