TECHNICAL REPORT NO. 1970 FISHERIES RESEARCH BOARD OF CANADA
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should be directed to the issuing PRB establishment which is indicated on the title page. FI SHERI ES RESEARCH BOARD OF CANADA TECHNI CAL REPORT NO. 196
A SURVEY OF THE BOTTOM FAUNA 1N LAKES
OF THE Q1(ANAGAN VALLEY. BRI 11 SH COLUMBI A
by
OLE A. SAETHER
This if the Thirteenth FR8 Technical Report from the
Fisheries Research Board of Canada
Freshwater I nstitute
Winnipeg, Manitoba. A Survey of the Bottom Fauna in Lakes of the Okanagan Valley, British Columbia
by
Ole A. Saether
Fisheries Research Board of Canada Freshwater Institute Sal University Crescent Winnipeg 19, Manitoba Ill.
Non-Technical Summary
Most lakes in glaciated regions were oligotrophic (low biological production) at the time of their formation. The general tendency is for these lakes to become more eutrophic (more productive) as they fill in with sediments. This proces~J the maturing of lakes, also known as natural eutrophication, is a very slow process. Indeed, many deep lakes have remained essentially unchanged for thousands or even tens of thousands of years. Biological productivity. however. is easily accelerated by man. Discharges of municipal or industrial wastes and extensive use of fertilizers have caused a large munber of lakes during the last few decades to become heavily populated with algae and, in shallow areas, rooted plants. The problems of this cultural eutrophication are well known. The changes of a lake from a nutrient-poor to nutrient-rich state affects all the living cOJIlllunities of the lake. In fact, the differences among communities in lakes, particularly the benthic couununity, formed the first base for classifying lakes into trophic (nourishment) types. It was discovered that in large, deep, clear lakes well supplied with oxygen. small midge-larvae of the genus TangtalL6U6 dominated. In smaller, shallower and more turbid waters the deeper layers were low in oxygen during periods of restricted circulation and large, blood-red midge-larvae of the genus Ch.iJwnomU6 were common. The large, deep lakes were later shown to be low in plant nutrients and with low populations of algae, while smaller lakes tended to be more richly supplied with nutrients and were characterized by high populations of algae. These findings led to the development of lake typology or the trophic classification of lakes. First two lake types were delineated: oligotrophic (low in nutrients) and eutrophic (rich in nutrients). Later lakes intermediate between the oligotrophic and eutrophic types were named mesotrophic. Further study of the bottom faunn and particularly the midges led to a division of deep water communities characterizing the different trophic levels. The main couununities can be divided into ultra- IV.
oligotrophic conununities (with for instance He.teItot/t..i..6.6ocl.a.diw hubp.UohlL6). moderately oligotrophic. mesotrophic (with for instance St.i.c..toch.iJwnorntL6). moderately eutrophic, and strongly eutrophic (with for instance Ch.iJwnomUh plwnO.6U6 and IJe.rn.iAe.duc..tu6 groups) conununities. At about the same time another approach to cOl1lnunity classification (the saprobic system) was being developed, based on animals living under conditions of moderate to severe pollution. While the levels of the trophic system are a function of the intensity of production, the levels in the saprobic system (from Greek, sapros=putrid) are a function of the intensity of decomposition. This latter system was originally founded on the theory that certain organisms are indicative of a certain level of pollution and that each of these organisms was able to live only at one particular level of pollution. However, there are few or no true saprobiontic animals in this restrictive sense. A few are saprophilous, Le. they prefer polluted areas but are also able to live in unpolluted localities. Perhaps the best example of such a saprophilous animal is the worm UmnociJLU.u.6 h066me.i.6teJLi. which is common in several areas of lakes in the Okanagan Valley. Any unusual increment in the density of a species associated with polluted environments or reduction in the number of species present can be regarded as useful evidence of pollution, the nature of which may be revealed by the identity of the surviving species. When assessing the relation between bottom fauna, lake enrichment and pollution one must, however, bear in mind that the distribution of invertebrates cannot be explained completely without taking both the temperature regime, lake morphology, and the zoogeographical distribution into consideration. Furthermore, among benthic animals, midges are better indicators of the oxygen level than of the trophic level. The oxygen level is not absolutely dependent on the primary production in the upper waters, but is strongly influenced by, among others, the relative volume of the deep water in the hypolimnion to that in the epilirmion. This means that lakes with nearly identical communities of bottom organisms may have different degrees of trophy. A strong correlation between trophic levels and bottom fauna composition thus v.
cannot always be expected, especially in mesotrophic lakes. In such lakes the number and weight of animals per area and the distribution with depth both of total bottom fauna and of forms characteristic for different trophic communities may be more important. This report is based on an attempt to determine pollution effects in three of the larger lakes of the Okanagan Basin (Okanagan. Skaha, and 050Y005) from a study of the bottom fauna. General characteristics of the lakes are summarized in the tabulation below together with information on the volumes of sewage currently (1968) discharged. It will be noted that Okanagan Lake has the lowest ratio of Se\lage effluent per lake volume and Skaha the largest ratio.with Osoyoos Lake occupying an intermediate position.
Lake Area Mean Max Vol. Theoret. PopUlation Annual sewage 2 3 8 km depth depth m xl0 water in drainage discharge in replace area mill. gallons ment time years
Okanagan 344 75 242 259.4 57.6 ca.40,000 1,000 Skaha 20 27 57 5.3 1.1 ca.20,OOO 438 Osoyoos 22 ca.lS 63 ca.l ca.5,000 60 Osoyoos 10 21 63 2.0 0.4 northern basin
In 1935 Rawson made a limnological study of Okanagan Lake including a survey of the bottom fauna. His results showed that the lake at that time was oligotrophic or even ultra-oligotrophic. The bottom fauna of the other two lakes has not been previously studied. In Okanagan Lake the gradation from eutrophic to oligotrophic communities at Station 13-17 in Vernon Bay, and around Station 4 (Station 1-6) at the sewer outlet from Kelowna indicates that major sources of VI.
