High production of nitrous oxide (N<sub>2</sub>O), methane (CH<sub>4</sub>) and dimethylsulphoniopropionate (DMSP) in a massive marine phytoplankton culture

Abstract

The production of large amounts of algal biomass for different purposes such as aquaculture or biofuels, may cause impacts on the marine environment. One such impact is the production of radiatively active trace gases and aerosols with climate cooling (dimethyl sulfide DMS and its precursor DMSP) and warming (N₂O and CH₄) effects. Total and dissolved DMSP, N₂O and CH₄, together with other environmental variables were monitored daily for 46 days within a massive microalgae monoculture of <i>Nannochloris</i> (Chlorophyceae) in an open pond system. The growth of this green microalgae was stimulated by the addition of N- and P-rich salts, resulting in exponential growth (growth phase) during the first 17 days observed by cell abundance (1 &times; 10⁶ to 4.4 &times; 10⁶ cell mL⁻¹) and Chl-<i>a</i> levels (from 1.4 to 96 mg Chl-<i>a</i> m^&minus;3) followed by a decrease in both Chl-<i>a</i> and cell abundance (senescence phase). Total DMSP (from 6.3 to 142 μmol m⁻³), dissolved DMSP i.e. 5.8 to 137 μmol m⁻³ and N₂O (from 8 to 600 μmol m⁻³) abruptly peaked during the senescence phase, whereas CH₄ steadily increased between 2 and 10 μmol m⁻³ during the growth phase. Different ratios between tracers and Chl-<i>a</i> during both phases reveal different biochemical processes involved in the cycling of these gases and tracers. Our results show that despite the consumption of large quantities of CO₂ by the massive algal culture, a minor amount of DMS and huge amounts of greenhouse gases were produced, in particular N₂O, which has a greater radiative effect per molecule than CO₂. These findings have important implications for biogeochemical studies and for environmental management of aquaculture activities

Methane-oxidizing seawater microbial communities from an Arctic shelf

“…Since the seawater was not pre-filtered through a larger pore-size filter, which would exclude larger particles but allow bacterial cells to pass, production of methane in microanoxic zones (de Angelis and Lee, 1994;Oremland, 1979) should be considered. Furthermore, several studies suggested pathways for methane production in oxygenated marine systems from methylated compounds or dissolved organic matter (Damm et al, 2010;Florez-Leiva et al, 2010;Karl et al, 2008;Repeta et al, 2016). The methane production rate of 0.06 nmol L −1 d −1 observed in our study is 2 to 6 orders of magnitude lower than previously published methane production rates under aerobic conditions (Damm et al, 2010;Karl et al, 2008).…”

Quantitative Measurement of Direct Nitrous Oxide Emissions from Microalgae Cultivation

“…However, no work was done to verify the production mechanism or quantify N 2 O emissions. More recently, Florez-Leiva et al 21 ABSTRACT: Although numerous lifecycle assessments (LCA) of microalgae-based biofuels have suggested net reductions of greenhouse gas emissions, limited experimental data exist on direct emissions from microalgae cultivation systems. For example, nitrous oxide (N 2 O) is a potent greenhouse gas that has been detected from microalgae cultivation.…”

Nitrous Oxide (N&lt;sub&gt;2&lt;/sub&gt;O) production in axenic &lt;i&gt;Chlorella vulgaris&lt;/i&gt; microalgae cultures: evidence, putative pathways, and potential environmental impacts

“…Nitrous oxide (N 2 O) is a major ozone-depleting atmospheric pollutant and greenhouse gas (Ravishankara et al, 2009;EPA, 2010). The production of this compound from microalgal and cyanobacterial cultures (henceforth referred to as "algae" for simplicity) was demonstrated more than 25 yr ago (Weathers, 1984;Weathers and Niedzielski, 1986) and has been suspected to cause measurable N 2 O emissions in various aquatic environments (Twining et al, 2007;Mengis et al, 1997;Wang et al, 2006;Oudot et al, 1990;Florez-Leiva et al, 2010). This mechanism is nevertheless often challenged as a significant source of N 2 O in algae-based ecosystems and many authors have attributed these emissions to associated bacteria (Law et al, 1993;Morell et al, 2001;Ni and Zhu, 2001;Harter et al, 2013;Ferrón et al, 2012).…”