changes in freshwater meiofauna communities along the groundwater-hyporheic water ecotone

Changes in Freshwater Meiofauna Communities along the Groundwater-Hyporheic WaterEcotoneAuthor(s): D. Dudley WilliamsSource: Transactions of the American Microscopical Society, Vol. 112, No. 3 (Jul., 1993), pp.181-194Published by: Wiley on behalf of American Microscopical SocietyStable URL: http://www.jstor.org/stable/3226677 .

Accessed: 25/06/2014 10:51

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Wiley and American Microscopical Society are collaborating with JSTOR to digitize, preserve and extendaccess to Transactions of the American Microscopical Society.

http://www.jstor.org

This content downloaded from 195.34.79.192 on Wed, 25 Jun 2014 10:51:36 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=black

http://www.jstor.org/action/showPublisher?publisherCode=amicros

http://www.jstor.org/stable/3226677?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


TRANSACTIONS

of the

American Microscopical Society

VOL. 112 July 1993 NO. 3

Changes in Freshwater Meiofauna Communities Along the Groundwater-Hyporheic Water Ecotone'

D. DUDLEY WILLIAMS

Division of Life Sciences, Scarborough Campus, University of Toronto, 1265 Military Trail, Scarborough, Ontario M1C 1A4, Canada

Abstract. The interstitial meiofaunas of two small rivers in southern Ontario, Canada were examined in cores taken along transects through their beds. Analyses of interstitial water revealed chemical discontinuities associated with the river margins; these discontinuities were deemed to represent the groundwater-hyporheic water interface. A classification analysis (TWINSPAN) showed that at Duffin Creek, tardigrades, mesostigmatid and oribatid mites, and enchytraeid worms occurred primarily in groundwater beneath the bank, whereas naidid and tubificid oligochaetes, prostigmatid mites, ostracods, and microturbellarians were more abundant on the hyporheic side of the interface. Nematodes and rotifers spanned the transect. In the Rouge River, enchytraeid worms, ascid mites, and Mononchus sp. (Nematoda) occurred on the groundwater side of the interface, whereas rotifers, naidid and tubificid worms, microturbellarians, tardigrades, lebertiid mites, and other nematodes were more common in the hyporheic zone. Ostracods spanned the transect. There were relatively few species common to the interstices of these two rivers; however, the cyclopoid copepod Diacyclops crassicaudis brachycercus was restricted to the hyporheic zones of both. The distributions of a few taxa were correlated with interstitial water chemistry.

Extending both downwards and laterally into the beds of streams with porous substrates is the hyporheic zone. It is a region bordered by epigean water above and by groundwater below and to the side. Its physical and chemical characteristics differ from those in both these adjacent water masses (Williams, 1989). Although its upper and lower boundaries are thought to shift according to seasonal and topographically related changes in the relative strengths of base

' I am grateful to Kathy Moore, Gerrie Dunn, Susan Dix, Marilyn Smith, and Knud Wall for technical assistance. The following taxonomic specialists identified or confirmed the identity of the meiofauna: Dr. B. A. Ebsary, Biosystematics Research Centre, Ottawa (Nematoda); Mr. R. Chen- galath, Canadian Museum of Nature, Ottawa (Rotifera); Dr. H. C. Yeatman, University of the South, Tennessee (Copepoda); Dr. J. R. Pickavance, Memorial University of Newfoundland (Oli- gochaeta); and Drs. V. Behan-Pelletier and I. M. Smith, B.R.C., Ottawa (Acari). Professor Nancy Williams commented on the manuscript. The research was funded by a grant from the Natural Sciences and Engineering Research Council of Canada.

TRANS. AM. MICROSC. Soc., 112(3): 181-194. 1993. ? Copyright, 1993, by the American Microscopical Society, Inc.



flow and surface flow, it is a unique interstitial ecotone (Williams, 1992). The fauna, termed hyporheos, consists: (1) of taxa derived from hypogean environments such as groundwater, subterranean waterbodies, and the soil; (2) of species from the benthos (particularly the early-instar larvae of insects); and (3) of the immature stages of a few taxa that, though not endemic to this habitat, typically occur there (e.g., the chironomid genera Krenosmittia and Lopescladius; Coff- man & Ferrington, 1984).

