The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO2 fluxes in a tropical hydropower reservoir

[摘要] Abundant research has been devoted to understanding the complexity of thebiogeochemical and physical processes that are responsible for greenhousegas (GHG) emissions from hydropower reservoirs. These systems may havespatially complex and heterogeneous GHG emissions due to flooded biomass,river inflows, primary production and dam operation. In this study, weinvestigated the relationships between the water–air CO₂ fluxes and thephytoplanktonic biomass in the Funil Reservoir, which is an old, stratifiedtropical reservoir that exhibits intense phytoplankton blooms and a lowpartial pressure of CO₂ (pCO₂). Our results indicated that theseasonal and spatial variability of chlorophyll concentrations (Chl) andpCO₂ in the Funil Reservoir are related more to changes in the riverinflow over the year than to environmental factors such as airtemperature and solar radiation. Field data and hydro\-dynamic simulationsrevealed that river inflow contributes to increased heterogeneity during thedry season due to variations in the reservoir retention time and rivertemperature. Contradictory conclusions could be drawn if only temporal datacollected near the dam were considered without spatial data to representCO₂ fluxes throughout the reservoir. During periods of high retention,the average CO₂ fluxes were 10.3 mmol m⁻² d⁻¹ based ontemporal data near the dam versus −7.2 mmol m⁻² d⁻¹ with spatialdata from along the reservoir surface. In this case, the use of solelytemporal data to calculate CO₂ fluxes results in the reservoir actingas a CO₂ source rather than a sink. This finding suggests that thelack of spatial data in reservoir C budget calculations can affect regionaland global estimates. Our results support the idea that the Funil Reservoiris a dynamic system where the hydrodynamics represented by changes in theriver inflow and retention time are potentially a more important forcedriving both the Chl and pCO₂ spatial variability than the in-systemecological factors.

[学科分类] 地球化学与岩石