741550.02.qxd 16/9/2002 2:25 PM Page 11 2 FRESHWATER HABITATS OF ALGAE John D. Wehr Robert G. Sheath Louis Calder Center — Biological Station Office of Provost and Vice President for and Department of Biological Sciences Academic Affairs Fordham University, California State University, San Marcos Armonk, New York 10504 San Marcos, California 92096 I. What is Fresh Water? IV. Wetlands II. Lentic Environments A. Functional Importance of Algae A. Major Lakes of North America in Wetlands B. Lake Basins B. Algal Diversity in Freshwater C. Lake Community Structure and Wetlands Productivity C. Algal Communities of Bogs D. Ponds, Temporary Pools, and Bogs V. Thermal and Acidic Environments E. Phytoplankton of Lakes and Ponds A. Thermal Springs F. Benthic Algal Assemblages of Lakes B. Acid Environments III. Lotic Environments VI. Unusual Environments A. Major Rivers of North America A. Saline Lakes and Streams B. Geomorphology of Rivers B. Snow and Ice C. The River Continuum and C. Other Unusual Habitats Other Models Literature Cited D. Benthic Algal Communities of Rivers E. Phytoplankton Communities of Rivers I. WHAT IS FRESH WATER? freshwater algae fall into a large, but ecologically meaningful collection of environments: all habitats that The study of freshwater algae is really the study of are at least slightly wet, other than oceans and estuaries. organisms from many diverse habitats, some of which One reason for such a broad scope is that inland saline are not entirely “fresh.” Although the oceans are clear- lakes, snow and ice, damp soils, and wetlands are ly saline (Ϸ 35 g salts L–1) and most lakes are relatively studied by phycologists and ecologists who also exam- dilute (world average < 0.1 g L–1; Wetzel, 1983a), there ine more traditional freshwater environments. Some is enormous variation in the chemical composition of genera with terrestrial species, such as Vaucheria, the nonmarine habitats that algae occupy. Conditions Nostoc, Chlorella, and Prasiola, also have species in lakes and rivers vary not only in salinity, but also found principally in streams or lakes (Smith, 1950; in size, depth, transparency, nutrient conditions, pH, Whitton, 1975). In North America, the variety of fresh- pollution, and many other important factors. Aquatic water habitats colonized by algae is very rich, and ecologists also use the term “inland” waters to encom- offers an enormous and fascinating range of environ- pass a greater range of aquatic ecosystems. Even this ments for their study. term may be unsatisfactory, because algae occupy The distinction between marine and freshwater many other habitats, such as snow, soils, cave walls, habitats is revealed in the variety of algae that occur and symbiotic associations (Round, 1981). in these environments. There are no exclusively fresh- Organisms grouped together in this volume as water divisions of algae, but certain groups exhibit Freshwater Algae of North America 11 Copyright © 2003, Elsevier Science (USA). All rights of reproduction in any form reserved. 741550.02.qxd 16/9/2002 2:25 PM Page 12 12 John D. Wehr and Robert G. Sheath greater abundance and diversity within fresh waters, (Hutchinson, 1957, 1967, 1975; Frey, 1963; Wetzel, especially Cyanobacteria, Chlorophyta, and Charophyta 1983a; Cole, 1994; Abel et al., 2000). This section (Smith, 1950). Within the green algae, conjugating summarizes some features of lentic environments as greens and desmids (Zygnematales, Chap. 9) comprise they pertain to the ecology and distribution of fresh- a very rich collection of species that almost exclusively water algae. occupy fresh water. Other groups, such as the diatoms and chrysophytes, are well represented in both spheres. A. Major Lakes of North America Other groups, particularly the Phaeophyta, Pyrrophyta, and Rhodophyta, exhibit greater diversity in marine Worldwide, the single largest volume of freshwater waters (Smith, 1950; Bourrelly, 1985). Most freshwater — nearly 20% of the world’s total — is located in Lake algae are best described as cosmopolitan, although Baikal, Siberia (23,000 km3), but the North American there are reports of endemic chrysophytes, green algae, Great Lakes (Fig. 1A) collectively represent the largest rhodophytes, and diatoms (Tyler, 1996; Kociolek et al. total volume of nonsaline water on Earth, approxi- 1998), and at least some species of cyanobacteria mately 24,600 km3 (Wetzel, 1983a). North America is (Hoffmann, 1996). Many algal taxa have particular home to many spectacular large and deep freshwater environmental tolerances or requirements, and are eco- systems, nearly half of all the world’s lakes greater than logically restricted, but still geographically widespread. 