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Soil organic carbon stocks in fluvial and isolated tropical wetlands from Colombia

Pérez-Rojas, Jonathan, Moreno, Flavio, Quevedo, Julio César, Villa, Jorge
Catena 2019 v.179 pp. 139-148
aerobic conditions, arid lands, bulk density, carbon sequestration, carbon sinks, chromium, ecosystems, fluvial soils, freshwater, hydrodynamics, macrophytes, mineral soils, peatlands, rivers, soil organic carbon, tropical soils, vegetation, Colombia
Freshwater tropical wetlands are valuable sinks of carbon (C) on the global scale. While much attention has been paid to forested peatlands, little is known about C stored in tropical freshwater mineral soil wetlands dominated by herbaceous and macrophyte vegetation, specially its spatial variability at the ecosystem level. Here we study the soil organic carbon of two tropical lowland wetlands (fluvial and isolated), located in the interandean valley of the Magdalena river in Colombia. Soil cores were extracted from 11 sampling zones distributed in the two wetlands, including the dryland adjacent to each wetland. They were sectioned into 2 cm-depth increments that were analyzed for C content. The average bulk density was higher (P < 0.001) in the fluvial wetland (0.87 ± 0.3 g cm−3) than in the isolated one (0.45 ± 0.3 g cm−3), the concentration of C (% Cr) was higher (P < 0.001) in the isolated wetland (11.1 ± 6.8%) than in the fluvial one (1.9 ± 1.1%) as well as the average soil organic carbon (6.4 ± 2.6 and 2.9 ± 1.1 t C ha−1 cm−1, respectively). Per unit area, the fluvial wetland had about twice as much storage capacity of C as the dryland, while in the isolated wetland the ratio was up to five times higher. Hydrogeomorphology was an important factor for the C storage in these ecosystems. The fluctuating hydrodynamics of the fluvial wetland seems to favor aerobic conditions and thus the prevalence of aerobic over anaerobic decomposition, lowering accumulation of C. This study makes an important contribution towards the understanding of C dynamics in different types of tropical wetlands and brings data to support their conservation.