A century-long trajectory of phosphorus export from the Mississippi River Basin to the Gulf of Mexico: A process-based modeling study

Abstract:

Excessive phosphorus (P) export from terrestrial ecosystems can cause eutrophication and hence degrade water quality in coastal regions. Modeling tools that connect P cycles in both land and aquatic systems are critical for assessing the impacts of environmental factors and anthropogenic activities on long-term dynamics of P exports. Here we integrated a riverine P transport module with a coupled carbon-nitrogen-phosphorus model, the Dynamic Land Ecosystem Model (DLEM-CNP), to simulate dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate organic phosphorus (POP), and particulate inorganic phosphorus (PIP) exports from the Mississippi River Basin to the Gulf of Mexico during 1900-2018. We further conducted factorial experiments to quantify the impacts of individual environmental factors, such as climate, atmospheric CO₂, land conversion, anthropogenic P inputs (i.e., synthetic fertilizer and manure), and legacy P that accumulated in agricultural soil. The results indicated that the total P exports increased significantly since the 1940s due to elevated anthropogenic P inputs. Precipitation controlled the inter-annual variations of POP and PIP, which dominated the variation of the total P loading. Erosion of soil P in extreme precipitation events contributed a large amount of P into the aquatic system. The legacy soil P in cropland enhanced current P export. Improved agricultural management strategies are needed to take advantage of legacy P and control the loss of P along the continuum from soil to water bodies.