Open Access
Numéro
Hydroécol. Appl.
Volume 22, 2022
Numéro d'article 1
Nombre de pages 26
DOI https://doi.org/10.1051/hydro/2021003
Publié en ligne 23 juin 2022

© EDF, hosted by EDP Sciences, 2022

1 Introduction

Since the beginning of the 20th century, the hydrographic network has been deeply modified by the creation of artificial reservoirs. This leads to a) the interruption of the ecological continuum of rivers (Jansson et al., 2000; Nilsson et al., 2005), b) changes in hydrological regimes (c) changes in sediment and nutrient fluxes (Jigorel et al., 2007; Van Cappellen & Maavara, 2016), and (d) global changes in biogeochemical cycles (Friedl & Wüest, 2002; Cole et al., 2007; Maavara et al., 2017).

The trophic surge hypothesis (TSH) (Grimard & Jones, 1982; Kimmel & Groeger, 1986; Hall et al., 1999; Turgeon et al., 2016) summarizes the trophic dynamics associated with impoundment. It highlights a short period of “trophic upsurge” related to: i) the colonization of vacant ecological niches created in this new ecosystem, and ii) flows of organic matter and nutrients, especially phosphorus (Ostrofsky, 1978) from the flooded area, which support primary production (Ostrofsky & Duthie, 1980; Robbins et al., 2020), greenhouse gas (GHG) emissions (Barros et al., 2011; Prairie et al., 2018) and feed the food web (Houel et al., 2006). This phase is followed by a “trophic depression”, and the establishment of a new “trophic balance”. These phases vary depending on the systems studied and can range in duration from a few years to several decades.

However, there is some confusion about the effects of impoundment and water level fluctuations, which commonly occur in reservoirs. Water level fluctuations may lead to soil and sediment erosion (Félix-Faure et al., 2019a, 2019b), littoral and benthic habitats degradation (Furey et al., 2004; Milbrink et al., 2011), sediment transfer (Blais & Kalff, 1995) toward the lake centre, and changes in lake metabolism (Houel et al., 2006) which also impacts the lake’s trophic status (Milbrink et al., 2011; Hirsch et al., 2017).

Unfortunately, there are few experimental measurements of trophic dynamics following impoundment (Lima et al., 2016; Turgeon et al., 2016) due to two major reasons. First, at least in France, most impoundments were established before the development of ecological monitoring programs (Pont et al., 1989). Second, sediment reworking during management operations may hamper their study. A possible approach to overcome these problems is to study natural lakes that were modified for hydroelectric production (Christie & Smol, 1996). In this case, the sedimentary chronicle begins before the onset of hydroelectric management and may allow, by comparison, an analysis of management effects.

The Alps are presently the main source of hydropower in Europe (Spitale et al., 2015). Reservoirs were generally formed by impounding portions of valleys, but natural lakes are also often used as reservoirs. These reservoirs are generally filled in the spring with snowmelt water and emptied in autumn-winter to support the electrical demand for heating (Spitale et al., 2015). In winter, water is drawn from under the ice of high-altitude reservoirs, so that the ice cover breaks up, collapses and slides along the slopes. The combination of soil freezing and ice sliding within the drawdown zone (Hellsten, 1997) further contributes to soil and sediment erosion.

Our aim was to document the ecological changes occurring in a lake managed as a reservoir, in relation to water level fluctuations. Our objectives were 1) to measure the temporal variation of sediment composition in relation to soil and sediment erosion of a high-altitude natural lake that has been utilized for hydroelectric production since 1976; 2) describe the ecological evolution of this lake using diatom and chrysophyte communities conserved in the sediment. These communities are typically used as indicators of current and past ecological status of water bodies (Dixit et al., 1992; Christie & Smol, 1996); and 3) discuss the relationships between the changes in water level and the ecological dynamics of lakes managed as reservoirs.

2 Material and methods

2.1 Study site

The plateau of Sept-Laux is a high altitude (about 2000 m asl.) valley in the mountain range of Belledonne (French Northern Alps). The peak elevation bordering the valley is about 2500 m asl. The granitic substrate of the plateau is homogenous and very poor in CaO (1.5 ± 0.1%wt) and MgO (0.7 ± 0.1%wt) (Gasquet, 1979; Debon et al., 1994; Debon & Lemmet, 1999). Neither mines, nor Pb/Cu/Ag anomalies are known in the local granite (Gasquet D., pers. comm.). According to a local meteorological station (Météo-France) at the Rivier d’Allemont (altitude: 1250 m asl.), corrected for altitude (0.5 °C/100 m, 50 mm precipitation/100 m), the average annual rainfall and temperature at the elevation of 2000 m asl. is about 2200 mm and 3 °C respectively. From November to April, snow covers the landscape and the surface of lakes is frozen. The soils are shallow, rich in pebbles, coarse textured, acidic and rich in organic matter. They vary between shallow Umbric Leptosols, rich in organic matter, between bare rock surfaces, Cambic Leptosols (Hyperdystric) rich in coarse elements, developed on scree’s slopes, and Entic/Humic Podzols on till or scree deposits close to the valley bottom. Shallow Histosols occur locally near waterbody (IUSS Working Group WRB, 2015). The soils are covered with subalpine meadows and ericaceous heaths below 2200 m asl. and alpine meadows above 2200 m asl., and show little evidence of erosion. The complete deforestation of the current landscape is linked to husbandry grazing and has not been locally dated. A small sheepfold was located on the north side of the lake (as reported on the IGN map dated from 1950 and on aerial pictures), and another close to lake Sagne, but they were presently ruined.

Several lakes and ponds are located on this plateau (Fig. 1A). Among them, Corne Lake (45°13’27”N, 6°04’40”E) has a surface of 8.4 ha and a volume of 1.45 hm3. It consists of a shallow depression (about 4 m depth) with a surface of 2 ha, connected to a deep depression (28 m depth) with a surface of 6.4 ha (Fig. 1B). Naturally, Corne Lake (altitude: 2096 m asl.) is fed by a small creek (mean autumn and winter discharge: 0.06 m3.s−1; mean spring discharge: 0.25 m3.s−1) flowing from Jéplan Lake (altitude: 2210 m asl., maximum depth: 2 m, area: 1.7 ha). The water of Corne Lake flows naturally downstream to Sagne Lake (altitude: 2040 m asl., maximum depth: 17 m, area: 6.5 ha). Discharge is very low (1–10 L.s−1) in the late summer, autumn and winter, and much higher (10–100 L.s−1) in the spring and early summer due to snow melt. The maximum altitude of the watershed of Corne Lake is 2500 m asl. and the area is 1.4 km2. Around Corne Lake, the dominant meadows species are Nardus stricta, Carex curvula, and Carex sempervirens on the western slope, and Festuca rubra, Gentiana acaulis, and Homogyne alpina on the steep slope along the northwest bank of the lake. The tributary (see below) crosses a small peaty area with Carex foetida, Carex nigra and Eriophorum scheuchzeri before flowing into the shallow depression, where Sparganium angustifolium is present. The lake is bordered to the north and east by coarse screes and is closed to the south by a small porous till deposit.

Since 1976, the water of Corne and Sagne lakes, which naturally flowed to the south, was pumped out and transferred to Cos Lake whose water naturally flows through Cottepens, Motte and Carré lakes to the North, in order to supply water to the hydropower plant of the Haut Bréda Valley (Fig. 1A). A small dike at the outlet of Corne Lake was built, rising its maximum water level by 2 m (to 2098 m asl.). Two pumping station were installed (Fig. 1B), one raising the water flow of Sagne Lake (intake depth 13 m) to Corne Lake, and another one raising the water flow from Corne Lake (intake depth 11 m below the natural level of the lake) to Cos Lake. At Corne, a pumping device was installed by (1) digging a 15 m deep vertical well in the moraine and the granitic bedrock (now covered by the building); (2) digging a 40 m long horizontal tunnel from the well bottom to the lake; (3) decreasing the lake water level to 2083 m asl.; (4) excavating and terracing about 400 m3 of moraine above the new pumping inlet, at 2085 m asl. The last two steps lasted two months (June 20 to August 22, 1976).

Since these developments, the water level of Corne Lake experienced strong seasonal variations. The lake level is 2 m higher in the summer and about 8 m lower in winter, so that the shallow depression gets empty (2088 m asl., see Figs. 2A and 2B). In the summer, the soils on the northwest, west and south banks of the lake are eroded by waves. In winter, the ice cover of the lake, formed in autumn when the water level is high, breaks along the shores, slides and erodes soils and sediments along steep slopes in the drawdown zone. During the spring flood, the creek flows directly to the deep depression and transfers sediments and erosion products from the shallow to the deep depression. In addition, the soil is locally eroded at the outlet of the pipe raising water from Sagne Lake.

