WATER QUALITY: Technical Information--Briefing paper on aquatic biology: "Phytoplankton" by George McCoy, WRD, Anchorage, Alaska. May 15, 1978 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 78.07 Subject: WATER QUALITY: Technical Information--Briefing paper on aquatic biology: "Phytoplankton" by George McCoy, WRD, Anchorage, Alaska. The attached general discussion of "Phytoplankton" by George McCoy is a continuation of the series of briefing papers on biological quality. Please circulate the briefing paper as widely as possible in all district and project offices. Thank you. R. J. Pickering Attachment WRD Distribution: A, B, FO-L, PO, S PHYTOPLANKTON George McCoy, Anchorage, Alaska INTRODUCTION Plankton is the community of suspended or floating organisms which drift passively with water currents (Greeson and others, 1977). The plant component of the plankton is called the phytoplankton. In its broadest sense the term phytoplankton includes algae, fungi, and bacteria. However, only the algae are considered in the following discussion. Phytoplankton, though usually inconspicuous, are extremely important in standing bodies of water (lakes, ponds, and the ocean). These organisms are the primary producers of organic matter and oxygen on which all animal life depends. The total photosynthetic production of organic carbon by phytoplankton is approximately equal to that of terrestrial vegetation. Because of the central importance of these organisms in aquatic ecosystems, it is lamentable that our understanding of the factors and processes that control distribution, periodicity, and seasonal variability of phytoplankton is vague and sometimes fragmentary. It is possible, however, to list the non-biotic and biotic factors that influence phytoplankton communities. KINDS OF PHYTOPLANKTON The most common freshwater phytoplankton are diatoms, green algae, and blue-green algae. Diatoms are distinguished by variously ornamented cell walls or frustules of silica. The ornamentation includes long thin lines which may be either slits or ridges in the frustule, pores which form a distinctive pattern, and in some species, spines. The pigment in diatoms is contained in structures called chloroplasts and is yellow-green or golden. Green algae have cell walls of cellulose, and the chloroplasts are grass green. These organisms may occur as single cells, colonies, or filaments (fig. 1). Blue-green algae differ from green algae and diatoms in that their cells have no chloroplasts or nuclei. They have photosynthetic pigments, but in many ways the structure of the cell is more like that of the bacteria than the structure of a plant cell. Other groups of phytoplankton that are important in some freshwater lakes are dinoflagellates (fire algae), euglenophyta (resembling pigmented protozoa) and, rarely, red algae. ENVIRONMENTAL FACTORS The physical nature of the aquatic environment affects both the abundance and species composition of the phytoplankton community. Warm waters typically have a greater abundance of phytoplankton than do cold waters. Given a warm body of water and a cold one with the same concentration of inorganic nutrients, the warm water probably would support a larger standing crop of phytoplankton simply because the metabolic rate of the organisms increases with temperature. In cold-water lakes, or under the ice in temperate warm-water lakes, diatoms often are the primary component of the phytoplankton. As the water warms, diatoms generally become less abundant and the green algae increase; if nutrients are abundant and as the water warms further, the blue-green algae become dominant. The depth of light penetration in water is the critical ecological factor that determines the depth at which phytoplankton can live in the water column. Light penetration is reduced by the surface disturbance, the amount of suspended particulate matter, and water color. The quantity of phytoplankton itself may affect the depth of light penetration and restrict phytoplankton to a narrow zone near the surface. The euphotic zone is the lighted zone in which the rate of photosynthesis is greater than the rate of respiration. The compensation depth is the depth at which the rate of photosynthesis is equal to the rate of respiration. Below this depth is the aphotic zone where respiration is greater than photosynthesis (fig. 2). P > R EUPHOTIC ZONE P = R COMPENSATION DEPTH P < R APHOTIC ZONE Figure 2.