Photoformation rate, steady-state concentration and lifetime of nitric oxide radical (NO ) in a eutrophic river in Higashi-Hiroshima, Japan

Photoproduction of nitric oxide in seawater

“…NO is produced and consumed during various microbial processes such as nitrification, denitrification, and anammox (Schreiber et al, 2012;Kuypers et al, 2018). Moreover, it is known that both phytoplankton and zooplankton can metabolize NO, and they are influenced by ambient (extracellular) NO concentrations (Singh and Lal, 2017;Wang et al, 2017;Astier et al, 2018).…”

“…Seto Inland Sea, Japan 8.7-38.8 × 10 −12 DAF-2 120 × 10 −12 0.5-2 3.55 × 10 −12 5-9 October 2009 Olasehinde et al (2010) Seto Inland Sea, Japan 1.4-9.17 × 10 −12 DAF-2 3-41 × 10 −12 0-0.4 0.22 × 10 −12 September 2013 and Anifowose andSakugawa June 2014 (2017) Kurose River, Japan 9.4-300 × 10 −12 DAF-2 ---- Olasehinde et al (2009) Kurose River (K1 4 × 10 −12 DAF-2 1.6 × 10 −12 0.06 -Monthly 2013 Anifowose et al (2015) Besides, in natural sunlit seawater, photolyzed dissolved nitrate (NO − 3 ) could be a source of NO through NO − 2 (Reaction 9); during the process of ammonium (NH + 4 /NH 3 ) oxidation into NO − 2 and NO − 3 , NO might be an intermediate (Joussotdubien and Kadiri, 1970), or NO could be produced through amino-peroxyl radicals (NH 2 O q 2 ) through Reactions (10) to (14) (Laszlo et al, 1998;Clarke et al, 2008).…”

“…Table 1 summarizes studies about photochemical production of NO measured in the surface waters of the equatorial Pacific Ocean Zafiriou and McFarland, 1981), the Seto Inland Sea (Olasehinde et al, 2009(Olasehinde et al, , 2010Anifowose and Sakugawa, 2017), the Bohai Sea and Yellow Sea (Liu et al, 2017;Tian et al, 2019), and the Kurose River (Japan) (Olasehinde et al, 2009;Anifowose et al, 2015). NO concentration was determined by the balance of the production and the removal process; thus, changes in NO production and removal rates could influence NO concentration in the seawater.…”

“…NO concentration was determined by the balance of the production and the removal process; thus, changes in NO production and removal rates could influence NO concentration in the seawater. In the surface seawater, the photochemical process was regarded as the main production process (Zafiriou and McFarland, 1981;Olasehinde et al, 2010;Anifowose et al, 2015). In Table 1, NO photoproduction rates varied among different seawater samples: the photoproduction rates in Kurose River (average: 499 × 10 −12 mol L −1 s −1 ) were the largest, which might be due to an increase in nitrite being released into the river because of agricultural activity during the study time.…”

“…However, NO concentration was about 1.6 × 10 −12 mol L −1 , at the lowest level, which was because of higher scavenging rate in river water. Anifowose et al (2015) found that NO lifetime, which was defined as the reciprocal of first-order scavenging rate constant of NO (Olasehinde et al, 2010) in Kurose River, was only 0.25 s. The lifetime of NO showed an increasing trend from river (several seconds) via inland sea (dozens of seconds) to open sea (dozens to hundreds of seconds), reviewed in Anifowose and Sakugawa (2017). However, NO showed higher concentration levels in coastal waters than in open sea; higher photoproduction rates in coastal waters than open sea, or other production processes in coastal waters, might account for this.…”