Effects of experimental warming and carbon addition on nitrate reduction and respiration in coastal sediments
Effects of experimental warming and carbon addition on nitrate reduction and respiration in coastal sediments
Date
2015-04
Authors
Brin, Lindsay D.
Giblin, Anne E.
Rich, Jeremy J.
Giblin, Anne E.
Rich, Jeremy J.
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Keywords
Anammox
Climate change
Continental shelf
Denitrification
Dissimilatory nitrate reduction to ammonium
Warming
Climate change
Continental shelf
Denitrification
Dissimilatory nitrate reduction to ammonium
Warming
Abstract
Climate change may have differing effects on microbial processes that control coastal N
availability. We conducted a microcosm experiment to explore effects of warming and carbon
availability on nitrate reduction pathways in marine sediments. Sieved continental shelf
sediments were incubated for 12 weeks under aerated seawater amended with nitrate (~50 μM),
at winter (4°C) or summer (17°C) temperatures, with or without biweekly particulate organic C
additions. Treatments increased diffusive oxygen consumption as expected, with somewhat
higher effects of C addition compared to warming. Combined warming and C addition had the
strongest effect on nitrate flux across the sediment water interface, with a complete switch early
in the experiment from influx to sustained efflux. Supporting this result, vial incubations with
added 15N-nitrate indicated that C addition stimulated potential rates of dissimilatory nitrate
reduction to ammonium (DNRA), but not denitrification. Overall capacity for both
denitrification and DNRA was reduced in warmed treatments, possibly reflecting C losses due to
increased respiration with warming. Anammox potential rates were much lower than DNRA or
denitrification, and were slightly negatively affected by warming or C addition. Overall, results
indicate that warming and C addition increased ammonium production through remineralization
and possibly DNRA. This stimulated nitrate production through nitrification, but without a
comparable increase in nitrate consumption through denitrification. The response to C of
potential DNRA rates over denitrification, along with a switch to nitrate efflux, raises the
possibility that DNRA is an important and previously overlooked source of internal N cycling in
shelf sediments.
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Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 125 (2015): 81-95, doi:10.1007/s10533-015-0113-4.