Journal of Paleolimnology19: 55–62, 1998. 55c 1998Kluwer Academic Publishers. Printed in Belgium.

Cladocerans and chironomids as indicators of lake level changes in northtemperate lakes�

Wolfgang HofmannMax-Planck-Institute of Limnology, P.O. Box 165, D-24302 Plon, Germany(e-mail: hofmann@mpil-ploen.mpg.d400.de)

Received 6 November 1995; accepted 26 April 1997

Key words:Cladocera, Chironomidae, subfossil remains, lake level, inshore/offshore sediments, planktonic/littoralratio

Abstract

Water level fluctuations affect the size of the pelagic zone relative to the size of littoral habitats, and thus mayinfluence the relative abundance of remains from planktonic and littoral cladocerans in sediment. The applicationof this planktonic/littoral ratio for the reconstruction of past water level changes is discussed using examplesof: (1) surficial profundal sediments from lakes of different water depths; (2) Holocene variation in a profundalsediment core; (3) horizontal variation in surficial sediments within a lake; and (4) long term variation in an inshoresediment core. The latter seemed to be the most promising application of this ratio. Maximum effects of waterdepth changes on the lake fauna are expected in the littoral zone. It is, however, difficult to read this effect directlyfrom subfossil cladoceran and chironomid assemblages from inshore sediments as shown by a sediment profilefrom a site exposed to a long term decrease of water depth.

Response of cladocerans and chironomids to waterlevel changes

Assemblages of cladoceran and chironomid remainsfound in profundal lake sediments constitute a sec-ondary thanatocoenosis originating from different lakehabitats and communities (Whiteside & Swindoll,1988; Frey, 1988). Among the Cladocera preserved insediments, zooplankton (i.e.,bosminids and daphniids)occur in the pelagic zone, while chydorids representlittoral benthos. Chironomids inhabit various benthichabitats ranging from littoral depths to the profundalzone.

The above communities will be influenced by waterlevel fluctuations in quite different ways. In the lit-toral zone, a vertical up- or downward shift in habitatwill occur. Profundal and pelagic communities are notdirectly affected by water depth changes via water level

� This paper is one in a series of papers to be published in the Jour-nal of Paleolimnology that resulted from a European Science Foun-dation Workshop, convened by Dr S. Harrison and Prof. B. Frenzel,entitled ‘Paleohydrology as reflected in Lake Level Change as Cli-matic Evidence for Holocene Times’.

fluctuations or sediment accumulation. In these cases,changes of water depth imply rather indirect effectswithin each community and should therefore produceweak signals. What will be altered is the size of the lit-toral, profundal and planktonic communities relativeto the total lake fauna. For zooplankton, such changeswill influence the size of their pelagic habitat (relativeto the littoral habitat), whereas the profundal communi-ty can be affected not only by the size of their profundalhabitat, but also by changes in temperature and oxy-gen concentrations, which are in turn related to waterdepth. The magnitude of such changes will depend onthe size, depth and morphometry of the lake. Suchchanges can be substantial in shallow stratified lakes,but insignificant in large, deep lakes.

The profundal chironomid fauna is likely to main-tain its basic structure dependent on the trophic stateof the lake as aTanytarsus-lugens-or Chironomus-community, provided the profundal situation is pre-served. However, morphometric eutrophication (sensuDeevey, 1955) produced by a fall in the water level or

Article: jopl 388 GSB: 703054 Pips nr 140007 BIO2KAP

*140007 jopl388.tex; 29/01/1998; 21:22; v.7; p.1

56

infilling by sediment may induce a shift from oligo-traphentic to eutraphentic taxa.

In eutrophic lakes even a marked reduction in waterdepth connected with a shift from stratified, dimictic tounstratified, polymictic conditions will only affect thepredominance of the genusChironomuswhen there isa shift to a clear state dominated by macrophyte veg-etation, but not when there is a turbid state with highphytoplankton biomass (Scheffer et al., 1993; Lund-beck, 1926). However, under oligotrophic conditions,the members of theTanytarsus-lugens-communitywilldisappear, because under temperate conditions only theprofundal zone provides the low temperatures requiredby these cold-stenothermal species (Brundin, 1956)and warm tolerant, littoral taxa will predominate. Inthe plankton such a drastic reduction of water depthmay suppress the truly pelagicBosminaspecies of thesubgenusEubosmina.

