Open AccessRiver geochemistry, chemical weathering, and atmospheric C O 2 consumption rates in the V irunga V olcanic P rovince ( E ast A frica)
Author(s) -
Balagizi Charles M.,
Darchambeau François,
Bouillon Steven,
Yalire Mathieu M.,
Lambert Thibault,
Borges Alberto V.
Publication year - 2015
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2015gc005999
Subject(s) - weathering , geology , drainage basin , alkalinity , geochemistry , dissolved organic carbon , nitrate , hydrology (agriculture) , environmental chemistry , chemistry , oceanography , cartography , geotechnical engineering , organic chemistry , geography
We report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289–1467 mg L −1 ) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (δ 13 C) of POC and DOC mean δ 13 C of −22.5‰ and −23.5‰, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH 4 to the atmosphere (4–5052 nmol L −1 ). Most rivers show N 2 O concentrations close to equilibrium, but some rivers showed high N 2 O concentrations related to denitrification in groundwaters. δ 13 C signatures of dissolved inorganic carbon suggested magmatic CO 2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO 2 ‐mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0–2779.9 t km −2 yr −1 ) and atmospheric CO 2 consumption (0.4–37.0 × 10 6 mol km −2 yr −1 ) rates were higher than previously reported in the literature for basaltic terrains.