2.2.1地表水和沉积物中氮的循环
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.
----
图2-2中展示了一种适用于水环境的氮循环修改表示方法。氮可以通过降水和沉降、表面径流、地下水入渗以及废水排放直接添加。此外，某些光合蓝藻和一些细菌物种可以固定大气中的氮。在水生环境中，氨化作用、硝化作用、同化作用和脱氮作用就如图2-2所示逐步发生。有机物的氨化作用是由微生物进行的。所形成的氨和硝酸盐可以被藻类和水生植物同化代谢，这可能会导致水质问题。氨化作用将会引起一定数量的氧气消耗，硝化作用则会使水中溶解氧含量降低。要氧化1.0毫克/升的氨基氮，则需要4.6毫克/升的氧气。脱氮作用则会产生氮气，随后溢出到大气中。由于需要缺氧条件，湖泊的缺氧下层（或下层）和流域和湖泊的沉积带是重要的脱氮作用区域。
2.2.2土壤和地下水中氮的循环
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.
----
图2-3展示了与土壤/地下水环境相关的氮循环的主要方面。氮可以从废水或废水渗出物、人工肥料、植物和动物物质、降水和尘埃沉降中进入土壤。此外，固氮细菌将氮气转变为植物可利用的形式。人类通过种植豆科作物（例如豌豆和豆类）增加了生物固氮的数量。据估计，由豆科作物固氮的氮现在约占总量的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.
----
通常土壤中90%以上的氮素为有机氮，其来源要么是存活的植物和动物中的有机氮，要么是来自于植物和动物残留物的分解所产生的腐殖土中的有机氮。其余的大多数则是紧密结合在土壤颗粒中的铵（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.
----
由于植物根系的同化作用和水通过土壤的淋溶作用，硝酸盐含量普遍较低。在许多地区，硝酸盐污染是主要的地下水质量问题。在耗氧土层的下方，占主导地位的反应是脱氮作用，该反应很少能够从肥料或废水排放中去除所有添加到土壤中的硝酸盐。因此，大部分未通过植物生长同化的氮最终以硝酸盐的形式进入地下水板块中。
2.3氮的来源
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.
----
氮素材料可能从自然或人为资源进入水生环境。此外，自然来源的数量常常因为人类活动而增加。例如，虽然降雨中预期有氮素，但化石燃料的燃烧或液态氨农业肥料的使用及其随后通过挥发释放到空气中会显著增加降雨中氮素的浓度。理解不同来源的氮素材料及其每个来源预期的数量是有用的。尽管导致特定污染问题的氮素来源通常很明显，但确定几个可能来源中哪个最重要可能会遇到困难。例如，如果一个因氮素而有过多水生植物生长的河流接受污水处理厂的排放、肥沃农田的排水和牧草地或饲养场的径流，那么来自处理厂的氮素贡献可能只占其他两个来源的一小部分。因此，在分析氮污染问题时，必须注意确保调查所有可能的来源，并准确估计每个来源预期的数量。一旦作出估计，氮控制措施可以针对更重要的来源进行定位。
2.3.1氮天然来源
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.
----
自然的含氮物质来源包括降水、尘埃沉降、非城市径流和生物固定。这些来源的含氮物质数量可能受到人为影响而增加。在完全自然的条件下确定可能预期的数量可能是相当困难的。
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.
----
为了尽可能接近“自然”的降水中的氮素物质水平，有必要从城市或农业区域远离地点采样。然而，即使这些数值也可能是有所怀疑的。在对瑞典降水养分水平的一项综述中，降雨中的总氮被引用为0.2 毫克/升。西部雪样本中的平均氮浓度主要位于锡尔拉内华达山脉，其中氨基氮为0.15 ppm、亚硝酸盐氮为0.01 ppm，并且硝酸盐氮为0.02 ppm。然而，这些数值在“自然条件下的代表性”是无法确定的。
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.
----
非施肥土地农村径流中的氮数量预计会有很大的变化，这取决于土壤侵蚀特征。一项研究发现，在华盛顿州的森林土地径流中含有0.13毫克/升的硝酸盐氮和0.20毫克/升的总氮。
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
----
生物固氮作用可以向土壤和水表层环境中添加氮。尤其值得注意的是其在湖泊富营养化过程中的作用。某些光合作用的蓝绿色藻类，例如Nostoc、Anabaena、Gleotrichia和Calothrix等物种，是常见的固氮菌。
据报道，威斯康星州门多塔湖（Lake Mendota）富营养化过程中约有14%的总氮量是通过固氮作用所添加的。然而，在寡营养的湖泊中氮固氮作用的作用尚未得到确立。
2.32人为氮源
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.
----
人类活动可能会增加水生环境中三个讨论的来源中添加氮的数量：降水、灰尘沉降和非城市径流。这些来源主要由于农田肥料施用和化石燃料的燃烧而增加。
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.
