Nitrogen Deposition in U.S. Coastal Bays and Estuaries

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by Jawed Hameedi, Hans Paerl, Mike Kennish, and Dave Whitall

Photo: Chesapeake Bay, MD

Unlike toxic chemicals such as pesticides fertilizer required to meet human demands. In recent years, that are intended as biocides (to cause biological harm), it has accounted for more than 90 million t of nitrogen fertil- nitrogen pollution in coastal bays and estuaries is primarily izers used worldwide (2004–2005 data), of which 11 million t a consequence of nitrogen fertilization to increase agricul- were used in the United States, 27 million t in China, and tural production and fossil-fuel combustion associated with a 11 million t in India.1 variety of human activities. It is a bit counterintuitive to think Only about 14% of nitrogen used as fertilizers results that the Earth, with an atmosphere containing 3.96 x 1015 t in crops and an even lesser amount in human food.2 The of nitrogen, would be deficient in nitrogen. This is because remaining amount is lost during food production, includ- nitrogen in the atmosphere exists predominantly as biologi- ing transportation and application of fertilizers, seepage cally inert dinitrogen molecules. Biological nitrogen fixation, to groundwater and surface water streams, spoilage and waste, crop residue, animal wastes, and volatilization to the atmosphere. The direct and indirect delivery of large Only 14% of nitrogen used as fertilizers results in crops; the rest is M. Jawed Hameedi, Ph.D., is the lead physical scientist at the National Centers for Coastal Ocean Science, National Ocean lost during food production. Service, National Oceanic and Atmospheric Administration, Silver Spring, MD; Hans W. Paerl, Ph.D., is the Kenan Distinguished Professor of Marine and Environmental mediated by bacteria, has remained the mainstay of agricul- Sciences, University of North Carolina, Chapel Hill, tural production throughout human history. However, the Morehead City, NC; Michael J. Kennish, Ph.D., is a research natural processes of nitrogen fixation and mineral sources of associate professor, Institute of Marine and Coastal Sciences, usable nitrogen cannot sustain food requirements for human Rutgers University, New Brunswick, NJ; and David R. Whitall, population growth, which in the 20th century rose from Ph.D., is a coastal ecologist at the National Centers for Coastal 1.65 billion to more than 6 billion. The Haber-Bosch process, Ocean Science, National Ocean Service, National Oceanic an developed in 1913, allowed for industrial-scale production of Atmospheric Administration, Silver Spring, MD. nitrogen-based fertilizers and now greatly supplements the E-mail: [email protected]. awma.org Copyright 2007 Air & Waste Management Association december 2007 em 19

deposition of nitrogen to coastal bays and estuaries, since all nitrogen-related atmospheric monitoring programs are land-based. In comparison, data on atmospheric deposition of nitrogen and its mass balance in coastal watersheds are considerable. For the forests in the Northeast, for example, it has been noted that more than 90% of nitrogen deposition would be retained in the watershed if the deposition rate was less than 7 kilograms per hectare per year (kg/ha/yr), which is among the highest values of inorganic nitrogen wet deposition calculated for the United States for 2005 (see Figure 2).5 According to this scenario, transport of nitrogen from the watershed to the estuary would be minimal. Atmospheric nitrogen deposition rates in the Figure 1. Relative contribution of nitrogen sources to different estuaries on the U.S. East Coast. Midwest and Far West are much Source: Nitrogen Pollution: From the Sources to the Sea, Science Link Publication, Volume 1, No.2; lower, predominantly less than Hubbard Brook Research Foundation: Hanover, NH, 2003; 24 pp. Reproduced with permission. 2 kg/ha/yr, and are not viewed as a significant source of impact on estuarine ecosystems. amounts of reactive nitrogen into coastal bays and estuaries The data noted above are for “wet deposition”; dry has become a matter of global concern, largely due to wide- deposition (not associated with precipitation) can add spread eutrophication and its adverse consequences on the substantially to total nitrogen inputs.3,6 Estimates of structure and functioning of coastal ecosystems.3,4 atmospheric deposition of nitrogen to coastal watersheds, based on the sum of wet and dry deposition, SOURCES OF NITROGEN range from 3 kg/ha/yr (low values mostly in the West) to Source attribution of nitrogen input to coastal waters and knowledge of its transport and sequestration in different environmental compart- ments are important requisites for establishing pollution abatement or mitigation strategies. Fertilizer applications; municipal sewage and certain industrial effluent discharges; leaking sewer and septic systems; aquaculture operations; fossil-fuel combustion (i.e., power plants and automobiles); runoff from farms, forests, and urban areas; atmospheric deposition of emissions from farms and fields; and inflow from adjacent coastal waters all contribute measurable amounts of reactive nitrogen to coastal bays and estuaries. The relative contributions of different nitrogen sources to a number of estuaries on the U.S. East Coast are summarized in Figure 1. There is a considerable dearth of data on direct atmospheric Figure 2. Inorganic nitrogen wet deposition from nitrate and ammonium, 2005.

