Nitrogen Pollution

Introduction Nitrogen pollution has become an imminent concern in environmental science because the pollutants often cause substantial harm to bodies of water throughout the world. The largest concern is dwindling aquatic life in formerly thriving aquatic ecosystems. Although nitrogen is not the only limiting nutrient which determines plant productivity, it produces the greatest growth response in plants in the marine environment. In ground forms of nitrogen such as nitrate and ammonium leach into streams, lakes, estuaries, and other water systems (Rosen & Horgan, 2005, Nitrogen and leaching concerns section, para. 1). Denitrification, which is the single most significant natural process that eliminates nitrogen, reduces only a minimal quantity of the pollutants. The majority of runoff nitrogen is then consumed by weeds and algae (Biello, 2008, para. 5). Excess fertilization from runoff nitrogen accelerates the process of eutrophication, and weeds and algae bloom copiously, robbing other plants of sustaining resources. Masses of aquatic life perish, and the overall integrity of the ecosystem diminishes in consequence to the exhaustion of resources that results from nitrogenous pollution (Biello, 2008, para. 6). In recent years, nitrogen pollution has become a point of interest because groundwater contamination has increased dramatically. This increase is a result of various changes in the environment and human lifestyle, which have caused new harm to the environment in the past 200 years. Measured bubbles in glacier ice show that nitrous oxide levels in the atmosphere stayed constant at approximately 285 parts per million (ppm) for thousands of years, but recently, this level has increased to 315 ppm (Bainbridge & George, 1999, Nitrogen and humans section, para. 1). Urbanization, industrialization, fertilizer usage, wastewater treatment plants, and atmospheric emissions are all modern issues that significantly contribute to nitrogen pollution (S. Halterman, personal communication). Dramatic rises in population also intensify nitrogen pollution as more people produce needs for more nitrogen-polluting sources. The rapidly changing culture of the world has caused harmful nitrogen pollution problems in the environment. Nitrogen Pollution Problems in Estuaries Estuaries are one type of ecosystem that is often affected by nitrogenous runoff. Estuaries are sections of streams and rivers that meet with the sea, where salt and fresh water merge and become a brackish mixture. These inlets are driven by ocean tides, but are protected by landforms from strong waves, winds, and sea storms. They include bays, lagoons, sounds, and sloughs and contain several types of habitats like marshes, beaches, mud flats, rocky shores, reefs, and tidal pools. Numerous estuaries on the coast of Massachusetts have been damaged in consequence of nitrogen pollution. The estuaries of interest in southeastern Massachusetts are mainly located in Cape Cod, Buzzards Bay, and the Islands. East coast estuary habitats are homes to a diverse assortment of marine life, including sea weeds and grasses, various shellfish and benthic macro invertebrates, and fish. Several species of birds, mammals, fish, and other wildlife breed in estuaries (“The Massachusetts Estuaries Project”, 2004, What are Estuaries? Section, para. 2). The increases in nitrogen load cause nuisance algal blooms that reduce water quality and to ultimately decrease biodiversity. Thus, even seemingly small escalations in nitrogen pollution can cause large scale effects on the overall ecological integrity of an estuary. The health of estuaries is important to humans for both commercial and recreational reasons. Approximately thirty million jobs in America come from the coastal industry, and 75% of commercial American fishing takes place in estuaries. Furthermore, Americans spend an average of ten days per year on the coast for entertainment or relaxation (“About Estuaries”, 2008, Why are estuaries important section, para. 1). Damage in estuaries causes problems not only for animals and plants but for humans as well. In response to the growing crisis, agencies have attempted to reduce the effects of nitrogen pollution by determining present loading rates and loading rates suitable to improve ecological conditions in estuaries. Sources and Factors Contributing to Nitrogen Pollution Multiple sources, both natural and cultural, account for the nutrients that entering the marine environments. Natural sources of nitrogen in waters include nitrogen fixation, bird and animal wastes, leaf and pollen deposition, and soil overspill. However, while these sources all contribute towards the total amount of nutrients, numerous cultural sources result in the majority of modern nitrogen problems. Significant increase in domestic and industrial waste waters, urban sewage and storm drain runoff, septic systems, and landfill drainage are sources that input pollutant nitrogen forms into water system. Recent increases in population have produced a need