NASQAN National Stream Quality Accounting Network |

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 streamflow normalized total load (the flow-weighted concentration obtained by dividing the load by the total volume of water flowing into the Gulf during the time period) of total nitrogen or phosphorus. This flow-weighted 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. As the amount of runoff from watersheds has a large effect on nutrient export, normalizing for streamflow can provide insight into other factors affecting nutrient transport (for example, changes in farm fertilizer use or implementation of best management practices). Each panel in the graphs includes a reference line at the mean value for the period 1980-1996 (which has been identified as the baseline period for determining reductions in the Gulf Hypoxia Action Plan 2008). The top panel also shows the 45 percent reduction goal for total nitrogen or total phosphorus identified in the 2008 Action Plan (a prorated reduction based on the 1980-1996 average load for a given month is used for the monthly graphs). 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.