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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.

Jamaica Bay is a small (50 km 2 ) tidal embayment located in Queens and Brooklyn, NY in the southwest corner of Long Island. The majority of the bay is part of the Gateway National Recreation Area overseen by the National Park Service. Over the last century the bay has been heavily impacted by man, and as a result suffers from poor water quality. There are two primary reasons for the poor water quality. The first is the four major water pollution control plants (WPCPs), operated by the New York City Department of Environmental Protection (NYCDEP), that discharge approximately 250 million gallons per day (MGD) of secondary treated effluent into the bay. The second reason is man made changes to the geometry of the bay including deep borrow pits used for fill to create the John F. Kennedy International Airport and the creation of islands in the bay, both of which contribute to poor circulation in the back end of the bay called Grassy Bay. As a result of the nitrogen loadings from the WPCPs and the poor circulation in the bay, the bay is highly eutrophic and suffers from high chlorophyll-a concentrations, and periods of hypoxia and unionized ammonia toxicity. The low dissolved oxygen levels violate water quality standards in Jamaica Bay set by the New York State Department of Environmental Conservation (NYSDEC).As part of an order-on-consent with the NYSDEC, the NYCDEP was required to develop a Comprehensive Jamaica Bay Water Quality Plan (CJBWQP) for nitrogen by October 2006 to reduce nitrogen levels in the bay. The reduction of nitrogen levels includes a limit on the nitrogen discharge from the WPCPs to a 12-month rolling average of 45,300 lb/day. The development of the plan included the use of a water quality model to analyze various remediation alternatives. Alternatives included several levels of nitrogen removal at the WPCPs, relocation of the WPCP outfalls, bay recontouring, aeration, and combinations of these alternatives. Costs were developed for each of these scenarios, and cost benefit curves were developed for improvements in dissolved oxygen, chlorophyll, and unionized ammonia.The development of the plan was complicated by several factors, which included multiple jurisdictions with competing interests; public resistance to certain alternatives; possible future water quality standards involving dissolved oxygen, unionized ammonia, and coastal nutrients; the rapid unexplained loss of marshes in the bay; and the fact that the majority of the alternatives would not attain water quality standards 100 percent of the time despite meeting the effluent nitrogen loading limit of 45,300 lb/day. This paper describes the development of this plan.

The work reported herein was conducted as part of the Water Quality Research Program (WQRP), Work Unit No. 32694. The WQRP is sponsored by Headquarters, U.S. Army Corps of Engineers (HQUSACE), and is assigned to the US. Army Engineer Waterways Experiment Station (WES) under the purview of the Environmental Laboratory (EL). Funding was provided under Department of the Army Appropriation No. 96x3 121, General Investigation. The WQRP is managed under the Environmental Resources Research and Assistance Programs (ERRAP). Dr. John Barko was Manager, ERRAP, and Mr. Robert Gunkel was Assistant Manager, ERRAP, for the WQRP. Technical Monitors during the study were Messrs. Pete Juhle and James Gottesman and Dr. John Bushman, HQUSACE. Principal Investigator of the Work Unit was Dr. Carl E Cerco, Water Quality and Contaminant Modeling Branch (WQCMB), Environmental Processes and Effects Division (EPED), EL.