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Graphs of annual and monthly total nitrogen and phosphorus load into the Gulf of Mexico from the Mississippi and Atchafalaya River Basin

The following graphs show time series of annual and monthly total nitrogen and phosphorus load* into the Gulf of Mexico from the Mississippi and Atchafalaya River Basin. These loads are determined as the sum of the loads from the NASQAN stations on the Mississippi River near St. Francisville, Louisiana and the Atchafalaya River at Melville, Louisiana. Each graph has three panels. The top panel shows annual or monthly total nitrogen or phosphorus load into the Gulf of Mexico. The middle panel shows the corresponding average annual or monthly streamflow. Finally, the bottom panel shows the average annual or monthly flow-weighted concentration (load divided by the total volume of water flowing into the Gulf during the time period) of total nitrogen or phosphorus. This concentration represents the average quantity of nitrogen or phosphorus transported by the river for a given volume of water. It thus normalizes the annual or monthly loads for the effects of streamflow. Because variations in streamflow have a large effect on nutrient export from watersheds, normalizing for this effect can provide insight into other factors affecting nutrient transport (for example, changes in farm fertilizer use or implementation of best management practices). Data used to produce these graphs are from Streamflow and Nutrient Delivery to the Gulf of Mexico.

Total Nitrogen Annual Loads All Monthly Loads January Loads February Loads March Loads April Loads May Loads June Loads July Loads August Loads September Loads October Loads November Loads December Loads

Total Phosphorus Annual Loads All Monthly Loads January Loads February Loads March Loads April Loads May Loads June Loads July Loads August Loads September Loads October Loads November Loads December Loads

*Load is a term that refers to the quantity of material in a river. Total load refers to the sum of material that is both dissolved and suspended. The term needs to be qualified, such as "annual load". Load is reported as mass (for example, kilograms or tonnes) and is not strictly synonymous with flux (also referred to as discharge). Flux is reported as a rate with units of mass per time (for example, kilograms per day or tonnes per year). If the reporting interval for a load is the same as the time step of a flux, then the mass will be the same (for example, an annual load of 100 tonnes is equivalent to a flux of 100 tonnes per year). Because of this correspondence, it is not uncommon to see the terms load, flux, and discharge used interchangably.