Seasonal Stable Isotope Trends In
Finger Lake Food Webs
Peter Smyntek, Mark Teece,
Kim Schulz, and Adam Storch
Overview
• Stable Isotope (SI) Basics & Food Web
Diagrams
• Why Consider Seasonality?
• Project Goal & Sampling Methods
• Seasonal Stable Isotope Patterns in
Seston of Several Finger Lakes
• Future Work
Stable Isotopes and Food Web Diagrams
Naturally Abundant Tracers
• Source Information: Where did our organic material
originate?
Food web diagrams – Who’s eating who?
12
Predators
9
Herbivores
6
δ15N ‰
Producers
3
Benthic
0
-38
-33
Pelagic
-28
δ13C ‰
Littoral
-23
Idealized Stable Isotope Food Web Diagram
14
Shark 12 ‰
12
10
δ15N ‰
Bob 9 ‰
+ 3 ‰ δ15N
Fish 6 ‰
8
6
4
2
Zooplankton
3‰
0
-31
-29
-27
δ13C ‰
-25
-23
Idealized Stable Isotope Food Web Diagram
14
Shark 12 ‰
δ15N ‰
12
10
Bob 9 ‰
8
6
Fish 6 ‰
4
2
Zooplankton 3 ‰
0
-31
-29
-27
δ13C ‰
-25
-23
Easy Stable Isotope Food Web Diagram
L. Ontario - August - 2002 Pelagic Food Web
15
Limnocalanus
, 14.8
Alewife, 12.2
13
15
δ N
11
Mysis, 11.0
Invasive, predatory
zooplankton
Cercopagis,
9.0
9
Trophic level
enrichment
Herbivorous
Zooplankton,
6.9
7
5
Seston
(Algae), 5.3
3
-31
-29
-27
-25
δ
-23
-21
13
C
δ15N value listed next to organism – error bars = ± 1 Standard Dev.
Difficult Stable Isotope Food Web Diagram
L. Michigan - September - 2002 Food Web - Offshore
14
Invasive, predatory
zooplankton
12
Alewife, 10.4
Cercopagis,
7.8
δ
15
N
10
8
6
Seston
(Algae), 5.1
Herbivorous
Zooplankton,
6.1
4
Herbivorous
zooplankton
Daphnia, 3.9
2
-31
-29
-27
δ15N value listed next to organism
-25
δ
13
C
-23
Finger Lakes Study Goal & Methods
Identify patterns in seasonal
stable isotope values at the base
of the food web (algae)
Finger Lakes Study Goal & Methods
Identify patterns in seasonal
stable isotope values at the base
of the food web (algae)
Methods
• Seston (algae) sampled monthly, May to
September 2003
• Prefiltered through an 85 µm nylon mesh and
collected on glass-fiber filters (0.7 µm pore size)
• Rinsed with 1% HCl to remove any carbonates
• Freezed-dried filters analyzed by Continuous
Flow Elemental Analysis Coupled to Isotope
Ratio Mass Spectroscopy
Seasonal Isotope Patterns in
Lakes of Different Trophic Status
• Keuka, Otisco, and Onondaga – deep, offshore
sites
– Oligotrophic, Mesotrophic, and Eutrophic
http://american-real-estate.net/images/community/maps/map2s.gif
δ13C Stable Isotope Patterns In Seston
-20
-22
-24
Sept.
July
-26
June
-28
May
-30
-27.8
-27.9
-28.7
Keuka
-28.7
August
-30.0
+2.2 ‰
-32
-34
-20
-22
-24
-26
July
-28
-29.0
-30
May
-32
June
+3.2 ‰
-34
-20
-22
August
-24
-25.3
Onondaga
-26
-28
-30
-32
-34
-31.1
-30.2
July
June
-33.7
May
Otisco
-30.6
-31.1
-32.2
August
Sept.
-33.4
M onth
+8.4 ‰
Why The Changes in Seston δ13C Signatures?
• Switch in algal inorganic carbon source
from dissolved CO2 to HCO3-
• Fixation of previously respired dissolved
CO2
δ15N Stable Isotope Patterns In Seston
12
Sept.