The littoral biocoenosis is more directly affectedby water level changes which should, in this zone,result in stronger signals. Water level changes of a fewmeters may cause a shift from an upper littoral to alower littoral, or to a eulittoral situation, connectedwith a direct and severe impact on the structure of thefauna involved. Hence, within a lake, there is consider-able variation with respect to the effects of water levelchanges on habitats and communities.

Reproduction of faunal responses by the subfossilrecord

In most cases, paleoecological studies are based onsediment profiles taken in the centre of a lake (i.e. onprofundal sediments). Cores from the centre of lakesof moderate to large size are generally insensitive tosmall changes in water depth, and under these condi-tions, the faunal elements originating from the profun-dal, littoral, and pelagic habitats can hardly be usedto get information about the former water depth. Allremains from the littoral are mixed together in the pro-fundal sediment and the original vertical structure ofthe fauna is not preserved. The most distinct effects ofwater level changes cannot be read from this secondaryassemblage.

Change within the pelagic, littoral, and profun-dal elements cannot be used directly as indicatorsof the former water level. However, as previouslyindicated, such fluctuations may change the relativedimensions of these habitats and consequently changethe proportion of each of these communities in rela-

tion to the total lake fauna. For instance, a rise inwater level may increase the pelagic zone and theabundance of planktonic organisms relative to the lit-toral habitat and its benthic fauna. Goulden (1964)considered changing proportions of subfossil littoraland planktonic cladocerans to be indicative of for-mer water depth changes. Alhonen (1970) termedthis the planktonic/littoral ratio and used this ratiofor the interpretation of Holocene cladoceran strati-graphies in Finnish lakes. Mikulski (1978) consideredthis ratio ((Bosminidae + Daphniidae)/Chydoridae) tobe an index of lake level oscillation (ILL).

The suitability of the planktonic/littoral ratio as anindicator of lake level changes will be discussed in fourdifferent cases: (1) lakes with different water depthswill be compared by analysis of surficial, profundalsediments; (2) Holocene variation within a lake will beanalysed using a profundal sediment profile; (3) thehorizontal variation within a lake will be analysedusing recent littoral, sublittoral and profundal sedi-ments; and (4) an inshore sediment profile will beanalysed to study the Holocene variation within a lake.Cases 2 and 3 partially refer to data from the eutrophicnorthern German Belauer See (surface area: 110 ha;maximum depth: 26 m; mean depth: 9 m) situatedabout 25 km southeast of Kiel (Schernewski, 1992).

Mueller (1964) compared the assemblages ofcladoceran remains in surficial deepwater sedimentsfrom 11 Madison (Wisconsin) and Indiana lakes, andfound a negative correlation between the P/L ratio ofthe lakes (i.e. the proportionof the volume of the pelag-ic zone relative to the area of the littoral region) and thepercentage of littoral elements, if Lake Mendota wasexcluded. No correlation was found between percent-ages of planktonic/littoral taxa and mean depth, maxi-mum depth, area, and volume of the lakes.This concurswith the results from 13 northern German lakes (Hof-mann, 1996), where there was a slight increase in thepercentages of planktonic cladocerans with decreas-ing mean depth, due to high abundances ofBosminalongirostris in shallow waters.

The dimension of the littoral area itself seems to bethe major component of the P/L ratio, which deter-mines the percentage of littoral cladocerans in theassemblage. An increase of the planktonic/littoral ratio(Alhonen, 1970) indicates a rising water level only ifit reduces the proportion of the lake surface which lieswithin the littoral zone. A rise may enlarge the lit-toral zone if large flat areas are inundated. Processesindependent of water level changes (e.g. a shift in theplankton community from well preserved taxa (e.g.

jopl388.tex; 29/01/1998; 21:22; v.7; p.2

57

Bosmina) to poorly or not preserved taxa (e.g.Daph-nia, copepods, rotifers) will affect the abundance ofplanktonic elements in the subfossil record and, con-sequently, the planktonic/littoral ratio.

