Reservoir and Lake Nutrient Criteria

A Different ApproachA Different Approach

D.V. Obrecht, J.R. Jones & M.K. Knowlton – MU Limnology

UMBRELLA APPROACH

1) Reference reservoirs and lakes – 75th percentile

2) All reservoirs and lakes – 25th percentile

3) EPA’s 304(a) criteria

Oxbow lakes (n=12)

TP = 212 ug/L

TN = 1.56 mg/L

Reservoirs (n=135)

TP = 45 ug/L

TN = 0.73 mg/L

Reservoir TP (µg/L) range of geomeans

Maysville (n=10) 182 116 – 300

Grindstone (n=5) 147 90 - 218

Unionville (n=10) 98 68 - 155

Long Branch (n=20) 48 30 - 115

Viking (n=16) 26 19 - 40

Forest (n=19) 23 14 - 44

STEP APPROACH

Designated Use

Impairment of use

Algal biomass

Nutrient levels

Criteria level

Drinking Water Supply

Impairments

-taste and odor

-clogging of filters

-algal toxins

There may be too many factors that influence water quality and too much variability within and among systems to allow for the setting of a single set of criteria to be used by

the state for regulation.

EPA allows some flexibility:

…(states can) develop their own criteria which reflect more locally representative conditions.

…prioritize their waters…..Such an approach should include a mechanism for evaluating the sensitivity of all waters…considering current and expected land use…

EPA memorandum, Nov. 14, 2001

A Different Approach!

A lake is a reflection of its watershed.

0 5 20 40 60 80

100

200

5

10

5

r = 0.622

25

50

Cropland (%)

To

tal

Ph

osp

ho

rus

(µg

/L)

A reservoir is also a reflection of its watershed,

and the intensity of that reflection is dictated by

hydrology.

Regression model resultsEquation r2

TP = 4.27 + 0.36 %crop 0.62

TP = 5.53 + 0.33 %crop – 0.50DH 0.73

TP = 5.20 + 0.35crop% - 0.37 DH + 0.12 FI 0.77

DH is dam height, a surrogate from reservoir morphology

FI is flushing index

Volume 100

outflow 100

outflow 200

inflow 100

inflow 50

inflow 200

Volume / Inflow = Residence Time (years)

outflow 50

Volume 100

Volume 100

RT = 2 years

RT = 1 years

RT = .5 years

1 3 5 7 9

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

= TP < 20 g/L

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

= TP 20 - 50 g/L

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

= TP 50 - 75 g/L

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

= TP 75 - 100 g/L

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

= TP > 100 g/L

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

Proportion crop

Short Res. Time

Med. Res. Time

Long Res. Time

> 40%

20 – 40%

10 – 20%

1 – 10%

< 1%

Proportion crop

Short Res. Time

Med. Res. Time

Long Res. Time

> 40% 116 ug/L 75 ug/L 47ug/L

20 – 40% 97 ug/L 80 ug/L 53 ug/L

10 – 20% 59 ug/L 54 ug/L 33 ug/L

1 – 10% 40 ug/L 27 ug/L

< 1% 17 ug/L

Residence Time (months)

0

50

100

150

To

tal

Ph

osp

ho

rus

(ug

/L)

>12 6-12 <6

>40% 20% - 40% 10% - 20% 4% - 10% crop =

>10 >106-10 6-10<6 <6 <2>2

Can we use agriculture to classify reservoirs?

Can we use agriculture to classify reservoirs?

USGS photo

Reservoirs were built into landscapes that had already been altered.

No Restoration

Water quality in a reservoir is a function of morphology/hydrology and location within the landscape.

7,600 – 34,000 ac

34,000 – 58,000 ac

58,000 – 87,000 ac

87,000 – 169,000 ac

Harvested acres of corn, 1920

30 counties

26 counties

36 counties

22 countiesBetween 11% and 21% of total Missouri land surface dedicated to just corn production in 1920!

Missouri’s reservoirs >10 acres in sizeYear completed # %

1800-1920 122 8

1920-1940 267 18

1940-1960 68 5

1960-1980 909 61

1980-1995 121 8

0 1 2 3 4

Residence Time (years)

0.0

0.2

0.4

0.6

0.8

Cro

p L

and

Use

(p

rop

ort

ion

wat

ersh

ed)

Protect

Improvements possible

Limited potential

This approach allows the state to:

-Identify and protect the reservoirs that have low watershed impacts.

-Identify and focus efforts on the reservoirs that have higher nutrient concentration than expected, given watershed land use and hydrology.

-Gauge the potential for successful nutrient reduction by looking at the factors that control in-reservoir nutrient concentrations. And focus limited resources ($$) on those reservoirs where improvements can be made.