A modified representation of the nitrogen cycle applicable to the surface water environmentis presented in Figure 2-2.4 Nitrogen can be added by precipitation and dustfall, surfacerunoff, subsurface groundwater entry, and direct discharge of wastewater effluent. Inaddition, nitrogen from the atmosphere can be fixed by certain photosynthetic blue-greenalgae and some bacterial species. Within the aquatic environment ammonification, nitrification, assimilation, and denitrification can occur as shown in Figure 2-2. Ammonification of organic matter is carried out bymicroorganisms. The ammonum thus formed, along with nitrate, can be assimilated byalgae and aquatic plants; such growths may create water quality problems. Nitrification of ammonium can occur with a resulting depletion of the dissolved oxygencontent of the water. To oxidize 1.0 mg/l of ammonia-nitrogen, 4.6 mg/l of oxygen isrequired. Denitrification produces nitrogen gas which may escape to the atmosphere. Because anoxicconditions are required, the oxygen-deficient hypolimnion (or lower layer) of lakes and thesediment zone of streams and lakes are important zones of denitrification action.
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圖2-2中展示了一種適用于水環(huán)境的氮循環(huán)修改表示方法。氮可以通過降水和沉降、表面徑流、地下水入滲以及廢水排放直接添加。此外，某些光合藍(lán)藻和一些細(xì)菌物種可以固定大氣中的氮。在水生環(huán)境中，氨化作用、硝化作用、同化作用和脫氮作用就如圖2-2所示逐步發(fā)生。有機(jī)物的氨化作用是由微生物進(jìn)行的。所形成的氨和硝酸鹽可以被藻類和水生植物同化代謝，這可能會導(dǎo)致水質(zhì)問題。氨化作用將會引起一定數(shù)量的氧氣消耗，硝化作用則會使水中溶解氧含量降低。要氧化1.0毫克/升的氨基氮，則需要4.6毫克/升的氧氣。脫氮作用則會產(chǎn)生氮?dú)猓S后溢出到大氣中。由于需要缺氧條件，湖泊的缺氧下層（或下層）和流域和湖泊的沉積帶是重要的脫氮作用區(qū)域。

2.2.2土壤和地下水中氮的循環(huán)

Figure 2-3 shows the major aspects of the nitrogen cycle associated with the soil/ground.water environment.5 Nitrogen can enter the soil from wastewater or wastewater effluentartificial fertilizers, plant and animal matter, precipitation, and dustfall. In addition,nitrogen-fixing bacteria convert.nitrogen gas into forms available to plant life. Man hasincreased the amount of nitrogen fixed biologically by cultivation of leguminous crops (e.g..peas and beans). It is estimated that nitrogen fixed by legumes now accounts forapproximately 25 percent of the total fixed.
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圖2-3展示了與土壤/地下水環(huán)境相關(guān)的氮循環(huán)的主要方面。氮可以從廢水或廢水滲出物、人工肥料、植物和動物物質(zhì)、降水和塵埃沉降中進(jìn)入土壤。此外，固氮細(xì)菌將氮?dú)廪D(zhuǎn)變?yōu)橹参锟衫玫男问健Ｈ祟愅ㄟ^種植豆科作物（例如豌豆和豆類）增加了生物固氮的數(shù)量。據(jù)估計，由豆科作物固氮的氮現(xiàn)在約占總量的25％。

Usually more than 90 percent of the nitrogen present in soil is organic, either in living plantsand animals or in humus originating from decomposition of plant and animal residues. Mostof the remainder is ammonium (NH4), which is tightly bound to soil particles.
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通常土壤中90%以上的氮素為有機(jī)氮，其來源要么是存活的植物和動物中的有機(jī)氮，要么是來自于植物和動物殘留物的分解所產(chǎn)生的腐殖土中的有機(jī)氮。其余的大多數(shù)則是緊密結(jié)合在土壤顆粒中的銨（NH4）。

The nitrate content is generally low due to assimilation by plant roots and leaching by waterpercolating through the soil. Nitrate pollution is the principal groundwater quality problemin mmany areas. Denitrification, which is the dominating reaction below the aerobic top layerof soil, rarely removes all nitrates added to the soil from fertilizers or wastewater effluents.Thus, most of the nitrogen which is not assimilated by plant growth eventually enters thegroundwater table in the nitrate form.
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由于植物根系的同化作用和水通過土壤的淋溶作用，硝酸鹽含量普遍較低。在許多地區(qū)，硝酸鹽污染是主要的地下水質(zhì)量問題。在耗氧土層的下方，占主導(dǎo)地位的反應(yīng)是脫氮作用，該反應(yīng)很少能夠從肥料或廢水排放中去除所有添加到土壤中的硝酸鹽。因此，大部分未通過植物生長同化的氮最終以硝酸鹽的形式進(jìn)入地下水板塊中。

