High altitude Nino lake in Corsica as paleo-environmental archive for late-Holocene
anthropogenic climatic change
Anaïs Passera
2016, University of Amsterdam
Bachelor Future Planet Studies, Major Earth Sciences
Under supervision of Dr. C. McMichael,Dr. B. Bomou & Dr. C. Castellani.
Abstract
Holocene climatic and environmental variations recorded in postglacial Corsican lacustrine sediments from the Nino Lake were investigated. High altitude lakes are potential archives to understand consequences of climatic and anthropogenic changes. Through a multiproxy approach, a geochemical analysis was effectuated to evaluate progressive eutrophication of lake Nino in Corsica. Total Organic Carbon (TOC), Nitrogen (N), Phosphorus (P) contents and mineralogical analysis were performed in order to investigate eutrophication,
climatic variability, and anthropogenic impact (e.g. increase in tourism, husbandry) over the last decades. The isotopic compositions of the lake demonstrated the environmental and anthropogenic related changes in the catchment primarily affected the stable isotopes in the lacustrine sediments. The increased input of P and soil erosion, altogether with a significant increase in anthropogenic related impacts, suggested that despite the remote location of lake Nino, human disturbances have triggered progressive eutrophication and sediment infilling of the Nino lake. In addition to this, the analysis of late-Holocene records resulted in three distinct hydrological periods with alternating more arid and wetter climatic regimes over the last decades indicating climatic changes on a local scale.
1.0 Introduction……….……….….… 3
2.0 Material and methods………....……….……….……4
2.1 Geographical setting of site……….………….….4
2.2 Past research on lake Nino……….………5
2.3 Methodology……….……….……….5
3.0 Results……….………..8
3.1 Sediment core lithology………..……….………8
3.2 Grain size analysis………..……….………..10
3.3 Geochemical analysis……….……….………11
4.0 Discussion………..……….……….13
4.1 Climatic variabilities during the late-Holocene….……….………..…….…………..13
4.1.1 Environmental significance……….…….13
4.1.2 Climatic trends………….……….……….………..13
4.1.3 Depositional environment………..……….………15
4.2 Evolution of eutrophication in lake Nino……….……….…..………….15
4.2.1 Phosphorus………..……….…….……15 4.2.2 C:N ratio……….……….…..16 5.0 Conclusion……….……….……….………17 6.0 References……….………...……….………….…………..19
1.0
Introduction
2In the last decades, anthropogenic influences have affected ecosystems and are drivers for twentieth century global climate change. Despite the significant climatic variations of the Pleistocene that were due to natural variabilities, the relatively stable climate of the Holocene is influenced by emerging civilizations that have an impact on natural processes and trigger climatic variations (Meyers & Lallier-Verges, 1999). To advance
our understanding of the potential effects of climate change, it is essential to disentangle the contributions of Holocene climatic variabilities and the anthropogenic evolution on former environmental changes.
Islands in the Mediterranean are an interesting field of study for understanding climatic changes in the Mediterranean Sea. It contains many undisturbed natural archives such as high altitude lakes, which record
climatic and anthropogenic influences (Simonneau, 2012). Those archives are crucial to understanding historic environmental conditions,but also provide archives of anthropogenic influences over time by studying its geochemical evolution (Simonneau, 2012). Even in the most remote places, archives such as ice cores, tree rings or lacustrine sediment deposits have recorded past climatic variations through stable isotopes and an increasingly number of studies demonstrate the value of deposited lake sediments as paleoclimatic records (Melton, 1965). Because organic matter in lakes can have different origins (algal production, terrestrial debris) it is relevant to qualify the different sources of organic matter in lacustrine sediments to determine former climatic regimes.
