Fingerprinting Sources of Suspended Sediments Mean 210 Pb Flux (pci/cm 2 /yr) 2.5 2 1.5 1 0.5 Sagatagan Kreighle Henderson George Long Diamond Duck Stahl Reference Lakes y = 0.65 + 4.8x R 2 = 0.58 Hook 0 0 0.05 0.1 0.15 0.2 0.25 Fish Dunns Beaver Conventional Tillage Be Fe Pb Cs Hg Be Fe Pb Cs Hg Streambank Bass George Be Fe Pb Cs Hg Richardson Minimum Tillage Be Fe Pb Cs Hg Tile Drainage Avg Sed Rate inorg. (g/cm 2 /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 Core Top 10 3 tons/yr 0 200 400 600 800 2008 1990 1970 Hey, Brain what are we going to do today Same thing we do every day Pinky try to figure out where the sediment comes from, and why it changes Down Core - 10 X faster than pre-settlement 1950 1930 1910 1890 1870 1850 1830 1810 mucho 133 dump trucks/day - Records erosion history of Minnesota s ag lands
Lake Pepin: Integrator of watershed scale erosion processes Sediment cores = window to the past Record erosion history of MN Watershed Bay City I Maiden Rock N W E II S km J III Lake Pepin 0 1 5 10 Lake City IV Pepin V MN River watershed, ~85% cultivated
What is the source of the sediment? Lake Pepin Sediment Accumulation History 0 200 400 600 800 2008 1990 1970 1950 1930 1910 1890 1870 1850 1830 1810 Field Erosion 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 Core Top 0 200 400 600 800 2008 1990 1970 1950 10 3 tons/yr -It s possible the reasons are related -Why does the rate change the way it does? - Do the sources also change? Down Core 1930 1910 1890 1870 1850 1830 1810 We can t solve the problem until we understand what is causing the changes.
Fingerprinting Sediment Sources with 210 Pb Constant Exposure to Atmosphere and Rain 0.25 0.2 Pb-210 Cultivated Field Suspended Sediment Activity (bq/g) 0.15 0.1 0.05 Non-field Erosion 0 Minimal Exposure to Atmosp. and Rain
Relative Contribution of Fields to Riverine Sediment 24% 31% S. Fork Crow = 25% 31% 26% Lake Pepin = 14% 28% 20% 16% 27% 30% 15% 14%
Redwood R. Chippewa R. Upper Carver Cr. S. Fork Crow R. Watonwan R. Upper LeSueur R. Cottonwood R. Carver Cr Bevens Cr High Island Blue Earth R. LeSueur R. 250 200 150 100 50 0 Field vs Non-field Sediment Loads Field Load Non-field Load Between Watersheds: - Non-field vary by: 400,000 - Field Load Vary only: 20,000 - Non-field highly variable! Load (1000's tons/yr)
Redwood R. Chippewa R. Upper Carver Cr. S. Fork Crow R. Watonwan R. Cottonwood R. Carver Cr Bevens Cr High Island Blue Earth R. LeSueur R. 800 700 600 500 400 300 200 100 0 Yields--- Field Yield Non field Yield Steeply Incised Watersheds Less Incised Field Yield Vary by 60 kg/ha Non-field Vary by 500 kg/ha Yield (kg/ha-yr)
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 express loading as is loading, increasing. some sources not really changing 6 Lake Pepin Sediment Loading 5 Field Non-Field Field load ~ constant Non-field accelerating & is now 6X natural rate Load (g/cm 2 -yr) 4 3 2 1 0 Prairie Ag. 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 0 200 400 600 800 2008 1990 1970 1950 1930 1910 1890 1870 1850 1830 1810 10 3 tons/yr 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 Rate due to artificial drainage + precip Rate due to loss of perennial cover 2008 1990 1970 1950 1930 1910 1890 10 3 tons/yr (inorganic sed.) 0 200 400 600 800 95% prairie gone Intensification of tile-drainage (& increasing precip) Natural Rate 1870 1850 1830 1810 Begin plowing prairie
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 effects of climate from artificial drainage Preliminary data--a hint at what we might find 800 Elk River (minimal tile drainage) LeSueur River (intense tile drainage) R 2 = 0 p = 0.71 R 2 = 0.17 p= 0.004 Runoff Ratio -May 600 400 200 1945 1965 1985 2005 1945 1965 1985 2005 Runoff Ratio = flow/precipition (normalizes flow to rainfall)
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 Glacial Lake Agassiz Non-Field 2006 70% 1964 67% 1950 50% 1940 40% Sediment Rate 3 2.5 2 1.5 1 0.5 Field Non-field 0 1940 2006
Climate is getting Wetter 8 Palmer Hydrologic Drought Index Avg. PHDI April - August 6 4 2 0-2 -4-6 y = -42.62 + 0.02x R 2 = 0.09 y = -41.38 + 0.02x R 2 = 0.08 Region 8 Region 7-8 1900 1920 1940 1960 1980 2000
Sedimentation Rate and Climate? Avg. PHDI April - August 6 4 2 0-2 -4 Palmer Hydrologic Drought Index y = 9.8-0x R 2 = 0 y = 16.68-0.01x R 2 = 0 Region 8 Region 7-6 1940 1950 1960 1970 1980 1990 1990 1980 1960 1940 0 1 2 3 4 5 6 7 8 9 2000 1940 1920 1900 1880 1860 1840 1820 1800 1700 1600 kg m -2 yr -1 1500 0 200 400 600 800 1000 10 3 t yr -1 2X
Trends in Sediment Accumulation Rates-- in Different Systems Factor Increase 10 Increase in Sed. Rate since Settlement 8 6 4 Pepin Reference Lakes Riverine systems Field + Non-Field Field Source Only Neat-O, but why are they different? 2 0 pre 1860 1900-1930 1940-1963 1963-1996
Effect of artificial drainage on flow and non-field erosion?? 800 Elk River (near Big Lake MN) Runoff Ratio Since 1940 Q/P - May 700 600 500 400 300 200 100 0 1200 1944 1952 y = -330.18 + 0.24x R 2 = 0 p = 0.71 1960 1968 1976 1984 1992 Le Sueur River Runoff Ratio Since 1940 y = -8064.41 + 4.22x R 2 = 0.17 p= 0.004 2000 Watershed with minimal artificial drainage Need to quantify and understand this difference 1000 800 600 400 200 0 1944 1952 1960 1968 1976 Q/P - May 1984 1992 2000 Watershed with dense artificial drainage
Lake Pepin Sediment Accumulation Rate Core Top 0 200 400 600 800 2008 1990 1970 1950 10 3 tons/yr (inorganic sed.) Hey, Brain what are we going to do today Same thing we do every day Pinky, Try to figure out where the sediment comes from, and why it changes Down Core 1930 1910 1890 1870 1850 1830 1810
Tracing Sediment Sources with Radioisotope Fingerprints. 1. 210 Pb and 137 Cs are deposited by rain 2. Different Sources = Different Concentrations 3. Fields have high concentrations why am I singing and what does it have to do with fingerprinting 4. Non-fields sources have ~ 0 Ravines, Streambanks, Bluffs Gullies 5. Suspended Sediment combination 6. Measure suspended sed. and compare to Source Fingerprints