Quantifying Groundwater Dependence of a Sub-Polar Lake Cluster in Finlandisotope Using Mass an Balance Approach E

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | G 1 erences ff ectiveness of ff , and B. Kløve 1 ) of all 67 lakes during the summer /E ) and mean turnover time (MTT) of the index) that is defined as the percentage TOT I , A.-K. Ronkanen TOT G I 1 9184 9183 , P. M. Rossi 2 H values of lakes are the result of seasonal ice cover pro- 2 δ O and , K. Rozanski 18 1 δ ) in northern Finland was carried out in the summer of 2013 to determine the 2 This discussion paper is/has beenSciences under (HESS). review Please for refer the to journal the Hydrology corresponding and final Earth paper System in HESS if available. Water Resources and Environmental Engineering Research Group, University of Oulu, Faculty of Physics and Applied Computer Science, AGH University of Science and on groundwater directly oret indirectly, al., and 2011). this dependence Understanding can groundwater vary and over lake time water (Kløve interaction is important not applying an isotope masslakes situated balance in approach a to relatively small quantify area the with similar groundwater climatic reliance conditions. of 1 Introduction The characterisation of groundwater dependentof ecosystems the (GDEs) Groundwater is Directivehydrology (EC, a and 2006). requirement contact These with systems aquifers are are often not complex well and established. their Lakes can be dependent ible surface inflow werethe calculated. dependence Here, of a a lakecontribution quantitative on of measure groundwater groundwater was ( inflow introduced toindex values for the of total the inflow lakesin of studied ranged water groundwater from to dependency 27.8–95.0 the %, among given revealing the large lake. di lakes. The This study shows the e hibiting evaporation during theto winter. calculate An the inflow-to-evaporation isotope ratiosof mass ( 2013 balance when approach the was isotopicThe compositions used normalised of relative the humidity lakesminal needed were lake in approaching situation a this for steady-state. approach oneevaporation came of rates the from lakes were assuming showing derived a thewas independently ter- highest possible isotope of to enrichment. any Since determine mass thelakes. balance total Furthermore, considerations, inflow it the ( groundwater seepage rates of those lakes revealing no vis- A stable isotope(90 km study of 67role of kettle groundwater lakes inflowations and in in ponds groundwater-dependent the lakes. situated Distinct on seasonal an fluctu- esker aquifer 1 P.O. Box 4300, 900142 Oulun yliopisto, Finland Technology, 30 Mickiewicza Av., 30-059 Krakow, Poland Received: 4 July 2014 – Accepted: 16Correspondence July to: 2014 E. – Isokangas Published: (elina.isokangas@oulu.fi) 4 August 2014 Published by Copernicus Publications on behalf of the European Geosciences Union. Abstract Hydrol. Earth Syst. Sci. Discuss.,www.hydrol-earth-syst-sci-discuss.net/11/9183/2014/ 11, 9183–9217, 2014 doi:10.5194/hessd-11-9183-2014 © Author(s) 2014. CC Attribution 3.0 License. Quantifying groundwater dependence of a sub-polar lake cluster in Finlandisotope using mass an balance approach E. Isokangas 5 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | H 2 ective ff 10. Lo- + O 18 δ · 8 = ) of the Rokua esker H 2 2 δ erent form (local meteoric water O in proportion with their e ff -space along the line known as the 18 δ H and 2 9186 9185 H) can be considered as ideal tracers for study- 2 O, 18 survey of the isotopic composition of all 67 lakes on the esker in ered from water level decline or eutrophication. Since the seasonal ff ff O isotope composition of meteoric waters cluster along the line called the global 18 The central aim of this study was to quantify the groundwater dependence of 67 ket- The methodology of isotope-aided studies of the water balance of lakes has been Heavy stable isotopes of water ( a long ridge formation, consisting mainlyshaped. of Ancient fine sea and banks medium sand surrounding (Pajunen, the 1995), esker was show that the esker was originally an and August 2013 comprised thecombined sampling with of water continuous in temperature allthe measurements 67 lakes. and lakes for aerial isotope thermal analyses, imaging of 2 The study area The Rokua esker aquiferlast deglaciation area, period situated 9000 in to northern 12 000 Finland, years ago was (Tikkanen, formed 2002). during As the ice retreated, have more fluctuations thanOn the drainage the lakes, other which hand,subsurface have the flow more can drainage stable transport lakes water phosphate are levels. tify to more the lakes. groundwater Therefore, trophic. it dependence Their was ofindex study important all to reflecting also lakes quan- on shows this the that dependence. esker and The propose large-scale an appropriate field campaign conducted in July launched in 2013. Thisat was understanding part the of hydrology of comprehensiveand an investigations ponds esker (2010–2012) have aquifer aimed su area whereisotopic some of behaviour the of kettle lakes thederstood selected based lakes on in thea the data large-scale study one-o collected area from wasorder 2010 already to to fairly quantify 2012, well theiried un- it dependence 11 was on lakes decided groundwater. on to Ala-aho the conduct et esker, al. show (2013), that who the stud- water levels in closed-basin seepage lakes these studies were generally focused on lakes spread over largetle areas. lakes and ponds situatedaquifer across occupying a relatively a small large area glaciofluvialtent (90 of km deposit the in interaction northern between the Finland. aquifer and To quantify the lakes, the a ex- dedicated isotope study was 2009; Turner et al., 2010; Yi et al., 2008), mostly in Canada and northern Sweden, climates (Gibson and Edwards, 2002; Gibson, 2002; Gibson et al., 1993; Jonsson et al., tion of the evaporating waterlocal body evaporation evolves line in (LEL), the whoseing slope the is local significantly or smaller globallake than meteoric water that water along characteris- lines. this The line1996; position is Gibson of strongly and the related Edwards, isotopic 2002; to composition Rozanski the of et water al., balance 2001). ofthoroughly the discussed lake in (e.g. a Gat, number of2005; review Gat papers and and textbooks (e.g.Although Bowser, Froehlich et 1991; several al., authors Gat, have 1995; applied Gonfiantini, isotope 1986; techniques Rozanski in et studying al., lakes 2001). in cold meteoric water line (GMWL), firstcally, determined this by Craig linear (1961): relationshipline may – LMWL). have Evaporation a fromremaining slightly liquid an di phase open is water enriched bodyfractionation in fractionates factors both isotopes accompanying so this that process. the Consequently, the isotopic composi- tracers (e.g. Dinçer, 1968; Shawnumerical et al., modelling 