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Purpose: Characterizations of soil aggregates and soil organic carbon (SOC) losses affected by different water erosion patterns at the hillslope scale are poorly understood. Therefore, the objective of this study was to quantify how sheet and rill erosion affect soil aggregates and soil organic carbon losses for a Mollisol hillslope in Northeast China under indoor simulated rainfall.Materials and methods: The soil used in this study was a Mollisol (USDA Taxonomy), collected from a maize field (0-20 cm depth) in Northeast China. A soil pan with dimensions 8 m long, 1.5 m wide and 0.6 m deep was subjected to rainfall intensities of 50 and 100 mm h−1. The experimental treatments included sheet erosion dominated (SED) and rill erosion dominated (RED) treatments. Runoff with sediment samples was collected during each experimental run, and then the samples were separated into six aggregate fractions (0-0.25, 0.25-0.5, 0.5-1, 1-2, 2-5, > 5 mm) to determine the soil aggregate and SOC losses.Results and discussion: At rainfall intensities of 50 and 100 mm h−1, soil losses from the RED treatment were 1.4 and 3.5 times higher than those from the SED treatment, and SOC losses were 1.7 and 3.8 times greater than those from the SED treatment, respectively. However, the SOC enrichment ratio in sediment from the SED treatment was 1.15 on average and higher than that from the RED treatment. Furthermore, the loss of < 0.25 mm aggregates occupied 41.1 to 73.1% of the total sediment aggregates for the SED treatment, whereas the loss of > 0.25 mm aggregates occupied 53.2 to 67.3% of the total sediment aggregates for the RED treatment. For the organic carbon loss among the six aggregate fractions, the loss of 0-0.25 mm aggregate organic carbon dominated for both treatments. When rainfall intensity increased from 50 to 100 mm h−1, aggregate organic carbon loss increased from 1.04 to 5.87 times for six aggregate fractions under the SED treatment, whereas the loss increased from 3.82 to 27.84 times for six aggregate fractions under the RED treatment.Conclusions: This study highlights the effects of sheet and rill erosion on soil and carbon losses at the hillslope scale, and further study should quantify the effects of erosion patterns on SOC loss at a larger scale to accurately estimate agricultural ecosystem carbon flux. [ABSTRACT FROM AUTHOR]

Rill erosion is recognized as an important process of water erosion on agricultural land. The objectives of this study are to examine the effects of rainfall intensity on rill network development and to present some indicators for a quantitative description of rill morphology. A soil pan (10 m long, 3 m wide and 0.5 m deep and with an adjustable slope gradient from 0 to 30°) was subjected to three successive rains under rainfall intensities of 50 and 100 mm h − 1 . The results showed that rainfall intensity significantly affected rill erosion, especially in the active period of rill network development. The magnitude of rill erosion was 28.5 and 33.1 kg m − 2 and contributed 78.6% and 76.2% to the soil loss under rainfall intensities of 50 and 100 mm h − 1 , respectively. The formation of rill network under the 50 mm h − 1 intensity was more complex than that under the 100 mm h − 1 intensity; for the latter rill networks developed fast and then varied slightly. The mean rill inclination angle ( δ mean ), rill density ( ρ ), degree of rill dissection ( μ ) and mean rill tortuosity complexity ( c mean ) increased with the increase of rains under the same rainfall intensity. The μ value was the optimal derivative morphological indicator to estimate rill erosion and morphology, which was followed in descending order by δ mean , c mean and ρ . [ABSTRACT FROM AUTHOR]