WATER QUALITY: Briefing paper on "Periphyton" June 22, 1978 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 78.10 Subject: WATER QUALITY: Briefing paper on "Periphyton" by George A. McCoy, WRD, Anchorage, Alaska The attached briefing paper on "Periphyton" by George McCoy is supplied for your information. Please distribute the paper as widely as possible in all district and project offices. R. J. Pickering Chief, Quality of Water Branch Attachment WRD Distribution: A, B, S, FO-L, PO PERIPHYTON George McCoy, Anchorage, Alaska INTRODUCTION We have all experienced the trauma of wading a stream with a slimy coating of "moss" on the stream bottom. The "moss" is really periphyton, the assemblage of algae, fungi, and bacteria which are attached to or live on submerged objects in streams and lakes. Periphyton will grow on almost any submerged object. It can occur as a thin film on silt or mud surfaces, on submerged branches, roots, logs or dock pilings, and rooted aquatic plants. It also occurs as floating or loosely attached layers in lakes or in the shallow areas of sloughs or slow moving areas of streams. Although periphyton organisms are usually microscopic, they often form masses or clumps that are visible to the unaided eye. Some genera form long entangled masses of thread-like filaments which are very conspicuous. These masses often contain several kinds of filamentous algae growing together; Cladophora, Ulothrix, Oedogonium, and Spirogyra are common members of such an association. They are usually attached to the rocks by rhizoids or root-like structures. These assemblages also commonly contain several species of diatoms. Many of the diatoms are attached to the substrate by a jelly-like substance. Other diatoms occur on stalks or in gelatinous tubes (figure 1). Still other diatoms, particularly those on mud and sediment, are motile. Clumps of periphyton also may form cushions on the surface of submersed objects. This is particularly true of the blue-green algae. Periphyton are undoubtedly the most important primary producers in the flowing water environment. Primary producers are those organisms which manufacture sugar from inorganic carbon through the process of photosynthesis. The periphyton are generally of secondary importance to phytoplankton in lakes, but several studies indicate that in some lakes they are equal to or even more important than phytoplankton. PHYSICAL FACTORS The physical factor which seems most obvious is the flow or motion of the water. Several studies have shown that some species of periphyton colonize only those areas in stream where the water is constantly moving by wave action. For certain species, the water must be moving at a velocity greater than some threshold value before these forms can grow. Moving water constantly replenishes the supply of nutrients to attach non-motile organisms. It has been shown that up to a certain point phosphorus uptake by algal cells and the amount of primary production increase as current velocity increases. Observations will reveal that periphyton commonly are most abundant at low flow when the water is clear, and are less abundant during and immediately after storm events or periods of high run-off, because they are scoured from the substrate. Temperature has essentially two effects on the periphyton community. All other factors being equal, the amount of primary productivity increases directly with temperature. Warm streams and lakes commonly have a larger standing crop of periphyton than do cold streams. Temperature also affects the species composition of the periphyton. Some organisms are specifically adapted to cold water. There are numerous examples of algae that occur only in cold mountain streams or in the arctic. Many green algae are found only in the summer, and most of these organisms seem to be able to tolerate water temperatures as high as 25 C. Still other organisms, including some blue-green algae, are adapted to hot springs and are absent from other environments. The effects of light intensity cannot always be separated from temperature. However, there are several species of periphyton that are found only in the densely shaded areas of streams, but occur over a wide range of temperatures. The few red algae that occur in freshwater appear to be adapted to low light intensities. Green algae, on the other hand, require a more intense light level and are very sparse in shaded streams. Diatoms as a group seem to occur over a wide range of light intensities, but some studies have indicated that the composition of the diatom community is different in shaded and unshaded areas. It has been demonstrated that light and temperature do not function independently. Algae in colder water seem to grow more efficiently with a higher light intensity than do periphytic algae in warm water. The nature of the substrate, its texture, stability, and porosity, undoubtedly affects the composition