Systematically variable planktonic carbon metabolism along a land-to-lake gradient in a Great Lakes coastal zone
J. Plankton Res. (
Systematically variable planktonic carbon metabolism along a land-to-lake gradient in a Great Lakes coastal zone
ANTHONY D. WEINKE 2
SCOTT T. KENDALL 2
DANIEL J. KROLL 1 2
ERIC A. STRICKLER 0 2
MAGGIE E. WEINERT 2
THOMAS M. HOLCOMB 2 5
ANGELA A. DEFORE 2 4
DEBORAH K. DILA 2 3
MICHAEL J. SNIDER 2
LEON C. GEREAUX 2
BOPAIAH A. BIDDANDA 2
0 SALISH SEA EXPEDITIONS
1 MUNSON MEDICAL CENTER
2 ANNIS WATER RESOURCES INSTITUTE
3 SCHOOL OF FRESHWATER SCIENCES
4 USC BARUCH MARINE FIELD LAB
5 HERMAN MILLER
During the summers of 2002 - 2013, we measured rates of carbon metabolism in surface waters of six sites across a land-to-lake gradient from the upstream end of drowned river-mouth Muskegon Lake (ML) (freshwater estuary) to 19 km offshore in Lake Michigan (LM) (a Great Lake). Despite considerable inter-year variability, the average rates of gross production (GP), respiration (R) and net production (NP) across ML (604 + 58, 222 + 22 and 381 + 52 mg C L21 day21, respectively) decreased steeply in the furthest offshore LM site (22 + 3, 55 + 17 and 233 + 15 mg C L21day21, respectively). Along this land-to-lake gradient, GP decreased by 96 + 1%, whereas R only decreased by 75 + 9%, variably influencing the carbon balance along this coastal zone. All ML sites were consistently net autotrophic (mean GP:R ¼ 2.7), while the furthest offshore LM site was net heterotrophic (mean GP:R ¼ 0.4). Our study suggests that pelagic waters of this Great Lakes coastal estuary are net carbon sinks that transition into net carbon sources offshore. Reactive and dynamic estuarine coastal zones everywhere may contribute similarly to regional and global carbon cycles.
coastal; pelagic; production; respiration; gradient
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The exchange of carbon between atmospheric, terrestrial
and aquatic pools is one of the largest biogeochemical
pathways on Earth, second only to the water cycle
(Schlesinger and Berhardt, 2013)
. The dual processes of
autotrophy and heterotrophy drive the biosphere’s
carbon cycle, making their quantification essential for
estimating the magnitude of carbon flux and quantifying
the net carbon balance of ecosystems. However,
measurements that enable such assessments, coupled
measurements of photosynthesis and respiration, are severely
lacking in aquatic ecosystems
(del Giorgio et al., 1997;
Karl et al., 2003; Serret et al., 2001)
.
Carbon and nutrients that run off or drain through the
terrestrial environments of watersheds pass through the
myriad of waterways consisting of streams, rivers, wetlands
and lakes on to receiving basins such as the Great Lakes
and the oceans
(Beman et al., 2005; Biddanda and Cotner,
2002)
. However, inland waters do not play a passive role as
mere conduits of carbon and nutrients in this worldwide
phenomenon. Indeed, recent studies have shown that
inland waters of the world, representing only 1% of the
Earth’s surface area, play a disproportionately large role in
the global carbon cycle
(Cole et al., 2007; Tranvik et al.,
2009)
. In particular, significant processing of terrigenous
nutrients and carbon occurs in land-margin ecosystems
such as streams, rivers, estuaries and coastal zones
(Marko
et al., 2013)
. It is estimated that annually of the about 5 Pg
of carbon entering the inland waters, 0.2 – 0.6 Pg of
carbon is buried in freshwater sediments (twice the annual
burial into oceanic sediments), and 0.7 – 4.0 Pg of
carbon is respired to the air in freshwater systems (equal to
the net uptake of carbon by the oceans). These estimates
lend credence to the emerging notion that inland waters
are highly reactive and play a crucial and hitherto
underappreciated role in regional and global carbon cycles
(Raymond et al., 2013; Wehrli, 2013)
.
The North American Great Lakes contain nearly 20%
of Earth’s liquid surface freshwater. Though large, they are
heavily human-impacted systems with stressors acting on
multiple fronts
(Cuhel and Aguilar, 2013; Evans et al.,
2011; Rothlisberger et al., 2010)
. Climate change, for
example, is resulting in warmer temperatures occurring
earlier in the year leading to earlier spring blooms followed
by a cascade of ecosystem effects
(Russ et al., 2004)
.
Furthermore, in recent years, invasive dreissenid mussels
have nearly eliminated the winter and spring blooms
(Kerfoot et al., 2010; Vanderploeg et al., 2010)
. Studies
suggest that the annual stream and river discharge into
southern Lake Michigan (LM), equaling 1% of its total
volume, have terrestrial subsidies of dissolved organic
carbon (DOC) and phosphorus 10 and 20 times higher
than LM, that support up to 20% of the phytoplankton
production and up to 10% of heterotrophic bacterial
production in southern LM
(Biddanda and Cotner, 2002)
. LM
is currently on its way to becoming as oligotrophic as Lake
Superior
(Evans et al., 2011; Mida et al., 2010)
, making
terrestrial subsidies of nutrients and organic matter more vital
than ever to its annual balance
(Johengen et al., 2008)
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