Post on 06-Jan-2016
description
Elon M. Malkin, David H. Hollander, Ernst B. PeeblesUniversity of South Florida College of Marine Science
Parallel Nitrogen Cycles in Southwest Florida’s Tidal Rivers: Selective Remineralization of Algal Material Supports Fish Biomass
Study Questions:
•What is the source of sedimentary recalcitrant nitrogen?
•What is the source of sedimentary labile nitrogen?
•Which of these pools are associated with fish production?
Southwest Florida: Land Development & Fisheries
1. Anthropogenic Land Development:N Drains into receiving waters
2. Estuarine Dependent Juvenile Fish:Occupy Receiving Waters Positively or negatively influenced by N
3. Sedimentary N Processing:N Transformation between land and fish
Land Use
Feather Sound
Alafia River
Wildcat Creek
Curiosity Creek
McMullen Creek
Frog Creek
Myakka River
Peace River
Study Sites: 8 Watersheds
SOM vs. Sedimentary Porewater NH4+
Sediment Organic
Matter (SOM)
NH4+
Sediment Porewater
NH4+ (SedNH4
+)
NH4+
NH4+NH4
+
NH4+ NH4
+
NH4+NH4
+
NH4+
NH4+
Labile Sediment Nitrogen Pool
RecalcitrantSediment
Nitrogen Pool
0
2
4
6
8
10
12
14
16
-2 0 2 4 6 8 10 12 δ15 N SedNH 4+ , ‰ AIR
δ15
N S
OM
,
‰ A
IR r2= 0.17
SOM
SOM vs. Sedimentary Porewater NH4+
What is the Source of Recalcitrant SOM?Approach: δ15N System Averaging to Account for Advection•Sample Collection: (Primary producers, SOM)•Each primary producer δ15N value averaged across sites•Each SOM δ15N value averaged across sites•Mean values of 1oP plotted against mean SOM values
River C
River A
River B
1 2 31 average value per 1oP1 average value for SOM
1 average value per 1oP1 average value for SOM
1 2 3
1 average value per 1oP1 average value for SOM
1 2 3
Collection Sites
-2
0
2
4
6
8
10
12
2 2.5 3 3.5 4 4.5 5
δ15
N,
‰ A
IR
δ15 N Sedimentary Organic Matter, ‰ AIR
r2= 0.33
r2= 0.45POMBMA
Microalgae is not Recalcitrant N
r2= 0.83
-2
0
2
4
6
8
10
12
2 2.5 3 3.5 4 4.5 5
δ15
N,
‰ A
IR
δ15 N Sedimentary Organic Matter, ‰ AIR
r2= 0.91
Emergent VegetationUpland Plants
Vascular Plant Detritus is Recalcitrant N
What is the Source of Sedimentary Labile NH4+?
Approach: δ15N Site Specific Values to Maximize Data Points
•Site Collections (various 1OP, sedimentary NH4+)
•Site Specific Values of 1oP plotted vs. sedNH4+
River C
River A
River B
1 2 33 values per 1oP, porewater NH4
+, SOM
1 2 3
1 2 3
Collection Sites
3 values per 1oP, porewater NH4
+, SOM
3 values per 1oP, porewater NH4
+, SOM
0
2
4
6
8
10
12
14
16
-2 0 2 4 6 8 10 12 δ15 N Sedimentary Porewater NH 4+ , ‰ AIR
δ15
N,
‰ A
IR
r2= 0.07
Mangroves
Upland Plants
Upland Plant Detritus is Not Labile N
r2= 0.32
0
2
4
6
8
10
12
14
16
-2 0 2 4 6 8 10 12
r2BMA = 0.99
δ15 N Sedimentary Porewater NH 4+ , ‰ AIR
δ15
N,
‰ A
IRBMA is Labile N
BMA
0
2
4
6
8
10
12
14
16
-2 0 2 4 6 8 10 12 δ15 N Sedimentary Porewater NH 4+ , ‰ AIR
δ15
N,
‰ A
IR
r2BMA = 0.68
POM is Labile NPOM
Approach: δ13C vs. δ15N plots for all available data:
Which N Pool Supports Fish Production?
Benthic Microalgae (BMA)Particulate Organic Matter (POM)
Fish vs. Upland Plants (UP)Mangroves (MAN)Emergent Vegetation (EM)
δ1
5N
‰ A
IR
012
34567
89
10
-26 -25 -24 -23 -22
δ13C ‰ PDB
1OC (Benthic inverts)
3:1 p
er T
L
ΔN
=3‰
ΔC=1‰1OP
Stable Isotopes Link 1oP to Fish
3:1 p
er T
L
ΔC=1‰
3:1 p
er T
L
δ1
5N
‰ A
IR
012
34567
89
10
-26 -25 -24 -23 -22
δ13C ‰ PDB
2OC (fish)
1OC (Benthic inverts)
ΔN
=3‰
ΔC=1‰
1OP
ΔN
=3‰
Stable Isotopes Link 1oP to Fish
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
What 1oP Support Fish Production? Fish
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
Mangroves Do Not Support All Fish FishMAN
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
Emergent Plants Do Not Support All Fish FishMANEM
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
FishMANEMUP
Upland Plants Do Not Support All Fish
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
FishMANEMUP
Vascular Plants Do Not Support All Fish
TB & CH POM
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
FishPOMBMA
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
Microalgae Supports Fish Production
TB & CH POM
0
2
4
6
8
10
12
14
16
-30 -28 -26 -24 -22 -20
FishPOMBMAINV
δ15
N,
‰ A
IR
δ13 C, ‰ PDB
Benthic Invertebrates are Intermediates
Conclusions: Parallel Nitrogen Cycles
Vascular Plant Cycle: Recalcitrant OM is Buried
Vascular Plants
Bulk SOM
Burial
Vascular PlantsPOM
Bulk SOMLabile SOM
Recycle
SedNH4+
BMA
Burial
Microalgal Cycle: Labile OM is Remineralized
Vascular PlantsPOM
Bulk SOMLabile SOM
Recycle
SedNH4+
BMA
Burial
Foodwebs Are Associated with Labile Cycle