Fingerprinting Sources of Suspended Sediments
Reference Lakes 2.5 y = 0.65 + 4.8x R 2= 0.58 /yr) 2 Richardson 2 Dunns Beaver 1.5 Minimum Tillage Fish Be Conventional Fe Hook
George Tile Drainage Stahl Tillage Pb Be Cs Be Henderson Fe Hg Fe 1 George Pb Bass Pb
Diamond Cs Pb Flux (pCi/cm Flux Pb Cs Hg Hg Long 210 Duck Kreighle Sagatagan Be 0.5 Fe
Mean Pb Cs Hg Streambank 0 0 0.05 0.1 0.15 0.2 0.25
2 Avg Sed Rate inorg. (g/cm /yr) Pasture
Be Fe Pb Cs Hg Sand Creek Suspended Sediment …the path to studying tile drainage
Shawn Schottler, Dan Engstrom and Dylan Blumentritt St. Croix Watershed Research Station--Department of the Science Museum of Minnesota Lake Pepin Sediment Accumulation History
103 tons/yr Core Top 0 200 400 600 800 2008
1990
1970
1950 “Hey, Brain what are we going to do today” 1930 1910
1890 “Same thing we do every day mucho… Down Core Pinky… 1870 133 dump trucks/day
…try to figure out where the 1850 sediment comes from, and 1830 why it changes” 1810 - Records erosion - 10 X faster than history of Minnesota’s pre-settlement ag lands Lake Pepin: Integrator of watershed scale erosion processes
• Sediment cores = window to the past
• Record erosion history of MN Watershed
Bay City
N I Maiden Rock W E II S
Lake Pepin J III km 05101
Lake City Pepin IV
V
MN River watershed, ~85% cultivated What is the source of the sediment ?
Lake Pepin Sediment Accumulation History
0 200 400 600 800 Field Erosion 2008
1990
1970
1950
1930
1910
1890
1870
1850
1830
1810
Non-field So What…. Sediment a serious pollutant Ag Fields assumed to be major source Spend many $$$$ to keep soil on fields BMP’s designed for fields
Can’t solve the problem unless we understand the problem
? ? Why does it change over time…?
Lake Pepin Sediment Accumulation Rate -It’s possible the reasons are related 103 tons/yr -Why does the rate change the way Core Top 0 200 400 600 800 2008 it does? 1990 1970 - Do the sources also change? 1950
1930
1910 We can’t solve the problem
1890 until we understand what is
Down Core causing the changes. 1870
1850
1830
1810 …Fingerprinting Sediment Sources with 210Pb
Constant Exposure to Atmosphere and Rain
0.25 Pb-210 0.2
0.15 Cultivated Field 0.1 Suspended Sediment Activity (bq/g) 0.05
Non-field Erosion 0
Minimal Exposure to Atmosp. and Rain Relative Contribution of Fields to Riverine Sediment
24% S. Fork Crow = 31%
Lake Pepin = 28% 31% 26% 25% 14% 16% 20%
27% 14% 30% 15% Field vs Non-field Sediment Loads
250
Field Load Between Watersheds: 200 Non-field Load - Non-field vary by: 400,000
150
- Field Load Vary only: 20,000 100
Load (1000's tons/yr) 50
0 - Non-field highly variable! Carver Cr Bevens Cr High Island LeSueur R. Redwood R. Chippewa R. Blue Earth R. Watonwan R. Cottonwood R. S. Fork Crow R. Upper Carver Cr. Upper LeSueur R. Yields--- 800 Field Yield 700 Non field Yield Steeply Incised
600 Watersheds
500 Less Incised 400
300
Yield (kg/ha-yr) Field Yield Vary 200 by 60 kg/ha 100
0 Non-field Vary by 500 kg/ha Carver Cr Bevens Cr High Island LeSueur R. Redwood R. Chippewa R. Blue Earth R. Watonwan R. Cottonwood R. S. Fork Crow R. Upper Carver Cr. From Hudak and Hajc, 2005 ..and now for Lake Pepin (= field + non-field) Field Non-field
2007 25% 75%
1996 28% 72%
1964 35% 65%
1940 70% 30%
Neat-O, but why does it change Non-field… if you expressloading as is loading, increasing…. some sources not really changing
Lake Pepin Sediment Loading 6
5 Field Non-Field
4 -yr) 2 Field load ~ 3 Prairie Ag. constant
2
Non-field Load (g/cm accelerating & 1 is now 6X “natural” rate 0 1840 1940 1964 1996 So…
% Sediment from non-field sources Ravens Creek = 70% Kasota Pond & integrator sites = 60-80% Lake Pepin = 65% Event TSS samples = >70%
…and Symbols of the L. Pepin Sed. Accumulation Rate
103 tons/yr 0 200 400 600 800 2008
1990
1970
1950
1930
1910
1890
1870
1850
1830
1810
Sed Rate is 10X pre-settlement
>65% of sed is non-field
Therefore RATE of non-field is not natural …why change: A hypothesis that needs testing
103 tons/yr (inorganic sed.) 0 200 400 600 800 2008 Rate due to 1990 artificial drainage Intensification + precip 1970 of tile-drainage (& increasing 1950 precip) 1930 Rate due to loss of perennial cover 1910 95% prairie gone 1890
1870
1850
Natural Rate 1830 Begin plowing prairie 1810 Blue Earth County, slide from MPCA Given that: Non-field inputs are significant and increasing
Hypothesize that: changes in riverine hydrology are mechanism for non-field inputs.
