Data for Modeling Time-Varying Nitrate in Groundwater on Long Island, New York, 1900-2019

This data release documents nitrate-nitrogen concentration, groundwater ages, age-weighted nitrogen loads, and aquifer and other characteristics that could be used to model time-varying nitrate concentration in groundwater on Long Island, New York. Concentration data consist of median annual nitrate concentrations at approximately 700 supply wells from 1988 to 2019 based on data provided by the Suffolk County Water Authority. Groundwater ages represent the residence times determined by particle tracking and a MODFLOW-NWT groundwater flow model (Walter and others, 2020, 2021). Age-weighted nitrogen loads are based on annual nitrogen loads applied to the land surface, 1900 to 2019 (Monti, 2024; Monti and others, 2024), and the distribution of groundwater ages of water captured by the supply wells. Aquifer and other characteristics include: the probability of overlying lignite or silt and clay from a texture model of the Long Island aquifer system (Finkelstein and Walter, 2020; Walter and Finkelstein, 2020); unsaturated-zone thickness and other characteristics from the groundwater flow model (Walter and others, 2020, 2020); the probability of low dissolved oxygen concentrations from a machine-learning model of the Northern Atlantic Coastal Plain aquifer system (DeSimone and others, 2020; DeSimone and Pope, 2020); land use; soil characteristics; and multi-order hydrologic position variables (Belitz and others, 2019). Groundwater ages, age-weighted nitrogen loads, and aquifer and other characteristics are provided for the supply wells and for selected point locations at five depth horizons in the upper glacial and Magothy aquifers. These point locations represent the vertical and horizontal centers of five layers of the three-dimensional grid used in the groundwater flow model of Walter and others (2020, 2021). Age-weighted nitrogen loads are provided for each year between 1900 and 2019 for the supply wells, to support modeling of these data. Age-weighted nitrogen loads also are provided at the selected point locations in the upper glacial and Magothy aquifers, for seven years evenly spaced years between 1900 and 2019, to support prediction of the time-varying, three-dimensional distribution of nitrate concentration in these aquifers of the Long Island aquifer system.