Agassiz National Wildlife Refuge Water Quality Investigation

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22 Φεβ 2014 (πριν από 3 χρόνια και 7 μήνες)

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Agassiz National Wildlife Refuge

Water Quality Investigation

James Graham,

U.S. Fish and Wildlife Service

Grand

Forks

Thief

River

Falls

Thief Lake

Thief River Watershed = TRW

1,077 sq. mi

Agassiz National Wildlife Refuge (USFWS)



26 different impoundments


26, 321 acres


Thief Lake Wildlife Management Area (MN DNR)



Thief Lake


7,100 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


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)

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.

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

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:
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

Coring Sites

Main 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 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

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.

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.

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

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
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

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


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
)