On the island of Corsica, many remote lakes are currently the centre of attention for tourists. The increasing tourist frequency in high altitude systems, in addition to the input of domesticated animals close to those lakes, triggered some changes in terms of eutrophication of those lakes. According to Rivier et al. (2005), some general recent signs of eutrophication in systems in Corsica were observed by Corsican mountain rangers as they noticed algal blooms, including the appearance of cyanobacteria and monitored a loss of species (Cauzaubon, 2006). The enrichment of lakes in Corsica in inorganic nitrogen by atmospheric inputs and phosphorus remobilization are the explanatory factors for eutrophication. The increase of inorganic nitrogen in aquatic ecosystems engenders uncertain prospects such as water acidification and eutrophication, which consequently causes a decrease in dissolved oxygen levels in the water column and affects the biodiversity. High altitude ecosystems are vulnerable to rapid changes and it is therefore essential to study earlier reactions on climatic changes in order to prevent ecological shifts towards irreversible conditions.
Past research applied multiproxy approaches to reconstruct last millennial paleoclimates in the Mediterranean based on stable isotope analysis. Paleoclimatic studies on sedimentary deposits in lakes have also been conducted elsewhere in Corsica (Reille et al., 1999), Sicily (Magny et al., 2007, 2011), on marine records in the Mediterranean (Rodrigo-Gamiz et al., 2011; Toucanne et al., 2012; Martinez-Ruiz et al., 2015) and speleothems records in Sardinia and Italy (Antonioli et al., 2003). The common assumption emerging from these studies concerned the alternating phases of major humidity and aridity during the Holocene. Since the chemical and biological conditions of high altitude lakes vary between warm and cold periods, lacustrine sediments are clear indicators of climatic variabilities (Reille et al., 1999). The primary productivity can be affected by changes in temperature resulting in an unstable the acid-base equilibrium and therefore influence eutrophication. In addition to this, the regional climate determines the types and quantity of vegetation occurring in the catchment, which influences erosion and thus sedimentation rates (Garcon et al., 2012).
Therefore, records in natural archives can reflect global and local climate change as they are anthropogenically and climatically influenced (Linello, 2012).
This study aims to reconstruct climate-induced environmental changes that occurred in the late-Holocene in a small glacial lake named Nino in North-West Corsica by investigating the geochemical and mineralogical evolution within lacustrine sediments to evaluate whether the lake is anthropogenically influenced and what effects this has on the high altitude system. It is assumed that the main cause for eutrophication of the lake is due to the excessive input of nutrients by tourists and husbandry. Geochemical data such as organic carbon concentrations (C), nitrogen content (N), C:N atomic ratios and phosphorus content (P) within a sediment core were analysed to determine their variations related to climatic and anthropogenic changes that have affected the lake in a decadal time-frame. The concentration and isotopic composition of sedimentary organic matter was studied in an attempt to assess the values of isotopes and C:N ratios as tracers identifying the distribution of terrestrial or algal organic matter in lacustrine sediments in order to reconstruct past climatic regimes.
2.0 Materials and methods
2.1 Geographical setting of siteCorsica, located in the Mediterranean Sea, is characterised by a steep relief, deep valleys and rigorous mountain ranges. Last Glacial Maximum left high mountain ranges above 2000 m altitude in Corsica with traces of erosion and sedimentation by which high altitude lakes were formed. Monte Cinto (2710m) dominates a North-West to South-East mountain range across Corsica with more than 100 peaks above 2000m altitude (Kuhlemann et al., 2005). Corsica was covered by glaciers during the Quaternary glacial period and in particular the last Würm
period (approx. 20000 BP)(Conchon et al., 1988). This geographical characteristic suggests a very complex elevation and slope steepness model. The gradual warming of the Earth during the Holocene resulted in the melting of these glaciers. Therefore, glacial sediments were deposited on Corsican mountains during the Würmian deglaciation (18000 BP) which resulted in the formation of steep valleys and lakes (Conchon et al., 1988).
