Runoff and Soil Loss from Revegetated Grasslands in the Hilly Loess Plateau Region, China: Influence of Biocrust Patches and Plant Canopies

Abstract

Biological soil crusts (biocrusts) cover up to 60–70% of the soil surface in grasslands rehabilitated since the Grain for Green project was implemented in the hilly Loess Plateau region in 1999, which exerted significant impacts on runoff and soil loss from revegetated grasslands. In the study, field plots were used to investigate runoff and soil loss in sites of a 4- and a 13-year revegetated grassland, with each exhibiting an early and a later successional biocrust, respectively. The objectives of the study were to (1) examine the role of biocrusts on runoff and soil loss during their early and later successional stages in a semiarid region under water erosion, (2) determine the influence of biocrusts on soil antiscourability with different runoff intensities, and (3) isolate the effects of biocrust patches and vascular plant canopies on runoff and soil loss from revegetated grasslands. Treatments used in both sites included (1) retaining biocrusts and plant canopies intact (CP), (2) retaining biocrusts without plant canopies (CNP), (3) retaining plant canopies without biocrusts (PNC), and (4) removing both biocrusts and plant canopies (NCP). The simulated scouring water flux was designed as 7.8, 12.0, and 16.0 L·min−1 to reflect local rainfall conditions. The results indicated that the runoff yield was increased by biocrust patches in their well-development stage. Runoff was increased by 15.1% when plant canopies were retained and 16.0% when plant canopies were removed in the 13-year revegetated grassland with the 12.0 L·min−1 scouring water flux. Compared with biocrust patches, plant canopies reduced runoff by 11.3% (with biocrusts) and 8.4% (biocrusts was removed) with the same scouring water flux. No significant difference was found in runoff yield with respect to the four treatments in the 4-year revegetated grassland. In contrast, 92% of the sediments were reduced for the formation of biocrusts in their early successional stage (cyanobacteria-dominated biocrusts) in the 4-year revegetated grassland with respect to CNP compared with NCP at the 12.0 L/min scouring intensity. No sediment was generated on either CP or CNP treatments in grassland revegetated for 13 years (moss-dominated biocrusts) with the same intensity of simulated runoff. Compared with biocrusts, plant canopies had a limited influence on soil loss. This amounted to reductions of 45 and 10% in soil loss for grasslands that revegetated for 4 and 13 years, respectively. The results of the study suggest that biocrusts play an important role in soil loss control from water erosion in semiarid regions, although there was a potential increase in runoff yield.