500 km2 (Hutchinson, 1957). Two of the most impres- The euglenophyte Colacium is almost exclusively epi- sive lakes are subarctic: Great Slave Lake (28,200 km2; zooic on aquatic invertebrates, but is widely distributed 614 m deep; deepest in North America) and Great Bear throughout North America (Smith, 1950; Chap. 10). Lake (30,200 km2; > 300 m deep) in the Northwest The chrysophyte Hydrurus foetidus is an exclusive Territories (Hutchinson, 1957). Crater Lake in Oregon inhabitant of cold mountain streams, but is distributed (Fig. 1B) is much smaller (64 km2 in area), but is the worldwide (Smith, 1950; Whitton, 1975, Chap. 12). deepest lake in the United States (608 m) and seventh Even specialized taxa such as Basicladia chelonum deepest in the world (Edmondson, 1963). The largest (Chlorophyceae), which is restricted mainly to the lakes on the continent are located in northern and shells of turtles, has been collected from many habitats temperate regions, although Great Salt Lake (Utah) is a throughout eastern North America (Smith, 1950; massive remnant lake (> 6000 km2) that has a mean Prescott, 1962; Colt et al., 1995). The actual distribu- depth (Ϸ 9 m) and very high salinity (130–280 g L–1) tion of apparently disjunct freshwater species must that fluctuate with available moisture, and occupies a therefore be viewed with some caution until detailed portion of the Pleistocene Lake Bonneville, which surveys have been conducted (see, for example, Linne had an area > 51,000 km2 and a depth of 320 m von Berg and Kowallik, 1996; Müller et al., 1998). (Hutchinson, 1957). Inland waters represent only about 0.02% of all water in the biosphere, and nearly 90% of this total is B. Lake Basins contained within only about 250 of the world’s largest lakes (Wetzel, 1983a). Nonetheless, it is fresh water that Sizes and shapes of lake basins (their morphome- is most important for human consumption and is most try) have profound effects on the physics, chemistry, threatened by human activities. Algal ecologists play and biology of lake ecosystems, and influence the com- an important role in the understanding of aquatic position of algal communities and their productivity. ecosystems, their productivity, and water quality issues Lake basins differ in morphometry as a result of the (Round, 1981; Brock, 1985a; Hoffmann, 1998; Dow forces that created them, many of which were cata- and Swoboda, 2000; Oliver and Ganf, 2000, strophic events from the past, principally glacial, Chaps. 23 and 24). This chapter examines the habitats seismic, and volcanic activity. Hutchinson (1957) of freshwater algae and how differences in these distinguished 76 different lake types based on their systems affect algal communities. origins; these were classified into a simpler scheme by Wetzel (1983a) that is summarized in Table I. Glacial activity is the most important agent in II. LENTIC ENVIRONMENTS North America. It created millions of small and large basins from the arctic south to the southern extent of Lentic environments include standing waters from the Wisconsin ice sheet. In this period (15,000–5000 the smallest ponds (a few square meters) to enormous years BP), many basins became closed by morainal bodies of water (e.g., Laurentian Great Lakes: deposits, including the Laurentian Great Lakes. Some 245,000 km2). Their formation, geography, limnology, morainal lakes occur at the ends of long valleys after and conservation have been covered in several texts glaciers have receded, including the Finger Lakes of 741550.02.qxd 16/9/2002 2:25 PM Page 13 2. Freshwater Habitats of Algae 13 FIGURE 1 Examples of different types of lakes in North America: A, Laurentian Great Lakes; B, Crater Lake, Oregon, a deep caldera lake; C, New York Finger Lakes; D, kettle lakes in Becher’s Prairie, central British Columbia; E, pothole lakes in Qu’appelle Valley, Saskatchewan; F, Louise Lake, a cirque in Mt. Rainier National Park, Washington. Photos A and C courtesy of U.S. Geological Survey EROS Data Center, reproduced with permission; photo B by R. G. Sheath; photo D by R. J. Cannings; photo E by P. R. Leavitt, reproduced with permission; photo F by J. D. Wehr. New York (Fig. 1C), which are elongate, radially basins within narrow valleys may form deep fjord lakes arranged basins that range from small ponds to large (Fig. 2A), or a chain of smaller lakes known as pater- lakes, such as Seneca (175 km2 area, 188 m depth; nosters. Several forces, including glacial scour and lava Hutchinson, 1957; Berg, 1963). However, most flow, combined to form the small (9.9 km2) but deep glacially formed lakes are small kettles scattered across (259 m) fjordlike Garibaldi Lake (Northcote and the continent (Fig. 1D and E). Glacial scouring in Larkin, 1963; Fig. 2B). Ice-formed (thermokarst) lakes, mountainous terrain may form deep amphitheater-like which result from freezing and thawing action in ice cirques (Fig. 1F), which are common from Alaska and soil, are common in the Arctic. All are shallow but through the western mountain ranges south to tropical vary from large elliptical basins (up 70 km2 area) to locations in Costa Rica (Haberyan et al., 1995). Glacial small (10–50 m diameter), “polygon” ponds (Fig. 2C), 741550.02.qxd 16/9/2002 2:25 PM Page 14 14 John D.