The Nino lake (42°15'N 8°56'E) is situated in ‘Haute-Corse’ region at 1743m altitude, and is a glacial lake surrounded by snow-streaked mountains and bordered by ancient moraines. The moraine-dammed lake was formed when the last moraine prevented meltwater from glaciers to leave the valley (Rivier & Dumont, 1988). Water origins from the Nino lake resulted from glacier flow from the southwestern flank of Punta Artica (highest peak in the watershed), up valley towards the North-West and North, spilling over a pass down into the Niolo (Colga valley). Lake Nino is an open lake, which means that there is an outflow which is the Tavignano river suggesting that the water level is mainly controlled by snow melt, precipitation and outflow of the Tavignano. Due to the geomorphological setting of the lake, a major part of the sediment driven by erosion derive from the surrounding mountains. The surrounding land is characterised by small rivulets in spongy peat called pozzines.
2.2 Past research on lake Nino
The Nino lake is characterised by an eutrophic environment covered by aquatic macrophytic vegetation types such as Potamogeton natans (floating pondweed) and menyanthes trifoliata (bogbean). A large part of the lake
4 Fig. 1. Geographical location lake Nino in Mediterranean basin. Retrieved from Google Earth.
is filled by sediments and accumulation of organic material that allowed the development of a vegetation cover forming shallow peat rivulets. The fauna (mainly domesticate animals), such as horses, sheep, cattle and wild pigs are an important source of organic enrichment that lead to strong macrophytic vegetation development and tend to trigger an eutrophic environment. Indeed, Rivier (1996) suggested that the Nino lake is subjected to significant organic enrichment due to the importance of the basin vegetation cover for the use of surrounding pasture and increasing hiking tourism (Rivier, 1996). The last glacier on the top of the Tavignano basin was indirectly dated by posterior sedimentation by reconstructed glaciation chronology (Conchon, 1988). Sediment cores were taken in the peat bogs at lake de Nino through 2.20 m of soil, which started with clear peat followed by a sequence of 70 cm of brown peat and 35 cm of blue clay lying on a granite substrate. Palynological analysis led to the interpretation that the base of the Allerød period (warm and moist global
interstadial that occurred at the end of the last glacial period) (76% tree-pollen where 45% came from Pinus larico and 5% Artemisia), was followed by the cooling of the Dryas period (33% tree-pollen where 20% came from Pinus larico and 21% Artemisia) and the warming of the Preboreal and then the climatic oscillations from the Atlantic, from the Subboreal and Subatlantic (Conchon, 1988). Calibrated data confirmed the contribution of the Atlantic to the brown peat found in the pozzine. The last moraine, close to the area where the cores were sampled, was attributed to the Older Dryas (Conchon, 1988). Correlations were proposed between the deglaciation chronology and the established chronology in marine sediment cores close to the Corsican island by the interpretation of flora and fauna, radiocarbon dating and oxygen isotopes (Conchon, 1988). Four series of glacial deposits were identified during the Quaternary from which the oldest originated from the pre-Würmian Stage. Nevertheless, despite stratigraphic studies, the geochronology of the Corsican glacial sequences has not been precisely studied yet (Kuhlemann et al., 2005).
Table. 1. Characteristics lake Nino, Corsica. 2.3 Methodology
In order to investigate paleoclimatic and paleo environmental records in the lacustrine sediments a mineralogical approach was effectuated to study climatic variations linked to human influence and the sedimentary processes of the watershed. Geochemical analysis was performed to evaluate the anthropogenic influences that affected lake Nino during the last years by the means of collected sediment cores. The chemical analysis was effectuated in laboratories at the University of Corsica, France, in collaboration with the University of Lausanne, Switzerland.
Sampling methods
A gravity sediment corer was created by the University of Corsica staff members in order to sample lacustrine sediment deposits. The collected sediment cores captured a historical record of water and atmospheric conditions that could span the past hundreds of years and could be used to reconstruct past environmental climates. It was made of a tubular system (Ø 50 mm) with a valve on top, weighted with a concrete mass of 6 kg which allowed the corer to descend in depth by gravity to penetrate into the sediment at the bottom. The valve allowed the water to escape during the descent through the tube and during the ascending it
closed which allowed a suction effect to occur. This suction effect was holding the caught sediments within the tube while ascending back to the water surface. To operate the gravity corer, a small boat was used. In the field, 4 different cores were sampled. Two in the shallow pozzines, one at each extremity of the lake and two sediment cores were collected by means of the boat at the centre of the lake. The pozzine samples were suitable for chemical analysis while the lake samples were too aqueous despite the longer drying periods.
