Ecological Applications, 17(5) Supplement, 2007, pp. S17–S30 Ó 2007 by the Ecological Society of America NLOAD: AN INTERACTIVE, WEB-BASED MODELING TOOL FOR NITROGEN MANAGEMENT IN ESTUARIES JENNIFER L. BOWEN, 1 JOY M. RAMSTACK, 2 S. MAZZILLI, 3 AND IVAN VALIELA 1,4 Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543 USA Abstract. Eutrophication of estuaries is an increasing global concern that requires development of new tools to identify causes, quantify conditions, and propose management options that address this environmental problem. Since eutrophication is often associated with increased inputs of land-derived nitrogen to estuaries, we developed NLOAD, a user-friendly, web-based tool that brings together six different published models that predict nitrogen loading to estuaries and two models that estimate nitrogen concentrations in coastal waters. Here we describe each of the models, demonstrate how NLOAD is designed to function, and then use the models in NLOAD to predict nitrogen loads to Barnegat Bay, New Jersey (USA). The four models that we used to estimate nitrogen loads to Barnegat Bay, when adjusted, all had similar results that matched well with measured values and indicated that Barnegat Bay receives roughly 26 kg NÁha À1 Áyr À1 . Atmospheric deposition was the dominant source of nitrogen to Barnegat Bay, followed by fertilizer nitrogen. Wastewater in Barnegat Bay is diverted to an offshore outfall and contributes no nitrogen to the system. The NLOAD tool has an additional feature that allows managers to assess the effectiveness of a variety of management options to reduce nitrogen loads. We demonstrate this feature of NLOAD through simulations in which fertilizer inputs to the Barnegat Bay watershed are reduced. Even modest cutbacks in the use of fertilizers on agricultural fields and lawns can be shown to reduce the amount of N entering Barnegat Bay. Key words: Barnegat Bay; coastal planning; eutrophication; management tool; nitrogen loading; nitrogen mitigation; resource managers; watershed–estuary coupling. INTRODUCTION Eutrophication of coastal waters is a principal worldwide agent of change (GESAMP 1990, Goldberg 1995, Bricker et al. 1999) that is closely associated with increases in the amount of new nitrogen (N) entering near-shore waterways. The increase in N loads and concentrations is largely driven by changes in land use and energy consumption associated with burgeoning populations on coastal watersheds (Howarth et al. 1996). The impact of eutrophication in estuaries is far reaching and includes increases in algal production, reduction in seagrass habitats, increases in the frequency of hypoxia, decreases in the density of benthic inverte- brates, reductions in scallop harvests, and many other alterations (Valiela et al. 1992, 1997b, 2000b). To effectively understand and manage the increasing enrichment of coastal waters, adequate methods are required to quantify the sources of nitrogen that are inducing eutrophication. There are many models avail- able that estimate land-derived nitrogen loads (Cole et al. 1993, Johnes 1996, Valiela et al. 1997a, Caraco and Cole 1999, Valiela et al. 2004, among others). Each model offers different levels of complexity, data demands, ease of use, and scale of application. The variety of nitrogen loading models that are available, and the diversity of structure and content of these models, makes it a demanding chore for a researcher or manager to select the appropriate model to answer the management question at hand. To facilitate this, and many other needs of scientists and managers interested in understanding the role that land-derived nitrogen plays in the eutrophication of their estuaries, we developed NLOAD (see Appendices A and B). We present NLOAD as a web-based tool that makes a suite of models more readily available for use by stakeholders, managers, decision makers, and research- ers interested in estimating or managing N loads from watersheds to specific estuaries. Stakeholders can use NLOAD to apply a variety of recent models to their specific estuarine system. Users of NLOAD are given descriptions of each of the models and are guided through a series of questions to help them select the model that is most appropriate for the data they have Manuscript received 24 May 2005; revised 8 December 2006; accepted 6 March 2006. Corresponding Editor: A. Townsend. For reprints of this Special Issue, see footnote 1, p. S1. 1 Present address: The Ecosystems Center, Marine Biolog- ical Laboratory, Woods Hole, Massachusetts 02543 USA. 2 Present address: St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix, Minnesota 55047 USA. 3 Present address: Environment and Natural Resources Service, Food and Agriculture Organization of the United Nations, Rome, Italy. 4 Corresponding author. E-mail: ivaliela@mbl.edu S17