Biomonitoring of dairy farm emitted ammonia in surface waters using phytoplankton and periphyton

The increasing environmental abundance of reactive N ('Nr') entails many adverse effects for society such as soil degradation and eutrophication. In addressing the global surplus of N, there is a pressing need to quantify local sources and dynamics of Nr. Although quantified as an important anthropogenic source of Nr, the spatiotemporal patterns of ammonia ('NH₃') emitted by dairy farming and its resulting pressure on local surface waters lacks quantification. Quantification could optimize farm management with minimized losses of valuable nitrogen and protection of freshwater ecology. This study aimed to unravel spatiotemporal dynamics of ammonia nitrogen emitted by a dairy farm in the atmospheric and aquatic geo-ecosphere. Atmospheric NH₃ and aqueous ammonium ('NH₄⁺') were determined over time, together with meteorological variables. Aquatic biomonitors (periphyton and phytoplankton) were employed to monitor the spatial impacts of cattle-stable emitted NH₃. Atmospheric NH₃ on the farm was significantly regulated by wind, sharply declining over increasing distances from the stable (average decrease in the dominant wind direction from 55.5 μg/m³ at 20 m to 5.8 μg/m³ at 500 m, in the other wind directions values decreased from 38.3 μg/m³ to 6.0 μg/m³). This was also reflected in local surface water concentrations of NH₄⁺, with average concentrations decreasing from 37.0 mg [NH₄⁺-N]/L at 65 m to 4.8 mg [NH₄⁺-N]/L in the dominant wind direction, and from 1.2 to 0.7 in other directions. Periphyton biomass, total N ("TN") and δ¹⁵N all significantly reflected spatiotemporal dynamics of atmospheric NH₃ and aqueous NH₄⁺, as did phytoplankton TN. The cattle stable significantly influenced local water quality through atmospheric spreading of NH₃, and both aquatic biomonitors were influenced by and reflected dairy farm emitted NH₃ with a sharp dilution over distance. This study strongly underlines the importance of atmospheric transport of dairy farm emitted NH₃ and its effects on local water quality.