Dissolved organic carbon loss fluxes through runoff and sediment on sloping upland of purple soil in the Sichuan Basin

Runoff is a major driver for dissolved organic carbon (DOC) diffusing into aquatic ecosystems. Transport of DOC in runoff is important in the C cycle of soils in an agricultural ecosystem. This study provides a combined dataset on DOC loss pathways and fluxes from sloping upland in the purple soil area of southwestern China. A free-drain lysimeter experiment was conducted to quantify DOC loss through overland flow (2010–2012), interflow (2010–2012) and sediment (2011–2012). Average annual cumulative discharges of overland and interflow were 58.3 ± 3.1 and 289.4 ± 5.4 mm, accounting for 6.8 and 33.8 % of the totals during the entire rainy season, respectively. Average annual cumulative sediment loss flux was 183.5 ± 14.6 g m−2. Average DOC concentrations in overland flow and interflow were 3.44 ± 0.36 and 3.04 ± 0.24 mg L−1, respectively. Average DOC content in sediment was 73.76 ± 4.09 mg kg−1. The relationship between DOC concentration and discharge in overland flow events could be described by a significant exponential decaying function (R = 0.53, P = 0.027). Average annual DOC loss fluxes through overland flow, interflow and sediment were 163.6 ± 28.5, 865.5 ± 82.5 and 9.4 ± 1.5 mg m−2, respectively, and total DOC loss was 1,038.5 ± 112.5 mg m−2. The results suggest that interflow is the major driver of DOC leaching loss on sloping upland. It is shown that interflow is fundamentally important for reducing DOC loss on sloping croplands in the Sichuan Basin and possibly beyond.