REGULATED RIVERS: RESEARCH & MANAGEMENT, VOL. 7, 31-43 (1992)

VARIATIONS OF THE HYPORHEIC ZONE THROUGH A RIFFLE IN THE R. MORAVA, CZECHOSLOVAKIA

OTAKAR STBRBA, VLADIMfR UVfRA, PRAVEEN MATHUR AND MARTIN RULfK Faculty of Natural Sciences, Palacky University, Svobody 26, 771 46 Olomouc, Czechoslovakia

ABSTRACT

We observed the dynamic changes in the hyporheic zone, both in the vertical (0-80 cm) and horizontal directions. Two stations with different hydrological conditions were compared, and subsequently related to two basic processes: infiltration of surface water into the sediments of the river bottom and repeated entry back to the surface stream. By comparing these two locations we attempted to show the existence of a continuous exchange of water between the surface of the river and the hyporheic zone in a process which we call ‘small bottom circulation’. At the same time, we also attempted to demonstrate that this process involves the self-purification of the infiltrated water. We presume that self- purification is realized both by means of physical processes (filtration, sedimentation and deposition) and by the biological decomposition of organic matter. Self-purification of the infiltrated water between the stations which were compared are proved, above all, by the values of 0,, BOD, COD, FPOM + CPOM, pH and conductivity. There are also remarkable differences in the qualitative composition in the macroinvertebrate community.

KEY WORDS Hyporheic Self-purification Macrozoobenthos Microphytobenthos Chemical studies

INTRODUCTION

A certain amount of the surface river water continuously infiltrates into the sediments of the river bed and after a certain amount of time, the infiltrated water returns to the surface stream. This local circulation between the surface river water and the hyporheic zone which is influenced by bed morphology, has been termed ‘small bottom circulation’ (Sttirba, 1990). At the same time, it was hypothesized that small bottom circulation has significance for self-purification. This self-purification, which takes place through the bottom sediments along the course of the river, is a combination of physical and biochemical processes. Of the physical processes, the most significant are filtration, sedimentation and deposition. During the passage of the infiltrated water, there is an intensive mineralization of the organic matter and a reduction of saprobity. Such mineralization is limited by oxygen content, which diminishes with retention time in the hyporheic environment. Small bottom circulation plays its most important role during low and minimum water levels, especially in artificially polluted rivers. At such times the river is heavily loaded with pollutants. Weak self- purification in regulated rivers is often caused just by the fact that sediment formation is not possible. Small bottom circulation is greater in natural lowland rivers where Sttirba (1990) asserts it makes a considerable contribution to maintaining B-mesosaprobity. While observing a rather wide spectrum of biotic and abiotic parameters, we attempted to demonstrate, as well as quantify, this function of the river bottom, particularly its importance for self-purification.

LOCALITY

The River Morava is one of the important rivers in Czechoslovakia, one of the tributaries of the Danube. The middle part of the Morava between Litovel and Olomouc flows through a protected area of deciduous woodland, part of the alluvial corridor which maintains its natural character with active channels, cutoff channels, pools and floodplain segments of different ages.

0886-9375/92/010031- 13$06.50 0 1992 by John Wiley & Sons, Ltd

Received 20 February 1991 Accepted (revised) 1 October 1991

32 0. STBRBA ET AL.

Figure 1. Map of Czechoslovakia with the Morava River and Olomouc

The study of the hyporheic zone was carried out on the River Morava 15 km to the north of Olomouc, in the vicinity of Sttpanov (Figure 1). In this section the Morava River has an average flow of 20 m3 s - ’ (Qmin = 4 m3 s-’, Qmax = 350 m3 s-l). The river bed is composed of alluvial gravel and sand, in which medium gravel (8-32 mm) dominates. In the deeper layers, finer fractions, especially fine gravel (2-8 mm) and medium-sized sand (0.25- 1 mm), are encountered (KolaEny, 1975).

Sample collection in this part of the river involved two stations where we assumed ‘small bottom circulation’ was active (Figure 2). Station A lies above a gravel riffle, where we assumed infiltration of surface water. Station B is on the downstream face of the riffle, 20 m below Station A at a place where the water comes from the hyporheic zone and returns to the river. The depth of the water during sampling was the same at both stations (30-50 cm).