Mueller (1964) also thoroughlydiscussed an uncer-tainty in the estimation of the proportion of planktonicand littoral elements caused by the chydorid,Chy-dorus sphaericus,which cannot be strictly assignedto either group. In the data set under discussion, thisspecies had percentages of>10% for ten and>40%for four of the 11 lakes, thus strongly influencing thecalculation of the ratios. In this case the specimens ofChydorus sphaericuswere ‘arbitrarily’ separated intolittoral and pelagic elements according to the P/L ratiosof the lakes.

Analysis of Holocene dynamics of the plankton-ic/littoral ratio within the same lake supports the viewthat water depth itself (i.e., the dimension of the pelag-ic habitat) does not considerably affect the proportionof planktonic cladocerans, if water depth is reducedby sediment accumulation. In the northern GermanSchohsee (zmax = 30 m) and in the Plon basin ofthe Großer Ploner See (zmax = 40 m), the percentageof planktonic elements remained more or less con-stant throughout the Holocene although water depthdecreased by 10 and 15 m, respectively (Hofmann,1986). Similarly, in a 28 m section of a sediment profilefrom the Belauer See (zmax = 26 m), a distinct increasein the littoral elements is evident if one considers theentire Holocene (shallowing by 28 m), but the patternis indistinct if one considers only the Late Holocene,when the lake shallowed by a further 10 m. This 10 mshallowing is still large relative to the water level fluctu-ations that have been inferred for many lakes (Figure 1).However, the evidence of the planktonic/littoral ratio islimited by uncertainty in the classification ofChydorussphaericus. The high proportions of chydorids in theupper 10 m indicate increasing production of the lit-toral zone as a result of eutrophication rather than waterlevel changes (Hofmann, unpubl. data). During theHolocene, in the region under discussion, significantwater level fluctuations, which might have changed thearea of the littoral region, did not occur (Gripp, 1953).

As water level fluctuations have a much strongereffect on a lake’s volume and consequently on the sizeratio of the pelagic and littoral habitat than does sedi-ment accumulation, they probably produce a more dis-tinct signal in the planktonic/littoral ratio. For instance,in Plußsee, a deep (zmax = 29.2 m) but rather small lake(14.3 ha), the upper 5 m of the water column comprises44% of the lake volume, whereas the lowermost 5 m

Figure 1. Belauer See, deep water core Q300: percentages of remainsfrom planktonic cladocerans (incl./excl.Chydorus sphaericus).

include only 2.3% (Overbeck & Chrost, 1993). How-ever, when the water level rises, the thermocline andlower boundary of the euphotic zone, which depend onthe fetch of the lake and light attenuation, respective-ly, will also move upward. Due to this compensatingeffect, the size of the epilimnetic and euphotic habi-tats will not change in the same proportion as waterlevel fluctuates. So far, no case study exists whichincludes well documented water level changes com-bined with an observation of the cladoceran plankton-ic/littoral ratio.

Mueller (1964) also analysed the horizontal distrib-ution of remains from planktonic versus littoral clado-cerans and found a typical pattern characterized bymaximum percentages of littoral elements nearest tothe shoreline, a steep decrease towards the metalimnet-ic area, and uniformly low values below as a result ofdirect deposition of remains combined with redeposi-tion. In the Belauer See, the same pattern was observedin surficial sediment samples taken 200 m apart in a gridthat covered the entire lake bottom (Garbe-Schonberg,unpubl. data). Above a depth of 4 m, the percent oflittoral cladocerans mostly varied from 43–45%. Thepercent declined as depth increased to 5 m (i.e. themetalimnetic area) and ranged around 20% from 5 mto 29 m (Figure 2). In detail, this distribution pat-tern identifies littoral and planktonic elements, as theformer increase above the 5 m water depth and the lat-ter decrease (Chydorus sphaericus, Bosmina coregoni

jopl388.tex; 29/01/1998; 21:22; v.7; p.3

58

Figure 2. Belauer See, surficial sediments: percentages of remainsfrom planktonic cladocerans against water depth (incl./excl.Chy-dorus sphaericus).

thersites). Moreover, it reflects different horizontal dis-tributions of theBosminaspecies present. Below 5 m,B. c. thersitesis more abundant thanB. longirostriswhile above 5 m the latter predominates (Figure 3),characterizingB. c. thersitesas a truly pelagic elementwhich avoids the inshore area, whileB. longirostrisisknown to inhabit the free water in the offshore as wellas in the inshore area (Flossner, 1972).

