Journal of Geophysical Research: Biogeosciences
2020
125
1
e2019JG005270
https://doi.org/10.1029/2019JG005270
ISSN impreso: 2169-8953 ISSN en línea: 2169-8961
bacterial membrane lipids (brGDGTs), altitude-temperature relations, Amazon headwaters, soil-river connectivity, riverine organic carbon transport, brGDGT proxy signal
We investigate the implications of upstream processes and hydrological seasonality on the transfer of soil organic carbon (OC) from the Andes mountains to the Amazon lowlands by the Madre de Dios River (Peru), using branched glycerol dialkyl glycerol tetraether (brGDGT) lipids. The brGDGT signal in Andean soils (0.5 to 3.5 km elevation) reflects air temperature, with a lapse rate of −6.0 °C/km elevation (r2 = 0.89, p < 0.001) and −5.6 °C/km elevation (r2 = 0.89, p < 0.001) for organic and mineral horizons, respectively. The same compounds are present in river suspended particulate matter (SPM) with a lapse rate of −4.1 °C/km elevation (r2 = 0.82, p < 0.001) during the wet season, where the offset in intercept between the temperature lapse rates for soils and SPM indicates upstream sourcing of brGDGTs. The lapse rate for SPM appears insensitive to an increasing relative contribution of 6-methyl isomer brGDGTs produced within the river. River depth profiles show that brGDGTs are well mixed in the river and are not affected by hydrodynamic sorting. The brGDGTs accumulate relative to OC downstream, likely due to the transition of particulate OC to the dissolved phase and input of weathered soils toward the lowlands. The temperature-altitude correlation of brGDGTs in Madre de Dios SPM contrasts with the Lower Amazon River, where the initial soil signature is altered by changes in seasonal in-river production and variable provenance of brGDGTs. Our study indicates that brGDGTs in the Madre de Dios River system are initially soil derived and highlights their use to study OC sourcing in mountainous river systems.
©2019. The Authors.
Kirkels Frédérique M. S. A., Ponton Camilo, West Valier Galy, A. Joshua, Feakins Sarah J., Peterse Francien
American Geophysical Union (AGU)
Washington, D.C., EE.UU.
Inglés
Articulo de revista academica