for more nitrogen-rich food (e.g. red meat), and thus there is now a frequent use of fertilizers in sustained agriculture and a greater number of animal farms. Nitrogen loading that comes from fertilizer and animal manure has become a prevailing source of pollution (Shannon & Brezonik, 1972, p. 719). Cultural sources also include atmospheric pollution from fossil fuel-burning industries, vehicles, and other sources which generate nitrogen emissions. More than half of these emissions are released into watersheds through precipitation (Bainbridge & George, 1999, Nitrogen and humans section, para. 3). In summary, numerous cultural sources intensify the loads of nitrogen that leach into water systems produced by natural sources. In addition to the sources which add nitrogen to estuaries, there are various factors that affect the build-up of nutrients. The watershed area and land use mix around estuaries affect the amount of water that flows into the ocean. Once in the estuary the nitrogen that came from the watershed together with nitrogen that is deposited directly on the surface is dispersed throughout the estuary. An estuary with a narrow opening to the ocean will retain for a longer time more nitrogen pollution than an estuary with a wide opening by affecting tidal flushing or water and nitrogen residence time (S. Halterman, personal communication). These factors must be taken into account when determining an ecologically healthy nitrogen loading level. Tidal flushing, pollutant dispersion, ocean currents, and water levels are all hydrodynamic processes that affect the movement of pollutants throughout estuaries (Howes et al. 2006, p. 63). Thus, hydrological watershed dynamics and hydrodynamics are factors that determine the movement of nitrogen, and thus change loading rates as well as ecological affects in estuaries. Effects of Excess Nitrogen The impacts of excess nitrogen residue in bodies of water are harmful to the environment. Eutrophication, the process during which the amount of organic material (mostly from algae) is increased, is the main result of the negative effects of nitrogen pollution. The impacts include unappealing odor and aesthetics, release of toxins from algae, alterations in species biomass and composition, loss of species diversity, and changes in the food web (Camargo & Alonso, 2007, Tables 2 & 3). Eutrophication is a natural process, but modern human activity has caused the process to accelerate and become detrimental; this is generally termed cultural eutrophication (Latimer, J., personal communication). When nitrogen pollutes groundwater and surface runoff which flow into larger bodies of water, the nutrients nourish aggressive weeds and algae that overrun the ecosystem and reduce the overall water quality (Brady, 2003, p. 9). Algae can synthesize toxins that when released can be consumed by other organisms (Camargo & Alonso, 2007, Occurrence of toxic algae section, para. 1). The excess algae prevent other plants from receiving nutrients, sunlight, and other resources. This causes a drop in habitual productivity of other plants, affecting food chains. Finally, the acceleration of the eutrophication process of weeds and algal blooms causes oxygen exhaustion. After the plants die, bacteria decompose and break down the plant material, consuming large quantities of oxygen in the process (Camargo & Alonso, 2007, Eutrophication section, para. 1). Oxygen depletion hinders the growth and survival of several other organisms, such as fish, invertebrates, and shellfish, thus decreasing biodiversity and the overall health of the ecosystem environment. Nitrogen pollution causes major problems in the estuaries of Massachusetts. Many waters have become aesthetically unappealing and do not support the natural ecology that was once present in the estuaries (“The Massachusetts Estuaries Project”, 2004, Why is this happening to our estuaries? Section, para. 2). Eelgrass is one of the first species significantly affected in estuarine ecosystems. Eelgrass beds are habitats and nursing grounds for various species of fish, benthic invertebrates, and crustaceans, and they prevent soil erosion (Epifanio, n.d., para. 1). Unfortunately, approximately 90% of the eelgrass beds along the Atlantic coast have been destroyed from human activity and pollutant nitrogen runoff (Epifanio, n.d., para. 2). The environmental effects from algal blooms and sea grass loss impact human uses of estuaries. The closing of beaches and declines in fishing business, tourism and property values are all consequences affecting coastal commercialism and recreation. Nitrogenous pollution effects impede the success of many fisheries, beaches, and properties (Clement et al., 2001, Introduction section, para. 2). Thus, the control of nitrogen pollution in coastal estuaries is important for numerous environmental, commercial, and recreational reasons. Mitigation and Reduction Techniques Various procedures must occur in order to mitigate and reduce polluting nitrogen loads. Because the effects from nitrogen