10
8.4
8
6
6.3
5.3
4
2
4.6
May
Keuka
6.3
June July
August
+3.8 ‰
0
-2
12
9.7
July
10
8
6
4
May
9.4
August
June
6.3
Otisco
5.6
2
+4.1 ‰
0
-2
12
10
June 9.3
8.4
8
August
4
2
0
-2
Onondaga
July
6
5.7
2.8
2.0
Sept.
May
M onth
+7.3 ‰
Why The Changes in Seston δ15N Signatures?
• Change in the availability of nitrogen
nutrients (nitrate and ammonium) for
algae
more uptake of 15N
• Increased recycling of organic
nitrogen, possibly through microbial
reprocessing
Summary
• Carbon and nitrogen isotope values exhibit
seasonal variation in aquatic systems
• Seston (algae) stable isotope values
become enriched (increase) over the
summer & may be more pronouced in
highly productive lakes
• Seasonal patterns in stable isotope values
can aid in the interpretation of food webs
Future Work
• Measure carbon and nitrogen stable
isotope values of zooplankton and fish
from Keuka, Otisco, and Onondaga
Lake
Acknowledgements
• Mark Teece, Kim Schulz & Adam Storch
• Carla Cáceres, Chris Hotaling, Elaine
Langer, Thomas Zengeya, & Jennifer
Libertore
• Syracuse University Geology Department &
Mike Cheatam
• National Science Foundation
Stable Isotopes and Food Web Diagrams
Naturally Abundant Tracers
• Source Information: Where did our organic material
originate?
Food web diagrams – Who’s eating who?
1.) Distinguish between pelagic, benthic, and
littoral carbon sources
2.) Understand trophic organization (producers,
herbivores and predators) with nitrogen isotopes
Seasonal Variation In Seston Carbon (µg Org C/L)
300
Sept.
µgOrg. C/L
250
200
August
May
Keuka
July
150
Oligotrophic
June
100
50
0
700
µg Org. C/L
650
600
July
M ay
Augus t
550
Otisco
500
450
400
Mesotrophic
June
350
300
3500
µg Org. C/L
3000
July
2500
Onondaga
2000
1500
1000
August
May
June
500
0
M onth
Sept.
Eutrophic
Seasonal Shifts in δ13C & δ15N
Lake Michigan 2002
-22
-23
-24
δ 13C
-25
Alewife
-26
Cercopagis
-27
Herbivorous
Zooplankton
Seston
(Algae)
-28
-29
-30
-31
June
July
August
September
Month
14
12
Alewife
10
Cercopagis
δ 15N 8
Herbivorous
Zooplankton
Seston
(Algae)
6
4
2
June
July
August
Month
September
Stable Carbon Isotope Values
and Lake Productivity
0
Keuka
δ13 C ‰
-5
-10
Otisco
-15
Onondaga
-20
-25
-30
-35
0
500
1000
1500
2000
µg Org C/L
2500
3000
3500
Average of All Finger Lakes
0
-5
-10
Average
-15
13
δ C (‰)
-20
y = -0.0027x - 27.725
2
R = 0.6038
Seneca Cayuga
Keuka
Otisco
-25
-30
Onondaga
-35
0
500
1000
Average µg Organic C/L
1500
Changes in Algal Isotope Values
15
Seasonal δ N - Seston - Lake Michigan 2002
Algal isotope values change more rapidly than their consumers
6.5
September,
6.0
15
δ N
5.5
4.5
July, 4.7
Daphnia
3.5
2.5
August, 2.3
1.5
Month
Seasonal Shifts in δ13C
Seasonal δ C - Michigan 2003
Seston
13
-22
-23
Total
Herbivorous
Zooplankton
δ
13
C
-24
-25
-26
-27
-28
Cercopagis
-29
-30
-31
May
June
July
Month
August
September
Alewife
Differences in Bond Strength
Energy
En = ½(n+1)hv
E0 for 12C – 12C bond
E0 for 13C – C (lower
vibrational frequency)
C – C bond length