a community of snow algae on a himalayan glacier: change of algal biomass and community structure...

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A Community of Snow Algae on a Himalayan Glacier: Change of Algal Biomass andCommunity Structure with AltitudeAuthor(s): Yoshitaka Yoshimura, Shiro Kohshima and Shuji OhtaniSource: Arctic and Alpine Research, Vol. 29, No. 1 (Feb., 1997), pp. 126-137Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1551843 .

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Arctic and Alpine Research, Vol. 29, No. 1, 1997, pp. 126-137

A Community of Snow Algae on a Himalayan Glacier: Change of Algal Biomass and Community Structure with Altitude

Yoshitaka Yoshimura and Shiro Kohshima Basic Biology, Faculty of Bioscience and Biotechnology, (c/o Faculty of Science), Tokyo Institute of Technology, 12-1, O-okayama 2-chome, Meguro-ku, Tokyo 152, Japan.

Shuji Ohtani

Biological Laboratory, Faculty of Education, Shimane University, Nishi Kawatsu, Matsue, Shimane 690, Japan.

Abstract A community of snow algae on a Himalayan glacier, the Yala Glacier (5100- 5700 m a.s.l.), Langtang region of Nepal Himalaya, were quantitatively analyzed. This is the first report on snow algae from the Himalayan region. In this glacier, 11 species of snow algae were observed: Chloromonas sp., Trochiscia sp., Me- sotaenium berggrenii, Cylindrocystis brdbissonii, Koliella sp., Ancylonema nol-

denskioeldii, Raphidonema sp., three Oscillatoriacean algae, and one unknown coccoid alga.

The algal biomass estimated by the total cell volume rapidly decreased as the altitude increased. In particular, the rate of decrease of algal biomass was

larger in the upper snow environment than in the lower ice environment. The structure of algal community represented by the proportion of each species to the total algal biomass also differed by altitude. From the difference of the algal community, we divided the glacier into three zones: the Lower Zone (5100-5200 m a.s.l.; stable ice-environment), with 7 species dominated by Cylindrocystis brdbissonii; the Middle Zone (5200-5300 m a.s.l.; unstable transition area between ice-environment and snow-environment), with 11 species dominated by Meso- taenium berggrenii; and the Upper Zone (5300-5430 m a.s.l.; stable snow-envi-

ronment), with 4 species dominated by Trochiscia sp. This vertical zonation of the algal community type and biomass may reflect the difference in summer climatic conditions with altitude. Species number and Simpson's diversity index was highest in the Middle Zone where environmental conditions frequently changed. Our results seems to agree with the intermediate disturbance hypothesis.

Since the snow algae in the accumulation area (>5250 m a.s.l.) of the glacier is annually stored in glacial strata, the algal biomass and community structure recorded in glacier ice-cores can be a new information source for the studies on

past climate change in this region.

Introdution

Though snow algae have been reported from various parts of the world and many reports were published (Kol, 1968), we still have very few reports from Himalayan glaciers. However, in a Himalayan glacier (the Yala Glacier in Langtang region, Nepal), Kohshima (1984a, 1984b, 1987a, 1987b) found a spe- cialized animal community consisting of cold-tolerant insects and copepods living on the glacier by feeding on algae and bac- teria growing in the snow and ice. He pointed out that the glacier is a unique freshwater ecosystem with very simple and special- ized biotic community on the basis of the primary production of these algae. Snow algae on this glacier were also reported to

play an important role in melting process of the glacier; they accelerated glacier melting and affected glacial mass balance by forming dark-colored materials on the glacier and reducing surface albedo (Kohshima et al., 1993). Moreover, as these algae were stored in glacial strata every year and ice-core samples recovered from this glacier contained many layers with algae of many years ago; the algae could be a new information source for the past environment study of this area by ice-core analysis (Kohshima, 1984b). Therefore, the study of snow algae on the glacier is important not only ecologically but also glaciological-

ly. However, ecological studies of snow algae on the glacier have not been carried out.

This study aimed to clarify change of algal biomass and

community structure with altitude quantitatively, in order to know basic characteristics of the algal community on the glacier; we also discuss their relationship with environmental factors on the glacier. Since the glacier ecosystem has a simple community with a small number of species and a clear altitudinal gradient of environmental factors within a small area, the results of this study are useful for clarifying ecological characteristics of each species and the algal community types. The study also provides basic information for the past environment study of this region by the analysis of "fossil" snow algae in the glacier ice core samples.

Methods STUDY AREA

The research was carried out at the Yala Glacier (28014'-15'N, 85036'-38'E, 5100-5700 m a.s.l.) in Langtang region of Nepal (Figs. 1, 2) during the monsoon season of 1991 from 10 to 27 August 1991. Algae for identification were collected again in 1994 (25 and 26 August).

? 1997 Regents of the University of Colorado 0004-0851/97 $7.00

126 / ARCTIC AND ALPINE RESEARCH



30 "N a •. LANGTANG REGION

NEPAL

28 "N KATHMANDU2

82 OE 200 km N

86 "E

YALA GLACIER

KYANGJING VILLAGE .