However, the only sample that was geochemically and mineralogically analysed was collected at the opposite side of the outlet of the lake inside a small pozzines (core LNE), for which the sample location is visualised in figure 4 .
After sampling, the sediment cores were conserved in a refrigerator until the beginning of the analysis in the hydrogeology laboratory of the University of Corsica. As a significant amount of water was present in the tubes, a little hole was pierced through the tube just 1 cm above the upper
sediment in order to release the water from the tube without mixing the chronology of the sediment deposits. The sediment core was vertically cut in half by a diamonds’ saw machine for different analysis. This was done with precautionary precise methods in order not to disturb the sediments with any type of elements that could have influenced the geochemical composition. After splitting the cores in the laboratory, an instant soil description was effectuated as the core could oxidize resulting in changing colours, losing important information on the original character.
Once the soil core description was finished of both pozzines cores, detailed sampling of the LNE core for mineralogical and geochemical analysis started. Every centimetre a fragment of sediment was collected with a spoon along the core section. Each sample was marked and placed in a small tube and then dried in an oven at 40 °C during 24 hours.
Analysis
● Mineralogical approach
A grain-size analysis was performed at the University of Corsica, using a column of sieves and a mechanical shaker. Each sample, previously dried, was separated in two parts and weighted. One of these parts was placed on top of the sieve column (six different size fractions >1mm, 500um, 250um, 125um, 63um, 63um), and then
shaken using the mechanical shaker with the help of water to facilitate the drainage. After shaking, each fraction was dried and weighted in order to construct a grain size distribution diagram. The remaining sampled part was crushed by a mechanical agate crusher and used for geochemical analysis at the University of Lausanne.
● Geochemical analysis: Phosphorus
Total phosphorus analyses was conducted at the University of Lausanne using the ascorbic acid molybdate blue method (Eaton et al., 1995). An amount of 100 mg for each sample powder was mixed with 0.5 ml of MgNO3 (1 M) into decontaminated glass bottles in order to degrade organic matter. After drying in oven at 100°C, the samples were heated in a furnace at 550°C for 2h30. After cooling, 10 ml of HCl (1M) was added to each sample and bottles are placed in ultrasonic disaggregation bath in order to liberate the phosphorus from the sediment matrix. After 14h of continuous shaking, samples were filtered and diluted ten times. 90 μl of molybdate mixing reagent and ascorbic acid was added into 3 ml of each sample solution. The intensity of the blue colour, depending to the phosphorus concentration, was quantified with an UV/Vis Perkin Elmer Lambda 25 spectrophotometer. The concentration of PO4 in mg/L was obtained by calibration with internal standard solutions with an accurate precision better than 5%.
Geochemical analysis: Carbon and Nitrogen
Geochemical analysis of 44 samples of carbon and nitrogen stable isotopes were collected every 1 cm from 0 to 44 cm. Total organic carbon (TOC) and nitrogen (N) abundances were determined with a CHNS Elemental Analyser Thermo Finnigan Flash EA 1112 on decarbonated and oven-dried bulk sediment samples. The samples were heated up to 900°C and the combustion products were extracted into a chromatographic column, in which they were converted into simpler components. The components were then measured by a thermal conductivity detector and recalculated in wt.%. Analytical precision and accuracy were determined by replicate analyses and by comparison with Organic Analytical Standard composed of purified DLMethionine, and are
6 Fig. 4. Location of collected pozzine core at opposite side of outlet (LNE).
respectively better than 0.1% (1σ) and 0.01% (1σ) for carbon and nitrogen determinations. The amount of TOC was recalculated in wt.% by taking into account the amount of CaCO3 wt.% measured on the same samples.
