Seasonal comparison of potential denitrification rates and nitrogen functional genes with sediment depths in the wetland, Korea

Abstract

<p>Wetlands provide not only habitats for a wide range of organisms but also ecological functions of degrading and removing pollutants from water body through a variety of physical, chemical and biological processes. Seasonal variation including recent increases in the frequency of floods and droughts have affected the hydrological environment of wetlands. Furthermore, these effects may result in changes in redox conditions in the nitrogen biogeochemical process in wetland sediments. Therefore, in this study, the potential denitrification rate and denitrification-related gene quantitative analysis was performed to investigate seasonal nitrogen dynamics of wetland sediments associated with surface and groundwater interactions in Baekseok reservoir wetlands (Gunsan-si, Jeollabuk Province, Korea). Sediment from two different sites (i.e., PA and PB) in wetland were collected with different depths in June and December 2019 to investigate seasonal effects on denitrification with sediment depths. Potential denitrification rate experiments were performed using the acetylene inhibition technique, and denitrification-related gene quantification was performed by qPCR analysis. As a result of potential denitrification rate, PA sites ranged from 2.67–3.27 ng N<sub>2</sub>O/g/hr and 3.13–15.13 ng N<sub>2</sub>O/g/hr in June and December, respectively. PB sites ranged from 2.43-6.30 ng N<sub>2</sub>O/g/hr and 5.47-6.30 ng N<sub>2</sub>O/g/hr. Overall, higher levels were observed at 0–10 cm, with higher denitrification rates in December than in June. The qPCR analysis showed that the narG, nirS and nosZ gene copy number ranges for the PA site in June showed 1.82 x 10<sup>6</sup> – 6.15 x 10<sup>7</sup> copies/g, and in December 7.71 x 10<sup>5</sup> – 5.97 x 10<sup>8</sup> copies/g. The narG, nirS and nosZ gene copy number ranges for the PB site in June showed 3.53 x 10<sup>5</sup> – 3.86 x 10<sup>8</sup> copies/g, and in December, 1.24 x 10<sup>6</sup> – 3.47 x 10<sup>8</sup> copies/g. Overall, both sites had higher copy numbers in December than in June, corresponding to an increase in potential denitrification rate in December.</p>