Seasonal Estimates of Instream Nitrogen & Phosphorus Loads from New England Watersheds Discharging to Long Island Sound, 2000 through 2020

Richard Bridge Moore , Richard A. Smith, Laura Hayes, Jennifer S Stanton, Craig J. Brown

Seasonally dynamic estimates of total nitrogen and total phosphorus loads delivered to Long Island Sound from New England watersheds are estimated by use of seasonally dynamic SPARROW (SPAtially Referenced Regression On Watershed attributes) models. These models are part of the larger Long Island Sound Study (LISS) a coordinated effort by the U.S. Environmental Protection Agency (EPA), the States of New York, Connecticut, and other New England States, and communities within the region, with the common goal of protecting and restoring the health of the aquatic environment of Long Island Sound. The models aid the LISS goals by improving the understanding of the sources, transport, and delivery of nutrients from New England watersheds southward to Long Island Sound. Seasonal estimates provide better information for management. These estimates advance our understanding of loads, indicate seasonal processes, and include ranges, extremes, and lags in the system from one season to the next.
Dynamic models allow seasonal loads to vary substantially season-to-season and year-to-year. The SPARROW models for this study use both dependent variables (the nutrients) and predictor variables that vary seasonally throughout 21 years, from 2000 through 2020. Significant source pathways in this framework, with probability levels (p-values) less than 0.05, include seasonally dynamic pathways such as atmospheric deposition, spring snowmelt, and groundwater input of nitrogen.