Hydrobiologia 240: 1-14, 1992.W.J. O'Brien (ed.), Toolik Lake - Ecology of an Aquatic Ecosystem in Arctic Alaska.© 1992 Kluwer Academic Publishers. Printed in Belgium.

The biogeochemistry and zoogeography of lakes and rivers in arcticAlaska

George W. Kling, W. John O'Brien, Michael C. Miller & Anne E. HersheyDepartment of Biology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Systematicsand Ecology, University of Kansas, Lawrence, KS 66045, USA;Department of Biological Sciences, Universityof Cincinnati, Cincinnati, OH 45221, USA; Department of Biological Sciences, University ofMinnesota-Duluth, Duluth, MN 55812, USA

Abstract

Water samples from 45 lakes and 8 rivers in arctic Alaska were analyzed for major anions, cations,nutrients, chlorophyll, zooplankton, and benthos. The waters were dilute (conductivities of 30 to843 #S cm- '), and their composition varied from Na-Ca-Cl waters near the Arctic Ocean to Ca-Mg-HCO 3 waters further inland. Sea salt input in precipitation was important in determining the chemis-try of coastal lakes, partly because of low groundwater flow and less time for water to react with shallowunfrozen soils. Further inland, variations in water chemistry among sites were related mainly to differ-ences in bedrock, the age of associated glacial drift, and the input of wind blown sediment. Variationsin zooplankton species composition among the lakes were related more to latitude, lake morphometery,and biotic interactions than to water chemistry. The presence of fish as predators mostly determined theoverall size structure of the zooplankton community. The chironomid taxa identified have been previ-ously reported from the Neararctic, except for Corynocera oliveri which is a new record. The abundanceof the widely distributed chironomid Procladius appears to be controlled by sculpin predation.

Introduction

The most recent general reviews of arctic limnol-ogy are by Hobbie (1980, 1984). Since then, therehave been further surveys or reviews on waterchemistry (Welch & Legault, 1986; Lock et al.,1989), on zooplankton (Haney & Buchanan,1987; Luecke & O'Brien, 1983), and on benthos(Hershey, 1985; Miller & Stout, 1989; Maciolek,1989; Hershey, 1990). Despite this recent re-search effort, there are large areas of arctic Alaskaand Canada that remain unexplored limnologi-cally.

In this study we present chemical, zooplank-ton, and benthos data for 45 lakes and 8 riversalong the oil pipeline in arctic Alaska, and rainchemistry data from the Toolik Lake area in the

foothills of the Brooks Range. About 30 of thesites were investigated for the first time. Sampleswere collected in June and July, mostly in 1988and 1990.

Site description

All study sites are located within several kilome-ters of the Dalton Highway on the North Slopeof Alaska (Fig. 1). There is continuous perma-frost under the entire area, and this north-southtransect includes sites in the Brooks Range(>900 m elevation), the foothills province (75-900 m), and the coastal plain (< 75 m). All lakesstudied are natural, with the exception of sites 14,48, 54, and 55, which are gravel pits or artificially

2

Fig. 1. Location of study sites on the North Slope of Alaska.Site numbers correspond to the numbers and names in Ta-ble 1. Enlarged areas are (A) Prudhoe Bay, (B)Toolik, and(C) Oksrukuyik drainage.

dammed (Table 1). Lakes near the coast are lessthan 2 m deep, and are formed by the action ofwind and thermokarst processes. Most lakes atelevations greater than 145 m are morraine-dammed or kettle ponds. The surficial geology ofthe region is summarized by Brown & Berg (1980)and Brown & Kreig (1983). Briefly, the coastalplain is underlain by Quaternary eolian, alluvial,and marine sediments. In addition to such recentsediments, the foothills province contains olderCretaceous and Tertiary sandstones, conglomer-ates, and siltstones. Most of these rocks are man-tled by extensive deposits of glacial drift of vary-ing age. In the Brooks Range, the Lisburnelimestone and dolomite group, and shales of Tri-assic to Pennsylvanian age are common.

Table . Location and morphometric data for study lakes andrivers. Site numbers correspond to sites in Figure 1.

