Seasonal Biotic Events in Two Colorado Alpine Tundra Ponds

Seasonal Biotic Events in Two Colorado Alpine Tundra Ponds EUGENE H. SCHMITZ • Reprinted from THE AMERICAN MIDLAND NATURALIST Vol. 61(4424-446. 1959 University of Notre Dame Press Notre Dame, Ind. Seasonal Biotic Events in Two Colorado Alpine Tundra Ponds' EUGENE H. SCHMITZ University of Colorado, Boulder The rugged terrain and the rigorous climatic conditions of the alpine tundra present a rather formidable picture to the field biologist. The long winter, deep snow, blizzards, and high winds make the alpine tundra relatively inaccessible for biological studies with ordinary equipment during much of the year. Even in the short summer, high winds, frequent cold showers, and summer blizzards are likely to occur at any time. It has long been generally recognized that such severe climatic conditions are remarkably restrictive upon the aquatic as well as the terrestrial biota of the tundra. With the exception of Neldner and Pennak (1955), who conducted a full open season study on a single Colorado alpine pond, the Amer- ican literature on tundra ponds is almost non-existent, being limited to brief descriptions, single visits, and casual observations. European investigators, such as Brink and Wingstrand (1949), Pesta (1933, 1935, 1943, 1948), Pichler (1939a, 1939b) , Stirnimann (1926), Thomasson (1951, 1952), and Turnowsky (1946), have produced a much more extensive array of literature, but like the majority of Amer- ican papers, these are brief descriptions and not full seasonal studies. It is the purpose of the present paper to give a limnological description of two small Colorado alpine tundra ponds, based upon observations and data gathered at relatively frequent intervals during the entire open season. Some routine physical and chemical determinations were conducted, but special emphasis was placed upon the ecology of the benthic fauna and zooplankton, with little regard to the botanical aspect. Acknowledgment. — I am especially indebted to Dr. Robert W. Permak for the confirmation of many taxonomic determinations and criticism of the manuscript. I am also grateful to Mr. H. B. Herrington for species determination of fingernail clam specimens. I am further indebted to Mr. Robert P. Hig- gins for assistance in the field determination of pond morphometry. DESCRIPTION OF PONDS Washboiler Pond (hitherto unnamed) and Dead Hat Pond (hitherto0 unnamed) are located in Summit County, Colorado, at 39 40' north latitude and 105° 52' west longitude. The ponds are situated only 30 meters apart at an elevation of 3,582 meters (11,750 feet) in a glaciated valley at the southwest foot of Mount Sniktau on 1 Contribution No. 35, Limnology Laboratory, Department of Biology, Uni- versity of Colorado. 424 1959 SCHMITZ : LIMNOLOGY OF ALPINE TUNDRA PONDS 425 Fig. 1. — Dead Hat Pond (arrow, slightly left of center) as seen from U. S. Highway 6 at the summit of Loveland Pass. the Continental Divide, well above timberline. Pennak (1941, 1958) suggests 3,200 meters elevation as the lower limit of the alpine limnological zone at this latitude. Dead Hat Pond can easily be seen from U. S. Highway 6 at the summit of Loveland Pass (3,656 meters), but Washboiler Pond is obscured from view by a small terminal moraine in the foreground (Fig. 1) . The alpine meadow in which the ponds are located lies in a valley surrounded on the west, north, east, and south by the summit of Loveland Pass, Mount Sniktau, Baker Mountain, and Lenawee Moun- tain, respectively. The valley was probably formed sometime in the late Wisconsin by the plucking action of a small glacier. The valley supports a typical alpine vegetation of which Carex spp., Salix sp., Ranunculus spp., Sedum sp., Gait ha sp., and Poa sp. are examples. Dead Hat Pond is located 30 meters east of Washboiler Pond, and both are roughly oblong in shape (Figs. 2, 3, 4, and 5) . Washboiler Pond is about 2 by 6 meters with a maximum depth of 0.56 meters (Fig. 4) . Dead Hat Pond is about 4 by 9 meters with a maximum depth of 0.50 meters (Fig. 5) . Dead Hat Pond differs from Wash- boiler Pond in that it has a small northeast "bay" with a maximum depth of 0.24 meters, and a small island in its eastern half, which supports a small Carex growth. The basins of both ponds are saucer-shaped, and receive drainage from melting snow banks on the north and west slopes, as well as water from showers, frequent in the alpine tundra. It may be noted that Dead Hat Pond probably receives a slight bit of drainage from the outlet of Washboiler Pond. The basins of these ponds should not 426 THE AMERICAN MIDLAND NATURALIST 61(2) ii Fig. 2. — Washboiler Pond, looking south. be confused with the staircase and thrust-pond types characterized by Ives (1941), but are merely saucer-shaped depressions in an alpine meadow. Both Washboiler Pond and