Relatively little is known about the features of the lower boundary of the zone; i.e., where it meets the true groundwater. Williams (1989) attempted to define this boundary in two small rivers in Canada by sampling the interstitial water and fauna along a transect from the channel into the bank on each river. The groundwater-hyporheic interfaces were located by examining these data for discontinuities. The hyporheos of these two rivers was dominated by insects, particularly larval chironomids. It harbored few harpacticoid copepods, bathy- nellacids, amphipods, or isopods, taxa reported to be common interstitial forms in other lotic systems (e.g., Danielopol, 1976; Pennak & Ward, 1986). Although Williams (1989) identified some of the non-insect components in the Canadian study, few details of these taxa were known at that time. Further taxonomic treatment of the samples now allows more specific characterization of this important meiofaunal fraction of the hyporheos. The purpose of the present paper is, therefore, to report on the distribution patterns of non-insect inver- tebrates, namely rotifers, nematodes, tardigrades, oligochaetes, microturbellarians, ostracods, copepods, and mites along the groundwater-hyporheic water ecotone of two small rivers in southern Ontario, Canada.

MATERIALS AND METHODS

The two rivers studied were Duffin Creek, Durham County (43?54'N, 79?05'W) and the Rouge River, Borough of Scarborough (43?52'N, 79?11'W). At the sampling points, the former was approximately 5 m wide and 20 cm deep (mid-river current, 60 cm/sec) when studied in August, whereas the latter was approximately 6 m wide and 45 cm deep (mid-river current, 40 cm/sec) in July. Both rivers run through a region of drumlinized till plain created by Pleistocene glaciation and, consequently, have beds composed of a mixture of sand, gravel, and cobble underlain by clay. Both are characterized as hardwater (>65 ppm Ca), alkaline (>200 ppm HCO3) rivers.

On Duffin Creek, five sampling stations were established along a horizontal line running from mid-river on to the bank. These stations were designated "margin" (the transition between the water and the land), "+1 m" (1 m into the river from the margin), "+2m" (2 m into the river), "-1 m" (1 m into the bank from the margin), and "-2 m" (2 m into the bank). On 24 August 1981, three replicate cores (using the 25-cm3 sample size standpipe corer described by Williams & Hynes, 1974) were taken at depth intervals between 10 and 20 cm from the surface down to the clay layer at each station. Three surface benthos samples also were taken using a Mundie sampler (Mundie, 1971) fitted with a 53-Anm mesh capture net. Faunal samples were preserved immediately with 10% formalin solution containing Rose Bengal in suspension. Samples of

182 TRANS. AM. MICROSC. SOC.



VOL. 112, NO. 3, JULY 1993

interstitial water (1 L) were taken immediately after coring was completed using standpipes (see Williams & Hynes, 1974). Interstitial water temperature, dissolved oxygen, pH, and specific conductance were measured in the field with portable meters, whereas other measurements were performed subse- quently in the laboratory.

Six sampling stations were set up on the Rouge River: 1 and 2 m into the river ("+1 m," "+2 m"), "margin," and 1, 2 and 3 m into the bank ("-1 m," "-2 m," "-3 m"). On 27 July 1981, cores, Mundie samples, and interstitial water were taken as at Duffin Creek. At each river, the level of the groundwater table under the bank was determined by digging small trenches adjacent to the sampling stations.

In the laboratory, animals and detritus were separated from inorganic residue by floating each sample in saturated calcium chloride solution. Animals were identified, counted, and stored in 70% ethanol.

To objectively determine any discontinuities in the distribution of the interstitial faunas, the data from the cores and Mundie samples were subjected to both ordination (DECORANA; Hill, 1979a) and classification (TWINSPAN; Hill, 1979b) analyses.

