#1TRACKING EROSION WITH SEDIMENT ASSOCIATED ISOTOPES IN YUNNAN. CHINA Thesis Defense Presentation The Thomas B. Neilson UNIVERSITY of VERMONT NSF#2• • Introduction Humans are one of the most effective geomorphic agents. on the planet . • Humans have been estimated to move more earth material annually than any other geomorphic or geologic process Erosion and sediment disturbance that results from human activity directly impacts fluvial systems as well as communities reliant on river resources.#3Introduction Long history of human influence on the landscape • . First recorded in 11th century AD Communism and subsequent opening and development severely impacted erosion Since the 1950's, China has maintained sediment yield monitoring stations throughout the country Data from these stations do not show a systematic increase in sediment yield as a result of land-use#4Question Have humans increased erosion over the long-term average through land-use change?#5Tour Guide 00:01 X N US Dept of State Geographer ©2009 GeoBasis-DE/BKG 2015 Google Data SIO, NOAA, US. Navy, NGA, GEBCO Google earth 38°57'33.81" N 95°15'55.74" W eye alt 6838.52 mi#6Field Sites Elevation (m) High: 5000 b Precipitation (mm/yr) H 0 Low : 0 Salween Yangtze Mekong a High: 1600 Basin 35 26°N Low: 600 e Basin 49 24°N 22°N Basin 11 98°E 100°E 98°E 100°E#7Experimental Approach Goals Determine long-term (~1,000 - 50,000 yr) average erosion rate Assess contemporary rates of erosion Determine what factors drive erosion . • Tectonic and lithologic controls Slope, rainfall, channel steepness, etc. Agriculture vs. Forest Tools In situ 10Be • Meteoric 10Be Excess 210Pb 137Cs Sediment Yield • Topographic analysis of DEM'S ● Analysis of land-use data Field observations#8n 10 Be In situ-produced 10Be t1/2 = 1.39 myr Produced within quartz grains from interaction between cosmic rays and oxygen Permanently entrained in mineral grain ~290 atoms/cm² y-1 production rate Useful for estimating basin-wide rates of erosion when measured in fluvial sediment 160#9Fallout Radionuclides (10 Bem, 210pbex Produced in the atmosphere Delivered to earth surface via precipitation and dust/dry-fall Can be mobilized in certain conditions (e.g. pedogenesis), but generally are assumed permanently sorbed to sediment · Preferentially adsorb to finer sediment particles 137Cs) 1954-1963- 137Cs Carbon 210pb Oxygen 226 Ra 222Rn. 7Be Cosmic rays Nitrogen Excess ph 210pb. Zupanc and Mabit, 2010#10Fallout Radionuclides (10Bem, 210Pbex, 10Bem (t1/2 = 1.39 myr) • • Atmospheric spallation reaction ~1.3 million atoms/cm² y-1 delivery rate Useful for assessing long-term erosion 210Pbex (t1/2 = 22.2 yr) • Naturally occurring as part of 238U decay series 1954-1963- 137Cs Carbon 226 Ra 222Rn. Fraction of total 210Pb in soil derived from 222 Rn gas that leaves soil Delivered back to soil through fallout 137Cs) 210pb Oxygen 7Be Cosmic rays Nitrogen Excess ph 210pb. Zupanc and Mabit, 2010 • • Integrates up to past 100 years of erosion 37Cs (t1/2 = 30.2 yr) Created from nuclear weapons testing in atmosphere Delivered to soil through fallout Only deposited globally from 1950's to 1970's Useful for assess erosion over past 50-60 years#11Depth (m) 3 N 1 137Cs profile 210Pbx profile ex Increasing Concentration Dominant type of erosion Sheetwash and Shallow Rills In situ 10Be