--Diagram of a lake showing euphotic zone, compensation depth and aphotic zone; P is rate of photosnythesis, R is rate of respiration. A third physical factor which may affect phytoplankton abundance and distribution within a body of water is wind. In shallow lakes, wind may cause a mixing action which stirs up the bottom sediments and adds nutrients to the water column, contributing to the productivity of the lake or pond. Wind also may affect the horizontal distribution of the phytoplankton of a lake, concentrating them on the windward side. This is an important consideration in phytoplankton sampling. Phytoplankton affect and are affected by the chemical composition of the water. Most phytoplankton have a narrow range of tolerance for salt concentration. Certain metals, including copper, lead, and aluminum are toxic to algae. Algae are more sensitive to copper than are aquatic animals, therefore copper has been widely used as an algacide. Some phytoplankton species are characteristic of lakes with hard water (high carbonate and bicarbonate content and alkaline pH) while others are found more often in soft water (low dissolved-solids concentrations and acid pH). Acid bogs, for example, have a unique algal flora, usually dominated by a group of green algae, the desmids. Phytoplankton are essentially autotrophic, that is, they produce their own food from inorganic substances. They require a large number of inorganic nutrients including inorganic carbon (usually derived from C02 or HC03~, nitrogen, phosphorous, potassium, sulphur, calcium, magnesium, silica, nitrogen and iron and a number of elements in trace quantities including zinc, copper, boron, molybdenum, and cobalt. In recent years, a large body of evidence has shown that many, if not most, are partly heterotrophic: l) they require one or more organic compounds for nutrition, or 2) growth is enhanced by the presence of organic compounds or growth factors such as sugar or a vitamin. With the recent concern over cultural eutrophication of lakes, the nutrients which limit growth of phytoplankton have been receiving an increasing amount of attention. Nutrient limitation is based on the concept that when one of the essential materials needed for growth approaches the critical minimum, that material will limit the amount of growth. Some investigators have argued that C02 is often the nutrient that limits phytoplankton growth; now, however, the consensus is that C02 limitation of primary production is restricted to a few rare instances, usually in soft-water lakes. In a few lakes a trace element, vitamin or other organic growth factor has been identified as limiting; however, most limnologists agree that phosphorous is most commonly the limiting nutrient. It was on this basis that Canada recently banned detergents containing phosphates within the drainage area of the Great Lakes. Nitrogen is sometimes a limiting nutrient but is secondary in importance to phosphorous. Nutrient-limitation is a complex phenomenon and may vary with the geology, geography, and sources of nutrient input into the lake. The limiting nutrient in a specific body of water may also change with the season. To even the casual observer, it must be obvious that plants alter the nature of the environment. Phytoplankton are no exception. Respiration and photosynthesis can alter appreciably the concentrations of C02 or oxygen in the water. A change in the C02 concentration will, of course, affect the pH. In lakes with hard water, the utilization of C02 by plants causes a shift in the chemical equilibrium which results in the formation of calcium carbonate from bicarbonate and dissolved calcium. The precipitation of calcium carbonate on the lake bottom and on the surface of algal cells takes the form of a hard encrusting layer called marl. This is such a prominent feature of some lakes that they are termed marl lakes. Phytoplankton communities also are affected by other organisms in the water column. Grazing by zooplankton and to a lesser extent by fish may affect both the abundance and species composition of phytoplankton. There have been many studies which show an inverse relationship between zooplankton density and phytoplankton standing crop. Virtually all standing bodies of water have a resident phytoplankton population. Slow moving rivers also maintain a phytoplankton community, and phytoplankton may be important in side arms or among thick growths of rooted aquatic plants in moderately fast-flowing streams. It has been determined that phytoplankton populations increase progressively downstream. Water samples from headwater streams primarily contain benthic algae that have been dislodged from the bottom. In slower moving waters near the mouth, true phytoplankton organisms can be found. Phytoplankton data from streams is difficult to interpret. It is often possible, from the taxonomic identification, to determine if an alga in the water column is a true planktonic organism or a benthic alga that has been dislodged. It is, however, much more difficult to determine if the organism has developed as part of the stream flora or has been washed in from lakes or swamps in the drainage. Several investigators have proposed that algae suspended in the water column in rivers and streams be termed drift algae. This terminology