SOME CHEMICAL AND BIOLOGICAL PROPERTIES OF A PINGO LAKE IN EAST CENTRAL ALASKA FEDERAL WATER QUALITY ADMINISTRATION NORTHWEST REGION ALASKA WATER LABORATORY College, Alaska ------- SOME CHEMICAL AND BIOLOGICAL PROPERTIES OF A PINGO LAKE IN EAST CENTRAL ALASKA by Frederick B. Lotspeich Ernst W. Mueller Paul J. Frey for the FEDERAL WATER QUALITY ADMINISTRATION DEPARTMENT OF THE INTERIOR ALASKA WATER LABORATORY COLLEGE, ALASKA Working Paper No. 1 ------- A Working Paper presents results of investigations which are to some extent limited or incomplete. Therefore, conclusions or recommendations—expressed or implied—are tentative. ------- 1 INTRODUCTION Pingos and pingo lakes are common in permafrost areas of Alaska. "Pingo" is an Eskimo word meaning "small hill;" a pingo is formed by an ice cone that uplifts the soil to form the low conical hill. The ice is derived from rising ground water under hydrostatic pressure that freezes beneath or between permafrost layers. Holmes, et.al.J treat these features in some detail and cite numerous data on their distribution, size and variability. This report describes a pingo lake in Big Timber Creek Valley which is about 280 km (175 miles) east of Fairbanks and 40 km (25 miles) west of 2 the Canadian border. Pingos which are open and collapsed are believed to be formed when the supply of ground water is cut off and the ice cone melts, allowing the overlying layers to collapse and form a small lake. Several of these pingos were observed in Big Timber Creek Valley. Lithology and attitude of the underlying basement rocks, topography, and orientation control circulating ground water that permits pingos to form. Foster^ mapped several pingos in the Mt. Fairplay area, all of which occur near valley floors on south facing slopes. The pingo described here is in the valley bottom but closer to the north facing slope; the creek flows westward on the north side of the lake. Other pingos in this valley were sited similarly to those mapped by Foster. The blue-green color of the water in this pingo lake drew our attention because it was so unlike the brown color in ox-bow lakes common in these ------- 2 valleys. Its general appearance resembled the one described by Krinsley^ near Circle, although it is smaller and does not have an outlet. The color of the water suggested that properties of the water were signi- ficantly different from other waters in the valley. For example, Likens and Johnson describe the chemistry of the lake near Circle City and found that it was meromictic, containing abnormally high quantities of lithium and strontium. With these thoughts in mind, we decided to investi- gate the properties of the lake. Figure 1 is an aerial view of the pingo. METHOD On September 14, 1967, we had the first opportunity to collect water and biological samples from the lake. The initial sample disclosed that pH, conductivity, and other chemical properties were significantly different from Big Timber Creek and that the flora and fauna were surprisingly abun- dant. With these data in mind, we visited the pingo again on May 3, and June 27, 1968. On May 3, the pingo still had 7 dm (2 1/2 ft.) of ice covering it, which in turn was covered by about 3 dm of slushy snow. During our approach to the lake, we noted a small contrasting area near the center of the lake in which was found a 1 dm (4 in) diameter hole through the ice. It is possible that this hole was caused by rising gas bubbles from anaerobic processes in the lake bottom. Two large diving beetles (Dytiscus) were observed in the overlying slush near the hole. A similar patch was noted in flying over another pingo one or two miles down the valley. Evidently, the causes were similar for these features. No samples were taken in May ------- 3 Figure 1. Aerial view of pingo lake showing its general shape and the surrounding vegetation; note the shrubs along the water!ine and the only leaning tree within the crater. ------- 4 because the overlying slush prevented collecting a representative sample. The lake was sounded through a hole cut in the ice and found to be about 5.5 m (18 ft.) deep with black mud on the bottom that changed to light gray on drying. On June 27, 1968, a temperature and