Effect of Aquaculture Reclamation on Sediment Nitrates Reduction Processes in Mangrove Wetland

Abstract

Sediment denitrification, anaerobic ammonium oxidation (anammox), and nitrate dissimilation to ammonium (DNRA) play an important role in controlling the dynamics of nitrates (NOx−) and their fate in estuarine and coastal ecosystems. However, the effects of land-use change on NOx− reduction processes in mangrove sediments are still unclear. Here, we used a mud experiment method combined with a 15N stable isotope tracer method to study the mechanism and ecological environment of the change of land use pattern on the sediment NOx− reduction processes in mangrove wetlands. Our study showed that most physicochemical parameters, NOx− reduction rates, and their gene abundances varied considerably. The denitrification, anammox, and DNRA rates in mangrove sediment cores were in a range of 1.04–4.24 nmol g−1 h−1, 0.14–0.36 nmol g−1 h−1, and 0–2.72 nmol g−1 h−1, respectively. The denitrification, anammox, and DNRA rates in aquaculture sediment cores were in a range of 1.06–10.96 nmol g−1 h−1, 0.13–0.37 nmol g−1 h−1, and 0–1.96 nmol g−1 h−1, respectively. The highest values of denitrification, anammox, DNRA, the contribution of denitrification and DNRA to total NOx− reduction (DEN% and DNRA%), gene abundances (nirS, Amx 16S rRNA, and nrfA), total organic carbon (TOC), total nitrogen (TN), and TOC/TN in sediments were generally found in the top layer (0–5 cm) and then decreased with depth, while the contribution of anammox to total NOx− reduction (ANA%), Fe2+, and Fe2+/Fe3+ were generally increased with sediment depth in both mangrove and aquaculture ecosystems. When mangrove wetlands are transformed into pools, some properties (including TOC, TN, and Fe3+), DNRA rates, DRNA%, and nrfA gene abundances were decreased, while some properties (including NH4+, TOC/TN, Fe2+, and Fe2+/Fe3+), denitrification rates, DEN%, nirS, and ANAMMOX 16S gene abundances were increased. Sediment organic matter (TOC and TN) content and Fe2+ both affected NO3− reduction rates, with organic matter the most prominent factor. Thus, aquaculture reclamation enhances N loss while reducing N retention in sediments of mangrove wetlands, which plays an important role in regulating the source and fate of reactive N in mangrove ecosystems.

Evaluation of the quality of mangrove ecosystems using macrozoobenthos as bioindicators in the Southern Coast of East Java, Indonesia

“…High nitrate levels have negative impacts on the environment such as eutrophication, increasing the growth of harmful algal blooms (HABs), decreasing water oxygen levels, and worsening the balance of the N biogeochemical cycle (Roberts et al 2012;Li et al 2014;Wei et al 2020), although mangrove vegetation can denitrify nitrate in the waters and sediment (Alongi 2020;Hao et al 2022). High nitrate levels will significantly disrupt mangrove growth and cause death because mangroves have reached a certain tolerance range (Hao et al 2022).…”

“…High nitrate levels have negative impacts on the environment such as eutrophication, increasing the growth of harmful algal blooms (HABs), decreasing water oxygen levels, and worsening the balance of the N biogeochemical cycle (Roberts et al 2012;Li et al 2014;Wei et al 2020), although mangrove vegetation can denitrify nitrate in the waters and sediment (Alongi 2020;Hao et al 2022). High nitrate levels will significantly disrupt mangrove growth and cause death because mangroves have reached a certain tolerance range (Hao et al 2022). Based on the results of this study, it can be concluded that the evaluation of the quality of the mangrove ecosystem, both restoration, and natural ecosystems, can be carried out using the diversity of macrozoobenthos, especially crabs and gastropods as bioindicators.…”