Agassiz National Wildlife RefugeWater Quality Investigation

James Graham,U.S. Fish and Wildlife Service

GrandForks

Thief RiverFalls

Thief Lake

Thief River Watershed = TRW1,077 sq. mi

Agassiz National Wildlife Refuge (USFWS)

26 different impoundments – 26, 321 acres

Thief Lake Wildlife Management Area (MN DNR)

Thief Lake – 7,100 acres11 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 = 10,810Thief River Falls Wildlife Area Office (MN DNR)

Eckvoll – 1,750 acresLost River Pool – 2,300 acresFarmes 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

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 migratingand breeding birds. Management will be within the capabilities of the wetland system as a whole…

Agassiz NWR Comprehensive Conservation Plan (2005)

Present Conditions

Thief River upstream of Agassiz NWR drains ~ 350 mi2 north and east of the Refuge.

Mud River drains ~ 160 mi2 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.

Agassiz National Wildlife Refuge Agassiz National Wildlife Refuge Water Quality ProjectWater Quality Project

Rochelle Nustad, USGS, Grand Forks, NDRochelle Nustad, USGS, Grand Forks, ND

Data Collection: 2008 - 2010

Results coming. Analysis in progress. Final report – summer(?) 2011

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

Sediment Dating & Fingerprinting Radioisotopes: 210Pb ,137Cs

137Cs: Bomb testing product,- Marker for 1963- Fingerprint of field erosion

210Pb: Natural, constant “fallout” - Dating tool back 150 years

- Fingerprint of field erosion

210Pb137Cs

decay

Coring SitesMain Ditch 11

Thief River Inlet

Agassiz Pool

Sediment Cores: An Archive of Erosion History

October 2008

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.

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

Effect of Main Ditch 11 (within Agassiz Pool)

Ditch~49ft. x 9.5ft. x 19,030ft.

Ditch 11Agassiz Pool

Sediment density = 1g/cm3

- 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

Effect of Main Ditch 11 (within Agassiz Pool)

Ditch~49ft. x 9.5ft. x 19,030ft.

Ditch 11Agassiz Pool

Sediment density = 1g/cm3

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.

Effect of Main Ditch 11 (within Agassiz Pool)

Ditch~49ft. x 9.5ft. x 19,030ft.

Ditch 11Agassiz Pool

Sediment density = 1g/cm3

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.

Pool elev. = 1140.2’ Pool elev. = 1140.5’

1948: 2006:

Non-Uniform Filling

Based on 210Pb 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

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

2010 Farm Services Agency Photo (exact date unknown)

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)

- roughly ¼ mi E. of radial gates

7.77’ deep

0.59’ deep

- roughly ½ mi. E. of radial gates

0.13’ deep

2.63 mi E. of radial gates

Non-field Erosion

Cultivated Field

Suspended Sediment

Minimal Exposure to Rain

Fingerprinting Sediment Sources with 137Cs (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

Ditch/river input, suspended sample (2009)(avg. of two samples May-June)

0.68 0.470.39

0.330.52

Agassiz Pool and Incoming River 137Cs Fingerprint

Surface sediment from core

0.35

0.70

0.27

0.460.6

0.50

Values = 137Cs concentration pCi/g

Avg (Fingerprint) = 0.47 pCi/g

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

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)

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)