Agricultural ammonia dry deposition and total nitrogen deposition to a Swiss mire

Abstract

Mires are among the ecosystems most affected by eutrophication caused by excessive nitrogen (N) inputs via N deposition of ammonium (NH4+), nitrate (NO3–), nitric acid (HNO3), nitrogen dioxide (NO2), and ammonia (NH3). As NH3 emissions are mostly generated by agriculture, a particular conflict of interest exists in areas where agricultural production systems are located nearby sensitive ecosystems, as often is the case in Switzerland. Therefore, this study aimed at quantifying and evaluating total N inputs to a mire in the Swiss Alpine foothills during 2007–2019, focusing on NH3 dry deposition. Three surface–vegetation–atmosphere transfer models were used to estimate dry deposition of NH3 based on micrometeorological data in combination with monthly passive sampler NH3 concentration measurements. NH3-N dry deposition summed up to 1.5–5.2 kg N ha–1 a–1, while total N loads were 11.5–14.2 kg N ha–1 a–1, well beyond the critical N loads for raised bogs (5–10 kg N ha–1 a–1), and also higher than the lower limits for oligotrophic fens and mountain hay meadows (10 kg N ha–1 a–1). Hence, the mire studied is most likely negatively affected by eutrophication, which could ultimately lead to biodiversity loss and ecosystem instability. This is particularly remarkable as the monthly NH3 concentrations at the study site (0.4–4.7 µg m–3) are comparatively low for Switzerland.