1) The study examined how stream carbon loss through leaf litter breakdown rates may be affected by warming temperatures using data from Coweeta Basin streams and Athens, Georgia streams. 2) Leaf packs were deployed in streams along a temperature gradient and breakdown rates were compared to predictions from the metabolic theory of ecology. 3) Preliminary results found relationships between faster breakdown rates and higher temperatures, though slopes were generally steeper than predicted, and variability was high. Including more disturbed Athens streams lessened the temperature effect relationship.

1. PREDICTING WARMING EFFECTS ON STREAM CARBON LOSS
USING LITTER BREAKDOWN RATES FROM THE COWEETA BASIN
Garrett Frandson1,2, Phillip Bumpers1, Amy Rosemond1, Seth Wenger1 , and Morgan Bettcher1
1Odum School of Ecology, University of Georgia, Athens, GA 30602
2Coweeta 2016 summer REU student, University of Central Arkansas, Conway, AR 72032
BACKGROUND
METHODS
ACKNOWLEDGEMENTS
DISCUSSION
REFERENCES
NSF Research Experience for Undergraduates awarded through
the Coweeta LTER program. Thanks to Kait Farrell, Chao Song,
and David Manning for aid in statistical analyses and
interpretations.
1. Wallace, J.B.; Eggert, S.L.; Meyer, J.L.; and Webster, J.R. (1997). Multiple
trophic levels of a forest stream linked to terrestrial litter inputs. Science. 277,
102-104.
2. Boyero et al. (2001). A global experiment suggests climate warming will not
accelerate litter decomposition in streams but might reduce carbon
sequestration. Ecology Letters. 14, 289-294.
3. Benstead, J.P. and Huryn, A.D. (2011). Extreme seasonality of litter
breakdown in an arctic spring-fed stream is driven by shredder phenology, not
temperature. Freshwater Biology. 56, 2034-2044.
4. Hieber, M. and Gessner, M.O. (2002). Contribution of stream detrivores, fungi,
and bacteria to leaf breakdown based on biomass estimates. Ecology. 83(4),
1026-1038.
5. Brown, J.H. et al. (2004). Toward a metabolic theory of ecology. Ecology.
85(7), 1771-1789.
6. Benfield, E.F. (2007). Decomposition of leaf material. Pp. 711-720. In: Hauer
and Lamberti (Ed.s) Methods in Stream Ecology, Academic Press.
RESULTS
STUDY SITE
HYPOTHESES
• The slope the log of breakdown rate as a function of inverse
temperature (1/kT where k is Boltzmann’s constant and T is in
Kelvin) should align with the activation energy’s range of values
(0.6-0.7 eV5) predicted by the MTE.
• Shredder breakdown rates will decrease with increasing water
temperature due to being cold-adapted and temperature-sensitive
organisms2.
• Microbial breakdown rates will increase with increasing water
temperatures as the additional heat drives faster enzymatic
activity5.
• Decomposition rates will be higher in Acer samples than in
Rhododendron samples due to Rhododendron leaves being of
tougher structure.
• Stream water temperatures are predicted to increase with
predicted trends in land use and air temperature increases.
• Headwater streams are crucial to aquatic ecosystems and the
global carbon cycle due to their processing of terrestrial carbon
inputs, primarily leaf litter, and their transport of foodweb-
supporting carbon to downstream systems1,2. Understanding the
effects of increasing stream water temperatures is thus crucial to
understanding large-scale ecosystem effects of climate change.
• The biological decomposition of leaf litter in streams is due to
shredding macroinvertebrates, fungi, and bacteria with the
macroinvertebrates and fungi contributing most3,4.
• The metabolic theory of ecology (MTE) may be used to make
predictions about the relationship between temperature and the
rates of many biological processes5, here specifically litter
breakdown.
• Examining leaf litter processing rates along a gradient of
temperature caused by seasonal progression and differences in
elevation, aspect, and shade should provide insight into expected
aquatic carbon processing responses to increasing stream water
temperatures.
Stream Mean Water Temperature (°C)
1: Albert Branch 15.81
2: Pinnacle Branch 15.84
3: Bee Branch 15.98
4: Big Hurricane Branch 16.28
5: Shope Branch 16.77
6: Copper Branch 16.41
7: Shope Fork (Forest) 17.22
8: Shope Fork (Gap) 17.24
9: Carpenter Branch 16.96
10: Sawmill Branch 17.99
11: Hugh White Creek 17.47
12: Upper Ball Creek 15.79
Athens: Tallassee Creek 23.09
Athens: Turkey Creek 23.07
Athens: Brooklyn Creek 22.16
Athens: Brickyard Creek 23.84
• Leaf packs consisting of 5.0 ± 0.1 grams of a fast-decaying (Acer
rubrum) or a slow-decaying (Rhododendron maximum) species
were deployed at 12 sites at the Coweeta Hydrologic Laboratory.
