Effects of a short-term experimental acidification on a microinvertebrate community: Rhizopoda, Testacea

GEORGES COSTAN' AND DOLORS PLANAS De'partement des Sciences Biologiques, Universite' du Que'bec a Montre'al, C. P. 8888, Succursale A , Montre'al, Que'.,

Canada H3C 3P8 Received July 10, 1985.

COSTAN, G., and D. PLANAS. 1986. Effects of a short-term experimental acidification on a microinvertebrate community: Rhizopoda, Testacea. Can. J . Zool . 64: 1224- 1230.

The effects of a short-term acidification on the density and diversity of testate Amoebae (Protozoa: Rhizopoda, Testacea) were investigated in seminatural conditions using an experimental set-up simulating a lotic ecosystem. Decreases in density were observed during sulfuric and nitric acid treatments (highly significant differences in the acidified channels compared with the nonacidified control channel). Diversity fluctuates with regard to variations in its two components, evenness and number of species. The reponse is qualitatively different (specific richness) but quantitatively nonsignificant (density), depending to the type of acid used.

COSTAN, G., et D. PLANAS. 1986. Effects of a short-term experimental acidification on a microinvertebrate community: Rhizopoda, Testacea. Can. J . Zool. 64: 1224- 1230.

Les effets d'une acidification a court terme sur la densit6 et la diversite des populations de ThCcamoebiens (Protozoa: Rhizopoda, Testacea) ont CtC CtudiCs en conditions semi-naturelles a l'aide d'un systkme experimental simulant un Ccosystkme lotique. Durant le traitement aux acides sulfurique ou nitrique, une diminution des densites a CtC notee (differences hautement significatives dans les canaux acidifiCs par rapport au temoin non-acidifiC). La diversite fluctue en fonction de la variation de ses composantes: rCgularitC et nombre d'espkces. L'effet est different qualitativement (richesse sp6cifique) mais non significatif quantitativement (densitC) selon le type d'acide utilisC.

Introduction Many studies have mentioned a spring pH depression in

poorly buffered waters of Precambrian zones in Scandinavia and North America that receive precipitation having pH values lower than 5.6 (Jeffries et al. 1979; Scheider et al. 1979; Keller 1983 among others). This depression of pH in small aquatic ecosystems (pools, ponds, streams) can result from factors other than spring snowmelt; this phenomenon is also associated with rain (Haapala et al. 1975; Pough 1976; Cook 1978). Communi- ty responses to intermittent pH depressions can be equal to, or greater than, those resulting from a gradual acidification process, which allows new species, able to cope with new conditions, to progressively invade the habitat.

Existing literature on the impacts of acidification on various communities are in relation to the gradual acidification process (see review by Haines 1981). Few studies have examined the effects of a sudden and intermittent drop in pH. In relation to this latter phenomenom, a recent study has examined primary production response (Parent et al. 1986), but nothing exists regarding secondary production.

Although microinvertebrates constitute an important part of secondary production (Schonborn 1962, 1977; Pace and Orcutt 1981 ; Cairns et al. 1983), most acidification studies on benthos refer solely to vertebrates or macroinvertebrates (Bell 1970; Fiance 1978; Raddum and Saether 198 1). In aquatic ecosystem studies concerning zooplanktonic and benthic communities, protozoa are rarely included.

For this reason, the testate Amoeba group was chosen as the basis for this study. Generally considered as acidophilic (Bonnet 1964; CoQteaux 1976) these organisms live and reproduce at pH levels as low as 3.0 and as high as 9.0.

Although these organisms possess specialized structures (contractile vacuoles) to assure osmotic pressure regulation

(Eisenberg-Hamburg 1929; Dawson 1945) or have developed defense strategies to cope with adverse conditions (cysts, precysts, "epiphragmes") , described by Bonnet ( 1959, 1960, 1964) and Chardez ( 1965), we can suppose that rapid modifica- tions of pH in their environment will greatly reduce the efficiency of these mechanisms. Aside from the European studies indicating pH preferences of certain species (Heal 1964; Chardez 1969), no study exists, to the best of our knowledge, that has examined the effects of an acidification process on these organisms. For this reason, we have chosen to examine the response of a testate Amoebae community of a small stream to a short-term acidification using two types of acid, H2SO4 and HN03, major constituents of acid precipitation. The short-term acidification approach is justified by observed drops in pH in streams in the eastern portion of the Canadian Shield after it rains (D. Planas, unpublished data).

