Wet and Dry Nitrogen Depositions in the Pearl River Delta, South China: Observations at Three Typical Sites With an Emphasis on Water‐Soluble Organic Nitrogen

Abstract

Inorganic nitrogen (N) deposition in China is among the highest in the world, yet organic N deposition in the country has not been well constrained. In this study, wet and dry depositions of both organic and inorganic N were observed for 2 years at three contrasting sites (urban-rural-forest) in the Pearl River Delta (PRD) region, South China. Determined annual total dissolved N (TDN) deposition rates were 39.8, 33.8, and 52.0 kg N ha −1 year −1 at the urban, rural, and forest sites, respectively. The contributions of NO 3 − -N, NH 4 + -N, and water-soluble organic N (WSON) to total N deposition were 26.7-37.8%, 34.6-40.9%, and 26.1-32.3%, respectively. Wet N deposition accounted for about 54-68% in total N deposition at the sites. It is worth noting that the deposition rates of WSON in the PRD were among the highest in developed regions in the world. In wet depositions, the concentrations and proportions of WSON were significantly higher during the harvest seasons, especially at the non-urban sites, mainly due to enhanced biomass burning in the period. In dry deposition, the seasonal pattern of WSON was inconsistent with that of NO 3 − -N or NH 4 + -N. Biological/soil organic N might be the important sources of WSON in dry deposition. Our results suggest that WSON contributed significantly to atmospheric N deposition in the PRD and more attentions should be paid to the WSON to get a true picture of N depositions and its impacts on the ecosystem.

Enhanced Wet Deposition of Water‐Soluble Organic Nitrogen During the Harvest Season: Influence of Biomass Burning and In‐Cloud Scavenging

“…Deposition samples were concurrently collected at three contrasting sites (one urban, one rural, and one forest) from September 2016 to August 2018. Detailed descriptions of sampling can be found elsewhere (Yu et al, 2020). Wet and dry deposition rates of NO 3 − ‐N, NH 4 + ‐N, and WSON, as well as spatiotemporal patterns of NO 3 − ‐N, NH 4 + ‐N, and WSON in wet and dry deposition at the three sites, were presented previously (Yu et al, 2020).…”

“…Detailed descriptions of sampling can be found elsewhere (Yu et al, 2020). Wet and dry deposition rates of NO 3 − -N, NH 4 + -N, and WSON, as well as spatiotemporal patterns of NO 3 − -N, NH 4 + -N, and WSON in wet and dry deposition at the three sites, were presented previously (Yu et al, 2020). Wet WSON deposition was found to represent a major fraction of total WSON deposition, and remarkably, there was a substantial increase of the wet deposition rate of WSON during fall at all the three sites.…”

“…The Pearl River Delta (PRD) city cluster is located in south China and considered as one of the largest megacities in the world with an area of 5.6 × 10 4 km 2 and a population of ~43 million and has experienced rapid industrialization in the last several decades. Previous studies found that WSON deposition rates at some sites of this region could reach 8–18 kg N ha −1 yr −1 in 2005–2009 (Fang et al, 2008; Li et al, 2012; Wang et al, 2013), and a recent study revealed that deposition rates of WSON at three contrasting sites were still as high as 9–17 kg N ha −1 yr −1 in 2016–2018 (Yu et al, 2020), which are among the highest levels of WSON deposition rates in developed regions worldwide (Cape et al, 2012; Cornell, 2011; Jiang et al, 2013; Neff et al, 2002). In the present study, we selected one station in this region, compared the chemical compositions in concurrently collected rainwater and aerosol samples, to explore the key sources and scavenging processes influencing wet WSON deposition in continental areas.…”

Improvement and Impacts of Forest Canopy Parameters on Noah-MP Land Surface Model from UAV-Based Photogrammetry

“…The gap area accounts for 3∼25% of forest area, and the average size is about 80∼100 m 2 , which makes it difficult to use a larger UAV to carry LiDAR instruments or other big equipment. UAV images over the study site were collected between August 2019 to September 2019, as part of a comprehensive observation experiment in CN-Din [35].…”

Improvement and Impacts of Forest Canopy Parameters on Noah-MP Land Surface Model from UAV-Based Photogrammetry

“…The vegetation is fairly homogeneous within the distance of ∼1 km in the direction of the dominant wind direction (Northeast). The measurements of UAV photographs were performed from August 2019 to September 2019, representing a comprehensive observation experiment of dry deposition measurement in CN-Din [30].…”