pollution are located in these areas (Fig. I, 2). In fact, nearly all the treated domestic sewage that enters the lake enters at these localities. Minor sources of pollution were also inferred from the distribution and abundance of bottom organisms near Summerland and at Westbank (Fig. 1, 7). The lake as a whole. however, seems to have a bottom fauna not untypic..l of large oligotrophic lakes except for the somewhat high percentage of oligochaete worms. If Rawson's results had not been available one could easily arrive at the erroneous conclusion that Okanagan Lake as a whole has not been affected by human activity. However, since Rawson's investigation in the 1930's there has been a significant increase in total numbers of bottom invertebrates at all stations with the exception of stations deeper than SO m. The densities of midges and worms, respectively, have increased by about 4 and 35 times (Tables 2-4). Also, Rawson found that oligochaete worms formed only 15 per cent of the total bottom fauna of the lake, whereas they made up 50-60 per cent of the total at the time of this survey. This means that the lake is not only polluted in certain areas, but that the bottom fauna of the whole lake (except perhaps below SO m) has changed toward a more mesotrophic conununity. However. the presence of a few species characteristic of ultra-oligotrophic communities such as He.tVLotllA.MOclttd.i.u6 6ubp<£OhU.6 ",~.S:tylodJrihu, heJLi.ng-UtnM indicate that the situation has not yet reached even moderate eutrophy. The few samples taken in Skaha Lake are not sufficient to· characterize the lake in detail. However, the presence of moderately oligotrophic to mesotrophic forms at Station 33 and 36 as well as the complete absence of chironomids other than PILoc.t.a.eU.u..6 at the deeper stations may indicate that a dramatic change in the bottom fauna has recently taken place. The oxygen deficit is not severe enough to eliminate species of Ch..Uwnomu&. If, however. the fauna formerly consisted of moderately oligotrophic to mesotrophic forms. deteriorating conditions (for instance low oxygen in deep water) may have eliminated oligotrophic and mesotrophic forms in the deeper parts. but not in the shallower parts where there is still enough oxygen. Since the more pollution tolerant species have not yet recolonized the deeper parts of the lake it VII.
is suggested that the inferred change must either have been very recent or something else such as high insecticide levels are preventing recolonization. In 1967 a heavey increase of algal growth took place in Skaha with the Secchi disc visibility decreasing to 1.0-2.0 m from 3.5-4.8 min 1966. Osoyoos Lake is moderately eutrophic in the northern basin and strongly eutrophic in the central basin, judging from the composition of the bottom fauna. The central basin may be culturally eutrophied by the surrounding communities. The few samples taken. however. were not enough to indicate centres of pollution or changes in the trophic level in the lake. The lake has probably been moderately eutrophic for a very long time. At some stations in Okanagan and Skaha Lakes chironomids with deformed mouth-parts and thickened body walls were found. The localities of their occurrence always seemed to be near the borderline of species distributions. Such deformities have only been mentioned once before in the literature and it is therefore not a common phenomenon. However. a combination of reaction to toxic compounds and borderline existence may be the explanation of these deformities. A possibility which should be investigated is that insecticides may be the toxic compounds involved. Insecticides. in contrast to other toxic compounds. are highly toxic to insects. but do not seriously affect worms. This may well explain the increase of worms in relation to insects during the past 3S years. The retention of a high number of worm species further supports this theory. 1.
A Survey of the Bottom Fauna in Lakes of the Okanagan Valley. British Columbia
Introduction
Prior to the signing of an agreement between the Government of British Columbia and the Government of Canada on an investigation of the lakes of the Okanagan Basin some preliminary studies were necessary to examine the requirements for a benthic sampling program and the problems involved. The Okanagan Lake chain (including the three lakes studied, Okanagan, Skaha, Osoyoos) in the interior of British Columbia drain an area of 2,400 square miles. 2 Okanagan Lake is the largest with an area of 344 km , a maximum 3 8 depth of about 242 m, a mean depth of 7S m. a volume of 259.4 m x 10 J and a renewal time of 57.6 years. The cities of Kelowna (population 20.000) and Vernon (population 12,000) discharge large volumes of sewage into the lake. In 1968 the city of Vernon added about 400 million gallons of primary and secondary treated, chlorinated domestic sewage to Vernon Creek which enters Okanagan Lake in the northeastern bay (Station 13, Fig. I, 2). The input from Kelowna was, in the same year 680 million gallons (chlorinated) sewage (D.A. Clarke, pers. CODUn.). The Kelowna sewage enters the lake through a sewage pipe with an outlet just south of Kelowna at a. depth of about 40 m (Station 4, Fig. 1,2). In addition to these major inputs smaller amounts of sewage enter Okanagan Lake: through Otter Creek at Station 18 (from a sewage lagoon near Armstrong), through Brants Creek in Kelowna at Station 10 (with waste from a cannery and a winery); at Westbank, Station 7 (from a sewage lagoon serving about 300 people); at Okanagan Mission just south of Kelowna through ground disposal system (100-150 people served); and at Summerland,Station 29 (D.A. Clarke, pers. comm.). 2 Skaha Lake has an area of 28 km , a maximum depth of 57 m, a mean 8 depth of 27 m, a volume of 5.3 m3 x 10 , and a renewal time of 1.1 years. In 1968 the city of Penticton (population 17,000) discharged 438 million gallons of domestic sewage (chlorinated, activated sludge) into the Okanagan River which flows into Skaha (D.A. Clarke, pers. comm.). 2 Osoyoos Lake is 22 km in area with a maximum depth of 63 m and a mean depth of the northern basin of 21 m. The volume of the northern basin 8 is 2. °m3 10 , and the renewal time 0.4 years. The city ov Oliver (popUlation 2,000) discharged about 60 million gallons of dome~tic sewage (chlorinated activated sludge and trade waste treatment) into the lake in 1968 (D.A. Clarke, pers. comm.). Of the three lakes studied only the bottom fauna of Okanagan has been studied previously. Rawson (1939) examined the lake in 1935 and found that the benthos was typical for an oligotrophic or even an ultra oligotrophic lake. Reports by Coulthard and Stein (1967, 1969), by the Technical Committee of the Okanagan Watershed Pollution Control Council and by South Okanagan Health Unit (D.A. Clarke, pers. comm.) indicated that cultural enrichment had taken place since the investigation by Rawson. Similar indications could be found in several newspaper articles on the deterioration of the fisheries in the lakes, the necessity of closing beaches because of an exces sive coliform bacterial count, etc. The preliminary results found by Patalas (pers. comm.) suggest that the plankton volume in Okanagan Lake today is about four times higher than that found by Rawson. This is, however, still a relatively low amount. A comparison between the data of Rawson (1939) and those of Coulthard and Stein (1967, 1969) indicates significantly higher nitrogen and chloride levels today in Okanagan Lake than three decades ago.
