1 The directional components of splash erosion at different raindrop kinetic energy in Chinese Mollisol region Fenli Zheng Wei HU Institute of Soil and Water Conservation, Northwest A&F University Institute of Soil and Water Conservation, CAS & MWR 3rd Conference of the World Association of Soil and Water Conservation Aug , Belgrade, Serbia

2  Splash erosion involves soil detachment and transport caused by raindrop impact. Raindrop impact is one of the principal erosion processes in Chinese Mollisol region and occupies 60%-90% of hillslope soil erosion (An et al., 2012).  In addition to soil properties, soil detachment and transport by raindrop impact is mainly affected by rainfall physical parameters (Fernandez-Raga et al., 2010; Liu et al., 2015; Park et al., 1983; Sharma et al., 1991). I Introduction  Currently, there are few literatures showing how rainfall physical parameters affects directional components (upslope, lateral and downslope) of splash erosion in Chinese Mollisol region.

3 The objective of this study is to qualify how rainfall physical parameters affected directional components (upslope, lateral and downslope) of splash erosion in the Chinese Mollisol region. The specific aims of this study are to investigate the effects of rainfall physical parameters on directional components of splash erosion characteristics; to select the key rainfall physical parameters affecting total and net splash erosion; to fit and validate the equations between total and net splash erosion with rainfall physical parameters. Objective

4 II Methodology  Soil pan with 50 cm-long, 50-cm wide and 40 cm-deep  Rainfall simulator: A side-sprinkle rainfall simulator system  Rainfall Intensity: 50 and 100 mm h –1  Raindrop falling heights: 3.5, 5.5, 7.5, 9.5, and 11.5 m  Soil: Chinese Mollisol SUSU SdSd SlSl SrSr Total splash: Net splash: Lateral splash:

5 Rainfall intensity (mm h –1 ) Raindrop median volume diameter † (mm) Raindrop falling height (m) Raindrop terminal velocity ‡ (m s –1 ) Raindrop kinetic energy (J m –2 mm –1 ) (0.04) (0.14)d6.48 (1.06)e (0.28)c6.77 (1.13)d (0.26)bc7.75 (0.82)c (0.18)b8.59 (1.04)b (0.26)a9.83 (1.06)a (0.03) (0.28)c**7.67 (0.16)d** (0.19)c8.52 (0.55)d** (0.21)c10.23 (0.45)c** (0.30)b**12.85 (1.12)b** (0.17)a*14.47 (0.66)a** List of rainfall physical parameters

6 III Results-- Total splash erosion Rainfall intensity (mm h –1 ) Raindrop kinetic energy (J m –2 mm –1 ) Splash erosion (g) Upslope Downslope Left slope Right slope Lateral slopeNetTotal (0.1) † c ‡ 1.5 (0.3)d1.5 (0.3)dA § 1.2 (0.3)dA1.3 (0.3)d 0.7 (0.3)c 4.9 (0.8)d (0.1)bc2.8 (0.2)c1.8 (0.4)cdA2.2 (0.2)cdA2.0 (0.3)d 1.4 (0.1)bc 8.2 (0.7)c (0.5)b3.6 (0.2)bc2.7 (0.2)cA2.7 (0.3)cA2.7 (0.6)c 2.1 (0.7)b 10.5 (1.8)c (0.4)b3.9 (0.9)b4.1 (0.4)bA4.8 (0.1)bA4.4 (0.3)b 2.3 (0.5)b 14.5 (1.4)b (0.6)a7.5 (0.4)a6.7 (0.6)aA6.5 (0.3)aA6.5 (0.4)a 4.5 (0.8)a 23.6 (1.4)a (0.3)c*8.9 (0.9)d*6.1 (0.9)dA*7.3 (0.3)dA*6.3 (0.3)e* 4.5 (0.2)c* 26.7 (0.3)e* (1.7)b**29.3 (4.2)c*24.3 (3.7)cA*22.2 (1.7)cA*22.8 (1.1)d* 15.8 (1.1)b* 89.2 (9.2)d* (1.2)b*33.9 (4.6)b*35.4 (3.5)bA*22.7 (1.9)cA*28.2 (1.6)c* 19.0 (1.6)b* (12.8)c* (0.9)a*56.3 (7.1)a**43.8 (6.0)aA*41.8 (1.2)bA*42.4 (2.7)b* 33.4 (6.8)a** (11.8)b* (1.8)a*59.8 (4.1)a*44.5 (5.6)aA**58.7 (8.9)aA*51.3 (4.1)a* 34.5 (4.6)a* (11.9)a* The directional components of splash erosion, net splash erosion and total splash erosion at rainfall intensities of 50 and 100 mm h –1 Total splash erosion significantly increased as rainfall intensity and raindrop kinetic energy increased (p < 0.05). When rainfall intensity increased from 50 mm h –1 to 100 mm h –1, total splash erosion significantly increased by 4.4 to 10.4 times.