Our main hypotheses were the following: (i) A sudden drop in pH, caused by the incorporation of acid, will affect these organisms in a direct (physiological) or indirect way through their food resource. (ii) Species richness and total number of organisms will decrease as a function of the length of acidifica- tion. (iii) A significant difference between the effects of the two types of acids should be observed. To verify these hypotheses, our work was performed in an experimental system (SCrodes et al. 1984) set up in seminatural conditions, which allowed us to control certain parameters (pH, flow rate, substratum) and to have a nonacidified true control.

Materials and methods The experimental system used is described in detail by SCrodes et al.

(1984). This system was set up parallel to a Canadian Shield stream, located in eastern Canada (ruisseau des Cascades, foret Montmorency , 47'19' N, 71'07' W) about 100 km north of Quebec City. The forest is dominated by balsam fir (Abies balsamea) in association with paper birch (~e tu l a papyrifera). A total of nine experiments were perfo-rmed

'present address: DCpartement de Biologie, UniversitC Laval, CitC between 1982 and 1983. The experiments started in June and lasted Universitaire , S te-Foy , QuC . Canada G 1 K 7P4. until September.

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

COSTAN AND PLANAS 1225

+ NET ( 2 0 p m pore d~ameter)

CERAMIC TILE

FIG. 1. Ceramic tile sampler (designed by J. Caumartin and G. Cos tan).

Unglazed ceramic tiles, having a surface area of 10 cmL, were deposited on plastic supports on the bottom of each channel, which had previously been covered with pebbles. Water diverted from the stream was then allowed to flow through the channels. A 4.-week colonization period preceded the start of the experiments; weekly samples taken in 1982 had shown that colonization was complete after 3 weeks. Two channels were acidified; the pH of the water was lowered to 4 .0 and maintained there throughout the acidification period. One channel was kept unacidified and used as a control. Before it was allowed to return to the stream, acidified water was neutralized with sodium hydroxyde (NaOH) to its initial pH level.

During the experiments, sampling periods were as follows: 1 day before acidification (- 24 h), at the start of acidification (0 h), 4 and 12 h after the start of acidification and until 24, 48, or 72 h depending on the length of the experiment. A final sampling was performed 24 h after the end of acidification (+ 24 h). Each sample comprised five replicates per channel.

To collect the ceramic tiles, a special sampler was constructed to fit the exact size of the tiles (Fig. 1). This sampler was also used to determine the importance of the other groups of protozoa (ciliates, flagellates) that are more rapid in their movements than testate Amoebae. Samples were fixed with Bouin Hollande and mounted on microscope slides according to Coiiteaux (1967). In a comparative study Lousier and Parkinson (1981) described this technique as the most accurate in terms of actual densities.

Samples were filtered on a 250-km screen to eliminate large particles and plant debris. Analysis of sediments from 15 samples confirmed the absence of testate Amoebae from this portion of the sample. Filtrate volumes were standardized at 125 mL and a 25-mL fraction, consisting of several aliquots, was subsampled for identifica- tion. Filtration was performed on Millipore filters, 25 mm in diameter with an 8.0-km pore size. Identification and cell counts were carried out on a phase contrast inverted microscope. Full and empty shells were counted seperately in order to estimate the biological activity of the community using the index proposed by Laminger et al. (1980).

Samples were taken on an random basis in the experimental channels; nonparametric statistical tests (Kruskall-Wallis, multiple comparisons, Mann-Whitney) were used to compare the different channels and to determine significant differences during the experi- ment. Preliminary tests showing the nonnormality of parameter distributions motivate our choice of nonparametric statistics. Absolute values of densities were used to perform the statistical tests. Physico- chemical parameters were analysed using the methods described by Parent et al. (1986).

