H.G. ones' end J.W. ~omero# '~nivenitk du Qukbec, Quebec; ' University of Wales, Aberystwyth

Snowmelt in a small boreal forest basin in eastern Canada: influence of concrete frost on the hydrology and chemical composition of surface waters

'Abdract

Bydrolog~caI and chemical data of streams during snowmell in a small boreal watershed in eas tm Canada (Lac U h m e ) ind iw~ that mpid runoff may occur during pix-mek and early melt periods due tu the v w of concrete &mt in limr and uppr organic mil horizons. Hydrolo~ical &ta showed that up to #% of the forest floor nay be pad in fiost in early spring Howcvcr, calcu tations for the percentmge of forest floor covered by concrete frost h n chemical data are culmplicatcd by leaching of liner and soil in ptchy frost wver and m a n tones. which gave iw to varying pcKentages of fmst eovcr (32% to 1 W!) depending m the stream a d chemical species chosen.

mmmd Ik h k hydrolog~ques et chimiques des ruisseaux pcndant la h t e des neiges dans un petit bassin versant h d w dr I'e4 du Canada (Lac Mlamme), diquent qu' un rukdlemen t rapide des eaux sur Ic .wI vets le r&au &surface p u t st: produirc en pkides avant la fontc cl pendant les premikms C*nements de fonte. et ceci. q d il y a unr couche de glaec compacte dans la litihe et IM horizons organiques du sol. Les donnks hydrologiques b n m t que jusqu'i #/o du sol du bassin el couvert dc g l m conpcle au rxwrs des premiers jours de pintemp, Par mire, le ~mlcul de la su6cie de la glace compactc p I'utilisation des &rut& chirniqws est compliquk par je lessivagr deu espbes chirniquts de la litihe et du sol danr Its urn= de couverture interrnitrente dt glace et dns

rivmimu. Ceci se i e u i t par une varitltion &lev& dm5 la wprticie calculk & glace compacte (32% b1oDbrb) dm I'espke uhimique choinic et le r u u w pris en consiclhtion.

hawern Canada, snow ~~eltwaters can be a rnujur k ta r in the availability and distribution of nutrients and solures in fmted watersheds. For cxmnple, snow only contributes 35% of the annual precipitation in thc Fo&

b Monimmency Bareal Forest Experimental Research Area (Lac Laflamme w a m k d ) In southern Q u h but more tb 50% af anouul nrwff occurs in the spring ( Papiow, 1989). At thc time of maximal ammlation prior to melt, Ibe snow a v e r also contains up to 45% of the annual nitrogen [N] precipitation load {18Y, NHs; 27%. NO3; hpiaeay 1987). Although some losses ofreadily biu-avaitable N WH4, NO,) me due to microbiological a%imilation m nriting snow (Jones, 1999). mcltwaters can deliver up to 3w& of tht annual N pmipilatim load to thc floor a the short (2-3 weeks) spring runolY In addition, wlutes and nutrients leachad from soil M ? o n s and littcr are dm madc available (Taylor and Jones, I 990).

The ovml l efficiency of nutrient uptake by the forest floor communities is dependent on many c o m i n g sndcornplm pruc- such as biological assimilatiun rat* physical adsorption and desorption and mmaval by hyhhgical -port, Nutrient uptake. e.g. N, will k favoured by relatively long residence times in the mil horizons dming melt that allow micmbiologi~l cmimunitieu tu w h i m growth and mots to assimilate N. In the caw of runoff lhat travels rapidly over the soil to thc streams md lake [he soil residence time of the melrwaters will k 1- and biological uptala ofN shwld be reduccd Reduced tail residence times will thus lead to increased export of nu-5 md solutcs from snow and litter to thc s t m u m and lakw of lhe hydrological network.

