The Mollisols region of Northeast China, which produces 50% of the country's rice, 44% of its soybeans, and 34% of its corn, is considered the "ballast" and "regulator" of food safety in China. However, over 666,700 gullies, which are a significant sign from highly productive agroecosystems to degraded landscapes, have developed in the region, functioning as a crucial pathway connecting upslopes to downstream channels. However, little is known about how gully regulates runoff, sediment, and nutrient loss processes in the catchment during snowmelt. This is not conducive to effective management of soil erosion and Non-point source pollution control in the agricultural gully-dominated catchments.

Therefore, a gully erosion research team led by Prof. Xingyi Zhang and Dr. Mingming Guo from the Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences monitored runoff, sediment, nutrient loss processes, hydrothermal changes, snowpack, freeze-thaw processes and changes in gully topography in situ at both the gully head (the upslope accumulated catchment of the gully head, CGH) and outlet of two representative and typical gully-dominated catchments (F1 and F2) during snowmelt in Mollisols region of Northeast China.

This study was published in Science of The Total Environment on June 3.

Runoff discharge of CGH and outlet exhibited a multi-peak trend during snowmelt, driven by the transition from snow melting to soil thawing. This transition resulted in distinct runoff patterns in both CGH and outlet, with significant differences in their response to air temperature.

The total runoff yield of CGH accounted for 57.8% in F1 and 40.6% in F2 of the total runoff yield of the outlet. Notably, the peak sediment concentration displayed a marked lag compared to the peak runoff discharge, primarily dominated by the increased sensitivity of gully erosion after the thawing of gully slopes.

Gully erosion was the main source of sediment yield in the catchment, contributing 98.2% in F1 and 96.6% in F2. Furthermore, nutrient concentrations exhibited a decreasing trend during snowmelt. The comparison of high nutrient concentrations in CGH and relatively low nutrient concentrations in outlet highlighted the gully's role in intercepting and diluting runoff nutrients.

Hysteresis analysis confirmed the differential contribution of CGH and gully to nutrient sources. CGH accounting for 50.9% and 93.3% of runoff TN and runoff TP loss, while contributing only 8.3% and 5.8% to sediment TN and sediment TP loss, respectively. These findings offer valuable insights for effective erosion control and nonpoint source pollution management in gully-dominated agroecosystems during snowmelt.