2013; (e.g. Yehdegho et KrabbenhoftCarr, al., 1980) et 1997; can al., Zuber, be 1983) used 1990; and to Stichler determine et the groundwater al., relianceing 2008; the of hydrological lakes. Winter cycle (e.g. and Clarkis and the Fritz, 1997). very Fractionation factor of enabling isotopesin of their isotopic water use abundances in within hydrologicaland studies, the as water it cycle governs (Gat, the 2010). changes At a global scale, the the ecology and eutrophicationthe of lake lakes, since nutrient groundwater1982; balance may Kidmose (Ala-aho be et al., a et 2013). keycontrolled al., Furthermore, element by the 2013; their in vulnerability dependency Belanger of onseepage lakes et groundwater to meters (Kløve al., pollution (Ala-aho et can et 1985; al., be al., 2011). Brock 2013; Methods et Rosenberry such al., et as al., 2008, 2013), environmental only for water resource management (Showstack, 2004), but also for understanding 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | O isotope C). ◦ 16 2 O/ ± 18 C ◦ H and 1 H/ 1.0 ‰, respectively. 2 ± erent recreational activities, such ff 0.1 and ) and geochemical parameters (silica, ± 2 and the discharge zones are situated in the 2 9188 9187 , pH, E.C., O H values are T 2 δ O and 18 δ The isotopic composition of water samples was analysed using CRDS technology Water quality parameters were analysed in the field using WTW Multi 3430 or Multi Kettle holes – long and narrow depressions – give Rokua esker its distinct character. ratios are reported astainty of relative the deviations reported from the VSMOW standard. Typical uncer- were collected by submergingpumped a for at bottle least inthe 10 water, min water facing was prior clear. upstream. to Thesampling Piezometers taking samples bottles groundwater were were (HDPE) collected samples were one orfor rinsed metre isotope until with below analyses the the the were colour water stored sampled of table. in water All the prior dark to at filling. awith Samples a cold Picarro temperature L2120-i (4 analyser.filtered Samples with (pore visible size colour 25 or µm) suspended prior matter to were analysis. The measured 350i meters for oxygen, ECnos and sampler, pH. approximately Samples 1 m ofthe below lake lake. the water If water were the surface collected depth and withwas of 1 more a the m than Lim- lake above 20 was the m, lessshape samples bottom than were and of 2 m, taken size, only from the one the lakes sample middle was had as taken between well. and Depending 1 if on it and their 4 sampling locations. Stream samples trients, water quality parameters ( major cations and anions) (Fig. 1).gust During 2013, the a field campaign total conducted ofthermal in images 67 July of and lakes lakes Au- and taken from pondsIn the were addition, air surveyed composite in for a precipitation the helicopter samplesing using same the were a parameters open FLIR mainly and thermal water collected camera. season oncesamples at a for the month station winter dur- on weresample the collected of esker the during once whole 2010–2013. a snowpack Precipitation depth. year before snowmelt by taking a uniform 3.1 Hydrological measurements and thermal imaging During 2010–2012, 11study lakes, area 13 four piezometers times per and year 11 to streams analyse the were stable sampled isotope composition in of the water, nu- 3 Materials and methods by their crystal clear water, which ison reflected the in lakeshores. the number The of lakesas holiday homes are swimming, and fishing widely hotels and used scuba forof diving di the (Anttila glaciofluvial and formation Heikkinen, ofbe 2007). Rokua, seen, The in has uniqueness been which recognised theNatura in actions many 2000 of ways. and ice, Some water of byto and the the Rokua be wind Finnish esker part can nature is of protected reserve thein by network. UNESCO this GeoPark Rokua network. Network was and recently is chosen currently the northernmost region them, creating kettle hole miresof (Pajunen, the 1995). area However, is the reflected alternatingas in kettle topography the lakes existence or of ponds. approximatelymore Peat 90 than started lakes 8000 to or years ponds, accumulate ago,(Pajunen, referred so in 1995). to the most Nevertheless, border of the regions the majority of kettle of the lakes lakes the and lakes ponds and are partly ponds are paludified characterised covered pine forests. Hydrologically, thethe Rokua largest esker in is Finland, and an itThe unconfined has recharge aquifer, two area one regional of groundwater of the moundssurrounding aquifer (Rossi peatlands, is et which 90 al., km partially 2014). confine the aquifer (Rossi etThe al., 2012). sizes of these1.5 kettle km long, holes and vary. 0.4 km They widedue can (Aartolahti, to be 1973). the Most 1 influence of the of to kettle groundwater 80 holes m in are the now deep, dry, past, but between peat 10 has m accumulated and at the bottom of of the esker is 100 mof above the sand surrounding ranges low-lying peatlands from andand 30 the m kettle layer holes thickness to form more aholes than rolling 100 were and m geologically formed above unique when theleft terrain (Aartolahti, bedrock. ice depressions 1973). Sea blocks in Kettle banks, were the dunes buried landscape. in The the ground ground surface and, of as the esker they is melted, mainly lichen- island that gradually rose from the sea (Aartolahti, 1973). Today, the highest elevation 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | is C), h ◦ ( s T . It covered ◦ is the height ), where z a T · 237.3 + a 17.3 T (10 m), r z exp( · 0.611 · describing the impact of turbulent h 1 − = C). ◦ a e kPa 1 − 9190 9189 is an empirical constant (0.15 can be used for (Harbeck, 1962) n 0.05 − L A · 5 cient in m km − is air temperature ( ffi ) a 10 s ered between the lakes depending on their size. In total, 52 T T ) at 2 m height · ff × 1 237.3 240 pixel sensor resolution and an opening of 24 − + s 17.3 × T 1.69 C) were installed 50–100 cm below the lake surface. In addition, ), (1) ◦ = a e exp( E · K − s ), , (2) e 2 n ( · 0.611 a r is the measured wind speed at the reference height z (km v z = r · v L s E r is the mass-transfer coe eddies of the windA on vertical transport of water vapouris from wind the speed (m lake s with area is the saturation vapoure pressure in kPa at surface wateris temperature the vapour pressure inrelative humidity the and air in kPa, v K s a a E = Wind speed measured at 10 m height was adjusted to the corresponding speed at Depth profiling was undertaken in the lakes for which no depth contour lines are Lake water temperature was measured continuously during the ice-free period in = v e e K z approach (Rosenberry etused: al., 2007; Dingman, 2008). TheE following expression was where: to calculate the volumes of the lakes. 