Two deployments were made, 4 replicate packs per site. Onset
HOBO Pendant water temperature and lux recorders were also
deployed with each leaf pack set on June 6, 2016. We contrasted
the response of breakdown with coarse mesh (including
invertebrates) and fine mesh (microbial breakdown only).
• The process was also conducted once with Acer leaves in four
streams in Athens, Georgia.
• Leaf packs were
retrieved approximately
six weeks after
deployment, and
recorders’ data were
downloaded. Packs
were kept on ice until
laboratory processing.
• Leaf packs were
processed and ash-free
• The expected negative relationship between temperature and
breakdown rate was at least suggested as a trend in all three
comparisons.
• The negative relationship and trends between 1/kT and
ln (breakdown rate) are equivalent to positive relationships and
trends between temperature and breakdown rate and
represented more than a doubling of breakdown rate across
Coweeta streams across a gradient of ~2oC.
• Rhododendron breakdown was slower than Acer but responses
to temperature were similar between the two species.
• There was a positive relationship between 1/kT and ln
(breakdown rate) for the coarse Acer leaves of deployment A but
not B. This was potentially due to the bags of deployment A
experiencing more burials which may lead to less colonization
and lower breakdown rates. Notably, three of the streams’ bags
with the lowest breakdown rates also had heavy burials.
Macroinvertebrate data was collected from only deployment A,
thus these burials confounded shredder response analysis.
Implications and next steps
• Steeper slopes in the relationships between breakdown and
temperature indicate greater effects on breakdown rates than
would predicted from MTE. Both our empirical data and MTE
predict faster losses of carbon via breakdown with increased
temperature.
• In our study, relatively high variability in breakdown rates resulted
in large confidence intervals; additional data (seasonal) will be
collected in the future to attempt to more accurately predict
temperature effects on breakdown.
• The contrast with streams in a more disturbed environment
(Athens, GA) gives insights into other aspects of temperature
effects. Slopes between breakdown and temperature were less
steep with inclusion of Athens data – indicating potentially
suppressed biological activity in disturbed streams.
• Future work may extend the duration of the study, increase the
number of bags in a deployment, capture and incorporate
dissolved nutrient and contaminant data, and deploy bags such
that depositional burials are less common.
Subset Slope
Figure
Intercept
Overall
Model’s
𝐑 𝟐
Figure
1
C. A.
-2.085
-3.673
0.363
C. R. -4.888
Figure
2
F. A.
-1.366
-4.315
0.459
F. R. -4.4842
Figure
3
C. A.
-0.512
-3.646
0.211
F. A. -4.096
Figure 2. The log of fine mesh breakdown rate against 1/kT
showed no significant relationship but a negative trend with
p=0.080. There was a significant effect of litter species on
breakdown rate. Slope is less steep (-1.37) than coarse mesh
but also steeper than MTE prediction; the 95% confidence
interval is large (-2.913 to 0.180).
Figure 3. We used sites in Athens, GA to extend the
temperature and in-stream condition range of our data. The log
of breakdown rate against 1/kT was statistically significant
(p=0.022); the slope (-0.51) was less steep than MTE prediction.
There was a significant effect of mesh size on breakdown rate.
Table 1 : Summary table of values for Figures 1-3. The
subsets are, respectively, coarse Acer, coarse
Rhododendron, fine Acer, fine Rhododendron, coarse
Acer, and fine Acer.
Figure 1. The log of coarse mesh breakdown rate plotted
against 1/kT showed no significant relationship but a trend
with p=0.077. There was a significant effect of litter species
on breakdown rate. Slope is steeper (-2.08) than MTE
prediction, (ca. -0.6); the 95% confidence interval is large
(-4.414 to 0.244).
dry mass calculations were done as per
standard methods6.
• Slopes between breakdown and temperature were compared to the
linear Arrhenius equation to assess whether empirical data matched
predictions from MTE.
Coweeta – Total breakdown Coweeta – Microbial breakdown
Coweeta – Athens
Total, microbial breakdown