Recovery and resilience of urban stream metabolism following Superstorm Sandy and other floods

Alexander J Reisinger,Sujay S Kaushal,Thomas R Doody,Peter M Groffman,Emma J Rosi,Heather A Bechtold

doi:10.1002/ecs2.1776

Abstract

AbstractUrban streams are exposed to multiple different stressors on a regular basis, with increased hydrological flashiness representing a common urban stream stressor. Stream metabolism, the coupled ecosystem functions of gross primary production (GPP) and ecosystem respiration (ER), controls numerous other ecosystem functions and integrates multiple processes occurring within streams. We examined the effect of one large (Superstorm Sandy) and multiple small and moderately sized flood events in Baltimore, Maryland, to quantify the response and recovery of urban stream GPP and ER before and after floods of different magnitudes. We also compared GPP and ER before and after Superstorm Sandy to literature values. We found that both GPP and ER decreased dramatically immediately following floods of varying magnitudes, but on average GPP was more reduced than ER (80% and 66% average reduction in GPP and ER, respectively). Both GPP and ER recovered rapidly following floods within 4–18 d, and recovery intervals did not differ significantly between GPP and ER. During the two‐week recovery following Superstorm Sandy, two urban streams exhibited a range of metabolic activity equivalent to ~15% of the entire range of GPP and ER reported in a recent meta‐analysis of stream metabolism. Urban streams exhibit a substantial proportion of the natural variation in metabolism found across stream ecosystems over relatively short time scales. Not only does urbanization cause increased hydrological flashiness, it appears that metabolic activity in urban streams may be less resistant, but also more resilient to floods than in other streams draining undeveloped watersheds, which have been more studied. Our results show that antecedent conditions must be accounted for when drawing conclusions about stream metabolism measurements, and the rapid recovery and resilience of urban streams should be considered in watershed management and stream restoration strategies targeting ecosystem functions and services.

Highlights

Urban stream ecosystems exhibit a multitude of physicochemical and biological changes in response to urban development (Walsh et al 2005, Wenger et al 2009, Kaushal and Belt 2012)
Baltimore was less affected than areas further north, large-scale flooding did occur, allowing us to test the effect of a storm on stream metabolism and its recovery in urban streams
It appears that hydrological extremes may override other environmental stressors in controlling stream metabolic activity, but the magnitude of flooding does not affect metabolic recovery

Summary

Introduction

Urban stream ecosystems exhibit a multitude of physicochemical and biological changes in response to urban development (Walsh et al 2005, Wenger et al 2009, Kaushal and Belt 2012). Nutrients and other chemical contaminants (Hatt et al 2004, Carle et al 2005), and biotic communities with decreased intolerant and increased tolerant species (Paul and Meyer 2001) These physicochemical and biological changes to urban streams are speculated to result in reductions in stream ecosystem functions such as metabolism and nutrient uptake, despite a limited amount of empirical evidence (Walsh et al 2005, Wenger et al 2009). Stream metabolism is an integrative metric of stream biological activity, and it represents the fundamental ecosystem functions of gross primary production (GPP) and ecosystem respiration (ER; Odum 1956, Hoellein et al 2013) Both GPP and ER can be simultaneously considered a driver of other ecosystem processes (e.g., metabolism controls nutrient uptake; Hall and Tank 2003) or as a dependent variable characterizing the response of different streams to extrinsic drivers (Mulholland et al 2001, Bernot et al 2010). The development of new technologies and modeling approaches (e.g., Grace et al 2015, Hall et al 2016) has allowed for rapid expansion of stream metabolism datasets and continuous records, allowing us to test the response of this fundamental ecosystem function to a range of environmental drivers

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Results

Discussion

Conclusion