Long-Term Trends in Nitrogen Removal by an Aridland Constructed Treatment Wetland
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CONSTRUCTED WETLANDS
Long-Term Trends in Nitrogen Removal by an Aridland Constructed Treatment Wetland Sawyer Treese 1 & Daniel L. Childers 1
&
Christopher A. Sanchez 2
Received: 1 June 2020 / Accepted: 2 September 2020 # Society of Wetland Scientists 2020
Abstract Cities are increasingly pursuing more sustainable and resilient infrastructure. The increased use of Urban Ecological Infrastructure (UEI), including constructed treatment wetlands (CTW), may be particularly important for aridland cities with scarce water resources. In this paper we document eight years of nitrogen (N) dynamics in an aridland CTW in Phoenix, Arizona, USA, where N removal must be balanced by the trade-off of atmospheric water losses. We have documented a “biological tide”, wherein transpiration-driven water loss is actively replaced by a slow movement of surface water into the marsh from adjacent open water areas. Our analysis combined long-term water budget data with nitrogen budgets for the vegetated marsh and the entire CTW system. The objective was to demonstrate how the biological tide enhanced N uptake in this aridland CTW. We attributed roughly 50% of the annual N uptake by the vegetated marsh to new water entering via the biological tide. Thus, while it seems counter-intuitive to design aridland CTWs to optimize transpirational water losses, our data suggested that careful design of the plant community and spatial configuration of vegetated marsh versus open water may enhance both the biological tide and N removal efficiency. Keywords Constructed treatment wetlands . Urban sustainability . Wastewater treatment . Nitrogen budget . Water budget . Transpiration
Introduction Urban living has become an increasingly common trend over the past two centuries. In fact, the proportion of human populations living in cities around the globe has increased from 10% to over 50% since 1900 and is projected to reach 80% by 2050 (Grimm et al. 2008). The increased density of urban systems offers opportunities for enhanced efficiency of infrastructure, but it also presents greater challenges for resource management. This is particularly true of water management in aridland cities. In the last century, cities have transformed into “sanitary cities” that rely on highly centralized, engineered, and expensive infrastructure designed to keep inhabitants healthy (Melosi 2000; Grove 2009). While this infrastructure can meet short-term demands, it often imposes large systemic inertias that hinder a city’s ability to
* Daniel L. Childers [email protected] 1
School of Sustainability, Arizona State University, Tempe, AZ, USA
2
Office of Resilience, Miami-Dade County, Miami, FL, USA
pursue novel or transformative new solutions to growing problems (Childers et al. 2014). To address these challenges, many cities are turning to Urban Ecological Infrastructure (UEI, sensu Childers et al. 2019) for more sustainable and resilient solutions. Constructed treatment wetlands (CTW) are a prime example of UEI (Greenway 2005); they provide cities with a relativ
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