Dissolved inorganic phosphorus export to the coastal zone: Results from a spatially explicit, global model

Here we describe, test, and apply a spatially explicit, global model of river-borne dissolved inorganic phosphorus (DIP) export called NEWS-DIP. Among the innovations in NEWS-DIP are increased spatial resolution (0.5 × 0.5°), explicit treatment of sewage, fertilizer, manure, and weathering P sources, and inclusion of reservoir retention and consumptive water use terms. The NEWS-DIP model performed better than pre-existing global models in predicting DIP yield for both calibration and validation basins (r2 = 0.72 and 0.56, respectively). NEWS-DIP predicts that of the 34 Tg of P yr-1 loaded on watersheds by human activity globally, approximately 3% reaches river mouths as DIP; anthropogenic sources account for 65% (0.71 Tg yr-1) of the DIP exported to the coastal zone, with the remainder (0.38 Tg yr-1) attributable to natural weathering processes; DIP yields range over 5 orders of magnitude, from less than 0.01 to 1153 kg P km-2 yr-1 with highest predicted DIP yields clustering in East Asia, Europe, and Indonesia; human sewage is the largest anthropogenic source of DIP to the coastal zone on all continents and to all ocean basins. NEWS-DIP also suggests that despite regional variability, at the global scale, non-point sources of DIP such as inorganic P fertilizer and manure are much less important in determining coastal export of DIP than point sources and natural weathering processes.