3.0 Results
The soil profile of the LNE sediment core is visualised on figure 5. This core was used for chemical analysis and the grain size analysis.
The core consisted of fine grained, dark coloured, organic rich material. The organic matter reached until approximately 5 cm depth. The structure of the rest of the core was quite silty clay loam, compact, greyish material. Some small darker laminations were discerned at 13-14 cm. Between 14 and 32 cm depth was the part of the core where the grain size analysis showed a higher amount of grains in the category < 63 um. At 30 cm depth, the structure of the clayey material became more grainy with loose material.
Fig. 5. Lithological core description sample Lake Nino Exit (LNE).
The second collected sediment core from the pozzines was located on the same side as the outlet of the lake visualized in figure 7. This core was not chemically analyzed but a soil description was effectuated. In comparison to the previous core, some more laminations and mottles were visible. The organic matter reached until approximately 3,5 cm depth. The soil was quite compact and moist. Less terrestrial debris such as straws were present. At 28 cm depth, the structure of the sediment became more grainy and grey. As this collected core was situated at close proximity of the outlet of the lake, the larger variety
8 Fig. 6. Lithological core description sample Pozzine Nino
of colors and laminations present is probably due to more intensive hydrologic related disturbances on sedimentary level. Therefore, it was more reliable to chemically analyze the first pozzine core (LNE) in order to limit vertical disturbances throughout the sedimentary succession of the core that could have affected the chemical chronology.
3.2 Grain size analysis
Fig. 7. Location pozzine core PNE.
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Grain size distribution of sediment core from Nino lake
< 63um > 63 um >125 um > 250um > 500um > 1mm
Depth (cm) Pe rc en ta ge o f gr a in s iz e fr ac ti o ns
Fig. 8. Grain size analysis on LNE sediment core sampled at lake Nino, Corsica. Abundancy of coarser grain sizes in the middle of the core.
The sieved sediment particle sizes ranged from < 63 um until > 1mm. According to the nomenclature developed by Udden (1914), Wentworth (1922) and Friedman (1978), sand ranges from 2 mm to 63 um, silt 63 – 2 um and clay consists of particles smaller than 2 um. A major part of the sediment core from the Nino lake consisted of silt and clay particles (<63 um) which accounts for 43.67 % of the total sediment. Furthermore, the coarser sand from 4 different fractions account for 45.88 % and the largest fraction (> 1mm) represents 10.44%. In the datasets of the three largest fractions (>1mm, 500 um, 250 um) there were a few outliers. The highest masses measured were obtained in the smallest fraction (<63 um) from which the mean weight of sieved fractions, 1.38 mg, and median, 1.40 mg, is also highest. A high proportion of the analysed sediment belonged to the silt & clay fraction(<63 um) whereas the rest of the core was separated into different size fractions of sand.
Fig.9. Boxplots & grain size distribution demonstrating the majority of silt & clay particles in the LNE core.
3.3 Geochemical analysis
Fig. 10. Comparison graph of Nitrogen, Phosphorus and Carbon from a sediment core (LNE) taken in the Nino lake, Corsica.. High Nitrogen concentrations correlate with high Carbon concentrations. A progressive increase of P throughout the core is visible.
Some significant similarities at certain points through the sediment core were observed. Three peaks of simultaneously N and C concentrations around 2, 20 and 39 cm depth. Despite the peak observable at 20 cm depth, there was no physical sign visible when comparing to the photographed sediment core. The N percentages range from 0 to 2.66 with a mean value of 0.73 and median 0.23. The C percentages range from 0 to 36.79 with a mean value of 7.89 and median 3.38.
As visualized in figure 10, an increase in P concentration along the sediment core is visible. Over the last 20 cm, the concentration of P tripled. At 1 cm, the P value is 1.49 mg/g. The highest P concentration is situated at 3 cm depth with a value of 1.62 mg/g. The lowest value is the last sample at 44 cm depth with a P concentration of 0.30 mg/g. The mean value of the P concentration throughout the core is 0.85 mg/g.
