Microflora distributions in quaternary paleosols on Mount Kenya, East Africa

CATENA

Vol. 13, 155-167

Braunschweig 1986

MICROFLORA DISTRIBUTIONS. IN QUATERNARY PALEOSOLS ON MOUNT KENYA, EAST AFRICA W.C. Mahaney and M.G. Boyer, North York SUMMARY When numbers of microorganisms in profiles of ground and buried soils on Mount Kenya were estimated by plate counting they were found to be consistently lower than those observed for other soils in different geographical regions. Numbers declined successively in deeper horizons and no evidence was obtained of irregular patterns of distribution controlled by soil forming processes, as observed frequently in certain Mollisols and Spodosols. The lower numbers and patterns of vertical distribution appear characteristic of younger Inceptisols and Entisols usually found in the alpine zone, and older Alfisols located in the Bamboo Forest region of Mount Kenya. The A horizons of the soils studied contain proportionately fewer of the total number of organisms in the A, B and C horizons than are observed in most soils. Estimates of organic matter suggest that this may be limiting since profile TV4a, with the highest counts, also had the.highest organic matter content. However, extreme climatic conditions, such as severe drought and diurnal frosts, or unknown soil parameters, may also regulate the numbers of micro- and macroorganisms. Organic and inorganic horizons of buried soils often exhibit higher counts of microorganisms than adjacent horizons of ground soils. However, bacteria and fungi do not appear to differ qualitatively from those in surface horizons. Taken in conjunction with other evidence obtained from the profdes we conclude that they are not indigenous, but introduced by root systems, or by upward movement of the water table contaminated with microorganisms. This appears to provide a means of determining which buried horizons are likely to be contaminated by biogeochemical processes, thus possibly affecting their radiocarbon ages. 1. INTRODUCTION The mountains of East Africa constitute a unique element of the equatorial region, as climatic factors imposed by latitude and altitude combine to produce a tropical alpine (Afroalpine) environment distinct from the alpine regions of other parts of the world (COE 1967). Biological ly,Mount Kenya (Figure I) is represented by a diverse zonal flora and fauna adapted to the rigors of the Afroalpine and rich in endemic species (FRIES & FRIES 1948, HEDBERG 1964). As a result vegetational zones far exceed in number, complexity, and richness, those of temperate alpine regions. Although Mount Kenya has been studied for many years, this is the first attempt to study the interrelationships between paleosols and their microbiological components. The mountain was subjected to intense glacial activity, mass wasting, and fluvial activity which profoundly altered its morphology over approximately 2.5 million years (NILSSON 1935, BAKER 1967). More recently, many of the geomorphological features of the mountain have been described (MAHANEY 1972, 1979, 1980, 1981, 1982a, 1982b), and a more cornISSN 0341-8162 © Copyright 1986 by CATENA VERLAG, D - 3302 Cremlingen-Destedt, W.Germany 0341-8162/86/5011851/US $ 2.00 + 0.25

156

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prehensive chronology is beginning to emerge (Figure 2) (COETZEE 1967, BAKER 1967, HASTENRATH 1984, MAHANEY 1984a and b). In our study five soils are examined with respect to their morphology, age, chemistry, and microbial composition.

2.

METHODS

Soil profiles are described according to the nomenclature of the SOIL SURVEY STAFF (1951, 1975) and BIRKELAND (1984). In sampling care was taken to avoid contamination from other horizons. Samples for microbial analyses were removed as subsamples of those collected for measurement of chemical and physical parameters, as discussed elsewhere (MAHANEY 1981, 1984a, MAHANEY et al. 1984). They were then representative of hori-

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zons as designated, rather than of specific depths. The subsamples were collected and placed in sterile scintillation vials in which the screw caps had been drilled and loosely plugged with cotton. The vials were stored in a carrying case which did not impede air exchange. Samples were analyzed microbiologicaUy from one week to four weeks after they were collcted. The time lapse was unavoidable. Several routine methods were employed to obtain estimates of the numbers of species of fungi and bacteria. Actinomycetes were counted when observed, but no media were employed to selectively isolate them. Dilution plate series were prepared