The areas where high percentages of the differentecological groups are found in the subfossil recordmatch the areas of their occurrence, showing thatthe major sedimentation pattern is produced by directdeposition of remains. As mentioned above, the mostdramatic ecological effects of change in water leveloccur in the littoral zone. For the reconstruction of theinfluence on the cladoceran fauna, a direct observationof the littoral community involved is required. Withrespect to sediment analysis, this observation is onlypossible if the structure of this assemblage is mainlydetermined by direct deposition of remains from lit-toral elements (i.e. by analysis of littoral sediments).

I tested how water depth changes are reflected bythe planktonic/littoral ratio based on inshore sedimentsfrom a former bay of the Belauer See which was filledup by sedimentation in the Subboreal period. Duringthis process, the sediment changed from fine detri-tus gyttja to coarse detritus gyttja and peat (Hofmann,1993). In this case, water depth did not change due

Figure 3. Belauer See, surficial sediments: percentages of remainsfrom the planktonic cladoceransBosmina coregoni thersites, Bosmi-na longirostris, andChydorus sphaericusagainst water depth.

to water level changes but was changed by sedimentaccumulation. For the benthic community, this shouldhave a similar effect as a fall in the water level (i.e.an upward shift from a sublittoral to an upper littoralsite combined with a horizontal shift towards the waterline).

In this case, the planktonic/littoral ratio clearlyreflects the shift from a deep water site towards littoralconditions (Figure 4), shown by a permanent long-termdecrease in the portion of planktonic elements from80% to 20%. As compared with the above mentionedrecent distribution pattern of the planktonic/littoralratio within the lake, the section with a sediment depthof 12–9 m would represent a site below 5 m waterdepth, whereas the 9–5 m and 5–2 m sections indicatesituations near and above the metalimnion, respective-ly. It is uncertain if beyond this major trend minoroscillations occurring in the 6–4 m section are due toshort-term water level changes. The above sedimentprofile provides us with the opportunity to observe howthe chydorid assemblage itself responded to the long-term changes of its environment. The samples from theSubboreal section (i.e. 780–230 cm) were grouped bycluster analysis on the basis of their chydorid com-position. The Renkonen-index was used as a mea-sure of similarity (Schwerdtfeger, 1975). The UPGMAmethod (unweighted pair-group method using arith-metic averages) was applied for clustering (Sneath &

jopl388.tex; 29/01/1998; 21:22; v.7; p.4

59

Fig

ure

4.B

elau

erS

ee,

insh

ore

core

A13

0:pe

rcen

tage

sof

rem

ains

from

plan

kton

iccl

adoc

eran

sex

cl.

Chyd

oru

ssp

haeric

us(b

lack

squa

res)

,in

cl.Ch.

sphaeric

us(w

hite

squa

res)

(%of

tota

lcl

adoc

eran

s),

perc

enta

ges

ofth

ech

ydor

idsp

ecie

s(%

ofto

talc

hydo

rids)

,and

faun

alzo

nes

sepa

rate

dby

clus

ter

anal

ysis

.

jopl388.tex; 29/01/1998; 21:22; v.7; p.5

60

Sokal, 1973). In the profile, three main units were sepa-rated (Figure 4): below 350 cm (CLU1), above 350 cm(CLU2) and the uppermost sample (230 cm; CLU3).In the first group, samples from>680 cm were locatedon a separate branch (CLU1a) together with two sam-ples from the section above. Within these clusters, nosubclusters were discernible (i.e. the samples were notarranged according to their sediment depth).

The pattern is mainly determined by the eight mostabundant species averaging>10% of the individuals inany of the clusters.Chydorus sphaericusseparates thesections below and above 350 cm and the uppermostsample is characterized predominantly by three taxa(i.e.Oxyurella tenuicaudis, Alonella excisa, andAlonaguttata). Although a long-term shift in the structure ofthe chydorid community of this site is obvious, thistrend can hardly be considered to be a direct indicationof decreasing water depth, because it does not repre-sent a succession from deep water to shallow waterspecies. Most of the species involved do not show adistinct preference for water depths and even for par-ticular habitats. The only predominant species in theuppermost 230 cm sample, which might indicate anupper littoral situation near the water line, isOxyurel-la tenuicaudis,which frequently occurs in small waterbodies, rice fields, swamps and mires (Flossner, 1972).

