129

T H E H O T S P R I N G S O F G R E A T B A R R I E R I S L A N D

1. Physical measurements and chemical analysis

by T . H . Wilson* and P.R. Moore*

with interpretation by M.P . Hochstein*

S U M M A R Y

Three groups of hot springs, with maximum temperatures between 50 C and 8 4 ° C , and several warm springs (20-25°C) occur in the Kaitoke Val ley, central Great Barrier Island. The waters arc nearly neutral and contain high concentrations of sodium chloride, potassium, and calcium.

Nearly constant molecular ratios of various elements imply that the springs originate from a common source. L o w S i 0 2 and high Ca concentrations, as well as low discharge temperatures compared with inferred high reservoir temperatures, indicate that the hot water travels a considerable distance between source and springs. Most of the hot and warm springs lie on a NNE-str iking fault line or fault zone.

I N T R O D U C T I O N

The hot springs of Great Barrier Island have received little attention since the early descriptions of Hochstetter (1867), Hutton (1868), and Winkelmann (1886). A survey of the main springs in the Kaitoke Valley, central Great Barrier Island (Fig. 1) was therefore considered to be a useful project in view of the lack of data on these springs.

Mapping, measurement of temperature and flow rate, and chemical analyses of the hot springs were carried out from 21 to 27 August, 1972, during the Auckland University Field Club 50th Anniversary Scientific Camp held on the island.

H I S T O R Y A N D P R E V I O U S O B S E R V E R S

The early Maori population of Great Barrier Island is believed to have.used the springs for curative purposes (Reed, 1946). The earliest description of the Kaitoke Springs (Fig. 1) is that of Hochstetter (1867), who states (p. 3) that they "have been recently discovered" (by early settlers). Hutton (1868) has given a fuller description of the Kaitoke Springs and South Peach Tree Springs, but did not visit the North Peach Tree Springs. Later descriptions of the Kaitoke and North Peach Tree Springs are given by Winkelmann (1886), who provided the first sketch maps of the springs.

•Department of Geology, University of Auckland.

130

Quaternary alluvium

Pliocene - Pleistocene rhyolite, breccia, sinter

U. Miocene - Pliocene andesitic pyroclastics and lavas

Jurassic basement greywackes

Geology after Thompson (I960!

and Hoyter (1954)

© Kaitoke Springs

South Peach Tree Springs

<S> Nor th Peach Tree Springs

M hot spr ings ( > 2 5 t )

x w a r m springs ( 2 0 - 2 5 ° C ) o springs not located

In. present survey

Kl w a t e r samples X t r a ck

•270 height in me t re s

Fig. 1: Geology and location of hot springs, Kaitoke Valley, central Great Barrier Island. Inset: Generalised geological map of Great Barrier Island showing the area studied, and probable fault line.

131

Little interest was taken in the springs during the following years. Bartrum (1921) does not mention the springs, while Herbert (1921) gives only a limited chemical analysis o f the "Great Barrier springs" done in 1904, and classifies them (p. 171) as "calcic sodic muriated waters". Some brief comments on the springs were made by Healy (1948), but it was not until Hayter (1954) that further measurements on the springs were carried out. Hayter however, does not appear to have visited the South Peach Tree Springs during his geological mapping of the area. The latest reference, a summary of all known data on the springs up to 1971, is included in a report by Petty (1972).

The "basement" rocks of Great Barrier Island, of probable Jurassic age, consist of indurated and contorted lithic sand-stones (or "greywackes") and siltstones, and are overlain by a late Miocene to Pleistocene volcanic sequence (Fig . 1). Andesitic pyroclastics, lavas, and minor intrusions of the Beeson's Island Volcanics (upper Miocene to Pliocene) cover the basement rocks in all except the northern and central eastern parts of Great Barrier Island. Gravity anomalies (Woodward and Reil ly , 1972) indicate that the total thickness of the andesitic volcanics is probably greater than 300 m (Bartrum 1921), but less than the 3 km considered by Ramsay (1971).

The andesites were tilted up to 30 to the east before eruption of rhyolitic lavas and breccias of the Whitianga Group (Pliocene to Pleistocene). Towards the end of this latest volcanic episode, hydrothermal activity resulted in the sinter deposits of Te Ahumata (Whitecliffs) and the associated gold-silver-antimony-arsemic-selenium mineralisation (Ramsay, 1971).

A l l the hot springs of the Kaitoke Valley located in this survey occur in the Beeson's Island Volcanics (Fig. 1). However, the rocks are generally deeply weathered, and no structures could be mapped.

The structural trend of basement rocks is generally NW to N N W (Bartrum, 1921; Hayter, 1954). Beeson's Island Volcanics in the south central part of Great Barrier Island strike N N W to NW with dips between 30 -50° east (Ramsay, 1971); further to the north the strike is generally NW (Hayward, 1973). Intrusive dykes, however, strike approximately N E , "parallel to a minor greywacke fold direction" (Thompson, 1960). Pliocene to Recent NE-trending faulting is imposed upon the older N N W trend (Ramsay, 1971), and Hayter (1954) considered a concealed N N E fracture to extend along the line of hot springs. Minor N to N E faulting is recorded by Hayward (1973) along the western coastline, while inferred fault trends of 140-160° and 100-120° were noted by Ramsay (1971; p. 47) in the Iona area of Whitecliffs.

G E O L O G I C A L S E T T I N G

D I S T R I B U T I O N A N D D E S C R I P T I O N O F SPRINGS

(Grid references, e.g. 926370, refer to the 1 inch to 1 mile map, sheets N30 and N 31,1st edition, October 1953).

132

14 5° L E G E N D

•2(65°) major hot spring

50° other hot springs (max temps)

14° *53°

f30

X

water temperature

temp at 15cm depth

f low rates ( l i t re/sec)

s t ream

drainage

track

(84°)

to Kaitoke (approx 5 km)

\

5 0 metres

s lump N ?y*4(75°) /60 '

"•'•-large Puriri

"3(55°)

f1B KAITOKE SPRINGS

August 1972

N swampy ground

wall

20° 56 i swampy

ground 42"

13° _5 metres

NORTH PEACH TREE SPRINGS

swampy

38° i /37°

ground

\ ill ;ream

X 1 a. i l l * c * ii

ill - -» . . o £

metres V SOUTH PEACH TREE SPRINGS

Fig. 2: Detailed map of hot springs, Kaitoke Valley, Great Barrier Island.

