Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee Debbie Arnwine Water Pollution Control 615-532-0703 Debbie.Arnwine@tn.gov.

Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee

Debbie ArnwineWater Pollution Control615-532-0703Debbie.Arnwine@tn.gov

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

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)

Site Selection

Random Selection

75 impounded streams

< 250 acres

Perennial stream with sufficient flow (during recon) to provide macroinver-tebrate habitat.

Suitable habitat to use TDEC’s semi-quantitative protocols

Rooted Bank Habitat

Riffle Kicks

Comparable bioregion and size to existing reference streams or project-specific

reference

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.

One upstream site was suitable.

Minimum observable impacts not associated with impoundment

Impoundments built for agricultural purposes were included.

Livestock pens built on dam.

Accessible

Site reconnaissance(200 recons to get 75 sites)

Other2%

No impound-ment4%

No comparable reference

1%

Insufficient habitat

6%

Intermittent7%

No access11%

No flow32%

Suitable37%

Site Characterization• Impounded 1960 - 1980 (50%)• Surface Discharge (69%)• Forested Drainage Area (77%)• 2nd Order Stream (53%)• < 50 acres (70%)

Macroinvertebrate SamplesSemi-quantitative Single Habitat Spring and Fall

Tennessee Macroinvertebrate Index (TMI)• Taxa Richness• EPT Richness• %EPT• %OC• NCBI• %Dominant• %Clingers• Ky % Nutrient Tolerant

95% Failed to Meet Biocriteria

Failed Spring and Fall

77%

Passed Spring and Fall

5%

Failed Spring only11%

Failed Fall only4%

Uncertain3%

Individual Biometrics

010

2030

405060

708090

100

Per

cent

fai

l

TR

EP

T

%E

PT

%O

C

NC

BI

%D

OM

%C

LIN

G

%N

UT

OL

Biometric

Dominant taxa indicative of nutrients and/or sluggish flow

Fall: Dominant = Cheumatopsyche and Glyptotendipes spp.

Spring: Dominant = Lirceus, Parametriocnemus and Polypedilum spp.

Example of biological data pre and post impoundment

13

3

9

00

2

4

6

8

10

12

14

Nu

mb

er o

f T

axa

EPT Taxa Intolerant Taxa

1997 Pre-impoundment 2003 Post-impoundment

FLOW

52% insufficient flow to sustain aquatic life at least one season (25% dry).

Precipitation generally at or above 25 year averageBristol Airport

0

2

4

6

8

10

12

Month

Inch

es

Avg precip. 1978 - 2002

Precip. 2003 - 2004

Headwater reference sites had adequate flow every season.

Comparison of discharge types

Standpipe Spillway Subsurface Multiple0

10

20

30

40

50

60

70

80

90

100

% M

aint

ain

flow

Geomorphology

49% relative stable channels typical of ecoregion

24% “G-type” –deeply entrenched, unstable banks, heavy sediment loads

20% E-Type in response to lack of flow. Small channel cut within original stream bed.

Original Channel

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30

Distance (feet)

Ele

vatio

n (fe

et) C

alcu

late

d

Incised Channel

D50 = Bedrock

Dominant bed material becomes smaller below impoundments

Ecoregion Reference Impounded65 Sand Silt66 ,67,68, 69 Boulder/Cobble Gravel71 Bedrock/Cobble Gravel74 Sand Silt

HABITAT70% of sites failed overall habitat

Sedim

ent

Sinuosit

y

Bank Vegetation

Bank Stabilit

y

Pool Varia

bility

Embeddedness

Epifaunal S

ubstrate

Velocity/

Depth

Riparian

Riffle Fr

equency0

102030405060708090

100

Perc

ent F

ailin

g re

gion

al g

uide

lines

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

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.

TEMPERATURE11% of sites exceeded criteria.

72% above fall reference temps.

24

68

1012

1416

1820

2224

65

e

66

d

66

e

66

g

67

g

67

h

68

a

68

c

71

f

71

g

71

h

74

a

74

b

TestRefEcoregion

Tem

p (

C)

pH

5% of sites had low pH

Suspended Solids

50% of sites had elevated suspended solids.

Land use associated with small impoundments contributes to the problem.

Iron and Manganese61% of sites above recommended iron criterion of 1000 ug/L

93% of sites above reference levels for manganese

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.

Periphyton

Excessive Macroalgae

20%

Dry6%

Excessive Microalgae

31%

Natural Algae Density

43%

Detailed Reporthttp://www.tn.gov/environment/wpc/publications/

(or at the back of the room!)

Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee

QUESTIONS?

Debbie ArnwineWater Pollution Control615-532-0703Debbie.Arnwine@tn.gov

www.tn.gov/environment/wpc/publications/