158

MAHANEY & BOYER

in replicates of three for both fungi and bacteria. For fungi a soil extract agar medium (SEA) was used (JAMES 1959). This was prepared from a standard soil because insufficient soil was available from each horizon. To the extract with agar, 0.2 g K2HPO41-11.0 g glucose 1-1and 1 percent rose bengal were added. The pH was reduced to 6.0 with 10 percent lactic acid, after sterilization. For bacteria, standard Difco nutrient agar was employed, supplemented by 1.0 g tryptone 1-1. The media were employed routinely for plate counts, while recognizing that any simple medium has limitations with respect to representation of the microbial population. Soil samples were homogenized in a mortar and pestle and then processed in sterile tap water. The pour plate method was employed for the enumeration of both bacteria and fungi. After inoculating, samples were incubated at 15°C in the dark for 9 days. Counts were made at appropriate dilutions and 95% confidence limits estimated.

3.

HELD AREA

The volcanic pile of Mount Kenya is approximately 100 km in diameter, and rises to a height of 5199 m (Figure 1). The paleosols forming the subject of this study are discussed in detail in the text and are located along the Naro Moru River Valley, the upper glaciated por-" tion of which is called the Teleki Valley (Figure 1).

3.1.

SITES

Site TV23 (Figure 1) is located on a moraine ridge at about 2990 m and it is the type locality for Teleki Till (MAHANEY 1982a and b). The dominant vegetation is referable to the Bamboo Zone (COE 1967) and is dominated by Arundinaria alpina. Associated ground vegetation is sparse, the total estimated at 30 percent cover. Scattered Cyperusrotundifolius, species of Carex, with clusters of Lycopodium saururus and Dryopteris inaequalis form much of the cover. Portions of the site had been recently opened by the activities of water buffalo (Syncerus caffer caffer) and elephant (Loxodonta africana). Where soils are disturbed large thaUose liverworts and mosses are common. Immediately offthe ridge the density of bamboo declines and woody species, characteristic of the Hagenia-Hypericum Woodland (COE 1967) and the Montane Forest Region, predominate. Soil profile (TV23, Figure 3) consists of a compound paleosol overlain with a ground soil with somewhat similar charcteristics. Both the buried and surface soils are Alfisols, which are more common below timberline on Mount Kenya. Heavy textures in the B2 horizons are the result of downward movement of clay in the profiles, which directly influences the development of blocky structures. Reddish colors in this profile result partly from the chemical composition of the parent material, which is ultra-basic in nature and high in iron (MAHANEY 1982a, 1982b). The surface soil in Teleki Till and the buried soil formed in older till ofpreTeleki age are representative of soils formed in the pre-Pleniglacial tills found elsewhere along the western flank of Mount Kenya. Tills of similar age occur in the same stratigraphic positions on the northern and eastern flanks of the mountain, but the prevailing vegetation is alpine moorland, not bamboo forest. The remaining sites, TV34, TV36, TV33 and TV4a are located near the head of Teleki Valley (Figure 1) in the upper Afroalpine zone at approximately 4100 m. Sites TV34 and TV36 (Figure 1), located in an end moraine of Liki III age in Teleki

MICROFLORA DISTRIBUTION, PALEOSOLS, MOUNT KENYA

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Valley (Figure 2), contain scattered individuals o f Senecio keniodendron, Lobelia telekii, Festuca pilgera, Agrostis trachyphylla a n d Alchimella agryrophylla, in addition to rarer species giving 50 to 60 percent cover.

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Profiles TV34 and I V 3 6 (Figure 4 A a n d B) make up the high and low members, respectively, of a soil catena (toposequence) in Liki III till (Figure 2). These soils are Inceptisols radiocarbon dated at - 12,500 yrs BP ( M A H A N E Y 1984a). Hues in both soils are brown and horizons are more difficult to differentiate than in the older TV23 profile. Higher contents o f gravel throughout, thinner sola, and wavy horizon contacts, attest to their young age and the severity of the alpine climate where the surface freezes nearly every night. The greater thickness of the A1 horizon in profile TV36 is probably the result of the downward m o v e m e n t of organic matter through the catena (for similar alpine toposequence processes

MICROFLORA DISTRIBUTION, PALEOSOLS, MOUNT KENYA

161

in the mid-latitudes see MAHANEY & SANMUGADAS 1983). Profile TV33, (Figure 5a) previously described by MAHANEY (1981), consists of two buffed Entisols with a surface Inceptisol formed in alluvial fan sediment. The lowermost Ab horizon dates at 4480 + 160 yrs BP (Gak-8215) and documents the time at which younger fan material buffed the lowermost Entisol in the sequence. The overlying Ab horizon was buried by younger fan material at 4310 + 180 yrs BP (Gak-8214) sugesting that A horizons form rapidly in the Afroalpine area (e.g. within a 170 year period, if the dates are taken literally without their standard deviations). The characteristics of the overlying Inceptisols are typical of the post-Darwin soil (for profile data see MAHANEY 1984a, 1984b, chronology see Figure 2). Tussock-forming grasses A. trachyphylla and F. pilgera dominate the site, giving approximately 80 percent cover. Needle ice activity and solifluction patterns are common on open ground. Site TV4a (Figure 1) is located 250 m downvalley from the Liki III moraine. Vegetation is entirely herbaceous, both herbs and forbs yielding about 80 percent cover. Dominant species include the tussock-forming grasses. Agrostis trachyphylla, Festuca pilgera as well as Poa schimperiana and the sedge Carex monostachya. Common herbs include Haplocarpha rueppelli, Carduus keniensis and Sagina afroalpina. Exposed portions of this site are rare with only occasional evidence of frost heaving. Profile TV4a (Figure 5B) is forming in outwash covering a mid-Holocene paleosol (MAHANEY 1982a, 1984a). A radiocarbon date of 1940 + 120 yrs BP (Gak-8273) for tile Ab horizon suggests that sandy outwash emplaced in a valley train during the middle to late Holocene weathered to produce an Entisol giving an Ab/Cloxb/C2oxb/Cub profile. Approximately 1900 radiocarbon years ago it is estimated this Entisol was buried by fresh pebbly alluvium in which an Inceptisol formed.

4.

RESULTS AND DISCUSSION

Altogether 12 soils and 84 horizons were investigated microbiologically. Those discussed here were taken as representative of a range of sites on Mount Kenya. Maximum counts of bacteria and fungi are invariably associated with the A horizons. Highest numbers are obtained from site TV4a (bacteria 16.7 x 104, fungi 23.1 x 103). Lowest counts are those found on the drier more exposed soils of the Liki III recessional moraines, and on the alluvial fan at site TV33 (Figures 4A, B and 5A). Counts are compared with those obtained from the A horizons ofother soils in different geographical regions (Table 1). The mean counts in soils on Mount Kenya appear to be an order of magnitude less than other estimates. Estimates of the weight loss on ignition as determined for the All horizons of TV23 and TV33 and the A1 horizons of TV34, TV36 and TV4a suggest organic matter is limiting in some soils (Table 2). Ranked in order of decreasing weight, TV4a is highest, followed by TV36, TV33, TV34 and TV23. TV4a supports the greatest total numbers of bacteria and fungi, but in the remainder, microorganisms do not correlate with weight loss. Estimates of organic matter in other soils of Mount Kenya have been determined by MAHANEY(1982a), using more precise methods. These estimates suggest that the organic matter content of many alpine and subalpine soils may be comparable to that in Podsolic and Chemozemic soils (TIMONIN 1935). While limitations to the numbers of fungi and bacteria in paleosols on Mount Kenya would not appear to be solely a consequence of organic matter content, they are also not directly related to microclimatic variables. For example, while numbers of microorganisms