133

The majority of hot springs occur at an elevation of 20-30 m above sea level along the western edge of the Kaitoke Swamp (Fig. 1). Most springs lie on a line bearing 0 3 0 ° , but the southern (933364) and most northern springs (928401, 927405) in the area studied lie off this line. The latter springs occur at an elevation of approximately 150-170 m but were not found during the present survey. The maximum distance between the known hot springs in the Kaitoke area is approximately 2 km.

To the north of the area studied no definite hot springs have been reported, but warm patches in the Harataonga Stream (5 km north-east) were noticed in the early 1930's (J . Petrie, pers. comm.), and Hayter (1954; p. 8) makes reference to a "soda spring" at Komahunga (Fonsac's Bay) approximately 6-7 k m to the north.

No warm mineralised springs are known to occur to the south of the prominent plateau of sinter and silicified sediments of Te Ahumata (Whitecliffs). However, Studt and Thompson (1969) recorded a high heat flow (3.4 x 1CT6

ca l /cm 2 sec) in a well drilled at Tryphena (N35/960275) in 1964; a maximum temperature of 34 .5°C was recorded at a depth of 207 m.

Kaitoke Springs (926370) This is the largest centre of thermal activity in the Kaitoke Valley and six

major hot springs, with temperatures ranging from 5 5 ° to 8 4 ° were located (Fig. 2). The areal extent of any one major spring is small (generally <0 .1m 2 ) and they occur either in or very near to the stream bed, which makes determination of the maximum temperature and flow rate difficult. However, the heat discharge of any one spring probably does not exceed 5 kcal/sec (Table 2); the total heat discharge of the Kaitoke Springs is estimated to be about 120 kcal/sec.

Only one spring (No. 1) showed any deposition of sinter, possibly because of more stable surroundings, and only minor rock alteration (i.e. clays) was seen (spring No . 4).

South Peach Tree Springs (930376) Hot water (maximum temperature 50°C) emerges in swampy ground at the

foot o f a small gully approximately 400 m down-stream from the Peach Tree Track crossing. The springs are easily found by following down the main stream on the right bank. No measurement o f heat discharge was possible, but it is probably about 3 kcal/sec.

North Peach Tree Springs (933383) These are the "Peach Tree Springs" of Hayter (1954). Several hot springs

were located, the maximum temperature recorded was 61 ° C , and the total heat discharge of the area was found to be about 10 kcal/sec (Table 2).

A bath dug in weathered andesite was probably constructed by gum diggers in the 1880's; it was certainly there when kauri bushmen worked the area in the late 1930's (J . Petrie, pers. comm.). The bath provides a rough approximation of the maximum rate of silica deposition, as the sides are now coated with an average 2 mm of sinter. Assuming a constant rate of deposition, with no change in acidity or chemical composition since 1930, the rate of formation of sinter is about 0.05 mm/year.

134

A sinter terrace appears to extend under swampy ground to the north, and a minimum 35 mm thickness o f sinter was measured in the stream bank. A t a rate o f deposition o f 0.05 mm/year this thickness implies that the springs have been active for at least 700 years.

Warm Springs East o f the North Peach Tree Springs and approximately 50 m downstream

(934383), a small flow o f water with a temperature of 19.5 C and a p H value of 6-7 was noted. Further to the north and approximately 300 m along the main track after crossing the "Peach Tree" stream, a small pig wallow (935385) was found which contained flowing water with a temperature of 2 0 ° C .

In the small valley immediately south of the North Peach Tree Springs, water was emerging from a swamp at 18°C, but no definite spring could be located. Proceeding further south along the main track, the next small stream was found to be supplied from a clear spring with a temperature o f 2 5 ° C (931378).

Table I: Summary of maximum temperatures of hot springs on Great Barrier Island recorded by previous observers.

Hochstetter (1867)

Hutton (1868)

Winkelmann (1886)

Jan. 1886

Herbert (1921)

1904

Hayter (1954)

This paper

August 1972

Kaitoke Springs 100°C? 93°C 86°C 83°C? >45°C 84°C

South Peach Tree Springs - 38°C - - - 50°C

North Peach Tree Springs - > 5 0 ° C 61°C - 63°C 61°C

C H E M I S T R Y O F T H E S P R I N G S

Results o f the chemical analyses of some of the hot springs are listed in Table 3, and the methods used for determination of the concentration o f the various constituents are listed in Appendix I, together with the sampling technique used. The locations of the springs sampled are shown in Fig. I.

It can be seen from Table 3 that the waters are nearly neutral sodium chloride waters with a high content of potassium and calcium. Although the springs from which samples K l , 3, 6 and N5 were taken are about 1.25 km apart, the concentration of the various constituents in these samples does not vary more than about ± 15%. From the nearly constant value of the various molecular ratios like N a / K , Na/Ca , C l / B etc. (see Table 3), it can be inferred that the thermal waters originate from a common source, and that the variation in concentration o f the various constituents is brought about by some dilution with groundwater.

If we compare the chemistry of the thermal springs from Great Barrier Island with that of hot springs from the Taupo Volcanic Zone and of thermal waters from other parts of New Zealand (Table 1 and 3 respectively by Ellis and

135

Table 2: Flow rates and heat discharge of hot springs, Great Barrier Island, August 1972.

Locality of Flow measurement (litre/sec)

(see Fig. 2)

Spring no. 3 0.03 38° 1.1 Spring no. 4 0.07 62° 4.3

Kaitoke Spring no. 5 Waterfall,

0.05* 71° 3.5*

right branch 3 13° 39 Above spring

Springs no. 5, right branch 1.8 2° 3.6 Left branch 2* 19° 38*

South Peach Tree Springs not measured - - 3*

North Peach bath 0.04 37° 1.5 Tree Springs downstream 0.44 19° 8.4

*estimated values •f the ambient temperature T ^ was taken as 13°C

Mahon, 1964), it can be inferred that the hot springs on Great Barrier Island lie somewhere between these two groups. The high concentrations of L i , Ca and Rb as well as the low N a / K ratio are similar to those found in waters from the Taupo Volcanic Zone, whereas the high concentrations of Ca, Na , and CI, are anomalous and show some similarities with the chemistry of some warm springs like those at Morere and Te Puia near the Bast Coast o f the North Island (Ellis and Mahon, 1964) and some hot springs at Mexicali (Mercado, 1966).

It is likely that some or even most o f the constituents in the thermal springs from Great Barrier Island are derived from leaching of acidic rocks (andesites and rhyolites) forming part o f a "hot water reservoir" (Ellis and Mahon, 1964, 1967). Leaching of acidic rocks by hot fluids certainly explains the presence of L i , Cs and Rb in the springs; the observed L i concentration of about 20 ppm is one of the highest observed in New Zealand thermal waters. Some other constituents might be derived from deep volcanic emanations as favoured by White (1970).

