Transport of soil-derived dissolved organic matter (DOM) via surface runoff and fracture flow in a cropland loamy soil during natural rainfalls

Dr Chen Liu1, Dr. Qing-song Xian1, Prof. Xiang-yu Tang1

1Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China

Being crucial for predicting the impact of C inputs on a watershed in rainfall events, an understanding of the dynamics and characteristics of soil carbon export, mainly in the form of dissolved organic matter (DOM), from the soil under particular land use types, particularly those associated with underground flows is still largely lacking. A field study was carried out using a 1500 m2 slope farmland plot in the hilly area of Sichuan Basin, Southwest China. The discharge of surface runoff and fracture flow was recorded and samples were collected in four representative rainfall events. For DOM characterization, concentration of dissolved organic carbon (DOC) and absorbance/excitation-emission matrix (EEM) fluorescence were analyzed. Soil water potential was also determined using tensiometers for understanding the runoff generation mechanisms. The DOCs for both surface and fracture flow showed significant responses to rainfall, with hydrological path being the primary factor in determining DOM dynamics. EEM-PARAFAC analyses indicated that the soil DOM mainly consisted of two terrestrial humic-like components with peaks located at Ex/Em 270(380)/480 nm (C1) and 250(320)/410 nm (C2), respectively. Concentrations of these components also responded strongly to rainfall, fluctuating in good agreement with the corresponding DOCs. Although there was no change in the presence of the components themselves, their relative distributions varied during precipitation, with the C1/C2 ratio increasing with the proportion of soil pre-event water. As the dynamic changes of soil-derived DOM characteristics can be successfully captured using spectroscopic techniques, they may serve as a tracer for understanding the hydrological paths for soil carbon transport in a specific soil during rains.

Biography: Dr. Chen Liu is a scholar working at the Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of Mountain Hazards and Environment, CAS, China. She has made research contributions in understanding the environmental behavior of the microcontaminants, their interactions with the soil and the transport hydrology with a goal to decrease the microcontaminants’ environmental risk. She got her M.S. and Ph.D. degrees both in environmental engineering from Sichuan University and has worked at the CAS institute since 2012.

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