Methods and Stations
The samples of benthos were collected ,September 9-11, 1969. In Okanagan Lake the sampling sites were concentrated around known sources of pollution with a few additional "unpolluted" localities included. In two other much smaller lakes, Skaha Lake and Osoyoos Lake, an attempt was made to select stations more representative for the different zones of the lake as a whole. A tall Birge-Ekman sampler weighted Idth 10 pounds of lead was used for the sampling. The samples were sieved through a 0.2 mm mesh size sieve whenever possible. Samples 1, 7, la, 11, 13, 14, 18, 24, 27, 28, 32, 36 and 42 were sieved through a 0.6 mm mesh sized sieve. In most cases the sediments filled up the sampler to about 2.5 inches from the top, i.e. ----_._------
3.
the preferred level mentioned by Flannagan (in press). Some of the littoral samples (1, 2, 10, 13. 28, 32, 42) contained only a couple of inches of sediments, mostly of sand, gravel or vegetation (Table 6). The samples were preserved with 4 per cent formalin. In addition to the bottom samples some exuviae and imagines were collected near Station 7 in Okanagan Lake.
Physical and Chemical Condition
Some selected measurements of temperature. oxygen and Secchi disc visibility are shown in Table 1. The oxygen values in the central stations of Okanagan Lake have not changed from the observations taken by Rawson (1939). While Rawson found a range of saturation values of 72 to 94 per cent. the present survey showed a range of 74-94 per cent (K. Patalas, pers. conun.). However. there seems to be some oxygen deficit in the northern bay. The oxygen deficit in Skaha Lake is not considered serious and corresponds to that expected in a mesotrophic lake, while Osoyoos Lake has an oxygen distribution characteristic of eutrophic lakes. Secchi disc visibility values are essentially the same in Okanagan Lake at present as those recorded by Rawson. They correspond with values found in harmonic oligotrophic lakes. In 1966 the visibility in Skaha Lake was 3.5-4.8 m. in 1967 it was 1.0-2.0 m (Clarke, pers. conun.). At the time of this survey the readings were 2.8 m, i.e. less than in the presumably more eutrophic Osoyoos Lake.
Notes on the Invertebrates Found
The species or species groups found in the different samples are shown in Table 6, while some additional records of chironomids (exuviae and imagines at Station 7) are listed in Table 7. Only a few species and species groups will be discussed here. Most of the species found are new to the areas west of the Rocky Mountains. 01 igochaeta
Naididae are found most commonly in the littoral zone associated wi th vegetation. A1r.c.te.ona.iA tomoncLi.. (Martin) was collected only from Osoyoos Lake. The dorsal chaetal bundles have about 6-8 needles [not 9 as mentioned by Brinkhurst (1964)], but the needles are so fine that 1,000 times magnification and phase or interference contrast is necessary to even see these needles. In other details the specimens are identical with those described by Brinkhurst (1964, p. 210). Among the Tubificidae collected, only UmnodJr.,i.t.,u.6 p1lO6uncLi..c.ota. (Verr.) is an indicator of oligotrophy. It is usually restricted to cold habitats. The two mature specimens found were taken in the deepest samples (87 and 117 m). Some of the immature UmnodJti..lu..6, however, may also belong to this species. Although this species occurs mainly in cold waters the English localities are a small pond, a polluted stream, and a canal (Brinkhurst 1965, p. 131). The other tubificids occur in all kinds of freshwater biotopes. However. Tub.i6ex .rub.i6ex (MUll.) and particularly WnncdJL.i.t.ul, ho66mwteJLi. Clap. can, by mass occurrence, be taken as indicators of low oxygen level and organic pollution. In such situations they are usually the only oligochaetes present. Stations with more than 1,000 individuals per m2 of L. ho66meA..6teJLi are represented in Fig. 1 by a solid circle. Localities with such conditions are situated near the polluted tributaries and in the more eutrophic northern bay of Okanagan Lake. In Skaha Lake and Osoyoos Lake most stations had either more than 1,000 L. ho66me.U:teJU 2 per m or less than 3 species of invertebrates per station. It should, however, be mentioned that 1,000 individuals per m2 is still a small density compared with the maximum of more than 100,000 individuals per 2 m reported from some grossly polluted localities. Rawson (1939) found that oligochaetes made up 15 per cent of the bottom organisms of Okanagan Lake, with chironomids accoWlting for 74 per cent (Table 2). During this survey the bottom fauna was found to be made up of 60 per cent oligochaetes and 33 per cent chironomids. Even excluding distinctly "polluted" localities the oligochaetes made up 52 per cent of the total (Table 3, 4). flowever, a wide diversity of oligochaetes seems, at the same time, to have been retained. Such an unusually high abundance of worms in relation to arth!"opods together wi th a high specific diversity of these worms, may, according to Brinkhurst (1966a) be taken to indicate pollution by insecticides possibly because of indiscriminate aerial spraying, washing water from hot-houses, or the release of sheep-dip to a stream or similar activities. Liebmann (1951, p. 699) mentions that as a rule the arthropods are much more resistant to toxic compounds than soft-walled invertebrates such as worms, mollusks and sponges. An exception to this rule is insecticides which though strongly toxic to arthropods, have little influence on worms and mollusks. In the Okanagan valley with its many orchards indiscriminate aerial spraying with insecticides may well have caused the undue abundance of worms in relation to arthropods. StylodJU..1.u.h heJLi.ng.ia.n.lUI Clap. is mentioned by Brinkhurst, Hamilton and Iierrington (1968, p. 11) as possibly having been introduced into the Great Lakes from Europe. If the identification of these immature specimens found in this area is correct the introduction theory is unlikely to hold up, since the accidental introduction of oligochaetes into lakes is most likely to take place by means of ocean-going vessels. The specimens found had a rounded prostomium and secondary annulation on anterior segments, i. e. in accordance with the description by Brinkhurst (1966b, p. 9). S. heJLi.n.g,ia.n.u.6 is often the most common oligochaete in the profundal lone of deep unproductive lakes of the palaearctic region. The occurrence at the deepest stations in Okanagan Lake is in accordance with this. K.i..n.c.cticUa.na he.xathec.a. Altman, the other lumbriculid collected, is the only oligochaete found which seems to be restricted to areas west of the Rockies. Chironomidae
(The nomenclature of Hamilton, Saether, and Oliver (1969) is followed here with the exception that SVlgeJttia. is retained as a subgenus of Phaenop6ectlut).