3.3 Evaporation from lakes Evaporation was calculated individually for all the lakes surveyed using a mass transfer mean depths of these new rasters were multiplied by the water surface areas in order interpolated cells. Interpolation rasters were extracted by surface water areas. The 3.2 Lake volumes The volumes ofprofiling the measurements, lakes contour lines were andlakes border determined were lines. estimated The in using water an elevation surface levelsSurvey levels presented ArcGIS of of in Finland, the environment the 2010a). basic using Lakeresults map morphology (National depth in was Land a mostly smooth interpolatedmethod surface using spline passing with that by 0.1 all weight the input and points 3 (ESRI, input 2014). points The Tension was used to calculate the values for the available (National Land Survey ofdepth-sounding Finland, radar 2010a). (resolution It 0.1 m)Typically, was two or carried profiles with out from with a theof a measuring shore measurement portable cable points to and di the GPSlakes deepest system. were point surveyed. were defined. The number next to the study site,lakes 1 was km conducted from on the 5 easternmostThis August lake 2013 camera studied. using had Thermal a 320 imaging Flirthe of Thermacam electromagnetic the P-60 spectrum thermal from camera. 7.5150 m to 13 above µm. the The lakes. imagingconditions was The (temperature taken image and by data helicopter relativestation were humidity) measured correlated with every 10 to data min. the from predominant the weather FMI Pelso weather 2013 for two lakesloggers on (pendant the temperature esker:001, data Ahveroinen accuracy logger (3.3 0.1 ha) UA-001-08the and and Saarinen surface conductivity water (15.3 logger ha). temperaturedatabase Hobo U24- of for the lake Finnish Environmental Oulujärvi Institute (92 (2013). 800 Lake ha) Oulujärvi was is located obtained east, from the where for which speed is adjustedneutral (2 stability m) cases). and 2 m height using the power law profile (Justus andv Mikhail, 1976): 5 5 20 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (4) (3) and 18 k erence C ff )) where N h − ) can be further simpli- 3 (1 2 k stands for equilibrium iso- C = L/V ε α 2 . ∆ 3 ) where ). (6) ); ε k 10 N C h × + ∆ ) + − ∗ ∗ ε ) can be further simplified to the following ε L/V (1 4 )( 18 k /α N ). 9192 9191 C h 3 = − ε (1 i 18 = ∆ ε E ε TOT I N ) N + ∆ N h N + ∆ ∗ h h ε/h − ∗ ε 1 ) − ε + ) N E N . (5) IT TOT (1 h I h δ N + − + h − − N N 1 (1 h − A h (1 are defined as in Eq. ( h δ 1 ective isotope fractionation ( ∼ = ε ff ∼ = ∼ = − ∆ ) the expression for the total inflow-to-evaporation ratio characterising the IT k IT IT 4 δ C δ δ 1 (terminal lake situation), Eq. ( δ − + − − and = ∆ ∗ stand for kinetic enrichment parameters. ∗ LS ε LS LS 2 ε k δ /E δ δ isotopic composition of thederground total inflow) inflow (‰) to the lake (precipitation,the surface total and e un- kinetic isotope enrichment ( C isotopic composition of atmospheric moisture over the lakemeasured (‰) steady-state isotopic composition of the lake (‰) equilibrium isotope enrichment (1–1 tope fractionation between liquid and gaseous phase (‰) evaporative enrichment total inflow to the lake (surface and undergroundevaporation fluxes rate plus rainfall) relative humidity over the lake, normalised to the temperature of the lake surface ∼ = = = = ∗ T A N ε ε δ TOT IT E If it can be further assumed that the isotopic composition of atmospheric water From Eq. ( The meteorological parameters necessary for the calculations (relative humidity, ε LS I δ δ δ δ h E δ ∆ ∆ TOT TOT δ I I vapour is in isotopic equilibrium with the total inflow, then Eq. ( where: ∆ When considering isotope andstate mass conditions, balances the under followingment hydrologic approximate of and expression isotope describing an steady- the evaporatinget al., isotope lake 2001): enrich- can be derived (e.g. Gat and Bowser, 1991; Rozanski thermal images. Using the derivedthe temperature lakes range, a was range calculated. formeasured The evaporation on from adopted one all method day, butidentical relies since only weather all the on conditions, lakes temperature itlake are di water is in temperature a highly is relatively probable similar small between that area the the with lakes. almost seasonal3.4 behaviour of Isotope the mass balance wind speed and air(Vaala-Pelso) temperature) of were obtained the from10 the Finnish km meteorological from Meteorological station the 5502 Institutecontinuous site. temperature (2014), measurements A from located one range ofSect. approximately the for 4.1), studied and the lakes, a Ahveroinen lakes’ standard (see deviation water of lake temperature water was temperature values evaluated determined using from formula: ∆ fied: ∆ where hydrological balance of the given lake can be derived: If 5 5 20 10 15 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | H 2 (7) δ 93 ‰ − C (June) 10.7 and ◦ − O and H values of 2 18 δ 9.55) was de- δ + 12.9 and C and a standard − O ◦ O and 18 97 ‰ and δ 18 − δ 28.19, is the best fit line of 7.77 − = C (January) to 13.2 ◦ O H 2 18 13.4 and δ δ − 10.9 − 5.09 erent types of water in the study area is = ff H 2 C, with a mean of 21.3 H plot that clearly indicate the contribution of ◦ 95 ‰), combined with reduced deuterium ex- δ 2 9194 9193 − δ O- C) during the period from 1 June 2013 to 31 Au- H values of groundwater were ◦ C. This temperature was used in the isotope mass 18 2 ◦ δ δ 13.1 and 0.87 − ± O space in Fig. 4. It comprises precipitation data collected 100 ‰, respectively). Slightly elevated mean O and 4.8 ‰) when compared to precipitation (12.8 ‰), indicate the C − ◦ 18 18 = δ δ O H- 18 2 erences in lake size (Fig. 3). Thus the surface water temperature ff δ δ C. Combining the results of continuous temperature measurements · values of precipitation samples collected during the years 2010–2013 ◦ 8 14.1 and δ k − − C T H values of piezometers MEA 2010 and MEA 1907 situated on the south- H δ ) the following expression for relative humidity normalised to the tempera- 2 2 + is the heavy isotope enrichment observed in the terminal lake. 6 ∆ ∗ δ δ T ε δ = − ∆ d values representing lake water data for the year 2013. The intersect of the LMWL 1 δ O and = Although the majority of groundwater samples cluster near the LMWL-LEL intersect, The local meteoric water line (LMWL) of Rokua ( The seasonal temperature patterns of the monitored lakes were very similar, de- 83 ‰ respectively, clearly indicating a substantial (ca. 55 %) contribution of lake water 18 N lake where the mean there are some data points(evaporated) in lake the water to groundwater.the This isotopic influence is composition illustrated ofδ in lake Fig. Ahveroinen 5, 1 showing eastern and and adjacent north-western groundwater. The sides− mean of the laketo were groundwater at the north-westernof side lake of water the lake. to A groundwater smaller can contribution (ca. be 10 %) seen on the eastern and western sides of the values of local groundwater ( cess ( presence