Effects of crust and shrub patches on runoff, sedimentation, and related nutrient (C, N) redistribution in the desertified steppe zone of the Tengger Desert, Northern China

Runoff and erosion are critical geomorphic processes in arid ecosystems, and they are strongly affected by vegetation patterns. Little is known about the influence of spot-structured vegetation on runoff and erosion in temperate deserts; especially the effects of vegetation patterns and human-induced disturbances on runoff-triggered nutrients redistribution are poorly understood. A series of simulated rainfall experiments were conducted in the Tengger Desert, northern China, to examine (1) the effects of shrub patches on runoff and erosion and related nutrients redistribution on hillslopes, (2) whether different amounts of water and nutrients are stored in the shrub patches compared to open inter-patch areas, and (3) how the runoff and erosion and related nutrients redistribution processes respond to human-induced disturbances. The results indicate that in undisturbed plots 53% of the applied water became runoff from crust patches and 55% of this was redistributed to the shrub patches. Water penetration was significantly deeper in shrub patches than in crust patches, and more than 75% of the sediments, 63% soil carbon, 74% nitrogen and 45 ∼ 73% dissolved nutrients triggered by runoff from crust patches were delivered to shrub patches. The disturbance of crust patches tended to result in the uniform distribution of water over the whole slope and the reduction of flow of vital resources from the crust patches to the shrub patches. Disturbance of macrophytic patches significantly degraded the capacity for resource capture and retention and thereby decreased resources, all of which are crucial for the maintenance of plant productivity and vegetation cover. The understanding of the function of patterned vegetation in the study area suggests that it represents an aspect of the ecosystem that requires careful management.