In the same Subboreal section of this profile, thechironomid fauna also showed a clear succession inwhich four phases were distinguished by cluster analy-sis (Figure 5). The dominant taxa separating the clus-ters wereTanytarsusgr. chinyensis, Cladotanytarsus,andCladopelmain the lowest section (765–397 cm;CLU1), Cricotopusand Glyptotendipesin the sec-ond (380–302 cm; CLU2), and againGlyptotendipesplusMicrotendipesandLimnophyesin the third section(290–260 cm; CLU3).

The most drastic change occurred in the zoneabove 250 cm (CLU 4) indicated by the predom-inance of Limnophyes, Micropsectra, Pentaneuri-ni, Polypedilum, and Chironomusand by a distinctdecrease inTanytarsus,which was the most abun-dant taxon in the three sections below. TheChirono-mus specimens from this zone differ in their men-tum morphology from the profundalCh. plumosusandCh. anthracinustypes found below and obviously rep-resent a taxon typical of the upper littoral situation.Similarly, the occurrence ofMicropsectra is clearlyisolated from the profundalM. coracinapopulation,which was extirpated in the Belauer See at the begin-ning of the Subboreal. This assemblage resembles chi-ronomid communities typical of small permanent and

temporary pools in which Pentaneurini,Limnophyes,Chironomus,andMicropsectraspecies are frequentlyfound (Schleuter, 1986), thus indicating a site near thewater line. This example also demonstrates that theinterpretation of subfossil faunal assemblages has toinclude the stratigraphic situation, otherwise the occur-rence of taxa likeChironomusandMicropsectrawouldbe considered indicators of profundal conditions.

As in the Cladocera, the chironomid fauna clear-ly changed in its structure when water depth declinedand the site shifted towards the water line. However,with the exception of the last phase, the succession perse cannot serve as evidence of water depth changes,which is primarily indicated by the sediment stratigra-phy. This is only partly due to insufficient taxonomicresolution and limited information on the ecology ofthe littoral taxa involved. Lake level fluctuations pri-marily affect, in various ways, the structure of the lit-toral habitat, as they may change sediment compositionand the zonation of the littoral vegetation (Digerfeldt,1986). The littoral fauna does not directly respond towater depth changes, but to changing ecological con-ditions caused by these fluctuations. Consequently, thefaunal response is a secondary and indirect reaction andwould likely produce a weaker signal than vegetationand sediment structure. Furthermore, the littoral zoneis characterized by high habitat diversity and there-fore by a patchy distribution of the fauna, which is notarranged in zones according to water depth. In the caseof the chydorids, the littoral habitat diversity combinedwith the euryoecious character of the species severelylimits the indicative potential of the faunal assemblagewith respect to water depth. A direct effect of waterdepth only occurs if it represents an extreme situationfor the aquatic fauna, which is the case at the aquat-ic/terrestrial boundary, where it will produce a clearsignal indicated by a distinct shift in the faunal struc-ture as shown above in the case of the chironomids.

In conclusion, two major points should be empha-sized: (1) The most promising approach to follow pastwater level changes is to observe the area where max-imum effects are expected (i.e. the littoral zone), and(2) to use elements which are directly affected (i.e.sediment composition and distribution of the aquaticmacrophytes) (Digerfeldt, 1986, 1988). With respectto faunal responses, the planktonic/littoral ratio of thecladocerans assemblages seems to present a comple-mentary parameter. Case studies on the dynamics ofthe littoral cladocerans and chironomid fauna involvedare needed to detect successional patterns, which werenot discernible in the example mentioned above.

jopl388.tex; 29/01/1998; 21:22; v.7; p.6

61

Fig

ure

5.B

elau

erS

ee,i

nsho

reco

reA

130:

perc

enta

ges

ofth

ech

irono

mid

taxa

and

faun

alzo

nes

sepa

rate

dby

clus

ter

anal

ysis

.

jopl388.tex; 29/01/1998; 21:22; v.7; p.7

62

Acknowledgments

I wish to thank Prof. John P. Smol and two anonymousreferees for their constructive criticisms and sugges-tions resulting in the present form of the paper.