Fig.11. Plotted TOC and Nitrogen in sediment core LNE, lake Nino.
TOC in this study took into account the organic and inorganic carbon. As measured at the laboratory of the University of Lausanne, there were no carbonates present in the sediment cores and therefore it was possible to presuppose that only organic carbon was present. On the first sight, the correlation between the C and N
content were remarkable. The correlation of both datasets reaches a value of 0.75. The first 5 cm of the core, C:N values exceed 10. Furthermore, quite strong variations occur with quite some values close to 0. The observed trend shows the increase in C:N ratio over time. The highest value occurs at 44 cm depth where the C:N ratio reaches 189.9. The sample at 34 cm has a value of 0 because there was no carbon detected. This exceeding high value could also be as a result of the measurement of fresh plant litter as there were quite some straws present at larger depth in the sediment core (see figure 5).
4.0 Discussion
4.1 Climatic variations during the late-Holocene
Dissection of a vertical profile of a sediment core is likely to reveal changes in particle sizes, which could indicate fluctuations of the regional climate. Deciphering transport mechanisms and inferring past climatic conditions can be effectuated by means of knowledge on minerals comprising the deposits in the lake basin. This grain size analysis reveals the environmental significance of sediment particle size distribution in order to reconstruct the evolutionary climatic history of the environment surrounding lake Nino. 4.1.1 Environmental significance
The particle size distribution is controlled by the physical energy of water in the lake. Fine-grained sediments indicate the high physical energy and coarse-grained sediments the low physical energy of water. From 14 to 32 cm in the sediment core, the smaller sized grains were dominant. Variations in the grain sizes indicated different climatic conditions. According to Blott & Pye, fine grains indicate humid climates (higher water level) while coarser grains indicate drier climates (lower water level). In the middle of the
12 Fig. 12. C:N ratio along sediment core LNE, lake Nino.
Table 2. C:N ratio data of LNE core.
Fig. 13. Superposed grain size fractions of LNE core.
sediment core, a larger proportion of the grain size present represented the very fine sand/silt particles while the upper and lower boundaries of the core had more abundant coarser grains (see fig. 13). The ‘coarse-fine-coarse’ sediment variation that was slightly observable in a certain periodic pattern reflects ‘weak-strong-weak’ changes in physical energy of the water, which demonstrates the ‘low-high-low’ fluctuations of the water level that was revealing the ‘dry-humid-dry’ succession of the regional climate trends at lake Nino.
As shown in Fig. 10 & 13, three peak values of coarser sediment particle size occur at depths of 2, 5, 13 and 40 cm, which indicate drier periods. A similar study effectuated by Blott & Pye validated this hypothesis by comparing sediment particle size and geochemical indexes. The synthetic analysis of multiple indexes revealed that sediment particle sizes is a very effective proxy of climatic variations (Blott & Pye, 2001).
4.1.2 Climatic trends
3 interesting periods were put in evidence in the sediment core of the Nino lake. As the core isn’t dated, it was difficult to give a name to the observed changes.
0-14 cm: Drier climate trends characterized by coarser grain sediments.
14-30 cm: Occasionally more humid climate as evidenced by the presence of some organic matter in this section of the core and finer sediment.
30-44 cm: Progressive warming trends of climate and less precipitation.
When comparing the granulometric results with the geochemical, the coarser grain sizes correspond with peaks for C:N values. This suggests the occurrence of high energy events as the sedimentary organic matter has terrestrial sources, which supports the theory of synchronously coarser grain sizes. Over time, the grain size of the sediment shows a similar pattern with the N and C evolution. The variability of C:N ratios in recent years went along with coarser grain sizes, indicating that some more climatic changes have occurred. The variations in C:N ratios might be related to climatic events, such as storms causing terrestrial debris to end up in larger quantities than usual inside the lake. However, there is no significant vegetation surrounding the lake, which makes the soil more vulnerable to erosion altogether with the increasing amount of animals present in the water catchment, which are a cause for land trampling. The absence of vegetation and the presence of animals, resulting in more erosion in the last years, have thus influenced the sources of the organic matter.
