Current scenario of gully erosion and its control strategy in Mollisols areas of Northeast China

Gully erosion is a destructive and dramatic form of land degradation, representing the soil loss of the top surface along drainage channels by water runoff and rainfall. Except for the Loess Plateau in China, the black soil (Mollisols) region of Northeast China has become the most severe affected area due to gullying. The gully erosion has posed a great threat to regional agricultural production and ecological environment, since the current gully erosion is ever-fragmenting the farmland to aggravate sloping land erosion, even to destroy the land. Since the 1970 s, considerable efforts have been made to gradually control gully erosion using various conservation measures, thereby mitigating property damage and losses. In this study, a systematic summary was proposed to clarify the characteristics, developing trends, and damages of gully erosion in the black soil region of Northeast China, integrating with the survey conducted by the National Gully Erosion Management Project and reports from the National Key R&D Program. The results demonstrated that the actual gully number of 295 663 in the region was probably underestimated by 50%, according to the gully density difference obtained from the satellite images and field investigation. The average size of gullies was an area of 1.23 hm2 with a length of 661.3 m. In the 88.7% active gullies, 60.2% developed in farmland was encroaching the arable land at an expansion rate of 7.39 km2 per year. As such, the ultimate goal of gully mitigation was to stabilize the erosion expansionand rehabilitate vegetation in the region. The recent control of gully erosion could firstly hinder the gullying development, and then restore the gully through ecological approaches. Different feasible measures were developed to construct the structures at gully headcuts, or various check dams in the gully bed, as well as soil and water conservation barriers along the gully bank, depending on the local conditions and resources. Four systems against gully erosion are available: 1) the corn stover and coal gangue can be filled to remediate gully on the farmland; 2) vegetation rehabilitation including the wicker check dams, continuous live wicker, and a shrub or an arbor plant enclosure can be achieved; 3) other bioengineering can be combined with engineering techniques; 4) the plant rehabilitation can be integrated with engineering techniques, such as drop structures at headcuts and soil check dams, masonry check dams, and gabion check dams in gully bed locations with the masonry against flow scour. Specifically, a systematic practice of gully erosion was established to identify the well-suited conditions of sites. The application of these practices depended mainly on the topography, gully size, and local economy. The specific locations and conditions were also defined for the bioengineering implementation in each system. In addition, some strategies were proposed for the control of gully erosion in the aspects of law and regulation perfection, integration of Mollisols conservation projects, innovation of remediation practices, and the priority of gullies in sloping farmland. The findings can provide scientific support and guidelines for the policy-making on the control engineering of gully erosion for better regional development in modern agriculture and ecological civilization construction.