Nitrogen Fixation in Seagrass Bed Sediments Dominated by Thalassia testudinum and Halodule wrightii
Rachel Capps Center for Environmental Diagnostics and Bioremediation University of West Florida, Pensacola, Florida
Thrope, et al. 1997
Seagrass Species Present in PBS Benefits of Seagrass Beds
Ecological Services Human Services • Nursery grounds • Storm buffering • Foraging grounds • Prevent erosion • Biodiversity • Decreased turbidity • Sediment stabilization • Commercial fisheries • Carbon sequestration • Recreational fisheries • Biogeochemical cycling Benefits of Seagrass Beds
Ecological Services Human Services • Nursery grounds • Storm buffering • Foraging grounds • Prevent erosion • Biodiversity • Decreased turbidity • Sediment stabilization • Commercial fisheries • Carbon sequestration • Recreational fisheries • Biogeochemical cycling Benefits of Seagrass Beds
Ecological Services Human Services • Nursery grounds • Storm buffering • Foraging grounds • Prevent erosion • Biodiversity • Decreased turbidity • Sediment stabilization • Recreational fisheries • Carbon sequestration • Commercial fisheries • Biogeochemical cycling • Recreational activities 95% loss of seagrasses 1950-1980
Lewis et al. 2008 Factors that affect seagrass health
• Light attenuation • Sulfide toxicity • Water depth • 300µM affects growth • Turbidity • 2,000µM kills • Plankton productivity • Nutrients • Epiphyte • Water column: nitrate, • Macroalgae ammonium, and • Temperature phosphate • Porewater: ammonium • Salinity and phosphate • Grazing • Disease Factors that affect seagrass health
• Light attenuation • Sulfide toxicity • Water depth • 300µM affects growth • Turbidity • 2,000µM kills • Plankton productivity • Nutrients • Epiphyte • Water column: nitrate, • Macroalgae ammonium, and • Temperature phosphate • Porewater: ammonium • Salinity and phosphate • Grazing • Disease Study Site
• Little anthropogenic pressure • Dominated by T.testudinum and H. wrightii Light, Temperature, and Salinity
• 58.7 – 72.6 % SI • 10.0 – 26.9°C • 12.4 – 28.9 PSU Sulfide Toxicity
2500
) Sulfide Toxicity M
µ 2000 ( n o i t
a Sep-15 r 1500 t n Nov-15 e c n Jan-16 o
C 1000
e Feb-16 d i f l Mar-16 u S
500 n Apr-16 e g o r d 0 y
H Thalassia Halodule wrightii Bare testudinum -500 Nutrients Porewater Nitrogen to Phosphorus Ratios 3.5
) 3 P I D (
e t a
) 2.5 h M p s µ ( o
h n 2 P o
i t c i a n r t a n g
r 1.5 e c o n n I
o d C
e 1 v l o
* s s i
D 0.5 * 0 0 10 20 30 40 50 *Atkinson and Smith Ammonium Concentration (µM) 1983 Nutrients Porewater Nitrogen to Phosphorus Ratios 3.5 Water Column
) 3 P I D
( Nutrient Concentrations
e t a
) 2.5 h M p s µ ( o
h n 2 P o
i t c i a n r t a n g
r 1.5 e c o n n I
o d C
e 1 v l o
* s s i
D 0.5 * 0 0 10 20 30 40 50 *Atkinson and Smith Ammonium Concentration (µM) 1983 Nutrients Porewater Nitrogen to Phosphorus Ratios 3.5
) 3 P
I N-limitation D (
e t a
) 2.5 h M p s µ ( o
h n 2 P o
i t c i a n r t a n g
r 1.5 e c o n n I
o d C
e 1 v l o
* s s i
D 0.5 * P-limitation 0 0 10 20 30 40 50 *Atkinson and Smith Ammonium Concentration (µM) 1983 The Nitrogen Cycle
Valence Remineralization -3 Organic N + NH4
N fixation nitrification
anaerobic ammonium oxidation ammonium N 2 oxidation 0
nitrous oxide N O reduction 2 dissimilatory +1 nitrate - - nitrite NO2 NO2 reduction reduction +3
