Quantifying sediment source contributions in an agricultural catchment with ephemeral and classic gullies using 137Cs technique

Authors: CHEN, HONG - Northwest A&f University; LIU, GANG - Northwest A&f University; Zhang, Xunchang; SHI, HONGQIANG - Northwest A&f University

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2021
Publication Date: 4/3/2021
Citation: Chen, H., Liu, G., Zhang, X.J., Shi, H. 2021. Quantifying sediment source contributions in an agricultural catchment with ephemeral and classic gullies using 137Cs technique. Geoderma. 398:115112. https://doi.org/10.1016/j.geoderma.2021.115112.
DOI: https://doi.org/10.1016/j.geoderma.2021.115112

Interpretive Summary: Ephemeral and classic gullies are widely distributed in the Mollisol Region of Northeast China, causing severe land degradation and grain yield reduction. However, their contributions to total soil loss in agricultural catchments have not been quantified systematically at various catchment scales. In this study, the fallout Cs-137 was employed as a tracer to quantify the contribution of fine sediment eroded from topsoil and subsoil (gully bank) by using a linear mixing mathematic model. Although the large variation of Cs-137 concentration was found in subsoil, the Cs-137 concentrations were significantly different between topsoil and subsoil for each sub-catchment and the whole catchment. The allocated proportion of both deposited and suspended sediment with different particle sizes showed the eroded fine sediment of the catchment mainly came from gully bank, accounting for about 90%, but the significant difference of apportionment between both deposited and suspended sediment was obtained in some catchments, indicating that caution must be exercised when sampling deposited sediment on stream bed. The result for suspended sediment showed contributions of subsoil for the catchment with classic gullies were greater than those with ephemeral gullies, and the contributions mainly came from gully erosion, especially gully head advance. This study provided valuable quantitative information of sediment sources with both ephemeral and classic gullies, and suggested soil conservation measures be concentrated on stabilizing gullies, especially stopping gully head advance. This work will provide useful information to soil conservationists for controlling downstream sediment discharge in the region.

Technical Abstract: Ephemeral and classic gullies are widely distributed in the Mollisol Region of Northeast China, causing severe land degradation and grain yield reduction. However, their contributions to total soil loss in agricultural catchments have not been quantified systematically at various catchment scales. In this study, the fallout Cs-137 was employed as a tracer to quantify the contribution of fine sediment eroded from topsoil and subsoil (gully bank) by using a linear mixing model. The results showed that the coefficient of variations (CVs) of Cs-137 activity for subsoil, ranging from 86.4 to 166.1%, were greater than those of topsoil varying from 18.2 to 39.9%. In topsoil, cropland had the greatest Cs-137 concentration of both <1 mm and <63 µm fractions, followed by forestland and road. Although the large variation of Cs-137 activity was found in subsoil, the Cs-137 activities were significantly different between topsoil and subsoil for each sub-catchment and the whole catchment. The allocated proportion of both deposited and suspended sediment with different particle sizes showed the eroded fine sediment of the catchment mainly came from gully bank, accounting for about 90%, but the significant difference of apportionment between both deposited and suspended sediment was obtained in some catchments, indicating that caution must be exercised when sampling deposited sediment on stream bed. The result for suspended sediment showed contributions of subsoil for the catchment with classic gullies were greater than those with ephemeral gullies, and the contributions mainly came from gully erosion, especially gully head advance. This study provided valuable quantitative information of sediment sources for agricultural catchments with both ephemeral and classic gullies, and suggested soil conservation measures be concentrated on stabilizing gullies, especially stopping gully head advance.