Are Microalgae New Players in Nitrous Oxide Emissions from Eutrophic Aquatic Environments?

Abstract

Anthropogenic activities cause the introduction of nitrogen (N) into aquatic environments where these N inputs drive the biological synthesis of nitrous oxide (N2O), a potent and ozone-depleting greenhouse gas. To assess the significance of N2O emissions to climate change, the Intergovernmental Panel on Climate Change (IPCC) estimates indirect N2O emissions from rivers, lakes, and estuaries by multiplying the amounts of N received by these ecosystems with specific emission factors. Interestingly, the IPCC recently increased the N2O emission factor associated with wastewater discharge into “nutrient-impacted (eutrophic) aquatic receiving environments” nearly four times based on experimental evidence of high N2O emissions from N-receiving eutrophic ecosystems. As microalgae can produce N2O, these organisms may contribute to the N2O emissions frequently reported in eutrophic aquatic bodies. If that is the case, estimating N2O emissions solely based on nitrogen inputs to water bodies might lead to inaccurate N2O budgeting as microalgae growth is often limited by phosphorus in these environments. Establishing the significance of microalgal N2O synthesis in eutrophic environments is, therefore, critical and may lead to considerable changes on how to budget and mitigate N2O emissions and eutrophication.