2.3氮的來源

Nitrogenous materials may enter the aquatic environment from either natural or man-causedsources. Further, the quantities from natural sources are often increased by man's activity.For example, while some nitrogen may be expected in rainfall, the combustion of fossilfuels or the application of liquid ammonia agricultural fertilizers with subsequent release tothe air through volatilization can increase rainfall concentrations of nitrogen substantially. Itis useful to have an understanding of the various sources of nitrogenous materials and tohave an appreciation of the quantities of nitrogen which may be expected from each.
Although the source of nitrogen causing a specific pollution problem is often obvious.difficulty may be encountered in determining which of several possible sources is mostimportant. As an example, if a stream with excessive aquatic growths due to nitrogenreceives effluent from a sewage treatment plant, drainage from fertilized cropland, andrunoff from pastures or feedlots, the contribution of nitrogen from the treatment plant maybe a small fraction of that from the other two sources. Thus, in analyzing a nitrogenpollution problem, care must be taken to ensure that all possible sources are investigatedand that the amount to be expected from each is accurately estimated. Once an estimate ismade, nitrogen control measures can be oriented toward the more significant sources.
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氮素材料可能從自然或人為資源進(jìn)入水生環(huán)境。此外，自然來源的數(shù)量常常因?yàn)槿祟惢顒佣黾?。例如，雖然降雨中預(yù)期有氮素，但化石燃料的燃燒或液態(tài)氨農(nóng)業(yè)肥料的使用及其隨后通過揮發(fā)釋放到空氣中會顯著增加降雨中氮素的濃度。理解不同來源的氮素材料及其每個來源預(yù)期的數(shù)量是有用的。盡管導(dǎo)致特定污染問題的氮素來源通常很明顯，但確定幾個可能來源中哪個最重要可能會遇到困難。例如，如果一個因氮素而有過多水生植物生長的河流接受污水處理廠的排放、肥沃農(nóng)田的排水和牧草地或飼養(yǎng)場的徑流，那么來自處理廠的氮素貢獻(xiàn)可能只占其他兩個來源的一小部分。因此，在分析氮污染問題時，必須注意確保調(diào)查所有可能的來源，并準(zhǔn)確估計每個來源預(yù)期的數(shù)量。一旦作出估計，氮控制措施可以針對更重要的來源進(jìn)行定位。

2.3.1氮天然來源

Natural sources of nitrogenous substances include precipitation, dustfall, nonurban runoffand biological fixation. Amounts from all may be increased in some way by man. It may bequite difficult to determine quantities which might be expected under completely naturalconditions.
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自然的含氮物質(zhì)來源包括降水、塵埃沉降、非城市徑流和生物固定。這些來源的含氮物質(zhì)數(shù)量可能受到人為影響而增加。在完全自然的條件下確定可能預(yù)期的數(shù)量可能是相當(dāng)困難的。

In order to find levels of nitrogenous substances in precipitation which are as close to“naturalas possible, it is necessary to take samples far from urban or agricultural areas.Even these values may be suspect, however. In one review of nutrient levels in precipitationtotal nitrogen in rainfall in Sweden was cited as 0.2 mg/1.6 The average concentration ofnitrogen in western snow samples, mainly in the Sjerra Nevada Mountains, was 0.15 ppm ofammonia-nitrogen, 0.01 ppm of nitrite-nitrogen and 0.02 ppm of nitrate-nitrogen. Howrepresentative such values are of “natural conditions cannot be determined with anycertainty.
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為了盡可能接近“自然”的降水中的氮素物質(zhì)水平，有必要從城市或農(nóng)業(yè)區(qū)域遠(yuǎn)離地點(diǎn)采樣。然而，即使這些數(shù)值也可能是有所懷疑的。在對瑞典降水養(yǎng)分水平的一項(xiàng)綜述中，降雨中的總氮被引用為0.2 毫克/升。西部雪樣本中的平均氮濃度主要位于錫爾拉內(nèi)華達(dá)山脈，其中氨基氮為0.15 ppm、亞硝酸鹽氮為0.01 ppm，并且硝酸鹽氮為0.02 ppm。然而，這些數(shù)值在“自然條件下的代表性”是無法確定的。