MATERIAL AND METHODS

Samples were collected during the period 20.10.1989 to 28.1 1.1990. The collection of macrozoobenthic samples was carried out by inserting a steel cylinder and a special grab ‘KULOCVAK’ (Sttrba and Holzer, 1977); the diameter of the cylinder is 140 mm. Seven sediment layers of 10 cm each (0-10, 11-20, 21-30, 3 1-40,41-50,51-60,61-70 cm) were collected from one inserted cylinder. The volume of each sediment layer was 1583 cm3. Each of these samples were transferred to a bucket which was filled up to a 5 1 mark by water from the measuring cylinder. Material obtained by filtering water from the measuring cylinder through a plankton sieve was then added to the bucket. The content of the bucket was then filtered through a sieve of pore size 1 .O mm. Next, 100 ml of water was taken from the filtrate and burned at a temperature of 550°C in order to measure fine particulate organic matter (FPOM). After repeated washing of the material caught in the sieve, coarse particulate organic material (CPOM) and macrozoobenthos was separated. CPOM was also burnt at 550°C and the macrozoobenthos was preserved by a 4 per cent formaldehyde solution. The resulting amount of the organic matter (FPOM + CPOM) from each layer was calculated for the volume of 1 m3 sediment.

Water samples from the hyporheic zone, for the determination of microbenthos and physical and chemical parameters, were taken by a new method (Sttrba, 1990), which involve the principle of siphoning (Figure 3). The water from the hyporheic zone communicates with surface water and water from the corresponding horizons of the hyporheic zone which enters the sampling pipe has the same high level as the level in the river. To maintain the difference in the level needed for using the siphoning principle, we used a heavy container (caisson), which was plunged into the water beside the sampling pipe. After suction from a rubber pipe, and under constant pressure, water flowed continuously from the hyporheic zone to the sampling bottle installed in the caisson. Using the method described above, we obtained samples of the river surface and of the hyporheic zone at the following depths: 20,40,60 and 80 cm. The microphytobenthic samples were preserved

RIFFLE-SCALE VARIATIONS 33

. . . . ................

20 rn 4 *

Figure 2. The field location and the sites of the sampling stations A and B (arrows indicating 'small bottom circulation')

in Lugol's iodine and then studied for quantitative and qualitative determinations. The evaluation was done on a counting chamber of the type Cyrus I.

Temperature was measured in the field by a Hg-thermometer & 0- 1"C, oxygen content was determined by a portable oximeter Oxi-96 (WTW) and pH by a portable pH meter OP-211/1 (Radelkis). NO;, PO:- were determined on a spectrophotometer VSU-2P (Zeiss). BOD and COD,, were studied according to Standard methods (A.P.H.A., 1975).

RESULTS

Chemical data (Table I ) The range of surface water temperature (0.8- 18.4"C) during the period studied corresponds closely to the

air temperature (2.1-21.2"C). Water temperature at a depth of 80 cm, however, showed a smaller variation (1.6-16.6"C) during the period under study, although its annual average is higher (9.OOC, 9.3"C at Station A and Station B respectively) than the temperature of the surface water (8.l"C). The average temperature of water at both the stations studied, has a tendency to increase with depth.

34 0. STERBA ET A L .

Figure 3. Scheme of the apparatus used for taking the sub surface water samples

Table I. Average annual values of the physical and chemical parameters

Depth/Station 0-surface 20 cm 40 cm 60 cm 80 cm

A B A B A B A B A B

8.1 8.3 8.8 8.9 8.9 9.1 9.0

80 80 33 13 7 4 5

7.41 7.49 7.01 647 6.77 6.29 6.71 274 281 299 414 342 490 375

15.5 16-5 8.3 5.8 4.7 3.3 2.9

3-6 3.3 2.2 2.7 3.1 1.8 2.3

5.1 6.0 5.1 3.5 3.7 2.7 3.2

31.8 31.6 31.1 29.7 30.4 24.9 28.3

9.2

3

6.27 506

1.9

2.5

3.0

22.8

9.0

4

6.70 380

2.3

3.1

3.2

23.1

9.3

2

6.27 50 1

1 .o 1.9

5.6

22.5

The oxygen saturation of the surface water was balanced to an average of about 80 per cent. The maximum monthly average of 94 per cent was recorded in April 1990 when the river was at a high water level. The minimum average values of 74 per cent and 68 per cent were measured in October 1989 and October 1990 respectively. 0, saturation decreased rapidly with depth at both sites but the decrease is most marked at station B. This can be seen clearly in the comparison of the seasonal courses as illustrated in Figure 4.