Site Latitude Longitude Elevation Area Max.(°.'N) ( .'E) (m) (ha) depth (m)

Lakes

4 Itkillik 68.235 Galbraith 68.286 Island 68.327 18 68.378 S13 68.389 S12 68.38

10 SIl 68.3811 S6 68.3812 S3 68.3813 Toolik 68.3814 Dam 68.3815 Camp 68.3816 NI 68.3817 N2 68.3818 NE2 68.3819 NE12 68.3920 NE14 68.4121 Itigaknit 68.4222 El 68.3824 Campsite 68.3625 01 68.3626 02 68.3527 03 68.3628 Elusive 68.3929 Moose 68.4030 Hanging 68.4131 Foggy 68.4132 F4 68.4134 George 68.4435 Anne 68.4436 Sag2 68.4437 Sagl 68.4542 Charles 69.0244 William 69.3545 Windy 69.5846 Silhouette 70.0547 Colleen 70.1348 Sag-c pit 70.1449 Bern 70.1750 Dune 70.1851 Maxine 70.2252 Carolyn 70.2153 Africa 70.2054 Borrow pitl 70.2055 Borrow pit2 70.20

RiversI West Atigun 68.162 Atigun 68.163 Mt. Roche 68.23

23 Kuparuk 68.3833 Oksrukuyik 68.5238 Oksrukuyik 68.4339 Sagavinirktok 68.5240 Alexa 68.5741 Sagcut 69.0143 Happy Valley 69.0956 Kuparuk 70.20

149.55149.30149.28149.35149.40149.39149.39149.39149.38149.36149.36149.36149.37149.38149.37149.37149.37149.40149.33149.11149.11149.12149.10148.30149.06149.06149.05149.04148.58148.56148.53148.52148.51148.38148.44148.32148.28148.15148.18148.17148.30148.35148.48148.56148.56

149.28149.27149.19149.24148.51149.01148.50148.52148.49148.50149.00

681802881747754754750731719719719720731724724693699663771864876892876525792785770754597556526510319145572415106622433

464422

62.017.61.00.30.41.14.0

1500.10.24.41.86.38.5

24.0153

2.979.52.7

17.13.0

3003.76.13.12.37.38.51.7

18.710.335.528.656.8

2311.0

90.01.5

18066.291.21.01.0

7.56.06.0

10.05.43.8

13.18.55.0

22.01.00.7

1410.74.0

14

6.0111216.2

> 12.44.7

17.221.110.5173.62.02.04.42.82.11.31.91.71.2

21.00.50.30.550.80.8

914914869731411628404360343290

3

3

The climate of the southern foothills and thecoastal plain is summarized in Table 2. There isa decreasing air temperature gradient movingnorthward toward the coastal plain. Total pre-cipitation is higher in the mountains, but overallthere are no distinct patterns across the NorthSlope. About 40% of the precipitation is unfro-zen on the coastal plain; moving southward thethaw season lengthens and the unfrozen precip-itation can reach 75 % of the total in the BrooksRange (Haugen, 1982). Most lakes on the coastalplain freeze in late September and thaw in lateJune or early July. In the warmer foothills, lakesusually freeze in early October and thaw in lateJune. Deeper lakes tend to freeze later in the falland retain their ice cover longer in the spring thando shallow lakes; for example, Hobbie (1984) re-ported ice cover on the 57 m deep Lake Schraderin late July and early August.

Methods

Temperature, conductivity, and pH were mea-sured in the field. Water samples were filteredthrough glass fiber filters (Whatman GF/C orGelman A/E, 1.0 jm pore size) or membrane fil-ters (0.45 /im pore size) and stored in polyethyl-

Table 2. Comparison of climate in the southern foothills atToolik Lake and Galbraith and in the coastal plain at Barrowand Prudhoe. Mean annual values and the range of monthlyvalues are given, except for precipitation from Prudhoe, Gal-braith, and Toolik where the range of annual sums is given.Toolik precipitation data are from Toolik River MS 117 site;Barrow data are from Hobbie (1980); Prudhoe and Galbraithdata are from Haugen (1982). All precipitation data are fromWyoming snow gauges except for Barrow.

Site Temperature Precipitation Insolation Wind(° C) (mm) (J/cm2 /d) (m/sec)

Galbraith - 8.8 210(- 30.5 to 12.7) (188 to 254)

Toolik -9.0 309 838 3.2(-31.7 to 12.4) (194 to 406) (o to 2168) (2.1 to 3.7)

Prudhoe -11.3 203( -31.9 to 9.4) (183 to 223)

Barrow 12.4 108 891 6.1(-28.3 to 4.1) (2.8 to 22.8) (0 to 2330) (5.6 to 6.8)

ene bottles for no longer than 4 months. Alkalin-ity was determined by potentiometric titration andthe titration curves were analyzed by the methodof Gran (Stumm & Morgan, 1981). In some sam-ples, dissolved inorganic carbon (DIC) concen-trations were determined by acidifying sampleswith phosphoric acid and purging with nitrogengas into a vacuum line. CO2 was collected bycryogenic distillation and gas pressure measuredby an electronic manometric gauge. Alkalinity wasthen calculated from DIC concentrations and pHusing the carbonate species relations in Stumm &Morgan (1981) and Plummer & Busenberg(1982). SO4- and C1- were analyzed using a Di-onex ion chromatograph. Water samples for cat-ion analyses were preserved in the field with HCI;Ca2 +, Mg 2 +, and Mn2 + were analyzed by flameatomic absorption spectroscopy, and Na+ andK+ by flame emission. Soluble reactive phos-phate (SRP), NO3 + NO2, and NH+ were de-termined on a Technicon Autoanalyzer. Themean deviation from cation-anion balance was4.8% (N= 50, SE = 0.9). Waters with ion imbal-ances greater than 10% were usually deficient inanions; alkalinity in these samples was calculatedfrom DIC concentrations rather than measureddirectly. Mineral equilibria calculations weremade using Gintelberg activity coefficients.