On the whole it is very likely that the thermal springs on Great Barrier Island come from a deep-reaching hot water system similar to that postulated for the geothermal fields in the Taupo Volcanic Zone, such as Wairakei, Waiotapu, Kawerau etc. A minimum temperature of 185°C can be inferred for thermal fluids o f the hot water reservoir under Great Barrier Island from the observed N a / K ratios (14.0 to 14.8), using graphs published, for example, by White (1970). Thermal fluids from the reservoir, however, must have been cooled

136

Table 3a: Analysis of hot spring waters from Great Barrier Island (concentration in ppm). For location see Fig. 1

Kaitoke Springs SPT* NPTf Kl K3 K6 S4 N5

Na+ 3508 3483 3942 3091 3291 K+ 420 418 450 360 400 Li+ 20 20 22 14 18 Cs+ 2.4 2.3 3.0 1.6 2.3 Rb+ 5.0 4.5 3.8 2.6 4.0 B 8 8 9 7 8 C a * 540 540 570 460 55 0 M g 2 + 2.2 2.2 2.4 2.0 2.2 F e 3 + 4 4 4 4 4 S i0 2 150 150 160 140 150 F ~ 1.51 1.51 1.47 1.26 1.28 H C 0 3 " 120 115 128 100 110 CI 6839 6732 7376 5729 6588 c o 2 22 22 22 22 22 A l 3 + 0.2 0.2 0.2 0.2 0.2 s o 4

2 " 3.3 3.3 3.3 3.3 3.3 NHj 0.4 0.45 0.45 0.3 0.4 H 2 S 0.14 0.14 0.14 0.12 0.12 As <0.1 <0.1 <0.1 <0.1 <0.1 Ag 0.06 — — — 0.06

Total dissolved solids 11800 11800 12050 9630 11600

PH 6.9 6.9 6.9 6.9 6.9 T(°C) 59° 65° — 50" 55°

Table 3b: Molecular ratios

Kaitoke Springs SPT* NPTf K l K3 K6 S4 N5

Na/K 14.2 14.2 14.9 14.6 14.0 Na/Ca 11.3 11.2 12.0 11.7 10.4 Ca/Mg 14') 149 144 139 152 Cl/B 260 260 250 250 25 0 Cl/F 2430 2390 2690 2440 2760

* SPT South Peach Tree Springs t NPT North Peach Tree Springs

137

700

300

Fig. 3: Concentration of S i 0 2 in thermal waters in relation to temperature (after Fornier and Truesdell, 1970).

significantly before coming to the surface. This would explain the low S i 0 2

concentration of about 150 ppm, which according to Fig. 3, points to an average temperature o f about 150°C to 160°C for the water somewhere between the reservoir and the springs (Mahon, 1966; Fournier and Truesdell, 1970). These temperatures would also explain the high Ca concentration, which presumably comes from leaching o f rocks outside the reservoir.

It is of interest to note that some gas occurred in spring N o . 5 (Kaitoke Springs); the gas was found to contain 16.8% of C 0 2 at normal temperature and pressure.

It seems likely that the hot springs of the Kaitoke area occur along a concealed NNE-trending fracture as suggested by Hayter (1954). The "soda spring" of Komahunga and the sinter plateau of Te Ahumata also lie on this line (Fig . 1). North-cast trending tectonic features are largely of post-Pliocene age, and the sinter and silicified sediments of Te Ahumata have been dated to be of approximately upper Pliocene-lower Pleistocene age (Ramsay, 1971). Hence, it is possible that hydrothermal activity on Great Barrier Island had already begun in the lower Pleistocene.

The remarkably high A g content of the Recent hydrothermal springs allows the postulation of a continuous mineralizing period for silver in the wake of rhyolitic volcanism on Great Barrier Island since the Pliocene (H.W. Kobe, pers. comm.).

The source of the thermal waters discharged in the Kaitoke area possibly lies at depth somewhere under the centre of the island, where zones of high permeability, in connection with intrusive contacts or fracture zones, provide channels for the upward movement of the hot fluids, which might rise up to the water table somewhere underneath the outcropping rhyolites (Fig. 1). From here

D I S C U S S I O N O F R E S U L T S A N D C O N C L U S I O N S

138

the hot water presumably flows towards the coast in the direction of the hydraulic gradient and some of it comes to the surface along an inferred fault or fault zone bordering the Kaitoke Swamp. This explanation involves a rather long path between reservoir and discharge area, which would explain the relatively low temperature of about 150°C for fluids along this path as inferred from the S i 0 2 content of the waters (such temperatures would also explain the relatively high Ca content), whereas much higher temperatures of at least 185° to 2 3 5 ° C can be inferred for the fluids in the convective column of the reservoir from the N a / K ratios. The discrepancy between temperatures inferred from S i 0 2 content and N a / K ratio makes it unlikely that the hot springs in the Kaitoke area are derived from a source lying more or less beneath the springs.

It is possible that temperatures up to 34 .5°C at a depth of 207 m found in a well drilled at Tryphena ( G . E . K . Thompson, pers. comm.), about 10 km SSE from the Kaitoke Springs, are caused by some horizontal flow of thermal waters, although a regional high heat flow might also explain these temperatures.

A C K N O W L E D G E M E N T S

The authors wish to thank the following: The Geology Department, University of Auckland for use of facilities; Mr J . C . M . Devereux, Otara Fertiliser Research, for assistance and use of a single ion electrode for fluorine determination; Mr J . Pybus, Auckland Hospital, for use of an Atomic Absorption apparatus; Mr G . E . K . Thompson, Geothermal Laboratory, DSIR, Taupo, for information on the well drilled at Tryphena; Dr P . M . Black for critically reading the manuscript; Dr 1I.W. Kobe for comment on the silver concentration; and finally Messrs James Petrie, Maramarua, for discussion on the area and Mike Quilter for valuable assistance in the field.

REFERENCES

Bartrum, J.A. 1921: Notes on the geology of Great Barrier Island, N.Z. Trans Roy. Soc. N.Z. 53: 115-27.

Ellis, A.J . ; Mahon, W.A.J. 1964: Natural hydrothermal systems and experimental hot water/rock interaction (Part 1). Geochim.Cosmochim.Acta 28: 1323-57.

Ellis, A.J . ; Mahon, W.A.J. 1967: Natural hydrothermal systems and experimental hot water/rock interactions (Part 11). Geochim.Cosmochim.Acta 31: 519-38.