has some merit, for it is much more descriptive of the organisms that are collected in a water sample from a stream than is the term phytoplankton. The phytoplankton population fluctuates rapidly during the course of a year. Phytoplankton may multiply very rapidly to a peak, or bloom and decline. Bloom conditions often are associated with warm summer weather, but they also may occur in the winter under ice cover. In a given body of water, not only can the phytoplankton density, usually measured in cells per milliliter, change from one day to the next, but the species composition of the phytoplankton may change with time. Figure 3 illustrates the kinds of changes that can be expected in the populations of different types of phytoplankton in a temperate lake during the year. In this hypothetical lake the diatoms are present in significant numbers all year, but are most abundant in the winter. Green algae peak in early summer, and the blue-green algae are dominant in the late summer. This figure is intended only as an example to illustrate seasonal changes. The pattern of phytoplankton changes and species composition may vary greatly from one lake to another, depending on the amount of available nutrients, geology of the area, and the climate. In oligotrophic soft-water lakes, for example, the diatoms may be the dominant organisms for the entire year. An example of the typical fluctuations of a phytoplankton population during the course of a year is illustrated in figure 4. The pattern of fluctuation in phytoplankton abundance may vary greatly from one lake to another. In figure 4 is shown a winter bloom in February and March and two summer blooms, one in June followed by a summer minimum and then a second bloom in August. In other lakes one or all of these blooms might not occur. It should be emphasized that phytoplankton may not be evenly distributed, horizontally or vertically, in a body of water. They will be most abundant at a depth where the light penetration is optimum for growth. Horizontal circulation patterns caused by current, wind, lake shapes location of inlets and outlets, and sources of effluents may cause an uneven horizontal distribution of phytoplankton. IMPORTANCE The importance of phytoplankton as the primary producers in freshwater and marine environments cannot be overemphasized. Phytoplankton are utilized as a food source by zooplankton and fish. Primary production is, of course, necessary for all levels of secondary production, from the smallest invertebrate to fish and aquatic mammals, and results in the production of organic compounds that are ultimately cycled to the fungi and bacteria which act as decomposers. Photosynthesis by aquatic plants, including phytoplankton, is an important source of the oxygen upon which aquatic forms of animal life depend. However, plants also respire, a process which utilizes oxygen. Given the right conditions - warm water (high rate of respiration), low light levels, and little or no wind (low rate of transfer from atmosphere to water) - phytoplankton may cause oxygen depletions in a body of water, resulting in fish kills or in severe mortality of certain aquatic insects. Lake Erie at one time produced large quantities of mayflies. The aquatic nymphs of these insects were an important source of food for the walleye. In the late 1950's, the large emergences of adult mayflies ceased. Simultaneously, the walleye fishery experienced a catastrophic decline. Several investigators have suggested that these changes resulted from periodic, short-term dissolved-oxygen depletions caused by a combination of dense phytoplankton populations and warm, calm nights. Phytoplankton can cause a myriad of other problems in water. Decomposing phytoplankton may accumulate on beaches and cause an unpleasant odor. The "fishy" smell associated with very productive waters is actually the odor of decomposing algae. Dense phytoplankton blooms may turn the water a soupy green color, or dead phytoplankton may accumulate on the surface of a lake and create a scum, thus lowering the esthetic value of the lake. Phytoplankton are sometimes toxic to animals. In the marine environment, the so-called "red tide" is actually a bloom of Gyllinodinium, a dinoflagellate. This organism secretes a toxin which accumulates in the flesh of some fish, and in the digestive glands of shellfish, causing them to be toxic to humans. In freshwater there have been numerous documented instances of livestock poisoning by blue-green algae. In this country, most of these incidents have occurred in the midwest. Toxicity of the algae has been reviewed by Gorham (1964) and Schwimmer and Schwimmer (1964, 1968). Phytoplankton often are used as indicators of environmental conditions. Numerous lists of indicator organisms have been compiled. However, the concept of indicator organism is gradually being