The quantities of nitrogen in nonurban runoff from non-fertilized land may be expected tovary greatly, depending on the erosive characteristics of the soil. One study found thatrunoff from forested land in Washington contained 0.13 mg/l of nitrate-nitrogen and 0.20mg/l of total nitrogen.
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非施肥土地農(nóng)村徑流中的氮數(shù)量預(yù)計會有很大的變化，這取決于土壤侵蝕特征。一項(xiàng)研究發(fā)現(xiàn)，在華盛頓州的森林土地徑流中含有0.13毫克/升的硝酸鹽氮和0.20毫克/升的總氮。

Biological fixation may add nitrogen to both soil and surface water environments. Ofparticular interest is the role of fixation in eutrophication of lakes. Certain photosyntheticblue-green algae, such as the species of Nostoc, Anabaena, Gleotrichia and Calothrix, arecommon nitrogen fixers.
As much as 14 percent of the total nitrogen entering eutrophic Lake Mendota, Wisconsin,was added by fixation. The role of nitrogen fixation in oligotrophic lakes has not beenestablished
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生物固氮作用可以向土壤和水表層環(huán)境中添加氮。尤其值得注意的是其在湖泊富營養(yǎng)化過程中的作用。某些光合作用的藍(lán)綠色藻類，例如Nostoc、Anabaena、Gleotrichia和Calothrix等物種，是常見的固氮菌。

據(jù)報道，威斯康星州門多塔湖（Lake Mendota）富營養(yǎng)化過程中約有14%的總氮量是通過固氮作用所添加的。然而，在寡營養(yǎng)的湖泊中氮固氮作用的作用尚未得到確立。

2.32人為氮源

The activities of man mayincrease quantities of nitrogen added to the aquaticenvironment from three of the sources discussed above: precipitation, dustfall, andnonurban runoff. These sources are increased principally by fertilization of agricultural landand the combustion of fossil fuels.
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人類活動可能會增加水生環(huán)境中三個討論的來源中添加氮的數(shù)量：降水、灰塵沉降和非城市徑流。這些來源主要由于農(nóng)田肥料施用和化石燃料的燃燒而增加。

Other man-related sources include runoff from urban areas and livestock feedlots, municipalwastewater effluents, subsurface drainage from agricultural lands and from septic tank leachfields,and industrial wastewaters.
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其他與人類活動相關(guān)的污染源包括城市區(qū)域的徑流和牲畜飼養(yǎng)場的排放、城鎮(zhèn)污水排放、農(nóng)業(yè)土地的地下排水以及化工行業(yè)的廢水排放。還包括房屋化糞池滲濾污染源。

concentrations in raw municipal wastewaters are well documented.4,8,9 ValuesNitrogengenerally range from 15 to 50 mg/l, of which approximately 60 percent is ammonianitrogen, 40 percent is organic nitrogen, and a negligible amount (one percent) is nitrite- andnitrate-nitrogen. Unless wastewater treatment facilities are designed to remove nitrogenspecifically, most will pass through the treatment works to the receiving waters or landdisposal site, An estimate for the total amount of nitrogen discharged into sewerage systemsin domestic wastewater is 0.84 million metric tons per year in the United States.>
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原始市政污水中的氮濃度已有詳實(shí)記錄。4,8,9氮值通常介于15至50毫克/升之間，其中約60％為氨氮，40％為有機(jī)氮，而亞硝酸鹽和硝酸鹽氮非常微量（僅為1％）。除非污水處理設(shè)施專門設(shè)計用于去除氮，否則大多數(shù)氮將通過處理工藝進(jìn)入接收水體或土地處置場。在美國，估計排入污水管道系統(tǒng)的總氮排放量為840,000噸/年。

Nitrogen discharged into individual septic tank systems can also create pollution problems.It has been estimated that up to 25 percent of the national population utilizes individualsystems,9 contributing up to 0.23 million metric tons of nitrogen annually. In aweli-operating septic tank system, most of the nitrogen leaving the tank will be converted tonitrate in the leaching field. This may then percolate downward to a groundwater table.Problems from high nitrate concentrations occasionally occur when septic tank wastedisposal is located near shallow welis used for water supply, particularly on the fringes ofurban areas where the population density may be fairly high.
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排放到單個化糞池系統(tǒng)中的氮也會造成污染問題。據(jù)估計，全國高達(dá)25％的人口使用單個系統(tǒng)，每年產(chǎn)生高達(dá)0.23百萬公噸氮。在運(yùn)行良好的化糞池系統(tǒng)中，大多數(shù)離開化糞池的氮會在滲濾場中轉(zhuǎn)化為硝酸鹽。這可能會向下滲透到地下水層。當(dāng)化糞池廢料處理靠近用于供水的淺井時，尤其是在人口密度較高的城市邊緣地區(qū)，高硝酸鹽濃度會時常引起問題。

