River geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

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 (delta C-13) of POC and DOC mean delta C-13 of -22.5 parts per thousand and -23.5 parts per thousand, 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 CH4 to the atmosphere (4-5052 nmol L-1). Most rivers show N2O concentrations close to equilibrium, but some rivers showed high N2O concentrations related to denitrification in groundwaters. delta C-13 signatures of dissolved inorganic carbon suggested magmatic CO2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO2-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 CO2 consumption (0.4-37.0 x 10(6) mol km(-2) yr(-1)) rates were higher than previously reported in the literature for basaltic terrains.