14 kg/ha/yr (high values in Delaware Bay, Chesapeake Bay, and some estuaries in the Gulf of Mexico). However, dry Table 1. Nitrogen concentration in coastal waters.14-16 deposition monitoring data are few and deposition rates are often derived from modeling estimates; it is estimated Nitrogen Type Concentration (µg-at/L) that on average 40% of the total nitrogen deposition to the Nitrogen (gaseous) 900 – 1100 watershed is dry deposition.7 There are even fewer moni- Nitrous oxide (gaseous) 0 – 0.25 toring data and modeling estimates of direct atmospheric deposition of nitrogen to the estuaries, but it is assumed to Nitrate (dissolved) 0 – 200 be lower than direct deposition on the watersheds, in part, Nitrite (dissolved) 0.03 – 10 because dry deposition is expected to be lower over water. Ammonium (dissolved) 0.03 – 100 In comparison with atmospheric deposition of nitrogen, agricultural fertilizer application adds considerably to surface Dissolved organic N 3 – 20 water runoff and groundwater flows. Fertilizer application is Particulate organic N 0.1 – 30 dependent on soil conditions, as well as the targeted crops, and varies considerably. For example, 298 kg/ha for wheat, Notes: Nitrogen concentrations are often given as the amount of nitrate (NO3), amount of nitrogen present in nitrate (NO3-N), or gram- 320 kg/ha for corn, and 434 kg/ha for potatoes in intensely atomic weight of nitrogen [quantity of element equivalent to its atomic 8 managed farms in the Columbia Basin, OR. More current weight in grams]. Using current standardized units, 1 mg NO3/L is equivalent to 0.23 mg NO -N/L, which, in turn, is equal to ca. 16 µg data on fertilizer nitrogen use in the United States can be 3 at NO -N/L. accessed from the U.S. Department of Agriculture (www.ers. 3 usda.gov/data/fertilizeruse). Additional fertilizer nitrogen sources include losses from turf grass and home gardens for which data are generally not available. A portion of the unutilized nitrogen in fertilizers seeps However, concentrations of different reactive nitrogen into shallow groundwater and aquifers near farms. Although species vary considerably as a result of biochemical processes, nitrogen concentration in pristine groundwater should chemical transformations, and mixing of water layers with be negligible, levels less than 8 µg-at N/L are considered different concentrations. typical of shallow groundwater unaffected by direct human Ambient concentrations of reactive nitrogen in near-sur- activities.9 Nitrogen concentrations in groundwater vary face coastal waters are generally less than 2 µg-at/L, while in considerably, typically ranging from nondetectable to estuaries that receive large amounts of municipal sewage, 400 µg-at N/L, with isolated observations being an order of agricultural runoff, industrial effluents, and groundwater magnitude higher.10,11 Soil and hydrological characteristics discharge, nitrogen concentrations typically approach or that would impact nitrogen flow and seepage at smaller spatial exceed 200 µg-at/L, with even higher concentration near scales, include fractions of artificially drained soils, irrigation the sources. intensity, as well as denitrification of nitrate by microbes in There are no quantitative criteria for nitrogen com- soil and vegetative cover. In addition, regional physiography pounds in U.S. coastal waters and estuaries to assess levels plays an important role in determining the relative amount of nutrient enrichment above which impairment of the of nitrogen delivered to an estuary via groundwater. As an ecosystem function, resources, and overall condition could example, base flow nitrate load accounts for approximately occur. Quite often, categories of good, fair, and poor are 26–100% of total nitrate load in Chesapeake Bay.12 derived from quartiles or percentiles of accumulated data, As part of a major study to assess environmental and socio- or based on individual opinions. Table 2 provides thresholds economic factors influencing the size and persistence of the for dissolved inorganic nitrogen that were used to character- hypoxic zone in the northern Gulf of Mexico, it was noted ize the condition of estuaries under the U.S. Environmental that large amounts of nitrogen fertilizers in the Mississippi Protection Agency’s (EPA) National Estuary Program. This River basin that are not used up by plants or fixed in the soil assessment was based on analysis of filtered surface water can leach into groundwater or run off into surface waters samples collected in late summer.17 during rainfall events. Major contributions are from fertilizers and mineralized soil nitrogen (58%), animal manure (16%), municipal and industrial point sources (9%), and other sources, including atmospheric deposition, ground- Table 2. Thresholds of dissolved inorganic nitrogen 13 concentrations (µg-at N/L) used in EPA’s National water, soil erosion, and urban runoff (16%). Estuary Program.

