Estimates of dry and wet deposition using tissue N contents and¹⁵N natural abundance in epilithic mosses in atmospheric NH_y-dominated areas

Abstract

Measurement of dry N deposition by physical methods is time‐consuming because it is usually difficult to measure directly. In this study, an alternative approach has successfully been proposed by coupling isotopic ratios with tissue N contents of epilithic mosses. The method is to use moss N contents to quantitatively estimate total N (TN) deposition and then to use 15N natural abundance in mosses to discriminate dry and wet deposition in atmospheric NHy‐dominated areas (NHy/TN > 0.75). On the basis of the isotopic balance between atmospheric NHy and moss tissue N and the correlation between atmospheric NHy concentrations and their isotopes, both wet and dry N deposition can be estimated. By the approach, we have estimated rainwater ammonium concentrations and contribution percentage of wet deposition to total N deposition (fwet) in some areas of southern China. The results indicated that rainwater ammonium concentrations increased relative to those reported previously in most cities, owing to stronger anthropogenic activity. The fwet values estimated in most sites were found to be slightly higher than those reported, because faster transformation rates due to higher SO2 emission later in acid rain areas of southern China favored deposition in the form of wet deposition instead of dry deposition. The largest uncertainty of the approach comes from the influence of NOx in the atmosphere, and thus it cannot be used in areas where NOx deposition is high. The presented isotopic approach represents a new application of moss biomonitoring for estimating atmospheric N deposition in NHy‐dominated areas.

Significant contributions of combustion‐related NH3 and non‐fossil fuel NOx to elevation of nitrogen deposition in southwestern China over past five decades

“…Thus, studies have shown that moss δ 15 N is an ideal integrator of site‐specific information of N deposition (Stewart et al, 2002) and mosses can keep original N contents and δ 15 N values during decades of storage (Peñuelas & Filella, 2001; Pitcairn et al, 1995). In the 2000s, moss monitoring networks were first established in Western Europe (Harmens et al, 2014), after which moss N contents have been widely used to quantify N deposition fluxes in Europe (Bragazza et al, 2005; Gerdol et al, 2014), South Africa (Wilson et al, 2008), and China (Qu et al, 2016; Xiao & Liu, 2011). However, very few moss studies have been conducted on temporal variations of regional N deposition (Delgado et al, 2013; Peñuelas & Filella, 2001; Solga et al, 2006; Wilson et al, 2008), with few studies in East Asia.…”

Ammonium first: natural mosses prefer atmospheric ammonium but vary utilization of dissolved organic nitrogen depending on habitat and nitrogen deposition

“…Consequently, the δ 15 N analysis of mosses can reveal dominant N sources and or N preferences in N assimilation. In studies in China, for example, the δ 15 N of mosses on bare rock showed low values in regions where inorganic N deposition was dominated by (Liu et al ., ; Xiao & Liu, ). However, the extent to which mosses rely on and the extent to which they use and DON remain open questions.…”

Pitfalls and New Mechanisms in Moss Isotope Biomonitoring of Atmospheric Nitrogen Deposition

“…Second, moss N bulk and δ 15 N bulk enable the high-resolution monitoring of anthropogenic N distribution at geographic scales that are difficult to achieve through direct sampling of the atmosphere. − On the basis of the generally higher δ 15 N of NO 3 – than RDN in deposition, − ,− moss N bulk and δ 15 N bulk were applicable to differentiate the dominant N form in deposition, facilitating a link between inputs of specific N species with ecosystem responses. − Because N deposition in most regions of Europe and eastern Asia has a higher RDN than NO 3 – –N deposition, , a general pattern of decreasing moss δ 15 N bulk with an increasing ratio of RDN or NH 4 + –N to NO 3 – –N has been established. ,,, Such a relation is now extended to evaluate N deposition in eastern Asia, where RDN is markedly higher than NO 3 – –N in deposition (e.g., NH 4 + –N/NO 3 – –N = 3.1–21.5 in China). , …”