The climate station at Toolik Lake consisted ofa Campbell Scientific data logger that recordedair temperature (Fenwall thermistor), wind speedat 5 m height (MET-ONE 014A anemometer),and solar radiation (LiCor 200SB pyranometer).Climate data are reported for the year from June1989 to June 1990. Precipitation samples werecollected using an Aerochem Metrics wet-dry col-lector.

Chlorophyll a (CHLa) was extracted in 90%methanol and concentrations were calculatedusing equations in Wetzel & Likens (1979).Zooplankton were collected using vertical or ob-lique hauls of a 100 or 335 #m mesh net. Non-parametric Spearman Rank correlations weremade between zooplankton occurrence andphysical-chemical variables.

One benthic sample was taken with an Eck-man grab in a subset of the lakes surveyed (Ta-

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ble 7). Samples were washed through a 200 btmmesh net. Residues were preserved with 95 % eth-anol. Chironomidae were sorted from residuesand identified to genus or species. For severalfoothills lakes, more extensive surveys were con-ducted independently using diver cores or anEkman grab (Hershey, 1985, Goyke & Hershey,this issue, Hershey, in press). Taxa whose esti-mated abundance exceeded 50 mg m- 2 were re-ported as abundant, other taxa were reported aspresent or absent.

Results and discussion

Physics

The temperature of surface waters decreased fromsouth to north along with air temperature. July isusually the warmest month on the North Slope,and midday water temperatures at this time ofyear ranged from 14 to 22 C in the foothills andfrom 6 to 14 C near the coast (Table 3).

In most of the shallow lakes light penetrated tothe bottom and secchi depth was equal to maxi-mum depth. In deeper lakes, secchi depth rangedfrom 2.5 to 9.0 m, and was similar to values inother arctic lakes (Hobbie, 1984). The variabilityin light transmission reflects the amount of sus-pended inorganic and organic material as well asthe dissolved organic material (Hobbie, 1984;Miller et al., 1986).

Chemistry

The rainfall at Toolik had a mean pH of 5.21 andconductivity of 2.9 tuS cm l in 1989 and 1990(Table 4). The dominant ions in this acid, dilutewater were Ca2 +, HCO3, and NH'. The mostdilute rain reported for Alaska is at the subarcticPoker Flats site in taiga forest (Table 4). The en-richment in Ca and Mg of rain at Toolik com-pared to Poker Flats may be related to the prox-imity of limestone and dolomite outcrops in theBrooks Range, about 20 km south of Toolik. Fur-ther enrichment of ions is seen in rain at Saqva-

qjuac on the northern coast of Canada. Here theeffects of sea salt are most noticable and there aremuch higher concentrations of Na, Mg, Cl, andSO4 compared to the rain at Toolik. There is lessinformation on the chemical composition of snowin the Arctic, although it appears that the propor-tions and concentrations of ions in snow are sim-ilar to those in rain (Hobbie, 1984; Cornwell, thisissue). Even less information exists on the chem-istry of dry deposition. One sample from Toolikshowed enrichment over rain in most ions, espe-cially K, SO4, and nutrients (Table 4).

In general the surface waters were also dilute(Table 3). Conductivity ranged from 30 to843 kuS cm- ', which is similar but slightly higherthan previously reported values for the Arctic (17to 322 #S cm- ; Rodhe, 1949; Kalff, 1968; Craig& McCart, 1975; Hobbie, 1984). The higher con-ductivity waters in our study were found within2 km of the Arctic Ocean. There are also someunusual meromictic lakes along the coast on is-lands in the Canadian high arctic that containtrapped seawater and have very high ionicstrengths (Jeffries et al., 1984; Ouellet et al., 1989).Perennial groundwater springs may have conduc-tivities up to 4546 pS cm - , although most springwaters fall in the conductivity range of surfacewaters (Craig & McCart, 1975). The pH of allwaters studied here was much less acidic than thepH of rain, and ranged from 6.85 to 8.46(mean = 7.68).

