Seasonal changes in primary production and respiration in a subtropical lake undergoing eutrophication
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Seasonal changes in primary production and respiration in a subtropical lake undergoing eutrophication Denise Tonetta
&
Mauricio Mello Petrucio
Received: 24 January 2020 / Accepted: 27 July 2020 # Springer Nature Switzerland AG 2020
Abstract The balance between gross primary production (GPP) and respiration (R) is frequently used to estimate the role of lakes in the carbon cycle. Seasonal changes in the carbon cycle of subtropical lakes are often underestimated, but changes in meteorological and limnological characteristics often follow the welldefined climatic seasons. Based on 1 year’s free-water dissolved oxygen and temperature measurements, we investigated the seasonal changes in primary production and respiration in subtropical Peri Lake in Southern Brazil, which is currently undergoing eutrophication. We expected that periods of high light availability and temperature would lead to a net autotrophic condition. Furthermore, we explored the seasonal coupling between GPP and R, expecting that different sources of organic matter would have different effects on the metabolic rates. We found that Peri Lake was predominately net heterotrophic (GPP < R). GPP was high during summer and autumn and low in winter, as was R, coinciding with the seasonal changes occurring in light and temperature. Light conditions were of essential importance for the variations in GPP, while respiration was fueled by both autochthonous and allochthonous
D. Tonetta (*) Department of Bioscience, Aarhus University, Frederiksborgvej, 399, 4000 Roskilde, Denmark e-mail: [email protected] M. M. Petrucio Department of Ecology and Zoology, Federal University of Santa Catarina, Florianópolis 88040-900, Brazil e-mail: [email protected]
organic matter. Constant external input of organic matter resulted in a generally low coupling between GPP and R. A tighter coupling between GPP and R was observed in spring as a result of higher productivity, while a decoupling in autumn was due to intensified allochthonous organic matter runoff caused by rainfall and wind. We found that higher productivity rates in summer did not shift the system to an autotrophic condition and that Peri Lake functioned as a carbon source, light and organic matter being the prime drivers for the metabolic rates. Keywords High frequency . Free-water metabolism . Net heterotrophy . Peri Lake . Eutrophication
Introduction Aquatic metabolism is an integrated descriptor of ecosystem functioning in which fixation of organic carbon by photosynthesis (GPP) and degradation of organic carbon (R) are the major pathways of carbon cycling (Cole et al. 2002). The balance between GPP and R is the net ecosystem productivity (NEP = GPP − R), which indicates whether the environment is net autotrophic (NEP > 0), where the excess organic material may either be exported to adjacent systems and/or accumulate within the system, or net heterotrophic (NEP < 0), where inorganic carbon is exported to the atmosphere (Lovett et al. 2006). Net autotrophy is commonly observed in eutrophic lakes
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