Coastal creeks as greenhouse gas hotspots: the role of nutrient availability and microbial activity

Abstract

Coastal creeks are ubiquitous in wetland ecosystems, and they act as conduits for significant inputs of nutrients and anthropogenic carbon from surrounding areas, making them potential hotspots for greenhouse gas (GHG) emission. To date, the spatiotemporal variations in GHG emission across different types of coastal creeks and their environmental drivers remain poorly understood due to the lack of observational data. A field investigation was carried out to analyze the concentrations and fluxes of CO₂ and CH₄ across three coastal creeks (designated as CC1, CC2 and CC3) within the Shanyutan Wetland in southeastern China. These creeks received exogenous input from different sources. The results indicated that CO₂ and CH₄ concentrations in all three creeks remained persistently oversaturated, with concentrations in the range of 14.5–61.5 µmol L⁻¹ and 1.1–11.8 µmol L⁻¹, respectively. The estimated emission fluxes varied in the range of 0.4–3.6 mmol CO₂ m⁻² h⁻¹ and 40.2–581.1 µmol CH₄ m⁻² h⁻¹. The mean CO₂ efflux over the four seasons was highest in CC1 (1.9 mmol m⁻² h⁻¹) and lowest in CC2 (0.8 mmol m⁻² h⁻¹). For CH₄ efflux, the highest value was in CC2, followed by CC3 and CC1. PO₄³⁻ availability was the primary factor affecting the change of CO₂ concentration and emission, while CH₄ were primarily regulated by DOC, DO, TDN and abundances of mcrA and pmoA genes. These results highlighted that coastal creeks are significant atmospheric GHG sources and exogenous inputs substantially influenced their variabilities.