Fournier, R.O.; Truesdell, A .H. 1970: Chemical indicators of subsurface temperature applied to hot spring waters of Yellowstone National Park, Wyoming, U.S.A. U.N. Symposium Development Utilisation Geothermal Resources, Pisa. Geothermics (special volume)

Hayter, I.B. 1954: The geology of the southern and part of the central portion of Great Barrier Island. Unpublished M.Sc. thesis, University of Auckland.

Hayward, B.W. 1973: A nole on the geology of the coastline west of Whangaparapara, Great Barrier Island. Tane 19 (this volume)

Healy, J. 1948: Thermal springs of New Zealand. Unpublished report, N.Z. Geological Survey File.

139

Herbert, A.S. 1921: "The hot springs of New Zealand" London. 284pp. Hochstetter, F. von 1867: "New Zealand" Stuttgart, 515pp. Hutton, F.W. 1868: Report on the geology of Great Barrier Island. Rep. Geol. Explor. Geol,

Surv. N.Z. 5: 1-7. Mahon, W.A.J. 1966: Silica in hot water discharged from drill holes in Wairakei, N.Z.

N.ZJ.Sci. 9: 135-44. Mercado, S. 1966: Aspectos quimicos del aprovediamiento de la energia geotermica Campo

Cerro Prieto, B.C. Simposium de la 4a. reunion de Sptes. Quimicos. Mexico, D.F. Petty, D.R. 1972: Springs of the Auckland Region. N.Z.G.S. Report 57. Ramsay, W.R.H. 1971: Geology of South Central Great Barrier Island. Unpublished M.Sc.

thesis, University of Auckland. Reed, A .H . 1946: "Great Barrier, Isle of enchantment". Reed, Wellington. 56 pp. Sellin, R.H.J. 1969: "Flow in channels" Macmillan. 149 pp. Studt, F.E.; Thompson, G.E.K. 1969: Geothermal heat flow in the North Island of N.Z.

N.ZJ.G.G. 12(4): 673-83. Thompson. B.N. 1960: Sheet 2B, Barrier (1st Ed.) "Geological map of New Zealand

1:250,000". D.S.I.R. Wellington, N.Z. White, D.E. 1970: Geochemistry applied to the discovery, evaluation, and exploration of

geothermal energy resources. U.N. Symposium Development Utilisation Geothermal Resources, Pisa. Geothermics (special volume).

Winkelmann, C P . 1886: Notes on hot springs nos. 1 and 2 Great Barrier Island, with sketches showing the temperature of the waters. Trans. Roy. Soc. N.Z. 19: 388-92.

Woodward, D.J.; Reilly, W.I. 1972: Sheet 2 Whangarei "Gravity map of New Zealand, 1:250,000" D.S.I.R., Wellington, N.Z.

A P P E N D I X 1

M E T H O D S U S E D IN S U R V E Y O F H O T S P R I N G S , G R E A T B A R R I E R I S L A N D

(1) Mapping and temperature measurements Maps (Fig. 2) are based on a tape and compass survey. A l l major springs

and most o f the minor springs were recorded, and their maximum temperature measured. Temperatures of streams were averaged where several measurements were made.

Temperatures of springs were measured with mercury thermometers, and in places with a 100°C dial thermometer (bimetallic strip type).

(2) Flow rate measurements Most flow rates were determined using graduated containers and a watch.

Other measurements were made using a V-notch weir constructed from galvanised iron sheet with a 6 0 ° notch and flow rates were calculated using an empirical formula given by Sellin (1969).

140

(3) Sampling of springs Water samples were taken from major springs which were discharging

above the main streams (Fig . 2). The water was collected in a plastic beaker and immediately transferred to a clean polythene bottle for later analysis in the laboratory, and also into glass ware for determinations of C 0 2 , H C 0 3 , H 2 S , and p H in the field.

(4) Chemical analyses

Element or compound

Total dissolved solids

Na, K , L i , Rb

Cs,Ca,Mg

B

F

CI

Silica

H C 0 3

Method

Evaporation in tare platinum basin with heating in muffle and subsequent weighing

Flame photometer

Atomic absorption on Techtron 5

Colorimetry, using quinalizarine

Single ion electrode

Titration with silver nitrate

Colorimetry, using molybdenum blue (confirmed gravimetrically)

Distillation and Nesslerisation Acid/base titration, in field

Turbidimetry

Colorimetry, using K C N S

Gutzeit method

Iodine titration in field

Colorimetry, in field

141

T H E H O T S P R I N G S O F G R E A T B A R R I E R I S L A N D

2. The Ultrastructure of Oscillatoria amphibia Agardh.

by J.P. Chalcroft*

S U M M A R Y

Light and electron microscopic investigations were made into the structure of the predominant blue-green alga found in the warm stream fed by the Kaitoke hot springs.

The motile filaments displayed several unusual ultrastructural features:

(1) Elaboration of the inside of the L 4 layer of the cell wall by a layer of fine microtubules aligned along the filament. (2) A conspicuous sheath of longitudinally aligned microfibrils apposed to the outside of the L4 layer. (3) Photosynthetic lamellae arranged in three loosely-stacked bundles of parallel sheets which are apparently associated with mesosome-like structures at the plasmalemma. (4) A regularly-spaced series o f electron-dense structures which bridge the spaces between the lamellae.

I N T R O D U C T I O N

A continuing source of fascination for visitors to many thermal spring areas is the often prolific growth of blue-green algae in pools and streams too hot for comfortable immersion of hands or feet. Many scientific studies on thermophilic blue-green algae have been reported from such widely separated regions as the U . S . A . , Iceland, and New Zealand. A recent review of such studies has been published by Castenholz (1969).

The ultrastructure of Myxophyceae, (blue-green algae), is of considerable interest. The Myxophyceae are not true algae, but share, in common with bacteria and actinomycetes, the prokaryote level o f cellular architecture, i.e. they lack membrane-bounded nuclei and discrete compartmentalized organelles such as mitochondria and chloroplasts. Photosynthesis in the Myxophyceae is carried out by sheets o f membraneous lamellae lying free in the cell cytoplasm. Indeed, apart from the presence of a multilayered cell wall enveloping the plasmalemma (true cell membrane), the structure of the blue-green algal cell has much in common with that o f the higher plant cell chloroplast. The ultrastructure of the Myxophyceae has been reviewed by Lang (1968).

During the visit by Auckland University Field Club to Great Barrier Island in August 1972, mats of a conspicuous and locally common species of blue-green

* CI- P.O. Box 9002, Hamilton North.

142

alga were sampled from the stream bed in the Kaitoke hot springs area [see accompanying paper by Wilson and Moore (1973)] . These mats proved to be 'unialgal' and were composed of a weft o f Myxophycean filaments. The component organism has been identified as Oscillatoria amphibia Argadh, (Schizothrix calcicola Argadh. in the revised classification of Drouet (1968) ). It has previously been reported from New Zealand at Tokaanu.