Among the Tanypodinae only species of PJt.oct.acU...u.6 .6. laL and a deformed Pentaneurini were found in the bottom samples. Some exuviae of Tanypu..6 sp., Ablabe.6my.ia. sp. and TlUene.mann.imy..ia sp., however, were collected at Station 7. Both PMc.t.ad..i.u..6 1.6 • .6VL J and PJt.ocla.d.i.u.6 IP.6.itOta..JtypU6) consisted of at least two species. Rawson (1939) did not mention PJtlJct.ac1i.u..6 .6. lo.J.:.. among the dominant genera of chironomids in Okanagan Lake. In the present survey, however, PJt.oc1..a.d..i.u..6 is one of the 2-3 dominant genera in Okanagan Lake. This change fits well with the manyfold increase of tubificids and with the fact that tubificids are often a main food of the mainly carnivorous PILOcla.cIi.u..6. Po.ttha6.tia. cf. !ong-imana. (K), PJt.o.tdnypu.6 cf. molt.i.o (Zett.) and Honoeu.amua cf. ba.tJtyph.ila K., the three Diamesinae found, are all characteristic in oligotrophic to mesotrophic lakes, but most commonly encountered in moderately oligotrophic lakes. The most abundant orthoclad in Okanagan Lake is HetetLO:tJti.....6.60ci.o..cii..u6 .6ubpilo.6U6 (K.). Brundin (1949, 1956) regards this species as the prime indicator of ultra-oligotrophic European lakes. In Okanagan Lake, however, it is found not only at the deepest stations but also at stations relatively close to sources of pollution (Stations 2, 3, 5) well as in the mesotrophic northern bay (Station 21, 22) (Fig. 2). Brinkhurst, Hamilton and Herrington (1968) found this species in the eastern part of Lake Erie, thus indicating that the species is either not so strictly confined to ultra-oligotrophic conditions as suggested by Brundin, or that the nearctic specimens have a slightly different ecology or that we in fact, have to deal with two morphological identical species (sibling species) one palaearctic and one nearctic. Rawson (1939) does not mention HeteJW:tJLi.6.6ocl.o.d.iu...6 from Okanagan Lake. He does, however, mention OJtt.hOcl.o..d.iU6 which probably in his terminology includes HUeJW.tJI.i..4.6oci.a.cUU6, CUc.otopu..6 ("PaJta.bL.i..c.hocla.d.iLu." group), a probable new genus near TW.6oci.a.cJ..i.u.6, and OlLtitoc1.acJ..i.u.6 {.6 • .6tA. J anne.c.te.n.6 Saeth. (previously recorded only from the littoral zone of a lake in Kenora, northwestern Ontario, and from a stream in Duck Mountains, i,fanitoba (Saether 1969, p. 64)). The immature stages of this species have certain features in common with the mainly lentic genera C'Li.c.otopu..6 and AcJt.i.c.otopu.6 as well as with the other subgenera of Olt.thoc.fA..d..i.uh. A larva presumably belonging to a new genus related to TW.6oc.fA..d..i.uh was found at Station 3, 5 and 12. It has relatively conspicuous paralabial plates without hairs, a single median labial tooth and seems to have only 4 segments in the antenna (Fig. 3 A-C). The C'Li.c.otopu..6 larvae of the IIpa.JtiJ..tJLi.choc.l.a.cU.u..6" type may be identical with C. alpic.ola. (Zett.). a cold-stenothermous boreoalpine species which in the Alps seems to be a profundal chironomid, i.e. contrary to other species of C'Uc.otopu..6. P.6e.ctJr.oc.f..a.diU6 1.6 . .6:tJr... J .6.imula.n6 (Joh.) was previously known only from New York and northwestern Ontario (Saether 1969, p. 84). The identity of the larvae and pupae from Okanagan Lake were confirmed by some male hypopygia prepared from male pupae. Exuviae of an unknown type probably belonging to a possible new subgenus of P.6e.ctJr.ocf..a.cUU6 were found at Station 7 (Fig. 3 D, E). The larvae of the Chiltol1omU6 .6a..Urta.tLi.U6 type may be identical with C. a.t/r...i...tib.<..a. f.lall. Larvae of C. a.t.Jt.,(;tib.<..a. which are without blood gills and have been reared from Lake Ontario (Johnson 1969). Also, Hamilton (in press) mentions C. cf. a..:t!t.ilib.<..a. from the deeper relatively well-oxygenated areas of some lakes in northwestern Ontario. C. a..tJr..i..;tiJ thus seems to be the only cold-stenothermic species of ClUJtonomU6 and is characteristic both in ultra-oligotrophic lakes and in the deeper layers of eutrophic lakes as long as the oxygen deficiency is not too severe. The author examined the chironomids in Lake Borrevann, Norway (0kland 1964), a eutrophic antlvraUJ'UL.6-ptwn0.6U6 lake. Here, too, cold stenothermic larvae of the .6aLi.naJt,iU6 type were present. These larvae may also be identical with C. a.t/t..i..ti.biA. Mall. or at least belong to a species with similar ecology. Larvae of the ChhLol1omlUl 06em.iJLe.duc.tu.6 type, Le. with small blood-gills on 10th segment and blood-gills of 11th segment reduced to about 2/3 as long as the segment is wide, were quite common in all three lakes. It is interesting to notice that one of the very few records from European lakes list·s this larval type together with C. haLi.naJLilUl type larvae in the above-mentioned Lake Borrevann. The larvae of the antllll4ci.nLL6, .thunrn.i. and plumOhi.UI types are, in Okanagan Lake, restricted to the littoral and littoriprofundal zones while the plwnOhlUl type in Osoyoos Lake also occurs in the profundal zone, Le. in accordance with the ecology of these larval types. Rawson (1939) mentions Cll..yp.tDch,i.lLlmomlUl as one of the dominant larval forms of Chironomidae in Okanagan Lake. However, PMa.c.h.iJtonomlUl, CJtyptocla.dopebno., HaAn.U.clUa, CJtyptotendipM, PaAacla.dopebno. and Cltyp.tochhLonomlUl, all of which are present in the lake, will probably all fall into the genus Cltyptoc.h.iJtonomlUl as he used it. There are at least two species of PaJLa..cta.dopehna present in Okanagan Lake. One of these may be identical with P. ObhCU/La. Brunk., a northern cold-stenothermic species which may be a glacial relict in more southern lakes. Exuviae presumably belonging to a new genus near Vemi.ClLyp.tDc.h.iJtonomlUl were found. At least two species of S.tictoc.h.iJl.onomtM were found, S. cf. lto06e.t1.6c.holdi. Zett. and S. cf. lU6.tJL.io Fabr. While S. h-iA.tJL.io is primarily a shallow water form, S. ltolJe.n..6c.holdi. is characteristic of median oligotrophic and mesotrophic lakes. The occurrence of these two species in Okanagan Lake is in accordance with this. S. cf. llohe.t1.6chotdi was found mainly in the presumably mesotrophic northern bays. A deformed SUctoc.h.iJtonomlUl possibly belonging to S. cf. 1l006e.Mc.ho.t.di. was found at a depth of 11 m in Skaha Lake. Also, two species of the subgenus SeJtge.nUa. of Phae.nop06e.c.tAa were found. One of them may be identical with SeJtge.ntia. ".tong.i..ve.n.:0t.i.6" in the sense of Wulker (1961). This species is primarily a northern inhabitant of shallow waters which has a somewhat wider ecological spectre than the closely related to S. c.o!l.auna Zett. characteristic of moderately oligotrophic to mesotrophic lakes. The Tanytarsinae in general are most common in oligotrophic to mesotrophic lakes. However, some species of ClA.do.ti1..ny:taJt.6UlJ t one of which mat be identical with that found in Okanagan Lake, nre often associated with mild pollution and may be quite resistant to low oxygen levels. Similar species may also be found among M.iCltOp6e.c..tA.a. and TanytaA6u.1,
Hydrachnellae
HygMbatu {Te.tJuz.batM I ne.o6ctopoJUL6 Marsh. has only been found in cold-stenothermic environments. The species of NeumaJtia. found is probably identical with N. pwtcta..ta Marsh. However, all species of Ne.umani.a. described by Marshall need revising.
