1. Agassiz National Wildlife Refuge Water Quality Investigation James Graham, U.S. Fish and Wildlife Service

2. Grand Forks Thief River Falls Thief Lake Thief River Watershed = TRW 1,077 sq. mi

3. Agassiz National Wildlife Refuge (USFWS) 26 different impoundments – 26, 321 acres Thief Lake Wildlife Management Area (MN DNR) Thief Lake – 7,100 acres 11 small impoundments on west end of Thief Lake – 210 acres *Moose River Impoundment (North Pool) – 1,250 acres *Moose River Impoundment (South Pool) – 2,250 acres Subtotal = 10,810 Thief River Falls Wildlife Area Office (MN DNR) Eckvoll – 1,750 acres Lost River Pool – 2,300 acres Farmes Pool (state-owned portion) – 245 acres Subtotal = 4,295 Total Wildlife Impoundment Surface Acres in TRW = 41,426 *shared mgmt. w/ Red Lake Watershed District

4. Objective 2.7: Managing Water Impoundments - Manage water impoundments as a complex of basins to provide wetland diversity and improve water quality for maximum benefits to migrating and breeding birds. Management will be within the capabilities of the wetland system as a whole… Agassiz NWR Comprehensive Conservation Plan (2005)

5. Present Conditions  Thief River upstream of Agassiz NWR drains ~ 350 mi 2 north and east of the Refuge.  Mud River drains ~ 160 mi 2 east of the Refuge.  Both of the above waterways enter and exit the Refuge in a channelized form.  Primary local land use is agriculture, including row-crop farming and small grains.  Drainage facilitated by more than 1,200 mi of county and judicial ditches in the TRW.  Sedimentation and nutrient loading (e.g., nitrogen, phosphorus) are primary water quality concerns in the TRW.

6. Agassiz National Wildlife Refuge Water Quality Project Rochelle Nustad, USGS, Grand Forks, ND Data Collection: 2008 - 2010 Results coming. Analysis in progress. Final report – summer(?) 2011

7. Questions to Answer 1.Where is the sediment coming from ? 2.What is the amount and rate of infilling ? 3.Is Agassiz Pool a net source of sediment ? 4. What is the effect of Main Ditch 11 ? Contracted the St. Croix Watershed Research Station (Science Museum of MN) to help answer the above questions. - Drs. Dan Engstrom and Shawn Schottler

8. Sediment Dating & Fingerprinting Radioisotopes: 210 Pb, 137 Cs 137 Cs: Bomb testing product, - Marker for 1963 - Fingerprint of field erosion 210 Pb: Natural, constant “fallout” - Dating tool back 150 years - Fingerprint of field erosion 210 Pb 137 Cs decay

9. Coring Sites Main Ditch 11 Thief River Inlet Agassiz Pool Sediment Cores: An Archive of Erosion History October 2008

10. Ditch 11 Agassiz Pool Things we know from the radioisotopes and composition…. Main portion of pool is accumulating slower than pool-wide average ~ 65% of the sediment is inorganic (was not produced in lake) Agassiz Pool is accumulating sediment Agassiz Pool is a trap of incoming sediment (likely a net producer of organic matter; e.g., algae) Pb inventory can be used to estimate total sediment.

11. Ditch 11 Agassiz Pool Total Sediment Accumulated 1938 – 2008 (Agassiz Pool) Agassiz Pool 23,000 tons/yr 1,600,000 tons >1,040,000 tons from off-Refuge inputs Lake Pepin ~700,000 tons/yr

12. Effect of Main Ditch 11 (within Agassiz Pool) Ditch ~49ft. x 9.5ft. x 19,030ft. Ditch 11 Agassiz Pool Sediment density = 1g/cm 3 - Main Ditch 11 is now essentially full within the Pool Holds 260,000 tons of sediment If spread over entire Pool = 3.2 cm deep

13. Effect of Main Ditch 11 (within Agassiz Pool) Ditch ~49ft. x 9.5ft. x 19,030ft. Ditch 11 Agassiz Pool Sediment density = 1g/cm 3 If spread over entire Pool = 3.2 cm deep 3.2 cm may not seem like a lot, but… - As little as 0.25 cm of sediment can significantly reduce total abundance and species richness of plants that emerge from seed banks. - sediment deposition can enhance the growth of certain plant species (i.e., narrowleaf and hybrid cattail) - Less than 0.5 cm of sediment can render aquatic invertebrate egg banks ineffective.

