AUTHOR=Lin Xianbiao , Lin Genmei , Zheng Yijie , Li Wenjing , Guo Peng , Fan Shiyuan , Kong Tiantian , Tian Dongfan , Sun Dongyao , Shen Zhuo 

TITLE=Nitrogen mineralization and immobilization in surface sediments of coastal reclaimed aquaculture ecosystems

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.1093279

DOI=10.3389/fmars.2022.1093279

ISSN=2296-7745

ABSTRACT=Nitrogen (N) mineralization and immobilization are two crucial processes driven by microorganisms especially in aquatic sediments, which may play significant roles in regulating water quality in aquaculture ecosystems. However, limited information is available about the quantitative importance of sedimentary N mineralization and immobilization in artificial systems. Here, a combination of incubation experiments with a 15N isotope dilution technique were employed, aiming to quantify N mineralization and immobilization processes in surface sediments (0–5 cm) of three types of aquaculture ecosystems (seabass, white shrimp, and green crab ponds) within the Pearl River Estuary (PRE). Our results showed that gross N mineralization (GNM) rate, gross ammonium (NH4+) immobilization (GAI) rate, relative ammonium immobilization (RAI) rate, and percentage of NH4+ mineralized per day (PAM) were in a range of 1.75–15.13 μg N g-1 d-1, 1.67–13.68 μg N g-1 d-1, 0.65–1.45, and 0.15–1.25%, respectively. The GNM and GAI rates in summer were significantly higher than their counterparts in winter (p<0.05), with no statistically significant differences among different aquaculture ecosystems (p>0.05). The GNM and GAI rates were both significantly related to overlying water nitrate(NO3−), as well as sediment moisture content, bulk density, organic matter, ferrous oxide (Fe2+), and microbial abundances. Moreover, the total mineralized and immobilized N in aquaculture surface sediment from the Guangdong-Hong Kong-Macao Greater Bay Area were estimated to be approximately 4.55×104 and 3.68×104 t N yr-1, respectively. Higher N mineralization relative to N immobilized fluxes indicated that the sediment serves as an important source of eutrophication in reclaimed aquaculture system of coastal wetland. Overall, our results strengthen the importance of N mineralization and immobilization in controlling the N budget in coastal aquaculture sediments, which improves the understanding of these two processes and relevant regulation mechanisms in the reclaimed aquaculture ecosystems.