RESULTS

In the Rouge River, which has a porous bed some 40 cm deep underlain by clay, changes in several chemical characteristics occurred from a point near the bank/surface water margin obliquely beneath the river. Levels of alkalinity, measured as mg L-1 of CaCO3 in July were similar for the river water and interstitial water immediately beneath the channel. However, on the bank side of the breakline, levels were considerably higher (Table I). Similar patterns were evident for specific conductance and dissolved carbon dioxide, although surface-water levels of the latter were lower. Nitrate-N levels were, conversely, much lower under the bank. There was no obvious breakline apparent in the levels of orthophosphate across the transect; concentrations were quite variable, although generally they were much greater in the interstices.

In August in nearby Duffin Creek, which has a deeper bed, two breaklines were evident. The first, typified by dissolved oxygen, organic matter, alkalinity, suspended solids, B.O.D., and carbon dioxide, ran from about the river margin obliquely beneath the bank. The second ran from near the margin obliquely beneath the river bed and was the profile reflected by nitrate-N and sulfide levels. Orthophosphate concentrations had a tendency to be higher in the interstices. Levels of both nitrate-N and orthophosphate were considerably lower in Duffin Creek than in the Rouge River (Table I). Further details on the interstitial water chemistry of these two rivers is given by Williams (1989).

Confirmation of the positions of the hyporheic boundaries, proposed on the basis of chemical discontinuities, in the two Canadian rivers came from an analysis of the distribution patterns of their respective faunas (cf. Williams, 1989). Ordination (DECORANA) and community classification (TWINSPAN) techniques indicated that, in both rivers, the factor most closely associated with community structure was linear distance from mid-river. In each system, a

183



TRANS. AM. MICROSC. SOC.

TABLE I

Chemical characteristics that identify the two water masses beneath both Ontario rivers

Concentration on Concentration on river side of bank side of

Characteristic breakline (x ? 1 SE) breakline ( +? 1 SE)

Rouge River

Alkalinity (mg L-1 CaCO3) 185.9 ? 2.5 281.4 ? 9.7

Specific conductance (mS) 2.4 ? 0.1 3.3 ? 0.1 Dissolved carbon dioxide (mg L-l1) 7.0 ? 0.7 17.2 ? 2.0 Nitrate-N (Ag L-1) 251.4 ? 40.7 13.8 ? 6.0

Orthophosphate (Mtg L-1) 240.0 ? 113.3 632.0 ? 167.7

Duffin Creek

Alkalinity (mg L-1 CaCO3) 201.8 ? 7.6 250.3 ? 17.2

Dissolved carbon dioxide (mg L-1) 6.8 ? 1.2 11.6 ? 1.3 Nitrate-N (Mg L-1) 57.8 + 18.4 21.7 ? 7.7 Orthophosphate (,ug L-1) 69.2 ? 11.3 66.3 ? 11.9 Dissolved oxygen (mg L-1) 3.5 ? 1.3 0.6 ? 0.3 B.O.D. (mg L-1 24 h-1) 0.3 ? 0.06 0.1 ? 0.03

Organic matter (% wt) 1.7 ? 0.7 3.8 ? 0.7

Suspended solids (g L-1) 3.1 ? 0.5 14.6 ? 4.5

Sulphide (mg L-1) 8.6 ? 1.5 11.4 ? 0.8

river community was distinguished from a community under the bank, and these were separated by a community characteristic of the river margin, the latter corresponding to the approximate position of the chemical breakline (the hyporheic-groundwater interface). Additionally, in Duffin Creek, the analysis distinguished between a surface (benthic) and a hyporheic community, indic- ative of the predicted upper boundary.

The nematode faunas of the two rivers were dissimilar, with only Tobrilus sp. (Enoplida) being common to both. In the Rouge River (Fig. 1A), Mononchus sp. was identified by TWINSPAN as an indicator species of the bank community and thus was found only in the groundwater. Prismatolaimus sp. and Tobrilus sp. were typically found in the hyporheic zone, but at the groundwater-hyporheic interface they coexisted with Mononchus sp. There was a positive linear relationship between total nematode density and the sulfide concentrations found in the interstitial water (y = 2.98x - 4.73; r2 = 0.364; P < 0.05).