Light and electron microscopic observations were performed on this material, and the results are presented here.

E C O L O G I C A L N O T E S

The Kaitoke hot springs area is unusual in two respects.

(1) The thermal effect o f each hot spring is limited in area to the outlet and surrounding ground to a distance of about one metre or less. There is no denudation of vegetation and the springs can often be overlooked by a casual observer. For this reason, much of the springs and warm stream area is heavily shaded. The predominant vegetation is regenerating bush (including Leptospermum scoparium J .R. et G . Forst, and Phyllocladus trichomanoides D . Don) , or dense stands of the fern Gleichenia flabellata R. Br. A t most locations in the warm streams, variations in light intensity occur continually due to interplay between the shading by large plants and the varying angle subtended by the sun. Illumination of the stream wil l tend to be low and inconstant. (2) The hot springs at Kaitoke arise beside or in the stream beds. There is thus an extremely steep thermal gradient from the springs to the water o f the streams. The thermal environments available are either those of the springs, which are generally too hot for many Myxophyceae, or that o f the stream, which would be expected to fluctuate considerably from season to season depending on the rainfall and consequent dilution of hot springs water by surface run-off.

Because of variations in light intensity, temperature, nutrient concentrations and water-flow rate, the photosynthetic organisms capable of colonizing the stream would be restricted to those with wide physiological tolerances, or those with lower tolerances but an ability to migrate to favourable regions. O. amphibia belongs to the latter class, and possesses another important attributem the ability of the filaments to intertwine into mats or wefts. The survival value of moti l i ty and weft formation for thermophilic Myxophyceae, especially Oscillatoria, has been discussed by Castenholz (1967, 1968). In summer, the mats of Oscillatoria at Kaitoke are usually extensive enought to form large curd-like masses on the surface of the main pool when it is used by bathers.

In the course of this investigation it was noted that the 'alga' was restricted to pockets in the stream bed where temperature ranged from 34 to 4 2 ° C. These pockets were usually associated with local hot water seepage, so it is possible that the organism is seeking a constant high supply of mineral salts rather than an optimum temperature.

Chemical analyses of some ions and dissolved gases of biological interest were carried out by Mr T. Wilson at the points where the two tributary warm streams

143

enter the Kaitoke bathing pool. These points were close to the regions where Oscillatoria was growing. The results for both stream branches are presented in Table 1.

M A T E R I A L S A N D M E T H O D S

Pieces of the dark-green mats found in the warm stream bed at the Kaitoke hot springs area were removed and transferred to plastic-capped 15 ml . phials filled wi th spring water. Pieces o f the mat were later observed with phase-contrast and bright field microscopy as simple water mounts covered with a slip. Despite considerable motil i ty of the filaments, some were photographed using a Leitz Orthoplan microscope with Orthomat camera. Some material previously fixed with osmium tetroxide was also used, but internal cell details were rendered less distinct after fixation.

For electron microscopy, the most satisfactory way to prepare filaments free from most grit and debris was to allow the organisms to grow in the capped phials maintained at about 4 0 ° C. and high light intensity. Several pieces of capillary tube were placed vertically in the phials, and, after several days, these were covered with a continuous weft o f Oscillatoria almost completely free from other micro-organisms, except a few bacteria. The capillary tubes were then removed and carefully scraped to remove the filaments. The scrapings were then treated with a 1% solution of osmium tetroxide in veronal acetate buffer at pH7.2, and from this stage, the preparative method for bacteria of Ryter and Kellenberger (1958) was followed. The material was dehydrated in acetone, then embedded in Epon , according to established practice (Kay, 1965). Thin sections were cut, then stained with uranyl acetate followed by lead citrate (Reynolds, 1963). Electron microscopy was performed using a Philips E M 2 0 0 instrument operated at 80 k V .

R E S U L T S

Under the light microscope the green mats from the stream were seen to consist of a tangled web of unbranched trichomes (filaments). Trichomes had a diameter of 2.5ju and an average length of 800u. N o sheaths were evident (Fig. 1). They were usually slightly curved, and demonstrated considerable gliding moti l i ty . Each trichome appeared to have a preferred direction of movement, although this could be reversed after a short time lag by repositioning the microscope field diaphragm within the object field. Trichomes were positively phototactic under these conditions. When trichomes were observed on the capillary tubes in the phials (using a stereoscopic microscope) oscillatory movements often involving considerable lengths of the filament were noted. Large numbers of trichomes dropping off the algal weft were presumably replaced by migration and rapid cell growth of those remaining.

When observed at high magnification, delicate septa could be recognised along the trichomes, spaced at 4 to 6/jl. Invaginations were not observed at the septa (Fig. 1). Conspicuous refractile cyanophycin granules were often present in the

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cells near the septa. Commonly, a granule was present on each side of a septum. A uniform diameter was maintained along the entire trichome, including the terminal cells which were merely rounded, not tapered at the extremities. Heterocysts were not present.

Thin sections of embedded trichomes examined by electron microscopy showed the basic cell architecture typical of the filamentous Myxophyceae (Figs. 2 & 3 ) .

The cell wall consisted of several well-differentiated layers distal to the plasmalemma. These wil l be described with reference to the numerical system of designation introduced by Jost (1965).

( L I ) A n innermost unstained layer about 10 nm. wide. (L2) A densely-stained layer about 6 nm. wide which showed no undulations, in

contrast to the plasmalemma and outermost wall layer. This was the central layer in the cell septum and, when favourably oriented, appeared double in the septum region.

(L3) A second unstained layer about 10 nm. wide. This and outer layers did not contribute to the structure of the septa.

(L4) (a) A moderately densely-stained amorphous layer about 10 nm wide. When favourably orientated, the layer seemed to contain very fine microtubules aligned almost parallel to the trichome axis (Fig. 5). These tubules had approximately the same outside diameter as the thickness of the plasmalemma unit membrane (i.e. 7nm.) and the diameter of their unstained lumens w •:> about 4 nm. These microtubules were apparently attached or fused to the next layer, L4(b) .

(L4) (b) A triple-layered structure with the general dimensions and staining properties of the typical unit membrane. The outermost leaflet stained slightly more heavily than the inner. The middle leaflet did not stain. This layer showed marked and frequent undulations when longitudinally sectioned in any direction, and often appeared to touch Layer L 2 .

Fig: 1. Bright field light micrograph of part of a trichome of O. amphibia. Note the rounded terminal cell and cyanophycin granules situated on each side of the septam. Magnification x 1020.

