Stability of Root-Soil-Complexes in Riverbanks with Different Vegetation Covers in Three Gorges Reservoir Region

Vegetation plays an important role in stabilizing soil and preventing soil erosion of slope. To reveal the stability of root-soil-complexes in riverbanks in WLFZ (water-level-fluctuation zone) of Three Gorges reservoir region, a research was conducted on four types slope, BS (bare slope), GS (slope of grass-herb), SS (slope of shrub) and FS (slope of forest), of similar soil texture and slope angle with different vegetation covers in Ruxi riverbanks. RLD (root length density), SWC (soil water content), FWC (field water capacity), ASS (soil anti-shearing strength) of each 10 cm soil layer in four types riverbank were measured. And the values of soil anti-erodibility and anti-scouribility in the 15 cm soil layer were also measured. The results showed that: (1) The EVs and EVe (enhancement value of soil anti-scouribility and of anti-erodibility) of SS were both larger and significantly higher than those of GS and FS while the values of GS and FS were small. (2) The RLD of GS, SS and FS was almost observed in the 30 cm surface soil layer and decreased with soil depth. FS had the highest RLD in every 10 cm soil layer and then the SS. (3) The SWC of BS increased with soil depth, but that of FS decreased with soil depth. The SWC and FWC of SS changed slowly in the 50 cm soil layer, and the FWC of FS and GS decreased with soil depth. The FWC of BS in 10 cm surface soil was the largest and then there was a trend of gradually increasing with soil depth in 20~50 cm layer. (4) The ASS value of GS was lower than those of other three slopes and that of FS had a little changes along the 30cm surface soil layer while it became higher at the 30~40 cm soil layer. The ASS mean of the SS was highest at 0~10 cm, 20~30 cm and 40~50 cm soil layer, however, that of BS at the 10~20 cm soil layer and that of FS at 30~40 cm soil layer were highest. It indicated that: (1) The soil anti-erosion capability of SS was better than that of FS and GS, and its physical soil properties in 50 cm layer w- - as more stable than that of others; (2) The surface soil of FS, especially 10 cm soil layer, had a better soil water retention; (3) The BS had a low soil stability because of the larger changes over the parameters of all layers, especially in the shallow soil. (4) SS also had a better anti-shearing stability in the 0~30 cm soil layer than GS and FS. In conclusion, this is perhaps better construction of vegetation increases stability riverbank of WLFZ significantly. Shrubs and forest played good roles in binding soil and stabilizing slope, which could improve the ecological effects. And SS riverbank was the best stable one. Thus, in vegetation reconstruction in the WLFZ, more attention should be paid to restoration of shrubs in riverbanks.