We studied three shallow lakes, which differ in their regime: el Triunfo, a clear vegetated shallow lake with abundant submerged vegetation (mainly Ceratophyllum demersum) and low phytoplankton abundances (35[degrees]51S, 57[degrees]52'W); El Burro, a turbid shallow lake with high abundances of phytoplankton (35[degrees]42'S, 57[degrees]55'W) and Yalca, an inorganic turbid shallow lake with high amounts of suspended solids (35[degrees]35'S, 57[degrees]55'W).
In El Burro and Yalca, bacterioperiphyton samples were taken at 3 (t1), 10 (t2) and 20 days (t3), whereas in El Triunfo, samples were taken at 3 (t1), 7 (t2), 10 (t3) and 17 days (t4).
El Triunfo exhibited the highest hybridization percentages (average 60.6%), intermediate values were observed in Yalca (average 47.6%), whereas El Burro showed the lowest values (average 29.5%).
Alphaproteobacteria was the most abundant group in the three shallow lakes and presented the highest hybridization percentage (average values: 46.5% in El Triunfo, 31% in El Burro and 54.2% in Yalca).
The Eubacteria hybridization percentages were similar in El Triunfo and El Burro (average values 77%, and 79.6% respectively), whereas Yalca showed the lowest values (65.4% on average).
On average, the second largest group was Betaproteobacteria in El Triunfo and Yalca (hybridization percentage 22.6% and 14.11% respectively), and Gammaproteobacteria in El Burro (hybridization percentage 24.6%).
In Yalca, Alphaproteobacteria showed an increase in their abundances with time (RM ANOVA factor: time P < 0.01; factor: bacterial group P < 0.02).
In Yalca, the lower values of DIN, conductivity and turbidity in comparison with those reported in previous studies (Allende et al., 2009) could be tied to a dilution effect due to an increase in the hydrometric level of the shallow lake (personal observation).
Samples 1-4: El Triunfo (samples taken at t0, t1, t2 and t3 respectively); samples 5-8: El Burro (samples taken at t0, t1, t2 and t3 respectively); samples 9-12: Yalca (samples taken at t0, t1, t2 and t3 respectively).
Samples 1-4: El Triunfo (samples taken at t1, t2, t3 and t4 respectively); samples 5-7: El Burro (samples taken at t1, t2 and t3 respectively); samples 8-10: Yalca (samples taken at t1, t2 and t3 respectively).