10 km

LANGTANG REGION

: Glacier

--.-- : Small peak & Mountain ridge

L: River

A 1 : Mt. Langtang Urung (7245 m a.s.I.)

A 2 : Mt. Langtang Ri (7239 m a.s.I.) FIGURE 1. Location of the Yala Glacier in Langtang region, Nepal.

The glacier is a plateau-shaped small glacier (about 4 km in length) without rock debris cover. Moribayashi and Higuchi (1977) classified Himalayan glaciers into two types: "debris- covered type" with rock debris covering the lower part, and "clean type" without a debris-covered area. According to their classification, the Yala Glacier is classified as a clean type glacier. The equilibrium line of this glacier during the research period was estimated by stake measurements to be about 5250 m. The equilibrium line falls between the upper part of the glacier, the accumulation area, and the lower part, the ablation area.

During the research period, the ablation area (below 5250 m a.s.l.) was a bare icefield without snow cover, and the accumulation area (above 5250 m a.s.l.) was a firn snowfield. The surface of the ablation area was covered with dark-colored mud- like material (cryoconite) containing much algae. In the accumulation area, dark-colored snow layers (dirt layers) containing algae and other windblown particles were observed in the surface snow strata. These two environments, the bare ice surface in the ablation area and the dirt layers in the firn snow of the accumulation area were main algal habitats in this glacier. In the Himalayan glaciers, both accumulation and ablation occur si- multaneously in summer season (monsoon season) (Ageta and Satow, 1978). In the summer season meltwater is supplied to the algae, allowing the main algal growth on the glacier to occur in this season.

SAMPLING

A quantitative sampling of snow and ice containing snow algae was carried out at six points on the glacier (5100, 5200,

5250, 5300, 5350, and 5430 m in altitude, respectively, Fig. 2). In the lower bare ice area (Fig. 3A) (5100-5250 m a.s.l.), surface ice (87-400 cm2, 2 cm in thickness) was collected with an ice axe, and in the higher firn area (Fig. 3B) (5300-5430 m) uppermost dirt snow layers (265-750 cm 2, 2 cm in thickness) were collected with a spoon. At each sampling point, 3 to 5 samples were collected. Collected samples were melted and kept in 250-mL clean polyethylene bottles and preserved as 3% formalin solution.

IDENTIFICATION OF ALGAE

Identification of the algae was carried out in the field with a microscope (Olympus CH-2) using fresh samples. Detailed identification and description were done by Ohtani in the laboratory of Shimane University using fresh and preserved samples which were collected in 1994 (in 1991 fresh samples were not transported to Japan, thus detailed identification could not be done).

ANALYSIS OF ALGAL BIOMASS AND COMMUNITY STRUCTURE

In this study, the algal biomass of each sampling point was represented by the total algal volume per unit area. Cell counts and estimations of cell volume were carried out with a microscope (Nikon Optiphot 2) in a laboratory of Tokyo Institute of Technology. Before microscopic observation, the samples were stained with 0.5% erythrosin (0.5 mL was added to 1 mL of the sample) and ultrasonicated for 1 min to loosen sedimented par-

Y. YOSHIMURA ET AL. / 127



71

(B)

- 5,200m

* 500m 5,100m

Photoangle Glacier lake

I-

LARGE ICE CLIFF CREVICE MELT WATER POND

DRAINAGE

FIGURE 2. Photograph (A) and drawing (B) of the Yala Glacier (5100-5700 m a.s.l.). Photo (A) was taken at 5090 m a.s.l. (arrow in B). Filled circles in (B) indicate the points where the sample were collected (5100, 5200, 5250, 5300, 5350, and 5430 m a.s.l.).

ticles. Two microliters of the processed sample water were mounted on a glass microslide under a coverslip (8 x 8 mm), and the number of algae was counted. Since the samples from the upper two points (5350 and 5430 m a.s.l.) contained very few algal cells, 50-100

I.L of the processed sample water was

filtered with a Millipore filter (JHWP01300) which became transparent with water and the number of algae on the filter was counted. The algal density was calculated as "cells mL-' and cells m-2". Mean cell volume was estimated by measuring the size of 50 to 100 cells for each species at each sampling point. The total algal biomass (mL m-2)was estimated to sum up each algal volume which was calculated to multiply the mean cell volume (mL) by the algal density (cells m-2). Community structure was represented by the mean proportion of each species in four samples to the total algal volume at each sampling point. The differences in the proportion of each species between the sampling points was statistically analyzed using t tests.

The species diversity was calculated by Simpson's diversity index D (Begon et al., 1990):

1 D -

> Pi2 i=1

where S is the total number of species in the community, Pi is the proportion of the ith species to the total algal volume.

NUTRIENT, pH, AND MINERAL PARTICLES

Nutrient Level

In order to know the nutrient level in snow and ice of the glacier, the following samples were collected and analyzed: meltwater of algal habitats and nonalgal habitats in the ablation area (5170 m a.s.l.), the dirt layer snow containing algae and granular




, .. . . . •

..*

.*

'~i'L?

