Distinguishing atmospheric nitrogen compounds (nitrate and ammonium) in lichen biomonitoring studies

• Published in: Environmental science--processes & impacts Vol. 23; no. 12; pp. 221 - 236
• Main Authors: Niepsch, Daniel, Clarke, Leon J, Tzoulas, Konstantinos, Cavan, Gina
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 15.12.2021
• Subjects: Air Pollutants - analysis; Air quality; Ammonium; Ammonium Compounds - analysis; Anthropogenic factors; Biological Monitoring; Biomonitoring; Emissions; Environmental Monitoring; Human influences; Humans; Lichens; Livestock; Metabolism; Nitrates; Nitrates - analysis; Nitrogen; Nitrogen - analysis; Nitrogen Compounds; Nutrient concentrations; Particulate emissions; Particulate matter; Potassium; Potassium chloride; Speciation; Xanthoria parietina
• ISSN: 2050-7887; 2050-7895
• DOI: 10.1039/d1em00274k

Nitrogen speciation, i.e. distinguishing nitrate (NO 3 − ) and ammonium (NH 4 + ), is commonly undertaken in soil studies, but has not been conducted extensively for lichens. Lichen total nitrogen contents (N wt%) reflect airborne atmospheric nitrogen loadings, originating from anthropogenic sources ( e.g. vehicular and agricultural/livestock emissions). Albeit nitrogen being an essential lichen nutrient, nitrogen compound ( i.e. NO 3 − and NH 4 + ) concentrations in the atmosphere can have deleterious effects on lichens. Moreover, N wt% do not provide information on individual nitrogen compounds, i.e. NO 3 − and NH 4 + which are major constituents of atmospheric particulate matter ( e.g. PM 10 and PM 2.5 ). This study presents a novel method to separate and quantify NO 3 − and NH 4 + extracted from lichen material. An optimal approach was identified by testing different strengths and volumes of potassium chloride (KCl) solutions and variable extraction times, i.e. the use of 3% KCl for 6 hours can achieve a same-day extraction and subsequent ion chromatography (IC) analysis for reproducible lichen nitrate and ammonium concentration determinations. Application of the method was undertaken by comparing urban and rural Xanthoria parietina samples to investigate the relative importance of the two nitrogen compounds in contrasting environments. Findings presented showed that lichen nitrogen compound concentrations varied in rural and urban X. parietina samples, suggesting different atmospheric nitrogen loadings from potentially different sources ( e.g. agricultural and traffic) and varied deposition patterns ( e.g. urban layout impacts). Despite potential impacts of nitrogen compounds on lichen metabolism, the approach presented here can be used for quantification of two different nitrogen compounds in lichen biomonitoring studies that will provide specific information on spatial and temporal variability of airborne NO 3 − and NH 4 + concentrations that act as precursors of particulate matter, affecting air quality and subsequently human health. Nitrogen speciation (NO 3 − and NH 4 + ) method from lichen material, using 0.05 g lichen, 3 mL of 3% KCl and 6 hours extraction.