WATER QUALITY: Technical Information--Briefing paper on aquatic biology: "Algal growth potential" by W. Thomas Shoaf March 27, 1975 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 75.18 Subject: WATER QUALITY: Technical Information--Briefing paper on aquatic biology: "Algal growth potential" by W. Thomas Shoaf The attached description of "Algal growth potential" by W. Thomas Shoaf (WRD,Doraville, Ga.) represents a continuation of the series of briefing papers on biological quality initiated by the Quality of Water Branch in August, 1974. Quality of Water Branch Technical Memorandum No. 75.17 transmitted the provisional method for determining algal growth potential (AGP) and announced the availability of the determination from the Doraville Central Laboratory. Please circulate the briefing paper as widely as possible in all district and projcct offices. R. J. Pickering Attachment WRD Distribution: A,B,FO-L,PO,S ALGAL GROWTH POTENTIAL W. Thomas Shoaf Algal growth potential is defined as the maximum algal mass (dry weight) that can be produced in a natural water sample under standardized laboratory conditions. The characteristic growth pattern for unicellular algae in a culture of limited volume is shown in Figure 1: (See hard copy for Figure 1) Algal growth potential is the algal mass present at stationary phase and is expressed as milligrams dry weight per litre of algae produced. Dry weight was chosen as a measure of algal growth because it is the most reliable parameter for all sample sources. Standardization of Analysis. The determination of the algal growth potential of a water sample using the natural algae present is perhaps most desirable. The presence of these algae and associated microorganisms suggests that they are suited to survive the environment in which they live, and their potential for accelerated growth is of primary interest in many situations. The primary difficulty in using indigenous algae is the time required for measuring growth of diverse forms of algae such as colonial, filamentous, or unicellular forms. In some instances, water samples contain few algae, and the introduction of foreign algae would be needed to insure a growth response. Algal growth potentials can only be compared when variables which affect algal growth, such as light and temperature, are standardized and controlled. The need for standardization of tcchniques for measuring algal growth potential for routine analysis was recognized by the Joint Industry/Government Task Force on Eutrophication (Bartsch, 1969). A cooperative developmental effort by the Soap and Detergent Association and the Environmental Protection Agency to produce a test for determining algal growth potential in natural water samples was the result (Bartsch, 1971). Selenastrum capricornutum was selected as a test organism for the following reasons: (l) It is a unicellular alga and its growth can be monitored accurately and rapidly with an electronic particle counter. (2) Selenastrum has been shown to tolerate acidic and alkaline waters as well as oligotrophic (nutrient-poor water) and eutrophic (nutrient rich water) conditions in aquatic environments (Forsberg, 1972). (3) It is listed among the most pollution-tolcrant algae by Palmer (1969). (4) The algal growth potential determined with S. capricornutum and the potential determined with the species indigenous to the water sample correlate well (Maloney and others, 1972). (5) The algal growth potential for various fresh water environments using S. capricornutum, as measured by the standard test (Bartsch, 1971), varies widely from 0.1 to 248 milligrams dry weight of algae per litre (National Lake Survey Program, 1973). Application. The design of a project is developed to meet a specific objective. All pertinent factors must be considered in planning if valid results and conclusions are to be obtained. It should be possible to evaluate algal growth potential data more effectively in light of other biological, chemical, and physical measuremcnts obtained by sampling at common sites. Various collection methods for streams and lakes have been described by Guy and Norman (1970), Goerlitz and Brown (1972) and Slack and others (1973). The objectives of algal growth potential tests might include the establishment of baseline data or determination of the growth controlling nutrient(s), the influence of a nutrient, or the source of a nutrient when several inflows are involved. One of the first items that should be determined when measuring algal growth potential is what constitutes a significant change. A certain degree of variability can be expected with any assay or survey; however, once the baseline data are established, experimentation can be conducted. The algal growth potential principle is based on Liebig's Law of the Minimum which recognizes that the development of a population is esscntially regulated by the substance occurring in minimal quantity relative to the requirements of the population. Algal growth potential measurements thus have been used frequently to derive information on the rcquired nutrients which are limiting algal growth. This type of measurement is usually designed to examine in detail only a few nutrients which preliminary testing indicates may be limiting or in short supply. The approach is to observe the effect that certain growth promoting substances (nutrients) have upon the algae. These substances may be of precise known composition (Bartsch, 1971; Miller and Maloney, 1971; Maloney and others, 1972) or their composition may be somewhat less known, such as that of an effluent which may flow into a lake or stream from a suspected nutrient source (Brown and others, 1969). The practice of adding such