FIG. 1. Total number of nematodes collected in three core samples (pooled total volume, 75 cm3 of substrate) at each of the 18 sampling points beneath the Rouge River (Fig. 1A) and 27

sampling points beneath Duffin Creek (Fig. lB), together with densities at two points on the surface of each river bed (also expressed as numbers/75 cm3 of substrate). The distributions of the most common species across the transects also are shown, as are the proposed locations of the groundwater- hyporheic water boundaries (stippled) derived from discontinuities in interstitial water chemistry [see Williams (1989) for further details]; * indicates a sampling location where no nematodes were found.

184



VOL. 112, NO. 3, JULY 1993

Dorylaimida : Monhysterida Dorylaimida Tylenchida Monhysterida Monhysterida

Hemicycliophora :Monhystera sp. :Monhystera sp. sp. I

Enoplida I , Enoplida Tobrilus sp.

Tobrilus sp. I Tobrilus sp. I

Dorylaimida (? n. gen.)

Tylenchida Hemicycliophora sp.

+2m B

Stream = -- Surface

4 Stream . 36 Bed

-10cm 27

-20

-30

-40

-50

-60

-70 , Z 7Z 72 _ _

-

185



Bdelloida Bdelloida I , t (unident.) I (unident.) I i Ploima - Notommatidae

Ploima , Ploima I Cephalodella sp. Cephalodella sp. Cephalodella sp., Notommata sp. I I

-2m -lm Margin +lm +2m B

297 v.\e~ 22 =====Stream 2?:" 86

---2 _ _ _ __ Surface

14 23 11 _ * Stream 25 3n30 Bed

25 3 15 53 65 -10cm

15 76 -20

17 53 -30

37 l7 35

16 -40

72 27 29

10cm

40-

50-

60-

70-

80-

90- -50 15 -60

21 -70

iii I I I III I ml I I I II I III i i i i

I .



VOL. 112, NO. 3, JULY 1993

In Duffin Creek (Fig. IB), Tobrilus sp. was found both in the groundwater and in the hyporheic water, as was Hemicycliophora sp. (Tylenchida). Monhystera sp. (Monhysterida) was found in the region of the groundwater-hyporheic water interface. Nematode density in this river was not correlated with any of the chemical characteristics measured.

In the Rouge River, rotifers were common in the hyporheic zone, but rare in the groundwater (Fig. 2A). Species identified were Cephalodella gibba (No- tommatidae) and Dicranophorus uncinatus (Dicranophoridae); unidentifiable bdelloids also were present. By contrast, in Duffin Creek, rotifers spanned the entire transect (Fig. 2B). A species of Cephalodella occurred both in the groundwater and the hyporheic water, whereas Notommata sp. appeared to be confined to the hyporheic zone. Bdelloids were common in both the groundwater and at the groundwater-hyporheic water interface (poor specimen preservation prohibited further identification).

Microturbellarians were confined mostly to the hyporheic zones of both rivers (Fig. 3A, B). They did not survive sample preservation and processing well, and their identities are uncertain; they are members of the Macrostomatida. They were more abundant in Duffin Creek, where they extended across the groundwater-hyporheic water interface into the damp soil of the bank above the groundwater table (Fig. 3B).

Four species of cyclopoid copepods and one species of harpacticoid copepod were collected in the Rouge River. Eucyclops agilis montanus (Brady), Dia- cyclops crassicaudis brachycercus (Kiefer), and Paracyclops fimbriatus (Fisch- er) occurred only in the hyporheic zone, although the first species ranged as far as the groundwater interface (Fig. 4A). The harpacticoid Attheyella nordenskioldii (Lilljeborg) was collected only from the groundwater. TWINSPAN identified Diacyclops nearcticus (Kiefer) as being a prominent species in the groundwater community.