Biological activity of testate Amoeba, during the experiment, was calculated using the index proposed by Laminger et al. (1 980):

Ni [ I ] / * = I - - N

where Ni is the number of living organisms and N is the total number of organisms. As the proportion of living organisms in the community increases, the index [ 11 decreases.

Results Physicochemical characteristics

Extreme values of the chemical characteristics measured in acidified and control channels in 1983 are given in Table 1. The stream that was used as a water source has a summer pH value close to neutrality, a low conductivity level, and is nutrient poor, as is reflected in ,the control data.

Parameters that showed variations during acidification were directly related to this treatment. One of these parameters, conductivity, showed a rapid increase at the start of acidifica- tion. Potassium increased considerably during the acid treat- ment, whereas other major cations, Ca, Mg, and Na, showed no variations in their concentrations. Total organic carbon (TOC) and total inorganic carbon (TIC) decreased slightly in the acidified channels. Results of physicochemical parameters are presented and discussed in detail in Parent et al . (1986).

Biological parameters Ninety-two species and varieties of testate Amoebae were

identified (Table 2). Many of these species are accidental and colonize mostly mossy and soil habitats. Among the purely aquatic species, 64% belong to the genus DlfJlugia, whereas the genus Centropyxis represents 1 8.5%. All species considered, we calculated an average density of 334 x lo3 organisms/m2 in 45 nonacidified samples.

Quantitative impact of acidification Results presented here are from the longest experiment, 72 h,

performed during the first stages of summer colonization. The pattern of response is similar to the one observed for the same period in 1982. Before the start of acidification, average densities for the three channels were around 400 x lo3 organisms/m2.

Figure 2 shows the evolution of average densities of living organisms in the acidified channels, expressed as a percentage of the control density. A highly significant difference (p<O.Ol) was observed between channel 1 (acidified with H2SO4) and the control for the 12-h acidification point. At this same point and at the 72-h acidification point and 24 h after acidification (+ 24 h), highly significant differences also existed between channel 3 (acidified with HN03) and the control.

Density values for each channel also showed significant differences during the experiment: for channel 1, between - 24 and 12 h and between 0 and 12 h. These differences also existed for channel 3 as well as differences between 4 and 12 h, and between -24,0, and 4 h compared with 72 and + 24 h. There were no significant differences between the acidified channels (1 and 3) or between the different sampling periods for the control.

Diversity, richness, evenness, and biological activity The evolution of the Shannon-Weaver diversity index and its

two components, evenness (Pielou 1966) and number of species, is shown in Fig. 3. The strongest diversity was observed at the 24-h acidification point in channel 1, whereas the lowest values for diversity appeared in channel 3 at the 72-

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

CAN. J. ZOOL. VOL. 64, 1986

TABLE 1. Range of values for the principal chemical parameters measured during acid treatment

CONTROL

Channel 1 Channel 3 Parameters Control (H2S04) (HN03)

pH Temperature ("C) Dissolved oxygen (mg-L-') Conductivity Total inorganic carbon (mg.LP') Total organic carbon (mg-L-') Nitrite and nitrate (pg-L-') Phosphates (pg-L-') Total phosphorus (pg.L-') Sulfates (rng.Lp') Calcium ( m g - ~ - ' ) Magnesium (mg-L-') Sodium ( m g . ~ ~ ' ) Potassium (mg-L-')

-CHANNEL 1 H2S04

c - 4 CHANNEL 3 HMO3

. . . - 24 48 +24 i TIME hours)

FIG. 2. Average community density in the acidified channels, expressed as a percentage of density in the control channel. ++, very significantly (pc0 .0 1) different compared with the control (calculated from the absolute values). Arrows point to the acidification period.

Discussion Species composition before acidification was very similar to

that observed in many European lotic habitat (Opravilova 1974, 1983; Schonborn 1975; Opravilova and Stepanek 1980). More- over, genus distribution in the community is similar, in terms of percent dominance, to those of the above-mentioned studies. Although certain species are ubiquitous (present in other biotopes), we can nevertheless talk about a specific composition of testate Amoebae that is characteristic of streams. The well-known cosmopolitan character of these organisms (Leidy 1879; Deflandre 1928, 1929; Van Oye 1944, 1956) also emerges from this study.

