Linking summer conditions to CO<inf>2</inf> undersaturation and CO<inf>2</inf> influx in a subtropical coastal lake

Publication Type:
Journal Article
Citation:
Limnology, 2015, 16 (3), pp. 193 - 201
Issue Date:
2015-08-11
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© 2015, The Japanese Society of Limnology. In this study, we tested the hypothesis that pCO < inf > 2 < /inf > and air–water CO < inf > 2 < /inf > fluxes in the surface waters of a subtropical lake vary on two time scales (diel and seasonally) and that CO < inf > 2 < /inf > concentrations would decrease during the day and in summer. We estimated the variability of pCO < inf > 2 < /inf > and the air–water CO < inf > 2 < /inf > flux from pH-alkalinity in four 48-h periods that were representative of each subtropical season. There was high variability in pCO < inf > 2 < /inf > and the air–water gas flux over 48 h, but there was no clear pattern between day and night. CO < inf > 2 < /inf > concentrations showed a strong positive correlation with heterotrophic bacterial biomass and a negative correlation with dissolved organic carbon concentrations and water temperature. The lake was predominantly diel and seasonally CO < inf > 2 < /inf > supersaturated; the highest CO < inf > 2 < /inf > efflux was observed in the spring and a CO < inf > 2 < /inf > influx was observed in summer. Our hypothesis was confirmed; pCO < inf > 2 < /inf > was lowest in summer and during the daytime in spring and summer due to physical and biological conditions that favoured photosynthetic activities. These findings suggest that temporal shifts in the microbial community and meteorological variables, which are indirectly related to temperature, may be important drivers of CO < inf > 2 < /inf > concentrations in Peri Lake. In conclusion, pCO < inf > 2 < /inf > and the air–water CO < inf > 2 < /inf > flux vary temporally (diel and seasonally) in the littoral zone of this subtropical coastal lake, with shifts between CO < inf > 2 < /inf > influx and efflux throughout the sampling periods.
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