Global Nitrogen Mass Flux From the Active Freshwater Aquifer Element Pool

The estimated current global mean nitrogen concentration (geogenic + anthropogenic) in the active continental freshwater aquifer element pool is 1.1 mg/L as N, or between four and five times greater than the assumed geogenic mean. This concentration, combined with groundwater flux, generates a continental mass flux of 17 Tg N/y (teragrams of nitrogen, as N, per year) as a result of direct ocean discharge (0.67 Tg N/y), endorheic basins (1.2 Tg N/y), and cold‐wet (0.82 Tg N/y); cold‐dry (1.4 Tg N/y); warm‐dry (1.6 Tg N/y); and warm‐wet (11 Tg N/y) exorheic basins. These values are derived from a geospatial machine learning algorithm and combined groundwater‐modeled recharge in an ArcGIS environment. This active continental freshwater aquifer mass flux is between 35% and 40% of the continental integrated riverine system discharge, thus a significant component of the Earth's active continental freshwater nitrogen budget. We estimate the active continental freshwater aquifer volume to be between 1.4 and 2.8 million km 3 suggesting a legacy of between 1.5 and 3.1 Pg as N (petagrams nitrogen as N) with mean residences of 90–180 years. Globally, the current average nitrogen concentration in groundwater is 1.1 mg/L, or more than 4 times the estimated natural uncontaminated value. This nitrogen contributes between 35% and 40% of the total nitrogen carried in the rivers on Earth. A freshwater aquifer volume of between 1.4 and 2.8 million km 3 combined with a concentration of 1.1 mg/L results in a mass legacy of between 1.5 and 3.1 Pg as N with a mean residence time of between 90 and 180 years. . The current nitrogen concentration in the active global aquifer element pool is 1.1 mg/L as N or 4 to 5 times the estimated geogenic mean A mass flux of 17 Tg N/y (Tetragrams of nitrogen, as N, per year) and is between 35% and 40% of the total nitrogen riverine flux The current global mass legacy is between 1.5 and 3.1 billion tons with a residence time of 90–180 years.