389 EUTROPHICATION INTRODUCTION For a considerable time, scientists have been aware of the natural aging of lakes, a process so slow that it was consid- ered immeasurable within the lifetime of human beings. In recent years, however, that portion of the nutrient enrichment or eutrophication of these and other natural bodies of water contributed by man-made sources have become a matter of concern. Many bodies of water of late have exhibited biologi- cal nuisances such as dense algal and aquatic weed growths whereas in the past they supported only incidental populations of these plants. Excessive nutrients are most often blamed in the scien- tifi c literature for the creation of the plant nuisances. Among the nutrients, dominant roles have been assigned by most researchers to nitrogen and phosphorus. These elements can be found in natural waters, in soils, in plants and animals, and in precipitation. Man-made sources for these nutrients are in domestic wastes and often in industrial wastes. This chapter concerns itself with the nature of algae, the environmental factors affecting their growth, the nature of the entrophication problem (sources, relative quantities of nutrients contributed by these sources, threshold limits for the growth of aquatic plants), and various techniques for the removal of those nutrients usually associated with the eutro- phication problem. THE PHYSICAL NATURE OF ALGAE Most bodies of water which can be considered eutrophic exhibit various predominant forms of algae at different times of the year. Algae that are important to investigators concerned with the eutrophication problem may be classifi ed into four groups which exclude all but a few miscellaneous forms. The four groups are: 1) Blue-green algae (Myxophyceae) 2) Green algae (Chlorophyceae) 3) Diatoms (Bacillariophyceae) 4) Pigmented flagellates (Chrysophyceae, Euglenophyceae) The basis for this classifi cation is the color of the organ- ism. Blue-green and green algae are self descriptive, whereas diatoms are brown or greenish-brown. Pigmented fl agellates can be brown or green. They possess whip-like appendages called fl agella, which permit them to move about in the water. It is not inferred by the above list that all algae are restricted to these colors. Rhodophyceae, for example, which are primarily marine algae, are brilliant red. Aquatic biologists and phytologists do not agree on the number of divisions that should be established to identify algae. Some authorities use as many as nine divisions while others use seven, fi ve and four. Nevertheless, the four divi- sions as suggested by Palmer will be used as they are adequate for the ensuing discussions. BLUE-GREEN ALGAE Blue-green algae as a group are most abundant in the early fall at a temperature range of 70 to 80°F. Data obtained from water sources in the southwestern and southcentral United States indicate that for this section of the country maximum growth occurs at the end of February and through- out much of April, May and June. When blue-green algae becomes predominant, it frequently indicates that the water has been enriched with organic matter, or that previously there had been a superabundance of diatoms. Blue-green algae are quite buoyant due to the oil globules and gas bubbles which they may contain. For this and other reasons they live near the surface of the water often producing offensive mats or blankets. Since these algae are never fl agellated, they are not considered swimmers although a few, such as oscillatoria and spirulina, are able to creep or crawl by body movements. Some of the common blue-green algae are anabaena, aphani- zomenon, rivularia, gomphosphaeria and desmonema. GREEN ALGAE Green algae are most abundant in mid-summer at a tem- perature range of 60 to 80°F. For water bodies in the south- western and southcentral United States, maximum growth occurs during the fi rst half of September with little variation throughout the remainder of the year. Like the blue-green algae, green algae usually contain oil globules and gas bub- bles which contribute to the reasons why they are found near the surface of the water. Green algae are distinguished by their green color which comes from the presence of chloro- phyll in their cells. Many of the green algae are fl agellates © 2006 by Taylor & Francis Group, LLC 390 EUTROPHICATION and due to their swimming ability they are frequently found in rapidly moving streams. Some of the common green algae are chlorella, spirogyra, chlosterium, hydrodictyon, nitella, staurastrum and tribonema. DIATOMS Diatoms are usually most prevalent during the cooler months but thrive over the wide temperature range of from 35 to 75°F. For water bodies in the southwestern and southcen- tral United States, diatoms thrive best in May, September and October with the maximum growth observed in mid- October. It is generally recognized that many diatoms will continue to fl ourish during the winter months, often under the ice. The reason for the increase in growth twice a year is due to the spring and fall overturn, in which food in the form of carbon, nitrates, ammonia, silica and mineral matter, is brought to the surface where there is more oxygen and a greater intensity of light. Diatoms live most abundantly near the surface, but unlike the buoyant green and blue-green algae, they may be found at almost any depth and even in the bottom mud. Diatoms may grow as a brownish coating on the stems and leaves of aquatic plants, and in some cases they grow along with or in direct association with other algae. In rapidly moving streams they may coat the bottom rocks and debris with a slimy brownish matrix which is extremely slippery. Lastly, diatoms are always single-celled and nonfl agellated. PIGMENTED FLAGELLATES No classifi cation of algae has caused more disagreement than that of the pigmented fl agellates. The diffi culty arises from the fact that hey possess the protozoan characteristics of being able to swim by means of fl agella, and the algae characteristic of utilizing green chlorophyll in association with photosynthesis. Thus they could be listed either as swimming or fl agellated algae in the plant kingdom, or as pigmented or photosynthetic protozoa in the animal king- dom. One of many attempts to resolve this problem has been the proposal to lump together all one-celled algae and all protozoa under the name “Protista.” This method, however, has not met with general acceptance. For the sanitary engi- neer the motility of the organism is of lesser importance than its ability to produce oxygen. The pigmentation character- istic associated with green chlorophyll and oxygen produc- tion is suffi cient criteria for separating these organisms into a class by themselves. Thus a distinction is made between pigmented fl agellates (algae) and nonpigmented fl agellates (protozoa). Pigmented fl agellates are more abundant in the spring than at any time of the year although there is generally con- siderable variation among the individual species. Apparently fl agellates are dependent on more than temperature. They are found at all depths, but usually are more prevalent below the surface of the water than at the surface. For