The drawdown zone extends over belts of flooded soils (surface area: 0.2 ha) and sediments (surface area: 0.3 ha) temporarily exposed to the air. The organo-mineral horizons of littoral soils are eroded, leaving an accumulation of coarse elements (Figs. 2B and 2C). Nevertheless, the original peaty zone north of the shallow depression is partly preserved. Lake sediments are partially eroded by the creek where the tributary reaches the shallow depression. Finally, the soils are eroded and only an accumulation of blocks remains at the outlet of the pipe which brings water from Sagne Lake.

The lake is dimictic and oligotrophic (Guénand, 2020; Guénand et al., 2020), with summer (2014–2016) phosphorus concentration ranging from 0.005 mg.L−1 to 0.012 mg.L−1 and chlorophyll a from 4 to 5 μg.L−1. The depth of the Secchi disk varies seasonally between 3 m and 5 m. Lake [Ca2+ + Mg2+] concentration is 0.08 meq.L−1. Surface water pH varies between 5.6 in the spring and 8.1 in the summer. The concentration of dissolved organic carbon (DOC) is 1 to 2 mg.L−1, and the conductivity is below 25 µS.cm−1 at depth. The oxygen content of the lake is 8–10 mg.L−1 at the surface and drops to 3–5 mg.L−1 near the sediment (Électricité De France, 2003). The characteristics of Sagne Lake are very similar.

The biological inventory of the lake (Jacob, 2006) shows a phytoplankton community dominated by Zygnematophyceae (65% of the biomass) (mainly Spondylosium planum) and diatoms (23%) (mainly Pinnularia sp. and Fragilaria sp.). A zooplankton community dominated by rotifer (mainly Conochilus unicornis); Cladocerans (Daphnia longispina) and Copepods (Cyclopoides sp.) are poorly represented (< 2%). The lake also holds a fish community resulting from the long-lasting introduction and breeding of minnow (Phoxinus phoxinus), loach (Barbatula barbatula), arctic char (Salvelinus alpinus), and brook trout (S. fontinalis). Presently, about 500 trout fry (Salmo trutta) are brought in each year for recreational fishing.

thumbnail Fig. 1

A: Hydroelectric network of the Haut Bréda Valley. Natural or managed lakes are in grey. Originally lakes Jéplan, Corne and Sagne flowed south while lakes Cos, Cottepens, Carré and Motte flowed north. The blue dotted lines represent the main natural creeks. Arrows demonstrate the present routes of water pumped from Sagne Lake to Corne Lake, and from Corne Lake to Cos Lake. B: Bathymetry of Corne Lake. The yellow stars show the locations of the two sediment cores.

A : Réseau hydroélectrique de la vallée du Haut Bréda. Les lacs naturels et réservoirs sont en gris. Initialement les lacs de Jéplan, Corne et Sagne se déversaient vers le sud alors que les lacs de Cos, Cottepens, Carré et Motte se déversaient vers le nord. Les lignes en pointillé bleu représentent les principaux ruisseaux naturels. Les flèches illustrent le trajet de l’eau pompée depuis le lac de Sagne vers le lac de Corne, et du lac de Corne vers le lac de Cos. B : Bathymétrie du lac de Corne. Les étoiles jaunes représentent les sites de prélèvements des carottes de sédiment.

thumbnail Fig. 2

A: Natural and modified lake water levels since the installation of hydroelectric facilities along a transect from the shallow (a) to the deep depression (b). B: Photo of Corne Lake during a partial emptying in the fall of 2014. The red line corresponds to the maximum water level of the natural lake; black and blue lines represent the maximum and minimum present water levels respectively. The yellow stars show the sampling locations of the two sediment cores. C: detail of eroded soils in the drawdown zone.

A : Niveau d’eau naturel et modifié par les installations hydroélectriques, le long d’un transect de l’anse (a) à la dépression profonde (b) du lac de Corne. B : Photo du lac de Corne durant une vidange partielle à l’automne 2014. La ligne rouge représente le niveau d’eau maximum du lac naturel ; les lignes noir et bleue représentent respectivement le maximum et le minimum du niveau d’eau actuel. Les étoiles jaunes représentent les sites de prélèvements des carottes de sédiment. C : détail des sols érodés de la zone de marnage.

2.2 Sampling

Two cores of sediment were collected in November 2016 with a Uwitec gravity core sampler. The first core measuring 24.8 cm was taken at the deepest point of the lake (Deep depression core) and a second core measuring 29.5 cm was taken in the shallow part (Shallow depression core) (Figs. 1B, 2A and 2B).

After soil mapping, two Leptosols and two Podzolized soils were sampled below meadow and heathland. Soils were collected horizon by horizon from a soil pit during the summer of 2016. Samples were dried in an oven at 40 °C until constant mass, then passed through a 2 mm sieve.

2.3 Analysis

Sediment cores were cut in two halves and visually described. One of the halves was cut in 1 cm-thick slices and sampled. Bulk density was calculated after drying at 105 °C.

2.4 Sediment geochemistry

The semi-quantitative mineral composition of one undisturbed half of each core was analysed using an XRF Core Scanner (Avaatech Core Scanner) at a 2 mm pitch. The X-ray beam was generated from a rhodium anode and a 125 microns beryllium window allowing a voltage range between 7 and 50 kV with an intensity between 0 and 2 mA. The surface of the core cut in half was protected from contamination by a plastic film. Calibration was done at 10 kV and 1 mA for 10 s to detect Si, Ca, Al, Fe, Ti, K, Mn and S, and at 30 kV and 0.75 mA to detect Sr, Rb, Zr, Br and Pb. The Si/Ti ratio was used as a proxy for biogenic silica and the Zr/Rb ratio as a proxy for particle size (Bajard et al., 2015). The concentration of bioavaila-ble phosphorus, extracted by bicarbonate, was measured on 10 samples (1 cm-thick slices) from each core, as according to Olsen et al. (1954).

2.5 Comparison of soil and sediment geochemistry

To compare soils and sediments, the relative percentage of oxides of major elements was measured with a portable ED-XRF spectrometer (S1 TITAN Bruker). Samples of soil horizons and sediment samples were taken every centimetre and were dried in an oven at 40 °C to constant mass prior to being grounded in an agate mortar. The measurements were made in a plastic container (diameter 32 mm). All samples were made in triplicates according to the GeoChem Standard internal calibration for 60 s (Shand & Wendler, 2014). Ratios of oxide contents (CaO/TiO2 for example) were used to compare the composition of soils and sediments.

The total carbon and total nitrogen contents as well as the δ13C and δ15N were measured at the Isotopie-Biochimie pole of UMR SILVA in Nancy (vario ISOTOPE cube Elementar, Hanau, Germany interfaced with a gas isotope ratio mass spectrometer IsoPrime 100).

2.6 Dating by radioelements

The activity of 137Cs and 241Am was measured using a HPGe gamma detector at the Chrono-Environnement laboratory (Besançon) and at the Physics Department of the Autonomous University of Barcelona (Spain). High activity of 137Cs and low activity of 241Am is related to the Chernobyl accident in 1986 (Appleby, 2000; Klaminder et al., 2012). However, 241Am measurements had large standard errors and therefore were not used (values in Tab. S1, Supplement Material).

Eight 1 cm-thick samples from the deep depression core, and five from the shallow depression core, as well as one living Characeae (Nitella sp.) sample, were collected in September 2017 from the lake inlet and radiocarbon (14C) dated at the LSCE laboratory (France). The 14C dates were converted to calendar age using the IntCal13 calibration curve (Reimer et al., 2013) in the R “clam” package (Wickham et al., 2019; Blaauw, 2020; R Core Team, 2020). Variation of bulk sediment 14C age is not related to the date of sediment deposition, but to the origin (atmospheric, terrestrial or mixed) of carbon atoms in the sediment (Tittel et al., 2019).

2.7 Microalgal communities

The same technical protocol was used for all samples (Smol, 1983). Organic matter was removed using hydrogen peroxide at 90 °C for 24 h (Wilson et al., 1996). Samples underwent 5 cycles of centrifugation at 4000 rpm for 10 min followed by rinsing with distilled water. Then sediment pellets were suspended in 20 ml of distilled water. These re-suspensions were then diluted (1/50 and 1/100) before being mounted on a thin blade using the Naphrax© resin (refraction index: 1.74). Optical microscope observations were made in phase contrast (Zeiss AxioImager, 100x objective Immersion Oil). For each of the dilutions, diatom valves and Chrysophyte cysts were counted until at least 400 siliceous shells were obtained. Only diatom valves made up of at least two-thirds of an entire valve were counted. Diatom genera were determined using the identification guides of Krammer & Lange-Bertalot (1991) and Lange-Bertalot et al. (2017) (Tab. 1). Chrysophyte cysts were only counted.

