Urban sustainability has been an increasing global concern. By the end of the current decade, more than half of all people on earth will be living in cities. As cities grow, they are increasingly reliant on the importation of natural resources to support processes within the urban center. In return for these inputs, cities export products, services, capital, and wastes, as well as unused natural resources.

"Water In? Water out? An Analysis of Water and Nitrogen Use in the City of New Haven," is a project begun in November 2002 by three FES professors-Shimon Anisfeld, Sheila Olmstead and Xuemei Bai. With student research assistants Hahn-Ning Chou and Ying Qiu, they are studying the flow of water and nitrogen through the urban ecosystem of New Haven. The project is supported by the Hixon Center for Urban Ecology and the Connecticut Sea Grant College Program.

Often water and nitrogen budgets are studied at the watershed level, however this project is unique in that the city limits are used as the boundary. This allows us to better understand anthropogenic influences on the flow of water and nitrogen in and out of cities. Part of the project includes constructing a model which can determine the factors affecting water usage. This article provides a brief overview of research currently in progress.

A natural resource that is essential to humans, and therefore cities, is water. Water is necessary to both sustain life and to drive the commercial, industrial, and agricultural sectors that sustain the livelihood of cities. However, this resource is strained by depletion of water sources, inadequate infrastructures, inefficient water consumption, and pollution.

Another important flow into cities is nitrogen. Nitrogen is a key plant nutrient and plays a crucial role in agriculture. Humans consume nitrogen as a component of food. It is therefore unsurprising that urban centers receive a large amount of nitrogen. However, not all the nitrogen is utilized and excessive nitrogen can be discharged into coastal zones. This can lead to problems such as eutrophication resulting in estuarine hypoxia, submerged aquatic vegetation decline, and harmful algal blooms.

New Haven is a medium sized city of 19.4 square miles with a population slightly more than 120,000. Recent increases in water consumption have led to the planned resumption of withdrawal from Lake Whitney. The city also receives large flows of water from the three rivers that drain into New Haven Harbor.

The water budget can be summarized by grouping water based on inputs either as controlled or supplied by the South Central Connecticut Regional Water Authority, or as uncontrolled, which is from precipitation. The outputs are the wastewater treatment plant discharges, evapotranspiration, combined sewer outfalls, stormwater outfalls, baseflow, are unaccounted for.

This research involved developing a huge dataset, using quarterly water uses data from the Regional Water Authority, house property data from the New Haven City Plan department, New Haven census data from the official website of U.S Census 2000 and daily weather data from the Bridgeport station of the National Weather Service from NOAA. With this data, water consumption patterns of the different sectors were analyzed. Water usage patterns differ dramatically across the different sectors: domestic, industrial, commercial and public authorities. For example, even within the residential sector there are varied ways to consume water: for drinking, food preparation, bathing, housekeeping, and lawn maintenance. The most significant variables for modeling residential water consumption in New Haven, which include demographic, socioeconomic and weather characteristics are being identified.

The main inflows to the nitrogen budget include food, atmospheric deposition, fertilizer application, Regional Water Authority supply, and nitrogen fixation. The outflows of the nitrogen budget are wastewater treatment plant discharge, stormwater, combined sewer overflow, and several other variables. The final product will be a detailed budget of nitrogen flow through New Haven from 1997 to 2002. Eutrophication from excess nutrients has been a serious problem in nearby Long Island Sound and it is hoped a better understanding of the nitrogen budget from an urban area may be useful in alleviating this problem.

Construction of the study's models are currently ongoing, but when completed the results will be useful to New Haven in determining ways to conserve water. In addition, since the city is right on Long Island Sound, a knowledge of urban nitrogen flows is essential in managing eutrophication which has been seriously affecting the coastal ecosystem.