Researchers at Huazhong Agricultural University (HZAU) have identified hillslope soils as a major source of dissolved organic matter in runoff during rainfall, providing new insights into watershed carbon transport and water quality protection.

The study, led by Professor Shi Zhihua's team from the College of Resources and Environment, was published in Environmental Science & Technology under the title "Molecular Evidence from FT-ICR MS and Bayesian Mixing Model Reveals Hillslope Soils as Dominant DOM Contributors during Rainfall".

Dissolved organic matter, or DOM, can interact with organic pollutants and heavy metals, affecting their adsorption, migration, and behavior in water. However, traditional methods have struggled to capture the changes in DOM sources over space and time during rainfall.

The team combined high-frequency runoff sampling, Fourier transform ion cyclotron resonance mass spectrometry, and a Bayesian mixing model to analyze rainwater, groundwater, riparian soil, hillslope soil, and runoff DOM during rainfall.

The results showed that hillslope soil contributed an average of 49.2 percent of runoff DOM, compared to 30.3 percent from riparian soil, 13.1 percent from groundwater, and 7.5 percent from rainwater. The contribution of hillslope soil increased from 42.4 percent at the start of rainfall to 57.6 percent at peak discharge.

The findings challenge the traditional view that riparian zones are the main sources of riverine organic matter and highlight the importance of upland soil and water conservation, especially as extreme rainfall events increase.

HZAU researchers integrate high-frequency sampling, FT-ICR MS fingerprinting and Bayesian analysis to trace watershed DOM sources. [Photo/news.hzau.edu.cn]