Modeling anthropogenic nitrogen flow for the Niantic River catchment in coastal New England

Abstract

This paper presents a nitrogen flux model that applies previously developed denitrification process equations for an entire catchment. These denitrification equations were previously applied on single flowpaths; this paper implements a model to apply these equations to all possible flowpaths within the catchment. The purpose of this paper is to describe a new modeling approach (GeoN) to represent and communicate the geospatial interaction between nitrogen sources and sinks within a catchment. This model is of use to local decision-makers because it identifies all areas that are prone to delivering large percentages of nitrogen to sensitive estuaries and those areas that are already providing natural denitrification of the system. The GeoN model utilizes a combination of ArcGIS hydrology tools and custom Python scripts to simulate the flow of nitrogen from a source to the catchment outlet. The model also simulates interactions with sinks that provide natural denitrification. The model is validated using 11 USGS stream gauge locations. A two one-sided t test (TOST) is performed to evaluate the equivalence between the measured and simulated values. The test shows that the modeled and measured values are not statistically different. The model also simulates overall catchment retention of nitrogen within the range established in the literature for a coastal New England catchment. This research introduces a model that simulates geospatial interaction of all nitrogen sinks and sources within a catchment allowing the identification of key areas with regards to water quality.