The surface waters fall into two distinct groupsof chemical composition. Within 20 km of thecoast, but excluding rivers that drain larger areas,waters had Cl followed by HCO3 as the dominantanions, and Na and Ca as the dominant cations.Further inland the waters were dominated byHCO3, and Ca and Mg. The sea is the majorinfluence on the relative proportions of ions incoastal waters. Ion ratios in these lakes are sim-ilar to seawater and sea spray, except for enrich-ment in Ca and HCO3 (Table 5). This enrichmentmay be due to eolian input of Ca-rich silt from thenearby Sagavanirktok River delta (Walker &Webber, 1979). Because permafrost acts as a sealand prevents subsurface drainage, these lakes aresimilar to other coastal lakes that are perched or

6

Table 4. Rain chemistry (mol L 1; ueq L- for alkalinity; pS cm- for conductivity) for (1) Toolik Lake site (wet only) withvolume weighted means (VWM): (2) Saqvaqjuac, Northwest Territories (VWM, bulk precipitation, 60 ° N 90 W, Welch & Legault1986); (3) Poker Flats Alaska site (VWM, wet only, 67 N 147 W, Galloway et al., 1982); (4) Sag River site (VWM, bulk pre-cipitation, 68 N 148 N, 1986). Dry deposition values are from Toolik Lake site on 2 Sep 89 and from Sag River site on 7 Jul

86. Sag River site data are from G. Shaver (pers. comm.). Symbol '<' indicates values below detection; blank spaces indicatemissing values. The relatively high alkalinity value at pH 4.34 (Toolik, 24 Jul 90) probably indicates the presence of organic acids

with pK values less than 4.4.

Date (pS cm ) (pmol L ')

Cond pH Ca Mg Na K Cl SO4 Alk PO4 NO3 NH 4

Toolik19 Jul 89 0.5 5.67 4.3 0.1 0.8 0.3 1.1 < 1.1 0.9 0.627 Jul 89 1.2 5.12 2.6 < 0.4 0.8 1.7 0.8 9.5 < 2.1 <

8 Aug 89 1.6 5.73 3.0 0.2 0.4 0.3 1.0 1.7 9.8 < 1.4 <

1 Sep 89 3.0 6.19 13.3 1.2 3.3 2.2 5.9 3.1 < 3.0 <25 Jun 90 4.3 4.98 2.1 0.2 0.3 0.1 1.5 4.9 13.1 < 2.0 <

5 Jul 90 5.4 4.53 3.4 0.3 < 0.4 3.8 3.9 15.5 < 3.9 <14 Jul 90 3.0 5.75 0.6 0.2 1.4 2.2 3.4 1.9 < 4.3 14.924 Jul 90 23.0 4.34 7.6 1.0 6.3 4.8 20.9 14.3 53.4 < 30.1 4.4

4 Aug 90 3.3 5.44 3.1 0.5 4.5 7.8 13.6 1.2 < 3.2 7.7

24 Aug 90 3.3 5.73 0.8 0.2 0.6 1.8 2.7 1.7 14.3 < 5.2 18.3VWM = 2.9 5.21 4.2 0.4 1.1 1.0 2.7 2.7 12.2 1.1 2.7 10.7

Saqvaqjuac 8.9 4.80 4.7 2.9 21.7 1.3 25.1 8.5 0.4 1.9

Poker Flats 4.96 0.05 0.1 1.0 0.3 2.6 3.6 1.9 1.1

Sag River 0.9 2.8 12.2

Dry Deposition2 Sep 89 46.3 7.11 15.2 12.0 21.7 36.0 24.5 37.4 21.9 30.4 28.07 Jul 86 2.7 15.1 8.8 2.0 4.5 2.4

isolated from large groundwater inputs; thechemistry of such coastal lakes is determinedmainly by atmospheric inputs (Kling, 1986).

In contrast to the input of sea salt to lakes nearthe coast, atmospheric precipitation had little in-fluence on the chemistry of inland lakes and riv-ers. In the inland waters there was substantialenrichment of all cations and HCO 3, and slightenrichment of SO4 compared to the proportionsof these ions found in rain (Table 5). This enrich-ment is due to weathering of bedrock, and is par-ticularly evident in the lakes that are known to liein or near the Lisburne limestone-dolomite for-mation (Table 5). Rock weathering plus the so-lution of evaporites explains most of the variationin surface water chemistry of the Mackenzie Riverbasin in arctic Canada (Reeder et al., 1972) andin other parts of the world (Meybeck, 1987).