NITROGEN CONCENTRATIONS Area Good Fair Poor A general range of observed concentrations of nitrogen and nitrogenous compounds in coastal waters and estuar- East Coast/Gulf < 7 7 – 35 > 35 ies is given in Table 1. While dissolved nitrogen gas is the West Coast < 35 35 – 70 > 70 most abundant form, it is of little consequence in terms of Puerto Rico < 3.5 3.5 – 7 > 7 biological productivity; its concentration is determined by its solubility constant, temperature, salinity, and pressure. awma.org Copyright 2007 Air & Waste Management Association december 2007 em 21 EFFECTS OF NITROGEN OVER-ENRICHMENT bay, nutrient-defined enrichment, depuration, and advection Linking Nitrogen Over-Enrichment to Eutrophication zones have been defined that have different properties in Both nitrate and ammonium are readily utilized during photo- terms of light limitation, silicon deficiency, nitrogen sources synthetic production of organic matter by phytoplankton, and influx, and dissolved oxygen concentration. Responding macroalgae, and submerged aquatic vegetation. Utilization to ambient conditions, the bay also exhibits strong gradients of ammonium is energetically more advantageous, especially in primary productivity, with the highest values in the Provi- under light-limited conditions. Excessive ammonium con- dence River estuary.23 centrations can also reduce nitrate uptake. Other forms of The establishment of nonindigenous grazers during nitrogen, including organic nitrogen, can become available the past two decades has had a profound effect on levels of for plant growth, either through direct uptake or through phytoplankton biomass in the water column, which, in use of inorganic forms of nitrogen resulting from breakdown some areas, has reduced primary productivity or shifted pri- of organic nitrogenous compounds. mary productivity to benthic macroalgae due to increased It is widely assumed that increased supply of nitrogen light availability and access to underutilized nutrient pool. enhances primary productivity of coastal bays and estuar- A five-fold decrease in the primary production and disap- ies because nitrogen is often the limiting nutrient for algal pearance of phytoplankton bloom in Suisun Bay (northern growth.18 To some extent, the underlying linearity in such a part of San Francisco Bay), following the introduction of relationship is based on a simple “lake model” developed in the Asian clam,24 and nuisance growth of a filamentous the early 1960s, a correlation between phosphorus inputs green alga in Lake Michigan are respective examples.25 and eutrophication in lakes worldwide.19,20 Such a model is Furthermore, climate fluctuations and changes, such as not reflective of the considerably more complex relation- the North Atlantic Oscillation or periodic increase in hur- ships between the highly varied amounts and forms of nitro- ricanes, strongly impact phytoplankton biomass, composi- gen and primary productivity in estuaries and coastal bays. tion, and productivity.26,27 Analysis of data from 51 estuaries showed that only 36% of the variance in phytoplankton could be explained by nitro- Linking Nitrogen Over-Enrichment to gen loading, and underscored the difference in response to Harmful Algal Blooms nutrient enhancement between lakes and estuaries, as well as Exceptionally high algal growth in coastal waters and estuar- complexity of such a relationship in different estuaries and ies sometimes results in massive accumulation or “blooms” coastal bays.21 The study also showed considerable scatter in of species that may be directly harmful to humans, fish, and the data and nonlinearity in the relationship between annual wildlife or cause substantial ecosystem perturbations.28,29 nitrogen loading and phytoplankton production with many Estimates of the economic impact of such blooms average outliers. For example, less than 5 mol of nitrogen loading US$75 million annually, including public health costs, loss per square meter was associated with phytoplankton primary of commercial fishing and aquaculture, recreation, and