The pH of the surface water was about 7.50 with a minimum of 7.17 in November 1989 and maximum of

RIFFLE-SCALE VARIATIONS 35

Station A

100 I

80

60

0, Saturation (46) 4 0

20

h " 10/081110812/88 1/80 2/80 3/00 4/80 6/80 6/90 7/90 8180 81901010011180

Station B

0, Saturatioi (%I

1

80

60

40

20

A Y

10/8911/8812/88 1/80 2/80 9/80 4 /00 5/80 8/80 7/80 8/80 8/0010/8011190

= s u r f W z o o m O 4 o c m l e o c m l E i 8 o c m

Figure 4. Seasonal variations of dissolved oxygen saturation at the surface and different horizons of the hyporheic zone at station A and station B

7.65 in April 1990. The decrease in pH with depth is quite obvious and remains regular down to a depth of 40 cm. At the 80 cm depth the values of pH remain nearly constant.

The average conductivity of the surface water was 275 p S cm-' and tendenced to increase with depth, with a steeper increase at station B. At 80 cm the conductivity reached the value of 380 p S cm-I and 510 p S em-' at station A and station B respectively.

The NO, concentration of the surface waters during the period under observation varied distinctly (Figure 5). Minimum concentrations, as low as 5 mg 1-' NO;, was recorded in the autumn period (August

Station A

I

20

15

NO, (mg/l)

5

i0/8011/0812/08 1/00 2/90 8/90 4180 5/90 8/00 1/80 8/90 ~l~OlOl~Olll80

=surf m 2 0 c m O s o c m m e o c r n B a o cm

Figure 5. Average monthly values of nitrate at the surface and at different horizons of the hyporheic zone at station A

36 0. STBRBA ET A L

-10-

-20-

-30-

cm -40-

-50-

-60-

to October 1990). In winter it increased markedly (27.75 mg 1-' average of March 1990) and at the onset of summer it again declined to a value of less than 5 mg 1-'. The levels of NO; in the deepest waters shows little variability, except for the 'peak' in February, and much lower concentrations.

The PO:- concentration did not show any clear patterns of variation with depth. The average yearly values are 1.7- 3.6 mg 1-'. The BOD of the surface water shows an average value of 6 mg 1- '. The BOD decreases to 40 cm and reaches 64 per cent of the surface value at Station A and 46 per cent at Station B. Then at station A the BOD slightly decreases up to the depth of 80 cm, whereas, at station B it rises, reaching values similar to the surface ones. Again, for COD, there was a decline with depth.

At station A, there is an increase in the amount of undissolved organic matter (FPOM + CPOM) up to the depth of 40 cm (Figure 6). In the deeper horizons, a considerable decrease of FPOM and CPOM was discovered. At station B the amount of detritus is considerably smaller but with a similar tendency in the vertical profile.

Microphytohenthos In all, 26 samples were collected from surface water and 20 pipe samples were taken each from Stations A

and B yielding 80 samples from different depths, from depths of 20, 40, 60 and 80 cm. Cilliates were often encountered in our samples but were not included in the present work. The average abundance of microphytobenthos at the surface was 31 1 cells ml- '. At 20 cm depth the abundance was 33 per cent and 28 per cent of the surface values, at stationsA and B respectively. At 80cm depth the abundance of microphytobenthos was quite low, 12 per cent and 9 per cent of the surface values, at stations A and B respectively.

The algal community comprised members of the classes Cyanophyceae, Chlorophyceae, Euglenophyceae, Dinophyceae and Bacillariophyceae. The relative abundance of these groups in the different depths of the hyporheic zone is illustrated in Figure 7.

Comparison of the seasonal dynamics of the Bacillariophyceae and Chlorophyceae at stations A and B is shown in Figures 8a,b. Bacillariophyceae were present in all the samples collected. The decline in the number of diatoms with depth is steep. At 20cm they declined to approximately 40 per cent of their surface abundance and at 40 cm, to 20 per cent of the surface abundance. However, they were present even at the greatest depth (80 cm) studied; 15 per cent and 11 per cent of the surface at station A and B respectively.

The second dominant group was Chlorophyceae. The decline in the number of green algae is of course much steeper. At the 20cm depth the abundance is only 20 per cent and 12 per cent of the surface at

FPOM + CPOM (g/ma)

0 1000 2000 3000 4000 5000 0,

-'OI - 80

Figure 6. Average annual values of FPOM + CPOM at different horizons of the hyporheic zone: Full lines station A, Broken lines station B

RIFFLE-SCALE VARIATIONS 3 1

Station A Station B

celislml 31 1 31 1

20 crn cells/ml

40 cm cells/rnl

60 crn cellslrnl

80 crn cells/rnl

102 88

49 36

33 42

37 28

Legend:

Figure 7. Distribution of the main groups of microphytobenthos in the different horizons of the hyporheic zone: B-Bacillariophyceae, Ch-Chlorophyceae, C-Cyanophyceae, D-Dinophyceae, E-- Euglenophyceae

stations A and B respectively. At 80 cm depth the abundance is only 8 per cent and 6 per cent of the surface at stations A and B respectively.