? Has tile drainage changed riverine hydrologic conditions
? Are changes in precipitation responsible
These two are linked--how do we disentangle them? Compare watersheds ‘with’ and ‘without’ drainage
Hydrologic Changes -over time -between watersheds -link to amount/density of drainage -“normalize to climate”
Relate magnitude and timing of:
-- hydrologic changes -- installation of drainage
to Pepin sedimentation rate changes Disentangling effectsofclimatefromartificial drainage Runoff Ratio -May 200 400 600 800 uofRto= lwpeiiin( Runoff Ratio =flow/precipition 1945 19651985 2005 Preliminary data--ahint (minimal tiledrainage) Elk River R 2 = 0p0.71 at whatwemightfind… 1945 19651985 2005 normalizes flowtorainfall) (intense tiledrainage) LeSueur River R 2 = 0.17p=0.004 Examine 14 other hydrologic parameters (monthly and seasonally)
e.g. runoff ratio, peak frequency, maximum flow, max flow duration, rate of increase, rate of decrease, flow:PDHI
- do they change over time - how do watersheds compare - are changes coincident with drainage, or climate - how much can be explained by drainage v. climate -Has drainage changed hydrologic conditions?
Model 2 Waterhsheds ( 1with, 1 “without”) Swat model: -calibrate to 1940-1970 -compare model predictions to actual 1970-2008 Summary
WHY? Not natural
Why has non-field sediment loading increased
How much is related to intensification of artificial drainage and/or increased precipitation?
Redwood River Reservoir---different river, same story…
Non-Field
Glacial 2006 70% Lake Agassiz 1964 67%
1950 50%
1940 40%
3 Field 2.5 Non-field
2
1.5
1 Sediment Rate
0.5
0 1940 2006 Climate is getting Wetter…
Palmer Hydrologic Drought Index 8 y = -42.62 + 0.02x R2= 0.09 6 y = -41.38 + 0.02x R2= 0.08
4
2
0
-2
-4 Avg. PHDI April - August -6 Region 8 Region 7 -8 1900 1920 1940 1960 1980 2000 Sedimentation Rate and Climate ?
Palmer Hydrologic Drought Index 6 -2 -1 y = 9.8 - 0x R2= 0 kg m yr 0123456789 y = 16.68 - 0.01x R2= 0 2000 4 19901980 1960 2X 1940 2 1940 1920 1900
0 1880 1860 1840 -2 1820 1800 1700 Avg. PHDI April - August Avg. PHDI April -4 Region 8 1600 1500 Region 7 0 200 400 600 800 1000 -6 103 t yr-1 1940 1950 1960 1970 1980 1990 Trends in Sediment Accumulation Rates-- in Different Systems
Riverine systems Increase in Sed. Rate since Settlement 10 Pepin Field + Non-Field Reference Lakes 8 Field Source Only
6 Neat-O, but why are they
Factor Increase 4 different?
2
0 pre 1860 1900-1930 1940-1963 1963-1996 Effect of artificial drainage on flow and non-field erosion ??
Elk River (near Big Lake MN) Runoff Ratio Since 1940 800 y = -330.18 + 0.24x R 2= 0 p = 0.71 700
600 Watershed with 500 minimal 400 artificial Q/P - May 300 drainage 200
100 Need to quantify 0 and 1944 1952 1960 1968 1976 1984 1992 2000
Le Sueur River understand this Runoff Ratio Since 1940 1200 y = -8064.41 + 4.22x R 2= 0.17 p= 0.004 difference
1000
800 Watershed with dense 600 Q/P - May artificial 400 drainage 200
0 1944 1952 1960 1968 1976 1984 1992 2000 Lake Pepin Sediment Accumulation Rate
103 tons/yr (inorganic sed.)
Core Top 0 200 400 600 800 2008
1990
1970
1950
1930 “Hey, Brain what are we 1910 1890 going to do today” Down Core 1870
1850 “Same thing we do every 1830 1810 day Pinky,
Try to figure out where the sediment comes from, and why it changes” Tracing Sediment Sources with Radioisotope Fingerprints.
1. 210Pb and 137Cs are deposited by rain “…why am I singing 2. Different Sources = Different Concentrations and what does it have to do with 3. Fields have high concentrations fingerprinting”
4. Non-fields sources have ~ 0 Ravines, Streambanks, Bluffs Gullies
5. Suspended Sediment combination
6. Measure suspended sed. and compare to Source Fingerprints