Nitrous oxide production from temperate and tropical oyster species in response to nutrient loading

Anthropogenic pollution, such as nitrogen (N), has the potential to increase greenhouse gas (GHG) emissions in marine ecosystems. Some organisms can be used as important biological indicators for GHG emissions to their environment based on their feeding habits. With large inputs of these anthropogenic pollutants, emissions of nitrous oxide (N₂O), a potent GHG, can be potentially increased from temperate invertebrates, though not much is known about tropical invertebrates. Thus, we compared N₂O emissions in response to N additions from the temperate oyster species Crassostrea virginica and compared it to a tropical species, Isognomon alatus, found in Puerto Rico. Oysters were exposed to two seawater treatments: (1) no nutrient addition (control) and (2) 100µM ammonium nitrate. Each treatment had 4-5 replicates. Measurements for dissolved N₂O and nutrients were taken at the start of the incubation and then at two, four, and five hours by collecting water samples of each tank. Dissolved N2O concentrations were analyzed using gas chromatography. We hypothesized that the N addition treatment would produce more N₂O for both Rhode Island and Puerto Rico. We found that there was no significant difference between the control and N enriched treatments for C. virginica over the short timespan, although the N enriched treatment did have a steady trend in increasing in N₂O concentration over time. Further analysis is needed for the I. alatus, though we expect an increase in N₂O emissions due to warmer water temperatures, which might enhance microbial metabolism and production of N2O. This differs from work previously done in a long-term experiment on C. virginica, which showed that N₂O significantly in the N enriched treatment over 28-days. Our study shows that short-term pulses of N may not potentially increase N₂O emissions, though further analysis is needed for longer-term exposures.