present purposes pigmented fl agellates can be divided into two groups: euglenophyceae which are grass-green in color and chrysophyceae which are golden-brown. Euglenophyceae are usually found in small pools rich in organic matter, whereas chrysophyceae are usually found in waters that are reasonably pure. Some of the more common pigmented fl agellates are euglena, ceratium, mallomonas, chlamydomonas, cryptomo- nas, glenodinium, peridinium, synura and volvox. MOTILITY Of additional value in the classifi cation of algae are their means of motility. Three categories have been established, namely: Nekton—algae that move by means of flagella. Plankton—algae that have no means of motility. Benthic algae—algae that attach themselves to a fixed object. NEKTON Nekton are the most active algae and are often referred to as “swimmers.” Due to their activity they use more energy and in turn release more oxygen during the daylight hours. Their cells are supplied with one, two, or more fl agella which extend outward from the front, side or back of the cell. These fl agella enable the organisms to move about freely in the aquatic environment and to seek food which, in the case of turbulent water, is constantly changing in location. In general nekton have the most complex structure of the three categories and come nearest to being simple animals. Nekton are the predominant algae found in swiftly moving rivers and streams. According to Lackey, results of tests performed on waters of the Ohio River show that certain nekton are the only algae that provide reliable clear-cut responses to the presence of pollution and thus are true indicator organisms. Five fl ag- ellates have been singled out on the genus level as being common and easily recognized. They are (1) cryptomonas, (2) mallomonas, (3) synura, (4) uroglenopsis, and (5) dino- bryon. Dinobryon is perhaps the most easily recognized due to its unique shape which resembles a shaft of wheat. Samples taken from several rivers indicate that these algae react adversely to the presence of sewage and are found in abundance only in clean water. Unfortunately not all experts agree on what constitutes clean water and what algae serve as indicator organisms. Patrick states that the “healthy” por- tion of a stream contains primarily diatoms and green algae. Rafter states that the absence of large amounts of blue-green algae is an indicator of clean water. Palmer lists 46 species which have been selected as being representative of “clean- water algae,” and these consist of diatoms, fl agellates, green algae, blue-green algae and red algae. In addition Palmer lists © 2006 by Taylor & Francis Group, LLC EUTROPHICATION 391 47 species of algae condensed from a list of 500 prepared from reports of more than 50 workers, as being representative of “polluted-water algae.” These consist of blue-green algae, green algae, diatoms and fl agellates. PLANKTON Plankton are free-fl oating algae which are most commonly found in lakes and ponds, although they are by no means lim- ited to these waters. Most species are unicellular; however, they tend to become colonial when their numbers increase, as in the formation of a heavy concentrated growth known as a “bloom.” An arbitrary defi nition of a bloom is that con- centration of plankton that equals or exceeds 500 individual organisms per ml. of raw water. Blooms usually show a pre- dominance of blue-green algae although algae from other classes can also form blooms. An algae bloom often becomes suffi ciently dense as to be readily visible on or near the water surface, and its presence usually indicates that a rich supply of nutrients is available. Other environmental factors may stimulate the formation of blooms, and a bloom of the same organism in two bodies of water may or may not result from identi- cal favorable environmental conditions. These growths are extremely undesirable in bodies of water, in general, and in potential water supply sources in particular for the following reasons: 1) They are very unsightly. 2) They interfere with recreational pursuits. 3) When the water becomes, turbulent, fragments of the mat become detached and may enter a water treatment system clogging screens and filters. 4) When the algae die (as a result of seasonal changes or the use of algicides), decomposition occurs, resulting in foul tastes and odors. 5) They may act as a barrier to the penetration of oxygen into the water which may result in fish kills. 6) They may reduce the dissolved oxygen in the water through decay or respiration within the bloom. 7) Some blooms release toxic substances that are capable of killing fish and wild life. 8) They may cause discoloration of the water. 9) They attract waterfowl which contribute to the pollution of the water. Some of the common blue-green algae that form blooms are anabaena, aphanizomenon, oscillatoria, chlorella and hydrodictyon. Synedra and cyclotella are common diatoms that form blooms and synura, euglena and chlamydomo- nas are common fl agellates that form blooms. Filamentous green plankton, such as spirogyra, cladophora and zyg- nema form a dense fl oating mat or “blanket” on the surface when the density of the bloom becomes suffi cient to reduce the intensity of solar light below the surface. Like blooms, these blankets are undesirable, and for the same reasons cited earlier. However, in addition, blankets also serve as a breeding place for gnats and midge fl ies, and after storms they may wash up on the shores where they become offensive. In many cases hydrogen sulfi de and other gases which are able to spread disagreeable odors considerable distances through the air are liberated. In large amounts, hydrogen sulfi de has been known to seriously discolor the paint on lakeside dwellings. BENTHIC ALGAE Benthic algae are those algae which grow in close associa- tion with a supply of food. That is, they seek out an aquatic environment where nutrients are adequate, then attach themselves to a convenient stationary object such as a sub- merged twig or rock. They may be found in quiet ponds and lakes or in fast-moving rivers and streams. In some cases they break away from their attachments and form unsightly surface mats, or they may re-attach themselves somewhere else. Chlamydomonas is such an organism, where in one growth phase it may be found attached to a fi xed object, and in another phase it may be dispersed throughout the water. Benthic algae include diatoms, blue-green algae, green algae and a few species of red fresh-water algae. None of the pigmented fl agellates are benthic. Most attached algae grow as a cluster of branched or unbranched fi laments or tubes and are fastened at one end to some object by means of an anchoring device. Others take the shape of a green felt-like mat (gomphonema), a thin green fi lm or layer (phytoconis), or a soft fragile tube (tetraspora). Some of the most common benthic algae are cladophora, chara, nitella, ulothrix, cym- bella, vaucheria and gomphonema. ENVIRONMENTAL FACTORS AFFECTING GROWTH OF ALGAE The effects of certain environmental factors on the growth of the aforementioned forms of algae have been fairly well defi ned. The most important