Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee Debbie Arnwine Water Pollution Control

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)

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

Macroinvertebrate Samples Semi-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

Individual Biometrics

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

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

Precipitation generally at or above 25 year average

Headwater reference sites had adequate flow every season.

Comparison of discharge types

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.

Dominant bed material becomes smaller below impoundments EcoregionReferenceImpounded 65SandSilt 66,67,68, 69Boulder/CobbleGravel 71Bedrock/CobbleGravel 74SandSilt

HABITAT 70% of sites failed overall habitat

Dissolved Oxygen 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.

TEMPERATURE 11% of sites exceeded criteria. 72% above fall reference temps.

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 Manganese 61% of sites above recommended iron criterion of 1000 ug/L 93% of sites above reference levels for manganese

Nutrients 41% exceeded NO2+NO3 criteria at least one season. 75% exceeded total phosphorus criteria at least one season.

Periphyton

Detailed Report (or at the back of the room!) Probabilistic Monitoring of Streams Below Small Impoundments in Tennessee

QUESTIONS? Debbie Arnwine Water Pollution Control