Catchments Scale Of Sediment Source In The Yuanjiang Dry-hot Valley-a Study Based On Composite Fingerprinting Analysis

The soil erosion in the hot dry river valley of Yuanjiang is intense,and the sediment content of the river is high.This not only poses a threat to the operation of cascade hydropower in the river basin,but also causes widespread concern in downstream countries.There is an urgent need to conduct research on the mechanism of erosion and sediment production in small catchments in order to provide scientific basis for regional comprehensive management of soil erosion,river sediment control,and benefits evaluation of water and soil conservation measures.In this study,four small catchments with different landscape patterns(fruit forest catchment,wildwood catchment,farmland catchment and comprehensive catchment)in the dry-hot valley of Yuanjiang were selected as the study area.We dynamically monitor the process of erosion and sediment production in small catchments,and use fingerprint identification techniques to quantitatively calculate the contribution rates of all potential sediment sources.Finally,we clarify the mechanism influence of landscape pattern on the erosion and sediment yield in small catchments in the dry-hot valley area by the erosion modulus calculated from the CSLE model and the sediment contribution rate results.The main research findings are as following:(1)Landscape pattern changes in the case area: From the three stages of 1990,2010 and 2015,the trend of farmland area reduction year by year,and the area of the fruit forest and the wildwood shows an increasing trend.Changes in landscape types in the study area during 1990-2015 were mainly reflected in the conversion of farmland into fruit forest and wildwood.In the period 1990-2010,the conversion of farmland to fruit forest was the main,while in 2010-2015 it was mainly the conversion of farmland into wildwood.(2)Sediment source changes in the small catchments: The contribution of sediment sources during the whole storm process in various small catchments was calculated by using the mixing model and discriminant function analysis(DFA)methods.Through comparative analysis,the fingerprints of different combinations of different landscape patterns are different.Among them,only one fingerprint,TC,was selected from fruit forest catchment;the TC and Co of wildwood catchment formed the best combination of fingerprints;the best composite fingerprints of farmland catchment was the frequency susceptibility,Al and Pb;there are also three kinds of fingerprints(TC,Ca and Pb)in the comprehensive catchment as the best composite fingerprints.From the sediment source calculation results from the four small catchments we can get: although the sediment contribution rates calculated by the two algorithms in an intra-storm runoff have different trends,the contribution rate of sediment sources in different small catchments during the rainstorm is gully > farmland> fruit forest> wildwood.The sediment contribution in the heavy rain process calculated by the mixing model is more varied in the changing trend.The average sediment source contribution rate of the entire storm rainfall calculated by the DFA and the erosion status of the basin is more relevant.Studies have shown that there are differences in the best fingerprinting factors for small catchments with different landscape characteristics.At the same time we believe that the DFA simulation results are better than the Mixing model in this study.(3)Analysis of characteristics of erosion and sediment production changes: The sediment contribution rate and annual sediment contribution of different potential sources in various small catchments in the study area can be obtained through direct calculation or indirect estimation.The results show that in the four target small catchments,the gully is the main source of sediment in the small catchment,the sediment contribution rate varies from 51.4% to 81.3%,and the average sediment contribution rate is 65.2%;followed by farmland,the scope of change 22.5%-38%,average 30.3%;followed by fruit forest,the sediment contribution rate varies from 7.4% to 24.9%,and the average sediment contribution rate is 15.1%;the wildwood contributes the least to the sediment and the contribution rate changes.The range is 3.2%-15.1% and the average contribution rate is only 9.2%.In the process of erosion and sediment production,the sediment contribution rate of the gully first decreases and then increases;while the contribution rate of potential sediment sources on the slope(through fruit forest,wildwood,and farmland)increases first and then decreases.Combined with the landscape pattern and the relevant data of erosion sediment production and sediment contribution we can obtain: the gully is the main source of rainstorm erosion,different sediment sources in different small catchments have differences in erosion and sediment production,the erosion and sediment production on the upland land shows the trend of farmland> fruit forest> wildwood.This paper aims to clarify the mechanism influence of landscape pattern on the erosion and sediment yield in small catchments in the dry-hot valley area by the calculation of landscape type change and erosion amount in potential sediment source area combined with quantitative analysis of sediment source contribution.The results show that the gully in the dry-hot valley is the main source of river sediment,and the landscape pattern of the small catchment has an important impact on the erosion and sediment production.The results provide scientific reference for the relevant departments to formulate the dry hot valley development plan and control soil erosion.