Consideration of solar radiation as a relevant parameter associated with cyanobacteria in a tropical monomictic aquatic system

Abstract Studies performed in Valle de Bravo (VB) reservoir in Mexico record the presence of cyanobacteria proliferation and microcystin LR (MC-LR), both from 1998 to 2022, related mainly to two environmental factors, nitrates (NO3) and temperature. We propose that these four parameters do not converge seasonally during stratification and mixing. We also suggest that solar radiation as a temperature effector could have a greater association between the parameters studied. We conducted laboratory tests to evaluate the intensity of light (rather than solar radiation) at different concentrations of NO3 to observe the growth of the model used, a wild-type cyanobacteria (M. aeruginosa) producer of MC-LR. The objectives of this study were to prove if there was a seasonal relationship between cyanobacteria and MC-LR with NO3 and temperature and to evaluate in vitro assay the association between light radiation and NO3 on the growth of the cyanobacterium Microcystis aeruginosa and MC-LR. Subsequently, wild-type microcystin-containing M. aeruginosa was cultured in different proportion of light radiation and NO3 (100, 50, 25 and 5%) to simulate the seasonal variation. The results showed that the algae did not proliferate due to the seasonal availability of NO3 but rather due to temperature. In vitro we observed that light radiation had a greater effect than NO3 on the growth of M. aeruginosa. The role of NO3 was inversely related to the presence of MC-LR but only with high light radiation. Therefore, we conclude that solar radiation governs the effect of NO3 for the proliferation of algae and cyanobacteria.