Dead Hat Pond possess drainage out- lets on the north and east northeast sides, respectively (Figs. 4 and 5) . Water-level fluctuations are common to both ponds during the summer months, especially after the snow banks have melted. However, frequent heavy showers and the resulting drainage periodically restore the ponds to their natural levels. The lowest maximum depth recorded during the open season was 0.3 meters in Dead Hat Pond on Sep- tember 10. The bottom deposits of Washboiler Pond and Dead Hat Pond are difficult to characterize. Bottom samples are black, mixed with decay- ing plant material, somewhat putrified, and emit hydrogen sulfide when disturbed. Lauterborn (1901) designates this type of deposit as saprope/, being largely derived from cellulose-rich detritus of higher plants or lama. In addition, coprogenic sediments, produced by the Fig. 3. — Dead Hat Pond, looking south. 1959 SCHMITZ : LIMNOLOGY OF ALPINE TUNDRA PONDS 427 action of the bottom fauna on settled planktogenic sediments (iivja), are present, which Naumann (1929) terms gyttja. Lindemann (1941) points out that sediments do not always appear as pure "genotypes," and that a certain amount of variation and intergradation must be expected. It should be noted that the bottom deposits of Dead Hat Pond are not as thick as those of Washboiler Pond, and that the sediments of the eastern half of Dead Hat Pond are intermixed with sand and pebbles. Washboiler Pond and Dead Hat Pond are aestival ponds in that they contain some water throughout the open season, but freeze to the bottom during the winter months (Welch, 1952) . Being in the alpine zone, they are characterized by short open seasons. The ice had completely disappeared by mid-July, but by late October both ponds had acquired an ice cover of sufficient thickness to support a person's weight. MATERIALS AND METHODS Visits were made to the site at intervals of 5 to 11 days from July 18, 1957 to October 19, 1957. All visits were made between 9:30 a.m. and 2:00 p.m. Since the route from the road to the site of the ponds was quite steep, the lightest and most compact equipment was essential. The hydrographic maps (Figs. 4 and 5) are the result of a series of photographs and routine measurements, carried out as follows. A grid, 10 meters square, was constructed of string and stakes over each pond, and the outline of each pond was sketched on graph paper according to the appropriate scale. The depth contours were inter- polated from a series of depth measurements made with a meter stick. A mapping compass was used to establish a north-south baseline. Surface and bottom temperatures were recorded for both ponds during each visit. A standard laboratory thermometer was utilized for this purpose. When temperatures were found to be variable in differ- ent areas of the ponds, mean surface and bottom temperatures were calculated for each pond. Four water samples were taken during the open season from each pond for purposes of color and pH determinations. Color determinations were carried out in the laboratory by means of the platinum- cobalt method (see Welch, 1948). For pH determinations, permanent Hellige discs were used in conjunction with the appropriate indicator solutions. Nine water samples were taken from each pond during the open season for routine free carbon dioxide and bound carbon dioxide determinations in the laboratory. Free carbon dioxide was determined by sodium hydroxide titration, and bound carbon dioxide was determined by hydrochloric acid titration. Phenolphthalein and methyl orange indicators were utilized in the sodium hydroxide and hydrochloric acid titrations, respectively. Results were calculated in parts per million (ppm) . 428 THE AMERICAN MIDLAND NATURALIST 61(2) Two 3.9 liter water samples were taken from each pond near the beginning and near the close of the open season, for residue determinations. In each case, the entire sample was evaporated in a large evaporating dish placed in a sand bath. The residue which remained in the evaporating dish was ignited at 600° C, and the loss on ignition by weight was determined. The amounts of organic residue and inorganic salts present were calculated in terms of milligrams per liter. Toward the close of the open season, a sediment sample was taken from each pond. An aliquot from each sample was dried and ignited at 600° C. The loss on ignition by weight was determined, and the percentages of organic matter and inorganic matter in the sediment were calculated in each case. The bottom fauna was sampled by means of a scoop (12 x 12 x 2.8 cm) constructed of heavy sheet metal. Each sample consisted of one-seventieth of a square meter. Two samples were taken from each pond during each visit, one near the area of maximum depth and one in a relatively shallow area.

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