parameters to be considered in the growth pattern are light intensity, temperature, pH and nutritional requirements. LIGHT INTENSITY Light is essential to all organisms which carry on photo- synthesis; however, requirements or tolerance levels differ greatly with the organism. For example, terrestrial species of vaucheria grow equally well in fully-illuminated soil and densely-shaded soil, while a number of blue-green algae grow only in shaded habitats. In addition, some algae are unable to endure in the absence of sunlight caused by sev- eral consecutive cloudy days, whereas certain submerged algae are unable to withstand exposure to full sunlight. Thus, an algae kill may be noted during a drought where © 2006 by Taylor & Francis Group, LLC 392 EUTROPHICATION shallow water prevents depth-dwelling algae from escaping the intensity of the sunlight penetration. Often muddy rivers are virtually algae-free due to the lack of penetration of the sunlight, the Missouri and the Mississippi being two such rivers. The distribution of algae at the various depths in a body of water is directly correlated with the intensity of illumination at the respective depths. This distribution would be diffi cult to express in general terms when dealing with algae on their species level. In addition, the depths at which these species would be found would change with such variables as growth phase of the organism, tempera- ture and the absorptive and refl ective characteristics of the water. It can be stated, however, that certain fresh-water red algae and blue-green algae are found only at consid- erable depths and that some diatoms exist in the bottom mud. In the most general terms it can also be stated that algae are found at all levels, but most commonly near the surface. The vertical distribution may also be related to the divi- sion of light rays into various spectral colors. This division varies with the concentration of dissolved color material, plankton and particulate matter, with the seasons, and with the depth. In colored water the violet-blue end of the spec- trum is absorbed more readily. As depth increases light rays divide differently with greater absorption occurring at the red end of the spectrum. The depth to which light penetrates has a direct infl uence on photosynthetic activity. The seasonal variation in this light and the resulting availability of certain dominant wave lengths may be the reason for fl uctuations in the composition of the algal population from spring to fall. Much more work is needed in this area. TEMPERATURE In general, temperature is not the key factor in determining the nature of the algal fl ora. Most species are able to grow and reproduce if other environmental conditions are favor- able. According to Patrick, however, the above statement is not true in the case of diatoms, where temperature changes are more important than any other environmental factor in infl uencing their rate of growth. Additional work in this area by Cairns indicates that certain diatoms grow best only at a specifi c temperature, and that at some temperatures they will not grow at all. Most algae are not affected by minor changes in pH brought about by the seasonal variations, growths of carbon- dioxide producing organisms, etc. Large changes such as would be caused by the introduction of industrial wastes or acid mine waters, will greatly affect algae, usually causing a decrease in population. The majority of algae thrive when the pH is near 7.0. Some blue-green algae prefer high pHs. Anacystis and coc- cochloric are found at about pH 10.0 with little or no growth below pH 8.0. Other algae such as eugleny mutabilis, cryp- tomonas erosa and ulothrix zonata prefer low pHs. NUTRITIONAL REQUIREMENTS AND TOXIC ELEMENTS FOR ALGAE Calcium Calcium is not an essential element for most algae, although some cannot develop without it. Calcium and Magnesium As bicarbonates they are a supplemental supply of carbon dioxide for photosynthesis. This accounts for the greater abundance of algae in hard-water lakes than in soft-water lakes. Iron Most algae grow best when the ferric oxide content of the water is between 0.2 to 2.0 mg per liter. Above 5 mg per liter there is a toxic effect unless it is overcome by the buffering action of organic compounds or calcium salts. Certain dia- toms (eunotia and pinnularia) are found in iron-rich water. Effl uent from steel mills may be toxic to most algae if the resulting iron concentration exceeds the toxic limitation. Copper Copper is extremely toxic to algae in the range of 0.1 to 3.0 ppm as copper sulfate; the sulfate form being used as an algi- cide. Some algae are able to tolerate large amounts of copper ion and are considered copper-sulfate resistant. Protococcus, for example, is not destroyed by 10 ppm of copper sulfate. Phenol At a concentration of up to 1.9 mg per liter, phenol appar- ently has no toxic effect on diatoms. Nitrates, Phosphates and Ammonia These are essential food elements necessary for growth. Nitrogen may be obtained from nitrates, nitrites or simple ammonia compounds. The primary source of these nutrients is from sewage treatment plant effl uents, although nitro- gen may be derived from the atmosphere, land runoff, etc. (See section on EUTROPHICATION.) In general as little as 0.3 to 0.015 ppm of nitrates and phosphates will produce blooms of certain species of algae, other conditions being favorable. Oil Streams polluted with oil are usually low in algae. One vari- ety of diatoms may be dominant in such waters. Salinity Increases in salinity up to about one percent do not affect the algae population. Signifi cant increases, such as caused © 2006 by Taylor & Francis Group, LLC EUTROPHICATION 393 by salt-brine wastes, may destroy most of the algae present, however. Certain fresh-water algae may become adapted to water with slowly increasing salinity. Hydrogen Sulfide At a concentration of 3.9 ppm, hydrogen sulfi de is toxic to most diatoms. Some resistant species are achnanthese affi nis, cymbella ventricosa, hantzschia amphioxys and nitzschia palea. Silica Silica is necessary for the growth of diatoms whose cell wall is composed of silica. Presently no limits have been determined (to the author’s knowledge). Vitamins Several vitamins in small quantities are a requisite to growth in certain species of algae. Chief among these vitamins are vitamin B-12, thiamine and biotin. These vitamins are sup- plied by bottom deposits, soil runoff and by the metabolites produced by other organisms. Micronutrients Substances such as manganese, zinc, molybdenum, vana- dium, boron, chlorine, cobalt, etc. are generally present in water in the small concentrations suffi cient for plant growth. Carbon Dioxide Carbon dioxide is necessary for respiration. If it is defi cient, algae may remove carbon dioxide from the atmosphere. Chlorine Chlorine is toxic to most algae and is used as an algicide in the range of 0.3 to 3.0 ppm. It is used as an algicide in the treatment plant and distribution system. Some algae, cos- marium for example, are resistant to chlorine. Protococcus, which is resistant to copper sulfate, is killed by 1 ppm of chlorine. Therefore, algae resistant to the