Seeing the light: urban stream restoration affects stream metabolism and nitrate uptake via changes in canopy cover

Alexander J Reisinger; Thomas R Doody; Peter M Groffman; Sujay S Kaushal; Emma J Rosi

doi:10.1002/eap.1941

Seeing the light: urban stream restoration affects stream metabolism and nitrate uptake via changes in canopy cover

Ecol Appl. 2019 Sep;29(6):e01941. doi: 10.1002/eap.1941. Epub 2019 Jun 26.

Authors

Alexander J Reisinger^{1

2}, Thomas R Doody³, Peter M Groffman^{1

4}, Sujay S Kaushal³, Emma J Rosi¹

Affiliations

¹ Cary Institute of Ecosystem Studies, Millbrook, New York, 12545, USA.
² Soil and Water Sciences Department, University of Florida, Gainesville, Florida, 32611, USA.
³ Department of Geology, Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, 20742, USA.
⁴ Brooklyn College Department of Earth and Environmental Sciences, City University of New York Advanced Science Research Center at the Graduate Center, New York, New York, 10031, USA.

PMID: 31155778
DOI: 10.1002/eap.1941

Abstract

The continually increasing global population residing in urban landscapes impacts numerous ecosystem functions and services provided by urban streams. Urban stream restoration is often employed to offset these impacts and conserve or enhance the various functions and services these streams provide. Despite the assumption that "if you build it, [the function] will come," current understanding of the effects of urban stream restoration on stream ecosystem functions are based on short term studies that may not capture variation in restoration effectiveness over time. We quantified the impact of stream restoration on nutrient and energy dynamics of urban streams by studying 10 urban stream reaches (five restored, five unrestored) in the Baltimore, Maryland, USA, region over a two-year period. We measured gross primary production (GPP) and ecosystem respiration (ER) at the whole-stream scale continuously throughout the study and nitrate (NO₃^- -N) spiraling rates seasonally (spring, summer, autumn) across all reaches. There was no significant restoration effect on NO₃^- -N spiraling across reaches. However, there was a significant canopy cover effect on NO₃^- -N spiraling, and directly comparing paired sets of unrestored-restored reaches showed that restoration does affect NO₃^- -N spiraling after accounting for other environmental variation. Furthermore, there was a change in GPP : ER seasonality, with restored and open-canopied reaches exhibiting higher GPP : ER during summer. The restoration effect, though, appears contingent upon altered canopy cover, which is likely to be a temporary effect of restoration and is a driver of multiple ecosystem services, e.g., habitat, riparian nutrient processing. Our results suggest that decision-making about stream restoration, including evaluations of nutrient benefits, clearly needs to consider spatial and temporal dynamics of canopy cover and trade-offs among multiple ecosystem services.

Keywords: canopy cover; ecosystem respiration; gross primary production; restoration; spiraling; urban stream.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Ecosystem*
Nitrates
Rivers*
Seasons

Substances

Nitrates