Based on long-term average hydrology simulations, it is estimated that 286 million pounds of nitrogen were delivered to tidal waters of the Bay in 2005 (including 20 million lbs deposited directly on tidal waters) compared to 358 million pounds in 1985. Point source loads are monitored and non-point source loads are simulated based on reported implementation of best management practices (BMPs) that reduce nutrient pollution. The simulation removes annual hydrological variations in order to measure the effectiveness of BMP implementation and converts the numerous BMPs, with various pollution reduction efficiencies - depending on type and location in the watershed - to a common currency of nitrogen reduction.
Atmospheric:
Approximately 96 million pounds* or 33% of the total nitrogen load to the Bay is due to sources that emit nitrogen to the atmosphere. (*includes 76 million pounds delivered from the watershed and 20 million lbs deposited directly on tidal waters, based on long-term average hydrology simulations.)
Nitrogen compounds are emitted to the atmosphere (on the order of BILLIONS of pounds of emissions). They include nitrogen oxides (NOx), ammonia (NH3) and organic nitrogen.
NOx are responsible for approximately 2/3 of the total nitrogen emissions that eventually end up as loads to the Bay. NOx are released into the air, primarily as a by-product of combustion - the burning of fossil fuels such as coal, oil or gas.
Types and Relative % Contribution of NOx Emission Sources from States* in the Chesapeake Bay Airshed**:
- Vehicles - 39% (on-road cars and trucks)
- Electric utilities - 27%
- Off-road mobile sources - 16% (boats, lawn mowers, construction equipment, etc.)
- Industry - 12%
- Area Sources - 6% (homes, small business, agriculture, etc.)
NH3 is responsible for approximately 1/3 of the total nitrogen emissions that eventually end up as loads to the Bay. NH3 is primarily released into the air by volatilization and emissions from industrial processes.
Types and Relative % Contribution of NH3 Emission Sources from States* in the Chesapeake Bay Airshed**:
- Agriculture - 80% (livestock and fertilized soils)
- Vehicles - 10%
- Others - 10% (off-road mobile, industry, utilities, area)
*14-States: MD, VA, PA, NY, WV, NJ, OH, KY, NC, SC, TN, IN, MI, and DE
** The estimated geographic area where emission sources have the greatest potential in depositing nitrogen to a watershed.
A portion of the nitrogen from these emissions is deposited on the Bay (approximately 20 million pounds) and its watershed (nearly 400 million lbs). However, not all of the nitrogen deposited on the watershed makes its way to the Bay. Most of it is used by forests and other vegetation, and in other biological processes before it reaches the Bay. Approximately 76 million pounds from all of the nitrogen that deposits actually reaches tidal waters of the Bay from the watershed. Based on what we know about land cover in the watershed, approximately
- 41 million pounds comes from forest lands,
- 20 million pounds comes from urban/suburban lands,
- 11 million pounds comes from agricultural lands and
- 4 million pounds comes from non-tidal waters.
These excessive nitrogen loads to the Bay could be reduced by further controlling emissions from the above mentioned sources beyond that which may be required for air quality purposes; by reducing/preventing the use of nitrogen containing-products; by using state of the art technology to generate products and power that leads to reduced or no nitrogen emissions; and by maintaining healthy forested watersheds, which help keep the air clean and take up much of the nitrogen that deposits.
Chemical Fertilizer:
Approximately 73 million pounds* or 26% of the total nitrogen load to the Bay is due to excess fertilizer from agricultural and urban/suburban areas in the Bay watershed. (*based on long-term average hydrology simulations). Of this total, approximately
- 44 million pounds comes from agricultural lands and
- 29 million pounds comes from urban/suburban lands.
These detrimental loads to the Bay could be reduced by using best management practices (BMPs) that ensure only the amount needed for crop and lawn growth is applied to the land and BMPs that prevent any excess from seeping into groundwater or reaching local waterways that lead to the Bay.
Manure:
Approximately 51 million pounds* or 18% of the total nitrogen load to the Bay is due to excess animal waste from agricultural areas in the Bay watershed (*based on long-term average hydrology simulations).
These detrimental loads to the Bay could be reduced by using best management practices (BMPs) that ensure only the amount needed for crop growth is applied to the land and BMPs that prevent any excess from seeping into groundwater or reaching local waterways that lead to the Bay.
Municipal and Industrial Wastewater:
Approximately 54 million pounds or 19% of the total nitrogen load to the Bay is due to municipal sewage treatment plants and industrial facilities that discharge treated wastewater to waterways in the Bay watershed.
These detrimental loads to the Bay could be reduced by using state of the art technology that reduces nitrogen concentrations in sewage treatment effluent and/or by changing industrial processes that result in wastewater containing less or no nitrogen.
Septic:
Approximately 12.4 million pounds* or 4% of the total nitrogen load to the Bay is due to septic systems that treat household wastewater and discharge effluent to groundwater in the Bay watershed (*based on long-term average hydrology simulations).
These detrimental loads to the Bay could be reduced by using state of the art technology that reduces nitrogen in septic system effluent.
Sources Not Accounted For in the Chart:
The ocean is also a significant source of nutrients to the Bay, but is not accounted for in this chart.
Contributions from tidal shoreline erosion are not included either.
Chesapeake Bay Program Office Phase 4.3 Watershed Model