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?