Fig: 2. Transverse ultrathin section of a trichome, showing the triangular orientation of the thylakoid stacks. Note mesosome (lamellasome) M. Ribosomes, and a cyanophycin granule occupy the centre of the cell. Magnification x 20,000.

Fig: 3. Longitudinal section of part of a trichome showing wall and sheath, W, a septum between cells, S, and the centrally situated nucleoplasm^ region, N. Magnification x 10,000.

Fig: 4. Grazing longitudinal section through sheath and cell wall layers Note the approximately longitudinal orientation of the sheath layer elements. Magi ation x 75,000.

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External to the cell wall layers was the sheath, which also displayed a layered ultrastructure. Because of the constancy of the sheath layers in this organism, it is thought desirable to label them numerically progressing distally from the cell wall in a manner analogous to the scheme used in cell wall nomenclature.

(51) A layer o f unstained material with an apparently globular substructure about 8 nm. thick.

(52) A thin stained layer about 5 nm. thick. (53) A second unstained layer with globular substructure, about 9 to 10 nm.

thick. (54) A relatively densely-stained layer about 6 nm. thick which, in trichomes

sectioned transversely (Figs. 2 and 5), or at angles grazing the sheath layers (Fig . 4), appears to consist of fine longitudinally oriented microfibrils.

Beyond the S4 layer were wisps of densely-stained material which were probably the remnants of the slime layer.

In many trichomes sectioned longitudinally, evidence of the so-called junctional pores (Lang, 1968) could be seen. These appeared as less densely-stained regions of the L 2 layer (Fig . 6). The pores were arranged in single rows about the trichome circumference on either side and adjacent to the septa. Two such girdles of pores are shown in Fig. 7 where an almost longitudinal surface section has grazed the septum of a trichome. Pore diameter of about 15 nm. and a spacing of about 25 nm. were observed.

Fig: 5. Highly magnified transverse section of a trichome showing details of cell wall and sheath structure. Arrows indicate two microtubules visible in the L4a layer. Magnification x 80,000.

Fig: 6. Highly magnified longitudinal section through a trichome. The arrows point to the two regions of lower electron density in the L2 layer close to the septum which correspond to the two rows of junctional pores girdling the trichome. The pair of parallel lines indicates the presumed cutting direction for the thin section of fig. 7. Magnification x 40,000.

Fig: 7. Oblique section through a trichome at the edge of a septum. Evidence of two rows of junctional pores (one in each cell) is visible. The conspicuous membrane seen transversely sectioned in places is the L4b layer. Magnification x 48,000. Fig: 8. Transversely sectioned trichome. Arrow indicates a typical interthylakoid bridge. Other bridges are visible nearby. Magnification x 25,000. Fig: 9. Longitudinal central section of a trichome, showing two cyanophycin granules on either side of a septum. Note regions of unstained material between granules and septum. Magnification x 26,000.

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of about 1 5 nm. and a spacing of about 25 nm. were observed. The itoplasmic cylinder of 0. amphibia was bounded by an undulating

plasnr 'e: la, which at intervals was associated with structures resembling bacterial , ^sosomes (lamellasomes). The lamellasomes also appeared to be connected with some of the photosynthetic lamellae. In longitudinal sections the photosynthetic lamellae (thylakoids) which occupied the greater part of the cell volume, appeared as spaced parallel sheets running from one septum to the next. In transverse sections the sheets were seen to be not simply arranged as coaxial cylinders, but rather three separate stacks in a triangular formation, the lamellasomes. then situated at the comer: (Fig. 2). Each stack consisted of about six to eight thylakoids in the specimens studied. Thylakoids consisted of pairs of closc^ apposed unit membranes giving a total thickness of about 20 nm. The electron-microscopical evidence on the structure and orientation of the thylakoids tends to suggest that they were derived by invagination of the plasmalemma only at the septa to form the triangular set of vesicles concon .n" ant with, or followed by, flattening and opposition of the vesicle membrane . to form photosynthetic lamellae. Spaces between the thylakoids were occupied by poorly stained material which appeared as circular profiles with dark centres in trichomes sectioned transversely (Fig. 8). This material was interpreter lo be glycogen. Similar structures have been named polyglucoside granules b Lang(1968).

Situate J ' rela' ' ly regulai intervals alon? the spaces between adjacent thylakoids , ore uft bserved darkly stained budging structures (Figs. 2, 8 and 9). Structure; resemoling ribosomes, bm iii nig slightly less censely, were closely apposed to the thylakoids; these . . re joined across the interthylakoid spaces by a column c moderately i ined .>.ai.e.ial. These "mtcrthvlakoid bridges" hau diameters i about 2 nm.. lengths f 50 nm., and often appeared to be positioned in reg r across ,. sta< of ' :yi^coids. Their spacing ranged upward from o0 nm. an icy were not always visible between thylakoids. The relatively unstained glycogen rosettes accumulate, between the bridges.

Randomly scattered on the inner or outer periphery of the thylakoid system were very densely s tah?d spherical bodies which were reminiscent o f chloroplast plastoglobuli ( l ipid granules).

The remaining axial regi u o f the cell .void of thylakoids contaii J the following cell organelles: — A t the centre of the cell, but extending most of the distance to the poles, was the nucleoid. The fibrous tangle of D N A stiands was intermingled with ci n ips of densely stained ribosomes and occasional small "empty" vesicles (Figs. 3 and 8). Close to the poles were dens y-stained large spherical globules which showed considerable evidence o f tubular substructure (Fig. 9). These correspond to the so-called cyanophycin granules (Lang, 1968). The granules of O. amphibia were commonly separated from the septum by a region containing unstained material.

D I S C U S S I O N

The results of the chemical analyses presented in Table 1 must be regarded as spot readings only, as no data on the range of values expected over a long period

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of time can be given. They are primarily included as a guide for possible future studies in the Kaitoke hot springs area. The pH values and temperatures are well within the limits tolerated by thermophilic Myxophyceae. The p H of the stream was the same as that of the hot springs, hence it would not be expected to vary with the season. The commonly accepted upper temperature limit for photosynthetic blue-green algae is 7 4 ° C. and their lower p H limit is approximately pH6.

Copeland (1936) has remarked that at Yellowstone O. amphibia has been found at temperatures ranging from 2 7 ° C. to 4 9 ° C . in waters ranging in p H from 8.1 to 8.95, but there is no evidence that it endures high temperatures. The only published study on the effect of pH on the "algal" population in a New Zealand thermal area was that carried out by Brock and Brock (1970), at Waimangu Cauldron near Rotorua.

