Stable isotopic characterization of nitrate wet deposition in the tropical urban atmosphere of Costa Rica

Abstract

Increasing energy consumption and food production worldwide results in anthropogenic emissions of reactive nitrogen into the atmosphere. To date, however, little information is available on tropical urban environments where inorganic nitrogen is vastly transported and deposited through precipitation on terrestrial and aquatic ecosystems. To fill this gap, we present compositions of water stable isotopes in precipitation and atmospheric nitrate (δ 18 O-H2O, δ 2 H-H2O, δ 15 N-NO3 -, and δ 18 O-NO3 -) collected daily between August 2018 and November 2019 in a tropical urban atmosphere of central Costa Rica. Rainfall generation processes (convective and stratiform) were identified using stable isotopes in precipitation combined with air mass back trajectory analysis. A Bayesian isotope mixing model forced with δ 15 N-NO3values corrected for potential 15 N fractionation effects reveal the predominant contribution of biomass burning and lightning to nitrate wet deposition. δ 18 O-NO3values in Caribbean convective rainfall reflect the oxidation chemistry of NOx sources whereas δ 15 N-NO3values in Pacific stratiform rainfall indicate the transport of nitrogen sources contributing to nitrate in atmospheric deposition. These findings provide necessary baseline information about the combination of water and nitrogen stable isotopes with atmospheric chemistry and hydrometeorological techniques to better understand wet deposition processes and to characterize the origin of inorganic nitrogen loadings in tropical regions.

Nitrate Legacy in a Tropical and Complex Fractured Volcanic Aquifer System

“…where the major nitrogen median contributions in mixed land use scenarios are driven by manure and sewage (∼45%) > SN (∼30%) > CF (∼17%) > atmospheric deposition (AD) (∼3%) (Fadhullahet al, 2020;Gribilla et al, 2020;Jung et al, 2023;Liu et al, 2021;Mao et al, 2023;Nyilitya et al, 2021;Saka et al, 2023;Yu et al, 2020). However, our results suggest greater nitrogen AD (Villalobos-Forbes et al, 2021) and manure and sewage contributions compared to the tropics. Interestingly, nitrate groundwater legacy in the northern slope of the Central Valley of Costa Rica has evolved from ∼30% to ∼15% in chemical fertilizer contributions, and from ∼21% up to ∼69% in manure and sewage inputs during the last decades, as a direct result of the crop area conversion to meet the increasing demand in the residential areas.…”

“…Groundwater samples were collected in production wells representing the Barva and Colima aquifer units and the elevation range. Endmembers (as liquids) were grouped into four categories: (a) fertilizers (i.e., potassium, magnesium, ammonium, and calcium nitrate salts commonly used on coffee plantations; N = 4) (Ca[NO 3 ] 2 , Mg[NO 3 ] 2 , KNO 3 , and NH 4 NO 3 ), (b) soils (i.e., soil water extracts from west and east high‐elevation forested headwaters; N = 2), (c) manure and sewage (i.e., septic tanks, dairy farms, and wastewater treatment plant affluents; N = 4), and (d) precipitation ( N = 156, 2018–2020; Villalobos‐Forbes et al., 2021). Fertilizer dissolutions were prepared in 100 mL volumetric flasks with a nitrate concentration of 10 mg/L in agreement with the maximum permissible nitrate concentration in drinking water for Costa Rica.…”

“…The standards used for the analysis were USGS34, USGS35, and IAEA-NO3. More details are described by Villalobos-Forbes et al (2021).…”

Tropical cities research boundaries: a bibliometric analysis to bridge the gaps through multi-dimensional and cross-disciplinary features

“…Furthermore, studies conducted on this subtopic have investigated atmospheric composition and air quality by examining photochemical processes (Soni et al, 2022), wet deposition of secondary atmospheric pollutants like nitrate (Villalobos-Forbes et al, 2021), ozone and particulate matter (PM) measurements (Barima et al, 2014;Salvador et al, 2022), the impact of biomass burning on PM composition (Yang et al, 2013), and the effects of peat-forest burning on PM (Lan et al, 2021).…”