Download What are the trophic positions of the stonefly species collected?

The ecological role of methane dynamics in the
Nyack aquifer of the Middle Fork of the
Flathead River, Montana
Amanda G. DelVecchia, Jack A. Stanford, Brian L. Reid,
Jon Graham, Bonnie K. Ellis
Canada
Nyack
WA
MT
ID
Stanford, J. A., M. S. Lorang, and F. R. Hauer. 2005. The shifting habitat mosaic of river ecosystems. Verh. Internat. Verein. Limnol.
29:123–136.
Ecology of the Nyack aquifer
A well-oxygenated, carbon-limited, and heterogeneous environment
n = 552 individuals
Flowpath
Channel – aquifer exchange
Vadose– aquifer interaction
1Valett
et al. 2013 Ecosystems, Smith et al. 2011 Geo. Chem. Acta
et al. 1993 J.NABS
3Craft et al. 2002 FW Biol.,
4Helton et al. 2015 L&O
2Ellis
•Generally well oxygenated1
•Low DOC (<2mg/L)
•Low microbial productivity2
•Limited by labile organic carbon3
•Labile DOC increases along flowpaths4
Ecology of the Nyack aquifer
Diverse and abundant macroinvertebrates use methane-derived carbon
Amphibitic stonefly species that
mature for 1-3 years in the aquifer:
•Isocapnia grandis
•Isocapnia crinita
•Isocapnia integra
•Paraperla frontalis
•Kathroperla perdita
DelVecchia, Amanda G., Jack A. Stanford, Xiaomei Xu. ‘Ancient methane-derived
carbon subsidizes a contemporary food web’. Nature Communications. In review.
Ecology of the Nyack aquifer
Diverse and abundant macroinvertebrates use methane-derived carbon
Methanogens
requires anoxia
production
Dissolved methane
requires DO
consumption
Methane-oxidizing bacteria
Direct or indirect consumption
DelVecchia, Amanda G., Jack A. Stanford, Xiaomei Xu. ‘Ancient methane-derived
carbon subsidizes a contemporary food web’. Nature Communications. In review.
How is the trophic and community ecology of hyporheic
stoneflies related to aquifer methane dynamics?
I.
What are the trophic positions of each stonefly
species in the context of the aquifer food web?
II. How are stonefly species assemblages related to
biogeochemical variables?
Methods
•
•
•
•
Sampled 20 3-inch wells
Sampled 1 and 4m below the baseflow water
table every 6 weeks in 2014-2015 for:
• Dissolved oxygen concentration (DO)
• Dissolved organic carbon concentration
(DOC)
• Dissolved methane concentration
(methane)
• Temperature
Used standard diaphragm pumping method to
collect stoneflies
Stable isotope analyses (δ13C, δ15N) of stonefly
biomass, OM pools, meiofauna
I. What are the trophic positions
of the stonefly species collected?
Trophic positions vary by species
What are the trophic positions of stonefly species?
δ15N (‰)
Raw stable isotope values show distinct trophic positions
•
•
•
Stoneflies have significantly different
trophic positions
Arranged on a gradient of methanederived carbon contribution
More depleted in 13C than any other
OM pools
δ13C (‰)
What are the trophic positions of stonefly species?
δ15N (‰)
Raw stable isotope values show distinct trophic positions
• MOB preferentially assimilate 14N,
causing them to have lower δ15N
values
• Expect positive relationship
between δ13C, associated with
methane-derived carbon in
biomass, and δ15N
• Need to assess relative trophic
levels by taking this into account
δ13C (‰)
What are the trophic positions of stonefly species?
Stonefly species show distinct trophic positions after correction for MDC in biomass
δ15N (‰)
Slopes vary by taxa
n = 719, R2 = 0.627, p < 0.0001
• Linear relationship because proportional (e.g. proportion basal resources
MOB  proportion of N in biomass depleted as a result)
• Varying intercepts because proportional relationship should remain
constant between species
δ13C (‰)
What are the trophic positions of stonefly species?
Intercepts
Intercept differences confirm distinct trophic positions
• Relative positioning of species
remains consistent
• Intercepts are significantly
different, confirming distinct
trophic positions even with
more conservative approach
δ13C (‰)
What are the trophic positions of the
stonefly species collected?
Trophic positions vary significantly by
species, consistent with differing use of
methane derived carbon resources and
differing trophic levels.
II. How are species assemblages
related to measured biogeochemical
variables?
Methane concentration is a significant predictor
of species assemblages
How are stonefly species assemblages structured?
Non-metric multidimensional scaling to determine relationship between community structure
(species assemblages) and biogeochemical variables
Log(methane)
DO
DOC
Temperature
Dayterm
Well
NMDS1
0.19
-0.34
-0.09
0.22
-0.15
NMDS2
0.98
-0.94
1.00
0.97
-0.99
R2
0.160
0.169
0.067
0.033
0.055
0.310
Pr(>r)
0.002
0.002
0.074
0.304
0.134
0.060
Log(methane)
DO
DOC
Temperature
Dayterm
Well
NMDS2
0.82
-0.99
0.97
0.81
-0.82
NMDS3
0.58
-0.16
-0.23
-0.58
0.57
R2
0.221
0.139
0.070
0.044
0.077
0.192
Pr(>r)
0.001
0.005
0.060
0.180
0.063
0.762
How are species assemblages related to
measured biogeochemical variables?
Assemblages are structured in part by
methane and DO concentrations, with
methane concentrations alone explaining
19% of variation.
Conclusions
•Stonefly species have unique trophic positions, consistent with differing contributions of
methane derived carbon to biomass and differing trophic levels.
•Stonefly species assemblages are structured in relation to biogeochemical variables,
especially methane and DO concentrations.
Implications:
•Stonefly species can coexist in the aquifer environment because their ecological niches are
unique in terms of aquifer biogeochemistry, underscoring the functional diversity present
in the aquifer ecosystem.
•Because methane is produced in anoxia but converted into a carbon source that is
accessible to the stoneflies in oxic conditions, and because stoneflies have varying use of
methane derived carbon resources, biogeochemical heterogeneity is important for
maintaining macroinvertebrate species diversity in the aquifer.
Acknowledgements
Advisor: Dr. Jack Stanford
Flathead Lake Biological Station, Polson, MT
Dr. Bonnie Ellis
Dr. Jon Graham
Dr. Gordon Luikart
Dr. Ryan Jones
All FLBS faculty and staff
Dr. Shawn Devlin
Adam Baumann and the FLBS Freshwater Research Laboratory
Dr. Ashley Helton
Dr. Geoffrey Poole
Dr. Anne Hershey
Dr. Steve Whalen
Dr. Tim McDermott
The Dalimata Family, West Glacier, MT
Field and lab Assistants:
Hannah Coe, Amelia Schirmer, Matt Bambach, Chad Reynolds,
Neal Jacobi, Clinton Begley, Chris Johnson, Emily Winter, Cailey
Philmon, and all others who have helped
Funding provided by the Jessie M. Bierman Professorship and a
philanthropically funded graduate fellowship from the University
of Montana
Thank you
How might 13C depletion occur in stoneflies?
Frequency within microbial community (%)
16S analysis of microbial community composition in gut contents
n=3
n=4
Methanogenic/
methanotrophic taxa
n=4
n=2
n=1
• Stoneflies consume methanogens
and methane oxidizing bacteria
• Do they preferentially consume these
microbes?
I. grandis
P. frontalis