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Recientemente se ha revalorado la relevancia de los sistemas acuaticos epicontinentales en el ciclo global del carbono, ya que estos tienen una gran capacidad de ser tanto sumideros de carbono, hacia sus sedimentos, como fuentes de carbono atmosferico. Sin embargo, la informacion acerca de los sistemas tropicales es aun heterogenea y escasa, situacion particularmente critica, dado que estos sistemas enfrentan problemas crecientes en el panorama del cambio global, contaminacion y eutrofizacion incluidas, particularmente esta ultima, asi como impactos de las estrategias de manejo (e.g., cambios en el nivel de agua). El estudio de la dinamica del oxigeno, criticado en el pasado, ha sido retomado y hoy es nuevamente utilizado ampliamente para estimar la produccion primaria y la respiracion ecosistemica ante la urgencia por estimar los flujos de carbono asociados a los sistemas acuaticos. Se revisan aqui, por ello, los aspectos metodologico-conceptuales asociados a la implementacion moderna del metodo de evolucion del oxigeno y se discuten las ventajas y los problemas asociados a esta metodologia, para facilitar y extender su aplicacion a los sistemas tropicales, donde su implementacion es muy conveniente. Se propone tambien una secuencia metodologica unificadora para hacer posible la comparacion entre estudios, y el escalamiento de los flujos de carbono, tanto espacial como temporalmente. Los inventarios de carbono en diferentes escalas (espaciales y temporales) son necesarios para entender la participacion y las respuestas de los sistemas acuaticos y regiones tropicales (en particular su papel como fuentes o sumideros de carbono) frente al cambio global.

Long-term and seasonal changes in production and respiration were surveyed in the Valle de Bravo reservoir, Mexico, in a period during which high water-level fluctuations occurred (2006–2015). We assessed the community metabolism through oxygen dynamics in this monomictic water-body affected by strong diurnal winds. The multiple-year data series allowed relationships with some environmental drivers to be identified, revealing that water level-fluctuations strongly influenced gross primary production and respiratory rates. Production and respiration changed mainly vertically, clearly in relation to light availability. Gross primary production ranged from 0.15 to 1.26 gO2 m−2 h−1, respiration rate from −0.13 to −0.83 gO2 m−2 h−1 and net primary production from −0.36 to 0.66 gO2 m−2 h −1 within the production layer, which had a mean depth of 5.9 m during the stratification periods and of 6.8 m during the circulations. The greater depth of the mixing layer allowed the consumption of oxygen below the production layer even during the stratifications, when it averaged 10.1 m. Respiration below the production layer ranged from −0.23 to −1.38 gO2 m−2 h−1. Vertically integrated metabolic rates (per unit area) showed their greatest variations at the intra-annual scale (stratification-circulation). Gross primary production and Secchi depth decreased as the mean water level decreased between stratification periods. VB is a highly productive ecosystem; its gross primary production averaged 3.60 gC m−2 d−1 during the 10 years sampled, a rate similar to that of hypertrophic systems. About 45% of this production, an annual average net carbon production of 599 g C m−2 year−1, was exported to the hypolimnion, but on the average 58% of this net production was recycled through respiration below the production layer. Overall, only 19% of the carbon fixed in VB is buried in the sediments. Total ecosystem respiration rates averaged −6.89 gC m−2 d−1 during 2006–2015, doubling the gross production rates. The reservoir as a whole exhibited a net heterotrophic balance continuously during the decade sampled, which means it has likely been a net carbon source, potentially releasing an average of 3.29 gC m−2 d−1 to the atmosphere. These results are in accordance with recent findings that tropical eutrophic aquatic ecosystems can be stronger carbon sources than would be extrapolated from temperate systems, and can help guide future reassessments on the contribution of tropical lakes and reservoirs to carbon cycles at the global scale. Respiration was positively correlated with temperature both for the stratification periods and among the circulations, suggesting that the contribution of C to the atmosphere may increase as the reservoirs and lakes warm up owing to climate change and as their water level is reduced through intensification of their use as water sources.