What is unusual in many of the waters studiedhere is the strong enrichment of ions in compari-son to the nearby Mackenzie or to the averagecomposition of the world's rivers. For example,Ca, Mg, and HCO3 are enriched by at least anorder of magnitude in the North Slope rivers ver-sus the Mackenzie (Table 5). This difference maybe due in part to the influence of the BrooksRange in Alaska. The Mackenzie River drains abasin of low to moderate relief, composed prima-rily of muskeg tundra as well as part of the Ca-nadian Precambrian shield (Reeder et al., 1972).The Sagavinirktok River, on the other hand,drains an area of relatively high relief, composedin large part of exposed rock in the Brooks Range.The headwaters of the Kuparuk River, althoughgeographically adjacent to the Sagavanirktok, areisolated from such exposed rock, and the chem-

7

Table 5. Average molar ion ratios in seawater, Toolik site rain, lakes less than 20 km from the coast, lakes more than 20 km fromthe coast, lakes associated with limestone outcrops, rivers, lakes lying in old glacial till (sites 7, 13, 15, 22) and in new glacial till(sites 11, 16, 17), the Kuparuk River (site 23), the Sagavinirktok River (site 39), the Mackenzie River (Reeder et al., 1972), andthe average for world rivers (Meybeck, 1987).

Site N Na:Cl Ca:CI Mg:Cl K:CI S0 4:Cl Alk:Cl

Seawater 0.86 0.02 0.10 0.02 0.05 0.004Coastal lakes 9 0.67+0.05 1.0+0.3 0.25+0.07 0.03+0.01 0.08+ 0.05 1.9+0.6

Toolik rain 10 0.41 1.6 0.15 0.37 1.0 4.5Inland lakes 30 3.4 + 0.3 85 + 14 16 + 3 2.0 + 0.3 4.4 + 0.9 142 + 24Rivers 11 5.8+ 1.0 60+ 10 17 + 3 1.4+0.4 9.8+2.7 132+20Limestone lakes 3 3.0+0.1 117 +11 26+5 1.4+0.2 15+6 227+24

Lakes new till 3 4.4+ 1.1 133 + 36 26+8 2.0+0.0 7.8 +4.7 229+ 27Lakes old till 4 2.7+0.2 31+3 6.5+0.5 1.3+0.1 1.6+0.5 64+5

Sagavinirktok 2.0 65 38 0.40 5.4 233Kuparuk 3.3 9.5 3.5 0.80 3.8 20Mackenzie 1.2 3.3 1.7 0.11 1.5 7.3World rivers 1.8 3.9 1.5 0.37 1.0 9.9

istry of the Kuparuk is similar to that of theMackenzie (Table 5). Craig & McCart (1975) andLock et al. (1989) also found higher conductivitystreams in the Brooks Mountains than in thefoothills province.

Another influence on surface water chemistryis the age of glacial drift in a drainage basin andthus the extent of primary rock exposure, soildevelopment, and weathering. Much of the foot-hills province on the North Slope was heavilyglaciated at some time in the Pleistocene, andHamilton (1982) has presented a glacial sequencewith at least five major stages. The glaciers car-ried rocks northward out of the Brooks Range tothe foothills, and the influence of the age of gla-cial drift is seen clearly in the chemistry of severallakes around Toolik. Toolik Lake is a complexkettle formed by melting ice blocks in a terminalmorraine of the relatively young Itkillik II glacia-tion (24 000 to 15000 yr BP). Most of the drain-age basin of Toolik Lake, and the land surface tothe immediate east of Toolik, consists of glacialdrift from the older Itkillik I glaciation(100000 yr BP). Lakes lying in the younger driftto the west have higher conductivities and arestrongly enriched in Ca, Mg, and HCO3 whencompared to lakes less than 1 km to the east but

surrounded by the older more weathered drift(Table 5; Fig. 1). This relationship between waterchemistry and the age of the land surface canbe extended by examining the Kuparuk Riverfurther to the east. The upper Kuparuk basin(area = 143 km 2; site 23) is covered by drift fromthe much older Sagavanirktok glaciation (mid-Pleistocene; Hamilton, 1982). The water drainingthis basin is the most dilute and has the lowest ionenrichments over rainfall of any surface water westudied (Table 3, 5). In addition, weathering ratesin the Kuparuk basin as measured by the exportof cations are as low as for any arctic or temper-ate zone site yet examined (Cornwell, this issue).

Our mineral equilibria calculations indicate thatthe product of Ca2

+ and CO32- concentrationswas from 1.3 to 4.0 times the value theoreticallyrequired for calcite (CaCO3) precipitation at eightsites (4, 11, 28, 30, 33, 34, 48, 51). It is unlikely,however, that such mineral precipitation exerts astrong influence on the overall major ion compo-sition of surface waters on the North Slope. Thisis because saturation indices are only approxima-tions of actual chemical equilibria, and a slightlypositive index value does not demonstrate min-eral precipitation (Nordstrom and Ball, 1989). Inaddition, our field measurements were made dur-

8

ing midday when photosynthesis is maximum andthus pH and CO2- concentrations are highest andprecipitation is most likely. Finally, the amount ofCa as a percentage of total cations does not de-crease as Ca concentrations increase across allinland sites, as would be expected if Ca is selec-tively removed by calcite precipitation.