162

MAHANEY& BOYER

Tab. 1: NUMBERS OF MICROORGANISMS IN SOILS OF DIFFERENT ORIGINS AND LOCATIONS Actinomycetes Soil Types Bacteria Fungi Temperate Podzol (GRAY & TAYLOR cited 9.8)<106 1.9)<105 1.1)<106 by WAKSMAN 1963) 7.1)< 108 --Brown Forest (KAURI 1978) 7.1)< 106 -7.4X 105 Agricultural Soil (WAKSMAN 1963) 1.0X 106 2.7X 104 8.9)< 104 Forest-Meadow Podzols (MISHUSTIN 1975) 2.3)< 106 2.8)< 104 1.2)< 106 Meadow Steppe Chernozems 2.3)<106 2.1)<104 1.1)<106 Dry Steppe Chestnuts 2.6)< 106 2.0X 104 1.5)< 106 Desert Steppe (Brown and Sierozems) 2.0X 106 6.1)<104 3.1X104 Tundra Gley Podzol 7.1X105 -_ Arctic Peat (BOYD) 1 3.2X 105 -Arctic Peat Loam 1.6× 105 -Arctic Sandy Loam 4.9)< 10 5 -Arctic Clay Arctic Sedge Moss Meadow (40-70% OM) 1.4)< 108 (WlDDEN 1977) 11.1)<106 Arctic Raised Beach (3% OM) Temperate Alpine Tundra (SHULLS & 1.5X 106 MANCINELLI 1982) Gravel (Antarctica) (BUNT & ROVIRA, cited 8 . 0 × 10 s -_ by HOLDING et al. 1974) 3 . 0 X 106 -_ Peat 3.4X 106 --Sand 4.2)< 102 1.3)< 104 Semi Arid Savanna (Kenya) (ARSHAD et al. 1982) 3.3X 105 2.7)< 105 1.2)< 103 6.7X 104 Semi Arid Savanna (Kenya) (KEYA et al. 1982)2 4.3X 105 9.1×101 2.4X 104 Semi Arid Savanna Tropical Alpine Soils (Average of 12) (BOYER & 5.4X 104 1.2X 103 MAHANEY, this paper) Samples taken durin 6 annual low, (Aug.). Numbers recorded during annual high reached a maximum of 1.4× 10°. Upper sample taken during dry season, lower sample during wet season. m

m

Tab. 2: WEIGHT LOSS ON IGNITION AND pH VALUES FOR A1AND A11 HORIZONS OF TV SOILS, MOUNT KENYA Soils Weight loss (average of two estimates) pH

TV23 16.5 4.7

TV34 17.8 5.2

TV36 19.9 5.5

TV33 18.3 5.4

TV4 35.6 5.6

in the A1 and All horizons are low in those soils most subject to freezing and drought (TV34, TV36, TV33, TV4a; Figures 4 A a n d B, 5 A a n d B), they are higher than numbers observed in TV23 (Figure 3), and considerably higher than the mean value cited for the A horizons o f all the soils investigated (Table 1).

FUNGI

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2,5

164

MAHANEY & BOYER

Numbers of bacteria and fungi decline more or less uniformly in successive horizons. Numbers of fungi decrease more rapidly than bacteria, but generally, when one is prevalent, the other is as well. The average distribution ofmicrofiora in the A, B and C horizons is respectively 56 percent, 36 percent, and 8 percent for bacteria; and 60 percent, 37 percent and 3 percent for fungi. Representative data from other sources led to the observation that higher proportions of the total are usually associated with the A horizon in soils from temperate and arctic regions (TIMONIN 1935, WAKSMAN 1963, CLARK 1967, MISHUSTIN 1975, WIDDEN 1977, KAURI 1978). Variations in distribution characteristic of soil processes, such as described for some Podsols and Chemozems by TIMONIN (1935), were not observed. Both the reduced numbers of microorganisms and their pattern of distribution may be characteristic of the less weathered Inceptisols and Entisols of the Afroalpine region. Some inconsistencies in the distribution of numbers of microorganisms are observed in the buried soil units. Microorganisms are detected at maximum @pths of 176-186 cm in the Ab horizon of TV23 even when horizons above it appear to be sterile (Figure 3). Examination of buried horizons in other profiles (TV4a and TV33, Figures 5Aand B) reveals microorganisms, particularly bacteria. In some intances buried mineral horizons, such as the lower Coxb in site TV33 (Figure 5A) and Cb in site TV4a (Figure 5B) contain relatively large numbers of both bacteria and fungi. The capacity of both inorganic and organic buried horizons to support the growth of microorganisms for long periods requires the periodic introduction of both microorganisms and organic matter. While infiltration of surface water cannot be ruled out, other means seem more probable. In TV23 (Figure 3) roots ofA. alpina, observed at the base of the profile, may provide a pathway for the migration of microorganisms and a continuing supply of organic matter. Profiles TV4a and TV33 (Figures 5A and B) do not contain living roots in the lower horizons. However, the base of each profde is in contact with the water table at 140 cm in TV33 and 86 cm in TV4a (Figures 5A and 5B). Given the nature of the sites, contact between contaminated surface waters draining the sides of the valley and the water table seems probable, and periodic changes in water levels could account for the contamination of the horizons above the lower Coxb (TV33) and Cnb (TV4a) (Figures 5A and 5B). Preliminary assessment of bacteria and fungi from paleosols do not reveal a specific buried soil flora. That is, fungi isolated from buried A horizons include species that are also isolated from surface soil horizons. Also, randomly isolated, bacteria classified by simple colonial cellular and staining characteristics do not produce statistically distinct groups. Introduction of bacteria and fungi into buried organic horizons, such as the upper Ab and lower Ab in site TV33 (Figure 5A), may affect 14C/12C ratios, and thus influence their radiocarbon ages. It is possible that some radiocarbon dates underestimate the age of burial and the data shown herein suggest that microbial composition may be used to determine if an horizon has been subjected to contamination by surface leaching and/or groundwater activity.