The ultrastructure of O. amphibia has not, to my knowledge, been studied previously. It differs from the published fine structure of other members of the genus Oscillatoria sufficiently in some respects, to warrant discussion.

The presence of demonstrable longitudinally-oriented wall microtubules and sheath microfibrils would appear to be relevant to any theories concerning gliding and oscillatory movements in the Myxophyceae. Various theories of motility propounded include mucilage secretion from the junctional pores, or a combination of possible asymmetric electrostatic fields at each pore, and contracting elements in the cytoplasm (Lang, 1968). Lamont (1969) has reported the presence of extracellular microfibrils lying roughly parallel to gliding stream-lines in two species of Oscillatoria which both execute screw-like gliding motion, but in opposite senses. Halfen & Castenholz (1970, 1971) have considered the problem of gliding motility at length in relation to their own ultrastructural findings with Oscillatoria princeps, Vauch. In frozen etched preparations and grazing sections of the ceil wall of this organism they demonstrated evidence for a parallel array of fibrils about 6 to 9 nm. wide, helically oriented to the trichome axis in the right hand sense with a pitch angle Table 1: Analyses of the two branches of the stream in the Kaitoke springs region where they enter the bathing pool.

True left-hand branch True Right-hand branch

Temp. ( °C) 32.0 35.0

pH 6.9 6.9

Dissolved O 2 6.0 6.5 (ppm)

Nitrate 0.5 0.5 (ppm)

Bicarbonate 46.0 48.0 (ppm)

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of 60 degrees, and suggested that they lay on the surface of the L 2 cell wall layer. When they investigated O. animalis A g . using the same techniques, they demonstrated a similar array of fibrils, this time oriented in a left hand helix at 60 degrees. The sense and angles of the fibrils observed correlated well with the observed rotations of the filaments during gliding. Halfen and Castenholz favour the theory advanced by Jarrosch (1964), that gliding is produced by undirectional waves of bending in the fibrils which act against the sheath or substrate, thus displacing the trichome.

O. amphibia appears to display oriented extracellular fibres at least as well as other species so far reported in the literature. O f special interest is the fact that in this species the fibrils seen were not noticeably skewed to the trichome axis. The question o f sense and magnitude of any rotation in O. amphibia is a subject for future study, since no microscopical studies and measurements were made on live material with this problem in mind. It was however noted that the trichome appeared to describe a slow right-handed helix o f unknown pitch during gliding, which is difficult to relate to the longitudinal orientation of the fibrils.

The demonstration of five separate layers in the cell wall of O. amphibia is of interest regardless o f any functional considerations for motil i ty. Jost (1968), in his investigation of the ultrastructure of O. albescens D C , demonstrated only four cell wall layers, equivalent to layers L I , L 2 , L 3 and L4(b) of O. amphibia. However, his preparative technique, involving permanganate fixation, may have been unable to preserve the delicate layer o f microtubules, i f they had existed in O. rubescens.

The orientation of thylakoids in triangular sets of stacks in O. amphibia contrasts wi th the radial orientation demonstrated for O. rubescens (Jost, 1965), and O. chalybea Mert. (Giesy 1964).

The poorly stained deposits situated between the thylakoids probably consist of glycogen, as has been demonstrated in the case of the blue-green alga Nostoc muscorum by Chao & Bo wen (1971).

The significance of the electron dense "bridges" spanning the spaces between many adjacent thylakoids remains an enigma. Similar bridges are illustrated in the paper by Chao & Bowen (1971) on Nostoc. It is tempting to speculate that they might represent a spacing or scaffolding structure to ensure optimum interaction between thylakoids and metabolites, and hence maximum biochemical efficiency.

A C K N O W L E D G E M E N T S

The author wishes to thank Messrs T . H . Wilson and P.R. Moore for the use of their chemical data during the preparation of this paper; Mr N . G . Lect for assistance wi th the electron microscopy preparations; Professor V . J . Chapman for the identification of the Myxophycean organism as Oscillatoria amphibia and Stephen Chalcroft for proof reading and constructive criticism.

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REFERENCES

Brock, T.D.; Brock, M.L. 1970: The algae of Waimangu Cauldron (New Zealand): Distribution in relation to pH. J. Phycol. 6: 371-5.

Castenholz, R.W. 1967: Aggregation in a thermophilic Oscillatoria. Nature. 215: 1285-6. Castenholz, R.W. 1968: The behaviour of Oscillatoria terebriformis in hot springs. J. Phycol.

4: 132-9. Castenholz, R.W. 1969: Thermophilic Blue-Green algae and the thermal environment.

Bacteriological Reviews. 33(4): 476-504. Chao, L.; Bowen, C.C. 1971: Purification and properties of glycogen isolated from a

blue-green alga Nostoc muscorum. J. Bacteriol. 105(1): 331-8. Copeland, J.J. 1936: Yellowstone thermal Myxophyceae. Ann. N.Y. Acad. Sci. 36. Drouet, F. 1968: Revision of the classification of the Oscillatoriaceae. Acad. Nat. Sci.

Philadelphia. Monograph 15: 370pp. Giesy, R.M. 1964: A light and electron microscope study of interlamellar polyglucoside

bodies in Oscillatoria chalybia. Am. J. Bot. 51: 388-396. Halfen, L .N. ; Castenholz, R.W. 1970: Gliding in a blue-green alga. A possible mechanism.

Nature. 225: 1163-5. Halfen, L .N. ; Castenholz, R.W. 1971: Gliding motility in the blue-green alga Oscillatoria

princeps. J. Phycol. 7: 133-145. Jarrosch, R. 1964: Gleitbewung und torsion von Oscillatorien. Osterreich Bot. J. Ill:

143-8. Jost, M. 1965: Die Ultrastruktur von Oscillatoria rubescens D C . Arch. Mikrobiol. 50:

21 1-245. Kay, D.H. 1965: Techniques for Electron Microscopy (2nd edition). Blackwell Scientific

Publications, Oxford. 549 pp. Lamont, H.C. 1969: Shear-oriented microfibrils in the mucilaginous investments of two

motile oscillatoriacean blue-green algae. J. Bacteriol. 97: 350-361. Lang, N.J. 1968: The fine structure of blue-green algae. Ann. Rev. Microbiol. 22: 15-46. Reynolds, E.S. 1963: The use of lead citrate at high pH as an electron opaque stain in

electron microscopy./. Cell Biol. 17: 208-212. Ryter, A. 1958: Etude au microscope electronique de plasmas contenaut de l'acide

desoxyribonucleique. 1. Les nucleoides des bacteries en croissance active. Z. Naturforsch. 13B: 597-605.