of an evaporation signalwinter in precipitation the is local most groundwater.does Furthermore, probably not some returned contribute of to to the groundwater the recharge. atmosphere via sublimation and itored during the period67 2010–2013 lakes (Table surveyed 1), in as July well and August as 2013 the (Table 2). isotopicfined compositions using of the (Fig. 5). The local evaporation linethe (LEL), and LEL lines yields the estimateprecipitation of ( the weighted annual mean An overview of the isotopicpresented composition on of the di during the period 18 Marchthe 2010–29 mean October isotopic 2013 compositions at of the the station selected located lakes, on streams the and esker, groundwater mon- 4.2 Local isotopic compositions From Eq. ( was derived to be 18.60 balance calculations. gust 2013 was usedThermal as images a collected basis onperatures for 5 that estimating August ranged the 2013 fromdeviation water yielded of 19.5 temperature comparable 0.87 to of surface water other 24.6 and tem- lakes. thermal images, an estimate of the mean surface water temperature of all lakes mean values of surface airfor temperature vary the from period betweenvaries 1959 from and 29 mm 2013 (Februarywarmest (Fig. and months 2). April) of The to the amountmonthly 79 year mean of mm relative are monthly (August) humidity June, precipitation for of July air the varies and same from August. period. 61 % Thespite The (May) long-term significant to (1970–2013) 91 di % (November). of lake Ahveroinen 1 (mean 18.60 4 Results and discussion 4.1 Climate and lake water temperatureThe data climate is strongly seasonal in the Rokua esker study area. The long-term monthly ture of the evaporating surface can be derived: h where 5 5 25 20 10 15 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) ) O T 6 δ 18 ) for ∆ δ O and /E 18 value of δ TOT N I h ) that applies 6 4 ‰ respectively. based on Eq. ( erence in isotopic − 93 ‰ for ff N − h erent depths (1 and 4 m). 57 to ff 1.1 and − − O curve in Fig. 6 can be used produced by the total inflow-to- 18 1 δ O data and the adopted value for − 18 , derived from Eq. ( N ratio for each lake was undertaken for day h 3 ratios obtained range from 1 (assumed /E /E 72 ‰, respectively. The di TOT 12.7 ‰ and from I 9196 9195 − TOT − I (14.2 ‰; Gonfiantini, 1986). Since the air and k C 5.6 to 8.5 and ) using measured − 6 − O of the lake water by ca. 1 ‰ over the six-month period H between these points was 2 O in lake Ahveroinen 1 at two di 18 value represented by the weighted mean isotopic signature δ δ 18 14.1 ‰. The IT δ − δ 13.4 ‰). It appears that the required groundwater inflow is in the , which is close to 137 m − 1 73 ‰ and O and − = − values: from 18 δ δ day GW 3 O ) was used to calculate the total inflow-to-evaporation ratio ( 4 18 ). Introducing the assumption that the total inflow to each lake also contains δ 8.7 and 5 − 5.6 ‰) and the − erence in the mean isotopic composition of the lake water between points 2 erence in O value during the ice-cover period stems from the gradual dilution of lake wa- ff ff = 18 O of lake Ahveroinen 1 reveals distinct seasonal fluctuations with peak-to-peak am- δ H respectively. This large variability reflects a wide spectrum of the heavy isotope Equation ( LS 2 18 δ each lake using normalised relative humidity, setting, their steady-state isotope enrichmentance, is which primarily in controlled by turnEq. their 3). can water bal- be characterised by the total inflow-to-evaporation ratio (cf. The isotopic composition ofa 67 wide range lakes of (July–Augustδ 2013 sampling campaign) covers enrichment of the lakes studied. Since Rokua lakes are situated in a unique climatic 4.4 Quantifying groundwater dependence of the studied lakes to assess the intensityand of the groundwater isotopic inflow, compositionthe when observed of the reduction groundwater volume of is ofis constant. the a As lake result of a is thesignature rough known ( admixture approximation, of a certainorder volume of of 150 groundwater m withevaporation a ratio specific for isotopic this lakeSect. derived 4.4). from isotope mass balance considerations (see (April–May), the lake starts torichment evaporate, of which water, results approaching inFreezing a steady-state of gradual value the heavy sometime lake isotope inin in en- the September–October. late autumnter stops with the groundwater evaporation flux. seeping The intothroughout systematic the the fall year. lake. Thus Figure the 6 declining shows parts that of the the lake is well mixed the di 4.3 Temporal variations in the isotopicThe composition seasonal of variability the in selected the lakes showing isotopic the composition changes of of lake waterδ is illustrated in Fig.plitude 6, in the order of 1 ‰. After the disappearance of ice cover during the spring north-west, which coincides withby the Ala-aho results et from seepage al.the measurements (2013). di conducted The directionand 3 of of groundwater flowcompositions between can points 2 also and 3 be was greatest noted during the from winter, e.g. in March 2011 respectively. The main direction of groundwater flow is therefore from south-east to meteorological station, and thenormalised mean relative air humidity and isfrom lake Eq. approximately water ( 63.1 temperatures. %, The a resulting similar value to that derived be considered to be awas terminal calculated lake. The using isotope the enrichment( isotopic for lake composition Kissalampi of ( of this the lake measured local in precipitation64.6 % August (the was 2013 intersect derived from ofthe Eq. LMWL-LEL kinetic ( – enrichmentlake cf. parameter temperatures Fig. were available 4). foralso The this period, calculated normalised using relative the humidity could field be data, i.e. the relative humidity measured by a nearby to terminal lakes. Lakesampled Kissalampi lakes showing (Table the 2) highest and isotope as enrichment it of did all not the reveal any surface outflow, can reasonably a groundwater component (50 %) changes the best estimate of the period 1 June–31 Augustvalue 2013 of using the the total relative inflow humidity value 64.6 % and from 64.6 to 66.6 %. A calculation of the 5 5 20 10 15 25 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C ◦ 1 to = values ) inde- 0.87 for lake 1 ± index. Its G 1 /E − G TOT I ratio resulting day values derived values derived index) obtained 3 ) depends in the G 4 /E G G ) derived from iso- 95.0 %. index. TOT I , mean depth 11.8 m, = TOT I 3 G and G m 6 /E 10 ratio is much weaker (Fig. 9); value (27.8 %) was obtained TOT × I G , mean depth 0.2 m, maximum /E 3 m 2.47 TOT 3 I = 10 V × 2 ratio across the whole range of this param- 2 % varies from 15–16 % for = ratios. Knowing the volume and total inflow, ± 9198 9197 /E V for Kissalampi pond to 5556 m /E 1 TOT I − TOT I day ratio derived for each lake using Eq. ( 3 C, and decreases by approximately 13 % when the tem- /E 27.8 % to