production, ranging from less than 1 to 600 g C/m2/yr. This tourism.30 Largely as a result of increased input of reactive observation does not imply lack of a cause-effect relation- forms of nitrogen, notably ammonium and nitrate, and ship between a micronutrient and primary productivity, but increased number of observations of harmful algal blooms underscores the complex interactions of several factors that (HABs) in recent years, nitrogen-related issues are stated or control the timing and levels primary productivity, including implied to include HABs.3,31 However, a direct relationship light availability, tidal mixing, flushing, sediment resuspen- between nitrogen over-enrichment of coastal waters—mostly sion, nutrient regeneration, and grazing. reported as concentration of dissolved inorganic nitrogen To complicate matters further, different forms of nitrogen in water—and incidence or duration of HABs has been (e.g., ammonium and nitrate ions) affect primary productiv- difficult to quantify. Several estuaries having exceptionally ity and accumulation of phytoplankton biomass differently. high nitrogen concentrations in the water (e.g., Delaware Estuaries that receive large amounts of wastewater discharge Bay) have no history of HAB occurrence. In such cases, fac- and little freshwater inflow result in large concentrations tors other than nitrogen availability, such as vertical mixing, of ammonium, which is often taken up preferentially by turbidity, flushing characteristics, and grazing control algal phytoplankton during photosynthesis and, as such, can out- growth and bloom outbreaks. compete nitrate as a nitrogen source, especially when light In addition to the well-documented role of dissolved inor- availability is restricted. This has been shown in turbid parts ganic nitrogen in promoting algal growth and bloom dynam- of San Francisco Bay where nitrate uptake occurs only rarely ics,3 dissolved organic nitrogen may play an important role. (i.e., when ammonium concentration is reduced due to dilu- This could be as regenerated nitrogen and as nitrogenous tion or other factors to approximately 4 µg-at/L or less).22 excretion sources, including urea and amino acids.32,33 Only Thresholds for ammonium impacts on primary productivity recently has the role of organic nitrogen in promoting harm- have not been established. ful algal blooms been documented in detail.28,34 Further, It has become evident that each estuary represents a several pelagic and benthic dinoflagellates that are associated mosaic of habitats and responds to nitrogen loading differ- with HABs are recognized as “mixotrophs,” meaning that ently. For example, Narragansett Bay, RI, has distinct zones they have a mixed nutritional strategy that includes utiliza- extending from riverine habitats off Providence to the sea- tion of organic molecules. Heterotrophic dinoflagellates ward opening of the Rhode Island Sound bay. Within the are an example of enzyme-mediated epidermal feeding.35

22 em december 2007 Copyright 2007 Air & Waste Management Association awma.org Recent insights into effective utilization of organic molecules matter must be accounted for when assessing eutrophic by several HAB species are significant since coastal runoff conditions in coastal and inland bays. and effluents from urbanized and industrially developed areas typically contain large amounts of organic nitrogen in Impacts on Human Health dissolved and particulate forms and this fraction is generally Extensive data exist concerning the adverse effects of nitrate not accounted for in “nutrient monitoring” in most coastal on human health, most notably the “blue baby” syndrome waterbodies. in infants. There is also concern about other health hazards (e.g., cancer, thyroid disease, diabetes) that could be associat- Impacts on Coastal and Inland Bays ed with chromic exposure to high levels of nitrate. However, Due to their small size, low freshwater runoff, and restricted these data relate to drinking water contamination, and have circulation, coastal and inland bays can be particularly vul- no relevance to nitrate levels in estuaries and coastal bays. nerable to impacts of wastewater streams, sewage flows, and Oxides of nitrogen that form in fertilized farms and fields, toxic chemicals from rapidly growing human populations automobile and aircraft exhausts, emissions from factories on the coast, increasing recreational uses, and, in some and power plants, and burning of biomass are important instances, intense