| It is necessary but difficult to evaluate the influence of gully land consolidation on water resources and water quality in the loess hilly-gully region.Based on the simulation system constructed in the rainfall simulation hall and through the rainfall simulation experiments in different rainfall intensities and channel land consolidation ratios,this study evaluated impacts of gully land consolidation project on land surface and underground runoff,analyzed responses of gully land consolidation project on nonpoint source pollutants emissions and also discussed the mechanism of gully land consolidation on precipitation distribution and nonpoint source pollutants emissions and preliminarily illuminated the impact of gully land consolidation on precipitation distribution and runoff quality.Results indicated that:1)the gully land consolidation project could regulate the distribution of precipitation,intercept rainfall runoff and promote the transformation of precipitation to soil water and underground runoff.The regulation level increased with the increase of gully land renovation ratio,rainfall intensity was an important factor which affects the regulation effects.Compared with the original gully,the average proportions of surface runoff,soil retention and underground residence from precipitation of three different rainfall intensities can be adjusted from 62:21:17 to 45:22:23 and 27:23:50 when the gully land consolidation ratios were designed as 30% and 60% respectively.The regulation level of precipitation distribution by gully land consolidation increased with the increase of rainfall intensity,the reduction of surface runoff coefficient was 0.13,0.17,0.20,0,18 and 0.21,respectively,the increase of soil retain coefficient was 0.00,0.02,0.01,0.02 and 0.02,respectively and the increase of groundwater runoff coefficient was 0.13,0.15,0.19,0.16 and 0.19,respectively as the rainfall intensity increased from 30 mm·h-1 to 150 mm·h-1.This results are useful in the enacting of flood control standards in watershed management engineering.The flood down reaches faced might be reduced by the gully land consolidation projects in the upper reaches and the gully land consolidation proportion was a main influencing factor.The increasing rainfall intensities might increase the reduction of design flood,but the gully land consolidation determined the relative reduction of design flood.However,the projects might face the threats of seepage destruction,especially in long duration rainfalls.2)the gully land consolidation project reduced the discharge of sediment,nitrate nitrogen,ammonium nitrogen and soluble phosphate in surface runoff and the decrease was influenced by the rainfall intensity.The gully land consolidation with a proportion of 30% and 60% can reduce the discharge of nonpoint source pollutants as follow: 33%~58% and 69%~82% of sediment output,respectively;32%~54% and 63%~74% of ammonium nitrate output,respectively;-19%~21% and 31%~48% of nitrate nitrogen output,respectively;and-27%~21% and 2%~50% of nitrate nitrogen output,respectively.The relative interception rate of nonpoint source pollutants by gully land consolidation first increased then decreased,which indicated that the effect of gully land consolidation on nonpoint source pollution in surface runoff is limited.3)the gully land consolidation project influenced the matter transportation in soil body and even increased the potential risk of groundwater runoff by agricultural fertilizers.The leaching of nitrate nitrogen in newly constructed land was much more intense and a layer which had a higher soil nitrate nitrogen content was found on the impermeable layer,which might bring more nitrate nitrogen to groundwater,however,no evidence showed that the transportation of ammonium nitrogen in soil body was influenced by gully land consolidation project.The gully land consolidation project increased the nitrate nitrogen concentration and discharge in groundwater.The gully land consolidation with a proportion of 30% and 60% increased the nitrate nitrogen concentration in groundwater runoff by 9%~17% and 3%~34%,respectively,and increased the nitrate nitrogen discharge in groundwater runoff by 74%~195% and 60%~337%,respectively.This project would also cause long-term soluble phosphate pollution to groundwater according to the experiments but had no effect on the ammonium nitrogen output in groundwater runoff. |
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