Gastropoda
All the snails found are mainly associated with vegetation. The 2 difference in average number per m found in Okanagan Lake by Rawson 2 2 (1939), 2 ind. per m , and in this survey, 46 indo per m is probably not significant as the snails found were mainly restricted to three stations, 7, 8 and 18.
Mollusca
P.i..6,icUum c.omp!l.e..6.6um Prime is, next to P. ClUeJLta.num (Poli), the most common P.i..6,iciium in North America. lierrington (1962) mentions depth of 20 m as the maximum depth where it has been collected. However, a specimen was found at a depth of 78.5 m in this survey and Rawson (1939) found a distribution range in depth from approximately 8 to 250 feet (76 m). The species is present at 12 out of 32 stations and the 2 average number of 79 ind. per m seems 10
2 to be significantly higher than that of 2 indo per m fOWld by Rawson (rable 2, 3).
Deformed Chironomids
Brinkhurst, Hamilton and Herrington (1968, p. 22) mention some deformed specimens of Ch.Ut.onomu.6 (ll. llVr... l from the wes tern part of Lake Erie. Chironomids deformed in similar ways were found on some stations in Okanagan Lake and Skaha Lake. PlLO.ta.n!:fPU6 cf. moJt.io at Station 17 (Fig. 3 F) a Chironomini at Station 9, a S.ti.ctochUwnomu.6 (Fig. 3 G), and a Pll.Oclo.cUU4 (P.ilotanYpu61 (Fig. 3 H) at Station 33 in Skalla Lake were extremely deformed with exceedingly thick exoskeletons, thickened and heavily pigmented head capsules. and very aberrant mouth parts. Less extreme deformations were found in a Tanytarsinae, a S.ti.ctochbwnomu.6 and a Ch.Ut.onOmtU llemUr.e.duc.tu.ll type at Stations 1. 7. and 33 respectively. All these defomed individuals were probably at the borderline of their ecological range judging by the distribution of species communi ties. These deformities are very conspicuous and since they have only been reported once previously in the literature it seems unlikely that species at the limits of their range should ordinarily be deformed in this manner. A severe oxygen deficit would not be expected to occur at any of the stations wi th defomed chironomids. A possible explanation is that the organisms are reacting to some toxic compound in the environment. There is no major manufacturing industry near the stations where they occurred in Okanagan Lake. However. the Okanagan valley has a great many orchards and insecticides could be the toxic substance to which the organisms are reacting. As mentioned above. insecticides are also a possible explanation of the undue abundance of worms in relation to arthropods when, at the same time. there is a high specific diversity of these worms. Furthermore it may possibly explain in part the reported deterioration of fisheries in Okanagan Lake. Laboratory studies in collaboration with Dr. A.L. Hamilton on the reaction of chironomids to different insecticides have been initiated. To date no causative agents have been isolated although it is still hoped 11.
that these experiments will eventually lead to a better understanding of the reasons for these deformities.
Discussion and Conclusions
Okanagan Lake
The bottom fauna of Okanagan Lake seems to have changed considerably since Rawson's (1939) investigation. Rawson (1939, Table 6) 2 gives a table of the average numbers of bottom organisms per m at various depths. This table is reproduced in Table 2. A comparison with similar information (Table 3. 4) from the present survey shows that in spite of the low number of samples in this survey there has been a significant increase in the total numbers for stations shallower than SO meters. There was also a significant increase in the total numbers of chironomids. oligochaetes. P.iA..i.di.wn and perhaps in the miscellaneous group. However, the most striking change is in the percentage distribution between different groups. Rawson found that oligochaetes formed only 15 per cent of the macrobenthos, while during this survey they made up 50-60 per cent of the fauna. This, together with the occurrence of deformed chironomids, is suggestive of insecticide pollution (see above). The trophic condition of the lake as indicated by the macrobenthos, as well as by other factors, differs from area to area and from station to station. The northern bay is by far the richest large area and can be classified as mesotrophic. According to Table 1 there may be a significant oxygen decrease in the bottom waters. However, the presence of a few He.teJr.ot.JLi6.6oc1..tuU.u.6 .6ubp.Uo.6U6 indicates that the situation has not reached even moderate eutrophy. This bay is not polluted by any incoming sewers or sewage-bearing streams and was mentioned by Rawson (1939) to be considerably richer than the rest of the lake. In the north-eastern Vernon bay a stream polluted by municipal waste 12
fro. Vernon enters. Accordingly there is a gradation outwards from the station at the outlet of this stream (Station 13) with only 1 specimen of UmnocVt.Uu.6 spp. through stations with more than 1,000 oligochaetes 2 per m and all recorded groups of Ch.i.Aonomu.6 f.6 . .6.tA.I, to Station 17 when the moderately oligotrophic to mesotrophic Su.ctoc.h.iA.onomu.6 cf.
