The Breathing of a Flooded Forest: Aquatic Metabolism Determined from Synchronous CO2 and O2 Dynamics Indicates Switches From Net Heterotrophy to Autotrophy and Back Over Annual Flood Cycle in the Pantanal of South America
Tuesday, 7 June 2016
Mark S. Johnson1, Higo José Dalmagro2, Michael J Lathuilliere1, Osvaldo Borges Pinto-Jr2, Nei K Leite3 and Eduardo G Couto4, (1)University of British Columbia, Vancouver, BC, Canada, (2)Universidade de Cuiabá, Cuiabá, Brazil, (3)UFSC Federal University of Santa Catarina, Department of Ecology and Zoology, Florianópolis, Brazil, (4)UFMT Federal University of Mato Grosso, Cuiabá, Brazil
Abstract:
CO2 exchange between wetlands and the atmosphere is the least well-constrained terrestrial-aquatic carbon flux. The degree to which terrestrial systems subsidize metabolism of aquatic ecosystems, and vice versa continues to be an area of active investigation worldwide. The line is particularly blurry for seasonally flooded forest ecosystems since the flood pulse imposes a switch between terrestrial to aquatic processes dominating within the same area. For example, organic matter that builds up in situ during the dry season (e.g. autochthonous material) becomes comingled with allochthonous materials that are transported laterally by the flood pulse, thus complicating source and sink determination for the ecosystem. In this presentation, we summarize results obtained using in situ gas sensors and other water quality and micrometeorological sensors deployed on a floating platform over an entire flood pulse in the Brazilian Pantanal near Poconé, Mato Grosso. The use of infrared gas analyzers within the water column (e.g. pCO2 sensors) in combination with dissolved oxygen sensors enabled two independent determinations of aquatic metabolism. Imbalances between CO2 evasion and O2 invasion (e.g. the breathing of the flooded forest) were used to evaluate the degree of net heterotrophy of the system. We determined that the forest was net heterotrophic during the first month of the flood cycle due to the active decomposition of autochthonous organic matter (litter layer on the ground surface) and allochthonous materials (floodwater derived dissolved and particulate organic matter) translocated into the forest. During the primary flood period, the system exhibited autotrophic characteristics as CO2 evasion and O2 invasion balanced on a daily basis for approximately two months. During the final month of the flood cycle when the flooded forest was draining, the water column again exhibited net heterotrophic conditions.