5.

CONCLUSION

The numbers of bacteria and fungi in profiles of several tropical alpine soils appear to be consistently lower than those observed in other soils from different geographical regions (Table 1). We conjecture that they may be numerically at the lower end of a sequence of soil types (MISHUSTIN 1975). The numbers of microorganisms in one of the soils, TV4a (Fi-

MICROFLORADISTRIBUTION,PALEOSOLS,MOUNTKENYA

165

gure 5B), are conspicuously higher than in the remainder. Because the organic matter as estimated by soil weight loss on ignition was also higher than other soils, it is postulated that the quantity or availability of organic matter may play a regulatory role with respect to microbial numbers in paleosols under alpine conditions. Organic matter in soils is widely recognized as the most significant factor regulating numbers and diversity of organisms (CLARK 1967, STOTZKY 1972). Where climatic conditions are severe, as evidenced by needle ice patterns and barren wind-dried soils (TV36 and TV33), microbial numbers may be enhanced. Toial numbers in these soils are greater than in soils not subjected to frost heaving. The known stimulatory effects of drying and moistening of soils (STEVENSON 1956) and of thawing, on microbial numbers (BOYD 1958, BOYD & BOYD 1964, BAKER 1970, HOLDIN et al. 1974), may play a role in counteracting the deleterious effects of needle ice, light, and drought. Neither total numbers of microorganisms, nor the distribution of numbers with depth, are correlated with the soil orders present as defined by the SOIL SURVEY STAFF (1975). Distributions with depth, which might distinguish Inceptisols, Entisols and Alfisols, as they do Chemozems (MISHUSTIN 1975) or Podsols (TIMONIN 1935), are not seen, although weathering, especially through its effects on the spatial, organo-mineral content, clay, and clay mineralogy of progressively weathered soils (STOTZKY 1972), might be expected to have a profound influence on the distribution of microorganisms. The low pH and paucity of clay minerals (MAHANEY 1982a) in a number of paleosols from Mount Kenya m~y be additional factors in suppressing the more luxuriant growth of microbial populations. The anomalies observed in distributions of microorganisms are those associated with buried soils (TV4a, TV33, Figures 5Aand B). Large numbers of bacteria, and less frequently fungi, are found in both organic and inorganic horizons. The presence of a fluctuating water table contaminated by surface waters appears to be the most reasonable explanation for their distribution. By comparing the distributions of microorganisms in the lower horizons of both TV33 and TV4a (Figures 5A and B), the greater numbers recorded in the lowest horizons are probably due to more recent saturation with ground water. In TV33 the very high numbers of bacteria in the upper Ab and their absence in the lower Ab suggest the possibility ofa rhizosphere effect (CLARK 1967) estimated from the horizon above, or by unobserved roots penetrating the horizon. In the abence of discernable numbers in some Ab horizons (TV33 upper Ab, Figure 5A) we suggest that the buried horizons are probably unable to support an indigenous flora without the periodic introduction of nutrients and organic materials. The contamination of buried horizons by microorganisms is not surprising, given their proximity to non-sterile horizons and the potential of gravitational water or roots to serve as a means of transport. Where present in soils for which 14C dates are desired, it might be possible to correct for both the extent of contamination, and the resulting metabolic activity. ACKNOWLEDGEMENTS This research was supported in part by grants from the National Geographic Society(Nos. 1576.76; 2306.81; and 2672.83), The Natural Sciencesand Engineering research CouncilofCanada 1983and 1984 (to W.C. Mahaney), and York University.Field work was authorized by the Officeofthe President (Kenya Research Permit OP 13/001/6C 17/54), Kenya Parks, and Geological Survey of Kenya. We are particularly indebted to Linda M. Mahaney for assistance in the field during 1976 and 1983/84, to students in the Mountain Geomorphology Field Schools (1976and 1983),and to LarryGowland (1976and 1983).Willieand Didi Curry, formerly ofNaro Moru RiverLodge, and Sueand Tor Allan (Hunters East AfricaLtd., Nairobi) provided invaluable assistanceand logisticalsupport. Moreover, Phil

