High Atmospheric Nitrate Inputs and Nitrogen Turnover in Semi-arid Urban Catchments

Krystin M. Riha, Greg Michalski, Erika L. Gallo, Kathleen A. Lohse, Paul D. Brooks, Tom Meixner

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

The influx of atmospheric nitrogen to soils and surfaces in arid environments is of growing concern due to increased N emissions and N usage associated with urbanization. Atmospheric nitrogen inputs to the critical zone can occur as wet (rain or snow) or dry (dust or aerosols) deposition, and can lead to eutrophication, soil acidification, and groundwater contamination through leaching of excess nitrate. The objective of this research was to use the δ15N, δ18O, and Δ17O values of atmospheric nitrate (NO3 ) (precipitation and aerosols) and NO3 in runoff to assess the importance of N deposition and turnover in semi-arid urban watersheds. Data show that the fractions of atmospheric NO3 exported from all the urban catchments, throughout the study period, were substantially higher than in nearly all other ecosystems studied with mean atmospheric contributions of 38% (min 0% and max 82%). These results suggest that catchment and stream channel imperviousness enhance atmospheric NO3 export due to inefficient N cycling and retention. In contrast, catchment and stream channel perviousness allow for enhanced N processing and therefore reduced atmospheric NO3 export. Overall high fractions of atmospheric NO3 were primarily attributed to slow N turn over in arid/semi-arid ecosystems. A relatively high fraction of nitrification NO3 (~30%) was found in runoff from a nearly completely impervious watershed (91%). This was attributed to nitrification of atmospheric NH4 + in dry-deposited dust, suggesting that N nitrifiers have adapted to urban micro niches. Gross nitrification rates based on NO3 Δ17O values ranged from a low 3.04 ± 2 kg NO3-N km−2 day−1 in highly impervious catchments to a high of 10.15 ± 1 kg NO3-N km−2 day−1 in the low density urban catchment. These low gross nitrification rates were attributed to low soil C:N ratios that control gross autotrophic nitrification by regulating gross NH4 + production rates.

Original languageEnglish (US)
Pages (from-to)1309-1325
Number of pages17
JournalEcosystems
Volume17
Issue number8
DOIs
StatePublished - Jan 1 2014

Keywords

  • N cycle
  • N deposition
  • gross nitrification
  • isotopes
  • runoff
  • urban ecosystems

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Environmental Chemistry
  • Ecology

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