copper ion may not be resistant to the chlorine ion and vice versa. Calcium Hydroxide (lime) An excess of lime in the water, as may be introduced during pH adjustment for coagulation, results in the death of certain algae. Five ppm of lime with an exposure of 48 hours has been lethal to melosira, nitzschia and certain protozoa and crustacea. THE EUTROPHICATION PROBLEM Of the factors previously discussed which promote the growth of algae, that factor which man has altered is the nutrient concentration in may of the natural waterways. In simplest terms, eutrophication is the enrichment of waters by nutrients from natural or man-made sources. Of the many nutrients which are added to the waters by man- made sources, nitrogen and phosphorous are most often cited by researchers as being the key nutrients responsible for the promotion of algae growth. In nearly all cases when the nitrogen and phosphorus level of a body of water increases, there will be a corresponding increase in the growth of algae and aquatic plants. Such growth greatly speeds up the aging process whereby organic matter invades and gradually dis- places the water until eventually a swamp or marsh is formed. Unfortunately, the process of eutrophication is often diffi cult to reverse in bodies of water such as large lakes where the fl ushing or replacement time for the waters can be in the order of years. The following sections provide the relative magnitude of natural and man-made sources of nutrient material associated with plant growth. SOURCES OF NUTRIENTS While it is recognized that certain algae require a number of chemical elements for growth, it is also known that algae can absorb essential as well as superfl uous or even toxic elements. Although every essential element must be present in algae, this does not mean that every element is essential. On the other hand, the absence of certain nutrient elements will prevent growth. Nutrients may be classifi ed as (1) “absolute nutrients,” which are those which cannot be replaced by other nutrients, (2) “normal nutrients,” which are the nutrients contained in the cell during active growth, and (3) “optimum maximum growth.” It may also be well to assign a broad meaning to the word “nutrient” and defi ne it as anything that can be used as a source of energy for the promotion of growth or for the repair of tissue. In evaluating the effects of nutrients on algae, care must be exercised to consider the interaction between nutrients and other physical, chemical or biological conditions. Rapid growth of algae may be stimulated more by factors of sun- light, temperature, pH, etc., than by an abundance of nutrient material. Tests performed with nitzschia chlosterium, in order to study the interaction of environmental factors showed that two identical cultures of the organism, when supplied with a reduced nutrient level, had a lower optimum light intensity and optimum temperature for maximum growth. Thus light intensity and temperature data should accompany data on nutrient concentration and growth rate. Of all the possible nutrients, only nitrogen and phosphorus have been studied in depth both in the fi eld and in the labo- ratory. This is because of the relative diffi culties associated with the study, analysis and measurement of trace elements, compounded by the minute impurities present in the regents and distilled water. In addition, nitrates and phosphates have a long history of use in agricultural fertilizers where determination of their properties have been essential to their economical use. © 2006 by Taylor & Francis Group, LLC 394 EUTROPHICATION The following are the most common sources of nitrogen and phosphorus in bodies of water: 1) Rainfall—Based on experimental data, it has been found that rainwater contains between 0.16 and 1.06 ppm of nitrate nitrogen and between 0.04 and 1.70 ppm of ammonia nitrogen. Computations based on the nitrogen content of rainwater show that for Lake Mendota, Wisconsin, approximately 90,000 pounds of nitrogen are available each year as a result of rainfall. Thus it can be seen that rainfall plays a significant role in building up the nitrogen content of a lake or reservoir especially if the surface area is large. An examination of the phosphorus content of rainwater of different countries shows that a number of concentrations may exist ranging from 0.10 ppm to as little as an unmeasur- able trace, the latter reported in the Lake Superior region of the United States. In view of the wide variation in the determinations, little can be stated at present regarding the degree of phosphorus build-up in impoundments resulting from rainwater. 2) Groundwater—Studies conducted on sub-surface inflows to Green Lake, Washington, show that this water contains approximately 0.3 ppm of phospho- rus. Other reports, however, claim that the amount of phosphorus in groundwater is negligible. Investigations into the nitrate content of groundwater pro- duced variable results; however, it can be stated that 1.0 ppm is a reasonable fi gure. The results of the above studies on both nitrogen and phosphorus can be summarized by stating that groundwater should not be discounted as a possible source of nutrients and that quantitative values should be obtained for the specifi c locality in question. 3) Urban Runoff—Urban runoff contains storm water drainage, overflow from private disposal systems, organic and inorganic debris from paved and grassed areas, fertilizers from lawns, leaves, etc. In view of the variable concentration of the above material, precise figures cannot be obtained on the phosphorus or nitrate content that would be meaningful for all areas. Studies conducted in 1959 and 1960 by Sylvester on storm water from Seattle street gutters shows the following nutrients: Organic nitrogen—up to 9.0 ppm Nitrate nitrogen—up to 2.8 ppm Phosphorus—up to 0.78 ppm soluble and up to 1.4 ppm total. 4) Rural Runoff—Rural runoff for the purposes of definition may be considered as runoff from sparsely-populated, wooded areas with little or no land devoted to agriculture. Investigations by Sylvester showed that the phosphorus content of drainage from three such areas in the state of Washington contained 0.74, 0.77 and 0.32 lb./acre/ year, or a total concentration of 0.069 ppm. The corresponding nitrate nitrogen concentration and organic nitrogen concentration amounted to 0.130 and 0.074 ppm, respectively. 