approximately 0.8 % for ◦ = TOT ratios tend to have shorter mean turnover times. I G /E resulting from the change in lake water temperature by G TOT I C. This uncertainty of lake water temperature leads to uncertainty as ) vary from 3 m ◦ GW I 0.87 ± C ◦ The uncertainty of the One of the major sources of uncertainty of MTT, The dependence of a lake on groundwater input can be quantified through an index Knowledge of the total inflow to each of the surveyed lakes ( Since the evaporation rates from the studied lakes were derived from Eq. ( depends on the actualrelative value change of of this index.varies from As ca. seen 37 in % for the lower panel in Fig. 11, the 18.6 regards the evaporation flux,for which each in lake. The turn mean influencesthe turnover the lake time MTT is increases by and reduced ca.perature by increases 16 % 0.87 by when the the samesensitivity amount. temperature A of to similar changes situation in occurs with lake the water temperature, via changes in the evaporation flux, introduces some uncertainties linkedin to the the evaluation assumptions process. madefor Although the and parameters no parameters obtained formal used for each uncertaintyderive individual the evaluation lake, range sensitivity was tests of carried were uncertaintiesas performed out mean associated to turnover with time, the total quantities inflow-to-evaporation ratio being and evaluated, the such for each individual lakediscussed is in the Sect. uncertainty 4.1, with regard the to temperature lake of water the temperature. As studied lakes was estimated to be et al., 2013). 4.5 Uncertainty assessment The above methodology for quantifying elements of water balance in the lakes studied induced by high loads of phosphorus brought to the lakes with groundwater (Ala-aho isotope enrichment of lakes (Fig. 7). for lake Kissalampi) to 14.8 for lake Siirasjärvi 2 and are functions of the measured of changing relative humidity oneter the obtained for the lakesfrom surveyed. the The change relative in changeapproximately in 1 relative % the humidity for highest by recorded values of this ratio (ca. 15). first instance on the uncertaintyto the of temperature the of relative the humidity lake of surface. The the upper atmosphere panel normalised in Fig. 11 illustrates the impact for Kissalampi pond, whichwere derived is for lakes comparable Kiiskeroinen to(95.0 (92.9 %). %), a Interestingly, Levä-Soppinen these (93.0 lakes terminal %) are and characterised lake. by Siirasjärvi The a 2 high highest degree of eutrophication defined as the percentage contribution ofto groundwater the inflow to given the lake. totalfor inflow Figure the of 10 lakes water summarises surveyedvisible during the surface the values inflow July–August of 2013 could this sampling be index campaign identified. ( for The which lowest no area ratio (Fig. 8). Thelakes link with between higher MTT and the tope mass balance considerations enableseach an individual evaluation lake of by theists subtracting groundwater and the inflow its precipitation to value and isTable 2, surface known). Such which water an inflow do evaluation (ifage not was it reveal rates undertaken visible ex- for ( surface theRokuanjärvi inflows. lakes 1. The listed in resulting groundwater seep- from 0.5 monthsdepth for 0.7 the m) to Pasko 9.1maximum pond years depth for ( lake 26 m), Saarijärvi withthe 2 the deepest ( mean of in all thelate the well order lakes with of surveyed. the 18 As mean depth expected, months. of the Lake the calculated Saarijärvi studied MTT lakes, 2 values expressed is as corre- the volume-to-surface pendently of any mass balancebe considerations, calculated the from total inflow thethe to assessed mean each turnover lake time could also oflake water volume to (MTT) total in inflow. each The lake calculated could MTT values be are quantified listed as in the Table 2. ratio They of range 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2013. , 1968. cult and associated with ffi ered by environmental iso- ff , last access: 28 February 2014. cial Journal of the European Union, ffi http://webhelp.esri.com/arcgisdesktop/9.2/ 10.1016/j.jhydrol.2013.07.014 9200 9199 ers another opportunity for quantifying ground- ff 10.1029/WR004i006p01289 index was derived only for lakes without a visible , 1961. G Applying_a_spline_interpolation = This work is funded by the 7th framework project GENESIS (226536), index of groundwater dependency of a lake proposed in this study, and de- G 10.1126/science.133.3465.1702 The The specific behaviour of lakes located in sub-polar regions, with their seasonal ice received: 28 January 2014. Brussels, 2006. index.cfm?TopicName 11 November 2013. of groundwater against pollution and deterioration, O Water Resour. Res., 4, 1289–1306, doi: doi: to a drainage lake; Lake Mendota, Wisconsin, Water Res., 16,1997. 1255–1263, 1982. and streams, J. Hydrol., 500, 144–156, doi: tapahtuneet muutokset, in: Rokuan AlueenEnvironment Järvet Centre Ja Lammet, Reports NorthOstrobothnia 5/2007, Ostrobothnia Regional edited Regional Environment Centre, by: Oulu, Heikkinen, 12–25, M.-L. 2007. andFlorida Väisänen, Lake, T., Water North Res., 19, 773–781, 1985. complex in Finland, Soc. Geogr. Fenn., 127, 1–53, 1973. Ala-aho, P., Rossi, P. M., and Kløve, B.: Interaction of esker groundwater with headwater lakes Aartolahti, T.: Morphology, vegetation and development of Rokuanvaara, an esker and dune References fined as a percentage contributionthe of given groundwater lake, inflow appears todency. Whereas the to total in be inflow this a ofsurface study straightforward, water inflow, the quantitative to it measure canand of also quantified be this by applied depen- other means. in cases where an inflow of this kind is present water seepage. As shown inisotope this study, composition observations of of seasonal lake changeswith water, in in a the particular survey stable during ofallow the groundwater the ice-cover isotope quantification period, composition of combined groundwater in fluxes the to vicinity those lakes. of the lakes studied, ages to lakes usingconsiderable conventional uncertainty. The methods study is presented here notoriouslytope demonstrates di mass the power balance of approach theanalysis iso- for of resolving lake this water issue. samples,observations, collected It may at appears lead the that right to anumber time a stable of and quantitative lakes isotope supplemented located assessment with in field of a the similar climatic water setting. balancecover of extending over a several months, large o The Rokua esker, with itsvided numerous a lakes unique located across opportunitytope a techniques to relatively in explore small quantifying area, thegroundwater the pro- possibilities in water a o balances sub-polar of climatic lakes setting. and The their quantification dependency of on groundwater seep- 5 Conclusions Finnish Meteorological Institute: Climate Data from Vaala-Pelso Meteorological Station, Data Finnish Environmental Institute: Environmental Information System (Hertta), Data downloaded ESRI: Applying a Spline Interpolation, available at: EC: Directive 2006/118/EC of the European Parliament and of the Council on the protection Dingman, S. L.: Physical Hydrology, 2nd Edn., Waveland Press, Long Grove, IL, 2008. Dinçer, T.: The use of oxygen 18 and deuterium concentrations in the water balance of lakes, Craig, H.: Isotopic variations in meteoric waters, Science, 133, 1702–1703, Clark, I. D. and Fritz, P.: Environmental Isotopes in Hydrogeology, Lewis Publishers, New York, Brock, T. D., Lee, D. R., Janes, D., and Winek, D.: Groundwater seepage as a nutrient source Belanger, T. V., Mikutel, D. F., and Churchill, P. A.: Groundwater seepage nutrient loading in a Anttila, E.