Diatom genera were grouped in relation to their ecological preferences following Van Dam et al. (1994), Passy (2007) and Rimet & Bouchez (2012) (Tab. 1). Diatoms of the low-profile guild are favored in nutrient-poor and high disturbance habitats, while high-profile guild diatoms are favored in nutrient-rich sites and in conditions of low flow disturbance. The abundance of diatoms of the motile guild increases along the nutrient gradient and decreases along the disturbance gradient (Passy, 2007). Benthic diatoms live on the sediment surface of shallow waters, whereas planktonic diatoms live in the water column.

The Diatom/Chrysophyte ratio (D/C ratio) was calculated as the total number of diatom valves/total number of Chrysophyceae cysts. The D/C ratio is typically higher in lakes of higher trophic state because Chrysophytes are favoured in oligotrophic environments (Smol, 1983, 1985). Conversely the D/C ratio is lower in oligotrophic, acidic and deep lakes (Rivera-Rondón & Catalan, 2017).

Table 1

Diatom genera according to their ecological guild.

Genre de diatomée en fonction de leur guilde écologique.

3 Results and discussion

3.1 Description of sediment cores

3.1.1 Sediment core in the deep depression

From 24.8 cm to 16 cm, the sediment was a green-coloured mud with a very low bulk density (BD: 0.14 ± 0.08 g.cm−3) (Fig. 3A). From 16 cm to 12.5 cm, the sediment was darker, and bulk density was slightly higher (0.16 ± 0.02 g.cm−3). A white lamina occurred from 12.5 cm to 12.2 cm. From 12.5 cm to 6 cm, the sediment was a green-coloured mud, visually identical to the bottom of the core, but interspersed with white laminae a few millimeters thick. From 6 cm to 2 cm, the sediment showed a continuous sequence of fine white sandy laminae. Bulk density ranged between 0.81 g.cm−3 and 0.37 g.cm−3. The last two centimetres consisted of a grey-green mud, with a lower bulk density (0.44 g.cm−3 to 0.33 g.cm−3).

thumbnail Fig. 3

Depth variation of the mineral and organic composition of the sediment core taken in the deep depression. A: BD: bulk density (g.cm−3); B: Pb: total lead (cps); C: 137Cs: 137-Cesium activity (bq.kg−1); D: Ti: titanium (cps); E: Si/Ti: silicon/titanium ratio (cps/cps); F: Corg: organic carbon content (%); G: C/N: carbon/nitrogen ratio; H: δ13C (‰).

Composition minérale et organique en fonction de la profondeur de la carotte de sédiment prélevée dans la dépression profonde. A : BD : densité apparente (g.cm−3) ; B : Pb : plomb total (cps) ; C : 137Cs : activité du 137-Cesium (bq.kg−1) ; D : Ti : titane (cps) ; E : Si/Ti : ratio silicium/titane (cps/cps) ; F : Corg : carbon organique (%) ; G : C/N : ratio carbone/azote ; H : δ13C (‰).

3.1.2 Sediment core in the shallow depression

The sediment was dark-grey. Between 29.5 cm and 23 cm it was slightly darker, and bulk density was lower (BD: 0.21 ± 0.03 g.cm−3). Bulk density increased from 23 cm to 13 cm, and stabilized around 0.4 g.cm−3 above (Fig. 4A). From 23 cm to the top, the sediment was slightly less dark and interspersed with slightly reddish bands located between 22.2 cm and 21.8 cm, 15 cm and 13 cm, 9.3 cm and 8 cm, 5.3 cm and 4.5 cm and between 1.8 cm and 1 cm from the surface respectively.

thumbnail Fig. 4

Depth variation of the mineral and organic composition of the sediment core taken in the shallow depression. A: BD: bulk density (g.cm−3); B: Pb: total lead (cps); C: Ti: titanium (cps); D: Si/Ti: silicon/titanium ratio (cps/cps); E: Corg: organic carbon content (%); F: C/N: carbon/nitrogen ratio; G: δ13C (‰).

Composition minérale et organique en fonction de la profondeur de la carotte de sédiment de l’anse. A : BD : densité apparente (g.cm−3) ; B : Pb : plomb total (cps) ; C : Ti : titane (cps) ; D : Si/Ti : ratio silicium/titane (cps/cps) ; E : Corg : carbon organique (%) ; F : C/N : ratio carbone/azote ; G : δ13C (‰).

3.1.3 Mineral composition of the sediment in comparison to surrounding soils

Along both cores (Figs. 3D and 4C), Ti was strongly and positively correlated with K, Fe, Si, Al (r = 0.99, 0.98, 0.87, 0.79 and r = 0.85, 0.97, 0.96 and 0.91 in the deep and shallow depressions respectively) and therefore was used as a proxy for the mineral element content.

In the deeper layers, bulk density and mineral contents (kcps) were very low (Figs. 3D and 4C), slightly higher in the shallow depression in which the creek flows. Detritic mineral matter increased upwards. In the deep depression, the mineral content (Ti index) peaked for the first time in the first white lamina (between 13–12 cm), then rose continuously up to 3.8 cm in relation to the occurrence of whitish laminae. In the shallow depression, the mineral content of the sediment increased continuously between 29 cm and 12 cm, and remained stable from 12 cm to the top of the core. In the last upper 4 cm and 2 cm of the cores (in the shallow and deep depressions respectively), the bulk density and content of detritic particles (Figs. 3A3D and 4A4C) were stable (shallow depression) or decreased (deep depression).

The SiO2/TiO2 ratio of the sediment decreased from the base to the top, from about 160 to 80 in the deep depression, and from about 200 to 100 in the shallow depression. In comparison, the average SiO2/TiO2 ratios of surface and deep horizons of soils were 80 and 110 respectively (Fig. S2). The CaO/TiO2 ratio decreased as well from the base to the top of the cores from 1.7 to 1.2 in the deep depression and from 1.7 to 0.8 in the shallow depression. In comparison, the average CaO/TiO2 ratio was 0.7 in soil surface horizons and 1.3 at depth (Fig. S3).

3.1.4 Sedimentary phases and chronology according to geochemical tracers

We assumed that the original lake composition (before hydropower management) was registered in the deeper centimetres of the sediment in both depressions (Figs. 3 and 4), which composition appeared relatively stable in comparison to upper layers. Then, the variations of geochemical tracers suggested two possible alternative chronologies.

Hypothesis A) The major Pb peak in the sediments of the shallow and deep depressions, at 21 cm and 19 cm respectively (Figs. 3B and 4B), is related to the peak of emissions of tetraethyl-Pb in the years 1973–1974. This peak was observed in many lake sediments in this region of the Alps (Arnaud et al., 2004; Giguet-Covex et al., 2011; Wilhelm et al., 2012), and more specifically in a small proglacial lake (Lac Blanc Belledonne) located 10 km from Corne Lake (Wilhelm et al., 2012). Hence, the decline of this peak may date back to the starting of the hydropower management in 1976. The peak of 137Cs between 15 cm and 12.5 cm in the deep depression and at 11.5 cm in the shallow depression, may date back from the Chernobyl nuclear accident, in 1986. This peak was also detected at Lac Blanc (Wilhelm et al., 2012). In the deep depression, the 137Cs peak was associated with an increase in total Pb, which may suggest that sediment reworking occurred and/or a possible contribution of the surface horizons of littoral soils. In this hypothesis, Phase I depicts the initiation of hydropower management.

Hypothesis B) The Cs peaks between 15 cm and 12.5 cm in the deep depression and at 11.5 cm in the shallow depression are related to the atomic bomb tests in the fifties. This peak is also detected at nearby lakes (Lac Blanc Belledonne in Wilhelm et al., 2012; lake Bramant in Guyard et al., 2007). The Pb peaks at 21 cm and 19 cm in the shallow and deep depressions respectively would be related to former local mining activities (Guyard et al., 2007) or atmospheric deposition from local smelters. The plateau of high Pb concentrations between 14 and 12 cm in the deep depression would be related to emissions of tetraethyl-Pb. The initiation of hydropower operation would be marked by the end of this plateau, and by the occurrence of the first mineral laminae in the deep depression (at 12 cm) possibly resulting from the erosion of the sediments in the shallow depression or from the earthworks made to set up the pumping devices. In this hypothesis, Phase I depicts a change in ecological conditions (possibly related to husbandry pressure?) and Phase II the initiation of hydropower management.

Phase II is related to the maximum in bulk density values in the shallow depression and to occurrence of mineral laminae in the deep depression (from the depth of 12 cm). The sequence of mineral laminae might be related to the extreme spring floods of 1982, 1987, 1995, 1999, 2002, 2004, 2005 and 2016, measured at Font-de-France. The fact that no lamina was noticed in the shallow depression is most likely related to their formation during the spring flood, when the shallow depression is by-passed. In addition, the activity of Chironomidae (living individuals were observed in the shallow depression’s core) might have diluted mineral inputs into the bulk sediment.

