Chapter 5 Activities

5. Atmospheric Deposition & Clean Machines



Atmospheric nitrogen deposition is a major source of nitrogen to water and land in Sarasota County. Anthropogenic sources of atmospheric nitrogen include emissions from fertilizer application; human, pet, and livestock waste; and fossil fuel combustion in power plants, vehicles, and outdoor power equipment. Natural sources include emissions from wild animal waste, lightning, forest fires, and soils. Atmospheric nitrogen compounds fall back to earth in dust or rain in the form of nitrogen oxides, ammonium, and nitrates (Figure 5.1). Direct deposition refers to the deposition of nitrogen directly onto a water body or landscape. Indirect deposition refers to the nitrogen that falls on land and then is carried to a receiving water body, often by stormwater or groundwater seepage.

Figure 5.1 Nitrogen emissions from vehicles, power plants, and livestock react in the atmosphere and fall back to the ground in dust and rain. Source: Gulf Coast Community Foundation

Nitrogen deposition rates vary widely, accounting for an estimated 9%-75% of total nitrogen loading for bays of the northeastern U.S. (Howarth 2006), 35%-71% for Tampa Bay (Poor et al., 2013a), and 30%-64% for Lakewood Ranch, FL (Jani et al., 2020). Mobile sources like vehicles and landscape machinery release nitrogen emissions close to the ground and can contribute four times more atmospheric nitrogen to the local watershed than regional power plant emissions (Poor et al., 2013b). A 2005 analysis of community energy use in Sarasota County showed that 9,843 tons (67%) of nitrogen oxides are emitted by vehicles, higher than the per capita national average (Sarasota County Government 2008). Total emissions from driving in the Sarasota-Bradenton metro area are up 61% since 1990 (Gately et al., 2019). Supporting public policy and educational outreach on the multiple benefits of curbing local ground-based emissions from vehicles and outdoor power equipment could significantly reduce atmospheric deposition in Sarasota County.

Because Sarasota’s airshed extends hundreds of miles, reducing atmospheric nitrogen generated by regional power plants is also an important strategy for protecting water quality in Sarasota County. Encouraging individual behaviors and public policies that increase energy efficiency and reduce electricity demand can reduce power plant emissions. Federal Clean Air Act regulations administered by the United States Environmental Protection Agency (EPA) have significantly reduced nitrogen oxide and nitrate emissions. As utilities replace coal-burning plants with cleaner natural gas and solar facilities, the transportation sector is on track to overtake electric power generation as the largest regional source of total emissions (USEPA 2018) (Figure 5.2). Growth in the electric vehicle market may offset a small part of this expected shift.

Figure 5.2 Florida carbon dioxide emissions by sector from the combustion of coal, petroleum products, and natural gas. Combustion of fossil fuels also emits nitrogen oxides that contribute to nutrient pollution. Source: United States Energy Information Administration

Activity 1:

Estimate Nitrogen Loading From Atmospheric Deposition Using Multiple Monitoring Stations Within Urban Areas

Atmospheric deposition, both direct and indirect, is a major source of nitrogen to water and land in Sarasota County. Additional monitoring stations along an urban-to-rural transect, including coastal areas, would significantly enhance understanding of atmospheric nitrogen loading to priority water bodies.

Activity 2:

Educate the Public About the Link Between Air and Water Quality and Choices to Reduce Nitrogen Oxide Emissions.

There is little awareness among the general public that air quality affects water quality. Improved public understanding of the link between air quality, water quality, and environmental and human health – especially with regard to motor vehicles and lawn care equipment – may be a catalyst for better transportation planning and lead to greater consumer adoption of clean alternatives.