-L. and Heikkinen, M.-L.: Rokuan pinta – ja pohjavesien vedenkorkeudet ja niissä programme. KR’s contribution wasuniversity partly of supported Science throughKirsti and the Korkka-Niemi and statutory Technology Anne fundsthermal (project Rautio imaging. of no. from the University 11.11.220.01). AGH of We Helsinki for would their like assistance to with the thank Acknowledgements. Renlund Foundation, Maa- ja vesitekniikan tuki r.y, and the Academy of Finland, AKVA- 5 5 25 20 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 10.1016/S0022- , 2011. , M., Moszczynska, A., ć , 2002. , 2013. , 1976. imek, J., Wachniew, P., Angheluta, V., Š , 2014. , 1996. 10.1016/j.envsci.2011.04.002 9202 9201 10.1029/2001GB001839 , 2013. 10.1007/s10040-013-1043-7 , 2012. , 2009. 10.1029/GL003i005p00261 10.1007/s10040-014-1127-z , 2002. 10.1002/wrcr.20198 10.1146/annurev.earth.24.1.225 10.1016/j.jhydrol.2012.02.026 10.1016/j.jhydrol.2009.07.021 interaction between andoi: esker aquifer and aon esker drained groundwater resources: fen, modeling22, future J. 1131–1145, scenarios doi: for Hydrol., management, Hydrogeol. 432–433, J., 52–60, direct measurements of seepage2975–2986, at doi: the sediment-water interface, Water Resour. Res., 49, by: Rosenberry, D. 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Pap. 272-E, US Geological Survey, Washington, 101– Karakaya, N., Kupfersberger, H., Kvœrner, J.,Muotka, Lundberg, A., T., Mileusni Preda,and E., Widerlund, A.: Rossi, Groundwater P., dependenttrends, Siergieiev, ecosystems, Environ. Part Sci. D., Policy, I: 14, Hydroecological 770–781, status doi: and using non-steady isotope mass balance, J. Hydrol., 264, 242–261, doi: stable isotopes: quantitative resultsCanada, and Nord. sensitivity Hydrol., analysis 24, 79–94, for 1993. two catchments in northern gaard, M., and Jeppesen, E.:seepage Focused lake groundwater (Lake discharge Væng, of Denmark):Hydrogeol. phosphorus implications J., to 21, for a 1787–1802, lake eutrophic doi: ecological state and restoration, 2010. tems, in: StableNo. Isotope 3, edited Geochemistry: by: a Levinson, A. Tribute A., to The Geochemical Samuel Society, Calgary, Epstein, 159–169, 1991. Special Publication 1694(02)00091-4 transpiration partitioning from aBiogeochem. stable Cy., 16, isotope 10-1–10-14, survey doi: of lakes in northern Canada, Global by: Lerman, A., Imboden, D. M., and Gat, J.225–262, R., doi: Springer-Verlag, Berlin, 139–165, 1995. tive, in: Isotopesedited in by: the Aggarwal, P.K., Water Gat, J.lands, Cycle. R., 139–151, and Past, 2005. Froehlich, K. Present F. O., and Springer, Dordrecht, Future the Nether- of a Developing Science, Rossi, P. M., Ala-aho, P., Ronkanen, A.Rossi, P. M., K., Ala-aho, P., Doherty, and J. and Kløve, Kløve, B.: Impact B.: of peatland Groundwater-surface drainage and restoration water Rosenberry, D. O., Sheibley, R. W., Cox, S. E., Simonds, F. W., and Naftz, D. L.: Temporal Rosenberry, D. O., Labaugh, J. W., and Hunt, R. J.: Use of monitoring wells, portable piezome- Pajunen, H.: Holocene accumulation of peat in the area of an esker and dune complex, Rokuan- National Land Survey of Finland: Digital Elevation Model, Helsinki, 2010b. National Land Survey of Finland: Basic Map, Helsinki, 2010a. Krabbenhoft, D. P., Bowser, C. J., Anderson, M. P., and Valley, J. W.: Estimating groundwater Justus, C. G. and Mikhail, A.: Height variation of wind speed and distribution statistics, Geophys. Jonsson, C. E., Leng, M. J., Rosqvist, G. C., Seibert, J., and Arrowsmith, C.: Stable oxygen and Harbeck, G. E. J.: A practical field technique for measuring reservoir evaporation utilizing mass- Kløve, B., Ala-aho, P., Bertrand, G., Boukalova, Z., Ertürk, A., Goldscheider, N., Ilmonen, J., Gonfiantini, R.: Environmental isotopes in lake studies, in: Handbook of Environmental Isotope Kidmose, J., Nilsson, B., Engesgaard, P., Frandsen, M., Karan, S., Landkildehus, F., Sønder- Gibson, J. J.: Short-term evaporation and water budget comparisons inGibson, shallow Arctic J. lakes J. and Edwards, T. W.Gibson, J. D.: J., Edwards, Regional T. W. D., Bursey, water G. G., and balance Prowse, T. D.: trends Estimating evaporation using and evaporation- Gat, J. R. and Bowser, C.: The heavy isotope enrichment of water in coupled evaporative sys- Gat, J. R.: Isotope Hydrology: a Study of the Water Cycle, Imperial College Press, London, Gat, J. R.: Oxygen and hydrogen isotopes in the hydrologic cycle, Annu. Rev. Earth Pl. Sc., 24, Gat, J. R.: Stable isotopes of fresh and saline lakes, in: Physics and Chemistry of Lakes, edited Froehlich, K., Gonfiantini, R., and Rozanski, K.: Isotopes in lake studies: a historical perspec- 5 5 30 25 20 15 10 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2010. O 18 δ seasonal signal (‰) , 2004. 4.02.4 1.2 7.6 1.3 4.03.8 0.9 3.3 0.5 8.6 0.9 6.4 0.5 10.410.210.2 0.8 0.9 0.9 − − − − − − − − − − 10.1016/j.jhydrol.2010.03.012 , 2008. 8.5 8.7 6.7 7.1 6.6 6.8 8.5 8.4 13. 10.0 1.2 6.8 7.7 12.7 8.6 0.5 13.3 10.4 0.6 11.211.8 3.6 5.4 1.3 1.2 13.1 9.8 0.8 12.9 9.2 0.7 12.9 10.2 0.5 10.7 2.6 2.2 12.9 10.2 0.7 12.9 10.2 0.8 13.1 9.8 0.8 13.1 9.8 0.9 12.9 10.2 1.0 13.0 10.0 0.9 10.7 2.6 1.0 11.0 5.0 3.1 13.4 10.2 0.5 13.1 9.8 0.7 13.2 9.6 0.9 12.1 6.8 2.2 13.1 9.8 0.8 12.8 9.4 1.0 13.1 10.8 1.0 13.4 10.2 0.5 9203 9204 − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − O (‰) d-excess (‰) Mean amplitude of 18 δ , B., and Watzel, R.: Use of environmental isotopes to ff , 2008. , 2013. 67 63 62 93 96 72 72 64 72 71 63 89 95 86 68 94 93 83 93 93 95 95 93 94 83 83 97 95 96 90 95 93 94 97 94 H ( ‰) − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − 2 10.1029/2004EO060002 δ 10.1016/j.jhydrol.2008.08.024 4. Kolmonen 2 5. Loukkojärvi 6. Saarijärvi 2 Streams: 1. Heinäjoki Groundwater: 1. MEA 106 Lakes: 1. Ahveroinen 1 2. Rokuanjärvi 3. Jaakonjärvi 7. Saarinen 8. Salminen 9. Soppinen 2. Hieto-oja 2. MEA 206 10. Tulijärvi 11. Vaulujärvi 3. Kangasoja 3. MEA506 4. Lianoja 4. MEA 706 5. Lohioja 5. MEA 1106 6. Matokanava 6. MEA 1807 7. Päiväkanava 7. MEA 1907 8. Rokuanoja 8. MEA 2010 9. Siirasoja 9. ROK 1 10. Soppisenoja 10. Siirasoja 1 harju 11. Valkiaisoja 11. Siirasoja 1 rinne 12. Siirasoja 1 hiekka 13. Siirasoja 1 turve Mean isotope composition of selected lakes, streams and groundwater, sampled four 10.1016/j.jhydrol.2007.11.008 10.1016/j.jhydrol.2013.04.018 adjacent groundwater field: and isotope study, J. Hydrol., 192, 247–270,pled 1997. isotope tracerdoi: method to characterize input waterof some to lakes, J. lakes, Hydrol., 61, J. 409–427, Hydrol., 1983. 