dissolved oxygen profile was obtained and water samples collected at 1-m intervals with a Van Doren bottle. Biological samples were also collected with an Ekman dredge, long-handled dip net, and standard Wisconsin plankton net. RESULTS AND DISCUSSION Figure 1 shows the appearance of the lake and gives some idea of the vegetation surrounding the flanks of the pingo. The water surface is roughly circular in plan and measures (by pacing) 33 x 30 m (100 x 90 ft.) with inside slopes "of 56 percent; depth was 5.5 m. The water was very clear and was bluish-green in color where it was deep enough so that the bottom was invisible. Flanks of the pingo slopes continued steeply upward from the water and were estimated to range in height from 2 to 10 m (6-30 ft.). These slopes were soft, sandy, and contained marks of concentric slump fissures. Height of the rim above the valley floor was estimated to be 20 m (60 ft.). The water level appears to be stable from year to year as evidenced by moderate sized willows growing at the water's edge. Other evidence of stability on the interior slopes of the pingo are the absence of an outlet, development of a moderate duff layer, and the fact that only one or two leaning trees were observed within the pingo (Figure 1). ------- 5 Table 1 shows the results of chemical analysis of water samples collected from the surface of the lake on September 19, 1967, and on June 27, 1968, from various depths. Figure 2 shows a plot of conducti- vity, dissolved oxygen and temperature versus depth; the thermocline appears to be 2 to 4 m below the surface. It is interesting to note that the conductivity begins to change abruptly below 1 m, whereas dissolved oxygen and temperature do not change rapidly until approximately the 2 m level. It appears from Figure 2 that the lake may be in the process of becoming chemically and thermally stratified; however, as turnover may have occurred only a few weeks previously (the lake was ice covered on May 3), the thermocline may become more pronounced later. It is possible, owing to the short warming cycle in these latitudes, that sufficient time may not be available between the spring and fall turnovers for a sharper thermocline to develop. Other chemical concentrations appear to parallel these observations. Total alkalinity, for example, ranges from 110 mg/1 at the surface to 163 mg/1 at the bottom. The pH ranges from 8.15 at the surface to 7.50 at the bottom. Although samples were not taken during the winter or during the period when the lake might have been expected*to turn over, it was not felt that the lake is permanently stratified, because the temperature recorded at the bottom was 5.6°C. In addition, the bottom water contained 0.2 mg/1 dissolved oxygen with only slight evidence of anaerobic processes. This lake, therefore, is probably a typical- hoiomictic lake, probably of the second class. That is, "thermally stratified, but with a bottom tempera- ture sufficiently above 4°C that extrapolation of the summer temperature curve involve significant increase in the heat entering the lake."6 ------- 6 TEMPERATURE 0 GDISSOLVED OXYGEN *--- XCONDUCTIVITY » 2- x 3- 3 5 7 9 13 II r 1 3 4 5* 6 7 ~8 mg/l T < > ( > > 1 360 380 400 4 20 440 460 480)imho/cm Figure 2. Plot of conductivity, temperature and dissolved oxygen with depth. ------- TABLE 1. CHEMICAL DATA FROM SAMPLES COLLECTED IN SEPTEMBER 1967 AND JUNE 1968 ^3 Fe (3)_ S04 (4) NO-2 (5) P05 Ca Mg Mn (6) T.A. Sr Cu K Na D.O (D T°C PH Cond mq/1 Surface - 8.20 433 .33 .0 77 .001 .10 45.6 11.4 .02 106.2 - .01 3.7 9.7 - (1967) Surface 15.6 8.15 361 .0 .1 - .001 .00 32 15.8 .01 110.6 .25 .02 2.7 9.7 8.3 (1966) 1 m 14.9 8.08 356. .21 .0 - .001 .00 36 15.4 .02 109 .28 .02 2.7 11.0 8.4 2m 14.6 7.90 396 .17 .0 - .002 .00 40 18.1 .03 124 .32 .02 2.7 13.7 8.4 3m 13.3 7.70 450 .02 .0 - .002 .00 52 19.6 .21 150 .30 .02 3.5 13.3 6.6 4m 9.0 7.58 457 .08 .0 62 .003 .03 48 21.2 .24 154 .40 .02 3.1 13.3 3.0 5m 6.9 7.52 462 .24 .0 91 .002 .00 49 20.0 .13 152 -38 .00 3.8 12.9 1.9 Bottom 5.6 7.50 462 .11 .0 77 .003 .16 51 20.6 .4 163 .38. .02 3.7 12.4 0.3 (1) ytnhos/Cm (4) as N (2)" as N (5) total as P0= - (3) as so=4 (6) total Alk as CaO^ ------- 8 Chemical stratification of this pingo