Evaluation of interrill erosion–induced aggregate turnover and its influence on sediment particles using rare earth elements

• Aggregate turnover is significantly accelerated by interrill erosion. • Aggregate turnover rate depends on aggregate size and soil texture. • The source of erosion sediment and its particle size distribution are related to the particle size of soil aggregate. The dynamic processes of aggregates have great impacts on the development of interrill erosion and further affect erosion sediment. However, little is known about the turnover of aggregates with different particle sizes and the sources of erosion sediment during short–term erosion. In this study, we employed rare earth elements to trace the transformation of soil aggregates of four size fractions (>2 mm, large macroaggregates; 2–0.25 mm, small macroaggregates; 0.25–0.053 mm, microaggregates; <0.053 mm, silt and clay fraction), and investigated the characteristics of aggregate turnover and sediment sources during interrill erosion in three land use types (natural forest (NF), artificial shrubland (AS), and abandoned meadow (AM)) through simulated rainfall experiments. Our results indicated that aggregate size distribution and soil texture significantly influence the regularity of runoff and sediment production regularity under interrill erosion. Erosion sediment was primarily composed of particles sized 0.25–2 mm and <0.053 mm, showing a “bimodal” distribution. Erosion sediment with particular particle size was mainly derived from aggregates in the slope with the same particle size transported by runoff, and the content of corresponding aggregates decreased with the extension of rainfall time, followed by＜0.053 mm aggregate and 2–0.25 mm aggregate. Moreover, the residual aggregates on the slope also showed an obvious turnover process. Large macroaggregates and small macroaggregates tended to be broken with cumulative breakage rates of 45.3 %–68.2 % and 33.2 %–48.5 %, respectively, and the overall aggregate breakage degree increased with time. In addition, runoff and eroded sediment were closely associated with the changes in topsoil structure and the transport of sediment. The contents of <0.053 mm and 2–0.25 mm sediment and the contribution rate of aggregates with corresponding sizes played important roles in the runoff coefficient and fractal dimension of sediment. Overall, this study explored the dynamic changes of soil aggregates and erosion sediment under interrill erosion, providing theoretical support for dissecting the mechanism of soil degradation at erosion sites.