The Ecological Engineering GroupBiological and Agricultural EngineeringUniversity of Arkansas

Algal Growth with Nutrient LimitationCompared to Light-Limiting Conditions in Ozark Streams

Andrea LudwigMarty Matlock, PhD, PE, CSEBrian Haggard, PhDBob Morgan, PE

EPA use attainability study

Research Goals

Identify a nutrient, periphytic chlorophyll-a relationship in Ozark streamsInvestigate circumstances of light-limitation to native algaePredict response of algal growth to differentiating canopy covers in the presence of variable nutrients

MethodologyMatlock periphytometers deployed at all sites

Chlorophyll-a used as indicator of abundance of algae

• Chlorophyll-a analysis done using trichromatic methods

Grab samples collected at each site and analyzed for nutrient concentrations

Light meters attached to Matlock periphytometers at selected sitesSite Selection

Coupled sites according to locations of WWTPs

Site Selection

The Matlock PeriphytometerAssembly

NutrientNutrientSolutionSolution

Lid w/ holeLid w/ holeGlass fiber filterGlass fiber filter

0.450.45 mm Nylon MembraneNylon Membrane

1 liter bottle1 liter bottle

NutrientSolution

Nutrients passivelydiffuse throughnylon membraneand GFF

FlowFlow

The Matlock PeriphytometerIn the field

Target PO4-P Level

0

25

50

75

Annual - average PO4-P (ppb)

An

nu

al -

av

erag

e ch

l a (

ug

/L)

0 100 200 300 400 500

Methodology

2-day and 14-day deployments of light meters

Sites chosen with comparison of light availability as single variable

Canopy cover used as indicator

MethodologyHardware

HOBO Micro StationSensed temperature and photosynthetic active radiation (PAR)

• Reading every 5 sec• Logged every 10 min

SoftwareBoxcarPro

ResultsOrtho Phosphate concentration to Chl-a

Relationshilp

y = 0.2545x + 0.4768

R2 = 0.069

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5

Average Ortho Phosphate

Ave

rag

e C

hl-

a

• Phosphorous concentrations only account for 7% of variability of chlorophyll-a across sites

Results Fourteen- and Two-Day Deployments

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0.0 100.0 200.0 300.0 400.0 500.0

Average PAR (uE)

Chl

orop

hyll

a (u

g/cm

2)

OSG030

SPG931UP

SPG931UP

SPG931DN

OSG930UP

OSG930DN

OSG045UP

OSG045DN

Site Avg Temp C

Avg PAR uE

Chlr a ug/cm2

OSG030 16.2 294.0 0.43

SPG931UP 16.4 133.1 0.06

SPG931UP 16.6 49.8 0.16

SPG931DN 21.2 30.3 1.88

OSG930UP 15.9 96.2 0.11

OSG930DN 17.5 468.2 0.11

OSG045UP 17.8 343.1 1.47

OSG045DN 17.4 68.9 0.31

• Two-day deployments of light meters provided inaccurate representation of average light availabilityto periphytometer

Results2-day deployments failed to give good representation of light conditions at sites

14-day deployments logged definite diurnal cycles and more data points

14-Day Deployment - SPG931UP

0

5

10

15

20

25

Day

Tem

pera

ture

C

0

200

400

600

800

1000

1200

1400

1600

PA

R u

E

Temp

PAR

14-Day Deployment - OSG030

0

5

10

15

20

25

Day

Tem

pera

ture

C

0

200

400

600

800

1000

1200

1400

1600

PA

R u

E

Temp

PAR

• Due to time restrictions, only one round of 14-day deployments were completed

ResultsFourteen-Day Deployments

00.05

0.10.15

0.20.25

0.30.35

0.40.45

0.5

0.0 100.0 200.0 300.0 400.0

Average PAR (uE)

Ch

loro

ph

yll

a (

ug

/cm

2)

OSG030

SPG931UP

Summary

Nutrient concentrations do affect algal growth

However, when nutrients are high and light is low, algal growth becomes light limited at very low production levels

Riparian zone management is critical for protecting nutrient enriched streams

Future Work / ImprovementsAdditional study of nutrient-limited situations in Ozark streamsRemoving any variability of nutrients in sites

Deployment of light meters and Matlock periphytometers at same site with different canopy covers

Defining a relationship of chlorophyll-a and nutrient concentrations with a second variable of light

Multiple light meter couples at sites with multiple nutrient and canopy characteristics

Acknowledgements

Eric CummingsBrian SchafferMatt BrutonDebrata SahooSujit EkkaKyle Kruger