is the result of limnological processes and is not believed to be caused by crenogenic processes as proposed by Likens and Johnson for the pingo near Circle, an area known to contain hot springs. Evidence against a live spring in this pingo are the stability of the water level and the absence of an outlet. Table 2 is a catalogue of organisms compiled from the 1967 and 1968 collections. The plankton is identified to genus and its relative abun- dance is indicated as follows: "xxx," abundant on every slide; "xx," present on every slide; "x," only a few specimens seen. The Benthos is identified to species or as near species as possible. In cases where the list reads Genus sp., for example Charoborus sp., this means there was only one species present for that genus. In cases where a letter has been affixed, for example Cricotopus sp. -A, there was more than one species present within that genus, but identification beyond genus was impractical. Except for the amphipods, the benthos in this lake was very sparse. Gammarus lacustris lacustris, apparently the only amphipod present, were there in very large numbers. They were very active, constantly moving about, and when an area was disturbed, numerous individuals could be seen scurrying for cover. They were taken both in dip net samples along the shore and from dredge samples from the deepest portion of the lake. The midges were the next most abundant group. Chironomous tendens was most numerous and was found in the deepest sections where the dissolved oxygen was at its lowest level. Cricotopus and Tanytarsus were considerably less numerous and were found only in the dip net samples from shallow water. The fingernail, clam,, Pisidium, was taken in fair numbers from all sections of the lake. Mayflies and phantom midges were present in most samples from the shallow water, but were not abundant in any area. Although annelids were collected from both ------- 9 TABLE 2. BENTHIC AND PLANKTONIC ORGANISMS COLLECTED FROM A PINGO LAKE IN EAST CENTRAL ALASKA PLANKTON ZOOPLANKTON Rotifera Kellicottia - x Notommata - x Keratella - x Cladocera Daphnia -xxx Ilocryptus -x Copepoda Cyclops -xxx Ostracoda C.ycloc.ypris -xxx Porifera SpongiHa -x PHYTOPLANKTON Zygnematales Desmidium Pleurotaenium Zygnema Zygnemopsis Euglenales Trachelomonas Oedogoniales Bulbochaete Cladophorales Cladophora Peridiniales Peridinium Nemalionales Lemanea Bacillariales Fragilaria -xxx Navicula Pinnularia -xx Epithemia -x Mougeotia -xx ------- 10 TABLE 2 CONTINUED BENTHOS Charales Chara sp. 01igochaeta Naididae Hirudinea Glossiphoniidae Helobdella stagnalis Amphi poda Gammaridae Gammarus lacustris lacustris Ephemeroptera Baetidae Centroptilum sp. Coleptera Dytiscidae D.ytiscus sp. Di ptera Dixidae Curculidae Chaoborus sp. Chironomidae Chironomus tendens Chironomus sp. Cricotopus sp. -A Cricotopus sp. -B Tanytarsus sp. Ceratopogonidae Bezzia sp. Pelecypoda Sphaeriidae Pisidium sp. ------- 11 shallow and deep water, only three specimens were found. All of the remaining organisms were represented by single individuals. The algae, Chara, was present in heavy masses to considerable depths. Although an extensive effort was made to collect a representative population, we do not suggest that the catalogue in Table 2 represents the entire population of the lake. We feel that the macrofauna are better represented than the microfauna, since the collector was basically interested in them and is, therefore, more thoroughly oriented toward their collection. ------- 13- BIBLIOGRAPHY 1. Holmes, William G., Hopkins, David M., and Foster, Helen. "Pingos in Central Alaska" U.S.G.S. Bulletin #1241-H. 1968. 2. Stager, J.G. "Progress Report on the Analysis of the Characteristics and Distribution of Pingos of the Mackenzie Delta" Canadian Geographer 7: 13-20. 1956, 3. Foster, Helen L. "Geology of the Mount Fairplay, Alaska" U.S.G.S. Bulletin #1241-13. 1967. 4. Krinsley, David B. "Birch Creek Pingo, Alaska" U.S.G.S. Prof. Paper 525, p. 133-136. 1965. 5. Likens, G.E., and Johnson, P.L. "A Chemically Stratified Lake in Alaska" Science 153: 875-877. 1966. 6. Hutchinson, E. "Treatise on Limnology" Vol. 1: Geography, Physics, and Chemistry, John Wiley & Sons, Incl., p. 1015. ------- |