Biogeochemical Cycling of Nitrogen in the Niger Delta Coastal Wetlands

Nitrogen cycling in coastal wetland ecosystems involves complex microbially mediated transformations that regulate nutrient export to coastal waters and greenhouse gas emissions to the atmosphere, yet these processes remain poorly characterised in the oil-impacted wetlands of the Niger Delta, South South Nigeria. This study investigates the rates and controlling factors of key nitrogen transformation processes, including nitrification, denitrification, and anaerobic ammonium oxidation (anammox), in mangrove and freshwater wetland sediments across a contamination gradient in Delta and Bayelsa States. Sediment cores are collected from six sites spanning a pristine reference mangrove, two oil-impacted mangrove sites, a recovering remediated site, and two freshwater herbaceous marsh sites. Laboratory incubation experiments using isotope pairing techniques with 15N-labelled nitrogen substrates quantify process rates under controlled temperature and salinity conditions. Microbial community composition at each site is characterised using 16S rRNA amplicon sequencing to relate functional microbial groups (Nitrospira, Thiobacillus, Candidatus Scalindua) to measured process rates. Environmental drivers including total petroleum hydrocarbon concentration, soil redox potential, salinity, organic carbon, and temperature are measured concurrently. Nitrogen export fluxes from wetland sediments to the water column are estimated using benthic flux chamber incubations. Findings are expected to demonstrate significantly suppressed denitrification rates in oil-contaminated sediments and elevated ammonium flux to overlying water, contributing to eutrophication in adjacent creeks. Keywords: nitrogen cycling, Niger Delta wetlands, denitrification, anammox, biogeochemistry