1lO.6Vt6chOldi predominates. Even at this station at a depth of 20 11., however, there was probably some effect of pollution since deformed specimens of the more or less oligotrophic species PJtotaYtyJXLh cf. moJt.io were found here. The middle of the northern basin apparently is not affected by pollution. With the exception of Station 24, all the animals found were either characteristic of oligotrophic lakes or else ubiquitous. Station
24 lies at a depth of 13 II, only about 8 II from land. The sediments contained large amounts of detritus, mostly wood chips, unlike the other stations in this area. Accumulated organic detritus deposited close to the shore may have created a localized eutrophic situation which resulted in a higher than normal number of oligochaetes and the presence of members of the ChiJwnomu.6 a.n.th.Ju:tcinUh and .6emi.-Jte.ductuh types. Stations 10 and 11 are situuted in a small bay receiving waste from cannery and winery factories in the city of Kelowna. Nevertheless there were few signs of pollution. The fauna was richer than most places in the lake, but this was mainly caused by the presence of vegetation. Station 12 just outside the above-mentioned stations had a typical oligotrophic fauna. Stations 1-6 surround the pipeline which discharges sewage from the city of Kelowna into the lake. The opening of this pipe is probably close to Station 4, a station at a depth of 45 m, where not a single animal was found! The stations surrounding the sewerpipe outlet show various signs of pollution. Station 6, about 100 m south of the sewer pipe outlet at a depth of 38 m, had just a single specimen of PItOc.l.a:.cLiu..6 .6 . .6tA. and high numbers of oligochaetes. Stations 1-5 north of the sewer outlet, and along the sewerpipe towards the shore, had a typical oligotrophic fauna, but with very high densitieli compared to other 13
stations in the lake. The stream entering the lake near Westbank carries some sewage. Stations 7-9 are situated in a small bay near this stream. The composition of the fauna at all three stations is characteristic of mesotrophic conditions although the inner station. 7. had two of the more typical eutrophic "indicator" species. Deformed chironomids were pr~sent on Station 7 and Station 9. The vegetation occurring in this bay is probably responsible for some of the higher densities and more eutrophic couununi ties. However. Station 7 had by far the highest densities in the whole lake. Station 8 and 9 also show relatively high densities. At Station 7. 138 specimens of Cl..a..do.tJ:tnlj.ta.lL6Uh were found, at Station 8 only 5 specimens. while Cla.dotany.ta.lL6U6 sp. was absent from Station 9. Some species of C1.adota.ny.t:.a1tJJfUI may be indicators of pollution or at least of eutrophic conditions. Station 29 is situated at a boat landing near Summerland. High numbers of UmnocilLi.l.u.6 ho66me..i.6,tw, Tubi6ex. .tubi6ex and the presence of only Ch.iJtonomU6 .thummi type larvae and PMctaeti.u6 (.s. ,stA. J 3Dong the chironomids shows that there is a considerable pollution here. The stations in the south end of the lake, 30-32, show::> no sign of pollution with a typical oligotrophic fauna composition in the deeper waters. As a whole the bottom fauna of Okanagan Lake shows considerable change since Rawson's (1939) investigation. However, the deeper waters show no apparent changes and the lake as a whole has still to be classified as oligotrophic although it no longer appears to be ultra oligotrophic.
Skaha Lake
The few stations taken from Skaha Lake are not sufficient to characterize the lake in detail. However, the presence of moderately oligotrophic to mesotrophic forms at Stations 33 and 36, as well as the complete absence of chironomids other than PJtoc.laeti.u6 at the deeper 14
stations and the presence of deformed chironomids indicates that a dramatic change in the bottom fauna may have taken place quite recently. The oxygen deficit in the deeper strata was not large enough to eliminate species of Ch.iJlonOma6. However their absence together with the presence of the above-mentioned moderately oligotrophic to mesotrophic forms, may indicate that a bottom fauna formerly dominated by mesotrophic forms has become extinct due to deteriorating conditions and for some reason or other has not as yet been replaced by more tolerant species. It is also possible that high insecticide levels are preventing the establishment of a more eutrophic fauna.
Osoyoos Lake
The northern and central basins of Osoyoos Lake are. according to the composition of the bottom fauna, moderately eutrophic and strongly eutrophic respectively. The central basin, in particular, appears to have been culturally eutrophied by the surrounding conununi ties. The northern basin is divided into two basins with an under-water ridge between Stations 39 and 40. This seems to be the only likely explanation of the differences between Station 39, at 36 m, with only PJt.oclacUU6 among the chironomids and high number of oligochaetes, and Station 40, at 44.S m, with several species of Ch.lJtonomU6 of which the oligotrophic to moderately eutrophic C. .6a.UnaJUU6 type dominates and relatively lower densities of oligochaetes occur. The difference is most likely explained by the better oxygen conditions at Station 40.
Future Investigations
A more intensive study will certainly change some aspects of the preliminary study, but the main conclusions are likely to remain the same. The main drawback with this survey is the scarcity of samples and stations and the lack of reared material to back up the identification of 15