1Cmils are frown dwing snowmclt then the rate of infiltration of meltwarn will diminish in rclation to unfrozm soils depending on the rnoisrurc content of the wilu prior ro freezing. (Kme and Stein, 1983). Concmc frost (fmzcn littcr and upper wil horizons) !ws been shown tu wcur in the Lee Laflamme wntershad under eMtain -l@cal d t i o n s ( Roulx and Stein, 1997). Rapid transfer af wlwater or rain Ifum the watetshed to mmrm and lakes avcr mnrrete fmsl (quickflaw) should k reflected by different hydrological responses and chemical mymition of the surface waters c o m ~ to r q w n s e s and chemical composition whm no frost is p m t . Howwcr. Proulx and Stein (ibis) only measured con- fwut in the Lac Laflammt warmshed during one winter (1989- 1990); they then simulated concrete W f o ~ ( ~ 1 in the years prior to I9W h m logical dnta. During the previous y e m no fietd m y $ or expwllnents had been carried out in the watemhd with the u bjtct of relating nmoff characteristics to concrete frost formation. Prior to 1990, data on surface w a r n during the spring lurmff w&9

pmaril y cmpilcd with regard to the Lac hfIamme ex.xperimenml pmpmme on lake aeidit~cation and for the input* mtput budgcts fw major mimic and cationic species ( Papineah 1987). Subsequent to the realisation that concrrtc Bw could play a significant role in surface runoff and the export uf N. we m e & to mxamiae the pst diita s&

on surface waters in thc light of simulated concretc frost occurrence during springmelt at Lac Laflamme. In this paper we annlyse the hydrological respnses and the chemishy of stream waters of the Lac bflmm

basin in springtimt to the estimtad wrurrcnce of frozen soils under the snow cover during a three-year perid, I 982- 83. 1983-84 and 19R4-85.

2 Study site

Lac Lnflamme (47" 19' N; 7 la 07' W; 780 masl) is a shallow headwater lake, 0.06 kid. set in a bml forest basin, 0.68 km2, 80 km north ofQutbcc City, T h e mximum depth of the lake is 5.3 niand lakc volume is 1 25tlf13 m3. The whole basin rests on impervious chmockitic gneiss covcrcd by ssndy till: till thickness varies from less than 0.5 rn on the summits 10 mre than I5 m undcr tht! lake. Ihe average annual mean tcmperaturc and precipitation are 0 . X and I424 mm and days with f m t number234 Approximtcly one third of the precipitation f~ l l s as snow. The snow cover starts to furm in late October and at the end of the accumularion seam the snow cover reacherr from 100 to 150 cm depth and 350 to 420 mm of snow water equivalent (SWE), The me1 t season generally extends from the cnd of March to mid-May. The hydrological network in the take basin is poorly &eloped cxoept for the stream carrymg rhc take discharge. Up to 94% of goundwuter flow recharges the lake - the rest. b?%, cxiting the basin through the dccp till under [he lake. Hower , during the spring melt period numerow hypodmic streams, pipe flows and s d i c e runoff a t ~ i n the lake s d c e at the shoreline particularly when h e water tablc is high (Roberge and Jones. 19911.

3 Methodology

Enviranmcnt Canada data sets on the chemical composition and loads of lake waters were obtained from the Lac Latlammc report series [Couture. 1994). Data an the chemical cnmp~sition d surfme nmoff, strcam and lake waters were obtained from research reporis and publications by INRS-Eau. A description of tfit me~hudalow may be hund in Joncs (1987). All other pcrtinmt rcfewnces m recorded where necessary.

Estimat~an of conclrte frost i a based on the work of Proulx and Stein (1997). The original methodology of Proulx and Stein, which is based on the consideration of precipitation. warm and cold cvents during snow accumulation and melt periods was slightly modified. The criteria wcre expxkd tu take into xcmmt the relationship beween snow watcr equivalent and amount of rain deposited on the pack dunng warm precipitation events and to the ~imc and mean temperature between the esrirnated fbmration of concrete frost during mid-winter and the springrnclt. The longer and warmer the period between formatian and springmelt the Iowvr the probability that concretc frost will wmin intact at the surface of the liner layer. The probability of occurrence of concrete fro^ was determined as 'high' (H) > 75%; 'medium'(M) x 50%; 'medium-low'(M1) a 25% and 'low'(L) < 5%. Each probability c las is expressed ills he % of rhc surface area of the basin r s t i d ro be covered by mcrctc Iiost bared on the surface area covered by concrete frost msured in 1980 by Pmulx md Stein (1997). Tablc I shows the prubabiiicy of cancrete frost in Ihe basin from 193 1-1982 ro 1989-1990.