Phase III corresponds to the upper centimetres of the core, and refers to the present state of the lake.

3.1.5 Organic composition of soils and sediments of the original lake

The carbon content of the organo-mineral A horizon of the soils ranged from 4% (Leptosol) to 12% (Entic Podzol). This content dropped below 4% in Entic Podzol at the depth of 30 cm. The C/N ratio of A horizons of Cambic and Umbric Leptosols was 10.5 and 14 respectively. In podzolised soils, the C/N increased from 14 to 16 with depth. Soil δ13C varied with depth, from −26.3‰ in the 0–15 cm layer to −25.3‰ below.

Along both cores in the shallow and deep depressions, the carbon content decreased upwards. In the original lake, while the two depressions were continuously connected, the carbon content in the shallow depression (13.4 ± 2.2%) was higher than in the deep depression (7.2 ± 1.2%). This may be related to higher benthic productivity in the shallow depression, and to the direct input flux of nutrients from the tributary. The higher δ13C in the shallow depression (−24‰) in comparison to the deep depression (−28‰) is in agreement with the general difference described by (France, 1995) between pelagic and littoral communities. Higher values may also be associated with a higher contribution of aquatic plants (Thevenon et al., 2012). In fact, Characeae individuals were observed in the littoral zone of the shallow depression. In both depressions, the C/N ratio (shallow depression: 10.8 ± 0.4; deep depression; 9.9 ± 0.2), suggests a mixed allochthonous (dissolved organic matter, suspended matter) and autochthonous (phytoplankton) origin of organic matter. This is confirmed by the high Si/Ti ratio (Figs. 3E and 4D) which indicated that biogenic silica (Bajard et al., 2015) was dominant. Bioavailable P was low: 0.036 ± 0.003‰ and 0.029 ± 0.006‰ in the deep and shallow depressions respectively.

The 14C age of bulk sediment carbon was old: from 4500 to 4300 years cal. BP in the deep depression and 5650 years cal. BP to 3450 years cal. BP in the shallow depression (Fig. 5 and Tab. S2). This very old age means, in the absence of carbonates in the watershed, that the carbon feeding the sediment, directly or through the trophic loop, does not come (or in a very small proportion) from atmospheric CO2. As dissolved organic carbon of pristine ecosystems is generally modern (Schiff et al., 1997; Marwick et al., 2015), this “old” carbon may originate from three processes. (i) Erosion and transport of soil carbon by the creek. For similar soils in the same environment, Egli et al. (2009) and Favilli et al. (2009) indicated that bulk soil 14C age range from approximately modern in upper horizons to about 2000 years cal. BP in Bs horizons, while recalcitrant organic matter or peat may be much older. This carbon input may cycle through deposition–resuspension cycles thereby enhancing remineralization and aging (Newbold et al., 1982); (ii) Atmospheric deposition of soot particles containing fossil carbon (Rose, 2015); (iii) Sediment carbon recycling: carbon annually mineralised, assimilated in the trophic chain, and back-sedimented (Abbott & Stafford, 1996; Wolfe et al., 2004).

thumbnail Fig. 5

Depth variation of bulk sediment radiocarbon age (years cal. BP) in the deep and shallow depressions.

Age 14C (years cal. BP) du sédiment en fonction de la profondeur des carottes de sédiment de la dépression profonde et de l’anse du lac de Corne.

3.1.6 Biological composition of sediments of the original lake

The composition of micro-algal communities preserved in the sediment reflected the oligotrophic status of the lake. The Diatom/Chrysophyte ratio (D/C in Figs. 6D6H) was very low (13.2 ± 1.8 and 5.4 ± 0.5 for the deep and shallow depressions respectively). Neutrophilic species dominated in both depressions (Figs. 6C and 6G) but acidophilic diatoms were more abundant in the shallow depression, possibly in relation to the presence of the Histosols along the shore.

In the shallow depression, benthic diatoms were dominant (75%). The percentages of high-profile, low-profile and motile diatoms were balanced (Fig. 6E), and (Fig. 6F). In the deep depression, tychoplanctonic diatoms (mostly species of the Staurosira genus) were dominant (80%) over benthic species, and diatoms belonged mostly (80%) to the high-profile guild (Fig. 6A) (Rimet & Bouchez, 2012) and (Fig. 6B). These compositions reflected the shallow water and physical disturbance by the creek in the shallow depression and conversely the depth and stability of water in the deep depression.

thumbnail Fig. 6

Depth variation of the diatom community composition by guild and D/C ratio in the deep (A, B, C, D) and shallow (E, F, G, H) depressions of Corne Lake.

Composition de la communauté de diatomée et ratio D/C en fonction de la profondeur des sédiments des carottes de la partie profonde (A, B, C, D) et de l’anse (E, F, G, H) du lac de Corne.

3.2 Processes driving the evolution of lake sediments according to the different phases

3.2.1 Trophic upsurge and changes in water level in Phase I

During Phase I the C/N ratio of the sediment decreased down to 8.8 in the deep depression and to 9.3 in the shallow depression. The 14C age of the bulk sediment decreased sharply to 1750 years cal. BP in the shallow depression (at the depth of 15 cm), and to 3000 years cal. BP and 1750 years cal. BP (at depths 15 cm and 13.5 cm respectively) in the deep depression. In addition, bioavailable P roses both in the deep (0.058‰) and shallow depressions (0.057‰). These changes might result from littoral soil flooding (hypothesis A) or as a consequence of changes in husbandry pressure in the vicinity of the lake (hypothesis B). Meadow soils along lakes are often enriched in P by cattle faeces (Bajard et al., 2018). According to hypothesis A (Phase I follows the initiation of hydropower management), the flooding and erosion of young (14C age < 200 years) topsoil organic matter, with a C/N higher than that of the sediment, resulted in a decrease in bulk sediment C/N and 14C age. The input of soil organic matter (and P) might have increased lake primary production (Ostrofsky, 1978; Bajard et al., 2018) and possibly atmospheric CO2 assimilation. The increase of δ13C in the shallow depression might also reflect an increased primary production (Thevenon et al., 2012), and/or a larger contribution of macrophytes. In addition, sediment drying and rewetting possibly increased P availability (Dieter et al., 2015). But an increase in husbandry pressure might have the same effects (hypothesis B). In fact, it may be noted that. the decrease of C/N in the shallow depression began earlier than Phase I (when total Pb peaked, at depth about 22 cm).

In comparison to the original lake, the proportion of benthic species progressively decreased in the shallow depression (while planktonic species increase), but increased in the deep depression, most likely as a result of the higher water level in the shallow depression, and of the physical transfer of sediment and benthic species from the shallow to the deep depression (hypothesis A). The proportion of high-profile and neutrophilic diatoms was also higher, while the D/C ratio and P concentrations were high, suggesting a trophic upsurge. However, all these changes did not occur simultaneously. For example, the major increase in the D/C ratio occurred in both depressions at 18/19 cm while the increase of benthic diatoms in the deep depression occurred later (16 cm). This suggests that the upsurge registered in the sediment during phase I did not only reflect the change in hydrology imposed by hydropower management (hence supporting hypothesis B).

3.2.2 Particle transfer and trophic depression in Phase II

When mineral sedimentation peaked (between 13 cm to 4 cm in the shallow depression and between 12.5 cm to 2 cm in the deep depression), the CaO/TiO2 and SiO2/TiO2 ratio of soil A horizons and sediments converged (Figs. S2 and S3). Nevertheless, the organic composition of cores in the shallow and deep depressions diverged. In the shallow depression, the C/N ratio, δ13C and bioavailable P returned toward the original lake values. But the radiocarbon age of the sediment remained young (< 1000 years cal. BP) possibly in relation to a larger contribution of atmospheric CO2. In the deep depression, with the increased contribution of detritic material, sediment δ13C increased significantly (down to −25.3 ± 0.4‰) to reach values in the range of old sediments of the shallow depression (about −24.1 ± 0.3‰) or soils (−25.6 ± 0.4‰). In this phase the bulk sediment carbon reverted to an old age (> 3500 years cal. BP). The increase in 14C age paired with the low C/N in the deep depression (compared to the shallow depression) may reflect the mineralisation and recycling of old carbon from different sources (soil horizons, shallow depression sediments).

The D/C ratio increased in both depressions in the beginning of this phase and later decreased (as in the beginning of Phase I), suggesting a new “upsurge-depression” cycle. In the shallow depression, the proportions of low-profile and acidophilic (mainly Psammothidium) and benthic (mainly Fragilaria) diatoms increased, which, in addition to the decrease in the D/C ratio, suggested a trophic depression. In the deep depression, the proportion of low-profile and benthic diatoms remained high in comparison to the original lake.