Copepods were far less common in the interstices beneath Duffin Creek, and only one species appeared to be present (although there were some juveniles that could not be identified). Diacyclops c. brachycercus was, as in the Rouge River, restricted to the hyporheic zone (Fig. 4B). Its distribution was related to the concentration of nitrate in the interstitial water (y = 0.37 - 0.06x + O.OO0x2; r2 = 0.457; P < 0.05).

Tubificid [primarily Limnodrilus hoffmeisteri (Claparede)] and naidid oligochaetes (Pristina sp.) were abundant in the hyporheic water of the Rouge River, with a few specimens extending past the interface and into the groundwater (Fig. 5A). Enchytraeids and immature tubificids were common in the

FIG. 2. Total number of rotifers collected in three core samples (pooled total volume, 75 cm3 of substrate) at each of the 18 sampling points beneath the Rouge River (Fig. 2A) and 27 sampling points beneath Duffin Creek (Fig. 2B), together with densities at two points on the surface of each river bed (also expressed as numbers/75 cm3 of substrate). The distributions of the most common taxa across the transects also are shown; * indicates a sampling location where no rotifers were found.

187



TRANS. AM. MICROSC. SOC. 188

FIG. 3. Total number of microturbellarians collected in three core samples (pooled total volume, 75 cm3 of substrate) at each of the 18 sampling points beneath the Rouge River (Fig. 3A) and 27

sampling points beneath Duffin Creek (Fig. 3B), together with densities at two points on the surface of each river bed (also expressed as numbers/75 cm3 of substrate).



189 VOL. 112, NO. 3, JULY 1993

Diac ne:

-3m -2m -Im Margin +1m

I

A +2m

I

cm- <1' k Eucyclops agilis Watr0cm-<l <1 ' ~ . montanus Eucyclops agilis montanus

20- ----Water Paracyclops fimbriatus Stream Table ' . -- , ,- surface

130- 2 4 2--._ Stream :-yclops _Bed 7 8 24 ycticus 7'2ac

7 Diacyclops Y//J V^nearcticus.. 15 72 17 nearcticus

/////, / ttheyella//Diacyclops * 43 22 Diacyclops c. ///nordenskioldii/ nearc c s brachycercus

//////d o///i//~ ear/////, Paracyclops fimbriatus

/.////////////////////Eucy Eucyclops a. montanus/ /2 71 ..LZ//&6Z//////// / niDiacyclops c. brachycercus

-2m -Im Margin +lm +2m

* * Diacylops crassicaudis 20- * ^^IUe_ brachycercus Stream

Surface

60- .~* 20 -10cm 80- *?2 8 -20

70- -30

80- * . . 8 . -40

90- -50

100- * 6 1 * -60

70/g, -70 1~~~~~~~~-70

FIG. 4. Total number of copepods collected in three core samples (pooled total volume, 75 cm3

of substrate) at each of the 18 sampling points beneath the Rouge River (Fig. 4A) and 27 sampling points beneath Duffin Creek (Fig. 4B), together with densities at two points on the surface of each river bed (also expressed as numbers/75 cm3 of substrate). The distributions of the most common

species across the transects also are shown.

I_

--- ~ ~ ~ ~ ~ ~ ~ ~ ~ _

I

I



moist soil of the bank, above the groundwater table, but also occurred in the groundwater, although in lesser abundance. Across the transect, total oligochaete densities were positively correlated with interstitial nitrate levels and the amount of organic matter present (r = 0.621 and 0.652, respectively).

Virtually all of the oligochaetes collected from Duffin Creek were immature, which made specific identifications problematic. Although the distribution profile among families was similar to that seen in the Rouge River (Fig. 5B), naidids dominated the hyporheic zone and also extended past the hyporheic-groundwater interface into the moist soil of the bank. Tubificids occurred primarily in the surface benthos and at the hyporheic-groundwater interface. Total oligochaete densities were, as in the Rouge, positively correlated with interstitial nitrate levels (r = 0.713), but also negatively with sulfide levels (r = -0.544).