profile Exponential meteoric 10Be profile “Bulge” meteoric 1ºBe profile 105 Integration Time (years before present) 104 103 102 10 1 In situ 10 Be Meteoric 10Be 210Pb 137CS ex Sediment yield Land use Rills, Shallow Gullies, Shallow Landsliding, Bank Failure/Channel Migration Deep Gullies and Landslides#12Going from 10Be concentration to erosion rate (or index) River sediment is average of upstream area The production (or delivery) rate of 10Be can be determined for the sampled watershed#13Going from isotopic concentration to erosion rate (or index) In situ 10 Be (10 Be₁): • Isotopic concentration of the sediment is compared to the rate of production, and the difference is attributed to land surface lowering Meteoric 10Be (1ºBem): The export rate of 10Bem on sediment is compared to the delivery rate, and a ratio is made >1 indicates more is leaving than being delivered <1 indicates more is being delivered than leaving IN OUT#14Sampling Collect active channel sediment from 54 locations throughout three watersheds Select sample sites to represent: • Basins that are primarily forested or agricultural Natural range of representative slopes in watershed • Range of basin sizes Sediment mixing above and below major junctions#15Extracting and measuring Be I CA HF DIGESTION UMNS HO#16Measuring 210Pbox and 137Cs Measurement done with germanium detector Counts radioactive decay at given energy levels, which are converted to concentration#17Sediment Mixing Results 1201 ◆ B35 Modeled 10Be, Concentration (104 atoms/g) 40- 40 4 4 35.21 • B49 ▲ B11 35.5 35.11 35.11 -1-1 -1-1 Line 49.3 49.51 49.4 + 149.1 49.2 49.5 49.5 11.135.3 11.2 35.4 f 35.4 40 120 Measured 10Be Concentration (104 atoms/g)#18Sediment Mixing Results Fraction difference in mixing (10Be, measured/modeled) 1.2 35.1 Dam Site 0.8 0.4 0 0.1 0.2 y = 0.14 +0.87x R² = 0.71 p = 0.0005 0.3 0.4 Fraction residual area#19Sediment Mixing Results 1.2 35.1 Dam Site y = 0.14 +0.87x R² = 0.71 p = 0.0005 16 12 8 0 Fraction difference in mixing (10Be, measured/modeled) 0.8 0.4 0.1 0.2 0.3 0.4 Fraction residual area 1ºBe, concentration (105 atoms/g) 1.6 1.2 0.8 Mean ■ Excluded ♦ B35 . B49 ▲ B11 0.4 4 3 2 1 0 0 0.2 0.6 0.8 1 0.4 Normalized basin area Basin 35 Basin 49 Basin 11#20Isotopic Results ? Normalized 10Be, (104 atoms/g) Normalized 10Be (107 atoms/g) m 210Pb Activity (Bq/kg) ex 10 2 TH 5 0 11 49 Basin all 11 35 49 all 0 11 35 49 all 11 35 49 all Basin ་་་ ག་ . -- “..] 3 BDL 11 6 BDL 35 5 BDL 49 Basin ".. all 11 35 49 49 all#21Elevation (m) Low: 700 0 וי 5 km Basin 35: Physical properties High: 4000 Slope (°) Low: 0 High: 30 33-53 54-72 Mean Basin Ksn 73-86 87-96 97-100 110-120 130-150 160-180 190-250 62% Cultivated Forest Water Wetland I Shrubland Grassland Artifical#22Basin 35: Isotopic Results 0 5 km 1.7-2.4 2.5-3 3.1 3.5 3.6-4.3 4.4 - 5.4 Normalized 10Be₁ concentration (104 atoms/g) 0.56 -0.65 0.66 0.81 Normalized 10Bem 0.82 - 1.2 1.3-1.6 1.7-1.9 concentration (107 atoms/g) m 4.82 Bq/kg 4.02 Bq/kg BDL ex 2.3-3.7 210Pb activity 3.8-4.6 (Bq/kg) 4.7-5.4 5.5-6.0 2-2.7 2.8-6.1 6.2-13 14 - 28 6.1 -6.7 6.8 7.3 7.4-8.5 8.6 11.8 11.9 15.6 5.5-6.4 6.5-6.9 7-9.7 9.8 13 14-27 29 - 65#23Basin 35: Long-term erosion 0 4 km 12-20 21-40 41-60 61-80 1ºBe, derived erosion rate 81-100 101-120 (mm/kyr) 121-140 141-160 161-180 181-210 35 0.09 0.20 0.21 0.40 0.41 -0.60 0.61-0.80 0.81 1.00 1.01 1.20 1.21-1.40 1.41 - 1.60 1.61 - 1.80 7.55 10Bem derived erosion index 35#24Controls of erosion in basin 35 Base level fall is primary control on long- and short-term erosion A Elevation (m) 3800 3400 3000 Footwall Relict Adjusting N. Arm S. Arm 2600 200 2200 0 5000 10000 Distance from outlet (m) 15000 20000 250 200 Erosion Rate (mm/kyr) 150 100 50 0 10 15 20 Hillslope Angle 100 0 25 25 Nested erosion rate (mm/kyr)#25Controls of erosion in basin 35 Base level fall is primary control on long- and short-term erosion Slope steepness determines long-term erosion rate Erosion Rate (mm/kyr) 250 200 150 100 50 Erosion Rate (mm/kyr) 0 10 60 110 160 210 Channel Steepness 250 200 150 100 50 0 10 15 20 Hillslope Angle 25 25#26Controls of erosion in basin 35 Base level fall is primary control on long- and short-term erosion Slope steepness determines long-term erosion rate Erosion rates increase after channels steepen and hillslopes respond Footwall Relict Adjusting N. Arm S. Arm D 70 - Anomalous 60 50 40 Normalized 10Be concentration (108 atoms/g) IN WAS Erosion Index 30 20 10 0 0 50 100 150 200 250 Erosion Rate (mm/kyr) E 2.0 Anomalous 7.55 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2- 0.0 10 15 20 25 Mean Basin Slope (°)#27Controls of erosion in basin 35 Base level fall is primary control on long- and short-term erosion Slope steepness determines long-term erosion rate Erosion Rate 210Pb Activity ex 35 4.02 Bq/kg 0 4 km Erosion rates increase after channels steepen and hillslopes respond Contemporary erosion. appears to be controlled by un-measured variable(s) 4.82 Bq/kg 2.87 Bq/kg#28Elevation (m) Low: 700 Basin 49: Physical properties 0 20 km High: 4000 Slope (°) 0: мот High: 30 33-53 54-72 Mean Basin Ksn 97-100 130-150 160-180 190-250 73-86 87-96 110 - 120 77% Cultivated Forest Wetland Water Grassland Artifical Shrubland#29Basin 49: Isotopic Results 0 10 km பட 1.7-2.4 2.5-3 3.1 3.5 3.6-4.3 4.4 -5.4 5.5-6.4 6.5-6.9 7-9.7 9.8-13 14-27 Normalized 10Be concentration (104 atoms/g) 0.56 -0.65 0.66 0.81 Normalized 1ºBem 0.82-1.2 concentration (107 atoms/g) 1.3-1.6 1.7 - 1.9 2-2.7 2.8-6.1 6.2 13 14 - 28 29-65 BDL 2.3 3.7 210Pb activity ex 3.8-4.6 (Bq/kg) 4.7 5.4 5.5-6.0 6.1 -6.7 6.8 7.3 7.4-8.5 8.6-11.8 11.9 - 15.6#30Basin 49: Long-term erosion 49 0 10 km 49 12-20 21-40 41-60 1ºBe, derived 61-80 erosion rate 81-100 101-120 (mm/kyr) 121-140 141-160 161-180 181-210 0.09-0.20 0.21-0.40 0.41 0.60 0.61-0.80 0.81 1.00 1.01-1.20 1.21 -1.40 1.41-1.60 1.61 1.80 7.55 10 Bem derived erosion index#31Erosion Rate (mm/kyr) Land Use Controls of erosion in basin 49 Concentration (atoms/g) 2 210Pb Activity ex (Bq/kg) LO 10 10 Bе m 200 100 0.5 × 107 0 0 0.2 Fraction Cultivated Land ° 0.4 1000 1100 1200 MAP (mm/yr) Climate 10 20 30 Mean Slope (°) 0 100 200 300 Mean k sn Topography 50 100 Median k sn о 0 1000 2000 Basin Relief (m) °#32Elevation (m) Low: 700 Basin 11: Physical properties High: 4000 19 km Slope (°) Low: 0 High: 30 Mean Basin Ksn 33-53 54-72 73-86 87-96 97-100 110-120 130-150 160-180 190-250 Cultivated Wetland Forest Water I Shrubland Grassland Artifical 48%#33Basin 11: Isotopic Results 0 10 km BDL 2.3 3.7 210Pb activity m 1.7-2.4 2.5-3 3.1 3.5 3.6-4.3 4.4 - 5.4 Normalized 10Be₁ concentration (104 atoms/g) 0.56 -0.65 0.66 0.81 Normalized 10Bem 0.82 - 1.2 