Table I Uccrrrrenae o~n~ncreleJrtst ill the Lac Lufimmr BLSUI, 1 98 1 -A2 to 1 989-90

4 Results and DIscusskn

4. I &tarrerice IJJ concrett* fml Table I shows that a high probability of concrcu: host occurred in the spring of 1983. There were three yeaa of h u m pmbabiliry. in the spring of l9114.1986, and 1988, and Wee years of low probability, 1 982, 1 985, and 1987. There was om year ot' intermediate probability (bw to d u r n ) in the spring of 1 989. we c h w the yearly q u m w 1983-1984-1 985 for this study, i.e. a three-year period where the probability of concrete frost formation declined from high to d i u m b low in a pmgrcssive mnner and for which the INRS-Eau data set was compatihlc.

Figure 1 reproduces the temperature and pmjpitation for the winter-spring periods of 1982-83.1983-84 aad 1984-85. The events that lead to thc formation of concrete frost in 1 982-83 can be seen to be the precipitation of Jgnmy 10- 1 1 (44 mm) fol bwcd by lhe cold p i a d of January 12-23 (mean tcmpemfm, - 14°C) and February 2-3 (60 mm) followed the cold period or February 4-1 3 ( m n temperature. - 1 6T). The major rain evcnt of March 20 (38 mm), wh~ch was followed by a wid period (-I 55°C. to March 25) was also conducive to the t m t i o n of cmmm fmst. In 1983-84, two pmipitation endlor melt events fullowed by cold penods could have resulted in h e formation

W t e frost. Thesc are the rain event of February 15 (20 m) during thc warm melt Per;od. February 12-19, l o w 4 by the cold period of Februwy 20-March 14 (mean ternperaturn. - 1 3 .hT 1 and the precipitation of March (14 mm) followed by the cold period u f March 24-29 (mean tcrqmaturc, -8°C) just prior to the me1 t period. In

there were no real conditions conducive to the formation of ccmcrctc frost; the main precipitation of April 15 (57 mm) occurred during the warm me11 period. In 1983 the melt period was from April 9 to May 1 1. in 1984

6 to May h and in 1985 from April 15 to May 9.

42 @fndogicaf respouse ofsurfnccr wuters tu rcrln-err-s~ow episodes To dttect my responses of runoff to concrete frost we examined the dischargc data for h e lake outler - particularly *ah respect to large inputs of water to he forest floor. Large amounts ctf mcltwatcr are discharged during the min =It but as corlcrete frost will break down during continual exposure ro meltwattr during melt ptriods, it c a m t exist hhg the main me1 r unless exceptional cold events occur. In the main m l t perid5 of 1982-83. 1983-84, and 1984 8 IUY prolonged cold periods occurred (Figurt: 1 ) and concrete frost mtnt havc h e n absent, Thus any influcnce of amme fiosts w w M be obi;ewcd during pw-melt or e a j l melt periods when the largcst inputs d water occur during mhn-sww events. We identified 2 rain-on-snow events in I983 during the ptc-melt and early melt period (Figure IA; March 20,38 mm, and April 17-1 8,20 mm): them were 2 rain-on-snow cvcnts in 1984 (Figure I B; M a d 22; H mm and April 6- 7,20 mm); in I 985 thm was one event (Figure l C; April 1 5- 16.57 mm),

Thwe is evidence from the daily discharge at the lake outtet during t h m 3 years that the degree of concrete , frasu is reflected by the flashiness [ tab orriur: and fall of discharge) and volurnc of water expwted from thc lake hrring precipitation events. Figure 2 shows the daily discharge during the mlt pcriad (Figure 2A) and a blo~*n-up m i o n of the discharge during the pre-me11 and early melt periods (Figure 2 R). In thc pre-melt md early mclt of rpring 1983, the lake discharge s h o w 4 3 distinct pcaks (Figure ZB), The first, Figure 2,83A, is the response of the Dltmhed to the precipitation event or38 mm (March 20); the second, 83 B. to a warm melt period and tbc thud. 83C. to the rain went of 20 mm (April 17- 18). In 1984 thc respows to the rain event- of March 22 (14 mm; 84A)

