Effects of urban stream burial on nitrogen uptake and ecosystem metabolism: implications for watershed nitrogen and carbon fluxes

• Published in: Biogeochemistry 2014-10, Vol.121 (1), p.247-269
• Main Authors: Pennino, Michael J, Kaushal, Sujay S, Beaulieu, Jake J, Mayer, Paul M, Arango, Clay P
• Format: Article
• Language: English
• Subjects: Biogeochemistry; Biogeosciences; Carbon; Channeling; channelization; Culverts; Daylighting; Dissolved organic matter; Earth and Environmental Science; Earth Sciences; Ecological function; Ecological research; ecosystem respiration; Ecosystem studies; Ecosystems; emissions; Environmental Chemistry; Floodplains; fluorescence; Headwaters; isotopes; Life Sciences; Lotic systems; metabolism; Nitrates; Nitrogen; primary productivity; Stream metabolism; Streams; Urban areas; Urban watersheds; Urbanization; Water temperature; Watersheds
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-014-9958-1

Urbanization has resulted in the extensive burial and channelization of headwater streams, yet little is known about the impacts of stream burial on ecosystem functions critical for reducing downstream nitrogen (N) and carbon (C) exports. In order to characterize the biogeochemical effects of stream burial on N and C, we measured NO₃ ⁻ uptake (using ¹⁵N-NO₃ ⁻ isotope tracer releases) and gross primary productivity (GPP) and ecosystem respiration (ER) (using whole stream metabolism measurements). Experiments were carried out during four seasons, in three paired buried and open stream reaches, within the Baltimore Ecosystem Study Long-term Ecological Research site. Stream burial increased NO₃ ⁻ uptake lengths by a factor of 7.5 (p < 0.01) and decreased NO₃ ⁻ uptake velocity and areal NO₃ ⁻ uptake rate by factors of 8.2 (p < 0.05) and 9.6 (p < 0.001), respectively. Stream burial decreased GPP by a factor of 11.0 (p < 0.01) and decreased ER by a factor of 5.0 (p < 0.05). From fluorescence Excitation Emissions Matrices analysis, buried streams were found to have significantly altered C quality, showing less labile dissolved organic matter. Furthermore, buried streams had significantly lower transient storage (TS) and water temperatures. Differences in NO₃ ⁻ uptake, GPP, and ER in buried streams, were primarily explained by decreased TS, light availability, and C quality, respectively. At the watershed scale, we estimate that stream burial decreases NO₃ ⁻ uptake by 39 % and C production by 194 %. Overall, our results suggest that stream burial significantly impacts NO₃ ⁻ uptake, stream metabolism, and the quality of organic C exported from watersheds. Given the large impacts of stream burial on stream ecosystem processes, daylighting or de-channelization of streams, through hydrologic floodplain reconnection, may have the potential to alter ecosystem functions in urban watersheds, when used appropriately.