1.3-1.6 1.7-1.9 concentration (107 atoms/g) 3.8-4.6 4.7-5.4 5.5-6.0 6.1 -6.7 2-2.7 2.8-6.1 6.2-13 14 - 28 6.8 7.3 7.4-8.5 8.6 11.8 11.9 15.6 5.5-6.4 6.5-6.9 7-9.7 9.8 13 14-27 29 - 65 ex (Bq/kg)#34Basin 11: Long-term erosion 0 9 km 11 11 12-20 21-40 41-60 10Be, derived 61-80 81-100 101-120 121-140 141-160 161-180 181-210 erosion rate (mm/kyr) 0.09 -0.20 0.21 0.40 0.41 -0.60 0.61-0.80 0.81 1.00 1.01 1.20 1.21-1.40 1.41 - 1.60 1.61 - 1.80 7.55 10Bem derived erosion index#35• Controls of erosion in basin 11 No 137Cs High 210Pbex, except at outlet where channel has been altered Contemporary sediment yield 50% lower than long- term average 0.56 -0.65 0.66 0.81 Normalized 10Bem 0.82 - 1.2 1.3-1.6 1.7 1.9 2-2.7 2.8-6.1 6.2-13 14-28 concentration (107 atoms/g) BDL 2.3 3.7 210Pb, activity ex 3.8-4.6 (Bq/kg) 4.7-5.4 5.5-6.0 6.1 -6.7 6.8-7.3 7.4-8.5 8.6 11.8 29-65 11.9 - 15.6#36Sediment transport path: working hypothesis Explain erosion using a conceptual model that follows sediment grains from source to export from the basin.#37Sediment transport path: working hypothesis 1. Begins on hillslope with low 137Cs and 210Pbex concentration 2. Enters agricultural terrace through irrigation diversion or direct transport 3. Sits near surface as it works through terrace network, from tread to riser to next terrace, accumulating 210Pbx the entire time 4. Finally enters main river channel and is exported from basin with higher 210Pbex concentration than it began with 4 3 2#38Sediment transport path: working hypothesis Accounts for: • • Absence of 137Cs in sediment High activity of 210Pbex Low contemporary sediment yield 4 3 2#39Primary Findings Basin 35: In transient landscape, knickpoint migration in response to base-level fall controls erosion Basin 49: In landscape that is adjusted to base-level, morphology controls long-term erosion while agriculture dominates contemporary erosion Basin 11: Diversion of water and sediment to terraces complicates interpretations of erosion#40Conclusions: What do we learn about the effects Chinese land-use policy? Change in pace of erosion coincides with extensive deforestation in 1950's - 1980's and top- down forest conservation policy from the 90's to present#41Conclusions: Does this method work? • • · Measuring four isotopes on the same samples means better temporal resolution of erosion . Can address drivers of contemporary and long-term erosion in one study Not all of the isotopes provide useful information in all settings Here, in situ 10Be and 210Pbex are most useful, followed by 137Cs • 10Bem is difficult to interpret and does not greatly improve our understanding of erosion#42Acknowledgements Special thanks to: Paul Bierman Amanda Schmidt Donna Rizzo Andrea Lini Veronica Sosa-Gonzalez Dylan Rood The UVM Geology Department National Science Foundation And many more...#43Questions?#44Empty#45~3 m + In Situ 10Be produced 160 10Be n n 160 10 Be Meteoric 10Be delivered + ? 