Evaluation of the environmental effects of intensive land consolidation: A field-based case study of the Chinese Loess Plateau

The large-scale implementation of the Grain for Green project on the Chinese Loess Plateau since 1999 has greatly increased the vegetation coverage and rapidly decreased the agricultural land by converting slope cropland to planted vegetation (forest and grasslands). However, the geological, hydrological, ecological, and agricultural effects of the Gully Land Consolidation (GLC) project launched at Yan'an City in 2011 to address these land-use problems are not clearly understood. To assess the project outcomes in this region, we examined 71 of the 193 subprojects (61 treated gullies and 10 untreated gullies); measured geological, hydrological, ecological, and agricultural indices in the field; and tested disturbed (n = 447) and undisturbed (n = 142) soil samples (e.g., particle size distribution, saturated hydraulic conductivity, bulk density, and heavy metal contents). We found that: (1) slope stability improved for 67 % of the subprojects, (2) severe swamping was found only for 2 % of the subprojects, (3) the average increase in NDVI was 0.0231, 69 % of treated gullies NDVI was increased, and (4) crop yield was overall improved. There were no significant differences between the treated and untreated gullies in soil texture, saturated hydraulic conductivity, bulk density, or heavy metal contents (Cr, Zn, Cu, Ni, Pb), although particle size contents (range of 0.05 mm - 0.20 mm) differed significantly (p < 0.05). To promote successful gully land consolidation, the GLC project should (1) prioritize slope stability and longterm maintenance of water preservation facilities in gullies, (2) use bioengineering to accelerate the maturation of newly created land, or develop new cropping system after the GLC project; (3) on the basis of Grain for Green, integrate the GLC project, and modern agriculture to be complementary.