The Cyanophyceae and Euglenophyceae on average occurred in very low numbers. In October 1990 we recorded a mass occurrence of Euglena and Phacus sp. (320 and 64 cells ml- ' respectively) in the surface water. This mass occurrence manifested itself also in the hyporheic water at station A.

Macrozoobenthos At station A, 14 vertical sampling pipes, up to a depth of 70 cm (for every 10 cm), were collected. Thus, in

all, 98 sediment samples were taken. The average abundance of macrozoobenthos in one sampling pipe

38 0. STERBA ET AL.

0

BACILLARIOPHYCEAE (Station A)

( b )

BACILLARIOPHYCEAE (Station B)

CHLOROPHYCEAE (Station A) CHLOROPHYCEAE (Station A)

Figure 8(a). Seasonal variation in abundance of Bacillariophyceae at the surface and at the different horizons of the hyporheic zone. (b) Seasonal variation of abundance of Chlorophyceae at the surface and at the different horizons of the hyporheic zone

(0-70 cm) was 3559 ind m-2. At station B, six sampling pipes were collected (42 samples) with an average abundance of 2905 ind m-2. Summary data are given in Figure 9. 83.8 per cent and 93.06 per cent of the organisms were found between 0-30 cm at stations A and B respectively. The number of animals decreased with depth, most noticeably, at station B. The deepest horizons of station A are characterized by taxonomically richer communities than at station B. The abundance of the surface macrozoobenthos shows two seasonal maxima which are also apparent in the hyporheic zone (Figure 10). The Trichoptera Chironomidae and Oligochaeta were also abundant in the autumn (October and November). The summer maximum, in June, is dominated by Chironomidae. The presence of the different taxa in individual horizons at both localities is clear from Table 11.

DISCUSSION

The structure and formation of channel bed sediments are important characteristics influencing all ecological functions of the river ecosystem. One of the most significant is the ability to self-purify. StZrba (1990) referred to the part played by the hyporheic zone in this process. The continual circulation of water between the

RIFFLE-SCALE VARIATIONS 39

0-1 0 cm indlm2

1 1-20 cm indIm2

21 -30 cm indlm2

31 -40 cm indlm2

41 -50 cm indim2

51 -60 cm indIm2

61 -70 cm indim2

Station A

1774

Station B

1633

022 074

395 200

23 1 6 4

164 1 0 6

92

91

11

u 21

Legend: h

I

H

Figure 9. Distribution of the main groups of the macrozoobenthos in the different horizons of the hyporheic zone: A-Amphipoda, Ch-Chironomidae, D-other Diptera, H-Hirudinea, 0-Oligochaeta, T-Trichoptera, Ot-Others

40 0. STeRBA ET A L .

MACROZOOBENTHOS

Figure 10. Seasonal variation of abundance of macrozoobenthos in the different horizons of the hyporheic zone

Table 11. Presence of taxa in the different horizons of the hyporheic zone

Depth (cm) 0-10 11 -20 21-30 3 1-40 41-50 51-60 61-70 Station A B A B A B A B A B A B A B

Gastropoda + + + + Oligochaeta + + + + + + + + + + + + + lsopoda + Amphipoda + + + + + + + + Ephemeroptera + + Trichoptera + + + + + + + + + + Tipulidae + + + Psychodidae + Ceratopogonidae + + + + + + + Chironomidae larvae + + + + + + + + + + + + + Chironomidae pupae + + + + + + + Athericidae + + + Elmidae +

Hirudinea + + + + + + + + + +

Limoniidae + + + +

surface stream and subsurface water in 'small bottom circulation' is most clearly demonstrated by the temperature and dissolved 0, data. 0, in the hyporheic zone is consumed in a number of intensive biological decomposition processes. There is an absence of sources of 0, in the hyporheic zone. Therefore with increasing depths there is a rapid decline in 0,. The amount of time the water is retained underground is also an important factor.

