During the statewide precipitation study, sample containers were placed in three Watershed Districts around the state to determine amounts and sources of total phosphorus loading from atmospheric deposition.  At each sampling location three sample containers were installed, bag 1, bag 2, and a dry bag.  Each sample bag had an important role in the overall study.  Each storm event’s phosphorus readings from sample bags 1 and 2 were averaged to take into consideration variability in the rain event and sampling system.  The dry bag was zipped shut just before the rain event took place.  This provided a measure of atmospheric deposition at that sampling location.  After the dry bag phosphorus concentration was determined, this value was subtracted from the average phosphorus value from bags 1 and 2.  The atmospheric tracking of the storm events were created based on this procedure.

The storm event tracking revealed a correlation between extremely high phosphorus concentrations and the elevation of the storm event.  Basically, the higher the phosphorus concentration the lower the air mass stayed during the 120 hours before it released its’ moisture.  All storm events that had a corresponding phosphorus concentration were spatially mapped in a Geographical Information System (GIS).  Each mapped storm event was further broken down to show the air mass elevations over the 120-hour tracking period.  Based on the storm event tracking, areas or sources of phosphorus loading are beginning to be identified.  Most storm events with the corresponding extreme or high phosphorus values either passed through large populated areas or originated and traveled through Southwestern/Midwest states at elevations less than 500 meters (m).  Storm events with low phosphorus concentrations appeared to be originating from or traveling through the Northwest states or Canada and the air mass stayed at elevations greater then 500 m.

The average phosphorus concentration in the dry bag values were used to rank the sampling locations based on local phosphorus deposition.  Local phosphorus deposition is the deposition of phosphorus into water bodies from local sources and is not influenced by regional areas via storm events.  Analysis of the dry bag data determined that the Thirty Lakes Watershed District ranked the highest with 0.275 mg/L, followed by the Bartusek house in the Shell Rock Watershed District with 0.081 mg/L.  Not far behind the Bartusek house was the Red Lake Watershed District, which had an average of 0.055 mg/L.  Out of the four sampling locations, the Court House in Shell Rock had the lowest local phosphorus average of 0.036 mg/L.