1. 2014 China Report under RAS5055
Impacts of land use changes on hillslope erosion and catchment sediment sources assessed by using FRN and CSSI techniques
Y. Li and H.Q. Yu
IEDA-CAAS
8 September 2014

2. Objectives
Overall objective is to establish soil redistribution-soil carbon patterns at catchment scale through combinative use of FRN and CSSI techniques for area-wide precision evaluation of land use change on soil carbon sequestration in China Loess Plateau.
Quantify changes in soil redistribution due to land use change by using FRNs analysis.
Identification of sediment sources by conbinative use of FRN fingerprinting and CSSI techniques.
Specific objective:

3. Case Study: Yangjuangou Catchment in Loess Plateau
Location: 36◦42N, 109◦31E
Area: 284ha
Soil : loess soil (Calciustepts)
Land use:
Before 1998: cultivated on steep hillslopes up to 40 degrees
After 1998: Conversion of cultivated steep hillslopes to vegetated

5. Change of land use compared to 1996 (%)
Change of land use area
Land Use type
Sum_Area_1996 (m2)
Sum_Area_2014
(m2)
Change of land use compared to 1996 (%)
Check dam farmland
65,859
93,349 42
Farmland
593,295
383,850
- 35
Forest
434,280
850,876 96
Fruit
244,387
7,560
- 97
Grass
37,948 -
Shrub
68,316
Slopeland
58,894
Terrace
363,953
350,723
- 4
Urban
115,593
35,973
- 69
Wasteland
855,152
1,111,126 30
Water
4,220
Total
2,837,677

6. Major land use change between 1996 and 2014 in Ynagjuangou catchment
Land use type
Area in 1996
(m2)
Area in 2014
Change
(%)
Farmland/check-dam farmalnd/slopeland
718,048
477,199
- 34
Forest/grass/shrub/wastedland
1,395,696
1,962,002
+41

7. FRN sampling following 1996
Gullied area and inter-gully area of the Yangjuangou catchment.
The reservoir is at the outlet of the catchment.
Sampling strategy
Soil sampling in 1996.
Re-sampling in 2013 & 2014
FRN sampling following 1996
CSSI sampling following the Protocol of CSSI.

8. 研究的人工林山坡 Cultivated hillslope in 1996
Forestland converted from cultivated hillslope since 1998) (Photo in 2012)

9. Change of soil erosion from hillslope following cropland conversion to forests estimated through repeated measurements of 137Cs techniques
After cropland conversion, soil erosion rates are significantly decreased in the below decreasing order: Summit (2.83 t/ha/yr）< Mid slope（-2.24 t/ha/yr）< lower slope (-5.16 t/ha/yr）< upper slope（-6.87 t/ha/yr).
As compared with the cropland in 1996, cropland conversion resulted in a reduction of more than 77% soil erosion from hillslope.

10. Identification of sediment sources using FRN fingerprinting and CSSI techniques
FRN Mixing Model
IsoSource Model

11. Basic principle of sediment sources estimated by using FRN mixing model
Multivariate Mix Model (Walling, 2005)

12. Changes in spatial patterns of mean 137Cs concentration and sampling numbers in Yangjuangou Catchment under different land uses between 1996 and 2014
Topography
Land use
137Cs (Bq/kg)
No. of samples
1996
2014
Inter-gully area
Cultivated hillslope
4.7±2.14 32 -
Forest land
8.25±3.22 18
0.93±0.11 20
Gully area
Cultivated gully slope/Gully wall*
1.45±0.76 10 0*
Check-dam farmland
3.5±1.52 4
0.47±0.21
Reservoir sediment
Sediment
3.37±1.14 90
0.14±0.08 30

13. Sediment contribution(%)
Sediment sources from gully area and inter-gully area (hillslope) in Yangjuangou catchment identified by using FRN (137Cs) Mixing model
Land use
Sediment contribution(%)　
Change(+-%)
1996
2014
Cropland (hillslope) 40 11
-78%
Forest land (hillslope)
10.5
Cultivated gully slope/Gully wall* 80
100%
Check-dam farmland
9.5 9
-5%

14. Field sampling for CSSI in 2014

15. C-13 in different fatty acids under specific land use types in Yangjuangou catchment
Land uses
Bulk 13C
Palm
Stear
Arachidic
Behenic
Lignoceric
No. of sample
Locust
-26.18
-31.61
-34.24
-35.89
-34.27
-38.66 10
Maize
-20.50
-30.56
-33.45
-30.34
-31.7
-33.77
Gully wall
-23.37
-31.54
-33.48
-30.36
-25.6
-35.17
Grass
-27.1
-30.07
-32.15
-32.44
-32.90
-33.17
Shrub
-27.5
-32.03
-31.31
-32.76
-29.56
-30.96
Sediment
-24.64
-32.86
-34.77
-30.23
-29.8
-33.87

16. Sediment sources from specific land use types using IsoSource based on CSSI data
C% in Soil
Iso% in Mix
Iso% in Mix/C% in Soil
Soil% in Mixture
Grass
1.5
12.5 8 3
Shrub
1.4
12.6 9
Locust
1.7
12.0 7
Gully wall
0.2
38.0
190 72
Maize farmland
0.5
24.9 50 19
264

17. Comparison of sediment sources by FRN Mixing model with CSSI based on 2014 samples from Yangjuangou catchment
FRN Mixing model with CSSI
The results from both FRN and CSSI are comparable.

18. Conclusions
FRN and CSSI techniques are very useful tools in quantifying impacts of land use change on soil erosion and associated sediment sources.
Grain to Green project in China, i.e. steep cropland conversion to forest and grassland has significantly reduced soil erosion and sedimentation.
FRN fingerprinting technique can be used to determine sediment sources from surface and sub-surface soil erosion processes influenced by land use changes.
CSSI analysis is very useful technique to identify sediment sources from specific land use types.

19. THANK YOU!