Impact of seasonal changes in stream metabolism on nitrate concentrations in an urban stream

Sarah H. Ledford, Laura K. Lautz, Philippe G. Vidon, John C. Stella

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Nitrate (NO3 ) dynamics in urban streams differ from many natural streams due to stormwater runoff, sewage inputs, decreased groundwater discharge, often limited hyporheic exchange, increased primary productivity, and limited carbon input. We investigated NO3 dynamics in a first-order urban stream in Syracuse, NY, which has urbanized headwaters and a geomorphologically natural downstream section. Twice-monthly water sampling, NO3 injection tests, NO3 isotopic analysis, filamentous algae mat density, and riparian shading were used to identify processes regulating NO3 dynamics in the stream over a 12-month period. The urban headwater reach had low NO3 (0.006–0.2 mg N/L) in the spring through fall, with a minimum uptake length of 900 m, no canopy cover, and high algae mat density. The downstream natural reach (100% canopy cover during the summer and low algae mat density) had nitrate concentrations between 0.6 and 1.2 mg N/L from winter to summer, which decreased during autumn leaf-off. In the urban reach, autotrophic uptake by filamentous green algae is a major NO3 sink in summer. In the natural reach, the addition of organic matter to the stream at leaf-off led to a decrease in NO3 concentration followed by an increase in NO3 concentration in winter as gross primary productivity decreased. This study shows that the balance between autotrophy and heterotrophy in urban streams is variable and depends on an interplay of drivers such as temperature, light, and carbon inputs that are mediated by the riparian ecosystem.

Original languageEnglish (US)
Pages (from-to)317-331
Number of pages15
JournalBiogeochemistry
Volume133
Issue number3
DOIs
StatePublished - May 1 2017

Keywords

  • Nitrate
  • Nutrient uptake
  • Seasonality
  • Surface water
  • Urban water chemistry

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes

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