Abstract
To understand the dynamics of planktonic prokaryotes in a subtropical lake and its relationship with carbon, we conducted water sampling through four 48-h periods in Peri Lake for 1 year. Planktonic prokaryotes were characterized by the abundance and biomass of heterotrophic bacteria (HB) and of cyanobacteria (coccoid and filamentous cells). During all samplings, we measured wind speed, water temperature (WT), pH, dissolved oxygen (DO), precipitation, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and carbon dioxide (CO2). DOC was higher in the summer (average = 465 μM – WT = 27°C) and lower in the winter (average = 235 μM – WT = 17°C), with no significant variability throughout the daily cycles. CO2 concentrations presented a different pattern, with a minimum in the warm waters of the summer period (8.31 μM) and a maximum in the spring (37.13 μM). Daily trends were observed for pH, DO, WT, and CO2. At an annual scale, both biological and physical-chemical controls were important regulators of CO2. HB abundance and biomass were higher in the winter sampling (5.60 × 109 cells L−1 and 20.83 μmol C L−1) and lower in the summer (1.87 × 109 cells L−1 and 3.95 μmol C L−1). Filamentous cyanobacteria (0.23 × 108–0.68 × 108 filaments L−1) produced up to 167.16 μmol C L−1 as biomass (during the warmer period), whereas coccoid cyanobacteria contributed only 0.38 μmol C L−1. Precipitation, temperature, and the biomass of HB were the main regulators of CO2 concentrations. Temperature had a negative effect on the concentration of CO2, which may be indirectly attributed to high heterotroph activity in the autumn and winter periods. DOC was positively correlated with the abundance of total cyanobacteria and negatively with HB. Thus, planktonic prokaryotes have played an important role in the dynamics of both dissolved inorganic and organic carbon in the lake.
Highlights
Lakes are sentinels of global change to the extent that their storage and transformation of organic matter changes with global warming, with which there are many concerns (Cole et al, 2007; Adrian et al, 2009; Tranvik et al, 2009)
The temperature dependence of community respiration and metabolic rates (Kosten et al, 2010; Yvon-Durocher et al, 2012), and of cyanobacteria dominance in shallow lakes (Kosten et al, 2012; Sarmento, 2012) suggest that in tropical and subtropical lakes, prokaryotes play a major role in carbon mineralization and production (Sarmento, 2012)
Wind speed was higher in August compared to the other months (ANOVA, Tukey-HSD, df = 48, p < 0.05), and significant daily variability was observed in the same period, with winds of 8.5 m s−1 in the morning
Summary
Lakes are sentinels of global change to the extent that their storage and transformation of organic matter changes with global warming, with which there are many concerns (Cole et al, 2007; Adrian et al, 2009; Tranvik et al, 2009). Lakes generally function as sources of carbon dioxide (CO2) to the atmosphere, mainly because of high inputs to and degradation through mineralization of terrestrial organic material in lakes (Cole et al, 1994, 2007; Kosten et al, 2010; Marotta et al, 2010a,b). Despite the studies on temporal and spatial variability of carbon fluxes among and within temperate and tropical lakes, little is known about the temporal dynamics in subtropical lakes and what factors drive carbon variability there. The temperature dependence of community respiration and metabolic rates (Kosten et al, 2010; Yvon-Durocher et al, 2012), and of cyanobacteria dominance in shallow lakes (Kosten et al, 2012; Sarmento, 2012) suggest that in tropical and subtropical lakes, prokaryotes play a major role in carbon mineralization and production (via primary production) (Sarmento, 2012)
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