Study On The Accuracy Of REE Tracing Soil Erosion And Sediment Sources

Rare earth element(REE)tracing is one of the most important element tracing methods,which plays an important role in soil erosion and sediment source study.However,REE that artificially mixed into soil,may not tightly combined with soil particles,and further affecting the accuracy of soil erosion and sediment source tracing using REE.This study combined simulated rainfall,REE tracing and composite fingerprinting approaches to analyze the distribution characteristics of REEs in different particle sizes of soil and sediment,to clarify the influence of particle size correction on soil erosion rate estimation based on REE tracing technique through comparing to results obtained using sediment weighting,and to determine the accuracy of soil erosion rate estimation and the sediment source identification using REE tracing.Results of this study is valuable for improving the quantitative identification accuracy of sediment sources by combing using of REE and composite fingerprint approaches,and has important for further study of sediment source.The main results are as follows:(1)In the original soils and sediment,Y and La were mainly enriched in <10 or<63 μm particles with,while Ce was mainly enriched in <125 μm particles with significantly higher enrichment degree in soil compared to sediment.Besides,the of Ce also obvious enriched in 500-1000 μm particles in sediment.Grain size distribution grouping of REEs according to their enrichment/depletion in different particle size ranges of source soils(red soil,black soil and aeolian sandy soil)and sediment showed that the enrichment grain size ranges of REEs were consistent with variation in enrichment degree for source soils before and after the anthropogenic release of REEs,and in source soils and sediment after release of REEs.The La in red soil and Y in black soil were always enriched in <10 or <63 μm particles weather anthropogenic release of them,while the particle size range of enrichment of Ce in aeolian sandy soil was changed from particle grain size ranges<10 or <63 μm before its release to <125 μm after it was released.When the source soils were red soil and black soil,La and Y were mainly significantly enriched in <10 μm particles for both soils and sediment.When the original soils contained aeolian soil(red soil-aeolian sandy soil,black soil-aeolian sandy soil,red soil-black soil-aeolian sandy soil),Y and La were mainly enriched in <10 or <63 μm particles with,and the of them was significantly lower enrichment degree in source soils compared to sediment,while Ce was mainly enriched in <125 μm particles with significantly higher enrichment degree in soil compared to sediment.Besides,the of Ce also obvious enriched in 500-1000 μm particles in sediment.Additionally,it is important to take serious consideration to the particle size variation of REE content in different grain size ranges between source soils and sediment in soil erosion rates and sediment sources estimation using REE considering obvious variation of particle sizes for different types of soil in erosion transportation processes.(2)Soil erosion rates based on REEs content in sediment adopting no particle size correction have smaller biases with the results based on sediment weighting compare to that obtained based on REEs content in the surface soil on slope after rainfall simulation.The results of the soil erosion rate estimated using REEs content in sediment adopting particle size correction factors selected from different grain size ranges show that grain size range of the particle size correction factor has important influence on erosion rate estimation.Comparing the erosion rates estimated by REEs content in the surface soil of the slope after rainfall,and by the REE content of sediment on condition of weather adopted particle correction factors from different particle grain size ranges regardless aeolian sandy soil was included in the source soil or not,soil erosion rates in majority of experiments(64.3%and 66.7% of experiment when aeolian sandy soil was included in the source soil and not,respectively)based on bulk sediment samples(i.e.,particle size <1000 μm)adopting no particle correction factor had lower biases compared to the weighting values.The deviations between the weighting values and the estimated erosion rates based on bulk sediment samples with no particle size correction factor were-13.9%-2.7% and-16.5%-10.2%,respectively,when aeolian sandy soil was included and excluded in the source soils.Additionally,it is helpful to obtain accurate erosion rate when corrected grain size using main particle size ranges.That is to say soil erosion rates corrected using fine particles(<10and 10-63 μm)for black soil and red soil,and using coarse particles(125-250 or 250-500 μm)for aeolian sandy soil have smaller biases compared to sediment weighting results.Thus,it is recommended to use sediment without particle correction to obtain accurate soil erosion rate by REE tracing technique.(3)Sediment source contribution can be accurately estimated using REEs content in sediment through the composite fingerprinting approach,and based on soil erosion rates estimated by REE tracing.The difference of sediment source contribution identified based on bulk samples using the composite fingerprinting approach had biases of 0.1%-17.8%to the sediment weighting results,and this difference were 0.1%-17.3% estimated based on erosion rates on condition of different source soil types and slope gradients.In rainfall processes,the change tendency of sediment sources identified by the composite fingerprint approach,estimated by erosion rates,and calculated using sediment weighting are consistent.Thus,it is clear that both the composite fingerprint approach and erosion rate estimated based on REE tracing technique can be used to accurately identify the source contribution.Additionally,the contribution of red soil was usually overestimated when screened the optimal fingerprints from fine particles(<10 μm),while the contribution of black soil was usually overestimated when screened the optimal fingerprints from relatively fine particles(63-125 μm)when red soil and black soils as sources.The contribution of red soil and black soil were usually overestimated when screened the optimal fingerprints from fine and relatively fine particles,while contribution of aeolian sandy soil was overestimated when screened the optimal fingerprints from relativity coarse particles(125-250 μm)and coarse particles(250-500 μm).This study focused on the influence of soil particle size on the distribution characteristics of REEs content,soil erosion rate estimation and sediment source identification based on REEs on aggregates dispersed soil.Results are valuable for understanding the influence of REEs’ grain size distribution on the accuracy estimating of soil erosion rates and sediment sources.However,the general feasibility of results obtained in this study need further study considering that the distribution characteristics of REEs in different particle sizes are closely related to soil types and surroundings.