3.2.3 Present state

In the upper centimetres of the cores (phase III), the detritic contribution decreased, especially in the deep depression. In fact, the fine material of soils in the drawdown zone has been eroded and the detritic pavement of gravels and stones slowed further erosion down. In addition, extreme spring floods did not occur between 2005 and our study. The D/C ratio reached minimal values, as well as the Si/Ti (biogenic silica index) while the detritic input (Ti index) decreased. Both indicators suggested that the lake reached a very low trophic level. Benthic (mainly Fragilaria) replaced tychoplanctonic (Staurosira) genera in the deep depression, while the proportions of other guilds remained comparable. Interestingly, the sediment carbon age returned young: 1650 years cal. BP and 1100 years cal. BP in the deep and shallow depressions respectively, which is close to that (700 years cal. BP) of a living macrophyte (Nitella sp.) sampled underwater close to the stream inlet (data on Fig. 5). It may be assumed that the carbon provided by the watershed (in the form of DIC, DOC or POC) has not changed in the last 50 years. The decrease of bulk carbon age may be related to an increased CO2 input. In fact, monitoring of lake CO2 concentration and exchange with the atmosphere showed a diffusion of atmospheric CO2 into the lake in the summer, whereas the lake emitted CO2 towards the atmosphere during the spring thaw (Chanudet et al., 2020).

4 Synthesis and perspective

The ecological evolution of Alpine lakes results from multiple pressures. Our study was designed to measure the effects of hydropower management on the sediment composition of a lake, assuming deep sediment layers could be used as a control. We therefore assumed that hydropower management was the main environmental agent changing the sediment composition and that the initiation of hydropower management would be easy to detect. As the application of classical dating methods to sediment cores was not conclusive, we used major changes in the biological and geochemical composition of the sediment to suggest a chronology in relation to water level changes. Nevertheless, the proposed chronology remained hypothetical and other environmental changes (e.g., increased husbandry pressure) may also have influenced the geochemical and biological evolution of the lake.

Our observations showed the erosion of littoral surface soil and sediment in the littoral zone, and an increase in the transfer of erosion products from the shallow depression to the deep depression. In a first phase, the C/N and 14C age of bulk sediment, decreased while the proportion of high-profile diatoms and the Diatom/Chrysophyte ratio increased. Concurrently benthic diatoms decreased in the shallow depression and increased in the deep depression. This evolution suggested a trophic surge (Grimard & Jones, 1982; Smol, 1983, 1985; Kimmel & Groeger, 1986; Turgeon et al., 2016), probably initiated by water level fluctuations. A second phase was characterized by a high rate of mineral sedimentation, mirroring the erosion of mineral soils of the drawdown zone, an increase in acidophilic genera within the shallow depression and a general long-lasting decrease of the D/C ratio. This upsurge-depression cycle is consistent with the observations of Milbrink et al. (2011) who demonstrated that the management of Nordic lakes for hydropower alters littoral ecosystems and contributes to increasing resident fish sizes in the short term, but conversely leads to a long-term decrease in size. In the current period, as littoral soils are eroded, the supply of soil particles from the drawdown zone to the lake has decreased. The mineral pavement of the drawdown zone breaks the continuum between the terrestrial and aquatic environments, especially in the shallow depression (Spitale et al., 2015). Over the long term, we suggest that the change in hydrology has resulted in a shift in microalgal communities towards planktonic genera in the shallow depression, and benthic genera in the deep depression.

The studied lake is representative of many subalpine lakes located on acid rocks. The very old radiocarbon age of deep sediment layers suggests that the metabolism of pristine Alpine lakes depends mainly on the input of old carbon, and on the internal recycling of sediment carbon (Caraco et al., 2010; Thevenon et al., 2012; Guillemette et al., 2017) and little from atmospheric CO2 input. Conversely, the young age of sediment carbon in recent years suggests a higher contribution of atmospheric CO2.

Authors contribution

Jim Félix-Faure: Study design, data acquisition and analysis, writing of manuscript.

Mathieu Ramon: Data acquisition and analysis.

Christine Hatté: Data acquisition, data analysis and writing of manuscript.

Frédéric Rimet: Data acquisition and analysis.

Jérémie Gaillard: Data acquisition and analysis.

Vincent Chanudet: Study design, data analysis, writing of manuscript.

Anne-Lise Develle: Data acquisition and analysis.

Jordi Garcia-Orellana: Data acquisition and analysis.

Etienne Dambrine: Study design, data acquisition and analysis, writing of manuscript.

Acknowledgments

The authors would like to thank Annie Millery (Carrtel, USMB) for technical assistance in the lab; Yann Guénand (Segula technologies; Carrtel, INRA) and Florent Arthaud (Carrtel, USMB) for their friendly collaboration; Pascal Perney and Laura Crépin (Carrtel-Thonon) for phosphorus analysis; Christian Hossan from the SYLVATECH analytic platform of INRA Nancy-Lorraine for 13C and 15N measurements; Damien Rius (Chrono-Environnement, Université de Franche-Comté) for measurement of 210Pb, 137Cs and 241Am activities; Agnes Barillier (EDF-CIH) and Frederic Jacob (EDF-CIH) for access to archived data; Emily Pecsi (Micreau, UQTR) for revision of English, Stéphane Descloux (EDF-CIH) at the origin of this project; and Jean Marc Baudoin (AFB) for his unwavering support.