Additional meiofaunal taxa were identified by TWINSPAN as characteristic of the different interstitial zones. For example, in Duffin Creek the ostracods were an indicator group for the hyporheic-groundwater interface, with mesostigmatid and oribatid mites also predominating in this region. Tardigrades predominated in the cores taken from the groundwater zone, whereas prostigmatid mites and a second species of ostracod characterized the hyporheic zone. In the Rouge River, the ascid mites Cheiroseius nr curtipes (Halbert) and Arctoseius cetratus (Sellnick) were identified as prominent members of the groundwater zone. The surface benthos and underlying hyporheic zone (TWIN- SPAN did not distinguish between these two regions in this river) was characterized by tardigrades and lebertiid mites, as well as by microturbellaria and rotifers.

DISCUSSION

Several of the chemical characteristics measured during this investigation indicate that, in both rivers, the interstitial water probably represented two masses, one primarily beneath the river bed, extending to roughly the margin, and the other extending away from the margin, beneath the bank. Williams (1989) proposed that these masses corresponded to the hyporheic water zone and the groundwater zone, respectively. Between these two zones was a region of transition deemed to represent the interface between the two water masses. Examination of the distribution patterns of the macrofauna largely supported the chemical evidence. Data on distribution of meiofauna reported here also reflect the subdivision of the water masses beneath these two rivers, with certain taxa standing out as biological indicators.

Nicholas (1984) concluded that no sharp distinction may be drawn between the nematode faunas of wet terrestrial environments and that of rivers, lakes, and ponds; i.e., the two faunas grade into one another. Evidence from both rivers studied here partially support this view, although, in the Rouge River, the nematode Mononchus sp. seemed to be a clear indicator of groundwater in that its numbers declined across the interface, and the species did not occur in the hyporheic zone. The Mononchidae are especially abundant in the soil, but some species of Mononchus are known to live in fresh waters (Poinar, 1983). The latter are predaceous, typically consuming other nematodes, rotifers,




VOL. 112, NO. 3, JULY 1993

-3m -2m -lm

4 I 4 Margin

i

A +lm +2m

4 4

imr re Tubificidae --.*nk 1ocm- 19 ^ immature

Water <1 Tubificidae 20- 3 3 T- - Tb - Stream

surface 30-

Tabis 4 2 32 31 Stream 30- 2 209 Stream ytraeidae 3 61

EPristinasp. <

72 61 136 Limnodrilus

////immmature 46 4 hffmeste //////Tubificidae //> 32 60 immature Tubificidae

////////////// Limnodrilus immature %////////C//////,lay .noffmeiste n-' T

//////////////////' ~"'"'i"cid ae/ Pristina sp. (Naididae)/// ....^ Tubf (adie -- 1

-2m -im Margin +lm +2m B

20- 30EN ^e _ ._ Stream

30- ,e""t* 16fTN ̂ ^Surface

-40 - - * . 10TNE -32NT Stream

50- 66N -10cm 60- 66N 15N

36TN -20 70- 4N -30

1ON . * E10N 80- -. 40

90- -50 100- 6 * 3N -60

-70

FIG. 5. Total number of aquatic and semi-aquatic oligochaetes collected in three core samples (pooled total volume, 75 cm3 of substrate) at each of the 18 sampling points beneath the Rouge River (Fig. 5A) and 27 sampling points beneath Duffin Creek (Fig. 5B), together with densities at two points on the surface of each river bed (also expressed as numbers/75 cm3 of substrate). For the Rouge River, the distributions of the most common taxa across the transects also are shown. In Duffin Creek, where most of the specimens collected were immature, the sizes of the letters (T, Tubificidae; N, Naididae; E, Enchytraeidae) reflect the relative numbers of worms belonging to the various families at each sampling point.

