Evidence and causes of recent decreases in nitrogen deposition in temperate forests in Northeast China.

High reactive nitrogen (N) emissions due to anthropogenic activities in China have led to an increase in N deposition and ecosystem degradation. The Chinese government has strictly regulated reactive N emissions since 2010, however, determining whether N deposition has reduced requires long-term monitoring. Here, we report the patterns of N deposition at a rural forest site (Qingyuan) in northeastern China over the last decade.

Large Seasonal Variation in Nitrogen Isotopic Abundances of Ammonia Volatilized from a Cropland Ecosystem and Implications for Regional NH Source Partitioning.

Ammonia (NH) volatilization from agricultural lands is a main source of atmospheric reduced nitrogen species (NH). Accurately quantifying its contribution to regional atmospheric NH deposition is critical for controlling regional air nitrogen pollution. The stable nitrogen isotope composition (expressed by δN) is a promising indicator to trace atmospheric NH sources, presupposing a reliable nitrogen isotopic signature of NH emission sources.

Patterns and drivers of atmospheric inorganic nitrogen deposition in Northeast Asia.

Elevated nitrogen (N) deposition due to intensified emissions of NH and NO is a global problem with profound consequences on living organisms and the environment. Although N emission rates are currently considered to be high in East Asia, reports on the current N deposition level and composition are still limited, especially in northeastern China, where official N deposition monitoring sites are unavailable. This limits our understanding of the spatio-temporal N deposition patterns and their influencing factors at regional to continental scales.

Isotopic imprints of aerosol ammonium over the north China plain.

Atmospheric PM poses a variety of health and environmental risks to urban environments. Ammonium is one of the main components of PM, and its role in PM pollution will likely increase in the coming years as NH emissions are still unregulated and rising in many cities worldwide. However, partitioning urban NH sources remains challenging.

Atmospheric nitrate formation pathways in urban and rural atmosphere of Northeast China: Implications for complicated anthropogenic effects.

Effects of human activities on atmospheric nitrate (NO) formation remain unclear, though the knowledge is critical for improving atmospheric chemistry models and nitrogen deposition reduction strategies. A potentially useful way to explore this is to compare NO oxidation processes in urban and rural atmospheres based upon the oxygen stable isotope composition of NO (ΔO-NO). Here we compared the ΔO-NO from three-years of daily-based bulk deposition in urban (Shenyang) and forested rural sites (Qingyuan) in northeast China and quantified the relative contributions of different formation pathways based on the SIAR model.

Multiyear Measurements on ΔO of Stream Nitrate Indicate High Nitrate Production in a Temperate Forest.

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (ΔO) of nitrate (NO) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha yr (average 94 ± 10 kg N ha yr) over the 4 years in this forest.

Fate of atmospherically deposited NH and NO in two temperate forests in China: temporal pattern and redistribution.

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the N-tracer method to investigate both the short-term (1 week to 3 months) and long-term (1-3 yr) fates of deposited NH or NO by following the recovery of the N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China.

Seasonal pattern of ammonium N natural abundance in precipitation at a rural forested site and implications for NH source partitioning.

Excess ammonia (NH) emissions and deposition can have negative effects on air quality and terrestrial ecosystems. Identifying NH sources is a critical step for effectively reducing NH emissions, which are generally unregulated around the world. Stable nitrogen isotopes (δN) of ammonium (NH) in precipitation have been directly used to partition NH sources.