References

Alhonen, P., 1970. On the significance of the planktonic/littoral ratioin the cladoceran stratigraphy of lake sediments. Comm. Biol.35: 1–9.

Brundin, L., 1956. Die bodenfaunistischen Seetypen und ihreAnwendung auf die Sudhalbkugel. Rep. Inst. Freshw. Res. Drot-tningholm 37: 186–235.

Deevey, E. S., 1955. The obliteration of the hypolimnion. Mem. Ist.ital. Idrobiol. 8: 9–38.

Digerfeldt, G., 1986. Studies on past lake-level changes. In Berglund,B. E. (ed.), Handbook of Holocene Palaeoecology and Palaeohy-drology. Wiley & Sons, Chichester: 127–143.

Digerfeldt, G., 1988. Reconstruction and regional correlation ofHolocene lake-level fluctuations in Lake Bysjon, south Sweden.Boreas 17: 165–182.

Floßner, D., 1972. Kiemen- und Blattfußer, Branchiopoda, Fis-chlause, Branchiura. Die Tierwelt Deutschlands 60: 1-499.

Frey, D. G., 1988. Littoral and offshore communities of diatoms,cladocerans and dipterous larvae, and their interpretation in pale-olimnology. J. Paleolimnol. 1: 179–191.

Goulden, C. E., 1964. The history of the cladoceran fauna of Esth-waite Water (England) and its limnological significance. Arch.Hydrobiol. 60: 1–52.

Gripp, K., 1953. Die Entstehung der ostholsteinischen Seen und ihrerEntwasserung. Schr. geogr. Inst. Univ. Kiel, Schmieder-Festband,11–26.

Hofmann, W., 1986. Developmental history of the Großer PlonerSee and the Schohsee (north Germany): cladoceran analysis, withspecial reference to eutrophication. Arch. Hydrobiol. Suppl. 74:259–287.

Hofmann, W., 1993. Dynamics of a littoral Cladocera assemblageunder the influence of climatic and water depth changes. Verh.int. Ver. Limnol. 25: 1095–1101.

Hofmann, W., 1996. Empirical relationships between cladoceranfauna and trophic state in thirteen northern German lakes: analysisof surficial sediments. Hydrobiologia 318: 195–201.

Lundbeck, J., 1926. Die Bodentierwelt norddeuscher Seen. Arch.Hydrobiol. 7: 1–143.

Mikulski, J. S., 1978. Value of some biological indices in casehistories of lakes. Verh. int. Ver. Limnol. 20: 992–996.

Mueller, W. P., 1964. The distribution of cladoceran remains in surfi-cial sediments from three northern Indiana lakes. Invest. IndianaLakes & Streams 6: 1–63.

Overbeck, J. & R. J. Chrost (ed.), 1993. Microbial ecology of LakePlußsee. Springer, New York, 392 pp.

Scheffer, M., S. H. Hosper, M.-L. Meijer, B. Moss & E. Jeppesen,1993. Alternative equilibria in shallow lakes. Trends in Ecology& Evolution 8: 275–279.

Schernewski, G., 1992. Raumzeitliche Prozesse und Strukturen imWasserkorper des Belauer Sees. EcoSys 1: 1–160.

Schleuter, A., 1986. Die Chironomiden-Besiedlung stehenderKleingewasser in Abhangigkeit von Wasserfuhrung und Fal-laubeintrag. Arch. Hydrobiol. 105: 471–487.

Schwerdtfeger, F., 1975. Synokologie. Parey, Hamburg, Berlin,451 pp.

Sneath, H. A. & R. R. Sokal, 1973. Numerical taxonomy. Chapman& Hall, San Francisco, 573 pp.

Whiteside, M. C. & M. R. Swindoll, 1988. Guidelines and limita-tions to cladoceran paleoecological interpretations. Palaeogeogr.Palaeoclim. Palaeoecol. 62: 405–412.

jopl388.tex; 29/01/1998; 21:22; v.7; p.8