*5.2.2 Lagoons hold animal waste*

Lagoons can be used for holding animal waste as a retention area to prevent unacceptable pulse of nutrient loads to receiving waters. Lagoons retain nutrients until a time when they can strategically and effectively utilized, however diligence is required due to there could be significant leakage on N to groundwater and volatilization of N as ammonia to the atmosphere. The volatilized N contributes to the flux of N to marine system [53].

#### **Figure 6.**

*Graphical representation of number of counties where manure nutrients exceed the potential plant uptake and removal, including pastureland application, modified from Howarth et al. [55].* 

#### *5.2.3 Composting of animal waste*

After animal waste is composited, it becomes easier to use it as effective fertilizers. However, during composting ammonia volatilization takes place, which contributes to the flux of N to marine system. In addition N volatilization lowers the quality of compost as fertilizer [53].

#### **5.3 Fossil fuel sources of nitrogen**

Fossil fuel combustion emits oxidized forms of N (NOx) to the atmosphere [51]. In United States fossil fuel combustion emits ~6.9 million metric tons of N per year to the environment (**Figure 7**). This is ~60% of the rate of N fertilizer use in the country [55]. Most of the N emitted from fossil fuel is deposited back on the landscape in rain and dry deposition with a significant contribution to nutrient pollution in coastal water [51]. Approximately half of the fossil fuel N emission comes from mobile sources, which includes automobiles, busses, trucks and off road vehicles [51]. Electric power generation produced ~42% of reactive N [63]. Reduction of N emission from fossil fuel combustion could be achieved through; encouraging less driving and more energy efficient vehicles and remove NOx from exhaust using catalytic converters [51]. Stricter emission standards should be applied to sports utility vehicles, trucks and off road vehicles [51]. Promote generation of electric power using fuel cells rather than traditional combustion would mitigate NOx emissions [35]. In addition, electric power plants built for example in the United States before Clear Air Act could be modified to modern standards [63].

#### **5.4 Urban and suburban sources**

Approximately 29% of population of the United States is served by septic tanks instead of sewers [61]. In some coastal areas, septic tanks are the primary sources of N to coastal water [64]. Reduction of N leakage from septic tanks in coastal areas could be accomplished through replacing septic system with sewers and nutrient removal sewage treatment [51].

#### **Figure 7.**

*Atmospheric NOx emissions in the United States of America from 1940 to 2000, modified from Howarth et al. [55].* 