FIGURE 3. Photographs of t'p- ical algal habitats. (A) Mud-like materials (crvoconite) containing algae on the ice surface at 5100 m a.s.l. (14 Aug.). (B) Dirt layers observed in a pit wall of the firn snow at 5350 in a.s.l. (21 Aug.). The algae were mainly contained in the dirt layers. Uppermost dirt layer which was formed in 1991 was collected (second dirt laver would be formed in 1990).

snow lacking algae in the accumulation area (5350 m a.s.l.), and the glacier lake water (5090 m a.s.l., outside of the glacier, see Fig. 2). To eliminate impurities, these samples were filtered with Millipore filters (HAWPO47XX) in the field just after sampling. Concentrations of cations (Na?, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-, PO43-) were measured by AA8200 (atomic absorption measurement) and Dionexl0 (ion chromatograph)

manufactured by Nippon Jarrell Ash Co., Ltd., respectively, in Nagoya University.

pH

The pH of the snow and ice in each sampling points was measured by a pH meter (HI1280 HANNA) just after melting at the field.




Mineral Particles

Dry weight of mineral particles in each sample were measured as following. After oven-drying (800C, 24 h) of 30 to 100 mL of sample water, a few drops of nitric acid were added and heated with Bunsen burner for about I h. Weight of the ashed

sample was measured as the weight of mineral particles.

Results LISTS OF SPECIES

The following eleven species were observed:

CHLOROPHYTA

Chloromonas sp. (Fig. 4-1,2)

Biflagellate vegetative cells elliptic to cylindric with rounded apices. A chloroplast without pyrenoids. A nucleus located at the center of cell. Cells 14-24 ?pm in diameter, 20-28 p~m in length. Asexual reproduction by formation of 4 daughter cells. Mother cell spherical, 28 p~m in diameter. Color of chloroplast was observed to be red in the field.

Trochiscia sp. (Fig. 4-3,4)

Cells spherical with thick cell wall (1-1.5 p~m) ornamented by fine granules which arranged at 0.8-prm intervals. Cells 10-20 pLm in diameter. Flagellate cells and dividing cells not observed in samples. Color of chloroplast was observed to be red in the field. Hoham et al. (1979) reported that a zygospore of Chloromonas brevispina (Fritsch) Hoham et al. was identical to typical cells of Trochiscia cryophila Chodat, T. nivalis Lagerheim, and T. rubra Kol. Because Trochiscia sp. in our study resembled to T. rubra in their figures, it is possible that it is also a zygospore of a species of Chloromonas.

Mesotaenium berggrenii (Wittrock) Lagerheim (Fig. 4-5,6)

Cells cylindric with rounded apices, 1 to 2 times longer than the width, 5-10 pLm in width, 8-20 p~m in length. Chloroplast plate- like, one to two, with one pyrenoid. Cell sap dark violet.

Cylindrocystis bribissonii (Ralfs) De Bary f. cryophila Kol

(Fig. 4-7,8)

Cells cylindric with rounded apices, 1 to 2 times longer than the width. Chloroplast axial usually two, with one pyrenoid. Cells of small group 14-18 p~m in width, 22-32 ?pm in length, cells of large group 24-28 pm in width, 26-37 pm in length. Cell sap some- times pale violet. (Our specimens are divided into two groups by cell width. Because the altitudinal distribution range of large and small group are almost same in the glacier, these two groups are treated as one species for quantitative study.)

Ancylonema noldenskioeldii Berggren (Fig. 4-10)

Filaments straight or slightly curved, consisting of 2-4-8 cells. Cells cylindric with truncate or rounded apices, 2 to 2.5 times longer than width, 7-15 pm in width, 15-30 pm in length. Chloroplast with one or two pyrenoids. Cell sap dark violet.

Koliella sp. (Fig. 4-9)

Cells usually solitary, two after cell division, spindle shape, lunate or s-curved with pointed apices, 2 sm in width, 16-26 pm in length.

Raphidonema sp. (Fig. 4-11)

Filaments straight or slightly curved, consisting of 2-4 cells. Cells cylindric with parallel margins, terminal cells gradually atten- uated to the apices, 2-4 prm in width, 12-25 p~m in length.

CYANOPHYCEAE

Oscillatoriacean alga 1

Trichomes 1.5 p~m in width, 1.5 p~m length. Cells about as long as broad.


Trichomes 1.5 pm in width, 3.0 prm in length. Cells about 2 times longer than the width.


Trichomes 4.0 pLm in width, 4.0 p~m in length. Cells about as long as broad.

UNKNOWN SPECIES

Coccoid alga

Cells spherical, chloroplast and pyrenoid not clear, 5-10 p~m in diameter.

DISTRIBUTION RANGE OF EACH SPECIES

From the distribution range of each alga (Fig. 5), the algae on the glacier were classified into following four groups.

(1) Upper and Middle area group: the algae of this group were distributed only above 5200 m a.s.l. Trochiscia sp. and

Raphidonema sp. belonged to this group. (2) Lower and Middle area group: the algae of this group

were distributed only below 5300 m a.s.l. Cylindrocystis brebissonii, Ancylonema noldenskioeldii, and three species of Oscil- latoriacean alga belonged to this group.

