Denitrification and the nitrogen budget of a reservoir in an agricultural landscape

Mark B. David, Lareina G. Wall, Todd V. Royer, Jennifer L. Tank

Research output: Contribution to journalArticle

Abstract

Denitrification is an important process in aquatic sediments, but its role has not been assessed in the N mass balance of upper-Midwestern (USA) reservoirs that receive large agricultural riverine N inputs. We used a 4400-ha reservoir to determine the role of denitrification in the N mass balance and effectiveness in reducing downstream transport of NO3-N. Sediment denitrification was (1) measured monthly (March 2002-March 2003) at eight sites in the Lake Shelbyville reservoir in central Illinois using the acetylene inhibition, chloramphenicol technique, (2) scaled to the overall reservoir and compared to N not accounted for in a mass balance, and (3) estimated indirectly using long-term (1981-2003) mass balances of N in the reservoir. Denitrification rates in the reservoir were high during spring and early summer of 2002, when maximum NO3-N concentrations were measured (10-14 mg NO3-N/L). We estimated that denitrification for the year was between 2580 and 5150 Mg N. Missing N from the mass balance was 3004 Mg N, suggesting that sediment denitrification was the sink. Areal rates of sediment denitrification in the reservoir ranged from 62 to 225 g N·m-2·yr -1, with rates a function of both denitrification intensity (μg N·g dry mass·h-1) and the overall mass of sediment present. From 1981 to 2003 the average NO3-N inlet flux was 8900 Mg N/yr. About 58% of the total NO3-N input was removed, and annual NO3-N removed as a percentage of inputs was significantly related to reservoir retention time (average = 0.36 yr for the 23 years, range = 0.21-0.84 yr). By scaling denitrification in Lake Shelbyville to other reservoirs in Illinois, we estimated a sink of 48 900 Mg N/yr. When combined with estimated in-stream denitrification, 60 900 Mg N/yr was estimated to be removed by sediment denitrification. This reduces riverine export from Illinois to the Gulf of Mexico, where the flux during the 1990s was about 244 000 Mg N/yr, and illustrates the importance of reservoir denitrification as an N sink in Midwestern agricultural landscapes.

Original languageEnglish (US)
Pages (from-to)2177-2190
Number of pages14
JournalEcological Applications
Volume16
Issue number6
DOIs
StatePublished - Dec 1 2006

Keywords

  • Agricultural watersheds
  • Denitrification
  • Mass balance
  • Nitrate
  • Nitrogen removal
  • Reservoirs
  • Retention time
  • Sediment
  • Stream export

ASJC Scopus subject areas

  • Ecology

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