<p>Coastal peatlands are increasingly threatened by seawater intrusion and salinity fluctuations under climate change. This study investigated nitrogen dynamics following a storm surge event in a coastal peatland (Hütelmoor) in Northeast Germany, combining surface water monitoring and controlled soil leaching experiments at two locations: a near-natural location (Heiligensee) and a rewetted, historically drained location (Moorhof). Surface water observations revealed pronounced spatial differences in post-flood nitrogen responses. At Heiligensee, ammonium (NH₄⁺) concentrations reached up to ~ 179 µmol L^–1 in early 2019 and remained elevated for several weeks, whereas Moorhof showed lower concentrations with rapid declines following the flood. Soil leaching experiments demonstrated that NH₄⁺ release responded to salinity exposure but was also modulated by location- and depth- specific soil hydro-physical properties. Particularly, subsoils (30–40&#xa0;cm) at Moorhof, characterized by low porosity and low saturated hydraulic conductivity (Ks), released the highest NH₄⁺ amounts (up to 3.86&#xa0;mg per sample) under brackish and saline conditions, identifying them as hotspots for nutrient release. Principal component analysis (PCA) showed that the first two components explained 81.5% of the total variance in NH₄⁺ release patterns, separating soils along a structural gradient (PC1: soil organic matter content, bulk density, porosity) and a hydraulic–nutrient gradient (PC2: macroporosity, Ks, NH₄⁺ release). These findings emphasize the need to account for both surface water dynamics and subsurface soil heterogeneity in coastal peatland restoration. Identifying location- and depth-specific nitrogen risks is essential to improve nutrient management and ecosystem resilience under future salinization scenarios.</p> Graphical Abstract <p></p>