Studies led by Prof. LI Lujun at the Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences (CAS) have revealed four decades of soil erosion dynamics and future risks in Northeast China's black soil region.

The researchers found that the high-risk center of soil erosion has gradually shifted from the Changbai Mountains to agricultural plains, including the Songnen Plain and the Liaohe Plain.

They also identified critical thresholds of key driving factors that trigger marked increases in erosion risk across different geomorphic units and projected erosion risks under three policy scenarios for 2030, providing insights for targeted black soil protection and zonal soil governance.

The two related studies were published in Ecological Indicators on Sept 5 and Catena on June 30, respectively.

Northeast China's black soil region is a major grain-producing area and an important ecological barrier for national food security. Long-term water erosion has thinned the black topsoil, depleted soil organic matter and reduced cropland productivity, posing a major challenge to sustainable agricultural development in the region.

Therefore, understanding long-term erosion dynamics, identifying thresholds for increasing erosion risk and projecting future risks are therefore important for targeted black soil protection and zonal soil governance.

Using the RUSLE model and multi-source geospatial datasets, the researchers reconstructed spatiotemporal patterns of soil erosion intensity, sensitivity and integrated risk across Northeast China's black soil region from 1980 to 2020. They then coupled the GeoDetector model with the Pettitt non-parametric change-point test to quantitatively identify critical thresholds of key driving factors that trigger marked erosion risk escalation across different geomorphic units.

The results showed that the regional high-risk center of soil erosion shifted substantially over the four decades, gradually moving from the Changbai Mountains to agricultural plains, including the Songnen Plain and the Liaohe Plain. The regional average erosion modulus initially increased before gradually declining. Soil erodibility in the Liaohe Plain showed an anomalous bimodal distribution, with both low- and high-erodibility zones each accounting for more than 30% of the total area. According to the researchers, this made the region highly vulnerable to abrupt increases in erosion risk under external disturbances.

Zonal threshold analysis showed that 65% vegetation coverage was sufficient to effectively curb erosion in the western grassland subregion, whereas the eastern agricultural plains required coverage of more than 82%. The rainfall erosivity threshold for erosion onset in the western grassland was 1,040 MJ·mm·hm^-2·h^-1·a^-1, well below that for mountainous areas.

GeoDetector analysis further showed that the interactive explanatory power of soil erodibility and land use reached 0.4979, far higher than that of any single factor, and that multi-factor synergistic amplification was the core mechanism driving the build-up of regional erosion risk.

Projecting Future Risks

Building on these findings, the researchers coupled the RUSLE and PLUS models to quantify the driving effects of land use change on soil erosion and simulated patterns of erosion risk differentiation under three 2030 policy scenarios: natural development, cropland protection and ecological protection.

The study found that the black soil region underwent substantial land use transitions over the past four decades, with cropland expanding by 3.04 × 10⁴ km². Of the newly added cropland, 41.2% was converted from forestland and 38.7% from grassland. Soil conservation capacity varied markedly across land use types: bare land had the highest average erosion modulus at 2,413.09 t·km^-2·a^-1, while shrubland showed the strongest erosion resistance.

Multi-scenario simulations indicated that indiscriminate cropland expansion at the expense of ecological space would cause irreversible black soil degradation. According to the researchers, protecting ecological land and improving the management of sloping cropland are essential for maintaining stable grain production while supporting long-term soil and water conservation.