of the periphyton community. The stability of the substrate is perhaps most important. A very different community will develop on fine shifting sand and silt than on course gravel or cobble. Larger or slower growing species require a durable, lasting substrate, consequently these organisms are not often found on aquatic vascular plants. CHEMICAL FACTORS The alkalinity and related parameters such as hardness and the pH of water have an important chemical influence on the periphyton community. Many organisms are equally abundant in soft and hard water, but others are restricted to acid or alkaline environments. In addition to differences in community composition, the density of organisms in soft or acid water is commonly much lower than in alkaline or hard water. Many species of periphyton are characteristic of salt water, while other species have a range of tolerance for salinity. In an estuarine environment there is a gradual but marked change in the community composition from the marine environment of the ocean through the tidal environment of the gradually freshening estuary to freshwater. Phosphate and nitrate are usually the most important inorganic nutrients. The addition of phosphorus and in some instances nitrate has been shown to enhance periphyton growth in laboratory streams. The increased growth of periphyton downstream from a sewage outfall is probably a direct result of phosphorus additions. In a uniform reach of a stream where there is no additional source of nitrogen or phosphorus, the concentration of these two substances will decrease gradually downstream. This is presumably caused by the uptake of phosphorus and nitrate by periphyton. Numerous studies have shown that the species composition of periphyton may be very different above and below a sewage outfall. Often diatoms are replaced by a luxurient growth of green and blue-green algae. Growth of blue-green algae is enhanced by additions of organic forms of nitrogen and phosphorus. Another inorganic nutrient that is necessary for the growth of some periphyton is silica. It has been suggested that flood waters carry increased amounts of silica which may stimulate the large increases in diatom populations that occur after a flood. BIOLOGIC FACTORS Periphyton organisms are opportunists. That is to say, the organism which can attach and grow most rapidly on a new substrate will probably be most successful in colonizing that particular habitat. Competition among periphyton organisms is not generally for nutrients but rather for available substrate space. Many invertebrates and certain fish feed on periphyton. These grazing animals play an important role in determining periphyton abundance and distribution, and their feeding patterns can cause irregular distribution of periphyton. The blue-green algae usually are avoided and may even be toxic to invertebrates and fish, but large quantities of diatoms and green algae may be consumed by grazers, often very rapidly. It is sometimes possible to see clear areas on stones around snails and limpets, and several caddis-fly larvae are known to graze on periphytic diatoms. METHODS OF COLLECTION There are a number of methods of collecting periphyton samples from natural substrates. These methods are illustrated and explained in Greeson and others (1977). Quantitative sampling of natural substrates for periphyton is difficult. If collections of periphyton from natural substrates are to be representative of the community in a reach of a stream, then a sampling scheme must be devised so that collections from all natural substrates found in that reach are obtained. Sampling programs using artificial substrates have the advantage of standardizing the physical environment. Although the communities that develop on artificial substrates are not necessarily representative of the communities present on natural substrates, artificial substrates do provide information that can be used to compare one site or one stream with another. This assumes, however, that the artificial substrates were exposed in a similar manner and for the same length of time. Artificial substrate samples can be compared for community structure. They also can be used to measure rate of colonization, or the biomass accumulated in a given unit of time in a given area; this information yields a relative measure of the productivity of a stream. Another useful measurement on periphyton samples is the autotrophic index. Autotrophic refers to organisms in which organic matter is synthesized from inorganic substances (photosynthesis) as compared to heterotrophic organisms, which require organic material as a source of nutrition. The autotrophic index is the ratio of biomass to chlorophyll a. A high value for this index indicates a community with a large number of heterotrophic organisms (bacteria and fungi). A low value indicates a community with predominantly autotrophic organisms. Artificial