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Snyder (formerly assistant Warden) and Bill Woodley, (Warden, Tsavo Park, Kenya) assisted with various phases ofthe 1976 work. Mr. Fred Pertet (Kenya Parks) assisted in a similar way in 1983/84.

REFERENCES

ARSHAD, M.A., MUERIA, N.K. & KEYA, S.O. (1982): Effect oftermite activities on the soil microflora. Pedobiologia 23, 161-166. BAKER, B.H. (1967): Geology of the Mount Kenya Area. Geological Survey of Kenya, Rept. 79, 78 p. BAKER, T. H. (1970): Yeast, moulds and bacteria from an acid peat on Signy Island. In: Antarctic Ecology ed. by M.W. Holdgate, 2. Academic Press, London, 717-722. BIRKELAND, P.W. (1984): Soils and geomorphology. Oxford Press, N.Y. 372 pp. BOYD, W.L. (1958): Microbiological Studies of Arctic Soils. Ecology 39, 332-336. BOYD, W.L. & BOYD, J.W. (1964): The presence of bacteria in permafrost of the Alaskan Arctic. Can. J. Microbiol 103, 917-919. CLARK, F.E. (1967): Bacteria in soil. In: Soil Biology, ed. by A. Burgess, and F. Raw. Academic Press, N.Y. 15-49. COE, M.J. (1967): The ecology of the Alpine Zone of Mount Kenya. Junk, The Hague, 136 pp. COETZEE, J.A. (1967): Pollen analytical studies in East and Southern Africa. In: Palaeoecology of Africa, ed. by E.M. van Zinderen Bakker, 3, 1-146. FRIES, E.R. & FRIES, Th.C.E. (1948): Phytogeographical researches on Mt. Kenya and Mt. Aberdare, British East Africa, K. Svenska Vetensk. Akad. Handl. III, Stockholm, 25(5). HASTENRATH, S. (1984): The glaciers of Equatorial East Africa. Reidel Publishing Co., Dordrecht, Holland, 353 pp. HEDBERG, O. (1964): Features of Afroalpine Ecology. Almquist and Wiksells, Uppsala, 144 pp. HOLDING, A.J., COLLINS, V.G., FRENCH, D.D., D'SYLVA, B.T. & BAKER, J.H. (1974): Relationship between viable bacterial counts and site characteristics in tundra. In: Soil Organisms and Decomposition in Tundra. Ed. by A.J. Holding, O.W. Heal, S.F. Machean Jr., and P.W. Flanagan. Tundra Biome Steering Committee, Stockholm, 49-77. JAMES, N. (1959): Plate counts of bacteria and fungi in a saline soil. Can. J. Microbiol, 5, 431-439. KAURI, R. (1978): Aerobic bacteria in the horizons of a beech forest soil. In: Microbial Ecology. Ed. by M.W. Lautit and J. Miles. Springer Verlag, 110-122. KEY& S.O., MUERIA, N.K. & ARSHAD, M.A. (1982): Population dynamics of soil micro-organism in relation to proximity of termite mounds in Kenya. J. Arid Environ. 5, 1-8. MAHANEY, W.C. (1972): Late Quaternary history of the Mount Kenya Afroalpine area, East Africa. In: Palaeoecology of Africa, ed. by E.M. van Zinderen Bakker, 6, 139-142. MAHANEY, W.C. (1979): Reconnaissance Quaternary Stratigraphy of Mt. Kenya. In: Palaeoecology of Africa, ed. by E.M. van Zinderen Bakker, 6, 163-170. MAHANEY, W.C. (1980): Late Quaternary rock glaciers, Mount Kenya, East Africa. J. Glaciology, 25, 492-497. MAHANEY, W.C. (1981): Paleoclimate reconstructed from paleosols: evidence from the Rocky Mountains and East Africa. In: Quaternary Paleoclimate, ed. by W.C. Mahaney, Geoabstracts, Norwich, 227-247. MAHANEY, W.C. (1982a): Chronology of glacial deposits on Mount Kenya, East Africa: description of type sections. In: Palaeoecology of Africa, ed. by E.M. van Zinderen Bakker, 14, 25-43. MAHANEY, W.C. (1982b): Correlation of Quaternary glacial and periglacial deposits on Mount Kenya, East Africa with the Rocky Mountains of Westem Wyoming, U.S. In: XI INQUA Congress, 1982, Abstracts, 208. MAHANEY, W.C. (1984a): Radiometric dating of Quaternary glacial and nonglacial deposits, Mount Kenya, East Africa. National Geographic Society Research Report Series. MAHANEY, W.C. (1984b): Late glacial and postglacial chronology of Mount Kenya, East Africa. In: Palaeoecology of Africa, ed. by J.A. Coetzee and E.M. van Zinderen Bakker, 16, 327-341. MAHANEY, W.C. & SANMUGADAS, K. (1983): Early Holocene soil eatena in Titcomb Basin, Wind River Mountains, Western Wyoming. Zeitschrift ~ r Geomorphologie, 27(3), 265-281. MAHANEY, W.C., HALVORSON, D., PIEGAT, J. & SANMUGADAS, K. (1984): Evaluation of Dating Methods used to assign ages to Quaternary deposits in the Wind River and Teton ranges, Western Wyoming. In: Quaternary Dating methods, ed. by W.C. Mahaney. Elsevier, Amsterdam, 355-374.