replaced by the more useful concepts of community structure, such as diversity or evenness, similarity coefficients, multivariate analysis, or biomass. Biomass is an especially useful parameter for phytoplankton populations if it is possible to measure the peak of the bloom. Upon inspection of figure 2, however, it should become apparent that many closely spaced measurements would be necessary to measure the maximum biomass. A measurement such as the relative proportion of the major groups (i.e., blue-greens, diatoms, greens) of algae can give some indication of the productivity of a system. However, the amount of information to be gained from a phytoplankton sample is maximized by identification to the species level. There are species of the diatom Navicula for example, that occur both as periphyton and phytoplankton and can be found in eutrophic, mesotrophic, and oligotrophic freshwater, as well as in estuaries and saltwater. To say that Navicula is the dominant genus in a phytoplankton sample gives us little information about the sample. Navicula semen, however, is found in cool water of low mineral content. Navicula secreta is found in freshwater of high mineral content and Navicula maculata occurs only in brackish water. In a study of Lake Michigan, Stoermer and Yang (1969) found Melosira distans (a diatom) to be abundant in the clean unpolluted areas, and Melosira granulata to be abundant only in eutrophic bays and inshore areas. Many species of Gomphonema are periphytic diatoms (living attached) while other species are strictly planktonic in occurrence. If the objective of a study is to detect gross changes in water quality, then a low level of taxonomic identification may suffice. Often gross changes can be detected by visual observation. The water may be colored by a dense phytoplankton bloom or there may be a floating "scum" of blue-green or green algae. Species identification is, however, necessary to detect subtle changes. The decision as to whether or not to include phytoplankton data in an investigation and the type of data to be included are ultimately dependent on the objectives of the investigation. SELECTED REFERENCES Beeton, A. M., 1961, Environmental changes in Lake Erie: Am. Fisheries Soc., v. 90, no. 2, p. 153-159. ____1965, Eutrophication of the St. Lawrence Great Lakes: Limnology and Oceanography, v. 10, p. 24Q-254. Davis, C. C., 1962, The plankton of the Cleveland Harbor area of Lake Erie in 1956 1957: Ecological Monographs, v. 32, p. 209-247. ____1964, Evidence of the eutrophication of Lake Erie from phytoplankton records: Limnology and Oceanography, v. 9, p. 275- 283. Fogg, G. E., 1966, Algal Cultures and phytoplankton ecology: Madison, Univ. of Wisconsin Press, 126 p. Greeson, P. E., Ehlke, T. A., Erwin, G. A., Lum. B. W., and Slack, K. V., eds., 1977, Methods for collection and analysis of aquatic biological and microbiological samples: U.S. Geol. Survey Techniques of Water Resources Inv., book 5, chap. A4, 332 p. Gorham, P. R., 1964, Toxic algae, in Jackson, D. E., ed., Algae and man: New York Plenum Press, p. 307-336. Hynes, H. B. N., 1970, The ecology of running water, Toronto, Univ. of Toronto Press, pp. 94-112. Kuentzel, L. E., 1969, Bacteria, carbon dioxide and algal blooms: Journal of the Water Pollution Control Fed., v. 41, p. 1737-1747. Likens, G. E., (ed.) 1972, Nutrients and Eutrophication, The limiting nutrient controversy. The American Society of Limnology and Oceanography, Special Symposia, Vol. 1, 328 p. Mitchell, Dee, 1972, Eutrophication and phosphate detergents: Science, v. 177, p. 816-817. Palmer, C. M., 1962, Algae in water supplies: U.S. Dept. Health, Education and Welfare, Division of Water Supply and Pollution Control, 88 p. Palmer, C. M., 1969, A composite rating of algae tolerating organic pollution: Journal of Phycology, v. 5, p. 78-82. Prescott, G. W., 1962, Algae of the western Great Lakes area: Dubuque, Iowa, W. C. Brown Co., 977 p. Rawson, D. W., l956, Algal indicators of lake types: Limnology and Oceanography, v. 1, p. 18-25. Reid, G. K., 1976, Ecology of inland waters and estuaries: New York, Reinhold Publishers, Corp., 375 p. (2nd ed.) Sakamoto, M.,, 1971, Chemical factors involved in the control of phytoplankton production in the experimental lakes area, northwestern Ontario: Jour of the Fisheries Res. Board of Canada, v. 28, p. 203-213. Schwimmer. D. and Schwimmer, M , 1964, Algae and Medicines in Jackson, D. E., ed., Algae and man: New York Plenum Press, p. 368-412. ____1968, Medical aspects of Phycology, in Jackson, D. E., Algae, man and environment: University Press, Syracuse., p. 279-358. Shapiro, Joseph, 1973, Blue-green algae - Why they become dominant: Science, v. 179, p. 382-384. Whitton, B. A., 1975, Algae, in Whitton, B. A. (ed.), Studies in Ecology: Volume 2, River ecology, University of California Press, Berkeley, p. 81-106.