Seasonal changes of soil erosion and its spatial distribution on a long gentle hillslope in the Chinese Mollisol region

Understanding seasonal soil erosion and deposition rates and their spatial distribution along sloping farmlands are necessary for erosion prediction technology and implementing effective soil conservation practices.To date seasonal change of soil erosion and soil redistribution on long gentle hillsiopes are not fully quantified due to the variable erosive forces in different seasons.A multi-tracer method using rare earth elements(REE)was employed to discriminate seasonal changes of soil erosion and its spatial distribution on a sloping farmland driven by snowmelt runoff,wind force and rainfall-runoff.A long-slope runoff plot with 5 m wide and 320 m long located in the typical Mollisol region of China was divided into eight segments,each of which was 40 m long and tagged with one of eight REE oxides.The spot method of a partial-area tagging scheme was employed and a grid-based layout was used for REE application.Results showed that annual soil erosion rate was 3251.01 km^(-2)for the whole runoff plot,in which snowmelt runoff erosion contributed 537.3 t km^(-2),wind erosion 363.11 km-2 and rainfall-runoff erosion 2350.6 t km^(-2).Surface runoff is the main external erosive force of hillslope soil erosion,accounting for 88.8%of the total annual soil loss.Furthermore,for the eight slope segments of the 320-m long hillslope,the sediment transport ratios of each slope segment caused by snowmelt runoff and rainfall-runoff erosion were more than 23.5%and 34.7%,respectively.The results will enrich the understanding of seasonal soil erosion on long hillsiopes.

Historical evolution of gully erosion and its response to land use change during 1968–2018 in the Mollisol region of Northeast China

Gully erosion is one of the most severe types of land degradation,hindering food production and sustainable agricultural development.However,the historical evolution process and the impact of land use change on gully erosion remain unclear.To address this issue,we conducted a field investigation on gully erosion in 2018 and interpreted land use and gullies using historical remote sensing images in 1968 and 1978 over an area of 84.48 km^(2).The study found that from 1968 to 1978 to 2018,all gully morphological parameters including gully length density and gully areal density increased significantly.The main origin of gully erosion found was from dry farmland.The annual soil loss rate induced by gully erosion was 1.46 mm during 1968–2018.Gully erosion rates were higher during 1968–1978 than during 1978–2018.Furthermore,the length,areal and volumetric erosion rates in gullies formed by multiple gullies merging was greater than that of newly formed gullies(NFG)and gullies developing continuously from a single pre-existing gully,while the widening rate of NFG was highest.The susceptibility of land use types to gully erosion was in the order of woodland<dry farmland<degraded land.The annual average increase in gully area was 871.09 m^(2) km^(-2) year^(-1) for parcels that were converted from woodland to dry farmland,which was 5.56 times and 1.78 times greater than that of woodland and dry farmland maintenance,respectively.Therefore,urgent implementation of ecological land use plans and gully erosion control practices is suggested for this region.