(3) Middle area group: the algae of this group were distributed only in a narrow area (between 5250-5300 m a.s.l.). Chlo- romonas sp. and Koliella sp. belonged to this group.

(4) All area group: the algae of this group were distributed all over the area studied on the glacier. Mesotaenium berggrenii and unknown coccoid alga belonged to this group.

POPULATION SIZES AND BIOMASS

Table 1 shows population sizes in cells per milliliter in each sample water and the algal biomass at each sampling point in milliliter per square meter. Algal cell density of the samples from the ablation area (1-11) was 50-100 times greater than that of the samples from the accumulation area (12-23), and the algal biomass of the ablation area was much greater than that of the accumulation area. Figure 6 shows the change of the algal biomass with altitude. On this glacier, the algal biomass decreased as the altitude increased, it decreased especially rapidly in the accumulation area above 5250 m a.s.l. The decrease rate per 100 m altitude in the accumulation area was 20 times larger than that of the ablation area (below 5250 m a.s.l.). This rapid decrease would be caused by some environmental factors which largely change by altitude especially in the accumulation area.




f % '

.I"

P

"A US

...OF

10,

.•...:..! ;

?.:.: •..:< -. . . ?

. -?

c s.?- --r?--C, ?h;,,.

r? ? :•..:: •

• ..•., . , ,

. . . . . ;...... .- . ,,;:.

FIGURE 4. Dominant and common species of snow algae which occurred in the Yala Glacier. 1: Vegetative cell of Chloromonas sp. with one nucleus (arrow n) stained by Azocarmine G. 2: Vegetative cell of Chloromonas sp. with two flagella (arrow J). 3: Trochiscia sp. with thick cell wall. 4: Cell wall ofTrochiscia sp. ornamented by small granules. 5: Vegetative cell of Mesotaenium berggrenii filled with dark purple cell sap (arrow cs). 6: ditto showing two pyrenoids (arrow p). 7: Vegetative cells of Cylindrocystis br6bissonii f cryophila. 8: ditto showing two pyrenoids (arrow p) and a nucleus (arrow n) stained by Azocarmine G. 9: Vegetative cells of Koliella sp. 10: A filament with 4 cells of Ancylonema noldenskioeldii, each cell filled with dark purple cell sap. 11, A filament with 4 vegetative cells of Raphidonema sp. Scale bars = 10 jun.




Species 5100m 5200m 5300m 5400m

Trochiscia sp.

Raphidonema sp.

Chloromonas sp.

Koliella sp.

Ancylonema noldenskioeldii .......

Cylindrocystis brdbissonii .......


Oscillatoriacean alga 2 .............-..............

Oscillatoriacean alga 3 ......... ..........

Mesotaenium berggrenii

Unknown coccoid alga

:very common - common .......... rare

FIGURE 5. Algal distribution range and relative frequency of occurrence on the glacier.

COMMUNITY STRUCTURE AND SPECIES DIVERSITY Figure 7 shows the altitudinal change of community struc-

ture which was expressed by the proportion of each species to the total algal biomass. The structure of algal community gradually changed with altitude. Although three dominant species (Cylindrocystis bribissonii, Mesotaenium berggrenii, and Tro- chiscia sp., Fig. 7A) made up a large part of the total biomass (about 65-95%) at all sampling points, the most dominant spe-

1-

0.1

E -J

0 0.01

0.001 5100 5150 5200 5250 5300 5350 5400 5450

Altitude (m)

FIGURE 6. Altitudinal change of algal biomass (mL m-2) which was estimated by measuring the total algal volume (mean values

_ SD).

cies changed with altitude. Thereby the glacier as an algal habitat could be divided into following three altitude zones with different algal communities (Figs. 5, 7).

(1) Lower Zone (5100-5200 m a.s.l.): seven species were observed-Cylindrocystis brebissonii, Mesotaenium berggrenii, Ancylonema noldenskioeldii, Oscillatoriacean alga 1, 0. alga 2, 0. alga 3, and unknown coccoid alga. The most dominant species was Cylindrocystis bribissonii. The proportion of this species was highest in this zone (75 t 9% (SD; n = 4), the difference in the proportion between zones was statistically significant; p < 0.01).

(2) Middle Zone (5200-5300 m a.s.l.): 11 species were observed-Cylindrocystis bribissonii, Mesotaenium berggrenii,

TABLE 1

List of collected samples, algal cell density, and algal biomass

Cell density Altitude Sampling (103 cells Algal biomass

Sample Date (m) area (cm2) Condition mL-') (10-7 mL m-2)

