Spatial and seasonal dynamics of riverine carbon fluxes of the Brantas catchment in East Java

Abstract

Dissolved and particulate organic and inorganic carbon concentrations and flux were measured from July 2005 to June 2006 in the Brantas River basin, a midsized tropical mountainous river and the second largest in Java. There were large seasonal differences in carbon fluxes. Dissolved inorganic carbon (DIC) fluxes were 9.3 times greater and dissolved organic carbon (DOC) fluxes were 532 times greater in the wet season (October to April) than in the dry season. These large contrasts in concentration lead to large differences in load between dry and wet months. In the wet season between January and April, DIC and DOC fluxes are 66% and 87%, respectively, of the total annual fluxes. Most of the annual fluxes of total suspended solids (2.7 × 106 t a−1), total dissolved solids (2.3 × 106 t a−1), DIC (0.26 × 106 t a−1), and DOC (0.2 × 106 t a−1) are transported into the Madura Strait. Accordingly, the Brantas River ranks number 17 among the top 20 rivers that originate at elevations above 3000 m. The concentration of DIC is consistently high all yearlong due to carbonate weathering in the river basin, except in the middle part of the basin, whereas the concentration of DOC is highly seasonal because of variations in biological activities. The total inorganic carbon concentration substantially exceeded the total organic carbon concentration, but the differences decreased from January to April when DOC increased sharply. The carbon budget indicates that the upstream river is a carbon source, and the middle sections of the river are a carbon sink. No carbon trapping was observed by the several impoundments over the basin while sediment trapping was obvious.