substances to a water sample is called spiking. In the case of chemical spikes, it is obvious that if increasing amounts of a limiting nutrient are added to a water sample, eventually another factor becomes limiting. The determination of how much and what to spike may be made easier when the concentration of the nutrient(s) of interest is known. Because algal growth in natural water samples can be limited by one or several nutrients in close succession, it might be necessary to test spikes of combinations of nutrients that could be limiting. When only one nutrient is limiting algal growth, it is likely that a correlation will be observed between the concentration of that nutrient and the algal growth potential. Some algal growth potential studies have shown correlations between orthophosphate and algal growth (Wang and others, 1972), while correlations also are likely for other nutrients in other aquatic environments. Interpretation of Results. Algal growth potential data which are derived in the laboratory under controlled conditions of light and temperature do not necessarily reflect conditions in the natural aquatic environment from which the sample was taken. Only the potential at a given time can be measured. In nature, daily and seasonal variations in the intensity and duration of light occur, which can effect algal growth. Changes in other environmental factors can be important as well. For example, the rate of algal growth roughly doubles with every 11!C (20!F) rise in water temperature between 0!C (32!F) and 32!C (90!F) (Ferguson, 1968). Growth can be inhibited by any suspended material, living or non-living, which interferes with the effective penetration of light essential to the algae. Grazing by invertebrates and fish, toxic materials entering the water, plant or animal excretions, or decay products from the algae themselves are all additional examples of factors that may inhibit growth potential. In the standard procedure described by Bartsch (1971), membrane filtration of the water sample to remove indigenous algae, bacteria, fungi and any other particles which might interfere is required. These microorganisms contain nutrients, which are not available to other algae while these organisms are living, but later become a source of nutrients as a result of decay after death. Thus, it is possible to measure a high concentration of algae during a "bloom" but observe a low algal growth potential. After cell death and decay, the algal growth potential will probably increase. This, as well as the other factors mentioned above, must be taken into consideration when attempting to make predictions about future algal growth. Summary. Algal growth potential is defined as the maximum algal mass (dry weight) that can be produced in a natural water sample under standardized laboratory conditions. Algal growth potential measurements are designed to establish baseline data, growth limiting factors (nutrients), and the influence and source of various growth promoting nutrients, so as to provide improved means for predicting and controlling excessive algal growth in aquatic habitats. Data can be compared only when the variables which control algal growth are standardized. Algal growth potentials derived in the laboratory may not reflect natural conditions because of insufficient light or temperature, grazing by invertebrates or fish, or the presence of any toxic materials. An understanding of the principle of the test and the factors that a#fect the expression of algal growth potentials is critical to proper data interpretation. REFERENCES CITED Bartsch, A. F., 1969, Provisional algal assay procedure: Corvallis, Oregon, U.S. Environ. Protection Agency, 61 p. Bartsch, A. F., 1971, Algal assay procedure: bottle test: Corvallis, Oregon, U.S. Environ. Protection Agency, 82 p. Brown, R. L., Bain, R. C., and Tunzi, M. G., 1969, Effects of nitrogen removal on the algal growth potential of San Joaquin valley agricultural tile drainage effluents: Paper presented before the Amer. Geophysical Union Nat. Meeting, San Francisco, Calif., 15 p. Ferguson, F. A., 1968, A nonmyopic approach to the problem of excessive algal growth: Environ. Science and Technol. v. 2, p. 188-193. Forsberg, C. G., 1972, Algal assay procedure: Jour. Water Pollution Control Federation, v. 44, p. 1623-1628. Goerlitz, D. F.,and Brown, E., 1972, Methods for analysis of organic substances in water: U.S. Geol. Sur.vey Tech. Water Resources Inv., Bk. 5, Ch. A3, p. 2-3. Guy, H. P.,and Norman, V. W., 1970, Field methods for the measurement of fluvial sedimcllts: U.S. Geol. Survey Tech. Water Resources Inv., Bk. 3, Ch. C2, 59 p. Maloney, T. E., Miller, W. E., and Shiroyama, T., 1972, Algal responses to nutrient addition in natural waters. I. Laboratory assays: Nutrients and eutrophication, Special Symposium, Amer. Soc. ' Limnol. and Oceangr., v. 1, p. 155. Miller, W. E.,and Maloney, T. E., 1971, Effects of secondary and tertiary wastewater effluents on algal growth in a lake- river system: Jour. Water Pollution Control Federation, v. 43, p. 2361-2365. National Lake Survey Program, 1973, Highlights: Corvallis, Oregon, Environmental Protection Agency, 5 p. Palmer, C. M., 1969, A composite rating of algae tolerating organic pollution: Jour. Phycology, v. 5, no. 1, p. 78-82. Slack, K. V., Averett, R. C., Greeson, P. E., and Lipscomb, R. G., 1973, Methods for collection and analysis of aquatic biological and microbiological samples: U.S. Geol. Survey Tech. Water Resources Inv., Book 5, Ch. A4, 165 p. Wang, W. C., Sullivan, W. T., and Evans, R. L., 1972, A technique for evaluating algal growth potential in Illinois surface water: Urbana, Illinois State Water Survey, Report of Investigation 72, 16 p.