----
其他与人类活动相关的污染源包括城市区域的径流和牲畜饲养场的排放、城镇污水排放、农业土地的地下排水以及化工行业的废水排放。还包括房屋化粪池渗滤污染源。
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.>
----
原始市政污水中的氮浓度已有详实记录。4,8,9氮值通常介于15至50毫克/升之间，其中约60％为氨氮，40％为有机氮，而亚硝酸盐和硝酸盐氮非常微量（仅为1％）。除非污水处理设施专门设计用于去除氮，否则大多数氮将通过处理工艺进入接收水体或土地处置场。在美国，估计排入污水管道系统的总氮排放量为840,000吨/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.
----
排放到单个化粪池系统中的氮也会造成污染问题。据估计，全国高达25％的人口使用单个系统，每年产生高达0.23百万公吨氮。在运行良好的化粪池系统中，大多数离开化粪池的氮会在渗滤场中转化为硝酸盐。这可能会向下渗透到地下水层。当化粪池废料处理靠近用于供水的浅井时，尤其是在人口密度较高的城市边缘地区，高硝酸盐浓度会时常引起问题。
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.
----
工业废水的氮含量因行业而异，其中某些产业的废水氮含量可能相当高，如肉类加工厂、牛奶加工厂、石油精炼厂、冰块生产厂、化肥制造厂、特定合成纤维厂以及使用氨水进行擦洗和清洁操作的工业。
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.
----
饲料批发市场的污水流失从氮的角度来说逐渐变得重要，这是由于饲养场的数量增加，同时分散饲养方式也越来越集中。尿素水解后，氨是饲养场废料的主要组成部分。氨氮浓度可达300毫克/升，有机氮含量最高可达600毫克/升。在美国，家禽畜牧业的总年氮负荷约为600万公吨。虽然多数家畜还是以小农场为主，但饲养场操作的趋势仍在不断发展。除非采取措施防止渗漏和流失，否则将出现严重的局部问题。
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.
----
城市径流可能在降雨期间和降雨后向水体投放大量氮。据报道，较为普遍的平均浓度为：辛辛那提的总氮为2.7毫克/升，华盛顿特区为2.1毫克/升，密歇根州安娜堡为25毫克/升，俄克拉何马州塔尔萨的有机氮为0.85毫克/升。此外，污水管道或联合管道溢流也可能增加氮的负荷。
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.
----
利用人工肥料的使用增加了非城市污水排放中的氮浓度。在俄亥俄州农村，种植冬小麦的1.45英亩土地的排放平均含总氮量为9毫克/升。在华盛顿的农业土地上，硝酸盐-氮的浓度为1.25毫克/升。在北卡罗来纳州的一个75英亩的场地上，包括草牧场、林地、玉米地和果园，排放水样的平均氮浓度为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
----
肥料施用后的农田地下灌溉排水可能含有高浓度的硝酸盐。加州圣华金谷农业区在1966年至1968年期间对地下管道排水系统进行监测，显示平均硝酸盐氮浓度为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.
----
就像人类的活动导致非城市径流和地下水排放中的氮浓度增加一样，降水和尘降中氮水平的增加也是如此。例如，加利福尼亚州春季降雨中高氨浓度是由于该地区使用了液体氨肥料。然而，除氮气以外的大部分大气氮都与风扬起的土壤有关，并可以通过重力沉降（干降）或降水返回地球，已进行了几项研究以确定预期从这些来源获得的数量。纽约州日内瓦的降雨中氨盐和硝酸盐氮浓度的10年平均值为1.1毫克/升。加拿大渥太华17年的雪样品中平均含0.85 ppm的无机氮。同一地区在同一时期的雨水中氨氮和硝酸盐氮的浓度分别为1.8毫克/升和0.35毫克/升。在俄亥俄州辛辛那提的降雨测量中，总氮和无机氮的浓度分别为1.27毫克/升和0.69毫克/升。对于俄亥俄州科希克顿附近的一个农村地区，分别为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.
----
引用来自安大略汉密尔顿市附近的研究表明，尘埃降落量与降雨量有关。研究结果发现每英亩每年的氮降落总量为5.8磅，其中约60%的氮是在雨天降落，这占测试期间监测日数的25%。
另一份位于西雅图的尘埃降落研究表明，可溶性硝酸盐氮的降落速率为每英亩每年的0.63磅。总尘埃降落中的硝酸盐氮浓度为700 ppm。
综上所述，表2-1显示了在加利福尼亚州旧金山湾流域的各种来源中排放的氮估计量。该湾流域人口约为450万，陆地面积为4,300平方英里，水面积约为450平方英里。由于高密度人口，最大的氮排放来源是市政和工业来源。该表仅作为示例呈现，每种情况都需要准确评估每个来源的重要性，应当谨慎对待。
