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Gregg Knutsen, Wildl ife Biologist - Agassiz NWR

Agass iz Nat ional Wi ld l i fe Refuge

- Wat er Qual i t y Over v iew -

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1948: 10 years after creation 2006: 66 years after creation

Change Over Time

Pool elev. = 1140.2 Pool elev. = 1140.5

Agassiz Pool ~ 10,000 acres

Sediment deltas forming

Emergent vegetation (largely cattail) is expanding- assisted by sediment infilling

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Cattail monocultures have low wildlife value and often indicate degraded wetlands.

Cattail management is one of the primary challenges in managing wildlife impoundments.

Many of Agassizs pools are either dense monotypic stands

of cattail, or75% cattail covered.

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Elevated nutrient loads (nitrogen, phosphorus)

Reduced maximum water depth due to sediment deposition- promotes cattail colonization via vegetative reproduction- reduces effectiveness of cattail management actions (flooding outcattails)

Introduction of exotic narrow-leaved cattail and establishment of hybrid cattail- both are invasive

Cattail Monocultures Why Do They Occur?

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Ditch 11

Agassiz Pool

Total Sediment Accumulated 1940 2008(based on 210Pb inventory)

210Pb inventory can be usedto estimate whole-pool sediment

burden and distr ibution

1,318,364 tons fromoff-Refuge inputs

(inorganic 65%)

~ 19,000 tons / year

AgassizPool

2,028,252tons

Field-eroded sediments arethe primary contributor to

Agassiz NWR infilling

http://www.smm.org/scwrs

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May 2006 CIR Image

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Main Ditch 11 looking east across Agassiz Pool

Constructed in 1910 to a mean depth of 9.5ft, top width of 59ft, and bottom width of 40ft

2013 nearly completely filled with sediment the entire length of 3.7 mi (within the Pool)

~260,000tonsofsedimentinditch

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Radial Gates

c

Agass iz PoolN LIDARPROFILEOFMAINDITCH11

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AgassizPoolModeledSedimentBudget

Letsusknowwhere

ourmainproblem

areasarelocated.

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U.S.GeologicalSurveyconductedawaterqualityassessmentof

AgassizNWRfrom20082010.

KEYFINDINGS:

Continuousmonitoring

of

Refuge

inflow and

outflow sites

concentrationsofunionizedammoniaDIDNOTEXCEED theMNwaterqualitystandard

MNwaterqualitystandardswereREGULARLYMETfordissolvedoxygenandpH

nitrateplusnitriteconcentrationswereLOWER atOUTFLOWsitesvs.inflowsites

likely

due

to

denitrification and

plant

uptake nitrogenlevelsdidnotexceedMNdrinkingwaterstandard

phosphorus levelsDIDNOTexceedMNsecoregionbasedwaterqualitystandards

Branch

1(JD

11)

had

signif.

greater

concentrations

of

total

phosphorus

andorthophosphorus thananyothersite

Waterqualitystandardsareforstreams notwetlands.

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U.S.GeologicalSurveyconductedawaterqualityassessmentof

AgassizNWRfrom20082010.

KEYFINDINGS:

Continuous

monitoring

of

Refuge

inflow and

outflow sites

Duringthe3yearstudy,anestimatedNETLOSSofsedimentfromAgassizPool

Likelyrelated

to

multiple

factors:

NewAgassizPooloutletstructure(2008)

drawdownofAgassizPoolinOct.2009 2010(firstsince2000)

baredirtdikesalongDitch11outletduetoconstruction(20082010)

Poolalready

heavily

laden

with

inorganic

sediments

EstimatedannualsedimentinputstotheRefugefrom20082010werealsomuch

lessthanthoseestimated from19402008

~19,000tons/year(19402008)

maximumof4,362tons/year(20082010)

Largedifferenceisanunknown,butmayhavemultipleexplanations..

Currently140,000

ac

of

CRP

in

Marshall

Co.

muchofwhichhasbeenenrolledsincelate1980s

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Muchhasbeenlearned,butstillmanyunknowns.

Refuge

impoundments

function

as

atrap

for

sediments

and

nutrients

wetlandhabitatdegradationresults

Refugemanagementhastheabilitytopassincomingsedimentsdownstream

andflush

previously

deposited

sediment

Whatistheratioofinorganic:organicsedimentthatexitsAgassizPool?

Targetedwaterqualitymonitoringwillcontinue(2013andbeyond)

occurred

at

inflow

sites

(2),

outlflow sites

(2),

and

within

Agassiz

Pool

(2012)

Sept.2012datashowthat6071%ofsuspendedsedimentatoutflowsites

isinorganic(notproducedinthePool) suggeststhatpreviously

depositedsedimentsarebeingflushedfromthePool

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Nonfield

Erosion

CultivatedField

SuspendedSediment

Minimal Exposureto Rain

FingerprintingSedimentSourceswith137Cs(basedonstudiesinMinnesotaRiverBasin)

ConstantExposure

to

Rain

0.38 (+/-0.32) pCi/g

~ 0.0 pCi/g

Fingerprint

Ratio: Field to

Non-field

http://www.smm.org/scwrs

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MN River Basin

Field Fingerprint ~ 0.38pCi/g

Non-Field ~ 0pCi/g

Agassiz Fingerprint = 0.50pCi/g

Reference fingerprint of Northern MN may be different

Reminder: 1.3 mil lion tons of sediment in pool from external sources

0.50 / 0.38 = 130% from field ???

What do fingerprints tell us about source of sediment?

Reference fingerprint of Northern MN may be differentVariable results, difficult to be precise

Field-eroded sediments arethe primary contributor to

Agassiz NWR infilling

http://www.smm.org/scwrs