5) Agricultural Runoff—Agricultural runoff is one of the largest sources of enrichment material and may be derived from two sources—wastes from farm animals and the use of nitrogen and phos- phorus-containing fertilizers. Farm-animal wastes add both large quantities and high concentrations of nutrients to adjacent streams and rivers. The large concentrations are due primarily to the practice of herding animals in relatively confi ned areas. A comparison on the nutrient value of animal wastes and human wastes has been made in a study by the President’s Science Advisory Committee. According to the fi ndings, a cow generates the waste equivalent of 16.4 humans, a hog produces as much as 1.9 humans and a chicken produces as much as 0.14 humans. The use of chemical fertilizers in the United States has grown almost 250% in the decade from 1953 to 1963. In 1964 the use of phosphorus-containing fertilizers and the use of nitrogen-containing fertilizers reached approximately 1.5 and 4.4 million tons, respectively, per year. Most all of this fertilizer is distributed to soil already high in natural-occurring nitrogen. When nitrogen fertilizer and natural soil nitrogen combine, there is a great increase in crop production, but also a greater opportunity for loss of this nitrogen in runoff. This loss will increase if the fertilizer is not properly applied, if it is not completely utilized by the crops, if the crops have a short growing season (the land being non-productive for a time), if the land is irrigated, and if the land is sloped. The addition of nitrogen-bearing fertilizers also increase the quantity of mineral elements in the soil runoff which are necessary for the growth of aquatic plants and algae. When applied, the nitrogen in the fertilizer is converted into nitric acid which combined with the minerals in the soil, such as calcium and potassium, rendering them soluble and subject to leaching. 6) Industrial Wastes—The nutrient content of indus- trial waste effluents is variable and depends entirely upon the nature, location and size of the industry. In some cases the effluents are totally free of nitrogen and phosphorus. The meat packing industry is one of the chief producers of nitrogen-bearing wastes. The greatest producer of phosphate- bearing wastes is most likely the phosphate-manufacturing industry itself. Most phosphate production in the United States is concentrated in Florida and as a result many severe local- ized problems of eutrophication have resulted in that state. Fuel processing industries and petroleum refi neries dis- charge vast quantities of nitrogen into the atmosphere both in the gaseous state and solid state as particulate matter. This nitrogen is then washed from the atmosphere by the rain and carried back to earth. In 1964, the 500 billion tons of coal used in the United States released about 7.5 million tons of nitrogen into the atmosphere, most of which has returned to be combined with the soil. This greatly exceeds the use of nitrogen in the form of fertilizers which, as previously stated, amounted to 4.4 million tons for that year. Thus, through the atmosphere we are bringing more nitrogen into the soil than © 2006 by Taylor & Francis Group, LLC EUTROPHICATION 395 we are taking out, and much of this excess ultimately gets washed out into our waterways. 7) Municipal Water Treatment—The water treatment plants themselves are to a degree responsible for adding to the eutrophication problem as approxi- mately 33% of the municipal water in the United States is treated with compounds containing phosphorus or nitrogen. Some of the commonly used nutrient-bearing chemicals or compounds are ammonia (in the use of chloramines) organic polyelectrolytes, inorganic coagulant aids, sodium hexametaphosphate, sodium tripolyphosphate, and sodium pyrophosphate. 8) Waterfowl—It has been estimated that wild ducks contribute 12.8 pounds of total nitrogen/acre/year and 5.6 pounds of total phosphorus/acre/year to reservoirs or lakes. A number of studies have been conducted on waterfowl, but it may be con- cluded that, although there may be some bearing on localized eutrophication, in general the overall effect is negligible. 9) Domestic Sewage Effluent—Undoubtedly the greatest contributor toward the eutrophication of rivers and lakes is the discharge from sewage treatment plants. Conventionally treated domestic sewage usually contains from 15 to 35 ppm total nitrogen and from 6 to 12 ppm total phosphorus. In addition there are a large number of minerals present in sewage which serve as micro-nutrients for algae and aquatic plants. Phosphorus in domestic sewage may be derived from human wastes, waste food (primarily from household garbage- disposal units), and synthetic detergents. Human wastes have been reported in domestic sewage at the rate of 1.4 pounds of phosphorus/capita/year. The largest source of phospho- rus, however, is from synthetic detergents which amounts to approximately 2.1 pounds/capita/year. Sawyer indicates that detergent-based phosphorus represents between 50 and 75% of the total phosphorus in domestic sewage. It should be noted that both the use of household garbage-disposal units and detergents is fairly recent, and accordingly they may be considered as contributing strongly to the development of the recently magnifi ed eutrophication problem. Not all the phosphorus entering a sewage treatment plant will leave the plant since chemical removal does occur during the treatment process. Calcium and metallic salts in large concentrations form insoluble phosphates which are readily removed. Very often phosphate-precipitating agents are present in waters containing industrial wastes, and when these agents are received at the plant, removals in the neigh- borhood of 60% may be realized. Nitrogen in domestic sewage is derived from human wastes and from waste food primarily from household garbage-disposal units. Human wastes, the major source of nitrogen, contributes an average of about 11 pounds of nitro- gen/capita/year. Some reduction in the nitrogen also takes place during the treatment of the sewage. Many plants treat the sludge anerobically which permits signifi cant release of the nitrogen. In general the removal amounts to between 20 and 50%. The higher percentage of removal occurs when fresh wastes are given complete treatment with no return of sludge nutrients to the effl uent. EUTROPHICATION STUDIES In recent years a considerable number of studies have been made on eutrophication and related factors. Most of the studies can be grouped into the following categories: 1) nutrient content of runoff, rainwater, sewage efflu- ent, bottom mud, etc. 2) nutrient analysis and physical distribution of nutrients in bodies of water before and/or after enrichment. 3) methemoglobinemia (illness in infants due to drinking high nitrate-content water) 4) toxicological and other effects on fish of high nitrate/high phosphate-content water 5) the chemical composition of plants in both eutro- phied and non-eutrophied waters 6) the nutrient values of various fertilizers, manures and other fertilizing elements 7) the nutrient value of various soils 8) the effects of eutrophication on aquatic plants, animals and fish 9) studies on specific algae under either controlled laboratory conditions or in a particular body of water, using artificial or natural environmental conditions 10) methods for the removal or reduction of nitrogen and phosphorus 11) nutrient thresholds for growth of algae and aquatic weeds 12) the effects of eutrophication on the oxygen balance. Of the above list, only studies conducted in the areas of (11) and (12) will be presented below. Work done in regard to (1) has already been presented. The removal or reduction of nitrogen and phosphorus (10) will be discussed separately as part of the subject matter in “CONTROL METHODS.” NUTRITIONAL THRESHOLDS FOR THE GROWTH OF ALGAE Studies conducted by Chu indicate that for growth on artifi cial media