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Low denitrification rates and variable benthic nutrient fluxes characterize Long Island Sound sediments

Abstract

Organic matter (OM) loading drives benthic metabolism and controls nitrogen (N), phosphorus (P), and carbon (C) cycling in coastal sediments. To better understand the influence of OM on benthic metabolism, we conducted sediment core incubations in Long Island Sound, NY (USA), an estuary heavily influenced by anthropogenic nutrient loading. Cores were collected during the summer and winter at five stations along a west to east transect representing a gradient of high to low nutrient inputs and subsequent OM deposition. Here we provide a comprehensive analysis of environmental drivers of benthic fluxes as well as the first directly measured rates of sediment denitrification and N-fixation, thus providing a missing piece of the N budget for Long Island Sound. Our findings show greatest sediment oxygen demand (SOD) in the western basin during the summer. Sediments were a source of dissolved inorganic N and P. Compared to historic SOD and ammonium fluxes, our measurements were about 50% lower, potentially reflecting larger scale perturbations (e.g., warming temperatures, decrease wind speed) or reduced N loading through improved management of wastewater treatment facilities. Sediments were a source of nitrous oxide (mean (± standard error): 8.63 ± 3.18 nmol m−2 h−1) and methane (23.80 ± 18.05 nmol m−2 h−1). Net sediment denitrification rates were low (10.34 ± 7.61 µmol N2–N m−2 h−1) and did not vary significantly across stations or seasons. These sediments have a N removal efficiency of ~ 30% with the potential to remove approximately 9% of the total land-based N load entering Long Island Sound.

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All of these data can be found here: https://doi.org/10.6084/m9.figshare.13022843.

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Acknowledgements

We thank Aidan Borkan, Craig Tobias, Sydney Twarz, and the University of Connecticut Department of Marine Sciences Vessel Operations for their help with sediment core preparation and collection. We also thank Qile Chen and Carly Langan for helping process sediment samples. Thanks to Nilotpal Ghosh for help with analysis of sediment percent carbon and nitrogen and to Cédric Fichot for allowing us to use his elemental analyzer. Funding for this project was provided to RWF through the Long Island Sound Study Research Grant Program which is conducted by Connecticut Sea Grant, based at the University of Connecticut at Avery Point, and New York Sea Grant, based at Stony Brook University.

Funding

Funding for this project was provided to RWF through the Long Island Sound Study Research Grant Program, which is conducted by Connecticut Sea Grant, based at the University of Connecticut at Avery Point, and New York Sea Grant, based at Stony Brook University.

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Contributions

RWF conceived of this project. CIM, ANA, ISM, and NER conducted the field work and processed samples. CIM conducted the statistical analysis and made the figures. CIM and RWF wrote the initial draft. All authors contributed to discussion and editing.

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Correspondence to Claudia I. Mazur.

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The authors have no relevant financial or non-financial interests to disclose.

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Mazur, C.I., Al-Haj, A.N., Ray, N.E. et al. Low denitrification rates and variable benthic nutrient fluxes characterize Long Island Sound sediments. Biogeochemistry 154, 37–62 (2021). https://doi.org/10.1007/s10533-021-00795-7

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  • DOI: https://doi.org/10.1007/s10533-021-00795-7

Keywords

  • Denitrification
  • Nutrient loading
  • Greenhouse gases
  • Sediment–water flux