350, 1–13, Stutsman County, North Dakota, USGSver, Water-resources 80–99, investigations 1980. report, USGS, Den- processes on lakewater water isotope balances tracers, J. in Hydrol., the 386, 103–117, Old doi: Crow Flats, Yukon Territory, Canada, using define the capture zone362, of 220–233, a doi: drinking water supply situated near a dredge lake, J. Hydrol., lake interactionsdoi: and its impactAm. Geophys. Un., on 85, 58, doi: lake water quality, J. Hydrol., 492, 69–78, Hydrological Cycle, Principals andHydrology, Applications, Vol. 111, Volume edited III, by: IHP-V, Mook, Technical Documents W. G., in UNESCO/IAEA, Paris, 1–117, 2001. Table 1. times per year during the period 2010–2012. Yi, Y., Brock, B. E., Falcone,Zuber, A.: M. On the environmental D., isotope method for Wolfe, determining the water B. balance components B., and Edwards, T. W. D.: A cou- Yehdegho, B., Rozanski, K., Zojer, H., and Stichler, W.: Interaction of dredging lakes with the Winter, T. C. and Carr, M. R.: Hydrologic setting of wetlands in the Cottonwood lake area, Turner, K. W., Wolfe, B. B., and Edwards, T. W. D.: Characterizing the role of hydrological Tikkanen, M.: The changing landforms of Finland, Fennia, 180, 21–30, 2002. Stichler, W., Maloszewski, P., Bertle Showstack, R.: Discussion of challenges facing water management in the 21st century, EOS T. Shaw, G. D., White, E. S., and Gammons, C. H.: Characterizing groundwater– Rozanski, K., Froehlich, K., and Mook, W.: Surface water, in: Environmental Isotopes in the 5 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | b b index index G (%) G (%) MTT (months) MTT (months) ) ) 1 1 − − day day 3 3 b b GW GW (m (m /E I /E I TOT TOT I I O O 18 18 δ δ ∆ (‰) ∆ (‰) O O 11.011.1 3.111.4 3.011.6 2.7 5.856.5 2.5 6.238.8 n.d. 7.6 7.027.3 n.d. 5.3 7.848.3 n.d. 6.810.3 1.34 n.d. 5.8 1.411.2 3.8 2.67 2.46.9 19.7 2.9 1.70 2.98.3 196.5 2.33 7.2 4.0 4.517.8 14.1 n.d. 5.8 6.38 25.49.0 137.3 n.d. 31.0 n.d. 6.37.5 n.d. 1.52 n.d. 5.1 26.36.8 n.d. 2.34 18.5 6.6 42.5 9.7 109.0 2.01 69.5 7.3 2.27.1 897.0 2.91 4.4 6.9 56.8 6.7 437.9 1.80 65.3 11.0 7.010.6 305.5 1.45 15.3 7.410.6 31.6 3.5 n.d. 3.58 41.37.2 50.2 3.5 n.d. 1.59 45.1 16.57.3 629.8 1.43 61.8 6.9 5.11 24.211.4 141.7 56.6 6.8 5.08 36.510.5 279.1 2.7 71.4 3.7 n.d.7.4 3.6 1.66 24.1 n.d. 57.5 7.6 1.72 108.9 6.7 7.24 44.5 7.5 16.5 6.5 15.4 4.80 76.3 11.2 16.9 46.9 n.d. 6.6 0.58.5 37.8 2.9 1.76 n.d. 12.87.9 1.87 5.6 n.d. 28.18.8 14.2 1.83 6.2 8.7 6.548.6 21.7 n.d. 5.3 6.6 55.1 10.5 58.8 2.50 409.3 5.5 56.8 7.412.1 3.6 2.06 12.36.6 5555.9 2.0 n.d. 2.72 14.17.6 24.4 1.8 n.d. 2.52 7.5 4.8612.3 40.5 15.5 58.3 6.5 10.43 60.1 7.4 177.0 1.8 55.9 56.8 18.77.7 180.7 1.36 87.8 6.7 18.7 60.6 1.85 12.9 6.4 11.30 52.6 6.0 1.1 63.9 231.8 669.5 1.76 72.4 1.93 67.6 23.5 30.3 32.9 1.5 84.9 92.9 79.7 40.4 36.8 54.1 45.4 93.0 56.6 58.7 7.8 6.3 1.97 94.6 39.0 59.2 7.16.8 7.07.3 7.36.5 6.85.6 1.60 7.68.5 1.48 8.57.4 17.0 1.69 5.610.8 12.2 1.34 6.712.7 15.1 3.3 1.00 36.610.4 26.8 1.4 2.46 29.27.3 3.0 3.7 1.78 5.36 26.36.4 348.7 6.8 14.85 53.4 17.79.6 332.8 n.d. 7.7 4.73 49.9 8.1 233.8 2.4 35.7 4.5 56.2 7.6 1.71 22.2 41.4 6.0 41.4 8.5 1.28 3.1 6.5 7.98.5 7.7 3.55 65.5 5.6 27.8 7.6 21.9 2.15 50.9 6.5 5.67.5 n.d. 1.88 6.56.5 95.0 n.d. n.d. 2.44 17.9 6.6 28.48.1 n.d. 2.50 7.6 84.7 7.9 327.5 17.6 1.90 6.010.9 87.6 19.4 1.82 58.3 6.2 39.1 8.7 59.1 3.2 18.5 1.33 25.78.0 43.8 n.d. 2.15 5.4 17.48.0 21.5 n.d. 2.06 6.1 5.78 10.0 268.2 n.d. 65.4 6.1 23.2 n.d. 2.59 n.d. 68.6 8.6 2.09 33.3 58.5 n.d. 2.11 57.2 n.d. 11.9 0.9 31.3 41.8 60.6 6.2 n.d. 25.7 19.9 n.d. n.d. n.d. 64.3 18 18 δ (‰) − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − δ − (‰) − − − − − − − − − − − − − − − − − − − − − − − − − − a a E (mm) E (mm) 9206 9205 Mean depth (m) Mean depth (m) Surface area (ha) Surface area (ha) ) ) 3 3 m m 3 3 (10 (10 Characteristics and isotope data for 67 lakes sampled during the July–August 2013 Continued. Name Volume Name Volume Lake No. 41 Lepikonjärvi 191 118 2.98 6.4 251 42 Kolmonen 1 35 700 0.68 5.3 270 434445 Kolmonen 246 Kolmonen 347 Hätäjärvi48 Kissalampi49 Valkiajärvi 21 89050 Hautajärvi 21 630 251 Keskimmäinen 0.5652 35 Siirasjärvi 217 800 2 0.5453 Siirasjärvi 1 58254 662 428 515 Telkkälampi 445 413 1.73 3.955 Maitolampi 4.0 1 8.36 0.3656 13.07 14.60 Taka-Salminen 23 126 273 57 Etu-Salminen 2.0 9701 273 58 7284 Pikku-Salminen 3.3 7.0 3.1 0.2 0.5659 364 48 757 892 Kylmäjärvi 258 60 0.34 Kourujärvi 1 233 196 238 453 7.31 39 232 0.25 279 61 856 Kourujärvi 1.56 2 4.162 Huttunen 5.8363 1.32 2.9 Saarijärvi 1 5.0 394 2.964 443 273 3.1 Pitkäjärvi 68 023 265 3.4 Pyöräinen 280 31 136 7.8966 240 3.0 284 Likainen 259 1.8367 54 Nimisjärvi 588 243 1.91 13 590 261 Ahveroinen 5.0 2 451 093 Tervalampi 1.49 3.7 76 1.36 077 7.93 1.6 239 33 763 257 670 1 515 3.76 840 396 3.7 256 1.0 167.53 5.7 29 707 16.30 8.28 260 2.0 261 1.1 239 0.79 4.1 0.4 248 205 230 3.7 238 268 Lake No. 1 Heinälampi 1764 0.22 0.8 286 234 Holma5 Koivujärvi6 1 Koivujärvi7 2 Pitkäjärvi8 1 Nurkkajärvi9 Luontolampi10 39 237 23 Ahveroinen 77811 1 76 884 Lianjärvi12 36 2.30 Syväjärvi 103 113 1.89 269 134 2.93 Soppinen 19 99514 Salminen 119 1.22 000 3.9315 1.7 Saarinen 0.4916 1.3 3.32 2.6 Kivi-Ahveroinen 39817 463 113 678 Irvi-Ahveroinen 254 3.0 6.818 257 81 630 Loukkojärvi 251 11.52 4.1 15.13 21619 018 3.6 681 Ylimmäinen 860 262 20 247 40 867 Hietajärvi 981 6.04 506 5.5721 25.31 275 3.5 0.8 Saarijärvi 249 222 15.32 1.07 Syväjärvi 126 2 45023 234 94 1.4 Pasko 2.7 313 231 3.924 2.85 Kuikkalampi 6.425 223 3.8 Soppisenlampi 118 242 8.93 225 2 243 46726 169 Kirvesjärvi 231 127 863 7.30 20.94 446 4.4 Tulijärvi 264 Kirvesniemi28 31.95 11 25 776 Jaakonjärvi 645 1.1 589 2 61729 Jaakonjärvi 2005 251 11.8 330 3.1 24.81 Maitolampi 0.61 0.59 2 5.8 237 65431 618 228 Kotalampi32 5497 0.82 240 Rokuanjärvi 1 13.47 2.4 223 33 13 594 Tervatienlampi 1.9 4.434 44 812 Valkiaislampi 0.4635 226 0.2 4.9 0.66 Ankkalampi 271 272 436 364 25 781 980 21 Saarilampi 970 2.04 137 164.59 268 233 Kiiskeroinen 1.2 3238 073 2.1 2.60 Jaakonjärvi 0.63 139 2.7 Vaulujärvi 2.2 103 700 275 40 0.70 12 Levä-Soppinen 271 044 6517 3.86 1.0 Anttilanjärvi 205 3.5 256 93 614 Hautajärvi 0.45 1 4.6 34 000 253 271 0.63 432 2.7 813 3.53 270 2.31 60 2.7 230 8.97 248 189 222 1.0 2.7 1.06 276 2.56 1.5 4.8 271 249 254 5.7 237 7.4 264 253 Calculated for the period 1 June–31Calculated August for 2013. lakes with no visible surface inflow. Table 2. Table 2. field survey. a b n.d. – not determined. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