, md April 6-7 (20 rnm, 84B) smn attenuald with respect to 83A and 83C. In 1985 thm was a very small response bo the rain event of April 15- I6 even thou~h the amount of rain was considerable 57 m.

Figure 2C shows the subsequent change of daily discharge (A discharge = m c a s d daily discharge- ! m e line bcharge (L s" x 1 $) as recorded before and a h each event) in the days following cach rain event. The increases in A discharge amutmts depicted by 83C ud 848 are different wen though the precipitation went was the same in hth cascs I20 mm, 2days). b 1983 and 1984 the respoose time. the time that pcaks rise from, and fall to, base line vahrcs, was between 4-6 days. In 1985. the year wit11 no concrete frost, the input of rain, 57 mm. completely infiltrated the soil and practically no change in dischargc was observed.

To better evaluate the rapidity of the ~mnsfer of rain input to surface warcra due to concrete &st formation we calcularcd the m u n r of discharge that fluwed ~hrough the lake during t h t respflnw pcripcriod as n percentage of the mginal rain-on-snow event. Figure 2D shows thal the rate of percentage lost per day was highest in the case of 83C. which diminished progressively for events 83A, 84A and 84B. No such pattern was abscmed with 85. The total m u n t of runoff as a percentage of the initial rain events (integration of peaks 83A, 83C. 84A, 848, and 85) is b w n in Table 2. The Table indicates that thr: Frrxntage runoff generally reflects thc progression in the occurrence of wncme frost for 1983, 1984, I985 but the wlcwlated runoff percentages are consistently lower than the estimated dues of thc percentage area of mnmte fiwt cover from metcornlogical data (Table I ).

43 Chemical composirim mpunse of s u r j i i watms to min-on-~now cpisodex We could not directly relate the chermcal cumpubitiotl o f the lake discharge to the prccipitdon events. 83A, X3C. 84A, MR, 85. Although the quantity of the lake vutlet discharge will reflect the a m n t of rain and rrseltwater inputs to the watcrshd the ckmiral cornpsition of the lake outlet waters will not d i m l y rcflcct those ofthe precipitation

' events as thc lake discharge draws not only on surface runoff and stream waters but a l ~ a on lake ice rtselrwarers. lalreshore snowbank meltwaters and shallow wd dwp groundwater inputs both during and after the rain events

I (Robergc and Jones, 1991). Howevcr. the data sets for 1983 and 1985 ~nclurlBd the chcmisq of streamwarers for the main tribumy. ET9. and the intermittent smm R6, R9. R 12, and R13. The latter ~tmms flow only during the snowmclt pcriad and are fed by surface runoff and particularly by hypdennic flow when thc water table is high

, (Rolwgc and Joncs, 199 1 ). Figure 3A shows the d u c ~ ivity for these strams in the premclt and early melt period of 1983. Thc decrcase in conductivity due to the flow of surface runoff over concrete fmst into the streambeds IS clearly rccordcd for all of these waters. No data was available for 1984. The conductivity of thc two streurn ET9 and R 13 in 1985 (Figure 3Bl also d c c t s the 85 event but to a lesser extent than the stream rcspanses in 1983. Ca, Mg, Na. and CI concentrations generally followed the same pattern as mductiwty. N Q valucs for streamwaters (Figure 3C, 3D) vary 1- than the partern for conductivity but the individual runoff events can still k mognised.

- 4- a.

liq% i 41- dl- Ill *\ 1 .