nitrate - nitrite NO3 +5 denitrification reduction oxidation The Nitrogen Cycle
Valence Remineralization -3 Organic N + NH4
N fixation nitrification
anaerobic ammonium oxidation ammonium N 2 oxidation 0
nitrous oxide N O reduction 2 dissimilatory +1 nitrate - - nitrite NO2 NO2 reduction reduction +3
nitrate - nitrite NO3 +5 denitrification reduction oxidation Nitrogen Fixation in Seagrass Beds
water column
oxic sediment layer
anoxic sediment layer Nitrogen Fixation in Seagrass Beds
leaves
water column
oxic sediment layer
sediment anoxic sediment layer Nitrogen Fixation Rates
400 A 350 ) d / 2 m
/ 300 2 N
l o
m 250 A
µ (
e t
a 200 R
n o i t
a 150 x i F
n e
g 100 o r t i B N 50
0 Thalassia testudinum Halodule wrightii Bare Nitrogen Fixation Rates
700 B 600 ) d / 2
m 500 / 2 N
l A o 400 m
µ (
Sep-15 e t
a 300 Nov-15 R
n
o Jan-16 i t
a A
x 200 i
F A
n A A
e A g
o 100 AB r t i N B 0 Thalassia testudinum Halodule wrightii Bare -100 Nitrogen Fixation & Ammonium
700
) 600 d / 2 m
/ 500 2 N
l o m
400 µ (
e t
a 300 R
n o i t
a 200 x i F
n e
g 100 o r t i N 0 0 5 10 15 20 25 -100 Porewater Ammonium Concentration (µM) Nitrogen Fixation & Ammonium
700
) 600 d / 2
m R = - 0.428 / 500 2 N
l o m
400 µ (
e t
a 300 R
n o i t
a 200 x i F
n e
g 100 o r t i N 0 0 5 10 15 20 25 -100 Porewater Ammonium Concentration (µM) Nitrogen Fixation & Sulfide Conc.
700
) 600 d / 2 m /
2 500 N l o m
400 µ ( e t a 300 R n o i t a 200 x i F n e 100 g o r t i
N 0 0 50 100 150 200 250 300 350 400 -100 Porewater Hydrogen Sulfide Concentration (µM) Nitrogen Fixation & Sulfide Conc.
700
) 600 d / 2 m /
2 500
N R = 0.626 l o m
400 µ ( e t a 300 R n o i t a 200 x i F n e 100 g o r t i
N 0 0 50 100 150 200 250 300 350 400 -100 Porewater Hydrogen Sulfide Concentration (µM) Sediment Organic Matter Content
1.6 A 1.4 A
) 1.2 % ( r e t t 1 a M c i n 0.8 a g r O t 0.6 n e c r e P 0.4 B
0.2
0 Thalassia testudinum Halodule wrightii Bare Nitrogen Fixation & OM
700
) 600 d / 2 m /
2 500 N
l o m
400 µ (
e t
a 300 R
n o i t
a 200 x i F
n e
g 100 o r t i N 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -100 Percent Organic Matter (OM) (%) Nitrogen Fixation & OM
700
) 600 d / 2 m / 2 500 R = 0.604 N
l o m
400 µ (
e t
a 300 R
n o i t
a 200 x i F
n e
g 100 o r t i N 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -100 Percent Organic Matter (OM) (%) Conclusions
• H2S concentrations are relatively low • N-limitation in seagrass • Higher nitrogen fixation rates in sediments colonized by seagrasses • Nitrogen fixation rates vary temporally in some • Weak inhibition by ammonium • Sulfate-reducing bacteria possibly responsible for the majority of nitrogen fixation • Activity of diazotrophic bacteria may be driven by sedimentary organic matter content Future Work
- • Water column NO3 concentrations • qPCR on nifH gene • Sampling continuing until August 2016 Acknowledgments
Mentors and Thesis Field and Lab Committee Members Assistants • Dr. Jane Caffrey • Stew Hood • Dr. Phil Darby • Josh Presley • Dr. Joe Lepo • Jenna Sleek • • Joe Moss Mike Murrell • Hillary Skowronski Funding • Gary Baine • Katelyn Knight • UWF CEDB • Chelsea Barfield • UWF Department of Biology • Taylor Beck • UWF SCAC • Ethan Morris • UWF GRSA • Katherine Haynes