1 11 Aug. 5100 300 Blackish cryoconite on ice, surface 256.0 409.1 2 16 Aug. 5100 150 Blackish cryoconite on ice, surface 257.0 570.3 3 23 Aug. 5100 87 Blackish cryoconite on ice, surface 189.0 694.3 4 26 Aug. 5100 230 Blackish cryoconite on ice, surface 371.0 1079.5 5 11 Aug. 5200 400 Blackish cryoconite on ice, surface 520.5 516.3 6 16 Aug. 5200 140 Blackish cryoconite on ice, surface 135.0 617.0 7 20 Aug. 5200 180 Blackish cryoconite on ice, surface 118.0 115.9 8 23 Aug. 5200 230 Blackish cryoconite on ice, surface 175.0 129.1 9 20 Aug. 5250 265 Blackish dirty snow, 5.5 cm below surface 111.0 167.6

10 23 Aug. 5250 265 Blackish cryoconite on ice, 8.5 cm below surface 450.0 296.4 11 24 Aug. 5250 375 Blackish cryoconite on ice, 7.5 cm below surface 367.5 194.8 12 11 Aug. 5300 600 Blackish dirty snow, surface 130.0 68.5 13 20 Aug. 5300 270 Blackish dirty snow, 9.5 cm below surface 83.8 45.1 14 23 Aug. 5300 265 Blackish dirty snow, 14.3 cm below surface 54.6 43.1 15 26 Aug. 5300 280 Blackish dirty snow, 7.2 cm below surface 104.0 78.3 16 11 Aug. 5350 450 Red dirty snow, surface 5.1 26.8 17 16 Aug. 5350 750 Blackish dirty snow, 3.5 cm below surface 4.4 5.2 18 17 Aug. 5350 300 Blackish dirty snow, 6.5 cm below surface 2.5 5.1 19 20 Aug. 5350 300 Blackish dirty snow, 13.0 cm below surface 4.9 13.2 20 21 Aug. 5350 274 Blackish dirty snow, 21.0 cm below surface 2.2 3.4 21 11 Aug. 5430 300 Blackish dirty snow, 7.0 cm below surface 1.2 3.8 22 16 Aug. 5430 750 Blackish dirty snow, 10.0 cm below surface 1.8 2.3 23 20 Aug. 5430 307 Blackish dirty snow, 20.0 cm below surface 0.9 1.8




(A)

100 Lower Zone Middle Zone Upper Zone

80 1

60 20

C. 40 -

20 Y

01.......-- ----J

5100 5150 5200 5250 5300 5350 5400 5450

Altitude (m)

(B) Lower Zone Middle Zone Upper Zone

30 7

25

20 7

15

10

5

5 50 68 5100 5150 5200 5250 5300 5350 5400 5450

Altitude (m)

FIGURE 7. Altitudinal change of community structure which was represented by the proportion of each algae to the total algal biomass. (A) Dominant species: Cylindrocystis br6bissonii (1), Mesotaenium berggrenii (2), Trochiscia sp. (3). (B) Undom- inant species: Oscillatoriacean alga 1 (4), Oscillatoriacean alga 3 (5), Ancylonema noldenskioeldii (6), Unknown coccoid alga (7), Raphidonema sp. (8). Other species (Chloromonas sp., Ko- liella sp., and Oscillatoriacean alga 2,) were not plotted because they were very rare (mean values

__ SD).

Trochiscia sp., Ancylonema noldenskioeldii, Raphidonema sp., Koliella sp., Chloromonas sp., Oscillatoriacean alga 1, 0. alga 2, 0. alga 3, and unknown coccoid alga. The most dominant species was Mesotaenium berggrenii. The proportion of this species was highest in this zone (46 ? 17% (SD; n = 11), the difference in the proportion of this species between zones was statistically significant; p < 0.05).

(3) Upper Zone (5350-5430 m a.s.l.): four species were observed-Mesotaenium berggrenii, Trochiscia sp., Raphidone- ma sp., and unknown coccoid alga. The most dominant species was Trochiscia sp. The proportion of this species was highest in this zone (75 ? 17% (SD; n = 8), the difference in the proportion of this species between zones was statistically significant; p < 0.01).

Each zones may provides the optimum environment for each dominant species on the glacier.

Figure 8 shows Simpson's diversity index (D) of each zone.

Lower Zone Middle Zone Upper Zone 5

4

x a 3

>2

5100 5150 5200 5250 5300 5350 5400 5450 Altitude (m)

FIGURE 8. Altitudinal change of the species diversity: Simp- son's diversity index (Begon et al., 1990) (mean values

_ SD).

The diversity index was highest in the Middle Zone. The highest value of this index in the Middle Zone is due to the largest species number and relatively large proportion of undominant species; especially Oscillatoriacean alga 1, Ancylonema noldenskioeldii, and unknown coccoid alga (Fig. 7B).

Discussion ENVIRONMENTAL FACTORS ON THE GLACIER

Figure 9 is a schematic drawing showing altitudinal change of environmental factors on the glacier, which are considered to affect the altitudinal change of algal biomass, community structure and species diversity.

Substrate Type and Stability of Meltwater

On the glacier there are two types of substrate which form frameworks of algal microhabitats: ice substrate in the ablation area and snow substrate in the accumulation area. In the ablation area below 5250 m a.s.l., algae live in the meltwater on the ice surface, in gap water between ice crystals, or in stagnant water in melt holes (cryoconite holes, small, water-filled depressions). In contrast, in the accumulation area above 5250 m a.s.l., they live in water films covering snow grains, or in gap water between them. Differences of the substrate of the habitats may affect algal growth conditions in many ways. For example, many small melt holes on the ice substrate provide a more stable water condition for algae, compared with unstable water in snow substrate area in which refreezing and draining off frequently occur.