The species composition in our three study channels was similar before acidification: no quantitative significant differ- ences were observed. The average densities obtained at the -24-h point express the homogeneity of our three channels. Generally, the acidification experiment had a negative impact on the community as a whole. Density curves show a similar decrease in the acidified channels, with the major impact

and +24-h points. Evenness was highest at 12 and 24 h of occuring at the 12-h acidification point. This observed pattern

acidification, whereas the number of species had a bimodal could be explained by the physiology of the organisms.

distribution, with the lowest values at the 12- (channel 1) and Although we are not aware of any studies on the physiology of

+ 24-h points (channel 3). testate Amoebae, it is possible that their osmotic regulatory

Table 3 shows a decrease in activity at the 4-h acidification mechanisms are considerably perturbed by the acid shock

point in the acidified channels; this decrease persisted until the (increase in hydrogen ion concentration in the extracellular

+ 24-h point. medium) and by chemical modifications of the habitat inherent to acidification, such as a marked increase in potassium possibly

Evolution of dominant species We analyzed in detail the changes in population density of the

two most abundant species, DifJZugia pristis and D . pulex, during the experiments. Figure 4 shows the average densities (m-*) of these species in the three channels during the experiment. Patterns were similar in channels 1 and 3; both showed a dramatic decrease of the two species. The strongest negative impact appeared at the 12-h acidification point. Significant differences between the acidified and control chan- nels were observed from the 12-h point until the end of the experiment.

Diflugia pristis increased considerably in the control chan- nels, whereas D . pulex showed an important but nonsignificant drop at the 12-h point and stayed relatively abundant, compared with the same period in the acidified channels, for the rest of the

released from sediments. However, we cannot explain why potassium is so high in comparison to other major cations. In a study on the role of K+ and ca2+ on the contractile vacuole of Paramecium caudatum (Protozoa, Ciliata) , Czarska ( 1964) shows that high concentrations of potassium decrease the workload of the contractile vacuole and consequently affect osmoregulation. Although variation exists between species and groups (Botsford 1926; Hopkin 1946; Patterson 1980, 198 1) in the response of the contractile vacuole, it is likely that under stress the response of these cellular inclusions could be similar.

The slight (nonsignificant) population recovery at the 24-h acidification point is due to subdominant species. This leads us to suppose that these species are more tolerant of new habitat conditions.

Food could also act as a factor or cofactor responsible for the experiment. decrease in density. Studies on testate ~moebae feed in~ are rare

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

COSTAN AND PLANAS

TABLE 2. List of species observed TABLE 2 . (concluded)