14. Effect of Main Ditch 11 (within Agassiz Pool) Ditch ~49ft. x 9.5ft. x 19,030ft. Ditch 11 Agassiz Pool Sediment density = 1g/cm 3 3.2 cm may not seem like a lot, but… - As little as 0.25 cm of sediment can significantly reduce total abundance and species richness of plants that emerge from seed banks. - sediment deposition can enhance the growth of certain plant species (i.e., narrowleaf and hybrid cattail) - Less than 0.5 cm of sediment can render aquatic invertebrate egg banks ineffective.

15. Pool elev. = 1140.2’Pool elev. = 1140.5’ 1948: 2006: Non-Uniform Filling Based on 210 Pb Inventory from the cores: - Main Pool is filling 1/3 as fast as whole Pool average - Emergent vegetation is expanding - Sediment infilling - assist vegetation expansion

16. Webster Pool Sediment Loading 1938 - 2008 Ditch 11 If whole basin estimate calculated earlier is correct Lake margins, inlet bays, and shallow areas = ~3000 acres 700,000 tons Main Pool ~7000 acres 660,000 tons Ditch 11 260,000 tons

18. 2010 Farm Services Agency Photo (exact date unknown)

19. Main Judicial Ditch 11 – looking east across Agassiz Pool  Constructed in 1910 to a mean depth of 9.5 ft., top width of 59 ft. and bottom width of 40 ft.  2010 – nearly completely filled with sediment the entire length of 3.7 mi (within the Pool)

20. - roughly ¼ mi E. of radial gates 7.77’ deep

21. 0.59’ deep - roughly ½ mi. E. of radial gates

22. 0.13’ deep 2.63 mi E. of radial gates

23. Non-field Erosion Cultivated Field Suspended Sediment Minimal Exposure to Rain Fingerprinting Sediment Sources with 137 Cs (based on studies in Minnesota River Basin) Constant Exposure to Rain 0.38 pCi/g ~0.0 pCi/g Fingerprint Ratio: Field to Non-field

24. Ditch/river input, suspended sample (2009) (avg. of two samples May-June) 0.68 0.47 0.39 0.33 0.52 Agassiz Pool and Incoming River 137 Cs Fingerprint Surface sediment from core 0.35 0.70 0.27 0.46 0.6 0.50 Values = 137 Cs concentration pCi/g Avg (Fingerprint) = 0.47 pCi/g

25. Field Fingerprint ~0.28 - 0.48 pCi/g Agassiz Fingerprint = 0.47 pCi/g Reference fingerprint of Northwestern MN may be different Variable results, difficult to be precise Reminder: >1,040,000 tons of sediment in lake from external sources ~15,000 tons/yr from external sources What do fingerprints tell us about source of sediment? Most importantly Agassiz is shallow and filling with agricultural inputs

26. Summary - Agassiz Pool is filling in - >65% of sediment comes from river/ditch inputs (external) - Ditch 11 is full and holds ~15% of current sediment burden - Margins and inlet areas have “filled” …. rate of infilling in open water areas may now accelerate - Erosion of ag. fields / uplands is dominate sediment source - These processes facilitate expansion of unwanted vegetation (e.g., narrow-leaved cattail)

27. Agassiz Pool Sediment Budget *based on Soil and Water Assessment Tool (SWAT Model) outputs - more coming in than going out - greatest amount of sediment entering from Thief River (versus Mud R.) - estimated that 57% of sediments that enter Agassiz Pool are deposited there. Thief River Watershed Assessment Project - RLWD (a past sediment investigation in the Thief River Watershed estimated ~ 67% of incoming sediment Is deposited)