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NITROGEN

The 21st Century Coastal Environmental Challenge

Nitrogen is a component of all living things and is essential to life itself. In environments that are not influenced by man, nitrogen is usually in short supply. However, human activity is dramatically changing this situation and there are negative consequences of having "too much of a good thing.” To address this growing problem and to ensure sustainability, control of nitrogen releases to the environment will become a top priority for communities across this country.

Nitrogen pollution is the number one threat to our coastal waters. An excess of nitrogen in coastal and estuarine waters can have cascading environmental consequences. Excess nitrogen can cause excessive phytoplankton (algae) growth which can in turn decrease water clarity and decrease dissolved oxygen. These water quality changes can adversely impact submerged plants like eelgrass which in turn creates a host of impacts to fisheries and other marine life. Nitrogen pollution also contributes to other air, water and land based environmental problems.

Unfortunately, many of our coastal embayments in the U.S. have excessive nitrogen levels. There has been much national press about the Mid-Atlantic States’ problems with Chesapeake Bay and the Mississippi River States’ impacts to the Gulf of Mexico. The New England states are in a particularly precarious position with respect to nitrogen for two reasons — the population density and the proximity to sensitive coastal waters.

  • Connecticut has been on the forefront of this issue due to concerns over Long Island Sound’s water quality problems, and as a result, developed a very successful nitrogen trading program for the wastewater treatment facilities.
  • Rhode Island and Southeastern Massachusetts, including Cape Cod, have begun tackling the nitrogen issue over the past few years.
  • New Hampshire has discovered that Great Bay is being impaired by nitrogen pollution and is in the process of developing waste load allocation studies to address this problem.
  • Maine is exploring nitrogen issues in Casco Bay.

Nitrogen pollution impacts both coastal and inland communities
All communities are affected by nitrogen pollution as all rivers ultimately transport inland nitrogen discharges to the ocean. As an example, inland Massachusetts and New Hampshire communities along the Connecticut River are apt to have nitrogen standards imposed on their wastewater treatment facilities to assist in the efforts to restore Long Island Sound.

Reactive nitrogen – a source of pollution
When we speak of nitrogen pollution, we are referring to the reactive forms of nitrogen, such as ammonia, nitrate and organic forms of nitrogen which are available to biota. The atmosphere is roughly 78% nitrogen gas which is unreactive. In a pristine environment, reactive nitrogen comes primarily from organisms that can incorporate (fix) nitrogen gas from the atmosphere into reactive nitrogen. These organisms include blue green algae, some bacteria found in soil and legume plants like clover and beans. In a balanced pristine environment, the nitrogen that is fixed into reactive nitrogen ultimately makes its way to the soil as nitrate  and is ultimately converted back to unreactive nitrogen gas by bacteria found in soil and wetlands. Soils and wetlands play an extremely important role in the nitrogen cycle and in maintaining this sensitive balance between the reactive and unreactive forms of nitrogen.

Sources of man-made reactive nitrogen
Human activity disrupts the sensitive nitrogen balance and results in excessive amounts of reactive nitrogen in the environment. The three major sources of man-made reactive nitrogen include:

  • Imported food for people and animals
  • Atmospheric emissions
  • Fertilizers

Imported food for people and animals
Much of the nitrogen in the food we eat ends up in the wastewater that we discharge to either septic systems or a sewer system. In the typical septic system, about 50% of the nitrogen ends up in the groundwater which ultimately flows to streams, rivers and/or coastal waters. If this groundwater flows through wetlands, a significant portion of this nitrogen can be converted to unreactive nitrogen; otherwise, very little of the nitrogen is removed from the groundwater. A portion of the nitrogen removed is concentrated in the septage, and some of this nitrogen can be introduced back to the environment depending on the septage disposal practices.

In the typical secondary wastewater treatment facility up to half of the influent nitrogen is removed and half or more is discharged to the environment. The portion that is removed is concentrated in the biosolids and depending on the stabilization/disposal practices, some portion of this nitrogen can be released back to the environment. With state of the art treatment processes that incorporate denitrification processes to convert reactive nitrogen to unreactive nitrogen, the nitrogen removal can approach 80 to 90%. Public and private wastewater disposal systems can account for less than 20% to more than 80% of the total watershed nitrogen load.

While some of the nitrogen in animal feed ends up as protein in the meat we buy, most ends up in animal manure. In many farm situations, animal manures contribute to significant groundwater and runoff pollution issues. Some of the nitrogen in manures also ends up in the atmosphere through ammonia volatilization which is returned back to the land through precipitation.

Atmospheric emissions
Atmospheric emissions of nitrogen oxides (NOx) caused by combustion of fuels and wastes (vehicles, power generation, heating, industry, incinerators, etc.) and emissions of ammonia from sources such as agriculture and biosolids processing. Precipitation and dry deposition contribute nitrogen to the groundwater and stormwater. Air emissions commonly account for between 10% and 35% of the total watershed nitrogen load.

Fertilizers
Fertilizers are used on agricultural land, golf courses and suburban land. In general, fertilizers are often over applied and at least 10% to 20%, sometimes much more, of the nitrogen ends up in the groundwater and runoff. Fertilizers commonly account from between 10% and 30% of the total watershed nitrogen load.

Nitrogen issues are not confined to Wastewater Treatment Facilities alone
Many people associate the coastal nitrogen problem with wastewater treatment facilities. While treatment plant upgrades are undoubtedly one of the first strategies to control nitrogen, this issue is much bigger than treatment plants alone. In highly urban environments like Connecticut, the majority of the coastal nitrogen loading is from treatment plants. In places like Cape Cod where most of the people rely on septic systems for wastewater disposal, about 80% of the nitrogen loads is from septic systems. In Connecticut the primary focus has been to require all the treatment plants in the state to add denitrification capabilities, and their next focus is on stormwater management. On the Cape, the septic systems are the principal nitrogen source that needs to be controlled. In the Chesapeake Bay watershed, only 20% of the nitrogen reaching the bay is from private and public wastewater sources, and they are focusing on land use and runoff as well as wastewater disposal. The relative contributions of nitrogen are very watershed specific.

Stormwater runoff
Runoff can also be a very significant source of nitrogen to coastal waters. This is not surprising given the magnitude of nitrogen in precipitation alone. Consider that the critical concentration of nitrogen in estuarine environments is typically in the range of 0.35 to 0.5 parts per million (ppm), and the average nitrogen concentration in rain is about 0.75 ppm. While much of this nitrogen is naturally removed from the rain that falls on forested and vegetated areas, no removal of nitrogen occurs for the rain that falls on impervious surfaces and directly over water bodies. Runoff also picks up additional nitrogen from over fertilization and other sources of nitrogen pollution deposited on the land. For these reasons, stormwater management and land use regulations can be an important component of nitrogen control. Further reductions in air emissions may also be needed to affect the desired level of nitrogen reduction.

Wright-Pierce is at the forefront of nitrogen management issues. Feel free to contact us for more information.

Article Written By:

William E. Brown, P.E.
President and CEO

Michael D. Giggey, P.E.
Vice President
Wastewater Practice Group

 


Nitrogen Control Strategies
  • Public education and awareness of our "nitrogen footprint”
  • Upgraded/expanded wastewater treatment facilities
  • Productive effluent discharge strategies that include effluent reuse
  • Creative on-lot wastewater disposal solutions
  • Improved stormwater management strategies
  • Land use regulations and regional nutrient management plans
  • Nitrogen-based zoning ordinances
  • Best management practices for fertilizer use
  • Best management practices in agricultural operations
  • Strategies to maximize natural denitrification
  • More stringent air emissions standards
  • Creative funding/financing strategies