Arcella catinus PCnard, 1890 A. vulgaris Ehrenberg , 1 830 Assulina muscorum Greef, 1 888 A. seminulum (Ehrenberg) Leidy , 1 848 Campascus minutus PCnard, 1899 Centropyxis aculeata (Ehrenberg) Stein, 1830 C. aculeata var. oblonga Deflandre, 1929 C. aerophila var. sphagnicola Deflandre, 1929 C. cassis Wallich, 1864 C. constricta (Ehrenberg) Deflandre, 1838 C. discoides (PCnard) Deflandre, 1902 C. ecornis Leidy, 1838 C. platystoma (PCnard) Deflandre, 1 890 C. sylvatica (Deflandre) Thomas, 1955 C. sylvatica var. minor Bonnet and Thomas, 1955 Cyclopyxis eurystoma Deflandre, 1929 C. kahli var. cyclostoma Bonnet and Thomas, 1960 C. puteus Thomas, 1960 Cyphoderia trochus PCnard, 1899 Diflugia acuminata Ehrenberg, 1838 D. amphoralis Cash and Hopkinson, 1909 D . bicornis PCnard, 1 890 D. bryophila PCnard, 1902 D. curvicaulis var. inflata Decloitre, 195 1 D. cylindrus Thomas, 1953 D. distenda (PCnard) Ogden, 1983 D . elegans PCnard, 1 890 D . glans PCnard, 1902 D. globularis (Wallich) Leidy , 1877 D. globulosa Dujardin, 1837 D . gramen PCnard, 1902 D. labiosa Wailes, 1919 D. lacustris PCnard, 1899 D. mamillaris PCnard, 1893 D. manicata PCnard, 1902 D. mica Frenzel, 1892 D. minuta Rampi, 1950 D. minutissima PCnard, 1904 D . molesta PCnard, 1902 D. oblonga Ehrenberg, 1838 D. oblonga var. schizocaulis (S tepanek) Chardez, 1957 D . parva Thomas, 1954 D. penardi Hopkinson, 1909 D . pristis PCnard, 1902 D. pulex Pknard , 1 902 D. rubescens PCnard, 189 1 D. tenuis PCnard, 1890 D. tricornis Jung, 1936 D . urceolata Carter, 1 864 D. venusta PCnard, 1902 D. viscidula PCnard, 1902 Diflugia sp. 1 Diflugia sp. 2 Diflugia sp. 3 Euglypha acanthophora Ehrenberg , 184 1 E. brachiata Leidy, 1878 E. ciliata Ehrenberg, 1843 E. denticulata Brown, E.filifera PCnard, 1890 E. laevis Ehrenberg, 1832 E. rotunda Wailes, 19 1 1 E. tuberculata Dujkardin, 184 1 Heleopera petricola Leidy , 1879 H. picta Leidy, 1879 Hyalosphenia elegans Leidy, 1879 H. elegans var. cylindricollis Chardez, 1962 Lesquereusia modesta Rhumbler, 1895

L. spiralis Ehrenberg, 1840 Nebela collaris Ehrenberg , 1 848 N. dentistoma PCnard, 1890 N. flabellulum Leidy , 1 874 N. griseola PCnard, 19 1 1 N. lageniformis PCnard, 1890 N. militaris PCnard , 1 890 N. penardiana Deflandre, 1936 N. tubulata Brown, 191 1 N. tubulosa PCnard, 1890 Paulinella chromatophora Lauterborn, 1895 Phryganella acropodia (Hertwig and Lesser) Hopkinson, 1909 Plagiopyxis labiata PCnard, 19 10 Plagiopyxis sp. Pontigulasia bryophila PCnard, 1902 P. vas Leidy , 1879 Pontigulasia sp. Pseudodiflugia gracilis Schlumberger, 1845 Quadrulella symetrica Wallich, 1863 Sphenoderia lenta Schlumberger, 1845 Tracheleuglypha dentata Moniez, 1888 Trigonopyxis arcula Leidy , 1 879 Trinema complanatum PCnard, 1890 T. enchelys Ehrenberg , 1838 T. lineare PCnard, 1890

TABLE 3. Biological activity (Iak index) values for the three channels during the experiment

Time Channel 1 Channel 3 Channel 5 (h) (H2S04) (HN03) (Control)

*One day before acidification. ?Final sampling 24 h after the end of acidification.

and incomplete; their diet is mainly composed of algae, bacteria, fungus and detritus (Deflandre 1953; Chardez 1964, 1970; CoQteaux and Devaux 1983), although certain species (notably those of the genus Nebela, of which at least one species, N. dentistoma, is abundant in our study) are predators of other testate Amoebae (Deflandre 1936). This possible alteration of the food resource during the acidification of a habitat has been suggested by numerous authors as an explanation. of the decreased densities of macroinvertebrates (e.g., Sutcliffe and Carrick 1973; Friberg et a l . 1980).

Results from Parent et a!. (1 985) on the effects of short-term acidification on periphyton biomass and productivity, for the same experiment, show a significant decrease in the acidified channels, compared with the control, from 4 h of acidification until the end of the experiment. Although this decrease in biomass was not observed in other experiments, variations in the specific composition of periphyton were observed (J. Caumartin, personal communication). These observations cor- roborate the hypothesis of an alteration of the food resource that could also explain the decrease in testate Amoebae density.

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

1228 CAN. J . ZOOL. VOL. 64, 1986

CHANNEL 1 H2S04

CHANNEL 5 Control

FIG. 3 . Shannon-Weaver diversity index and its components versus time.