Air Temperature and Growth Period

Air temperature on the glacier decreased linearly as the altitude increased depending on a lapse rate. During the research period, mean air temperatures on the glacier were about 1.10C at 5100 m a.s.l. and -0.90C at 5430 m a.s.l. (estimated from meteorological data collected at Kyangjing village, 3920 m a.s.l.; see Fig. 2 [Nepal Department of Hydrology and Meteorology, 1993] and a lapse rate of 0.60C 100 m-'. Difference in air temperature affects the length of melting period. Since water supply is essential for algal growth, the length of algal growth period may decrease as the altitude increase.




Lower Zone Middle Zone Upper Zone

Ablation area. Accumulation area

Ice substrate . I Snow substrate 5100m 5200m 5300m 5400m

High a >' Low

............Growth perio ."':'. :

Long a .

Short

Thin -

> Thick

--.....

Light intensity .

,, ,,

Strong - Weak

Mineral particms

Rich - Poor

FIGURE 9. Schematic drawing of altitudinal change of environmental factors on the glacier.

Snow Cover and Light Intensity

The amount of light which algae receive on the glacier dif- fers due to the thickness of the snow covering their habitats. Without snow cover on their microhabitats, they would directly receive strong light; in contrast, with snow cover, they would receive diffused weak light penetrating the snow cover. During the research period, snow fell almost every day in the higher part of the glacier, and the thickness of the snow cover increased as the altitude increased. At the beginning of the research period (11 Aug.), the lower end of the snow cover was at about 5350 m a.s.l.; at the end of the research period (26 Aug.) it was at 5200 m a.s.l. (Fig. 10).

Nutrient Conditions

Table 2 shows the results of chemical analysis of the samples. The ion levels of all samples from the glacier (2-5 in Table 2) were lower than that of the glacier lake water (1) locating lower side of the glacier (5090 m a.s.l., see Fig. 2). It means that the nutrient level of snow and ice of the glacier was very low, even compared with that of a typical oligotrophic freshwater locating a similar elevation in the same region. The table also shows that there are no difference in the ion level between the ablation area samples (2-3 in Table 2) and the accumulation area samples (4-5). The result suggests that the nutrient level in

25

20 - [ 11 Aug. 26 Aug.

E 15

-• 10

5-

5100 5200 5250 5300 5350 5430

Altitude (m)

FIGURE 10. Change of thickness of snow cover on the algal habitats with altitude.

snow and ice of the glacier does not largely change by altitude. Hoham et al. (1989) reported that concentration of S042-, NO3-, and NH4( were lower in samples containing algae compared to control samples lacking algae because the algae depleted nutrients for their growth and development in their life cycles. Our results also showed that concentration of NO3- in samples from

algal habitats (2 and 4) was lower than those of control samples without visible algae (3 and 5). This may be due to the same reason.

Since, the all samples were filtered just after sampling to eliminate impurities, these results suggest that the main nutrient sources of snow algae are organic and inorganic windblown particles deposited in their habitats; many such particles were found in the dirt layer snow of the accumulation area and the surface of the ablation area. Previous studies also reported that nutrients for snow algae were mainly supplied as windblown dust and litter (Hoham, 1976) and windblown materials from the sea (Newton, 1982). The windblown particles found in the algal habitats of the glacier contained a large number of mineral particles (80-90% in total dry weight). Since mineral particles on the

glacier decreased as the altitude increased (Fig. 11), the nutrient condition in the lower zone would be relatively richer than the

upper zone.

TABLE 2

Chemical analysis

Samplea Na K Ca Mg Cl NO3 SO4 PO4

1 0.04 0.14 2.30 0.09 0.07 0.17 0.77 ND 2 0.03 ND ND 0.01 0.10 ND ND ND 3 0.06 ND 0.12 0.02 0.18 0.01 0.12 ND 4 0.36 ND ND 0.01 0.02 ND 0.02 ND 5 0.16 ND ND ND 0.01 0.04 0.01 ND

Detection limit 0.02 0.06 0.06 0.004 0.002 0.005 0.006 0.013

a 1: glacier lake water at 5090 m a.s.l. 2: meltwater on algal habitats in the ablation area at 5170 m a.s.l. 3: meltwater of the surface ice lacking visible

algae in the ablation area at 5170 m a.s.l. 4: dirty layer snow containing algae in the accumulation area at 5350 m a.s.l. 5: granular snow lacking visible

algae at 5350 m a.s.l. All samples were filtered in the field just after collecting; ion levels in mg L-'. ND means "not detected."




100

10 E

0.1 I

5100 5150 5200 5250 5300 5350 5400 5450

Altitude (m)

FIGURE 11. Altitudinal change of dry weight of mineral particles (g m-2) contained in the algal habitats (mean values ?