Wilson, T.H.; Moore, P.R. 1973: The Hot Springs of Great Barrier Island. 1. Physical measurements and chemical analysis. Tane 19 (this volume)

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T H E H O T S P R I N G S O F G R E A T B A R R I E R I S L A N D

3. A Note on the Possible Occurrence of Pathogenic Amoebae in the Hot Springs Bathing Pools.

by J.P. Chalcroft.*

I N T R O D U C T I O N

In recent years, public attention has been drawn to the question of the safety of thermal swimming pools in the North Island of New Zealand, following a series o f deaths of young people soon after they had swum in certain thermal pools near Rotorua. The disease contracted by these unfortunate individuals was diagnosed as primary amoebic meningoencephalitis by Mandal et al. (1970). These authors suggested that the pathogen belonged to the order Myxomycetales (slime moulds). However, in a recent review of the subject of pathogenic soil amoebae, Culbertson (1971) has suggested that the details reported in the four case histories presented by Mandal et al. (1970) point to the pathogen being Naegleria sp. a free-living soil amoeba with a recognised ability to become a pathogen under suitable conditions.

Carter (1970) has described in detail the pathological changes induced in mice following experimental infection with Naegleria isolated from two human victims of primary amoebic meningoencephalitis. The sensitivity of his method was such that typical disease symptoms developed in a mouse into which only about forty amoebae were inoculated.

During the visit to Great Barrier Island in August 1972, samples were taken from the hot bathing pools at Kaitoke and North Peach Tree springs in order to test for the presence of pathogenic strains of Naegleria using the experimental pathology techniques of Carter (1970).

E X P E R I M E N T A L P R O C E D U R E

Ten female albino mice about two months old were kindly provided by the Small Animal Dept. Ruakura Agricultural Research Centre, Hamilton. The animals were fed food pellets and water ad libitum for the duration of the experiment. They were housed in a warm room except for the period of one week while they were on the island, where only very basic comforts could be provided. On the return trip to the mainland they were subjected to altitudes ranging to 700 m, unpressurized, for an hour.

On the last day of my visit to the island, and again at Hamilton two weeks later, each mouse was separately anaesthetized with ether and placed ventral side uppermost. While still lightly anaesthetized, several drops of a warm, freshly-shaken suspension of debris and silt in pool water were placed on its nose

*P.O. Box 9002 Hamilton.

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so that they were drawn completely into the nasal cavities during breathing. The mice were then placed back into their box to regain consciousness. Two groups, each of five mice, were used. One group was treated with a suspension from North Peach Tree Springs pool , the other group with a suspension from the Kaitoke Springs pool . N o uninoculated control group was used since the results of successful infection by pathogenic amoebae would be unequivocal, ter­minating with death at seventy-two hours after infection (Carter, 1970). Diagnosis o f the cause of any deaths was to be made by examination of the animal's cerebro-spinal fluid for amoebae, thus enabling detection of any false positive results.

In a separate experiment at Hamilton two mice were intranasally inoculated with a prolific growth of an unidentified amoeba discovered grazing on a culture of Kaitoke hot pool Oscillatoria growing in a capped phial. The inoculation method was the same as that used with the mice taken to Great Barrier Island.

R E S U L T S

After inoculation, the mice were kept under observation for one week, when they were again inoculated with further samples from the warm pools, which had been kept in warmed sealed phials in the laboratory. After a further week, the mice were progressively culled for other research purposes over a two week period. During the total period after first inoculation of about four weeks, no mouse showed symptoms of any disease, so the tests for pathogenic amoebae at the Great Barrier hot pools sampled arc regarded as negative.

The experimental inoculation of two mice with samples containing the herbivorous amoeba also gave negative results. These mice were kept for a fortnight after inoculation.

D I S C U S S I O N

Too much reliance should not be placed on the results of the simple screening experiment described, as the number of mice and number of samples from each pool are far too small to constitute a statistically significant sample. Secondly, as I was not able to provide a second control in the experiment by treating another group of mice with a sample of known pathogenic Naegleria, an element of doubt remains concerning the efficiency of my inoculation technique and the possibility of these mice having a natural resistance to amoebic infection. In this type of experiment, a negative result is always less significant than a positive one, regardless o f sample size, therefore visitors to the pools should take normal precautions against accidental intranasal inoculation while bathing in the hot pools. This should not be difficult at present as both pools are quite shallow, however they might be deepened in the future as the island's population grows.

The pools situated in the Kaitoke hot springs area, which are surrounded by soil banks and fed by natural springs in the bush, would be classified as 'high risk' according to the reported statements of the medical officer in Rotorua (Christmas, 1972).

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In my personal opinion, the risk of contracting amoebic meningoencephalitis from the Great Barrier Island hot pools studied is low, even when long periods are spent in the pools, because of their relatively high salinity. The South Australia Health Department has advised residents in areas o f risk in that state to treat swimming pools with salt to a final concentration of 0.6%, which is stated to be sufficient to cause instant disintegration of pathogenic amoebae, (Hailstone, 1972). From data obtained for the Great Barrier hot springs by Wilson and Moore (1973) the average concentration of sodium chloride in the water is about 0.8%. At the time they were measured (August 1972) the Kaitoke hot springs contributed about half the total volume of water in the stream and bathing pools. In summer, the surface drainage at Kaitoke Springs should be sufficiently low to allow the concentration of sodium chloride in the bathing pools to rise to about 0.6%. At North Peach Tree Springs, virtually all the water in the bath is supplied from the hot spring, therefore the salinity of this pool should always be high enough to prevent survival of pathogenic amoebae.

REFERENCES

Carter, R.J. 1970: Description of a Naegleria sp. isolated from two cases of a primary amoebic meningoencephalitis, and of the experimental pathological changes induced by it. J. Path. 100: 217-244.

Christmas, J.C. 1972: Health officer warns: Al l New Zealand bush pools may harbour amoeba. The Times (Hamilton, N.Z.) June 6th: 26.

Culbertson, C.G. 1971: The pathogenicity of soil amoebas. Ann. Rev. Microbiol. 25: 231-254. Hailstone, B. 1972: Search for killer disease. The Times (Hamilton, N.Z.) June 13th.: 4. Mandal, B.N.; Gudex, D.J.; Fitchett, M.R.; Pullon, D.H.H.; Malloch, J.A.; David, C M . ;

Apthorp, J. 1970: Acute Meningoencephalitis due to amoebae of the Order Myxomycetale (Slime mould). N.Z. Med. J. 71, : 16-23.

Wilson, T.H.; Moore, P.R. 1973: The hot springs of Great Barrier Island. 1. Physical measurements and chemical analysis. Tane 19: (this volume).

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