Over the last few decades, gas membrane diffusion has been applied to elaborate chemical analyses, leading to the development of a series of gas sensing techniques for environmental monitoring. This work reviews the gas sensors that incorporate the gas membrane diffusion mechanism with either electrochemical or optical transducers, and concludes the theoretical relationship between the detection signal and the mass transfer parameters across the membrane, such as membrane thickness, gas diffusion coefficient and driving force. It also envisages that, with the availability of modern electronic and computing technology, the in-situ membrane diffusion rate of a target species is proportional to its real-time concentration in the sample and can be readily measured. Such a measuring principle is promising in developing the next generation of gas sensors based on membrane diffusion to achieve real-time and continuous monitoring of important trace gases (e.g. CO2, SO2, NH3) in the natural environment (water, soil and air).Griffith Sciences, Griffith School of EnvironmentFull Tex

Estuaries play a key role in moderating the flow of nitrogen (N) to marine ecosystems. However, the magnitude of this N removal can vary dramatically both within and between estuaries due to the benthic habitats present. Here, we compare denitrification, coupled nitrification–denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) across a mosaic of benthic habitats in the subtropical Noosa River Estuary, Australia. Using ¹⁵N tracer techniques and passive pore‐water samplers, we show that coupled nitrification–denitrification was the dominant pathway for N₂ production across all habitats, with higher rates in vegetated habitats (10–70 μmol N m⁻² h⁻¹) compared to bare sediments (0.9–2 μmol N m⁻² h⁻¹). Unusual pore‐water profiles in the macroalgal sediments suggest the presence of sulfur‐driven anoxic nitrification of NH₄⁺ to NO₃⁻ and N₂. A benthic N budget showed that combined denitrification and coupled nitrification–denitrification accounted approximately 96% of the N₂ production, while DNRA accounted for 9% of total NO₃⁻ reduction pathways in the Noosa River Estuary. The macroalgae habitat contributed 76% of total N removal via N₂ production and 65% of N retention via DNRA, despite accounting for only 25% of the total surface area. We show a strong relationship between seagrass and macroalgae area and N₂ production (r² = 0.8; p < 0.01), and as such, the capacity to mitigate reactive N loads in estuaries may decrease with the large‐scale loss of seagrass and other vegetated habitats.