Contribution of humic substances as a sink and source of carbon in tropical floodplain lagoons

Author(s)

Bianchini, Jr., Irineu ^{[1, 2]} ; da Cunha-Santino, Marcela Bianchessi ^{[1, 2]}

Affiliation

^[1] Univ Fed Sao Carlos, Dept Hidrobiol, Rodovia Washington Luiz, Km 235 Cx, BR-13565905 Sao Carlos 676, SP - Brazil

^[2] Univ Fed Sao Carlos, Programa Posgrad Ecol & Recursos Nat, Rodovia Washington Luiz, Km 235 Cx, BR-13565905 Sao Carlos 676, SP - Brazil

• Document type: Journal article
• Source: Journal of Soils and Sediments; v. 18, n. 4, p. 1232-1241, APR 2018.
• Web of Science Citations: 0

Abstract

We evaluated the decay of humic (HA) and fulvic acids (FA) in order to discuss the contribution of these substances as a sink and source of carbon in a tropical lagoon. Experiments were conducted under aerobic and anaerobic conditions using FA and HA isolated from decomposition of Oxycaryum cubense submitted to 10 and 60 days of degradation. HA and FA were added to water samples from a tropical floodplain oxbow system, the Inferno Lagoon. The mineralization chambers were incubated in the dark at 21.0 A degrees C. The carbon balance, electrical conductivity, pH, and optical density were measured over 95 days. The results from the carbon budget were fitted with a first-order kinetics model. The mineralization of refractory fractions predominated for both FA and HA. Overall, although the mineralization pathway yields varied according to the type of resource and oxygen availability, the mineralization half-lives were quite similar (49 to 64 days), suggesting a similar microbial catabolism efficiency during the decay of humic substances. The short-term routes are represented by biochemical oxidations, and the immobilization and labile fractions (varying from 0 to 30%) of FA and HA supported these processes. A yield varying from 61.0 to 91.3% represents a carbon source degradation in the middle term (ca. 2 months) considering the ecosystem. In tropical floodplain lagoons, there are three carbon routes: (i) the IN1, representing a short-term pathway (hours to days) in the carbon transformation and (ii) IN3, a middle-term carbon source from HA and FA mineralization to the water column and subsequently to the atmosphere. A third route (IN2) supported the heterotrophic metabolism of the lagoon acting as a transitory sink of carbon. (AU)

• FAPESP's process: 07/08602-9 - Potential prodution of greenhouse gases in sediments of marginal lagoons
• Grantee: Irineu Bianchini Júnior
• Support Opportunities: Regular Research Grants