Figure I Tempranrw and precipitation, Lac Lajlamme,Jbr the whter-spring perinds nf 1982-83, 1983-84 and 1984-85

Ahkm d~seharge vs preclpitltlon: avant, praelplhUon mm. duration. D

P 2 Chunp c!fduilv di.~r.harge fA dischar~:e = measureddniiy dischnrgp- haso line disrharg~ (L i' x I Oh) a v w'tlrrlml k:/vre und uBer each event) in the days jolt owing earit rrrijr evmi

I Gnrrcte frwt pfirnlage utrd ~ntrrl runo#'as a perceritage oj' inciderrt precipirntion for ruin-on-.molrl events. pm-mdt unJ curb: melt period? 1983, 1984. and I985

, PmclpWtlon, ~ x l # Response, days Total runm, ~wld % F-5 %

23.56 5 5.31 22.5 *75 12.40 7 4.89 39.4 *75 0 .M 4 1.21 13.9 -50

12.40 5 1.60 12.9 -50 35.34 11 1.87 5.3

Shamwaber e hemlstry: PremeharJy melt, 1983

Day(Mareh 01 - April 29)

Day(March 01 - April 29)

Streamwatier chemistry: Premeharly melt, 1985

DaflMarch O l - April a)

Streamwater c hemlstry: Premelt.early melt, 1985

D

F m 3 Smmwatcr chcmi~try, ~prlng meltprriod, lac bflammc, @kc, IRBJ a d ISA8S

We also attempted to calculate the concrete frost area uf the watershed that contributed to quickflow by assuming that the chcmical load carried by quickflow would cyud h e iwmse in meam chemical load of the speck in question during and after the rainsn-snow event.

where Sdis the area of the watershed conhbuting to quickflow; V , is the volume of the precipitatim event; /CJb is the mean concentration of the 1 y simeter runoff: Qe and Qp are the daily discharge of measured event flow and estimated base flow r e s e v e l y ; and [C,,] nnd [Chhj are the chmical concenttations of the daily discharge for entlt flow and base flow respectively. We selected thc data for the main stream ET9 (Figure 3) for the 83C event aad estimated the area from the discharge risc and fall for the 3- and &day penods after the event (Figure 2C) . The calculated menn percentage arm of mwctc frost @', XI 00 %) using C1 as a conmative tracer was 32% (x ) and

45% (x ); using Sa as a tracer the ntimated area war 60% (x: ) and 85% (z ). However, the percentage

arca using Na eoneenrra~ianr gave values of 2 1 1% (x' ) and 452% (z ) and 246% (x: ) and 335% (2 )

using Ca cuncentm~iuns. This is indicative of relatively increased leaching of these l a m species prdmbly fiom k t liaer md in m a s of patchy concrete frost andor the local input of soil waters from riparian zones during the rain-on- snow events. The effect of patchy concrete frost would have greater repercussions on the chemical composition of waters entering the streams than on the volume of water - pmicularly if the concrete frosts patches are relatively close to each other but relalively remuved from stream reaches. We found rhat the values ofSd x 100 % varied according to the streams (e.g. R 12, R6) and chemical spcics used. Patchiness of concrete frosts is r major problem witb respect to the methodology that we have employed and future research should take into account the precise dishbution of wncrete frost and its relationship to s l m reaches and recharge areas.

5 Conclusion

The hydrology and chemistry of streams in a small boreal forest watershed shows that rapid runoff due to concrete h s t may occur dwing springmelt in some years during the pre-melt and early melt perids. H ydrolagical data in the Lac Laflamme basin indicated that up to 40?4 of the forest floor may be covered in frost in early spring. However, cdculations fur h e percentage of forest floor coveted by concrete h s t from chemical data gave varying percentage cum (32% to 452%) depending on the streams and the chemical species chosen. The patchy nature of concrete frost distribution is thought to be a major factor in the determination of contributing areas of quickflow during the springmelt.

References

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Jones, H.G. 1999, The ecology uf snowavered syslems: A brief overview of nutrient cycling and life in the cold. Hvdvol. Proc. 13.21 35-2 147.

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h u l x . S. and Stein, J. 1997. Classification of meteorological conditions to aswss the potential for concrete frost formation in boreal forest floors. Can. J Fur. Rex. 27,953-958

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