River inflow and retention time affecting spatial heterogeneity of chlorophyll and water–air CO<sub>2</sub> fluxes in a tropical hydropower reservoir

Abstract

Abstract. Much research has been devoted to understanding the complexity of biogeochemical and physical processes responsible for the greenhouse gas (GHG) emissions from hydropower reservoirs. Spatial complexity and heterogeneity of GHG emission may be observed in these systems because it is dependent on flooded biomass, river inflow, primary production and dam operation. In this study, we investigate the relationships between water–air CO2 fluxes and phytoplanktonic biomass in Funil Reservoir, an old and stratified tropical reservoir, where intense phytoplankton blooms and low partial pressure of CO2 (pCO2) are observed. Our results showed that Funil Reservoir seasonal and spatial variability of chlorophyll concentration (Chl) and pCO2 is more related to changes in river inflow over the year than environmental factor such as air temperature and solar radiation. Field data and hydrodynamic simulations reveal that the river inflow contributes to increased heterogeneity in dry season due to the variation of reservoir retention time and river temperature. Contradictory conclusion can be drawn if temporal data collected only near the dam is considered instead of spatial data to represent CO2 fluxes in whole reservoir. The average CO2 fluxes was −17.6 and 22.1 mmol m−2d−2 considering data collected near the dam and spatial data, respectively, in periods of low retention time. In this case, the lack of spatial information can change completely the role of Funil Reservoir regarding GHG emissions. Our results support the idea that Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in river inflow and retention time is potentially more important force driving both Chl and pCO2 spatial variability than in-system ecological factors.

Freshwater methane and carbon dioxide fluxes : Spatio-temporal variability and an integrated assessment of lake and stream emissions in a catchment

“…Stream or river water inflows into lakes could also lead to spatial variability in CH4 Murase et al, 2003;Yamada et al, 2001). Higher CO2 fluxes were observed in littoral zones and close to macrophytes in some studies (Pacheco et al, 2015;Rudorff et al, 2011;Soja et al, 2014), but the opposite, with higher central CO2 fluxes, has also been reported (Schilder et al, 2013). Gas exchange velocity (k; a physical parameter which governs gas exchange rates) can be spatially heterogeneous within the lakes, resulting in spatially variable diffusive CH4 and CO2 fluxes (Hofmann, 2013;Schilder et al, 2013;Vachon & Prairie, 2013).…”

Spatiotemporal variability of lake pCO2 and CO2 fluxes in a hemiboreal catchment

“…Spatial variability in pCO 2aq and CO 2 fluxes are now increasingly addressed, e.g., in tropical and boreal reservoirs [ Pacheco et al ., ; Roland et al ., ; Teodoru et al ., ] and Amazon floodplain lakes [ Rudorff et al ., ], and have been linked to river inputs, littoral zones, and photosynthesis. The variability of k with fetch or distance to shore has been highlighted, and it has been found to affect CO 2 fluxes [ Schilder et al ., ; Vachon and Prairie , ].…”

“…As few studies have assessed the variability and the key drivers for pCO 2aq and CO 2 fluxes from lakes integrating spatiotemporal variability, there is a great risk that present assessments are biased. For example, previous intensive pCO 2aq measurements were typically designed to either cover large space under a short time (gas equilibrator screening or manual samples in several points [e.g., Borges et al ., ; Pacheco et al ., ; Roland et al ., ]) or long time in specific locations (sensors collecting data or calculated pCO 2aq from one or a few points over time [e.g., Åberg et al ., ; Huotari et al ., ; Pacheco et al ., ]). Therefore, studies including both spatial and temporal variabilities are needed to better understand variability and to develop representative approaches for large‐scale assessments of lake CO 2 fluxes.…”

Modelagem do regime térmico de um reservatório tropical de abastecimento público, Juiz de Fora, MG, Brasil

“…Os resultados apresentados por Pacheco et al (2014), ao investigar o Reservatório do Funil, localizado no município de Resende -RJ, mostram que a variabilidade espacial da concentração de clorofila (Chl) e CO 2 está mais relacionada a mudanças no fluxo do rio ao longo do ano do que fatores ambientais, tais como temperatura do ar e radiação solar. Nesse sentido, quando o fluxo do rio atuar como regulador da temperatura de um reservatório, também será capaz de condicionar processos físicos, químicos e biológicos, visto que a temperatura é um fator físico que interfere diretamente na estrutura das comunidades biológicas e processos ecossistêmicos.…”