To reduce nutrient loads to waterways, scientists first need to determine where those nutrients are coming from. Pennsylvania's Nutrient Management Act, besides focusing on agricultural nutrients, ordered an investigation of how other sources of nutrients contribute to pollution of the state's waters. Using four years of data from 85 watersheds, Penn State's Environmental Resources Research Institute provided the Department of Environmental Protection with a snapshot of nutrient sources across the state.

Atmospheric deposition
(48.7 percent nitrogen; 7.1 percent phosphorus)
Atmospheric deposition arising from agriculture, industry, and urban areas contributes most of the nitrogen load to the state's waters. Atmospheric deposition may be wet, in the form of rain or snow, or dry, in the form of gases or particles. Thirty-seven percent of the atmospheric deposition in the state comes from agriculture, and 63 percent from industrial and urban areas. "Nitrogen in synthetic fertilizers and manure can rise as a gas, then come back down," says Barry Evans, senior research assistant at the Environmental Resources Research Institute. "Also, a lot of the nitrogen that rises from the combustion of fossil fuels, such as coal and oil, comes back down as wet or particulate matter."

Urban storm water runoff
(8.4 percent nitrogen; 10.8 percent phosphorus)
Not truly a separate nutrient source, urban runoff includes nutrients from the other categories, plus runoff from construction. "When you have precipitation coming down on an urban area, it's not hitting a clean table," Evans says. "It carries away nutrients and sediments from such things as food products and dead animals." Like septic systems and nonagricultural fertilizers, runoff from all those miles of highways and parking lots doesn't appear to contribute substantial amounts of nitrogen or phosphorus, but it's probably more significant in urbanized watersheds.

Golf courses and lawns
(0.3 percent nitrogen; 0.2 percent phosphorus)
Fertilizers applied to maintain velvet-green golf courses and lawns don't contribute a lot of nutrients on a statewide basis. "But golf courses and lawns could be responsible for up to 30 percent of the nutrient load in urban areas," Evans explains. "In these areas, nonagricultural uses of fertilizers may need to be controlled."

Septic systems
3.4 percent nitrogen; 13.1 percent phosphorus)
"Even in the best septic systems, some nutrients will migrate into the surface and groundwater," says Evans. "Although septic systems don't appear to contribute a lot of nitrogen or phosphorus on a statewide basis, they're likely to contribute more of the nutrient load in the more heavily populated watersheds."

Agriculture
(39.2 percent nitrogen; 68.8 percent phosphorus)
By far, agriculture is the number one source of phosphorus pollution in the state and second highest source of nitrogen. Combined, atmospheric deposition and agriculture account for 88 percent of the nitrogen and 76 percent of the phosphorus load to surface and groundwater.