Diurnal sampling reveals significant variation in CO2 emission from a tropical productive lake

Abstract

It is well accepted in the literature that lakes are generally net heterotrophic and supersaturated with CO 2 because they receive allochthonous carbon inputs. However, autotrophy and CO 2 undersaturation may happen for at least part of the time, especially in productive lakes. Since diurnal scale is particularly important to tropical lakes dynamics, we evaluated diurnal changes in pCO 2 and CO 2 flux across the air-water interface in a tropical productive lake in southeastern Brazil (Lake Carioca) over two consecutive days. Both pCO 2 and CO 2 flux were significantly different between day (9:00 to 17:00) and night (21:00 to 5:00) confirming the importance of this scale for CO 2 dynamics in tropical lakes. Net heterotrophy and CO 2 outgassing from the lake were registered only at night, while significant CO 2 emission did not happen during the day. Dissolved oxygen concentration and temperature trends over the diurnal cycle indicated the dependence of CO 2 dynamics on lake metabolism (respiration and photosynthesis). This study indicates the importance of considering the diurnal scale when examining CO 2 emissions from tropical lakes.Keywords: pCO 2 , CO 2 flux, diurnal variations, tropical productive lake.Amostragem diurna demonstra variação significativa na emissão de CO 2 em um lago tropical produtivo Resumo É amplamente aceito na literatura que lagos são em geral heterotróficos e supersaturados com CO 2 já que recebem carbono alóctone. Porém, autotrofia e insaturação de CO 2 podem ocorrer em pelo menos parte do tempo, especialmente em lagos produtivos. Como a escala diurna é particularmente importante para a dinâmica de lagos tropicais, variações diurnas na pCO 2 e no fluxo de CO 2 através da interface ar-água foram avaliadas num lago tropical produtivo do sudeste do Brasil (Lagoa Carioca) durante dois dias consecutivos. Tanto a pCO 2 quanto o fluxo de CO 2 foram significativamente diferentes entre o dia (9:00 às 17:00) e a noite (21:00 às 5:00), confirmando a influência desta escala na dinâmica do CO 2 na Lagoa Carioca. Foram registradas heterotrofia e emissão de CO 2 pela lagoa apenas durante a noite, enquanto durante o dia não houve emissão significativa. Variações na concentração de oxigênio dissolvido e na temperatura ao longo do dia indicaram a dependência da dinâmica do CO 2 no metabolismo (respiração e fotossíntese) deste lago. Este estudo indica a importância de se considerar a escala diurna na avaliação da emissão de CO 2 por lagos tropicais.Palavras-chave: pCO 2 , fluxo de CO 2 , variações diurnas, lago tropical produtivo.

Generalized Additive Models of Climatic and Metabolic Controls of Subannual Variation in pCO2 in Productive Hardwater Lakes

“…Such low productivity values were found most frequently in the mesotrophic Lake Diefenbaker, while strongly positive relationships between pH and Chl a occurred often in the most shallow lakes (Wascana, Buffalo Pound; Figure ). In general, the observed Chl a concentrations needed for net CO 2 release were low relative to those found in other eutrophic lakes where out‐gassing may predominate even under the most productive conditions (Chl a >40 μg/L; Huttunen et al, ; Reis & Barbosa, ), although outgassing was predicted even in our sites at similar algal production provided other predictors were set to values favoring outgassing (e.g., low oxygen and high TDN).…”

“…Metabolic control of CO 2 flux in these hardwater lakes does not appear to be as strong as that observed in boreal or soft water regions where microbial metabolism of DOC (Lapierre & del Giorgio, ; Sobek et al, ) or photosynthesis (Maberly, ; Reis & Barbosa, ) regulates pCO 2 , albeit with variable allochthonous contributions of respired or otherwise derived DIC (Bogard & del Giorgio, ; Weyhenmeyer et al, ). These results fit within the larger matrix of lake types along gradients of DIC, DOC, nutrients, and alkalinity and suggest that moderately hardwater lakes are more likely to capture atmospheric CO 2 at a given level of productivity than would dilute lakes (Reis & Barbosa, ), those with high DOC loads (Huttunen et al, ), or hardwater systems with chronic oversaturation of DIC (Marcé et al, ). Further, because such systems often coincide with intensively fertilized agricultural regions, there exists the possibility that many of these systems will fall below the global average estimate of lake CO 2 flux (Raymond et al, ).…”

Methane and Carbon Dioxide Emissions From Reservoirs: Controls and Upscaling

“…Diurnal changes in the relative rates of CO 2 uptake (photosynthesis) and production (respiration) can be pronounced, particularly in productive waterbodies, leading to higher emission rates during hours of darkness. This pattern has been reported for a wide range of lentic ecosystems including lakes in northern Europe, Canada, Brazil, and China (Du et al, 2018;Erkkila et al, 2018;Natchimuthu et al, 2014;Reis & Barbosa, 2014;Spafford & Risk, 2018;Vesala et al, 2006). Perhaps more relevant to the current study are reports from a eutrophic lake and reservoir in the southcentral United States (Liu et al, 2016;Xu et al, 2019).…”

Ecophysiology matters: linking inorganic carbon acquisition to ecological preference in four species of microalgae (Chlorophyceae)

“…). Fluctuations are also possible within a day as a result of C i depletion during the day and in particular by entrainment of CO 2 ‐rich water from depth (Maberly , Reis and Barbosa ). Consequently, the ability to acclimate to changing CO 2 conditions, for example, using HCO 3 − more effectively, is ecologically relevant.…”