agricultural operations. Examples on the contributors to the formation of smog and ozone, which, in northeastern coast of the United States include Great South turn, can lead to a variety of respiratory and cardiovascular Bay (NY), Barnegat Bay (NJ), Rehoboth Bay (DE), Newport ailments. Nitrogen emissions also contribute to the forma- Bay (MD), and southern Chincoteague Bay (VA). They often tion of fine particular matter that exacerbates respiratory show multiple signs of habitat impairment, including high symptoms associated with air pollution. On occasions, high chlorophyll levels, occurrence of harmful and nuisance levels of nitrogen (inorganic or organic) may be an impor- algal blooms, depleted dissolved oxygen, loss of submerged tant co-factor for the onset, severity, and duration of certain aquatic vegetation, and impaired biotic communities and harmful algal blooms, which, in turn, may pose human harvestable fisheries. Progressive eutrophication, fairly well health risk through inhalation of toxic aerosols or dermal documented in such bays, can eventually lead to permanent exposure to toxins or ingestion of tainted seafood. loss of essential habitats, diminished life support, and a marked decline in human use of the coastal resources and amenities.36 Several coastal bays with long-term data have demon- Developing water quality strated probable impacts of nitrogen enrichment by a shift in dominant primary producers, from the slower growing criteria for nitrogen has remained seagrasses to faster growing macroalgae (seaweeds) and even faster growing phytoplankton. Further, there is increas- a daunting task. ing evidence of the prevalence of brown tide, caused by a cyst forming alga Aureococcus anophagefferens that may have been introduced in the region via ballast water in the 1980s. NITROGEN CONTROL STRATEGIES Such blooms, though not toxic, are often quite dense and Regulatory Control and Abatement can cause discolored water, reduced seagrass growth due to Historically, federal environmental laws and regulations for decreased light penetration, and recruitment failures of com- coastal waterbodies and estuaries have focused on point- mercially important shellfish.37 Occasionally, high concen- source discharges of toxic chemicals and water-related habi- trations of raphidophytes (microalgae) have been noted in tat impairment issues. The Clean Water Act Amendments Delaware’s Inland Bays, situated on the Atlantic Coast. That of 1977 and provisions of the Great Lakes Critical Program may be a consequence of selective grazing by zooplankton Act (1990) required development of standards, criteria, and along with other environmental co-factors that may converge pollution abatement strategies to address critical water to offer a competitive advantage to the microalgae.38 pollution issues in the United States, including nitrogen It is important to note that moderate or highly eutrophic and phosphorus over-enrichment. Criteria guidance is conditions may occur in certain bays, despite low levels of often expressed as pollutant concentration that will assure dissolved inorganic nitrogen (DIN) in the water column. attainment of designated uses of a waterbody (e.g., drinking For example, in the Barnegat Bay-Little Egg Harbor Estu- water supply), propagation of fish and wildlife, and for recre- ary in New Jersey, nitrate-plus-nitrite concentrations are ational, industrial, agricultural, and navigational purposes. typically < 4 µg-at N/L and the highest ammonium con- Criteria can be numeric (e.g., 1 mg/L of nitrate-N) or narra- centration are usually < 2.5 µg-at N/L.36 Despite these low tive (e.g., free from conditions injurious to human health). DIN concentrations, this estuary is plagued by high expres- However, the Clean Water Act stipulates protection for “exist- sions of eutrophic symptoms, most notably negative biotic ing” uses of the waterbody (i.e., those that were attained as of responses. Low DIN levels in the system largely reflect rapid November 28, 1975; the date when the original water quality uptake by algae and vascular plants, rather than steady-state standards took effect). In other words, states may not remove conditions. Therefore, biotic processing of DIN, notably designated uses if they are existing uses, and are expected to plant assimilation and sequestration, as well as the role assure support for such uses through water quality criteria of considerable, but largely unmonitored, flux of organic and other antidegradation measures. awma.org