5 research outputs found
Effects of experimental warming and carbon addition on nitrate reduction and respiration in coastal sediments
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.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.This material is based upon work supported by the National Science Foundation by OCE-
0852289 to JJR and OCE-0852263 and OCE-0927400 to AEG, and Rhode Island Sea Grant to
JJR
Similar temperature responses suggest future climate warming will not alter partitioning between denitrification and anammox in temperate marine sediments
Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Global Change Biology 23 (2017): 331-340, doi:10.1111/gcb.13370.Removal of biologically available nitrogen (N) by the microbially mediated processes
denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability.
Although few studies have examined temperature responses of denitrification and anammox,
previous work suggests that denitrification could become more important than anammox in
response to climate warming. To test this hypothesis, we determined whether temperature
responses of denitrification and anammox differed in shelf and estuarine sediments from coastal
Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was
further assessed in a 12-week laboratory microcosm experiment. Temperature responses, as
characterized by thermal optima (Topt) and apparent activation energy (Ea), were determined by
measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging
from 3 to 59°C. With a few exceptions, Topt and Ea of denitrification and anammox did not differ
in Rhode Island sediments over the seasonal cycle. In microcosm sediments, Ea was
somewhat lower for anammox compared to denitrification across all treatments. However,
Topt did not differ between processes, and neither Ea nor Topt changed with warming or carbon
addition. Thus, the two processes behaved similarly in terms of temperature response, and this
response was not influenced by warming. This led us to reject the hypothesis that anammox is
more cold-adapted than denitrification in our study system. Overall, our study suggests that
temperature responses of both processes can be accurately modeled for temperate regions in the
future using a single set of parameters, which are likely not to change over the next century as a
result of predicted climate warming. We further conclude that climate warming will not directly
alter the partitioning of N flow through anammox and denitrification.This material is based upon work supported by the National Science Foundation
under Grant No. OCE-0852289 to JJR and OCE-0852263, OCE-0927400 and OCE1238212 to
AEG, and Rhode Island Sea Grant to JJR.2017-05-2
Nitrogen interception and export by experimental salt marsh plots exposed to chronic nutrient addition
Author Posting. © Inter-Research, 2010. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 400 (2010): 3-17, doi::10.3354/meps08460.Mass balance studies conducted in the 1970s in Great Sippewissett Salt Marsh, New England, showed that fertilized plots intercepted 60 to 80% of the nitrogen (N) applied at several treatment levels every year from April to October, where interception mechanisms include plant uptake, denitrification and burial. These results pointed out that salt marshes are able to intercept land-derived N that could otherwise cause eutrophication in coastal waters. To determine the long-term N interception capacity of salt marshes and to assess the effect of different levels of N input, we measured nitrogenous materials in tidal water entering and leaving Great Sippewissett experimental plots in the 2007 growing season. Our results, from sampling over both full tidal cycles and more intensively sampled ebb tides, indicate high interception of externally added N. Tidal export of dissolved inorganic N (DIN) was small, although it increased with tide height and at high N input rates. NH4+ export was generally 2 to 3 times NO3– export, except at the highest N addition, where DIN export was evenly partitioned between NO3– and NH4+. Exports of dissolved organic N were not enhanced by N addition. Overall, export of added N was very small, <7% for all treatments, which is less than earlier estimates. Apparent enhanced tidal export of N from N-amended plots ceased when N additions ended in the fall. Nitrogen cycling within the vegetated marsh appears to limit N export, such that interception of added N remains high even after over 3 decades of external N inputs.Support
for this analysis and for site maintenance was provided by
many federal agencies, especially the National Science Foundation
(OCE-0453292, DEB-0516430) and, for the past 12 yr,
through the institutional support of the Coastal Systems
Program SMAST-UMD