Variations in diversity can be explained by its components, evenness and number of species. The strong diversity at the 24-h acidification point in channel 1 resulted from a sharp increase in evenness following the disappearance of the dominant species, whereas the number of species was still relatively high as a result of constant immigration into the system. Even though the number of species increased slightly in the acidified channels at the 24-h point, the organisms did not seem to proliferate, since total density stayed between 3 and 3.5 times lower than that in the control channel. We can suppose that species entering the system cannot survive or do not resist the new environmental conditions, since we observed another decrease in species richness at the 72-h point, which continued to the +24-h point, particularly in channel 3.

N I

E 9 loo CHANNEL 1 ( H 2 ~ 0 4 )

75 - 50 -

-, , Difflugia pristis - Difflugia pulex 25 -

CHANNEL 3 (HN03)

75 - 50 -

o-- Difflugia pristis - Difflugia pulex 25 -

FIG. 4. Evolution of average density of dominant species as a function of time. Arrows point to the acidification period.

On the whole, diversity fluctuated but no marked decrease was observed (except for the two last points in channel 3), in contrast to long-term acidification studies on stream macioinl- vertebrates (e. g., Hall and Likens 1980; Hall et al. 1980).

According to Legendre (1973), evenness is inversely propor- tional to the biological activity of the habitat, and in fact we can observe a decrease in biological activity when evenness increases. The index of biological activity proposed by Laming- er et al. (1973) is interesting because it corresponds to a more rapid and simplified method of calculating species' "weight" and their contribution to the biological activity of the commu- nity. It is therefore inevitable that biological activity is inversely proportional to evenness since the latter is a function of the dominance of one or more species in the community.

Quantitative and qualitative patterns of testate Amoebae populations in the acidified channels are generally very similar. One should also note that the population changes of dominant

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

COSTAN AND PLANAS 1229

species in the control channel could result from competition and (or) another aspect related to the life cycle of these species.

Acknowledgements This work was supported by NSERC and FCAC grants to D.

Planas and an FCAC student fellowship to G. Costan.

BELL, H. L. 1970. Effects of pH on the life cycle of the midge Tanytarsus dissimilis. Can. Entomol. 102: 636-639.

BONNET, L. 1959. Dekystement, phase trophique et enkystement chez Plagiopyxis minuta (Thecamoebiens) . Incidences systematiques . C . R. Hebd. Seances Acad. Sci. 249: 2617-2619.

1960. Kystes et tropophases chez Plagiopyxis minuta Bonnet (Thecamoebiens). Bull. Soc. Zool. Fr. 85: 43-52.

1964. Le peuplement thecamoebiens des sols. Rev. Ecol. Biol. Sol, 1: 123-408.

BOTSFORD, E. F. 1926. Studies on the contractile vacuole of Amoeba proteus. J. Exp. Zool. 45: 95- 139.

CAIRNS, J., JR., J. L. PLAFKIN, R. L. KAESLER, and R. L. Lowe 1983. Early colonization patterns of diatoms and protozoa in fourteen freshwater lakes. J. Protozool. 30: 47-5 1.

CHARDEZ, D. 1964. Sur la nutrition de Centropyxis discoides (Penard) Deflandre (Rhizopoda, Testacea). Bull. Inst. Agron. Stn. Rech. Gembloux, 32: 305-308.

1965. Kystes de resistance chez Hyalosphenia papilio Leidy (Rhizopoda, Testacea). Bull. Inst. Agron. Stn. Rech. Gembloux, 33: 488-490.

1969. Contribution ii la faune Thecamoebienne de 1'Islande (Protozoa, Rhizopoda, Testacea). Bull. Inst. R. Sci. Nat. Belg. 45: 1-16.

1970. Etudes sur Centropyxis aculeata (Ehrenberg) Stein (Protozoa, Rhizopoda, Testacea). Bull. Rech. Agron. Gembloux, 5: 76-86.