There is a significant content of dissolved organic matter due to the decomposing biological processes in the upper layers of sediments (Williams and Hynes, 1974; Williams, 1989). In our example, again there is a perceptible difference between the value of BOD and COD in the two stations. The decrease in value of both parameters with depth is due to the retention of the water in the sediment, most significantly at station 9.

Changes in the physical and chemical conditions in different layers of the hyporheic zone have been investigated by several authors, for example Husmann (1968,1971); Williams and Hynes (1974); Pennak and Ward (1986); Williams (1989) and others. Our findings were in general agreement with the cited authors especially with regard to the tendency for several factors to change with depth in the channel bed. In Table 111, correlation coefficients between several parameters of the compared stations are shown. It is evident that the relationships between pH, 0, and NO; at station A are very distinct with increasing depth, much more so than at station B.

Table 111. Correlation coefficient between the chosen parameters

Depth Temperature Dissolved oxygen NO; Po: -

Pararne ters (cm) ("C) (mg1-l) PH (mg 1 - l ) (mg1-l)

Station A Temperature ("C)

Diss. 0, (mg I - ' )

PH

Station B Temperature ("C)

PH

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

Surface 20 40 60 80

1.OOoo - 0.6677* 1 .OOoo - 0.3302 1 ~OOoO - 0.48 17t 1 ~oooo - 0.297 1 1 ~oooo - 0.4394t

1.oOOo 1 ~oooo 1 ~oooo 1 ~oooo 1 ~oooo

1 .OOoo - 0.6343* 1 .OOoo -0.0550 1 ~oooo 0.1231 1 ~oooo -0.1444 1 .OOoo - 0.3873

1.oOOo 1 .oOOo 1 .oOOo 1 .oOOo 1 ~OOoO

0.08 1 1 - 0.2309 -0.3234 -0.3570 -0.3701

-0.0175 0.59 14* 0.7003* 0-7994* 043375*

1 .oOOo 1 .oOOo 1 .oooo 1 .oOOo 1 .oOOo

0.0507 - 0.1254 - 0.1525 -0.3861 - 0.47091-

- 0~009 1 0.6760* 0.5085t

- 0-2082 - 0.0294

1 .oOOo 1 .oOOo 1 .oOOo 1 .oOOo 1 ,oOOo

- 0.4789* - 0.5066t -0.5738* -0.5283t -0.3676

0.495 5 t 0.5853t 0.6405* 0.7013* 0.9636*

0.3378 0.4465t 0.4773t 0.8202* 0.8349*

1 .oOOo 1.oOOo 1 ~OOoO 1 ~OOOO 1 ~oooo

-0.5102* - 0.2 1 36 - 0.0346

0.1313 -0.3655

0.48461- 0.1974

-0.1563 - 0.1 104 - 0.008 1

0.2721 0.5509t 0.2722

- 0.1 11 1 0.3478

1 ~OOOO 1 ~OOOO 1~0000 1 .oOOo 1.oOOo

0.1504 0.0263 0.2588 0.1 137 0.2586

-0.251 5 -0.0334 -0.1 045 - 0.0643 - 0.2057

-0.0758 -0.2788 - 0.0734 - 0.0726 - 0.2685

- 0.3778 - 0-2394 -0.1157 - 0.0395 -0.1660

1 .oOOo 1 .oOOo 1.oOOo 1 .oOOo 1.oOOo

0.1782 0.1 842 0.2867 0.2779 0.1 529

- 0.2 1 38 -0.2282 -0.2219 - 0.2 173 - 0.2438

-0.0113 -0.3936 -0.2951 - 0.33 1 6 - 0.1 994

- 0.3 101 - 0.1 574 - 0.0289

0.0709 0.0286

1 .oooo 1 .oOOo 1 ~oooo 1 .oOOo 1 ~oooo

* values are significant at 1% level t values are significant at 5% level

42 0. STBRBA ET AL.

Conductivity regularly increases with increasing depth (Williams, 1989) and the period of retention of water underground. This is in accordance with the changes in the mineralization of organic matter which increases the concentration of the conductive ions.

The quantitative and qualitative occurrence of algae both in surface water and at greater depths is subject to seasonal changes. At 20 cm depth, a shift is observed as compared to the situation on the surface. At deeper horizons seasonal variations are inconspicuous and the number of algae is at a very low level, as also recorded by PouliEkova (1987). However, it is extremely interesting that the algae reach such deep sediment layers, where the conditions are quite unfavourable. Wasmund (1989), suggested that the transport of interstitial water is responsible for carrying the algae into the deeper sediment layers. The circulation of interstitial water in sandy sediments can reach considerable depths (Hesslein, 1980; Grimm and Fisher, 1984), transporting the algae slowly into the deeper zones. Algae probably penetrate into the ground waters by infiltration, though active penetation can not be ruled out, as was suggested by Harper (1969), Round (1978), Heckman (1989, Wasmund (1989). However, the probability of algal penetration to different depths is evidently not the same in all taxa. The Bacillariophyceae penetrates most easily, its size and shape here playing quite a significant role.