Copyright 2007 Air & Waste Management Association december 2007 em 23 It has been well recognized in the scientific community and private industries. A Nitrogen Management Consortium that observations and inferences from eutrophication in coordinated development of nitrogen load targets that were lakes had limited applicability to coastal bays and estuaries. estimated to improve water clarity that would be sufficient for As a follow-up, EPA has produced documents on technical allowing natural recovery of seagrasses. The actions started guidance for developing nutrient criteria in estuaries and with wastewater treatment upgrades, and subsequently coastal waters.39,40 The strategy also promoted dialog and involved improved stormwater treatment, changes in fertil- partnership among the federal government agencies, state izer manufacturing processes and agricultural practices, and tribal governments, and local organizations to address increased use of reclaimed water (thus reducing surface scientific issues, as well as technological feasibility of control- water discharge from wastewater treatment plants), and ling excessive nutrient input coastal waterbodies. However, significant reductions in atmospheric deposition of nitrogen developing water quality criteria for nitrogen has remained from local electric power plants. Seagrass cover in the bay a daunting task, in part, because of complex biogeochemical has increased more than 30% in comparison with estimated cycling of nitrogen and its delivery to coastal bays and estu- seagrass cover in 1982. A subarea of the bay, Old Tampa aries in vastly different amounts, chemical forms, and rates, Bay, has not shown such recovery and El Nino events have and, in part, due to its multitude of effects, which include occasionally impeded seagrass recovery.42 It is anticipated unsafe drinking water, soil acidity, smog, eutrophication, that federal and state initiatives to promote cleaner-burning ozone depletion, and greenhouse warming at different fuels, improve fuel economy for automobiles, and expand concentrations. mass transit systems will further reduce nitrogen input to the As noted earlier, presently there are no nationwide bay and facilitate seagrass recovery in the area. numerical criteria to limit nitrogen pollution in coastal bays and estuaries in the United States. As of May 2007, only a Nutrient Trading handful of states had approved criteria for nitrogen for entire The 2000 Chesapeake Bay Agreement and related multistate classes of rivers and streams (www.epa.gov/waterscience/ cooperative and regulatory initiatives established allocations criteria/nutrient/strategy/status.html) for nitrogen and phosphorus delivered to the Chesapeake The EPA document, National Strategy for the Development Bay and its tidal tributaries to meet applicable water quality of Regional Nutrient Criteria, outlines the preferred regional standards and placed caps on the loads of these nutrients approach for developing nutrient criteria and standards that may be discharged into the Chesapeake Bay watershed. for different types of waterbodies and provides guidance Such initiatives require point source dischargers of nitrogen on measurements and indicators to state governments and and phosphorus to achieve significant additional reduc- recognized tribes.39 A National Estuaries Experts Workgroup tions of these nutrients to meet the required cap on the was formed in 2006 to provide guidance on this matter, and is total quantity of nutrients entering a waterbody. For several expected to produce its observations and recommendations reasons, nutrient trading in coastal waters and estuaries has by the end of 2007. remained remarkably slow and restrained since the publi- Also, there are no toxicological benchmarks for nitrogen cation of water quality trading policy by EPA in 2003. The concentrations in the United States for protection of coastal reasons may include adequate nutrient control technolo- and estuarine organisms. In Canada, an interim guideline gies already in place in major wastewater treatment plants, intended for protection of coastal fauna and flora from direct government subsidies and “green payments” to farmers for toxicity of the nitrate ion, but not necessarily from impacts controlling nonpoint source discharges, uncertain trading 10 of eutrophication, is 16 mg NO3/L. ratios (e.g., between a treatment plant effluent and crop cover planting), and unexplored issues of buyer liability. It Nitrogen Management