Concentrations of dissolved nutrients were ingeneral low; the mean values were 0.16 ,uM forSRP, 3.3 M for NO3, and 1.7 MM for NH'.These low concentrations are expected becausealgal productivity is often limited by phosphorusalone or by co-limitation of phosphorus plus ni-trogen in arctic surface waters (Hobbie, 1980;Miller et al., 1986; Whalen & Cornwell, 1985). Inaddition to this biotic control, several studies havedescribed the inorganic adsorption of phospho-rus on iron hydroxides in some arctic lakes(Prentki etal., 1980; Cornwell, 1987; Sugai &Kipphut, this issue). This mechanism may ulti-mately limit the regeneration of phosphorus fromsediments, although it is unclear how widespreadthe phenomenon is in arctic surface waters.A third potential control on dissolved nutrientconcentrations is the mineral precipitation ofPO4 with calcium. Mineral equilibria calcula-tions on the 41 sites where Ca2+ and SRP datawere available indicate that all waters weresupersaturated with respect to hydroxyapatite[Ca6(PO4 )3OH, pKsp = 55.9] by 5 to 15 orders ofmagnitude. Clearly the SRP concentrations arenot controlled by hydroxyapatite formation inthese waters. There are, however, reports of moreamorphous mineral forms, such as fl-tricalciumphosphate [-Ca3(PO4)2, pKsp = 22.0], that con-trol concentrations of dissolved PO4 (Fergusonetal., 1971; Snoeyink & Jenkins, 1980). Suchamorphous mineral precipitation may play a rolein controlling levels of PO4 in arctic waters - wefound 13 lakes that were supersaturated by up to12 times with respect to -tricalcium phosphate(sites 5, 15-17, 19, 20, 28-32, 36, and 52). Atpresent the relative importance of these biotic andabiotic controls on nutrient concentrations, aswell as the seasonal variation of each control, isunknown in arctic freshwaters.

Seasonal variations in surface water chemistry

are related mainly to dilution by snowmelt andrunoff, and to concentration by evaporation andby exclusion from ice. These mechanisms can in-crease or decrease chemical concentrations ofmajor ions in arctic lakes and rivers by up to 30fold (Howard & Prescott, 1973; Schindler et al.,1974; Prentki et al., 1980; Cornwell, this issue). Itis unlikely, however, that such seasonal variationsstrongly affected the major chemical groupingsdescribed above because all lakes were sampledduring a short time span in late June and earlyJuly. Year to year variations of alkalinity in thefoothills lakes Toolik and N2 are reported byKling et al. (this issue); maximum concentrationchanges over periods of 5 to 14 years were about2 fold, although typically the variability was muchless than that.

Zooplankton

We identified 11 species of zooplankton in sam-ples from these lakes (Table 6). Daphnia midden-dorphiana was the most common cladoceran andDiaptomus pribilofensis was the most commoncopepod found. All species are Holarctic in dis-tribution (Roen, 1962; Tash & Armitage, 1967;O'Brien, 1975; Moore, 1978; Haney & Bucha-nan, 1987).

The most striking overall pattern of species dis-tribution is the paucity of cladocerans in thecoastal plain lakes. It is possible that overwinter-ing embryos had not yet emerged at the time ofour sampling in early July, although Stross et al.(1980) found that Daphnia middendorphiana em-bryos hatched at ice-out and produced a brood ofyoung by mid-July in the tundra ponds at Barrow,further north than our lakes. Low temperaturesand short growing seasons associated with highlatitudes are thought to decrease the diversity andlimit the distribution of cladocerans in the Arctic(Poulsen, 1940; Moore, 1978; Hebert & Hann,1986), which is consistent with our findings.Haney & Buchanan (1987) also suggest that pho-toperiod and light transmission in water may limitthe distribution of Daphnia in the Arctic.

We found no significant correlations with any

Table 6. Zooplankton species composition in the study lakes; 'x' indicates presence and ' -' indicates absence.