most planktonic algae fl ourish if the total nitrogen con- tent ranges from 1.0 to 7.0 ppm and the total phosphorus content ranges from 0.1 to 2.0 ppm. If the nitrogen is reduced below 0.2 ppm and the phosphorus below 0.05 ppm, the growth of algae appears to be inhibited. The same inhibiting effect is cre- ated when the nitrogen or phosphorus content is raised above 20.0 ppm. The lower limit of the optimum range of nitrogen © 2006 by Taylor & Francis Group, LLC 396 EUTROPHICATION varies with the organism and with the type of nitrogen. For ammonia nitrogen the optimum range varies from 0.3 to 5.3 ppm and for nitrate nitrogen the optimum range falls between 0.3 and 0.9 ppm. Below these values the growth rate decreases as the concentration of nitrogen decreases. Apparently the use of the various forms of nitrogen by algae is not constant throughout the year. Tests conducted at Sanctuary Lake in Pennsylvania (1965) indicate that the order of preference for the three forms of nitrogen—ammonia- nitrogen, nitrate-nitrogen, and nitrite-nitrogen—are defi ned by three seasonal periods, which are: Spring (1) Ammonia nitrogen (2) Nitrate nitrogen (3) Nitrite nitrogen Midsummer (1) Ammonia nitrogen (2) Nitrite nitrogen (3) Nitrate nitrogen Fall (1) Ammonia nitrogen (2) Nitrate nitrogen (3) Nitrite nitrogen The amount of nitrogen in the aquatic environment is important to algae because it determines the amount of chlo- rophyll that may be formed. Too much nitrogen, however, inhibits the formation of chlorophyll and limits growth. Laboratory studies on algae conducted by Gerloff indicate that of all the nutrients required by algae, only nitrogen, phos- phorus and iron may be considered as limiting elements, and of these three, nitrogen exerts the maximum limiting infl u- ence. Approximately 5 mg of nitrogen and 0.08 mg of phos- phorus were necessary for each 100 mg of algae produced. The corresponding nitrogen/phosphorus ratio is 60 to 1. Hutchinson cites phosphorus as being the more impor- tant element since it is more likely to be defi cient. When phosphorus enters a body of water, only about 10% is in the soluble form readily available for algal consumption. During midsummer total phosphate may increase greatly during the formation of algal blooms, while soluble phosphate is unde- tectable due to rapid absorption by the growing algae. Very often during warm weather these blooms are stimulated by the decomposition and release of soluble phosphates from the bottom sediments, deposited by the expired blooms of previous seasons. Thus when phosphates are added to a lake, only a portion of the phosphates are used in produc- ing blooms. The blooms thrive and consume phosphates for only a short time, and a signifi cant amount fi nds its way to the bottom sediments where it will be unavailable to further growth of aquatic vegetation. Prescott examined a number of algae and concluded that most blue-green algae are highly proteinaceous. Aphanizomenon fl os-aquae, for example, was shown to con- tain 62.8% protein. Green algae were found to be less pro- teinaceous. Spirogyra and cladophora, for example, contain 23.8 and 23.6% respectively. Thus it can be concluded that the nitrogen requirement (for the elaboration of proteins) depends on the class of algae, and that blue-green algae would require more nitrogen than green algae. Provasoli examined 154 algal species to determine the requirements for organic micronutrients. He found that although 56 species required no vitamins, 90 species were unable to live without vitamins such as B 12 , thiamin and biotin, either alone or in various combinations. He concluded that these vitamins are derived from soil runoff, bottom muds, fungi and bacterial production (B 12 ), and from a natural resid- ual in the water. Ketchum and Pirson conducted a series of examina- tions on the inorganic micronutrient requirements of algae and concluded that a number of elements are necessary for growth. No numerical values were assigned to the require- ment levels. Those elements shown to be essential were C, H, O, P, H, S, Mg, Ca, Co, Fe, K and Mo. Those elements which may be essential (subject to further study) were Cu, An, B, Si, Va, Na, Sr, and Rb. In summation, absolute values and nutrient thresholds cannot be set at this time because too little is known regard- ing the requirements of individual species. It might be stated in general terms, however, that nitrogen and phosphorus are two essential nutrient elements related to the production of blooms, and that if they are present in the neighborhood of 0.2 ppm and 0.05 ppm, respectively, algal growths will increase signifi cantly. NUTRITIONAL THRESHOLDS FOR THE GROWTH OF AQUATIC PLANTS Studies conducted by Harper and Daniel indicate that sub- merged aquative plants contain 12% dry matter of which 1.8% are nitrogen compounds and 0.18% are phosphorus compounds. Hoagland indicates that when the nitrate content of water is high, nitrates may be stored in aquatic plants to be reduced to the usable ammonia nitrogen form as required. Subsequent investigations show that ammonia nitrogen can be substituted for nitrate nitrogen and used directly. Light apparently is not a necessary factor in the reduction of the nitrogen. Muller conducted a number of experiments on both algae and submerged aquatic plants, and concludes that exces- sive growths of plants and algae can be avoided in enriched waters if the concentration of nitrate nitrogen is kept below 0.3 ppm, and if the concentration of total nitrogen remains below 0.6 ppm. OXYGEN BALANCE Recently, attention has been given to the effect of the intense growths of algae on the oxygen balance of natural water- ways. It has been established that the dissolved oxygen concentrations may exhibit wide variation throughout the course of the day. This variation is attributed to the ability of algae to produce oxygen during the daylight hours, whereas they require oxygen for their metabolic processes during the hours of darkness. © 2006 by Taylor & Francis Group, LLC EUTROPHICATION 397 In addition, since algae are organic in nature, they exert a biochemical oxygen demand (BOD) on the stream oxygen resources as does other materials which are organic. Extensive tests were run on the Fox River in Wisconsin by Wisniewski in 1955 and 1956 to examine the infl uence of algae on the purifi cation capacity on rivers. In the most general terms, the studies indicate that algae increase the B.O.D. by adding organic matter capable of aerobic bacte- rial decomposition and by the respiration of the live cells which utilize oxygen during the absence of light. In the presence of light, algae produce oxygen and as a result may cause a “negative” B.O.D. for a production of oxygen in excess of that required for the normal B.O.D. require- ments or aerobic bacterial stabilization. In addition to the above, the following specifi c conclusions were drawn from the tests: 1) The oxidation rate resulting from the respiration of live algae was much lower than that obtained by the biological oxidation of the dead algae. 2) The ultimate B.O.D. of live algae was practically the same as for dead algae. 