References

  • Abbott M.B. & Stafford T.W., 1996. Radiocarbon geochemistry of modern and ancient Arctic Lake Systems, Baffin Island, Canada. Quat. Res. 45(3): 300–311. DOI: 10.1006/qres.1996.0031. [Google Scholar]
  • Appleby P.G., 2000. Radiometric dating of sediment records in European mountain lakes. J. Limnol. 59(S1): 1–14. DOI: 10.4081/jlimnol.2000.s1.1. [Google Scholar]
  • Arnaud F., Revel-Rolland M., Bosch D., Winiarski T., Desmet M., Tribovillard N. & Givelet N., 2004. A 300 years history of lead contamination in northern French Alps reconstructed from distant lake sediment records. J. Environ. Monit. 6(5): 448–456. DOI: 10.1039/B314947A. [CrossRef] [PubMed] [Google Scholar]
  • Bajard M., Etienne D., Quinsac S., Dambrine E., Sabatier P., Frossard V., Gaillard J., Develle A.-L., Poulenard J., Arnaud F. & Dorioz J.-M., 2018. Legacy of early anthropogenic effects on recent lake eutrophication (Lake Bénit, Northern French Alps). Anthropocene 24: 72–87. DOI: 10.1016/j.ancene.2018.11.005. [CrossRef] [Google Scholar]
  • Bajard M., Sabatier P., David F., Develle A.-L., Reyss J.-L., Fanget B., Malet E., Arnaud D., Augustin L., Crouzet C., Poulenard J. & Arnaud F., 2015. Erosion record in Lake La Thuile sediments (Prealps, France): Evidence of montane landscape dynamics throughout the Holocene. The Holocene 26(3): 350–364. DOI: 10.1177/0959683615609750. [Google Scholar]
  • Barros N., Cole J.J., Tranvik L.J., Prairie Y.T., Bastviken D., Huszar V.L.M., del Giorgio P. & Roland F., 2011. Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude. Nat. Geosci. 4(9): 593–596. DOI: 10.1038/ngeo1211. [CrossRef] [Google Scholar]
  • Blaauw M., 2020. Clam: Classical age-depth modelling of cores from deposits. R Package Version 234, https://CRAN.R-project.org/package=clam. [Google Scholar]
  • Blais J.M. & Kalff J., 1995. The influence of lake morphometry on sediment focusing. Limnol. Oceanogr. 40(3): 582–588. DOI: 10.4319/lo.1995.40.3.0582. [Google Scholar]
  • Caraco N., Bauer J.E., Cole J.J., Petsch S. & Raymond P., 2010. Millennial-aged organic carbon subsidies to a modern river food web. Ecology 91(8): 2385–2393. DOI: 10.1890/09-0330.1. [CrossRef] [PubMed] [Google Scholar]
  • Chanudet V., Gaillard J., Lambelain J., Demarty M., Descloux S., Félix-Faure J., Poirel A. & Dambrine E., 2020. Emission of greenhouse gases from French temperate hydropower reservoirs. Aquat. Sci. 82(3): 51. DOI: 10.1007/s00027-020-00721-3. [CrossRef] [Google Scholar]
  • Christie C.E. & Smol J.P., 1996. Limnological effects of 19th century canal construction and other disturbances on the trophic state history of Upper Rideau Lake, Ontario. Lake Reserv. Manag. 12(4): 448–454. DOI: 10.1080/07438149609354284. [Google Scholar]
  • Cole J.J., Prairie Y.T., Caraco N.F., McDowell W.H., Tranvik L.J., Striegl R.G., Duarte C.M., Kortelainen P., Downing J.A., Middelburg J.J. & Melack J., 2007. Plumbing the global carbon cycle: Integrating inland waters into the terrestrial carbon budget. Ecosystems 10: 171–184. DOI: 10.1007/s10021-006-9013-8. [Google Scholar]
  • Debon F., Cocherie A., Ménot R.-P., Vivier G. & Barféty J.-C., 1994. Datation du plutonisme magnésien varsique des massifs cristallins externes des Alpes: l’exemple du granite des Sept Laux (massif de Belledonne, France). Comptes Rendus Acad Sci Paris t. 318, série II: 1797–1504. [Google Scholar]
  • Debon F. & Lemmet M., 1999. Evolution of Mg/Fe ratios in Late Variscan plutonic rocks from the external crystalline Massifs of the Alps (France, Italy, Switzerland). J. Petrol. 40(7): 1151–1185. [CrossRef] [Google Scholar]
  • Dieter D., Herzog C. & Hupfer M., 2015. Effects of drying on phosphorus uptake in re-flooded lake sediments. Environ. Sci. Pollut. Res. 22(21): 17065–17081. DOI: 10.1007/s11356-015-4904-x. [CrossRef] [PubMed] [Google Scholar]
  • Dixit S.S., Smol J.P., Kingston J.C. & Charles D.F., 1992. Diatoms: Powerful indicators of environmental change. Environ. Sci. Technol. 26(1): 22–33. DOI: 10.1021/es00025a002. [Google Scholar]
  • Egli M., Sartori G., Mirabella A., Favilli F., Giaccai D. & Delbos E., 2009. Effect of north and south exposure on organic matter in high Alpine soils. Geoderma 149(1-2): 124–136. DOI: 10.1016/j.geoderma.2008.11.027. [CrossRef] [Google Scholar]
  • Électricité De France I.U.-R., 2003. Chute des Sept Laux. Demande de renouvellement de concession. Mise à jour: Novembre 2007. Grenoble: Électricité De France. [Google Scholar]
  • Favilli F., Egli M., Sartori G., Cherubini P., Brandova D. & Haeberli W., 2009. Application of relative and absolute dating techniques in the Alpine environment. Studi Trentini Sci. Natinali Acta Geol. 85: 93–108. [Google Scholar]
  • Félix-Faure J., Gaillard J., Descloux S., Chanudet V., Poirel A., Baudoin J.-M., Avrillier J.-N., Millery A. & Dambrine E., 2019a. Contribution of flooded soils to sediment and nutrient fluxes in a hydropower reservoir (Sarrans, Central France). Ecosystems 22(2): 312–330. DOI: 10.1007/s10021-018-0274-9. [CrossRef] [Google Scholar]
  • Félix-Faure J., Walter C., Balesdent J., Chanudet V., Avrillier J.-N., Hossann C., Baudoin J.-M. & Dambrine E., 2019b. Soils drowned in water impoundments: A new frontier. Front. Environ. Sci. 7(53). DOI: 10.3389/fenvs.2019.00053. [Google Scholar]
  • France R., 1995. Carbon-13 enrichment in benthic compared to planktonic algae:foodweb implications. Mar. Ecol. Prog. Ser. 124: 307–312. DOI: 10.3354/meps124307. [CrossRef] [Google Scholar]
  • Friedl G. & Wüest A., 2002. Disrupting biogeochemical cycles – Consequences of damming. Aquat. Sci. 64: 55–65. DOI: 1015-1621/02/010055-11. [CrossRef] [Google Scholar]
  • Furey P.C., Nordin R.N. & Mazumber A., 2004. Water level drawdown affects physical and biogeochemical properties of littoral sediments of a reservoir and a natural lake. Lake Reserv. Manag. 20(4): 280–595. DOI: 10.1080/07438140409354158. [Google Scholar]
  • Gasquet D., 1979. Étude pétrologique, géochimique et structurale des terrains cristallins de Belledonne et du Grand Chatelard traversés par les galeries E.D.F. Arc-Isère-Alpes Françaises. Available at: https://tel.archives-ouvertes.fr/tel-00537312. [Google Scholar]
  • Giguet-Covex C., Arnaud F., Poulenard J., Disnar J.-R., Delhon C., Francus P., David F., Enters D., Rey P.-J. & Delannoy J.-J., 2011. Changes in erosion patterns during the Holocene in a currently treeless subalpine catchment inferred from lake sediment geochemistry (Lake Anterne, 2063 m a.s.l., NW French Alps): The role of climate and human activities. The Holocene 21(4): 651–665. DOI: 10.1177/0959683610391320. [CrossRef] [Google Scholar]
  • Grimard Y. & Jones H.G., 1982. Trophic upsurge in new reservoirs: a model for total phosphorus concentrations. Can. J. Fish. Aquat. Sci. 39(11): 1473–1483. DOI: 10.1139/f82-199. [CrossRef] [Google Scholar]
  • Guénand Y. 2020 Rôle de l’hydrologie sur la variabilité saisonnière hydro-biogéochimique d’un lac alpin. Cas des lacs alpins naturels ou équipés pour la production hydroélectrique. Thèse USMB, 173 p. [Google Scholar]
  • Guénand Y., Perga M.-E., Chanudet V. & Bouffard D., 2020. Hydropower operations modulate sensitivity to meteorological forcing in a high altitude reservoir. Aquat. Sci. 82(3): 60. DOI: 10.1007/s00027-020-00734-y. [Google Scholar]
  • Guillemette F., Bianchi T.S. & Spencer R.G.M., 2017. Old before your time: Ancient carbon incorporation in contemporary aquatic foodwebs. Limnol. Oceanogr. 62(4): 1682–1700. DOI: 10.1002/lno.10525. [Google Scholar]
  • Guyard H., Chapron E., St-Onge G., Anselmetti F.S., Arnaud F., Magand O., Francus P. & Mélières M.-A., 2007. High-altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the Western French Alps (Lake Bramant, Grandes Rousses Massif). Q. Sci. Rev. 26(19-21): 2644–2660. DOI: 10.1016/j.quascirev.2007.07.007. [CrossRef] [Google Scholar]
  • Hall R.I., Leavitt P.R., Dixit A.S., Quinlan R. & Smol J.P., 1999. Limnological succession in reservoirs: a paleolimnological comparison of two methods of reservoir formation. Can. J. Fish. Aquat. Sci. 56(6): 1109–1121. DOI: 10.1139/f99-047. [CrossRef] [Google Scholar]
  • Hellsten S.K., 1997. Environmental factors related to water level regulation – A comparative study in northern Finland. Boreal Environ. Res. 2: 345–368. [Google Scholar]
  • Hirsch P.E., Eloranta A.P., Amundsen P.-A., Brabrand Å., Charmasson J., Helland I.P., Power M., Sánchez-Hernández J., Sandlund O.T., Sauterleute J.F., Skoglund S., Ugedal O. & Yang H., 2017. Effects of water level regulation in alpine hydropower reservoirs: an ecosystem perspective with a special emphasis on fish. Hydrobiologia 794(1): 287–301. DOI: 10.1007/s10750-017-3105-7. [CrossRef] [Google Scholar]
  • Houel S., Louchouarn P., Lucotte M., Canuel R. & Ghaleb B., 2006. Translocation of soil organic matter following reservoir impoundment in boreal systems: Implications for in situ productivity. Limnol. Oceanogr. 51(3): 1497–1513. DOI: 10.4319/lo.2006.51.3.1497. [CrossRef] [Google Scholar]
  • IUSS Working Group WRB, 2015. Base de référence mondiale pour les ressources en sols 2014. Rapport sur les ressources en sols du monde No106, Mise à jour 2015. Rome: FAO. [Google Scholar]
  • Jacob F., 2006. Amenagement Hydroelectrique du Font de France. Étude environnementale de deux lacs. Rapport additif 2006. Électricité de France et SAGE environnement. [Google Scholar]
  • Jansson R., Nilsson C. & Renöfält B., 2000. Fragmentation of riparian floras in rivers with multiple dams. Ecology 81(4): 899–903. DOI: 10.1890/0012-9658(2000)081[0899:FORFIR]2.0.CO;2. [CrossRef] [Google Scholar]
  • Jigorel A., Bouedo A., Nicolas R. & Morin J.-P., 2007. Stockage du phosphore dans les sédiments d’un réservoir eutrophe (Gouet, Bretagne, France). J.P. Lobo, J.M.P. Vieira, Eds. Guimaraes, France: International Association of Hydrological Sciences, 15 p. [Google Scholar]