Lake :

5 Galbraith x . ... x x .....6 Island - x . .. x x7 I8 - - x x - x x x ....8 S13 x - - - x - x x - x x9 S12 x . ... x x - - x x -

10 Sl x . ... x x - x x -11 S6 - x x - - x x - x - -12 S3 x - x x x x x x x - -13 Toolik x x x x x x x x ....14 Dam x . ... x x x15 Camp x . x x x16 N1 x . . .. x x x ....17 N2 - x x - x - x x ....18 NE2 - x x x x x x x ....19 NE12 x . ... x x x ....20 NE14 x - x - - x x .....21 Itigaknit x .. .. x x x22 E1 - x x - - - x x . . .24 Campsite x x - - x x x x25 01 - - - x - x x .....26 02 - - - x - x x x ....27 03 - x - x - - x x ....28 Elusive x x - - -x -x29 Moose x -x - x - x x30 Hanging x x . .. x x . .31 Foggy - x x - - -x x ....32 F4 x - - - -34 George x . x - -- -35 Anne x - - - - x x - x x 36 Sag2 x - - - - x x ..37 Sagl x . x - - - x42 Charles x - - x - x x x - x44 William .- x - x45 Windy x - -- -- x46 Silhouette x . - - - - x47 Colleen x - - - - x x x - - x48 Sag-c pit x - - - - - x49 Bern x . .... x x -- x -50 Dune -...-.- x - -- x51 Maxine x - - - - x x x - -52 Cx - - - - x - - - x53 Africa x - - - - x x -53 Africa x - - - - x - - - - x -

10

species and chlorophyll a concentration in thelake, although our data consist only of single timepoints and chlorophyll concentrations may bequite variable seasonally. Similarly, there werevery few significant correlations between individ-ual species and chemical variables. The presenceof Holopedium gibberum was negatively correlatedwith conductivity and the dominant ions contrib-uting to ionic strength: HCO3-, Ca2 +, and Mg2 +(Spearman Rank, P<0.001 for all). We know ofno field studies or experiments demonstrating theintolerance of Holopedium to high conductivity.Some rotifers are intolerant of waters with con-ductivities above about 400 yS cm- (less thanour study lakes; Green, 1986), but some copep-ods appear to be limited only by much more con-centrated waters (LaBabera & Kilham, 1974). Itis also possible that these correlations are spu-rious and result from the collinearity of latitudeand ionic strength; Holopedium is absent in coastallakes, which as a group have much higher con-ductivities than inland lakes.

O'Brien et al. (1979) summarized the zooplank-ton community structure in arctic lakes andponds. In general, lakes without planktivorousfish contain mainly large-bodied zooplanktonspecies, while lakes with fish contain mainlysmall-bodied species. The presence of fish is re-lated to lake depth, with lakes shallower than 3to 4 m generally lacking fish. In the present studywe found that, for example, presence of the large-bodied Brachinecta was negatively correlated withdepth (r = - 0.49, P <0.002), while the small-bodied Daphnia longiremis was positively corre-lated with depth (r = 0.44, P < 0.005). There aresome exceptions, however, in that several of thelakes in the Toolik area contain either fish or nofish as well as both large and small-bodied zoop-lankton. The exclusion of large-bodied zooplank-ton by fish in these lakes appears related to thedensities of predator and prey, and to the effi-ciency of predation (O'Brien etal., 1979). Oursurvey results have extended these general con-clusions to about 20 new lakes on the North Slope(Table 6). O'Brien et al. (1979) found Toolik Laketo be especially anomalous because it containedboth large and small-bodied cladocerans and

copepods in the presence of planktivorous fish. Inaddition to Toolik, we have identified two otherfoothills sites containing fish and with a similarplanktonic zooplankton community: lakes Elu-sive and Campsite. These three lakes have quitedifferent chemistries, but they are all relativelylarge, relatively deep, or both. It is unclear atpresent how these common characteristics influ-ence zooplankton community structure, althoughpredator avoidance in habitats made complex bydepth or area may play a role.

Benthos

The distribution of Chironomidae among lakessurveyed is presented in Table 7. Because only asingle Ekman sample was collected for many ofthe lakes, these data represent the most abundanttaxa and provide only a general indication of chi-ronomid diversity and distribution.

Stictochironomus rosenschoeldi, Heterotrisso-cladius spp., and Procladius spp. were the mostwidely distributed taxa. Stictochironomus andHeterotrissocladius usually co-occurred and wereabundant when present in foothills lakes (Ta-ble 7). However, Heterotrissocladius was found inonly the largest of the coastal plain lakes (# 47,Lake Colleen), whereas Stictochironomus ap-peared to be even more widespread on the coastalplain than in the foothills (Table 7). Stictochirono-mus is associated with a wider range of trophicconditions than Heterotrissocladius; it is indicativeof ultraoligotrophic to mesotrophic conditions,whereas Heterotrissocladius is generally associatedwith ultraoligotrophic to oligotrophic conditions(Saether, 1979; Pinder & Reiss, 1983; Cranstonet al., 1983).

Procladius is widely distributed across lentichabitats worldwide (Fittkau & Roback, 1983).Goyke & Hershey (this issue) suggest that slimysculpin, a benthic feeding fish, are important indetermining Procladius abundance. For example,in foothills lakes predatory chironomids (prima-rily Procladius) were significantly less abundant inlakes with sculpin than in lakes without sculpin.In the present survey Procladius appeared to be

11

Table 7. Chironomidae from North Slope lakes. Lake numbers correspond to sites in Table 1. Asterisks indicate data fromHershey (1985b, in press) and Goyke & Hershey (in press). 'A' indicates abundance > 50 mg m- 2, and 'X' indicates abundance< 50mg m 2.