pollution take place over long periods of time, it is difficult to mitigate the sources after the consequences have already occurred (“Embayment restoration”, 2003, Executive summary background section, para. 1). Reduction of nonpoint sources is the primary focus because most manageable point sources of nitrogen pollution (i.e., municipal wastewater facilities) have been reduced by law. Adjusting tidal flushing by dredging channels, altering inlets, or improving culvert design improves the hydrodynamics of an estuary and can reduce nitrogen levels by up to 20% (“Embayment restoration”, 2003, Executive summary tidal flushing section, para. 2). Managing polluted overflow that comes from dirty street gutters, storm drains, and sewers through the National Pollutant Discharge Elimination System (NPDES) can also significantly decrease nitrogen pollution. NPDES permits require treatment of both dry weather and storm-water sources that flow into estuaries (“Embayment restoration”, 2003, Executive summary stormwater control and treatment section, para. 1). The mitigation of human waste from sewage and septic systems is important because they account for almost 90% of controllable polluting sources (“The Mass. approach to restoring estuaries”, 2008, slide 17). The remaining controllable non-point source of nitrogen pollution is runoff from fertilizers used in sustained agriculture. Prevention of fertilizer over-application is critical to reduce fertilizer runoff because nutrient not absorbed by crops leaches into groundwater. A further technique to reduce loading rates from agriculture without decreasing total application is to split application times such that fertilizer is applied in smaller amounts but in more frequent intervals. Slow release fertilizers can also decrease excess nitrogen (Rosen & Horgan, 2008, Nitrogen and leaching concerns section, para. 6). Various preventive and mitigation procedures can be collectively used to obtain healthy loads of nitrogen that leach into coastal estuaries. Methods of Determining Loading RatesTwo groups in the southern Massachusetts region have developed tools to estimate nitrogen inputs to estuaries. One has worked with state management officials to set nitrogen reduction targets to restore estuarine water quality. Essentially, the teams have forecasted nitrogen loading rates for the areas but used different models containing different components. The first of the two projects is the MEP, which is conducted by the Massachusetts Department of Environmental Protection (MA DEP) and the School for Marine and Science Technology (SMAST) at the University of Massachusetts Dartmouth. The MEP begins to resolve nitrogen pollution problems by first studying the sources of the pollution in each estuary. Researchers generate a digital elevation model of the area contributing excessive nutrients to each estuary and determine the current nutrient loads (“The Massachusetts Estuaries Project”, 2004, How can we fix this problem? section, para. 1). The land uses, stream inputs, and sediment nitrogen recycling systems are determined. The MEP has a second part to their work – a coupled estuarine model which aims to predict nitrogen concentrations in the estuary itself. To help estimate nitrogen dispersion, the hydrology, hydro-dynamics, and current water qualities over multiple years are required. The conditions of the estuary affected by nutrients are assessed in different parts of the estuary. Finally, by using indicators such as eelgrass and benthic macro-invertebrates to compare loading rates in decidedly healthy points and unhealthy points, a target water quality is determined (S. Halterman, personal communication). This target water quality value can then be used to calculate a total maximum daily load (TMDL), which is the nitrogen loading rate necessary to maintain a healthy estuarine nitrogen concentration in parts per million (ppm) or milligrams per liter (mg/L) (Howes et al., 2003, Executive summary section, para. 4). The AED-EPA method is strictly devised to estimate watershed (and direct atmospheric deposition of) nitrogen loading to estuaries and makes no attempt to determine estuarine nitrogen concentrations or water quality targets. The team also delineates the watershed and determines the various land uses. Deposition from the atmosphere, wastewater, and fertilizers are estimated to determine the relative importance of all sources of nitrogen. The results of the AED-EPA model can be expressed as a total annual mass per year, or on a mass per area of estuary per year basis (Latimer & Rego, 2008, “Developing nutrient load-response relationships”). Unlike the MEP, the AED-EPA model does not consider watershed water flow lines and does not predict a target loading rate (J. Latimer, personal communication). In summary, the AED-EPA method appears to require fewer resources than the method used by the MEP. The purpose of this report it to compare the nitrogen loading estimates of the two models.

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