COOK, R. P. 1978. Effect of acid precipitation on embryonic mortality of spotted salamanders (Ambystoma maculatum) and Jefferson salamanders (Ambystoma jeflersonianum) in the Connecticut Valley of Massachusets. M. S. thesis, University of Massachusets, Arnherst.

COOTEAUX, M. M. 1967. Une technique d'observation des Theca- moebiens du sol pour l'estimation de leur densite absolue. Rev. Ecol. Biol. Sol, 4: 593-596.

1976. Dynamisme de l'equilibre des Thecamoebiens dans quelques sols climaciques. Mem. Mus. Nat. Hist. Nat., Ser. A, zoo1 .

COOTEAUX, M. M., and J. DEVAUX. 1983. Effet d'un enrichissement en champignons sur la dynamique d'un peuplement thecamoebien d'un humus. Rev. Ecol. Biol. Sol, 20: 5 19-545.

CZARSKA, L. 1964. Role of the K+ and ca2+ ions in the excitability of protozoan cell. Chemical and electric stimulation of contractile vacuoles. Acta Protozool. 11: 287-296.

DAWSON, J. A. 1945. Studies on the contractile vacuole of Amoeba dubia. J. Exp. Zool. 100: 179-191.

DEFLANDRE, G. 1928. Le genre Arcella Ehrenberg. Arch. Protistenkd. 64: 152-287.

1929. Le genre Centropyxis Stein. Arch. Protistenkd. 67: 322-375.

1936. Etude monographique sur le genre Nebela Leidy (Rhizopoda, Testacea). Ann. Protistol. 5: 201 -286.

1953. Thercamoebiens. In Traite de zoologie. Edited by P. P. Grasse. Masson et Cie, Paris. pp. 97- 149.

EISENBERG-HAMBURG, E. 1929. Recherches comparatives sur le fonctionnement de la vacuole pulsatile chez les infusoires parasites de la grenouille et chez les infusoires d'eau douce. Influence de la pression osmotique, des electrolytes et du pH. Arch. Protistenkd. 68: 45 1-470.

acidification on the dynamics of allochtonous leaf material and benthic invertebrate communities in running waters. In Ecological impact of acid recipitation. Edited by D. Drablfls and A. Tollan. SNSF Project, 9s-NLH, Norway. pp. 304-304.

HAAPALA, H., P. SEPPONEN, and E. MESKUS. 1975. Effect of spring floods on water acidity in the Kiminkijoki area, Finland, Oikos, 26: 26-3 1.

HAINES, A. T. 1981. Acidic precipitation and its consequences for aquatic ecosystems: a review. Trans. Am. Fish. Soc. 110: 669-707.

HALL, R., and G. LIKENS, 1980. Ecological effects of experimental acidification on a stream ecosystem. In Ecological impact of acid precipitation. Edited by D. Drablfls and A. Tollan. SNSF Project, As-NLH, Norway. pp. 375-376.

HALL, R., G. LIKENS, S . FIANCE, and G . HENDREY . 1980. Experimen- tal acidification of a stream in the Hubbard Brook Experimental Forsest, New Hampshire. Ecology, 61: 976-989.

HEAL, 0 . W. 1964. Observations on the seasonal and spatial distribution of Testacea (Protozoa: Rhizopoda) in sphagnum. J. Anim. Ecol. 33: 395-4.12.

HOPKIN, D. L. 1946. The contractile vacuole and the adjustment to changing concentration in freshwater amoebae. Biol. ~ ~ 1 1 . (Woods Hole), 90: 158- 176.

JEFFRIES, D. S., C. M. COX, and P. J. DILLON, 1979. Depression of pH in lakes and streams in central Ontario during snowmelt. J. Fish. Res. Board Can. 36: 640-646.

KELLER, W. 1983. Spring pH and alkalinity depressions in lake Superior tributaries. J. Great Lakes Res. 9: 425-429.

LAMINGER, H., K. GEISLER-MORODER, A. SIESS, E. SPISS, and B. SPISS. 1980. Populations dynamik terrestrischer Protozoen (Testa- cea, Rhizopoda) in zentralpinen Lagen Tirols. !, Untersuchungen subalpiner Boden im Raum Obergugl (Tirol/Osterreich). Arch. Protistenkd. 123: 280-323.