MICROFLORADISTRIBUTION,PALEOSOLS,MOUNT KENYA

167

MISHUSTIN, E.N. (1975): Microbial associations of soil types. Microbial Ecology 2, 97-118. NILSSON, E. (1935): Traces of ancient changes of climate in East Africa. Geografiska Annaler ¥ 1(2), 1-21. SHULLS, W.A. & MANCINELLI, R.L. (1983): Comparative study of metabolic activities of bacteria in three ecoregions of the Colorado Front Range, USA. Arctic and Alpine Research 14, 53-58. SOIL SURVEY STAFF (1951): Soil Survey Manual. U.S. Gov't. Printing Office, Washington, D.C., 503 pp. SOIL SURVEY STAFF (1975): Soil Taxonomy. Agriculture Handbook 436. U.S.D.A., Washington. 754 pp. STEVENSON, I.L. (1956): Some observations on the microbial activity in remoistened air-dried soils. Plant and Soil 8, 170-182. STO'I'ZKY, G. (1972): Activity, ecology and population dynamics of microorganisms in soil. Critical Reviews in Microbiology 2, 59-137. TIMONIN, M.I. (1935): The microorganisms in profiles of certain virgin soil in Manitoba. Can. J. Res. 13c, 32-46. WAKSMAN, S.A. (1963): Soil Microbiology. Wiley, N.Y., 236 pp. WlDDEN, P. (1977): Microbiology and decomposition on Truelove Lowland. In: Truelove Lowland, Devon Island, Canada. A High Arctic Ecosystem, ed. by L.C. Bliss. University of Alberta Press, 505-530.

Addresses of authors: William C. Mahaney, Department of Geography, Atkinson College York University North York, Ontario M3J 1P3 Michael G. Boyer, Department of Biology and Centre for Research on Environmental Quality York University, North York, Ontario M3J 1P3