Patterns and sources of atmospheric nitrogen deposition in Yancheng, Eastern China, indicated by moss N concentration and δ15N signatures

Özet

Excess N deposition from human activities has caused large-scale negative impacts on global ecosystem health and services. However, despite its importance, atmospheric N deposition in Yancheng remains poorly studied. Herein, spatial distributions of atmospheric N deposition and its probable sources were determined using ordinary kriging interpolation analysis of tissue N concentrations and δ15N signatures from 68 moss samples from sites around Yancheng. Hotspots of moss N concentration (1.0–2.5%) and, thus total N deposition (TN), were found in the northeast and west, with an overall decreasing tendency from west to east. TN averaged 18.18 kg N ha−1 yr−1. Moss δ15N varied between −7.76‰ and 1.28‰, with an overall increase from the center to surrounding areas. Negative moss δ15N values revealed that NH3 from agriculture and urban sewage were the main sources of atmospheric N deposition. Based on moss δ15N values, it could be concluded that wet deposition of NO3 −- N and NH4 +- N accounted for 20% (3.56 kg N ha−1 yr−1) and 66% (12.07 kg N ha−1 yr−1) of TN, respectively. Overall, 30% of the region exceeded the critical N deposition load for terrestrial ecosystems (20 kg N ha−1 yr−1), and given current average trends in increasing N deposition, all areas in the Yancheng region are predicted to surpass the critical load within the next 19 years. A long-term N mitigation strategy for the entire region should, thus, be at the forefront of governmental policymaking, with areas of Yancheng experiencing high N deposition requiring urgent attention.