  • Kimmel B.L. & Groeger A.W., 1986. Limnological and ecological changes associated with reservoir aging. In: Reservoir fisheries management: Strategies for the 80’s (G.E. Hall, M.J. Van Den Avyle, Eds.). Bethesda, Maryland: Reservoir Committee, Southern Division of American Fisheries Society, pp. 103–109. [Google Scholar]
  • Klaminder J., Appleby P., Crook P. & Renberg I., 2012. Post-deposition diffusion of 137Cs in lake sediment: Implications for radiocaesium dating. Sedimentology 59(7): 2259–2267. DOI: 10.1111/j.1365-3091.2012.01343.x. [CrossRef] [Google Scholar]
  • Krammer K. & Lange-Bertalot H., 1991. Susswasserflora von mitteleuropa 2. Bacillariophyceae 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. Stuttgart: Gustav Fischer Verlag. [Google Scholar]
  • Lange-Bertalot H., Hofmann G., Werum M. & Cantonati M., 2017. Freshwater benthic diatoms of Central Europe: Over 800 common species used in ecological assessment. Schmitten-Oberreifenberg: Koeltz BotanicalBooks. [Google Scholar]
  • Lima A.C., Agostinho C.S., Sayanda D., Pelicice F.M., Soares A.M.V.M. & Monaghan K.A., 2016. The rise and fall of fish diversity in a neotropical river after impoundment. Hydrobiologia 763(1): 207–221. DOI: 10.1007/s10750-015-2377-z. [CrossRef] [MathSciNet] [Google Scholar]
  • Maavara T., Lauerwald R., Regnier P. & Van Cappellen P., 2017. Global perturbation of organic carbon cycling by river damming. Nat. Commun. 8(1): 15347. DOI: 10.1038/ncomms15347. [CrossRef] [Google Scholar]
  • Marwick T.R., Tamooh F., Teodoru C.R., Borges A.V., Darchambeau F. & Bouillon S., 2015. The age of river-transported carbon: A global perspective: The age of river-transported carbon. Glob. Biogeochem. Cycles 29(2): 122–137. DOI: 10.1002/2014GB004911. [CrossRef] [Google Scholar]
  • Milbrink G., Vrede T., Tranvik L.J. & Rydin E., 2011. Large-scale and long-term decrease in fish growth following the construction of hydroelectric reservoirs. Can. J. Fish. Aquat. Sci. 68(12): 2167–2173. DOI: 10.1139/f2011-131. [Google Scholar]
  • Newbold J.D., Mulholland P.J., Elwood J.W. & O’Neill R.V., 1982. Organic carbon spiralling in stream ecosystems. Oikos 38(3): 266. DOI: 10.2307/3544663. [CrossRef] [Google Scholar]
  • Nilsson C., Reidy C.A., Dynesius M. & Revenga C., 2005. Fragmentation and flow regulation of the World’s large river systems. Science 308: 405–408. DOI: 10.1126/science.1107887. [CrossRef] [PubMed] [Google Scholar]
  • Olsen S.R., Cole C.V., Watanabe F.S. & Dean L.A., 1954. Estimation of bioavailable phosphorus in soils by extraction with sodium bicarbonate. Soil and Water Conservation Research Branch, Agricultural Research Service. United States Department of Agriculture. [Google Scholar]
  • Ostrofsky M.L., 1978. Trophic changes in reservoirs: An hypothesis using phosphorus budget models. Int. Rev. Gesamten Hydrobiol. Hydrogr. 63(4): 481–499. DOI: 10.1002/iroh.19780630403. [CrossRef] [Google Scholar]
  • Ostrofsky M.L. & Duthie H.C., 1980. Trophic upsurge and the relationship between phytoplankton biomass and productivity in Smallwood Reservoir, Canada. Can. J. Bot. 58(10): 1174–1180. DOI: 10.1139/b80-146. [Google Scholar]
  • Passy S.I., 2007. Diatom ecological guilds display distinct and predictable behavior along nutrient and disturbance gradients in running waters. Aquat. Bot. 86(2): 171–178. DOI: 10.1016/j.aquabot.2006.09.018. [CrossRef] [Google Scholar]
  • Pont D., Chappaz R., Brun G. & Champeau A., 1989. Interactions zooplancton-poissons dans une retenue oligotrophe de mise en eau récente (Ste-Croix, Provence, France). Rev. Sci. Eau 2(4): 777–792. DOI: 10.7202/705054ar. [Google Scholar]
  • Prairie Y.T., Alm J., Beaulieu J., Barros N., Battin T., Cole J., del Giorgio P., DelSontro T., Guérin F., Harby A., Harrison J., Mercier-Blais S., Serça D., Sobek S. & Vachon D., 2018. Greenhouse gas emissions from freshwater reservoirs: What does the atmosphere see? Ecosystems 21(5): 1058–1071. DOI: 10.1007/s10021-017-0198-9. [CrossRef] [PubMed] [Google Scholar]
  • R Core Team, 2020. R: A Language and Environment for Statistical Computing. Vienna, Austria: R Found. Stat. Comput., https://www.R-project.org/. [Google Scholar]
  • Reimer P.J., Bard E., Bayliss A., Beck J.W., Blackwell P.G., Ramsey C.B., Buck C.E., Cheng H., Edwards R.L., Friedrich M., Grootes P.M., Guilderson T.P., Haflidason H., Hajdas I., Hatté C., Heaton T.J., Hoffmann D.L., Hogg A.G., Hughen K.A., Kaiser K.F., Kromer B., Manning S.W., Niu M., Reimer R.W., Richards D.A., Scott E.M., Southon J.R., Staff R.A., Turney C.S.M. & van der Plicht J., 2013. IntCal13 and Marine13 radiocarbon age calibration curves 0–50 000 years cal. BP. Radiocarbon 55(4): 1869–1887. DOI: 10.2458/azu_js_rc.55.16947. [CrossRef] [Google Scholar]
  • Rimet F. & Bouchez A., 2012. Life-forms, cell-sizes and ecological guilds of diatoms in European rivers. Knowl. Manag. Aquat. Ecosyst. (406): 01. DOI: 10.1051/kmae/2012018. [Google Scholar]
  • Rivera-Rondón C.A. & Catalan J., 2017. The ratio between chrysophycean cysts and diatoms in temperate, mountain lakes: Some recommendations for its use in paleolimnology. J. Paleolimnol. 57(3): 273–285. DOI: 10.1007/s10933-017-9946-2. [CrossRef] [Google Scholar]
  • Robbins C.J., Yeager A.D., Cook S.C., Doyle R.D., Maurer J.R., Walker C.M., Back J.A., Whigham D.F. & King R.S., 2020. Low-level dissolved organic carbon subsidies drive a trophic upsurge in a boreal stream. Freshw. Biol. 65(5): 920–934. DOI: 10.1111/fwb.13478. [Google Scholar]
  • Rose N.L., 2015. Spheroidal Carbonaceous fly ash particles provide a globally synchronous stratigraphic marker for the Anthropocene. Environ. Sci. Technol. 49(7): 4155–4162. DOI: 10.1021/acs.est.5b00543. [CrossRef] [PubMed] [Google Scholar]
  • Schiff S.L., Aravena R., Trumbore S.E., Hinton M.J., Elgood R. & Dillon P.J., 1997. Export of DOC from forested catchments on the Precambrian Shield of Central Ontario: Clues from 13C and 14C. Biogeochemistry 36(1): 43–65. DOI: 10.1023/A:1005744131385. [CrossRef] [Google Scholar]
  • Shand C.A. & Wendler R., 2014. Portable X-ray fluorescence analysis of mineral and organic soils and the influence of organic matter. J. Geochem. Explor. 143: 31–42. DOI: 10.1016/j.gexplo.2014.03.005. [Google Scholar]
  • Smol J.P., 1983. Paleophycology of a high arctic lake near Cape Herschel, Ellesmere Island. Can. J. Bot. 61(8): 2195–2204. DOI: 10.1139/b83-238. [CrossRef] [Google Scholar]
  • Smol J.P., 1985. The ratio of diatom frustules to chrysophycean statospores: A useful paleolimnological index. Hydrobiologia 123(3): 199–208. DOI: 10.1007/BF00034378. [CrossRef] [Google Scholar]
  • Spitale D., Angeli N., Lencioni V., Tolotti M. & Cantonati M., 2015. Comparison between natural and impacted Alpine lakes six years after hydropower exploitation has ceased. Biologia (Bratisl.) 70(12): 1597–1605. DOI: 10.1515/biolog-2015-0185. [CrossRef] [Google Scholar]
  • Thevenon F., Adatte T., Spangenberg J.E. & Anselmetti F.S., 2012. Elemental (C/N ratios) and isotopic δ15Norg, δ13Corg compositions of sedimentary organic matter from a high-altitude mountain lake (Meidsee, 2661 m a.s.l., Switzerland): Implications for Lateglacial and Holocene Alpine landscape evolution. The Holocene 22(10): 1135–1142. DOI: 10.1177/0959683612441841. [CrossRef] [Google Scholar]
  • Tittel J., Hüls M. & Koschorreck M., 2019. Terrestrial vegetation drives methane production in the sediments of two German reservoirs. Sci. Rep. 9(1): 15944. DOI: 10.1038/s41598-019-52288-1. [CrossRef] [Google Scholar]
  • Turgeon K., Solomon C.T., Nozais C. & Gregory-Eaves I., 2016. Do novel ecosystems follow predictable trajectories? Testing the trophic surge hypothesis in reservoirs using fish. Ecosphere 7(12): e01617. DOI: 10.1002/ecs2.1617. [CrossRef] [Google Scholar]
  • Van Cappellen P. & Maavara T., 2016. Rivers in the Anthropocene: Global scale modifications of riverine nutrient fluxes by damming. Ecohydrol. Hydrobiol. 16(2): 106–111. DOI: 10.1016/j.ecohyd.2016.04.001. [CrossRef] [Google Scholar]
  • Van Dam H., Mertens A. & Sinkeldam J., 1994. A coded checklist and ecological indicator values of freshwater diatoms from The Netherlands. Neth. J. Aquat. Ecol. 28(1): 117–133. DOI: 10.1007/BF02334251. [CrossRef] [Google Scholar]
  • Wickham H., Averick M., Bryan J., Chang W., D’Agostino McGowan L., François R., Grolemund G., Hayes A., Henry L., Hester J., Kuhn M., Lin Pedersen T., Miller E., Milton Bache S., Müller K., Ooms J., Robinson D., Paige Seidel D., Spinu V., Takahashi K., Vaughan D., Wilke C., Woo K. & Yutani H., 2019. Welcome to the tidyverse. J. Open Source Softw. 4(43): 1686. DOI: 10.21105/joss.01686. [Google Scholar]
  • Wilhelm B., Arnaud F., Enters D., Allignol F., Legaz A., Magand O., Revillon S., Giguet-Covex C. & Malet E., 2012. Does global warming favour the occurrence of extreme floods in European Alps? First evidences from a NW Alps proglacial lake sediment record. Clim. Change 113(3-4): 563–581. DOI: 10.1007/s10584-011-0376-2. [CrossRef] [Google Scholar]
  • Wilson S.E., Cumming B.F. & Smol J.P., 1996. Assessing the reliability of salinity inference models from diatom assemblages: An examination of a 219-lake data set from western North America. Can. J. Fish. Aquat. Sci. 53(7): 1580–1594. DOI: 10.1139/f96-094. [Google Scholar]
  • Wolfe A.P., Miller G.H., Olsen C.A., Forman S.L., Doran P.T. & Holmgren S.U., 2004. Geochronology of high latitude lake sediments. In: Long-term Environmental Change in Arctic and Antarctic Lakes. Developments in Paleoenvironmental Research (J.P. Smol, R. Pienitz, M.S.V. Douglas, Eds.). Dordrecht: Springer Netherlands, pp. 19–52. DOI: 10.1007/978-1-4020-2126-8_2. [CrossRef] [Google Scholar]

