Nitrogen and Warming Effects on Nitrous Oxide Production Associated with Coastal Macroinvertibrates

Author

Melanie H. Gárate, University of Rhode IslandFollow

Date of Award

2016

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Biological Sciences

First Advisor

Serena Moseman-Valtierra

Abstract

Bivalve shellfish potentially reduce excess nitrogen in the water column, however they can also be involved in the emission of nitrous oxide (N₂O), a potent greenhouse gas. Environmental controls on N₂O production from bivalves have not been well quantified. We tested responses of N2O production by three bivalves (Mytilus edulis, Mercenaria mercenaria and Crassostrea virginica) to nitrogen (N) loading and/or warming after immediate (1 day) and short-term (14-28 days) exposure. This two-factor laboratory study had four treatments: (1) ammonium nitrate (N) addition (targeting 100μM-N), (2) warming (22^oC), (3) N addition + warming and (4) no N addition or warming (control, 19^oC). Potential N₂O production rates were higher in response to N additions for all bivalves, particularly with short-term exposures. Warming had a small but significant impact on N₂O production from M. mercenaria, confounded by a significant interaction of exposure X warming and exposure X nitrogen X warming. Similarly, C. virginica also showed a significant interaction of exposure X warming, indicating that longer exposure to warming may influence N₂O production from this species. M. edulis showed the highest N₂O production rates, reaching 252 nmol N₂O ind^-1 hr^-1, more than an order of magnitude higher than the previously largest reported rates. However, mass-specific rates (7.5 nmol N2O g^-1 hr^-1) were the same order of magnitude as previous studies. Notably, N₂O production associated with M. edulis were obtained while the organisms had poor health, which likely induced high respiration rates and was probably caused by hypoxic water conditions. We also examined the influence of macro-epifauna on the N₂O production associated with M. edulis via removal of macro-epifauna. There was no significant difference in N₂O produced by M. edulis with and without epifauna, which suggests that N₂O production may be largely due to gut microbial activity and microbial biofilms on the shells from M. edulis. In summary, our study indicates a strong influence of N on the potential N₂O emissions rates of prominent bivalves, which should be considered when incorporating them into coastal N mitigation strategies.

Recommended Citation

Gárate, Melanie H., "Nitrogen and Warming Effects on Nitrous Oxide Production Associated with Coastal Macroinvertibrates" (2016). Open Access Master's Theses. Paper 899.
https://digitalcommons.uri.edu/theses/899