1-10 m? 10 Be made and retained in quartz Production = 2.9 *102 atoms cm-2 y-1 10 Be mobile in soil ? retained by oxides Delivery = 1.3 x 106 atoms cm-² y-1#46. • Field area Three river basins in the Mekong watershed, Yunnan Provence, China Basins range from 200- 2000 km² Moderate to high relief 2 (Up to 1800 m) Intensive land use, primarily agriculture and forestry 45°0'0"N- 30°0'0"N- 15°0'0"N- 0°0'0"- 80°0'0"E 100°0'0"E 120°0'0"E 32°30'0"N China Chengdu -30°0'0"N 35 -27°30'0"N Xiaguan Kunming -25°0'0"N 49 Calcutta Myanmar -22°30'0"N Hanoi 90°0'0"E 95°0'0"E 100°0'0"E 105°0'0"E#47. Methods Four sediment associated isotopic systems Cosmogenic • . Meteoric 10Be In situ 10 Be Short-lived Unsupported 210Pb 137Cs 14C to date terraces and "paleo" in situ 10Be erosion rates Daily sediment yield data from Chinese Government hydrology stations (18-23 years) Remotely sensed land-use classification#48Results Basin 11 Basin 49 Basin 35 10Be, Concentration 10Be Concentration 210Pb Activity 4.82 Bq/kg 4.02 Bq/kg 0 5 km 0 10 km பட 0 10 km 2.87 Bq/kg 1.7-2.4 2.5-3 3.1 3.5 3.6 4.3 4.4 5.4 Normalized 10Be concentration (104 atoms/g) 0.56 0.65 0.66 0.81 Normalized 10Bem 0.82 1.2 concentration 1.3 1.6 (107 atoms/g) BDL 2.3-3.7 210Pb activity 3.8-4.6 4.7 5.4 5.5-6.0 (Bq/kg) 5.5-6.4 6.5 6.9 7-9.7 9.8 13 14-27 1.7 1.9 2-2.7 2.8 6.1 6.2-13 14-28 29-65 6.1-6.7 6.8 - 7.3 7.4-8.5 8.6 11.8 11.9 - 15.6#4910 Be Results 0 4 km 35 35 55 11 11 0 9 km Erosion Rate (mm/kyr) 12-20 21-40 41-60 200- 61-80 81-100 150 101-120 121-140 100 141 - 160 161-180 50- 181-210 || 11 35 49 Basin 0 10 km 49 0.09 -0.20 Erosion Index 0.21 -0.40 8 0.41 -0.60 0.61-0.80 6- 0.81 1.00 1.01-1.20 4. 1.21-1.40 1.41 1.60 1.61-1.80 2. 7.55 0 11 35 49 Basin 49 49#50Basin 11 Basin 49 Basin 35 Elevation (m) Low: 700 0 Hgh: 4000 Elevation above sea level Hillslope angle Normalized channel steepness 5 km 0 20 km 19 km Slope (°) Low: 0 Hgh: 30 33-53 54-72 Mean Basin Ksn 73-86 87-96 97-100 110-120 130-150 160-180 190-250 Cultivated Forest Wetland Water Shrubland 62% Grassland Artifical 48% 77% Land-use#51Results 70 60 60 Anomalous Normalized 10Be Concentration 10 (10 atoms/g) 40 50 50 210pb Activity (Bq/kg) 40 30 50 20 20 y = 849x 2 x 107 R2 = 0.69 p < 0.0001 0 18 16 0.5 1 1.5 2 2.5 Normalized 10 Be, Concentration (105 atoms/g) 20 14 12 14 10 00 CO < 2 0 0 0.5 1.5 2 2.5 3 Normalized 10 Be, Concentration (105 atoms/g) 3 18 16 14 12 10 210pb ex Activity (Bq/kg) 8 CO 2 0 0100 0 10 Anomalous 40 50 60 70 20 30 Normalized 10 Be Concentration (107 atoms/g) m#52Isotopes used for contemporary erosion Unsupported 210Pb t1/2 = 22.2 yr Naturally occurring as part of 238U decay series Fraction of total 210Pb in soil derived from 222Rn gas that leaves soil Delivered back to soil through fallout • 1 1/2 = 30.2 yr • +112 137CS Created from nuclear weapons testing and accidents Delivered to soil through fallout • Only deposited globally from 1950's to 1970's#53Controls of erosion in basin 11 • Modest statistically significant relationships between long-term measures of erosion and MAP and relief Unclear what, if any, processes might be driving these relationships – likely - result of extensive agriculture Erosion Rate (mm/kyr) 10Be Concentration (107 atoms/g) y = -0.6541x + 895.14 R2 0.42989 p = 0.008 90 80 70 60 50 40 30 20 10 0 1260 1280 1300 MAP (mm/yr) 1320 1340 8 7 CO 5 + 32 1 y 55250x 107 R² = 0.33109 p = 0.025 Erosion Index 0.9 y = 0.0007x-0.1893 0.8 R2 0.33036 0.7 p = 0.025 0.6 0.5 0.4 0.3 0.2 0.1 1 9 0.0 0 500 1000 1500 0 Basin Relief (m) 500 Basin Relief (m) 1000 1500#54Sediment mixing in a river network Sediment can be collected at a variety of locations in the basin The sample will be a mixture of sediment derived from all of the tributaries