SD).

BIOMASS AND ENVIRONMENTAL FACTORS

The algal biomass on the glacier decreased as the altitude increased. In particular it decreased very rapidly in the ablation area above 5250 m a.s.l. This biomass decrease was probably due to many factors; for example, the shorter growth period, the weaker light intensity, and the lower nutrient level in the higher part of the glacier. However, the light intensity seems to be the most important factor especially in the ablation area. Because, snow cover reduces light intensity exponentially (Richardson and Salisbury, 1977), and the frequency and thickness of the snow cover on the algal habitat gets larger as the altitude in- creases in the accumulation area (Table 1, Fig. 10).

COMMUNITY STRUCTURE AND ENVIRONMENTAL FACTORS

Figure 9 suggests that the algal habitats on the glacier can be divided into "ice-environment" and "snow-environment"9 (Table 3). Ice-environment represents ice substrate, much meltwater which is relatively stable, a long growth period, open exposed habitats (the algae receive strong radiation), and rela-

tively rich nutrient conditions. On the other hand, the snow- environment represents snow substrate, less meltwater which is relatively unstable, a short growth period, shaded habitats (the algae receive diffused radiation), and relatively poor nutrients. The ice-environment and snow-environment corresponded to the Lower Zone and the Upper Zone, respectively. The Middle Zone is a transition area between these two environments. In this zone, environmental conditions were not stable; the two types of conditions exchanged frequently. When snow accumulation exceeded melting and snow cover occurred at this area, the algal habitat of this area became a "snow-environment"-like condition; shaded habitat on ice or snow substrate, the amount of meltwater decrease because of the increase of the surface albedo. On the other hand, when melting exceeded accumulation and snow cover disappeared, the algal habitat in this area became a "ice-environment"-like condition, i.e., an open exposed condition in which meltwater supply increase because of the decrease of the surface albedo.

From this view point and distribution range of each species (Fig. 4), we can categorize glacier algal species into the follow-

ing four groups: snow-environment specialists, ice-environment specialists, generalists, and opportunists. The upper and middle area groups (Trochiscia sp. and Raphidonema sp.) seemed to be snow-environment specialists which were adapted to the snow- environment, because they were not found in the Lower Zone (ice-environment). The lower and middle area groups (Cylindro- cystis bribissonii, Oscillatoriacean alga 1, 0. alga 2, and 0. alga 3,) seemed to be ice-environment specialists, because they were not found in the Upper Zone (snow-environment). The all area group (Mesotaenium berggrenii and unknown coccoid alga) seemed to be generalists which were able to grow well in both the snow-environment and the ice-environment. The middle area

group (Chloromonas sp. and Koliella sp.) distributed only in the Middle Zone, seemed to be opportunists which can grow in some special set of conditions that occasionally occur in the Middle Zone.

We can explain the zonation of the three algal flora on the

glacier as follows (Fig. 7, Table 3). In the stable snow-environment of the Upper Zone, a snow-environment specialist (Tro- chiscia sp.) becomes dominant in competition with generalist species (Mesotaenium berggrenii and unknown coccoid alga). In

TABLE 3

Characteristics of algal community and environment of each flora zone

Flora zone Lower Zone Middle Zone Upper Zone

Altitude (m) 5100-5200 5200-5300 5300-5430

Dominant species Cylindrocystis bribissonii Mesotaenium berggrenii Trochiscia sp. Number of species 7 11 4

Species diversity 1.3-2.1 2.0-4.3 1.1-2.1

Environment Ice-environment Ice/Snow environment Snow-environment

Stability Stable Unstable Stable

Substrate Ice Ice/Snow Snow

Air temperature (?C)a -0.1-2.4 -1.2-1.8 -2.1-0.9

Amount of water Much Middle Little

Growth period Long Middle Short

Snow cover (cm) 0 0-7.2 0-21.0

Light intensity Strong Strong/Weak Weak

pH 4.9-5.4 4.9-5.5 5.2-5.9

Mineral particles (g m-2: dry weight) 18-68 5.8-133 0.5-9.8

aAir temperature was estimated from meteorological data (Nepal Department of Hydrology and Meteorology, 1993) collected in Kyangjing (3920 m a.s.1.) and a lapse rate of 0.6?C 100 m-'.




contrast, in the stable ice-environment of the Lower Zone, an ice-environment specialist (Cylindrocystis bribissonii) becomes dominant in competition with generalist species (Mesotaenium berggrenii and unknown coccoid alga). In the Middle Zone where the growth conditions frequently change between ice-environment and snow-environment, biomass of a generalist species (Mesotaenium berggrenii) exceeds those of specialists, and opportunist species temporally survive.