The nitrogen content of industrial wastes varies dramatically from one industry to the nextAmong those industries whose wastewater nitrogen contents may be quite high are meatprocessing plants, milk processing plants, petroleum refineries, ice plants, fertilizermanufacturers, certain synthetic fiber plants, and industries using ammonia for scouring andcleaning operations.
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工業(yè)廢水的氮含量因行業(yè)而異，其中某些產(chǎn)業(yè)的廢水氮含量可能相當(dāng)高，如肉類加工廠、牛奶加工廠、石油精煉廠、冰塊生產(chǎn)廠、化肥制造廠、特定合成纖維廠以及使用氨水進(jìn)行擦洗和清潔操作的工業(yè)。

Feedlot runoff constitutes a source of nitrogen which has become significant as a result ofthe increased number of concentrated, centralized feedlots. Ammonium is a majorconstituent of feedlot waste as a result of urea hydrolysis. Ammonia-nitrogen concentrations may reach 300 mg/l4,8,10 and organic nitrogen concentrations of up to 600 mg/lhave been reported.8,10 The total annual nitrogen load from livestock in the U.S. isestimated to be 6.0 million metric tons.4 While the majority of the animals are apparentlystill raised on small farms, the trend toward feedlot operations is continuing, and unlesssteps are taken to prevent drainage and runoff, serious localized problems can occur.
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飼料批發(fā)市場的污水流失從氮的角度來說逐漸變得重要，這是由于飼養(yǎng)場的數(shù)量增加，同時分散飼養(yǎng)方式也越來越集中。尿素水解后，氨是飼養(yǎng)場廢料的主要組成部分。氨氮濃度可達(dá)300毫克/升，有機(jī)氮含量最高可達(dá)600毫克/升。在美國，家禽畜牧業(yè)的總年氮負(fù)荷約為600萬公噸。雖然多數(shù)家畜還是以小農(nóng)場為主，但飼養(yǎng)場操作的趨勢仍在不斷發(fā)展。除非采取措施防止?jié)B漏和流失，否則將出現(xiàn)嚴(yán)重的局部問題。

Urban runoff can contribute significant quantities of nitrogen to receiving waters during andafter periods of precipitation. Average concentrations which have been reported are 2.7 mg/ltotal nitrogen in Cincinnati, 2.1 mg/1 total nitrogen in Washington, D.C., 25 mg/l totalnitrogen in Ann Arbor, Michigan, and 0.85 mg/l organic nitrogen in Tulsa, Oklahoma.Sanitary or combined sewer overflows can also add to the nitrogen load.
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城市徑流可能在降雨期間和降雨后向水體投放大量氮。據(jù)報道，較為普遍的平均濃度為：辛辛那提的總氮為2.7毫克/升，華盛頓特區(qū)為2.1毫克/升，密歇根州安娜堡為25毫克/升，俄克拉何馬州塔爾薩的有機(jī)氮為0.85毫克/升。此外，污水管道或聯(lián)合管道溢流也可能增加氮的負(fù)荷。

The use of artificial fertilizers has increased the nitrogen concentrations which can beexpected in nonurban runoff, In rural Ohio, runoff from a l.45 acre field planted in winterwheat contained an average of 9 mg/l total nitrogen. For agricultural land in Washingtonthe nitrate-nitrogen concentration was 1.25 mg/1，On a 75-acre site in North Carolinawhich consisted of grassed pasture, wooded pasture, corn field, and orchard, the meannitrogen concentration in the runoff was 1.2 mg/1.
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利用人工肥料的使用增加了非城市污水排放中的氮濃度。在俄亥俄州農(nóng)村，種植冬小麥的1.45英畝土地的排放平均含總氮量為9毫克/升。在華盛頓的農(nóng)業(yè)土地上，硝酸鹽-氮的濃度為1.25毫克/升。在北卡羅來納州的一個75英畝的場地上，包括草牧場、林地、玉米地和果園，排放水樣的平均氮濃度為1.2毫克/升。