insect larvae. A more detailed study of a few localities in Okanagan and Skaha Lakes together with a study of the benthos of Kalamalka and Woods Lakes will be carried out in the near future. In Skaha Lake the distribution of moderately oligotrophic to mesotrophic forms as well as that of deformed chironomids is of special interest. A future study will hopefUlly show a recolonization of the deeper part by more tolerant species. The problem of deformed chironomids is presently under investigation and may well prove to be useful as a means of detecting the presence of some forms of pollution.
Acknowledgments
I am much indebted to Mr. J. F. Flannagan, H. N. C. BioI., Fisheries Research Board of Canada. Freshwater Institute, Winnipeg. who participated in the field collections, identified Turbellaria, Hirudinea, Amphipoda. Ephemeroptera. Trichoptera and Mollusca. and gave advice, criticisms and corrections of the preliminary manuscript. Thanks are also due to Dr. A. H. Clarke, National Museum of Natural Sciences. Ottawa. who verified and corrected the identifications of the gastropods, Dr. D. A. Clarke. Medical Health Officer, South Okanagan Unit. Kelowna. B. C.• for valuable information on the lakes and the input of sewage. to Mr. Rich Kusat, Department of Fisheries and Forestry. Vancouver, B. C.• for help during the field collections, and to Dr. J. R. Vallentyne, Fisheries Research Board of Canada, Section Leader, Eutrophication Section, Freshwater Institute. Winnipeg, for advice. criticism and corrections of the preliminary manuscript. 16
References
Brinkhurst. R.O. 1964. Studies on the North American Aquatic Oligochaeta. I: Naididae and Opiocystidae. Proc. Acad. Nat. Sci. Philad. 116: 195-230. 1965. Studies on the North American aquatic Oligochaeta. II. Tubificidae. Ibid. 117: 117-172. 1966a. Studies on the North American aquatic Oligochaeta. III. Lumbriculidae and additional notes and records of other families. Ibid. 118: 1-33. 1966b. Detection and assessment of water pollution using oligochaete worms. Water Sewage Works. !!!: 398.401. 438-441. Brinkhurst. R.O .• A.L. Hamilton and H.B. Herrington. 1968. Components of the bottom fauna of the St. Lawrence. Great Lakes. Brundin. L. 1949. Chironomiden und andere Bodentiere der stidschwedischen Urgebirgsseen. Ein Beitrag zur Kenntnis der bodenfaunistischen Charakterzuge schwedischer oligotropher Seen. Rep. Inst. Freshwater Res. Drottningho1m. ~: 1-914. 1956. Die bodenfaunistischen Seetypen und ihre Anwendbarkeit auf die Siidhalbkugel. lugleich eine Theorie der produktionsbiologischen Bedeutung der glazialen Erosion. Ibid. 37: 186-235. Coulthard, T.L. & J.R. Stein. 1967. A report on the Okanagan Water Investigation 1967. Manuscript report prepared for the Water Resources Service B.C. Department of Lands, Forests and Water Resources. 57 p. 1969. A report on the Okanagan Water Investigation 1968-69. Ibid. 74 p. Flannagan, J. F. In press. Efficiencies of several grabs and corers in sampling freshwater benthos. J. Fish. Res. Board Can. 17
Hamil ton, A. L. In press. Zoobenthos of fifteen lakes in the Experimental Lakes Area, northwestern Ontario. J. Fish. Res. Board Can. Hamilton. A. L.• O.A. Saether & D.R. Oliver. 1969. A classification of the nearctic Chironomidae. Tech. Rep. Fish. Res. Board Can. 124: 1-42. Herrington, H.B. 1962. A revision of the Sphaeriidae of North America (Mollusca: Pelecypoda). Misc. Publ. Mus. Zoo!. Univ. Mich. .!!!: 1-74. Johnson. M.G. 1969. Structure and production in benthic macroinvertebrate cOlIDnlDlities of Lake Ontario. Typewritten dissertation presented to the Faculty of the Graduate Sch'ooI, University of Toronto. Liebman. H. 1960. Handbuch der Frischwasser-und Abwasser-Biologie. Biologie des Trinkwassers, Badewassers, Tischwassers, Vorfluters und Abwassers. II. R. Oldenbourg. MUnchen, 1149 p. pkland, J. 1964. The eutrophic lake Borrevann (Norway) - an ecological study on shore and bottom faWla with special reference to gastropods, including a hydrographic survey. Fo1. linmol. Scand. 13: 1-337. Rawson, 0.5. 1939. Physical and chemical studies, plankton and bottom fauna of Okanagan Lake, B.C., in 1935 with appended data from adjacent smaller lakes. Pp. 3-26 in: Clemens. W.A., 0.5. Rawson & J. L. Mettugh. A biological survey of Okanagan Lake, British Columbia. Bull. Fish. Res. Board Can. 56: 1-70. Saether, O.A. 1969. Some nearctic Podonominae, Diamesinae. and Orthoc1adiinae (Diptera: Odronomidae). Ibid. 170: 1-154. WUlker, W. 1961. Studien zur Morphologie, Bio1ogie und Verbreitung der GattWlg SeJtgen.tia Kieff. (Dipt. Chironomidae). Arch. Hydrobiol. Suppl.. 2S: 3Q7-331. ;:: ~ ~ ~ ~ ,. ~ N 0 c .; .; 0 ~ ;; ;;: :i ;:: :3 ~ -- ~ . g § ~ ~ t;- ;:: N .; ~ ,.; .s ~ ~ ~ .; .; N ~ i g ~ :': :i ~ ~ -- " 0 ~ ~ e .; ~ ~ ": .; ~ ~ N ~ .; " A :i ::: ;:: " ~ £, " " : :3 ~ ;:: ~ ~ i ~ ~ ~ N ": ~ ~ ,,; ~ -.; .; .,; ~ ~ ~ ~ ~ :;: :i ::: e " " ~ ~ 1 ~ 0 N 0 ~ N .; C ": ;:: ~ .; N ~ ~ ~ ~ ~ g g :i :i ::: e ~ ~ -
~ ~ e ~ N ~ ~ ~ N ~ .; s: 1 .,; ~ .; ~ -.,; ~ . :z ::: ~ :'; ::: - :5 ~ I :5 ~ ~ ~ ~ ~ e ~ 0 ~ ~ ~ N ~ N ~ ~ ~ e ::: ~ I ~ ~ .,; ~ .; ~ ~ ~ ~ ~ :: :i ~ ~ "
. 0 ": e ~ ~ ~ ~ .,; ~ . g ::: :i -e .; .; " .;
~ . 0 0 0 0 0 ~ ~ ~ 0 0 ~ ~ 0 ~ 0 ~ 0 ~ 0 :d ~ g g ... l- ... ~ ::: g ~ ~ ~ :i :;: 0. ~ .~ I ·W§' s W· Table 2. The average numbers of bottom organisms per m2 in Okanagan Lake 1936 (from Rawson 1939).
All All Depth (m) 0-1 1-5 5-10 10-20 20-30 30-50 50-75 75-125 Depths Depths
No. of samples 20 29 22 18 12 14 15 4 135 per cent
Qlironomidae 113 260 405 356 206 313 300 188 268 73.6 Oligochaeta 20 26 36 40 23 110 68 102 53 14.6 Ephemeroptera 67 8 23 17 5 0 0 0 15 4.1 Amphipoda 32 11 35 21 0 0 0 0 12 3.3 Trichoptera 24 9 7 8 0 0 0 0 6 1.6 2 0.5 P..i.6..i.cUum 0 3 0 I 0 6 5 0 Gastropoda 9 1 4 0 0 0 0 0 2 0.5 Mis ce llaneous 22 3 3 13 2 0 3 0 6 1.6 ------
All organisms 287 321 513 456 236 429 376 290 364 99.8 Table 3. The average numbers of bottom organisms per m2 in Okanagan Lake, September 9-11, 1969. All localities included.