7 Total splash erosion significantly increased as raindrop kinetic energy increased at the same rainfall intensity (p < 0.05). The relationships between total splash erosion and KE at rainfall intensities of 50 and 100 mm h –1 were power functions.

8 III Results--The directional components of splash erosion  As rainfall intensity increased from 50 mm h –1 to 100 mm h –1, splash erosion from upslope, downslope and lateral slope significantly increased by 4.5 to 12.5, 4.9 to 13.4, and 3.8 to 10.4 times, respectively (p < 0.05).  Splash erosion from upslope, downslope and lateral slope significantly increased as raindrop kinetic energy increased at the same rainfall intensity (p < 0.05).  The relationships between the directional components of splash erosion and KE at rainfall intensities of 50 and 100 mm h –1 were described by power functions.

9  Splash erosion from downslope, lateral slope and upslope occupied 32.2%, and 26.3% and 14.5% of total splash erosion, respectively. Rainfall intensity (mm h –1 ) Raindrop kinetic energy (J m –2 mm –1 ) Contributions to total splash erosion (%) UpslopeDownslopeLateral slope (2.5) † abC30.2 (2.9)abA27.1 (2.2)aB (1.0)aC34.5 (1.9)aA23.8 (1.7)aB (1.5)abC33.9 (3.4)aA26.4 (1.9)aB (1.8)bC26.9 (3.9)bA30.6 (2.8)aB (2.3)abC31.7 (2.0)aA27.5 (0.2)aB (4.8)aC33.6 (1.6)aA24.3 (4.3)aB (1.0)aC32.8 (2.4)aA25.6 (1.0)aB (1.3)aC31.7 (1.9)aA26.4 (0.6)aB (0.6)aC34.1 (2.5)aA25.8 (0.7)aB (1.0)aC31.8 (1.1)aA27.2 (0.4)aB III Results--The contributions of the directional components of splash erosion to total splash erosion

10 III Results-- Net splash erosion  Net splash erosion also significantly increased with the increasing rainfall intensity (p < 0.05). When rainfall intensity increased from 50 mm h –1 to 100 mm h –1, net splash erosion significantly increased by 5.4 to 13.5 times (p < 0.05).  Net splash erosion significantly increased as raindrop kinetic energy increased at the same rainfall intensity (p < 0.05).  The relationships between net splash erosion and KE at rainfall intensities of 50 and 100 mm h –1 were power functions.

11  Pearson correlation analysis was performed to determine the key rainfall physical parameter. III Results--Key rainfall physical parameter selection  Based on the correlation matrix, the correlation coefficient of total and net splash erosion with KE and D 50 was > 0.8. Thus, KE and D 50 were the key indicators for analyze how both impacts total and net splash erosion. Correlation matrix for total splash erosion (S T ) and net splash erosion (S N ) and each rainfall physical parameter: raindrop kinetic energy (KE), rainfall intensity (RI), raindrop median volume diameter (D 50 ), and raindrop terminal velocity (V m ). STST SNSN KERID 50 VmVm STST 1 SNSN ** 1 KE0.905 ** ** 1 RI0.775 ** ** ** 1 D ** ** ** 1 VmVm 0.669**0.658**0.877** ** 1

12  30 samples were randomly selected from 40 samples for establishing the equation.  The regression equations between total and net splash erosion with KE and D 50 were fitted. All equations were significant at the 95% confidence level. III Results-- Equation fitting

13 III Results--Equation validation Total splash erosion Net splash erosion  Prediction accuracy of two equations was satisfactory.  The remaining 10 samples were used to validate the equations.

14  Total splash erosion, directional components of splash erosion and net splash erosion on hillslope significantly increased as rainfall intensity and raindrop kinetic energy increased (p < 0.05).  Splash erosion from downslope, lateral slope and upslope occupied 32.2%, and 26.3% and 14.5% of total splash erosion, respectively.  Raindrop kinetic energy and raindrop median volume diameter were the key indicators affecting both total and net splash erosion. IV Conclusions

15  Raindrop kinetic energy and raindrop median volume diameter were the key indicators affecting both total and net splash erosion.  The equations between total and net splash erosion with both parameters of KE and D 50 were fitted. Prediction accuracy of the two equations were acceptable.  Preventing raindrop impact by using conservation tillage can effectively reduce soil erosion in Chinese the Mollisol region. IV Conclusions

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