[Relationship between gully density and characteristics of watershed channel network in typical black soil region in...

We selected sixty-four survey units in the typical black soil (soil sub-class) distribution area of Northeast China, including 32 complete small watersheds and 32 non-closure small watersheds. All gullies were identified through high-resolution image visual interpretation. The Strahler stream order method was used to classify the gullies. We calculated the parameters such as small watershed characteristics, gully density (line and area density of gullies), and gully network characteristics. By analyzing the relationship between gully density and watershed characteristics, gully network evolution, and fractal dimensions, we explored the activity level and developmental potential of gullies in the black soil region. The results showed the line density of gullies in the surveyed watersheds ranged from 0.60 to 11.45 km·km^-2, with an average of 2.09 km·km^-2, and 35.9% exceeded moderate erosion levels. The area density of gullies ranged from 7136 to 160323 m²·km^-2, with an average of 31752 m²·km^-2. The highest gully order in small watersheds reached level 8, with 1662 first-order gullies accounting for 67.8%. The fractal dimension fitting curve of the network exhibited linear patterns, indicating significant fractal characteristics in the gully network. The tributary development was higher in the central and southern parts of the typical black soil distribution area, with greater complexity in the gully network. All surveyed watersheds were in the juvenile stage of gully development and were in an accelerated growth phase. There were no significant differences in gully density and gully network characteristics between the two types of small watersheds. Gully line density showed significant correlations with average watershed slope, shape coefficient, maximum gully order, and network fractal dimension, but no significant correlation with survey unit area. These findings would help clarify the spatial variation and deve-lopmental potential of gully density, providing a theoretical basis for gully erosion investigation and prevention in black soil regions.