C] [ T National Land y y the 9208 9207

. P [mm] P 1. The study site of Rokua esker aquifer area. Digital elevation model b

ure The long-term (1959–2013) monthly mean values of surface air temperature and The study site of Rokua esker aquifer area. Digital elevation model by the National

Fig of(2010) Finland Survey

C] [ T 524 525 526 527 523 522 Figure 2. the amount of precipitation(Finnish recorded Meteorological at Institute, the 2014). station located 10 km south-west of the study site Figure 1. Land Survey of Finland (2010b). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

24 -5

-6

C] [ T Streams Precipitation Groundwater Lakes 2013 Lakes 2010-2012 Rokua LMWL GMWL Rokua LEL -7 -8 28.19 of this study. The Rokua evaporation + + 9.55 -

-9 O O 18 18 δ δ = 0.990 = 2 best fit line of the data points representing lakes representing points data the of line fit best

R² = R² = 0.993 R -10 Rokua LEL: Rokua O (‰) O Rokua LMWL: = 5.09 = the 18

H = 7.77 H 7.77 = δ 2 H 2 δ 9210 9209 δ within the scope -11 erent appearances of surface water (lakes, streams) ﬀ -12,5 -12 1961] LEL) was defined as defined was LEL)

GMWL: -

Craig Craig [ August 2013 campaign. August -13 -13,0 - ine l

O relationship for different appearances of surface water (lakes, streams) and

P [mm] P 18 δ

100) -14 - - -13,5 H -99 -89 -91 -93 -95 -97 vaporation vaporation 2 O relationship for di 14.1, e - (

. δ 18

4 C]

T [ T δ

-15

ocal ocal l

H (‰) H -50 -60 -70 -80 δ -90

H– 2 -100 -110 2

Figure groundwater in the study area, investigated ( line the July during sampled

δ Daily mean surface water temperatures of lakes Oulujärvi (92 800 ha) (Finnish Envi-

545 546 539 540 541 542 543 544 538 Figure 3. ronmental Institute, 2013), Ahveroinen 12013, (3.3 ha) compared and with Saarinen the (15.3located ha) surface in during air the the east, temperature summer next datamark to of the the for study period the site, used same 1 in km period. the from calculations Lake the easternmost of Oulujärvi lake evaporation is and studied. Vertical isotope lines mass balance. Figure 4. and groundwater inevaporation the line (local study evaporation area, line –representing investigated LEL) lakes was sampled within deﬁned during the as the the July–August scope best 2013 ﬁt of campaign. line this of the study. data The points Rokua Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

O isotope

25 Sep 2013 Sep 18

O value value O 18 2013 Jun

meter depths. depths. meter

Mar 2013 Mar

Dec 2012 Dec

Sep 2012 Sep August 2013 sampling campaign.

- Jun 2012 Jun July

the ) as a function of the measured Mar 2012 Mar /E Ahveroinen 4 1, m

TOT

I Dec 2011 Dec

ed ed relative humidity derived from terminal lake

4 m).

s Sep 2011 Sep 9212 9211

lake Ahveroinen 1, observed at 1 and at 1, observed 4 Ahveroinen lake Jun 2011 Jun in

O in lake Ahveroinen 1, observed at 1 and 4 m depths.

O Mar 2011 Mar 18 18 δ

Ahveroinen 1 1, m Dec 2010 Dec Sep 2010 Sep O values (‰) of lake Ahveroinen and adjacent groundwater. The mean δ mean The groundwater. adjacent and Ahveroinen lake of (‰) values O

18 Jun 2010 Jun O) for 67 Rokua lakes surveyed during ‰ at both sampled depths (1 m and depths both sampled ‰ at O values (‰) of lake Ahveroinen and adjacent groundwater. The mean

18  18

 δ Mar 2010 Mar . Mean δ Mean . 5

. The ratio of total inflow to evaporation ( . Seasonal variations of δ 7 6

ure

-8,60 -8,80 -9,00 -9,20 -9,40 -7,60 -7,80 -8,00 -8,20 -8,40 Mean

Seasonal variations of

O (‰) O δ text details). for (see ression 18 F site 1 is 8.5 for nrichment nrichment ( Figure e The calculations were performed for exp normali Maximum depth of the lake is 4.8 Maximum m. the lake depth of Figure

548 549 550 551 552 553 554 555 556 547

27 26

O isotope

Sep 2013 Sep

Jun 2013 Jun 2013 August August 2013, as a as 2013, August - -

meter depths. depths. meter

Mar 2013 Mar

Dec 2012 Dec Sep 2012 Sep August 2013 sampling campaign. -

) as a function of the measured Jun 2012 Jun July /E

the

) as a function of the measured Mar 2012 Mar TOT

I /E

Ahveroinen 4 1, m Rokua lakes surveyed surveyed lakes Rokua in July

TOT

I Dec 2011 Dec ed ed relative humidity derived from terminal lake s

9214 9213 in the in the Sep 2011 Sep ) ) in the Rokua lakes surveyed in Julyin surveyed lakes Rokua the in ) those lakes.

lake Ahveroinen 1, observed at 1 and at 1, observed 4 Ahveroinen lake Jun 2011 Jun MTT MTT in

O Mar 2011 Mar 18 water ( water

/E ratio for

Ahveroinen 1 1, m Dec 2010 Dec TOT

epth. epth. Sep 2010 Sep O) for 67 Rokua lakes surveyed during the July–August 2013 sam-

18 Jun 2010 Jun δ O) O) for 67 Rokua lakes surveyed during 18 ∆ 

 Mar 2010 Mar the of function I

. The ratio of total inflow to evaporation ( . Seasonal variations of δ . Mean turnover time of water ( . Mean turnover water time of . Mean turnover time of time turnover Mean . 7 6 9 8

-8,40 -8,60 -8,80 -9,00 -9,20 -9,40 -7,60 -7,80 -8,00 -8,20

O (‰) O δ text details). for (see ression 18 ure g The ratio of total inﬂow to evaporation ( nrichment nrichment ( Mean turnover time of water (MTT) in the Rokua lakes surveyed in July–August 2013, Figure e The calculations were performed for exp normali Maximum depth of the lake is 4.8 m. Maximum the lake depth of Figure Fi a plotted as Figure Figure d water mean of function

561 562 563 564 565 557 558 559 560 570 571 572 566 567 568 569 Figure 8. as a function of mean water depth. Figure 7. isotope enrichment ( pling campaign. The calculations wereterminal performed lake for expression normalised (see relative text humidity for derived details). from Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

28 27

low of water water of low August 2013 August August 2013, as a as 2013, August - -

Rokua lakes surveyed surveyed lakes Rokua in July

9216 9215 in the in the ) ) in the Rokua lakes surveyed in Julyin surveyed lakes Rokua the in ) those lakes. groundwater groundwater dependency of lakes in the Rokua study area. MTT MTT the ratio for those lakes. water ( water /E ratio for

/E TOT percentage contribution of groundwater inflow to the total inf total the to inflow groundwater of contribution percentage epth. epth. TOT I the index quantifying

G index quantifying the groundwater dependency of lakes in the Rokua study function of the of function I

. The G . Mean turnover time of water ( . Mean turnover water time of . Mean turnover time of time turnover Mean . 10 9 8

The ure g Mean turnover time of water (MTT) in the Rokua lakes surveyed in July–August 2013,

Figure as defined is index The lake. given to the Fi a plotted as Figure Figure d water mean of function

574 575 576 577 573 570 571 572 566 567 568 569 Figure 10. Figure 9. plotted as a function of the area. The index isinflow of defined water as to the the given percentage lake. contribution of groundwater inflow to the total Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C). ◦ index G

/E 29 TOT I

index index (in %), as a

ee text for details. text details. for ee G erent temperatures: increased S

. ﬀ the

C) o

in increased and decreased by

change change

: panel

evaporation evaporation ratio (in %) as a function of - to Bottom - 9217 %). %).

inflow

the total change change of

: panel

erent values of relative humidity: increased and decreased by 2 % with C with respect to the temperature assumed in the calculations (18.6 Top ﬀ ◦ . C with respect to the temperature assumed in (18.6 to the assumed the calculations C temperature with respect o

igure igure 11 F value, for two different values of relative humidity: increased and decreased by 2 % with respect to the value assumed in the calculations (64.6 function of the value of this parameter, for two different temperatures: 0.87

578 579 580 581 582 583 584 Top panel: change of the total inﬂow-to-evaporation ratio (in %) as a function of value, for two di /E TOT respect to the value assumed in the calculations (64.6 %). Bottom panel: change in the I (in %), as aand decreased function by of 0.87 theSee value text of for this details. parameter, for two di Figure 11.