191

S . _

I I

I z z z z z z z z z z lr z z z z z z z z z z zz z z z z /'I



TRANS. AM. MICROSC. SOC.

tardigrades, small oligochaetes, and protozoa (see Goodey, 1963). By contrast, Prismatolaimus sp. revealed a reverse distribution profile. This genus includes many species reported from fresh waters, although some occur in damp soil (Goodey, 1963; Kiihnelt, 1976). In Duffin Creek, Monhystera sp. occurred only in the transition zone. Whereas most monhysterids are marine, a few species are known from soil and fresh waters (Poinar, 1983). The difference in distribution profiles of Tobrilus sp. between the two rivers is difficult to reconcile (widespread in Duffin Creek but primarily restricted to hyporheic water in the Rouge), but may be attributable to different species at the two sites. Most species in this genus have been recorded from fresh waters, but occasionally they occur in moist soil. Tobrilus gracilis is known to live several centimeters deep in anaerobic mud in Neusiedlersee, a large shallow lake in Austria (Schie- mer et al., 1969). The genus also is commonly represented in Lake Baikal (Schiemer et al., 1969). Species of Tobrilus, Mononchus, Dorylaimus, and Monhystera have all been recorded from the sediments in an alpine lake in Austria (Bretschko, 1973). Dorylaimids were found in the interstices of both Ontario rivers. These are generally large, robust nematodes whose prey includes other nematodes and oligochaetes, but mite eggs and small insect larvae as well. They also eat algae, detritus, and microorganisms (Poinar, 1983). Nematodes have been reported to be most abundant where the organic content of the sediment is high (Nicholas, 1984). No such relationship was observed during the present investigation, although nematode density was correlated with that of several representatives of other taxa that may have served as prey: in Duffin Creek, nematode densities were positively correlated with those of the following: larval chironomids, r = 0.863; oligochaetes, r = 0.820; microturbellarians, r =

0.789; copepods, r = 0.866; ostracods, r = 0.821; in the Rouge River, nematode densities were correlated only with those of ceratopogonid larvae, r = 0.626.

Whereas most of the rotifers were restricted to hyporheic water, a congeneric conflict in distribution (Cephalobdella sp. widespread in Duffin Creek, but C.

gibba only in the hyporheic zone in the Rouge) similar to that seen in the nematodes (Tobrilus sp.) occurred. Again, this might be attributable to specific requirements, or perhaps to differences between the interstitial environments of the two rivers. The genera of rotifers encountered were more characteristic of the littoral zone of lakes (Edmondson, 1959), although several species of rotifers are known to inhabit soil (Wallwork, 1976).

Differences among the environmental requirements of species may explain the anomalous distributions seen in some of the rarer taxa: e.g., the tardigrades (in the groundwater zone in Duffin Creek but in the surface/hyporheic zone in the Rouge) and the ostracods (hyporheic zone and hyporheic-groundwater interface in Duffin Creek).

In the Rouge, distribution of the copepod Diacyclops nearcticus was restricted to the groundwater, whereas that of D. crassicaudis brachycercus in both rivers was restricted to hyporheic water. Diacyclops nearcticus is seldom found in collections, perhaps because it inhabits rarely sampled habitats such as wells. D. c. brachycercus, too, is uncommon and occurs in wells in North Carolina, New York, and Quebec. This species has been found also in very

192



VOL. 112, NO. 3, JULY 1993

small temporary puddles and appears to have drought-resistant capacity (H. C. Yeatman, personal communication). Attheyella nordenskioldii in the Rouge appeared to occur only in the groundwater zone, but it also is known from the benthos of temporary streams; however, the species does retreat into the groundwater when these streams dry up (Williams & Hynes, 1976). A. nordenskioldii nordenskioldii is known to inhabit small tundra ponds and brooks in the arctic (Borutskii, 1964). Harpacticoids, in general, frequently and surprisingly are abundant in the moist soils of both temperate woodlands and arctic tundra (Wallwork, 1976).

The distribution of aquatic and semi-aquatic oligochaetes also provides a useful guide to the location of interstitial water masses. However, in this case, interpretations require both qualitative and quantitative data.

