Nitrogen regulation by natural systems in “unnatural” landscapes: denitrification in ultra-urban coastal ecosystems

Abstract

Dense cities represent biogeochemical hot spots along the shoreline, concentrating fixed nitrogen that is subsequently discharged into adjacent coastal receiving waters. Thus, the ecosystem services provided by natural systems in highly urban environments can play a particularly important role in the global nitrogen cycle. In this paper, we review the recent literature on nitrogen regulation by temperate coastal ecosystems, with a focus on how the distinct physical and biogeochemical features of the urban landscape can affect the provision of this ecosystem service. We use Jamaica Bay, an ultra-urbanized coastal lagoon in the United States of America, as a demonstrative case study. Based on simple areal and tidal-based calculations, the natural systems of Jamaica Bay remove~24% of the reactive nitrogen discharged by wastewater treatment plants. However, this estimate does not represent the dynamic nature of urban nitrogen cycling represented in the recent literature and highlights key research needs and opportunities. Our review reveals that ecosystem-facilitated denitrification may be significant in even the most densely urbanized coastal landscapes, but critical uncertainties currently limit incorporation of this ecosystem service in environmental management.

A Review on Coastal Urban Ecology: Research Gaps, Challenges, and Needs

“…Since then, urban ecology research topics have evolved to include ecological and social science approaches (Grimm et al, 2000) and currently, urban ecosystems are recognized as a complex coupling of ecological processes and human dynamics, as defined by Alberti (2008) and Pickett et al (2008). Research on urban ecology is diverse and includes studies on biodiversity patterns [e.g., urban biodiversity in Faeth et al (2011); biotic homogenization in McKinney, 2006], species distributions (e.g., birds in Marzluff, 2001), ecosystem functions (Groffman et al, 2004;Rosenzweig et al, 2018), development processes (e.g., Antrop, 2004), drivers of change (e.g., Grimm et al, 2008), ecosystem services (Bolund and Hunhammar, 1999;Daily, 2003), human well-being (Pacione, 2003;Van Kamp et al, 2003;Dallimer et al, 2012), social-ecological systems (Barthel et al, 2010;Grimm et al, 2013), and sustainability (Wu, 2008(Wu, , 2014. Pickett et al (2016) introduced three phases in the way urban ecology has evolved.…”

Emerging Wetlands From River Diversions Can Sustain High Denitrification Rates in a Coastal Delta

“…This biochemical transformation can be supported by nitrate diffusion and infiltration into sediment and soils from overlying water (i.e., direct denitrification NO 3 − →N 2 ) or by NO 3 − generated from nitrification within these substrates (coupled nitrification‐denitrification: NH 4 + → NO 3 − →N 2 ). Because these N transformations can potentially ameliorate eutrophication (i.e., N enrichment) in inland and coastal waters (Alldred & Baines, 2016; Mitsch et al., 2005), denitrification is considered a key ecosystem service in coastal zones that are often subjected to high N loads as a result of human impacts (Coleman et al., 1998; Cook et al., 2006; Rosenzweig et al., 2018).…”

“…Wetlands are increasingly impacted by human activities that cause a wide range of eutrophic conditions (Rosenzweig et al., 2018; Zhang et al., 2019). Because wetlands can assimilate N under anoxic conditions—through enhanced denitrification—they are sometimes used to reduce excess N. Unfortunately, there is an increasing loss of wetlands and their ecosystem services (i.e., denitrification) as a result of other human impacts such as major changes in land use/change (e.g., urbanization, agriculture infrastructure construction) and the negative effect of nutrient loading on coastal wetland stability.…”

Inorganic Nitrogen Production and Removal along the Sediment Gradient of a Stormwater Infiltration Basin

“…In the Morse et al study [26], while 58% of incoming inorganic N was denitrified in a stormwater basin when standing water was present, only 1% of incoming dissolved inorganic N was denitrified when there was rarely standing water after rainfall entered the basins [27]. While only a few studies have looked at denitrification in SIBs [27][28][29], we know from studies of natural systems (that also have periodic flooding such as coastal marshes) that shallow sediments periodically inundated by tidal water could enhance the occurrence of anoxic conditions needed for denitrification [30]. Within a constructed wetland, the denitrification potential was higher at the inlet trough than at mid and outlet locations [31].…”