水保所知识产出(1956---)知识库

Soil loss caused gully erosion can be substantial in agricultural catchments in the Mollisol region of northeast
China. However, their contributions to total soil loss have never been quantified systematically at various spatial
scales. Here we selected an agricultural catchment with ephemeral and classic gullies in Keshan county, Hei-
longjiang province. The fallout 137 Cs activity adjusted to fine fraction of < 63 μ m was employed as tracer to
quantify the contribution of fine sediment eroded from topsoil and subsoil (gully bank) in the whole catchment
and each sub-catchment by using a linear mixing model. The results showed that the coefficient of variations
(CVs) of 137 Cs activity for subsoil, ranging from 86.4 to 166.1%, were greater than those of topsoil varying from
18.2 to 39.9%. In topsoil, cropland had the greatest 137 Cs concentration in both < 1 mm and < 63 μ m fractions,
followed by forestland and road. Although the 137 Cs activity varied greatly in sources, the contrasting concen-
trations between sources render 137 Cs an effective tracer for distinguishing topsoil and subsoil contributions to
sediment discharge. The allocated proportions of both deposited (bed) and suspended (trap) sediment with
different particle sizes showed the eroded fine sediment (<63 μ m fraction) of the catchment mainly came from
gully bank, accounting for about 90%, but the significant difference of apportionment between deposited and
suspended sediment was obtained in some catchments, indicating that caution must be exercised when taking
deposited sediment out of bed materials. The result for suspended sediment showed contributions of subsoil in
catchment with classic gullies were greater than those with ephemeral gullies, and the gully head and bank were
the primary sediment sources. This study provided valuable quantitative information of sediment sources for
agricultural catchments with both ephemeral and classic gullies, and suggested soil conservation measures be
concentrated on stabilizing gullies, especially controlling gully head advance.