at Local and Regional Levels is also evident that nutrient trading may not be effective in Concerned about harmful or undesirable consequences coastal bays and estuaries where nonpoint source discharge of excessive nitrogen input to the estuaries, a number of of nutrients is predominant. regional or local communities and government agencies have taken steps to control nitrogen delivery to coastal bays SUMMARY and estuaries. One of the earliest such steps was taken by the The presence of excessive amounts of biologically reactive Town of Falmouth, MA, which, through a by-law, tied water- nitrogen in coastal bays and estuaries has been recognized shed development to water quality in adjacent waterbodies as a major environmental issue. For the most part, this is due and laid the foundation of the PondWatch monitoring to its role in enhancing phytoplankton growth that, in turn, program in 1987. In recent years, several computer-based can lead to algal blooms, oxygen consumption in seawater tools and models have been developed for predicting nutri- and on the seabed, altered patterns of primary productiv- ent loading to estuaries and evaluating impacts of different ity, changes in species composition, and shading effects on nitrogen management options, including reducing wastewa- macrophytes and seagrass beds. Of particular concern is ter inputs, preserving forested tracts, reducing fertilizer use, the occurrence and magnitude of harmful algal blooms, for and altering zoning ordinances.41 which nutrient over-enrichment could be the primary or an Restoration of seagrass acreage in Tampa Bay, FL, through important co-factor. nutrient load reductions and lowered phytoplankton biomass Nitrogen sources to coastal waters and estuaries are is an example of collaboration among government entities diverse and include wastewater effluents, certain industrial

24 em december 2007 Copyright 2007 Air & Waste Management Association awma.org discharges, surface water runoff, groundwater discharge, the 14. Sharp, J.H. The Distribution of Dissolved Inorganic and Organic Nitrogen in the Sea. In Nitrogen in the Marine Environment; E.J. Carpenter, D.G. Capone, Eds.; atmosphere, and influx from the coastal ocean. Atmospheric Academic Press: New York, NY, 1983; pp. 1-35. deposition can be a relatively major source of nitrogen to 15. McCarthy, M.; Pratum, T.; Hedges, J.; Benner, R. Chemical Composition of Dissolved Organic Nitrogen in the Ocean; Nature 1997, 390, 150-154. estuaries, particularly in areas where other nitrogen sources 16. Tyrrell, T. The Relative Influences of Nitrogen and Phosphorus on Oceanic are relatively small. There are very few estuaries for which a Primary Productivity; Nature 1999, 400, 525-531. 17. National Estuary Program Coastal Condition Report; EPA-842/B-06-001; U.S. Envi- balance sheet of nitrogen input and export has been devel- ronmental Protection Agency, Washington, DC, 2006; 445 pp. oped. This is due to a lack of coherent monitoring programs 18. Nixon, S.W. Coastal Marine Eutrophication: A Definition, Social Causes, and Future Concerns; Ophelia 1995, 41, 199-219. that can provide a continuum of observations from the 19. Guildford, S.J.; Hecky, R.E. Total Nitrogen, Total Phosphorus, and Nutrient watershed to the coastal ocean, and in different environ- Limitation in Lakes and Oceans: Is There a Common Relationship; Limnol. Oceanogr. 2000, 45, 1213-1223. mental matrices to calculate or simulate source attribution 20. Hoyer, M.V.; Frazer, T.K.; Notestein, S.K.; Canfield, D.E. Nutrient, Chlorophyll, of analytes of concern. and Water Clarity Relationships in Florida’s Nearshore Coastal Waters with Comparison to Freshwater Lakes; Canadian Journal of Fisheries and Aquatic Sciences The apparent complexity of nitrogen’s role in promot- 2002, 59, 1024-1031. ing eutrophication has occasionally rekindled debate on 21. Cloern, J.E. Our Evolving Conceptual Model of the Coastal Eutrophication Problem; Marine Ecology Progress Series 2001, 210, 223-253. the comparative influences of nitrogen and phosphorus on 22. Wilkerson, F.P.; Dugdale, R.C.; Hogue, V.E.; Marchi, A. Phytoplankton Blooms primary productivity in coastal and marine waters, particu- and Nitrogen Productivity in San Francisco Bay; Estuaries and Coasts 2006, 29, 401-416. larly where mixing between surface and deeper waters is 23. Carey, D.; Desbonnet, A.; Colt, A.B.; Costa-Pierce, B.A. State of Science on Nutrients more pronounced. 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