substrates commonly made of polyethylene strips, plexiglass, or glass microscope slides are suspended in the water for a period of at least 14 days. After retrieval, it is possible to determine chlorophyll or biomass per unit area of the substrate. These determinations yield a relative measure of the productivity of the water. It is also possible to measure the species composition of the community and to compare it directly with the community on a substrate from a different site. DISTRIBUTION AND OCCURENCE The variations of physical and chemical factors in moving waters cause periphyton to be distributed in a very nonuniform manner in a stream. Some organisms will occur near springs, others in slow moving water or in pools. The community structure also may vary with the nature of the substrate or the degree to which the site is shaded. The amount of periphyton and the kinds of species in the community also will vary seasonally. These seasonal changes are caused by a variety of physical and chemical influences, including lights temperature, ice cover, flow, and changes in available nutrients and dissolved solids. In large slow-moving rivers, however, the seasonal changes are not as great as in small swift streams. It is likely that the environment in a large river varies less in response to climatic fluctuations. IMPORTANCE Periphyton often are used as indicators of environmental conditions. A few algal species have a well-defined habitat preference. From the occurrence of one of these species in a body of water it is possible to infer certain characteristics about this environment. However, the majority of algal species have a broad range of tolerance for habitats or too little is known of their physiology for them to be of value in interpretating the environment unless they are very abundant. If, however, the entire community is considered, then certain associations of organisms may be discerned from which we can infer that certain conditions exist in that environment. The concept of indicator species, where a particular species is used to indicate a specific kind of pollution, or type of water is, at present, of limited value. However, a large growth of green filamentous algae in a stream usually indicates an abundant supply of nutrients. The use of whole communities to compare certain aspects of rivers or sites in a particular river is useful, but often cumbersome. The use of mathematical comparisons such as diversity indices, similarity indices, dendrograms, and multivariate analyses are useful methods for determining similarities and differences between communities. These techniques often require some form of computer analysis and will become more useful as we gain a better understanding of the physiology and ecology of the individual organisms. Selected references Evans, D., and Stockner, J. G., 1972, Attached algae on artificial and natural substrates in Lake Winnipeg, Manitoba: Jour. of the Fisheries Res. Board of Canada, v. 29, p. 31-44. Greeson, P. E., Ehlke, T. A., Irwin, G. A., Lium, B. W., and Slack, K. V., 1977, Methods for the collection and analysis of aquatic biological and microbiological samples: U.S. Geol. Survey Techniques of Water Resources Inv., book 5, chap. A4, 332 p. Hynes, H.B.N., 1970, The ecology of running waters: Toronto, Univ, of Toronto Press, p. 54-78. Olson, T. A., and Odlaug, T. 0., 1972, Lake Superior periphyton in relation to water quality: U.S. Environmental Protection Agency; Water pollution control research series, 18050 DBM 02/72, 253 p. McCoy, G. A., 1974, Preconstruction assessment of biological quality of the Chena and Little Chena Rivers in the vicinity of the Chena Lakes flood control project near Fairbanks, Alaska: U.S. Geol. Survey Water-Resources Inv. 29-74, 84 p. McIntire, C. D., 1966, Some factors affecting respiration of periphyton communities in lotic environments: Ecology, v. 49, p. 918-929. ______1969, Physiological--ecological studies of benthic algae in laboratory streams, Part I: Jour. of the Water Pollution Control Fed., v. 40, p. 1940-1952. ______and Phinney, H. K., 1965, Laboratory studies of periphyton production and community metabolism in lotic environments: Ecological Monographs, v. 35, P. 237-258. Palmer, C. M., 1962,Algae in water supplies: U.S. Dept. Health, Education, and Welfare, Division of Water Supply and Pollution Control, Public Health Service publication No. 657, 88 p. ______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, 11. C. Brown Co., 977 p. Reid, G. K., 1976, Ecology of inland waters and estuaries: 2nd Ed. New York Reinhoid Publishers, Corp., 375 p. Tilley, L. J., and Haushild, W. L., 1975, Use of productivity of periphyton to estimate water quality: Jour. of the Water Pollution Control Fed. v. 47, p. 2157-2171. Whitton, B. A., 1975, Algae, in Whitton, R. A., Ed., Studies in ecology, v. 2, River ecology: Berkeley, California, Univ. of California press, p. 81-106.