LEGENDRE, L. 1973. Phytoplankton organization in Baie des Chaleurs (Gulf of St. Lawrence). J. Ecol. 61: 135-149.

LEIDY, J. 1879. Freshwater rhizopods of North America. United States Geological Survey Territories, Washington, DC.

LOUSIER, J. D., and D. PARKINSON. 198 1. Evaluation of a membrane filter technique to count soil and litter Testacea. Soil Biol. Biochem. 13: 209-213.

OPRAVILOVA, V. 1974. Testacea (Protozoa: Rhizopoda) of the river Bobrava in Moravia. Vest. Cs. Spolec. zool. 38: 127- 147.

OPRAVILOVA, V., and M. STEPANEK. 1980. Some less frequent forms of Testacea (Protozoa: Rhizopoda) in small streams of the CSSR. Vestn. Cesk. Spol. Zool. 44: 128-138.

PACE, M. L., and J. D. ORCUTT, JR. 1981. The relative importance of protozoans, rotifers and crustaceans in a freshwater zooplankton community. Lirnnol . Oceanogr . 26: 822-830.

PARENT, L., M. ALLARD, D. PLANAS, and G. MOREAU. 1986. The effects of short-term and continuous experimental acidification on biomass and productivity of running water periphytic algae. In Impacts of acid rain. American Society for Testing and Materials, Philadelphia. In press.

PATTERSON, D. J. 1980. Contractile vacuoles and associated struc- tures: their organization and function. Biol. Rev. 55: 1-46.

1981. contractile vacuole complex behavior as a diagnostic character for free-living Amoeba. Protistologica, 17: 243-248.

PIELOU, E. C. 1966. The measurement of diversity in different types of biological collections. J. Theor. Biol. 13: 13 1 - 144.

POUCH, F. H. 1976. Acid precipitation and embryonic mortality of spotted salamanders, Ambystoma maculatum. Science (Washing- ton, D.C.), 192: 68-70.

RADDUM, G. G., and 0 . A. SAETHER. 198 1. Chironomid communities in Norwegian lakes with different degrees of acidification. Verh. Int. Ver. Theor. Angew. Limnol. 21: 399-405.

SCHEIDER, W. A., D. S. JEFFRIES, and P. J. Dillon. 1979. Effects of FIANCE, S. B. 1978. Effects of pH on the biology and distribution of acidic precipitation on Precambrian freshwaters in southern Ontario.

Ephemerella funeralis (Ephemeroptera). Oikos, 31: 332-339. J. Great Lakes Res. 5: 45-5 1 . FRIBERG, F., C. OTTO, and B. S. SVENSSON. 1980. Effects of SCHONBORN, W. 1962. Die 0kologie der Testaceen im oligotrophen

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.

1230 CAN. J. ZOOL. VOL. 64, 1986

See, dargestellt am Beispiel der Grossen Stechlinsees. Limnologica, 1: 111-182.

1975. Studien uber die Testaceenbesiedlung der Seen und Tumpel des Abisko-Gebeites (Schwedisch-Lappland). Hydrobio- logia, 46: 1 15- 139.

1977. Production studies on Protozoa. Oecologia, 27: 171-184.

S~RODES, J-B., G. MOREAU, and M. ALLARD. 1984. Dispositif experimental pour 1'Ctude de divers impacts sur la faune benthique d'un cours d'eau. Water Res. 18: 95-101.

SUTCLIFFE, D., and T . CARRICK. 1973. Studies on mountain streams in the English Lake district. I. pH, calcium and the distribution of invertebrates in the River Dudson. Freshwater Biol. 3: 437-462.

VAN OYE, P. 1944. Au sujet de la distribution geographique des Rhizopodes. Biol . Jaarb. 25: 83-9 1 .

1956. La distribution geographique des Rhizopodes: nouvelles conceptions de la biogeographie. Bull. Soc. Bot. Nord. Fr. 9: 53-62.

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Tex

as A

&M

Uni

vers

ity o

n 11

/14/

14Fo

r pe

rson

al u

se o

nly.