Although we have some previous reports on snow algae of the glaciers, descriptions on their distribution pattern on a glacier which can be compared with our results are very limited. In a equatorial glacier of New Guinea (Kol and Peterson, 1976), Me- sotaenium berggrenii was found both in the snow area and ice area. This species has been recorded from the ice area in Alaskan glaciers (Kol, 1942), the snow and icefield of Signy Island (Kol, 1972) in the Antarctic, and the snow areas of Spitsbergen (Kol and Eurola, 1974) in the Arctic. According to Kol (1968), Me- sotaenium berggrenii is a common species of the snow and ice fields of both Hemispheres. These reports support our assump- tion that Mesotaenium berggrenii is a generalist species which can grow in both the snow-environment and the ice-environment. In the Greenland icefield, Cylindrocystis bribissonii was abundant in cryoconite holes on the icefield of the ablation area (Gerdel and Drouet, 1960). They reported this species as C. cy- lindrospora, but Prescott et al. (1972) indicated that C. cylin- drospora is a synonym of C. bribissonii. The cryoconite of Greenland seems to have a similar structure to the dark-colored mud-like material of the Lower Zone in the Yala Glacier, in terms of consisting of C. bribissonii and mineral particles loose- ly bound by the filaments of blue-green algae. Though we supposed this species to be an ice-environment specialist, it has been reported from both in ice and area on Alaskan glaciers (Kol, 1942). Trochiscia spp. which we supposed to be a snow-environment specialist were reported in both ice and snow area on the Columbia Glacier on Alaska (Kol, 1942), but her descriptions on the habitats of these species were not clear.

It is still unclear which is the most important environmental factor that affects the algal community structure. However, the frequency and thickness of snow cover seem to be very important, because it drastically changes the light condition of algal habitats. Many studies reported that light intensity was one of the most important factors determining flora of snow algae (Fu- kushima, 1963; Garric, 1965; Kol, 1968; Pollock, 1970; Hoham and Blinn, 1979). For example, it is reported that in open exposed areas red snow mainly containing Chlamydomonas nivalis (Bauer) Wille was observed (Stein and Amundsen, 1967; Tho- mas, 1972; Hoham and Blinn, 1979), and in shaded areas (under or near tree canopies), green snow of Chloromonas nivalis (Cho- dat) Hoham et Mullet (Hoham and Blinn, 1979) and orange snow of Cryocystis granulosa Kol (Hoham, 1980) was observed. Pollock (1970) concluded that green snow was characteristic of shaded snowbanks, red snow received sunlight for at least one half of the day, and orange snow received an intermediate amount of sunlight. Thomas and Duval (1995) suggested that the habitat differences between red snow species and green snow species (sun vs. shade) were due to the differences in responses to ultraviolet radiation.

SPECIES DIVERSITY AND ENVIRONMENTAL FACTORS

Difference of species diversity among the three flora zones also can be explained by the above mentioned view. The largest species number and the highest species diversity in the Middle Zone could be explained by the presence of generalist and op-

portunist species, and the unstable condition of this area which prevents specialists from excluding other species. In contrast, under the relatively stable conditions of the Upper Zone and the Lower Zone, specialist species have enough time to occupy a large part of the resources and exclude other species, then the species number and diversity index decrease. The idea that the large species diversity in the Middle Zone is sinply due to the large variety of conditions in this area can not explain the fact that the same species, Mesotaenium berggrenii, was most dominant at all samples in this zone.

The unstable conditions of the Middle Zone were primarily due to the stability of the snow cover. For the algal community of this area, a drastic change of growth conditions by unstable snow cover could be a great "disturbance" and the highest diversity seemed to be maintained by the frequent change of the snow cover condition. In this sense, our results seems to agree with the "intermediate disturbance hypothesis" (Connell, 1978) that the highest diversity is maintained at intermediate levels of disturbance.

GLACIER ALGAE AS A SIGNAL OF CLIMATE CHANGE

The above-mentioned altitudinal zonation of the algal biomass and community on the glacier should change reflecting the local climatic condition of this region; for example, if the climate becomes cooler, algal biomass at some altitude will decrease and the Upper Zone flora will extend to a lower altitude. Thereby, algal biomass and community structure in an ice core which was annually stored in glacial strata in the accumulation area, may reflect the summer conditions of past years, and can be a new information source for the studies on past climate changes of this area. Species zonation will be an especially important information source in the analysis of ice core samples from warm- er regions as the Himalaya, in which data on chemical and iso- topic contents are not reliable because of heavily mixing.

Acknowledgments We wish to express our sincere thanks to the staffs of the

Department of Hydrology and Meteorology (DHM) belonging to the Ministry of Water Resources, His Majesty's Government of Nepal. They kindly provided us their temperature data and supported our field works. We are very much obliged to the Sherpa people and people of Langtang village who helped our works in Nepal, especially in Langtang Valley. We also thank Dr. N. Kanamori of the Water Research Institute, Nagoya Uni- versity for the chemical analysis. We appreciate Dr. Ronald Ho- ham and Dr. William H. Thomas for providing critical reviews. This study was aided by the Moritani foundation for Science (chief: Shiro Kohshima 1991), a Grant-in-Aid for Scientific Re- search (chief: Shiro Kohshima 1992, chief: Yutaka Ageta 1994, No. 06041051) from the Ministry of Education, Science, Sports, and Culture of Japan.

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Ms submitted March 1996




a community of snow algae on a himalayan glacier: change of algal biomass and community structure...

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