3) A linear relationship was found to exist between the five-day B.O.D. of suspended matter and volatile suspended solids concentration. 4) The B.O.D. increases with increases in suspended solids, the latter consisting largely of algae. Additional work was done in this area and reported in 1965 by O’Connell and Thomas. They note that the oxygen produced by photosynthetic plants is affected greatly by changes in the availability of light due to cloud cover, turbidity in the water, etc., and therefore it may be too variable to be used as a reliable factor in evaluating the oxygen resources of a river. Another variable may be the loss of oxygen to the atmosphere during the daylight hours, caused by excess oxygen production and localized supersaturation. An important consideration is the type of photosynthetic plants which are prevalent in a river. According to the above authors, if benthic algae and/or rooted aquatic plants are predominant (in lieu of phytoplankton), there will be little benefi cial effect on the oxygen balance. In addition night- time absorption of oxygen through respiration can seriously reduce daily minimum concentrations of dissolved oxygen. Determination of the effects of the benthic algae oscillato- ria along a fi vemile stretch of the Truckee River in Nevada indicated that on the average of the organism produced 72.5 pounds/acre/day of oxygen through photosynthesis. Oxygen uptake for these same organisms amounted to an average of 65.4 pounds/acre/day. An examination of the oxygen profi les indicated that the oxygen variation throughout the day ranged from 2 (at night) to 13 (during daylight) parts per million. It is dissolved oxygen variations such as the above which has been responsible for the disappearance of high quality game fi sh in many of our natural waterways. CONTROL METHODS TO PREVENT EUTROPHICATION There are a number of methods which attempt to limit the amounts of nutrients in bodies of water once the point of eutrophy has been reached. Some of these include dredging and removing bottom sediments with an inert liner, harvesting the algae, fi sh, aquatic weeds, etc., and diluting the standing water with a water of lower nutrient concentration. Although these methods may have their proper application, if eutrophi- cation is to be decelerated, nutrient removal must start before wastes are permitted to enter the receiving waters. Regarding the specifi c nutrients necessary to be removed, most researchers have placed the blame of eutrophication in waters to the inorganic forms of phosphorus and nitrogen. A smaller number of researchers are claiming that the algae– bacteria symbiosis relationship might be responsible for the rapid growth of blooms and that the amount of algae pres- ent in natural waters is in direct balance with the amount of carbon dioxide and/or bicarbonate ions in the waters. They further argue that an external supply of the above elements is necessary for the growth of algae populations. Since nei- ther theory has been proved conclusively to date, the control methods given will be for the removal of nitrogen and phos- phorus since it is these nutrients which most researchers lay to the blame of eutrophication and which have been there- fore subsequently studied in detail. NITROGEN REMOVAL Land Application It has been found that nitrogen-bearing waters, when perco- lated through soil are subjected to physical adsorption and biological action which removes the nitrogen in the ammo- nium form. It appears, however, that the nitrate form of nitrogen remains unaffected. At present this process is only at the theoretical stage, and to the author’s knowledge no full-scale application has been attempted. Considerable land area would be involved which may prove a deterrent. Anaerobic Denitrification In this process, the nitrate present in sewage is reduced by denitrifying bacteria to nitrogen and nitrous oxide gases which are allowed to escape into the atmosphere. In order to satisfy the growth and energy requirements of the bacteria, methanol in excess of 25 to 35% must be added as a source of carbon. The removal effi ciency ranges from 60 to 95%. The major advantage to anaerobic denitrifi cation is that there are no waste products requiring disposal. This process is still primarily in the experimental stage at this date. Ammonia Stripping Ammonia stripping is an aeration process modifi ed by fi rst raising the pH of the wastewater above 10.0. At this pH the © 2006 by Taylor & Francis Group, LLC 398 EUTROPHICATION ammonia nitrogen present is readily liberated as a gas and is absorbed into the atmosphere. Aeration is usually accom- plished in a packed tray tower through which air is blown. This process is suited to raw sewage where most of the nitrogen is either in the ammonia form or may be readily converted to that form. In secondary treatment processes the conversion of ammonia nitrogen to nitrate nitrogen can be retarded by maintaining a high organic loading rate on the secondary process. Effi ciency of nitrogen removal by ammonia stripping is excellent with 80 to 98% reported. There is also the advantage that there are no waste materials which must be disposed of. PHOSPHORUS REMOVAL Chemical Precipitation Precipitation of phosphorus in wastewater may be accom- plished by the addition of such coagulants as lime, alum, ferric salts and polyelectrolytes either in the primary or sec- ondary state of treatment, or as a separate operation in ter- tiary treatment. In general, large doses in the order of 200 to 400 ppm of coagulant are required. However, subsequent coagulation and sedimentation may reduce total phosphates to as low as 0.5 ppm, as in the case of lime. Doses of alum of about 100 to 200 ppm have reportedly reduced orthophos- phates to less than 1.0 ppm. Phosphorus removal by chemical coagulation generally is effi cient with removals in the order of 90 to 95% reported. Additional benefi ts are gained in the process by a reduction in B.O.D. to a value of less than 1.0 ppm. Both installation and chemical costs are high, however, and the sludges pro- duced are both voluminous and diffi cult to dewater. Sorption Sorption is the process of passing wastewater down- ward through a column of activated alumina whereby the common form of phosphate are removed by ionic attraction. Regeneration of the media is accomplished by backwash- ing with sodium hydroxide followed by acidifi cation with nitric acid. Contrary to alum treatment, this process has the advantage in that sulfate ions are removed and thus the sulfate concentra- tion is not increased. Since no salts are added, the pH and the calcium ion concentration remain unchanged. The process is effi cient with more than 99% removal reported. The process should be limited to wastewater with a moderate amount of solids so as not to clog the media. REMOVAL OF NITROGEN AND PHOSPHORUS Biological (secondary) Treatment In the secondary method of sewage treatment, bacteria uti- lize soluble organic materials and transform them into more stable and products. In the process nitrogen and phosphorus are removed from the wastes, utilized to build new cellular materials, and the excess is stored within the cell for future use. For each pound of