Effects of Growing Season Flow Regime on Stream Periphyton Growth in a Coastal Plain Stream

David Diaz, M.S. Candidate, EcologyAdvisors Dr. Paul V. McCormick, Dr. Alan CovichThesis Defense: September 18th 2015

OutlineBackground: Rationale and site

descriptionPart 1: Influence of discharge and

nutrient availability on periphyton biomass and composition

Part 2: Effects of discharge-grazer interactions on periphyton biomass and composition

Conclusion

Rivers and streamsEcosystem servicesHuman and environmental water

needsEnvironment flows

Environment flowsFlow: Key Driver

*http://projects.inweh.unu.edu/

Lower Flint River BasinAgricultural water withdrawalsDrought

Seasonal flow patterns in a coastal plain stream

Seasonal Hydrograph of Ichauwaynochauway 1970-2015

Algal mats

Flow-periphyton relationshipsEcological importance of

periphytonFlow effects on periphyton

OutlineBackgroundPart 1: Influence of discharge

and nutrient availability on periphyton biomass and composition

Part 2: Effects of discharge and grazer interactions on periphyton biomass and composition

Conclusion

Site

Discharge and nutrients

HypothesesStudy 1: Higher periphyton

accumulation at lower discharge due to reduced shear stress

Study 2: More nutrient limitation at lower discharge.◦Phosphorus is limiting nutrient

Methods- Experimental designStudy 1:

◦5 discharge treatments across 15 channels 3 replicates : L, ML, M, MH, H (20 fold range across

treatments) 4 tiles/channel, 2-3 days for 28 Days Samples processed for AFDM, chl a and other

pigments Study 2:

◦Same discharge treatments Nutrient enrichment : Control, Phosphorus,

Nitrogen + Phosphorus Sampled every 2-3 days for 33 days. Processed for

AFDM, chl a and other pigments

AnalysisBiomass accumulation patterns

modeled using polynomial regression◦Growth rates estimated from linear

coefficients◦Rates compared among treatments using

95% confidence intervals

ANOVA analysis and Tukey’s significance test to compare maximum values of AFDM, chl a and for pigment concentrations.

Results

All models significant at p<.05 level. R^2>

A A

A A

B

4 7 11 14 18 21 25 280

500

1000

1500

2000

2500LMLMMHH

Day

AI R

atio

*

*

*

* = Statistically Significant

Autotrophic Ratio= AFDM/chl a

*

*

*

*

*

*

Total Pigments

Diatoms

Green Algae

Pigm

ent

Conc

entra

tion

(nm

ol/c

m2 )

Pigm

ent

Conc

entra

tion

(nm

ol/c

m2 )

Pigm

ent

Conc

entra

tion

(nm

ol/c

m2 )

Day

Day

Day

*

*

*

*

Flow :0159*Nutrients.084

Control P N+P0

0.51

1.52

2.53

3.54

Pig

men

t con

cent

ratio

n(n

mol

/cm

2)

Diatoms

Control P N+P0

5

10

15

20

25

30

35

Pig

men

t con

cent

ratio

n(n

mol

/cm

2)

Control P N+P0

5

10

15

20

25

30

35

HMHMMLL

Control P N+P0

0.51

1.52

2.53

3.54

HMHMMLL

Control P N+P0

0.10.20.30.40.50.60.70.80.9

Pig

men

t con

cent

ratio

n(n

mol

/cm

2)

Green Algae

Control P N+P0

0.10.20.30.40.50.60.70.80.9

HMHMMLL

Total Pigments

Day 4

Day 4

Day 4 Day 33

Day 33

Day 33

Part l SummaryGreater accumulation of AFDM

(higher AI ratio) at higher discharge

Diatom dominance in all treatments. Higher relative abundance of green algae in lower treatments

Nutrient enrichment effect greatest at higher discharges

BackgroundPart 1: Influence of discharge and

nutrient availability on periphyton biomass and composition

Part 2: Effects of discharge and grazer interactions on periphyton biomass and composition

Conclusion

Periphyton-Grazer Interactions

HypothesisSnail grazers can limit periphyton

biomass under a range of periphyton growth conditions related to discharge.

MethodsMarked and weighed snails

◦Used similar ambient density for treatments

3x2 factorial design. 3 discharge treatments (L,M,H)and 2 grazer treatments.

AnalysisAccumulation patterns modeled using

polynomial regression◦Average growth rates estimated from

linear coefficients◦Rates compared among treatments using

95% confidence intervals2-way ANOVA and Tukey’s significance

test used to compare maximum values of AFDM, chl a and for pigment concentrations.

Snail growth

Results

*

*

*

** *

* *

AI RATIOS

L M H0

5

10

15

20

25

30

Un-grazedGrazed

Pigm

ent c

once

ntra

-tio

n (n

mol

/cm

2)

Total Pigments

Day 4

L M H02468

1012

Un-grazedGrazed

Pigm

ent c

once

ntra

-tio

n (n

mol

/cm

2)

Diatoms Day 4

L M H0

0.20.40.60.8

11.21.41.61.8

UngrazedGrazed

Pigm

ent c

once

ntra

-tio

n (n

mol

/cm

2)

Green Algae Day 4

L M H0

5

10

15

20

25 Total Pig-ments

Day 33

*Grz=.011*Dch=.008*Grz x Dch= .045*

L M H0123456789

10 Diatoms Day 33

*

Grz=.011*Dch= .025*Grz x Dch=.073

L M H0

0.20.40.60.8

11.21.4 Green Algae Day 33

* *

Grz=.582*Dch=.152*Grz x Dch=.464

Part ll SummaryAFDM and chl a pigment

concentrations increased with discharge. Diatom dominance in all discharge treatments.

Grazers had greater effect at higher discharges

Snail growth rate decreased with higher discharge

ConclusionRapid periphyton accumulation potential

during the summer growing season◦High light availability◦Stable flow regime

Local flow conditions control periphyton patterns◦Accumulation rates and maximum biomass◦Mat heterotrophy◦Taxonomic composition

Grazers exert limited control over periphyton

ImplicationsClimate Change: Drought duration

and frequency influence stream primary production

Human water Use: Changes in instream flows affect periphyton spatial patterns

Lower flow conditions may become more common in the future

Food web dynamics

Acknowledgements• Special thanks to Dr. McCormick and

Dr. Covich• Jones Center Staff and Students• Chelsea Smith, J.R Bolton, Steve

Shivers• Committee- Dr. Steve Golladay, Dr.

Mary Freeman, Dr. Susan Wilde• Dr. Matt Waters

Questions

QUESTIONS?