Clearly, the distribution profiles of many of the taxa comprising the interstitial meio- and macrofaunas of lotic systems may be used as an aid to identifying discrete subsurface water masses. However, our current knowledge of the basic biology and ecology of most of this fauna is sketchy. Perhaps such information will enable us, in the future, to refine the use of indicator species, and to elucidate interactions between surface and subsurface populations and communities, as well as their roles in processing the considerable reservoir of organic matter that accumulates in the form of detrital particles and biofilms in the interstices of stream beds.

LITERATURE CITED

BRETSCHKO, G. 1973. Benthos production of a high-mountain lake: Nematoda. Verh. Int. Verein. Theor. Angew. Limnol., 18: 1421-1428.

BORUTSKII, E. V. 1964. Crustacea. Fauna of the U.S.S.R., Vol. 3 (4), Freshwater Harpacticoida, Israel Progr. Sci. Transl., pp. 1-396.

COFFMAN, W. P. & FERRINGTON, L. C. 1984. Chironomidae. In Merritt, R. W. & Cummins, K. W., eds., An Introduction to the Aquatic Insects of North America, Kendall/Hunt, Dubuque, Iowa, pp. 551-653.

DANIELOPOL, D. 1976. The distribution of the fauna in the interstitial habitats of riverine sediments of the Danube and the Piesting (Austria). Int. J. Speleol., 8: 23-51.

EDMONDSON, W. T., ed. 1959. Rotifera. In Edmondson, W. T., Freshwater Biology, Wiley, New York, pp. 420-494.

GOODEY, T. 1963. Soil and Freshwater Nematodes. Methuen, London. 544 pp. HILL, M. 0. 1979a. DECORANA-A Fortran Program for Detrended Correspondence Analysis

and Reciprocal Averaging. Ecology and Systematics, Cornell University, Ithaca, New York. 52 pp.

1979b. TWINSPAN-A Fortran Program for Arranging Multivariate Data in an Ordered Two-way Table by Classification of the Individuals and Attributes. Ecology and Systematics, Cornell University, Ithaca, New York. 90 pp.

KUHNELT, W. 1976. Soil Biology. Michigan State University Press, East Lansing. 483 pp. MUNDIE, J. H. 1971. Sampling benthos and substrate materials, down to 50 microns in size, in

shallow streams. J. Fish. Res. Board Can., 28: 849-860. NICHOLAS, W. L. 1984. The Biology of Free-living Nematodes. Clarendon Press, Oxford.

251 pp. PENNAK, R. W. & WARD, J. V. 1986. Interstitial faunal communities of the hyporheic and adjacent

groundwater biotopes of a Colorado mountain stream. Arch. Hydrobiol. (Suppl.), 74: 356- 396.

193




POINAR, G. 0. 1983. The Natural History of Nematodes. Prentice-Hall, Englewood Cliffs, New Jersey. 323 pp.

SCHIEMER, F., LOFFLER, H. & DOLLFUSS, H. 1969. The benthic communities of Neusiedlersee. Verh. Int. Verein. Theor. Angew. Limnol., 17: 201-208.

WALLWORK, J. A. 1976. The Distribution and Diversity of Soil Fauna. Academic Press, London. 355 pp.

WILLIAMS, D. D. 1989. Towards a biological and chemical definition of the hyporheic zone in two Canadian rivers. Freshwater Biol., 22: 189-208.

1992. Nutrient and flow vector dynamics at the hyporheic-groundwater interface and their effects on the interstitial fauna. Hydrobiologia (In press)

WILLIAMS, D. D. & HYNES, H. B. N. 1974. The occurrence of benthos deep in the substratum of a stream. Freshwater Biol., 4: 233-256.

1976. The ecology of temporary streams I. The faunas of two Canadian streams. Int. Revue Gesamten Hydrobiol., 61: 761-787.



changes in freshwater meiofauna communities along the groundwater-hyporheic water ecotone

Documents