Lake 5 6 7* 11 12 13* 16 17* 19* 20 21 22 34 43 45 47 49 51 52 53

ChironominiChironomus

CryptochironomusPagastiellaParachironomusPhaenopsectraPolypedilumStictochironomus rosenschoeldi A

TanytarsiniCladotanytarsusConstempellina brevicosaCorynocera ambiguaCorynocera oliveriMicropsectraParatanytarsus XStempellinella XTanytarsus

TanypodinaeProcladius A XAblabesmyiaArctopelopia X

ProdiamesinaeMonodiamesa bathyphila

DiamesinaeProtanypus saetheri

OrthocladiinaeAbiskomyia virgoCorynoneuraCricotopusEukiefferiellaHeterotrissocladius AHydrobaenusMesocricotopus XLimnophyesParacladius quadrinodosusParakiefferiella XPsectrocladiusTheinemanniellaZalutschia

A XX

A XX

XX XA A X

XA

XA X X

XX

A

XXA

X X

X XA XXX X

X X A X

A X

A

X XXX

X XX

X

XX

X

XXX

X X

A X AX

AXAAXA

AX X A

X

X X

A X A XXAA AX

A A A X

X X X X

X

A

AXX

XXX

XA A

X XX XX A

X

X

X A

X

XXA

XA

A

XX XX X

abundant (> 50 mg/m 2) in six of the nine lakeseither known to lack sculpin (lake 22) or pre-sumed to lack sculpin due to shallow depth (lakesnumbered > 34). By comparison, Procladius wasabundant in only three of the ten deeper lakes inthe foothills (Table 7), and sculpin occur in at

least nine of these (Hanson et al., this issue; lake 5has not been surveyed for sculpin).

Of the less frequently encountered taxa, mostappeared in both foothills and coastal plain lakes(Table 7). The distribution of these taxa is Hol-arctic, and they are generally associated with oli-

X AX X A

X

A

XX

X

XX X X X

12

gotrophic conditions (Saether, 1979, 1983; Cran-ston et al., 1983; Fittkau & Roback, 1983; Pinder& Reiss, 1983). However, Corynocera oliveri hasbeen previously reported only in the Palaearctic(Pinder & Reiss, 1983) except as a subfossil(Walker & Mathewes, 1988). Eukiefferiella andThienemanniella are typically lotic, thus theiroccurrence in foothills lakes El and N1(Eukiefferiella only) is unusual.

Summary

We examined the biogeochemistry of 45 lakes and8 rivers on the coastal plain and the foothills re-gion of arctic Alaska. Water chemistry was con-trolled by three major factors: (1) rainfall and seaspray strongly affected the concentrations and ra-tios of major ions within 2 km of the Arctic Ocean,and dust blown from the Sagavinirktok delta en-riched some lakes in Ca2 + and HCO3 relative tothe proportions found in sea water; (2) proximityto the Brooks Range mountains and especially tolimestone and dolomite outcrops produced verydistinctive calcium and magnesium rich waters inseveral lakes and rivers; and (3)increasing ageand thus extent of weathering of glacial drift sur-rounding lakes in the foothills region determinesthe overall ionic strength of surface waters - themost dilute lakes and rivers lie in the oldest ter-rain. Nutrient concentrations are controlledmostly by biological uptake, although adsorptionof P on iron hydroxides and precipitation ofamorphous calcium phosphate minerals may alsobe important. We identified 11 species of zoop-lankton and 32 species of chironomids from thestudy lakes. These taxa are in general widely dis-tributed throughout the Neararctic. The effects oflower temperatures with increasing latitude seemto explain more of the variation in zooplanktonspecies distribution than does water chemistry.Biotic interactions with zooplanktivorous fish arealso a major determinant of zooplankton com-munity composition and size structure. Althoughlarge-bodied zooplankton are nearly always elim-inated in lakes with fish, we have identified threelakes that are exceptions to this generalization; it

is at present unclear how the common factors oflarge area, great depth, or both shared by theselakes affect the zooplankton community. Fishpredation may determine the abundance of thecommon chironomid Procladius in these lakes.

Acknowledgements

We thank G. Kipphut, B. Moller, C. Bauman,B. Peterson, W. Rowe, K. Foreman, K. Regan,M. Dornblaser, J. Mcrae, and J. Laundre for helpin the field and lab. This research was supportedby the National Science Foundation grantsBSR8702328, DPP8722015, and DPP8320544,and by the A. W. Mellon Foundation.

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