The quality of the substrate probably has the greatest influence on the macrobenthic utilization of the hyporheic zone. Bishop (1973) showed a distinct discontinuity in the distribution of zoobenthos between layers 0-10 and 11-20cm, which corresponds to the physical effect of the substrate-the first layer was composed of coarse gravel, of about 5 cm diameter. With the absence of mud and detritus, interstitial spaces were free and the fauna comprised filter-feeders and phytophages (algivores), which preferred this environment. In lower layers, mud and detritus accumulated-the substrate was more compacted with a sharp decline of 0, levels, but more detrital food was accessible to the detritiphages present. The effect of the substrate on the distribution of zoobenthos was also characterized by Williams and Hynes (1974), Hynes et af. (1976).

The next physical factor is the flow of water in the hyporheic zone (Williams and Hynes, 1974), which is related to the fluctuation of the water level in the surface stream, the permeability of the substrate, and the morphology of the bed. Thus, we found a high taxonomic diversity in deeper horizons (50-70cm), at station A, on the upstream slope of the riffle (an area of downwelling) and a very poor community at station B on the downstream face (an area of upwelling). The zoobenthic community at station B was probably affected by the different gravity of water having a long residence time in the substrate.

Organic pollution of the surface stream in October and November was related to sugar-beet processing. On the surface of the river bottom a massive growth of bacteria (SphaerotiEus) took place. BOD behaved differently than in summer months, showing almost double the values. Together with the organic pollution, the lower temperatures of the surface water may have stimulated the migration of Trichoptera, Chironomi- dae and Oligochaeta (to 70 cm) and Hirudinea (to 50 cm) at station A.

ACKNOWLEDGEMENTS

The authors acknowledge and thank Dr Milena Krgkova and Dr Milan Elfmark of the Computer Centre U.P. Olomouc, who generously helped us with computer statistics and graphs, as well as Troy McGrath for help with the English text.

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Harper, M. A. 1969. ‘Movement and migration of diatoms on sand grains’, Brit. Phycol. J., 4, 97-103. Heckman, Ch. W. 1985. ‘The development of vertical migration patterns in the sediments of estuaries as a strategy for algae to resist drift

Hesslein, R. H. 1980. ‘In situ measurements of pore water diffusion coefficients using triated water’, Can. J. Fish. Aquat. Sci., 37,545-551.

cycling’, Hydrobiologia, 111, 219-228.

with tidal currents’, fnf. Revue ges. Hydrobiol., 70(1), 151-164.

RIFFLE-SCALE VARIATIONS 43

Husmann, S. 1968. ‘Langsamfilter als Biotopmodelle der experimentalokologischen Grundwasserforschung’, Gewiisser und Abwiisser,

Husmann, S . 1971. ‘Eine neue Methode zur Entnahme von Interstitialwasser aus subaquatischen Lockergesteinen (A new method for

Hynes, H. B. N., Williams, D. D., and Williams, N. E. 1976. ‘Distribution of the benthos within the substratum of a Welsh mountain

KolaEnjl, M. 1975. Fauna podzemnich poiifnich vod s ohledem nu strukturu sedimentu, Diplomova prace PfF UP Olomouc, 55 pp. Pennak, R. W. and Ward, J. V. 1986. ‘Interstitial faunal communities of the hyporheic and adjacent groundwater biotopes ofa Colorado

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Round, F. E. 1978. ‘On rhythmic movement of the diatom Amphora ovalis’, Brit. Phycol. J., 13, 311-317. Sttrba, 0. 1990. ‘ & h i dno a samofiMni. Sbor.ref.ze sem. RiEni dno’, f%.S u Geogrufickj ustav &A V Bmo, Kupuiovice, zaii 1990,

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Williams, D. D. and Hynes, H. B. N. 1974. ‘The occurrence of benthos deep in the substratum of a stream’, Freshw. Biol., 4,233-256.

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taking interstitial water out of submerged layers of sand and gravel)’, Arch. Hydrobiol., 68(4), 519-527.

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