All All Depth (m) 0-1 1-5 5-10 10-20 20-30 30-50 50-75 75-125 Depths Depths
No. of samples 2 7 5 6 4 4 1 3 32
Stations 1,13 7,10, 8,9,11, 16,17, 2,5,12, 3,4,6, 25 23,26 All per 14,18, 15,19 20,21, 31 22 30 Stations cent 27,29, 24,28 32
Olironomidae 200 1943 1307 696 1322 433 222 148 1012 32.5 Oligochaeta 200 3638 1546 652 1800 3733 89 104 1876 60.2 Ephemeroptera 0 20 35 0 0 0 0 0 10 0.3 Amphipoda 0 32 160 0 0 0 0 0 32 1.0 Trichoptera 0 13 0 0 0 0 0 0 3 0.1 P.iA- All All Depth (m) 0-1 1-5 5-10 10-20 20-30 30-50 50-75 75-125 Depths Depths No. of samples 1 5 5 6 3 1 1 3 25 Stations 1 10,14. 8,9,11, 16,17, 2,12, 22 25 23,26, per 18,27, 15,19 20,21, 31 30 cent 32 24,28 Ol.ironomidae 400 1138 1307 696 1052 400 222 148 841 38.6 Oligochaeta 356 1698 1546 652 844 4755 '89 104 1127 51. 7 Ephemeroptera 0 18 35 0 0 0 0 0 11 0.5 Amphipoda 0 44 160 0 0 0 0 0 41 1.9 Trichoptera 0 18 0 0 0 0 0 0 4 0.2 P.... .i.d.i.um 0 142 0 59 148 0 0 15 62 2.8 Gastropoda 0 53 187 0 0 0 0 0 48 2.2 Miscellaneous 0 44 62 67 0 88 15 0 44 2.0 ------All organisms 756 4155 3297 1474 2044 5243 426 177 2178 99.9 Table 5. The average number of bottom organisms per m2 in Skaha and Osoyoos Lakes. September 11 J 1969. Lake Skaha Osoyoos Depth (m) 5-20 30-50 All depths All Depths 10-20 20-30 30-50 All depths All depths No. of samples Stations 33,36 34 ,35 All Sta. per cent 38,42 41 39,40 All Sta. per cent 37 Qlironomidae 726 22 444 11.4 489 0 1576 827 15.0 Oligochaet& 3240 3133 3199 82.2 3200 1733 7311 4551 82.7 Amphipoda 237 0 142 3.6 0 0 0 0 0.0 p.u.i.cLi.um 148 0 89 2.3 0 0 0 0 0.0 Miscellaneous 30 0 18 0.5 22 578 0 124 2.3 ------All organisms 4389 3155 3892 100.0 3711 2311 8887 5502 100.0 _rof.po ~.u.~(lIlll.l ~.,. ..,....~'I •. .(t) ...... '11. 1(1l .ll&U ...~.'I•. ... o.tuotlOU_U. HI} .u.-~("_.) '(') S4ot&oLo.","~1oo1"" T"'jutooW~. (lIl1I.) J(l) '(1) R(f) .(.1 illS) U{f) '0' 3{Jl Itf'MUooo~(Sooot)o.ll(ll Ill) f{IJ Ill) _Cf) ~ ...' ...... u ....(a•.) 11(1) $01(') nel) 10(1) 16m 3Ul ~""'__ CI•. .m 10(1) ~~btl. 1m ~.,. cf.hl6'cot«.,_ ~~tt ~""('"",.p. PUet ~..u...,. ~ I'iol"",,,,:,,- ~ I'iol"",,o,. ~_tA.<.f_. liWoat-,..._s.,. Jk.oc.tooo~~. 'COoIOUia~lId_. , ...:.Iu.-"•• ,n_ ..... or 0,..,1- ,.....;,~.~,~,--;~;;;--;-;;:;----;--;;;--;:;---::::-~-=-~---.:...---::,,-CC-- " "u ~·cl., ruuj 46 " .1HI1l ~.u_ ... _,dft~I., I... ~U.~('h.) ~.~ (11;111.) Mou ...... u.Pl•. ""'",.....Mtu'l•. r.....'"~'"-.e-Il.l I~_~...... , ~ ...,~~ (CI...) ~-...- ~.f._~ (...... ) ~.,. ~-....: nllU. CuI~llotudl.... S4~cf.""""",- (I... ~'UfII&l.u(l..l ...... ~(Soo....l ~.p. U .....IU... t...... , ,...... -.. ho:Ie.tUiI>o (•• H.... l.". r..>ddu06 ('oiUt&orPuol .pp. ,..~<.f.-u (Zett.) ~~.,ct&ilUM.,. '''piloo... (~.) ~=~c.lUWf" ~ •.u...w..'YPO a..w"_.~~ ,,~ CMM.-..Mdt...w ... · d,,-': '1J>Oo """"'...... o-t-....ypo llicMt.. P~.....p. e.w.ut"~'p. ,~.,. ~.,. P'=_·~' ~.,. ...._o\lIt4L(IeU.) ~~d. Ultou (M,.) ~~~l __.u.u.lSufu.t<..a1 ""._..~' ~.~ ~_. .•. ~ ....,. T_tMa...pp• ...... -...eu IJu.uk(u' -=~1lonIt. ~,,"==,Id. '~~I"'~ Ilo.(_'~$a, ""'1-.1 1Io1l. P~_tou ~_S.T ,...=~ ...u.:- ...... - {"Ill ~ ~ ~ :;; ~ ~ E ; 2 N ~ 8 ~ ~ ::: : ~ i 11 ~ ~ ill ;l! § ~ tI ; ~ ~ ~ :: :: lil N N ~ :;; :: M .u ~ N " ~ 2 :: ~ :!: ;l! N N ~ l!: ~ N ~ . :: ~ a ~ ;l; ; i N ~ ~ ~ ~ ~ N ~ ~ ; M ~ ~ ~ - --~------Table 7. Exuviae and male imagines of Chironomidae fOWld at Westbank, Okanagan Lake, September 9, 1969. No. Collected PMcto.d.i.1JJ> 16. 6tJt.1 spp. A + B 22 TOJtYPw sp. AbtabeAmy.(.a Tltie.ne.ma.tt!Jnj.ia Pllo.taJ'lypu.6 cf. molLio (Zett.) Po.t.th0.6.tia cf. long.unana (Kieff.) He.h.JtOVLiuoctacUu.6 cf. 6ubp.il.o6w (Kieff.) OlLthoclacLi.w 16.6Vt.1 0Jt11.e.c.ten.6 Saeth. 74 CJl.i.co.topu,> spp. A. B. C 44 P6 DEGREE OF ENRICHMENT AS INDICATED BY DISTRIBUTION OF CHIRONOMIOS C::.~d.~ ~cf.~ O~d!2;!q!W!!!!! MorodlOmtSOcf.~~ • ~$IlP,ue.pt ~Q'CUIl 01 lI'llI Ch/fonomkloe,ot IIIO$f onIY~Il'" ..nI OKANAGAN LAKE SYSTEM -N-I I DEGREE OF 0A0IMEIlT AS tOCATED BY DlSTRI8lJTION OF OUGOCHAETS. .... 1tGllOOOper .... ot o Ol'9QChoelo.bullft&lhanlOOO per .... oI~!!ll!!!I!I!I!I! MoreltvllOOOper .... 01 lImnodfll.... ~ • 3 lpecli'l of Ill'Ifrtebratfl Of leu per '!lllion OKANAGAN LAKE SYSTEM ~ c ~/~l (~e:,.t~X I \ ~ )Yo E F Fig. 3. A-C. Genus near TW4ocl.o.diu4. Larva. A. Labiu.. B. Nandible. C. Antenna. O-E. Genus near P06tU1t.ce.tad.iu.6 or new subgenus of P4eevwetadilU>. Pupa. D. Tergites VI-VII. E. Thoracic horn. F-H. Deformed chironomids. F. Bodywall of PJlotaJ1!1,PU6 cf. 1IlO4l0. G. SUctocJUItonollltL6 sp .• labillJl. H. PJUlc.tad.iu6 IP4ili.t4nypu6I.