new cellular material produced, assuming the material to be in the form of C 5 H 7 NO 2 , about 0.13 pounds of nitrogen and about 0.026 pounds of phospho- rus would be removed from the sewage. In the actual opera- tion of this process not all of this nitrogen is removed unless additional energy material in the form of carbohydrates is added. Although it may be possible to eliminate all the nitrogen, a considerable amount of soluble phosphorus may remain, possibly because of the high ratio of phosphorus to nitrogen in sewage, attributable to synthetic detergents. Much of this phosphorus can be removed by absorption on activated sludge fl oc when it is later separated and removed. This process offers a 30 to 50% removal of nitrogen and about a 20 to 40% removal of phosphorus without the spe- cial addition of carbohydrates. Reverse Osmosis The process of reverse osmosis consists of passing wastewa- ter, under pressures as high as 750 psi, through a cellulose acetate membrane. The result is the separation of water and all ions dissolved therein. In actual practice the process has been plagued with diffi culties primarily due to membrane fouling or premature failure of the membrane. In addition some nitrate and phosphate ions escape through the membrane. Removal effi ciency ranges from between 65 to 95% (for nitrogen). Electrodialysis Like reverse osmosis, electrodialysis is a non-selective demineralization process which removes all ions which would include the nitrate and phosphate ions. Essentially an electric current is used in conjunction with a membrane inserted in the line of current fl ow to separate the cations and anions. The problems that have developed in the operation of this process include membrane clogging and precipitation of low-solubility salts of the membrane. Acidifi cation of the water and removal of some of the solids prior to treatment has been effective in minimizing these problems, although it adds to the cost. Removal effi ciency ranges from between 30 to 50% (for nitrogen). Ion Exchange In the ion exchange process wastewater is passed through a media bed which removes both anionic phosphorus and anionic nitrogen ions and replaces them with another ion from the media. Regeneration of ion exchangers is com- monly accomplished with inexpensive sodium chloride, and frequently the salt is salvaged by recycling the backwash water. Diffi culties in the process may be caused by fouling of the exchange resin due to organic material and reduction in © 2006 by Taylor & Francis Group, LLC [...]... acceptance and which will clarify and expand our present knowledge Conferences dealing with unique and local problems involving algae and eutrophication are ongoing (See References Eutrophication, #53, 55, 56 and 57, at the end of this article.) ACKNOWLEDGMENTS My sincere appreciation is extended to Mr Robert G Wieland who helped in the preparation of the manuscript and to the Research Foundation of the... 53 White, E., 1983 Lake eutrophication in New Zealand—A comparison with other countries of the Organization for Economic Cooperation and Development, New Zealand Journal of Marine and Freshwater Research, 17, 437–444 54 Birge, W.J., J.A Black and A.G Westerman, “Short-Term Fish and Amphibian Embryo-Larval Tests for Determining the Effects of Toxicant Stress on Early Life Stages and Estimating Chronic... continuous culture of Nitzschia Closterium and Tetraselmis sp., Jour of Limnology and Oceanography, Vol 9, 1964 4 Carrol, D., Rainwater as a chemical agent of geological progress— A review, Geological Survey Water—Supply 1535-G, 1962 5 Fruh, Gus E and G.F Lee, The effect of eutrophication upon the water resources management of the Yahara river basin, report of the Water Chemistry Program, Univ of Wisconsin,... Wisconsin, Madison, Wisc 6 Putnam, H.D and T.A Olson, an investigation of nutrients in western lake Superior, School of Public Health Report, Univ of Minnesota, 1960 7 Sylvester, R.O and G.C Anderson, A lake’s response to its environment, American Society of Civil Engineers, Sanitary Engineering Div., 90, 1964 8 Sawyer, C.N., Causes, effects and control of aquatic growths, Jour of the Water Pollution Control... characteristics of algal physiology, Seminar on Algae and Metropolitan Wastes, Robert, A., Taft Inst., Cincinnati, Ohio, Apr., 27–29, 1960, p 41 400 EUTROPHICATION 13 Ingram, W.M and G.W Prescott, Toxic fresh-water algae, Amer Midland Naturalist, 52, 1954, pp 75–87 14 Derby, R.L and D.W Graham, Control of aquatic growths in reservoirs by copper sulfate and secondary effects of such treatment, Proc Amer Soc of. .. Palmer, Mervin C and W.M Ingram, Suggested classification of algae and protozoa in sanitary science, Sewage and Industrial Wastes, 27, 1955, pp 1183–1188 5 Silvey, J.K.G and A.W Roach, Studies on microbiotic cycles in surface waters, Jour of the Amer Water Works Assn., Jan., 1964, p 61 6 Lackey, James B., Two groups of flagellated algae serving as indicators of clean water, Jour, of the Amer Water.. .EUTROPHICATION the exchange capacity due to sulfates and other ions The former may be reduced by removing the organic matter from the resin with sodium hydroxide, hydrochloric acid, methanol and bentonite The efficiency and cost of nitrogen and phosphorus removal by ion exchange depends largely on the degree of pretreatment and/ or the quality of the water to be treated Removal of nitrogen... Francis Group, LLC 10 Sylvester, R.O., An engineering and ecological study for the rehabilitation of Green Lake, Univ of Washington, Seattle, Wash., 1960 11 Restoring the quality of the environment, report of the Environmental Pollution Panel, President’s Science Advisory Committee, The White House, Wash., D.C., 1965 12 Sauchelli, V., Chemistry and Technology of Fertilizers, ACS Monograph Series No 148,... medium on the growth of planktonic algae—Part I, Jour of Ecology, 30, No 2, 1942, pp 284–325 26 Chu, S.P., The influence of the mineral composition of the medium on the growth of planktonic algae—Part II, Jour of Ecology, 31, No 2, 1943, pp 109–148 27 Dugdale, V.A and R.C Dugdale, Nitrogen metabolism in lakes III; Tracer studies of the assimilation of inorganic nitrogen sources, Limnology and Oceanography,... 1953 15 Borchardt, J.A., Eutrophication causes and effects, Jour of the Amer water Works Assn., June 1969, pp 272–275 16 Thomas, S and J.W Burger, Chlamydomonas in storage reservoirs, Jour of the Amer Water Works Assn., July, 1933 17 Smith, Gilbert M., The Fresh-Water Algae of the United States, McGraw-Hill, N.Y., 1933, p 13 18 Mackenthum, K.M and W.M Ingram, Limnological Aspects of Recreational Lakes, . farm animals and the use of nitrogen and phos- phorus-containing fertilizers. Farm-animal wastes add both large quantities and high concentrations of nutrients to adjacent streams and rivers growth phase of the organism, tempera- ture and the absorptive and refl ective characteristics of the water. It can be stated, however, that certain fresh-water red algae and blue-green algae. high nitrate-content water) 4) toxicological and other effects on fish of high nitrate/high phosphate-content water 5) the chemical composition of plants in both eutro- phied and non-eutrophied