Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee
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Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee
Debbie ArnwineWater Pollution [email protected]
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2003 probabilistic study of 75 streams downstream of small impoundments• Macroinvertebrates• Nutrients• Dissolved Oxygen• Temperature• pH• Suspended Solids• Iron and manganese• Habitat• Flow and morphology• Periphyton Density
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Over 195,000 small man-made lakes and ponds in Tennessee
1,302 recorded in databases
Potential for public access (safe dams)Built after 1992 (ARAP)
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Site Selection
Random Selection
75 impounded streams
< 250 acres
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Perennial stream with sufficient flow (during recon) to provide macroinver-tebrate habitat.
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Suitable habitat to use TDEC’s semi-quantitative protocols
Rooted Bank Habitat
Riffle Kicks
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Comparable bioregion and size to existing reference streams or project-specific
reference
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Upstream Reference not Feasible
• Impoundment flooded entire headwaters
• Second impoundment immediately upstream
• Drainage area upstream not 80% within same bioregion.
• Stream size too small upstream of impoundment.
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One upstream site was suitable.
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Minimum observable impacts not associated with impoundment
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Impoundments built for agricultural purposes were included.
Livestock pens built on dam.
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Accessible
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Site reconnaissance(200 recons to get 75 sites)
Other2%
No impound-ment4%
No comparable reference
1%
Insufficient habitat
6%Intermittent
7%
No access11%
No flow32%
Suitable37%
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Site Characterization• Impounded 1960 - 1980 (50%)• Surface Discharge (69%)• Forested Drainage Area (77%)• 2nd Order Stream (53%)• < 50 acres (70%)
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Macroinvertebrate SamplesSemi-quantitative Single Habitat Spring and Fall
Tennessee Macroinvertebrate Index (TMI)• Taxa Richness• EPT Richness• %EPT• %OC• NCBI• %Dominant• %Clingers• Ky % Nutrient Tolerant
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95% Failed to Meet Biocriteria
Failed Spring and Fall
77%
Passed Spring and Fall
5%
Failed Spring only11%
Failed Fall only4%
Uncertain3%
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Individual Biometrics
0102030405060708090
100Pe
rcen
t fai
l
TR EPT
%EP
T
%O
C
NC
BI
%D
OM
%C
LIN
G
%N
UTO
L
Biometric
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Dominant taxa indicative of nutrients and/or sluggish flow
Fall: Dominant = Cheumatopsyche and Glyptotendipes spp.
Spring: Dominant = Lirceus, Parametriocnemus and Polypedilum spp.
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Example of biological data pre and post impoundment
13
3
9
00
2
4
6
8
10
12
14
Num
ber
of T
axa
EPT Taxa Intolerant Taxa
1997 Pre-impoundment 2003 Post-impoundment
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FLOW
52% insufficient flow to sustain aquatic life at least one season (25% dry).
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Precipitation generally at or above 25 year averageBristol Airport
0
2
4
6
8
10
12
Month
Inch
es
Avg precip. 1978 - 2002Precip. 2003 - 2004
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Headwater reference sites had adequate flow every season.
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Comparison of discharge types
Standpipe Spillway Subsurface Multiple0
10
20
30
40
50
60
70
80
90
100
% M
aint
ain
flow
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Geomorphology
49% relative stable channels typical of ecoregion
24% “G-type” –deeply entrenched, unstable banks, heavy sediment loads
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20% E-Type in response to lack of flow. Small channel cut within original stream bed.
Original Channel
00.20.40.60.8
11.21.41.6
0 5 10 15 20 25 30Distance (feet)
Ele
vatio
n (fe
et) C
alcu
late
d
Incised Channel
D50 = Bedrock
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Dominant bed material becomes smaller below impoundments
Ecoregion Reference Impounded65 Sand Silt66 ,67,68, 69 Boulder/Cobble Gravel71 Bedrock/Cobble Gravel74 Sand Silt
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HABITAT70% of sites failed overall habitat
Sedim
ent
Sinuosit
y
Bank Vegetation
Bank Stabilit
y
Pool Varia
bility
Embeddedness
Epifaunal S
ubstrate
Velocity/D
epth
Riparian
Riffle Fr
equency0
102030405060708090
100
Perc
ent F
ailin
g re
gion
al g
uide
lines
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Dissolved Oxygen
Fail 5 mg/L21%
Fail trout streams
3%
Fail Blue Ridge
3%Fail NRTS
1%
Pass DO Criteria
72%Based on instantaneous day time measurement
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DO Measurements do not tell the whole story.
• Instantaneous measurement during daylight hours.
• Presence of algae at most sites indicates possible large diurnal swings.
• 17% of sites supersaturated.• Percent saturation at 77% of sites below 10th percentile of reference data.
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TEMPERATURE11% of sites exceeded criteria.
72% above fall reference temps.
2468
1012141618202224
65e
66d
66e
66g
67g
67h
68a
68c
71f
71g
71h
74a
74b
TestRefEcoregion
Tem
p (C
)
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pH
5% of sites had low pH
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Suspended Solids
50% of sites had elevated suspended solids.
Land use associated with small impoundments contributes to the problem.
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Iron and Manganese61% of sites above recommended iron criterion of 1000 ug/L
93% of sites above reference levels for manganese
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Nutrients
NO2+NO3 TP Both05
101520253035404550
FallWinterSpringSummer
% e
xcee
d cr
iteria
41% exceeded NO2+NO3 criteria at least one season.
75% exceeded total phosphorus criteria at least one season.
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Periphyton
Excessive Macroalgae
20%
Dry6%
Excessive Microalgae
31%
Natural Algae Density
43%
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Detailed Reporthttp://www.tn.gov/environment/wpc/publications/
(or at the back of the room!)
Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee