Dry and wet deposition of inorganic nitrogen compounds to a tropical pasture site (Rondônia, Brazil)

Abstract

Abstract. The input of nitrogen (N) to ecosystems has increased dramatically over the past decades. While total N deposition (wet + dry) has been extensively determined in temperate regions, only very few data sets exist about wet N deposition in tropical ecosystems, and moreover, experimental information about dry N deposition in tropical environments is lacking. In this study we estimate dry and wet deposition of inorganic N for a remote pasture site in the Amazon Basin based on in-situ measurements. The measurements covered the late dry (biomass burning) season, a transition period and the onset of the wet season (clean conditions) (12 September to 14 November 2002, LBA-SMOCC). Ammonia (NH3), nitric acid (HNO3), nitrous acid (HONO), nitrogen dioxide (NO2), nitric oxide (NO), ozone (O3), aerosol ammonium (NH4+) and aerosol nitrate (NO3-) were measured in real-time, accompanied by simultaneous (micro-)meteorological measurements. Dry deposition fluxes of NO2 and HNO3 are inferred using the ''big leaf multiple resistance approach'' and particle deposition fluxes are derived using an established empirical parameterization. Bi-directional surface-atmosphere exchange fluxes of NH3 and HONO are estimated by applying a ''canopy compensation point model''. Dry and wet N deposition is dominated by NH3 and NH4+, which is largely the consequence of biomass burning during the dry season. The grass surface appeared to have a strong potential for daytime NH3 (re-)emission, owing to high canopy compensation points, which are related to high surface temperatures and to direct NH3 emissions from cattle excreta. NO2 also significantly accounted for dry N deposition, whereas HNO3, HONO and N-containing aerosol species were only minor contributors. We estimated a total (dry + wet) N deposition of 7.3–9.8 kgN ha-1 yr-1 to the tropical pasture site, whereof 2–4.5 kgN ha-1 yr-1 are attributed to dry N deposition and ~5.3 kgN ha-1 yr-1 to wet N deposition. Our estimate exceeds total (wet + dry) N deposition to tropical ecosystems predicted by global chemistry and transport models by at least factor of two.

Atmospheric nitrogen budget in Sahelian dry savannas

“…The mean deposition flux (dominated by dry deposition processes) is 5.2±1.0 kgNha −1 yr −1 . These values are of the same order as deposition fluxes calculated in a tropical pasture site in Brazil, giving a range of NH 3 fluxes between 6 and 12 kgNha −1 yr −1 (Trebs et al, 2006).…”

“…The direction of the net flux will depend on the strength of the volatilization process and environmental conditions. The NH 3 compensation point has been widely studied for temperate climate vegetation (Sutton et al (2007) and references therein), Trebs et al (2006) have also described a detailed N budget in a tropical pasture site in Brazil, but the lack of micrometeorological data in the Sahel prevents from parameterizing and estimating, for example, stomatal emissions, cuticular desorption emissions, cuticular recapture of stomatal emissions (Sutton et al, 1998), key points for the compensation point concept. As a consequence, the emission and deposition fluxes of NH 3 are estimated individually in this study.…”

Vertical structure and diurnal variability of ammonia exchange potential within an intensively managed grass canopy

“…A diurnal pattern of the NH 3 exchange has been observed in Brassica napus , barley (Schjoerring et al, 1993) and grassland (Trebs, et al 2006), with highest NH 3 emission rates typically occurring during the daytime and low rates at night. Reported diurnal variations in apoplastic NH + 4 and H + concentrations are small van Hove et al, 2002).…”

Aerosol Inorganic Composition at a Tropical Site: Discrepancies Between Filter-Based Sampling and a Semi-Continuous Method

“…The integrating samplers were mounted outside the house within a fenced-off area (for details see Trebs et al 2006). The filter sampling periods were 12 hours daytime and 12 hours nighttime during the late dry (biomass burning) season, 24 hours during the transition period, and 48 hours during the onset of the wet season.…”