Subsurface irrigation drainage from fertilized cropland can contain high concentrations ofnitrates. In agricultural areas of California's San Joaquin Valley, monitoring of subsurfacetile drainage systems between 1966 and 1968 showed average nitrate-nitrogen concentrations of 19.3 mg/1
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肥料施用后的農(nóng)田地下灌溉排水可能含有高濃度的硝酸鹽。加州圣華金谷農(nóng)業(yè)區(qū)在1966年至1968年期間對地下管道排水系統(tǒng)進(jìn)行監(jiān)測，顯示平均硝酸鹽氮濃度為19.3毫克/升。

in the same way that increased nitrogen concentrations in nonurban runoff and subsurfacedrainage have been caused by man's activities, increased nitrogen levels in precipitation anddustfall have also resulted. For example, high ammonium concentrations in spring rains inCalifornia are due to the use of liquid ammonium fertilizers there. Most atmosphericnitrogen (other than nitrogen gas), however, is associated with soil picked up by the windand can be returned to earth by gravitational settling (dry fallout) or in precipitation, andseveral studies have been conducted to determine the quantities to be expected from such sources. The 10-year average of ammonia- plus nitrate-nitrogen concentrations in rainfall atGeneva, New York, was 1.1 mg/1. Snow samples from Ottawa, Canada, over 17 yearscontained an average of 0.85 ppm inorganic nitrogen. Rainwater from the same area forthe same period had concentrations of 1.8 mg/1 ammonia-nitrogen and 0.35 mg/nitrate-nitrogen. In rainfall measurements at Cincinnati, Ohio, total and inorganic nitrogenconcentrations were 1.27 and 0.69 mg/l, respectively. For a rural area near Coshocton.Ohio, the respective concentrations were 1.17 and 0.80 mg/1.
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就像人類的活動導(dǎo)致非城市徑流和地下水排放中的氮濃度增加一樣，降水和塵降中氮水平的增加也是如此。例如，加利福尼亞州春季降雨中高氨濃度是由于該地區(qū)使用了液體氨肥料。然而，除氮?dú)庖酝獾拇蟛糠执髿獾寂c風(fēng)揚(yáng)起的土壤有關(guān)，并可以通過重力沉降（干降）或降水返回地球，已進(jìn)行了幾項(xiàng)研究以確定預(yù)期從這些來源獲得的數(shù)量。紐約州日內(nèi)瓦的降雨中氨鹽和硝酸鹽氮濃度的10年平均值為1.1毫克/升。加拿大渥太華17年的雪樣品中平均含0.85 ppm的無機(jī)氮。同一地區(qū)在同一時期的雨水中氨氮和硝酸鹽氮的濃度分別為1.8毫克/升和0.35毫克/升。在俄亥俄州辛辛那提的降雨測量中，總氮和無機(jī)氮的濃度分別為1.27毫克/升和0.69毫克/升。對于俄亥俄州科?？祟D附近的一個農(nóng)村地區(qū)，分別為1.17毫克/升和0.80毫克/升。

A study made near Hamilton, Ontario, was cited which related dustfall to rainfall. It wasfound that the nitrogen fall totaled 5.8 lb per acre per year. Approximately 6l percent ofthe nitrogen came down on rainy days, which constituted 25 percent of the days monitoredduring the test.
In a study on dustfall in Seattle the fall rate for soluble nitrate-nitrogen was 0.63 lb peracre per year, The concentration of nitrate-nitrogen in the total dustfall was 700 ppm.
As a summary to this discussion of sources of nitrogen, Table 2-1 shows estimates ofnitrogen quantities discharged from various sources in the San Francisco Bay Basin.California. The bay basin has a population of about 4,500,000 people, a land area of4,300 square miles, and a water surface area of about 450 square miles. Because of the highpopulation density, the greatest amount of nitrogen discharged is from municipal andindustrial sources This table is presented only as an example. Care must be taken for eachcase to accurately evaluate the significance of each source.
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引用來自安大略漢密爾頓市附近的研究表明，塵埃降落量與降雨量有關(guān)。研究結(jié)果發(fā)現(xiàn)每英畝每年的氮降落總量為5.8磅，其中約60%的氮是在雨天降落，這占測試期間監(jiān)測日數(shù)的25%。

另一份位于西雅圖的塵埃降落研究表明，可溶性硝酸鹽氮的降落速率為每英畝每年的0.63磅。總塵埃降落中的硝酸鹽氮濃度為700 ppm。

綜上所述，表2-1顯示了在加利福尼亞州舊金山灣流域的各種來源中排放的氮估計量。該灣流域人口約為450萬，陸地面積為4,300平方英里，水面積約為450平方英里。由于高密度人口，最大的氮排放來源是市政和工業(yè)來源。該表僅作為示例呈現(xiàn)，每種情況都需要準(zhǔn)確評估每個來源的重要性，應(yīng)當(dāng)謹(jǐn)慎對待。