Supplementary Material

Figure S1. Depth variation of the diatom community composition by genera in the deep and shallow depression of Corne Lake.

Figure S2. Profiles of SiO2/TiO2 ratio in A) two Leptosol and two Podzolized soils which were characteristic of Corne Lake watershed, and B) sediment of the deep and shallow depression.

Figure S3. Profiles of CaO/TiO2 ratio in A) two Leptosol and two Podzolized soils which were characteristic of Corne Lake watershed, and B) sediment of the deep and shallow depression.

Table S1. Values of 137Cs and 241Am in relation to depth in the deep and shallow depression of Corne Lake.

Table S2. Values of radiocarbon analyses by depth in the deep and shallow depression of Corne Lake.

(Access here)

All Tables

Table 1

Diatom genera according to their ecological guild.

Genre de diatomée en fonction de leur guilde écologique.

All Figures

thumbnail Fig. 1

A: Hydroelectric network of the Haut Bréda Valley. Natural or managed lakes are in grey. Originally lakes Jéplan, Corne and Sagne flowed south while lakes Cos, Cottepens, Carré and Motte flowed north. The blue dotted lines represent the main natural creeks. Arrows demonstrate the present routes of water pumped from Sagne Lake to Corne Lake, and from Corne Lake to Cos Lake. B: Bathymetry of Corne Lake. The yellow stars show the locations of the two sediment cores.

A : Réseau hydroélectrique de la vallée du Haut Bréda. Les lacs naturels et réservoirs sont en gris. Initialement les lacs de Jéplan, Corne et Sagne se déversaient vers le sud alors que les lacs de Cos, Cottepens, Carré et Motte se déversaient vers le nord. Les lignes en pointillé bleu représentent les principaux ruisseaux naturels. Les flèches illustrent le trajet de l’eau pompée depuis le lac de Sagne vers le lac de Corne, et du lac de Corne vers le lac de Cos. B : Bathymétrie du lac de Corne. Les étoiles jaunes représentent les sites de prélèvements des carottes de sédiment.

In the text
thumbnail Fig. 2

A: Natural and modified lake water levels since the installation of hydroelectric facilities along a transect from the shallow (a) to the deep depression (b). B: Photo of Corne Lake during a partial emptying in the fall of 2014. The red line corresponds to the maximum water level of the natural lake; black and blue lines represent the maximum and minimum present water levels respectively. The yellow stars show the sampling locations of the two sediment cores. C: detail of eroded soils in the drawdown zone.

A : Niveau d’eau naturel et modifié par les installations hydroélectriques, le long d’un transect de l’anse (a) à la dépression profonde (b) du lac de Corne. B : Photo du lac de Corne durant une vidange partielle à l’automne 2014. La ligne rouge représente le niveau d’eau maximum du lac naturel ; les lignes noir et bleue représentent respectivement le maximum et le minimum du niveau d’eau actuel. Les étoiles jaunes représentent les sites de prélèvements des carottes de sédiment. C : détail des sols érodés de la zone de marnage.

In the text
thumbnail Fig. 3

Depth variation of the mineral and organic composition of the sediment core taken in the deep depression. A: BD: bulk density (g.cm−3); B: Pb: total lead (cps); C: 137Cs: 137-Cesium activity (bq.kg−1); D: Ti: titanium (cps); E: Si/Ti: silicon/titanium ratio (cps/cps); F: Corg: organic carbon content (%); G: C/N: carbon/nitrogen ratio; H: δ13C (‰).

Composition minérale et organique en fonction de la profondeur de la carotte de sédiment prélevée dans la dépression profonde. A : BD : densité apparente (g.cm−3) ; B : Pb : plomb total (cps) ; C : 137Cs : activité du 137-Cesium (bq.kg−1) ; D : Ti : titane (cps) ; E : Si/Ti : ratio silicium/titane (cps/cps) ; F : Corg : carbon organique (%) ; G : C/N : ratio carbone/azote ; H : δ13C (‰).

In the text
thumbnail Fig. 4

Depth variation of the mineral and organic composition of the sediment core taken in the shallow depression. A: BD: bulk density (g.cm−3); B: Pb: total lead (cps); C: Ti: titanium (cps); D: Si/Ti: silicon/titanium ratio (cps/cps); E: Corg: organic carbon content (%); F: C/N: carbon/nitrogen ratio; G: δ13C (‰).

Composition minérale et organique en fonction de la profondeur de la carotte de sédiment de l’anse. A : BD : densité apparente (g.cm−3) ; B : Pb : plomb total (cps) ; C : Ti : titane (cps) ; D : Si/Ti : ratio silicium/titane (cps/cps) ; E : Corg : carbon organique (%) ; F : C/N : ratio carbone/azote ; G : δ13C (‰).

In the text
thumbnail Fig. 5

Depth variation of bulk sediment radiocarbon age (years cal. BP) in the deep and shallow depressions.

Age 14C (years cal. BP) du sédiment en fonction de la profondeur des carottes de sédiment de la dépression profonde et de l’anse du lac de Corne.

In the text
thumbnail Fig. 6

Depth variation of the diatom community composition by guild and D/C ratio in the deep (A, B, C, D) and shallow (E, F, G, H) depressions of Corne Lake.

Composition de la communauté de diatomée et ratio D/C en fonction de la profondeur des sédiments des carottes de la partie profonde (A, B, C, D) et de l’anse (E, F, G, H) du lac de Corne.

In the text

Les statistiques affichées correspondent au cumul d'une part des vues des résumés de l'article et d'autre part des vues et téléchargements de l'article plein-texte (PDF, Full-HTML, ePub... selon les formats disponibles) sur la platefome Vision4Press.

Les statistiques sont disponibles avec un délai de 48 à 96 heures et sont mises à jour quotidiennement en semaine.

Le chargement des statistiques peut être long.