Fig. 14. Geochemical data with grain size analysis from sediment core LNE. The upper part of the core shows and increase in N, P, C and a major part consists coarser sized grains. This is characterizing a drier climate, which in this case goes along with more terrestrial debris altogether with an increase in P over time. Some slight similar patterns of the different proxies re observable.
The consequences of climate change were previously studied on mountain lakes in Corsica, the Creno, Bastani and Capitello lake were subjected to drier circumstances in 2005 and 2007 (Somot, 2005). Those lakes, situated within 100 km distance of lake Nino, could therefore reflect some similarities. Even though drier
circumstances in 2007, the water level of the lake seemed to be more elevated than it was in 2011, which was
visible on the Google Earth images on figure 15. The water surface decreased over the last years, probably as a result of more frequent droughts, higher atmospheric temperatures due to climate change and infilling of the water basin by eroding sediments. Periods of drier climate may have lowered water levels and created peat bogs, the pozzines, in the former lake basin. In the future, the water level of the lake is likely to drop even more until the final stage of lake succession where the lake will completely disappear and only pozzines will remain present in the catchment.
Fig. 15. Satellite images Nino lake retrieved from Google Earth.
Kagalou et al.(2008) effectuated a similar case study and discovered the eutrophication of the
Pamvotis lake in western Greece in the Mediterranean went along with the appearance of a warmer, drier climate which caused an increase in N and C. There was a higher production rate of organic material due to higher temperatures which supplied more C of allochtonous origin to the lake. In addition to this, the drier climatic circumstances slightly dropped the water level of the lake, resulting in a reduction in redox potential and therefore an increase in metabolic activity an N content of the water (Kagalou et al., 2008). The observed patterns in the Pamvotis lake correspond to the geochemical findings on the Nino lake. As the granulometry of the upper sediment core revealed larger grains, corresponding to a drier climate in the last years, and the C and N concentrations also increased in the upper layers the case study of Greece could be compared to the Nino lake. The findings of Kagalou demonstrate the progressive eutrophication of the Pamvotis lake, which could reflect the prospective scenario of the Nino lake which is currently experiencing eutrophication.
4.1.3 Depositional environment
The morphology of the lake altogether with climatic trends and land use in the catchment controlled the deposition rate of lake sediments. Anthropogenic activities that have triggered rapid changes of sedimentation (e.g. settlement events, tourist frequency etc.) are often correlated with historical events. Lakes without surrounding wetlands are most sensitive to such changes (Klump et al., 2006). Lake Nino belongs therefore to a category of lakes that are more resistant to changes in sedimentation rates as the surrounding pozzines function as a buffer for registering anthropogenic changes. However, the sedimentation rate at lake Nino was influenced by the composition of plant and animal species present in the catchment. More and more animals were present at the lake due to increased husbandry, which is a cause for higher sedimentation rates due to trampling of the surrounding lands. Therefore, the upper layers of the collected core accumulated quicker than the soil layers beneath. It is thus difficult to effectuate the dating of the core and some future, more elaborated research has to be effectuated for this.
4.2 Evolution of eutrophication in lake Nino
Inferring climate change from lacustrine sediments is very complex as the response of a lake to climatic variations is dependent on the hydrologic and geomorphologic setting of the basin. Due to the altitude of lake Nino, the threat of urbanisation is not substantial. On the other hand, the escalation of tourist frequency at the lake and increasing animal husbandry induces livestock trampling of the surrounding land. Animal and human
excretions have noticeable effects on the water quality in terms of eutrophication and nitrate presence and can therefore be retraced in lacustrine sediments. Therefore, the increased tourist frequency over the last decade does not remain unnoticed.
4.2.1 Phosphorus
Phosphorus is an essential factor for water quality of lakes. Animal waste can result in elevated levels of soil P and P-sensitive water bodies such as lakes are affected by this nonpoint-source pollution. Several studies have shown correlation between phosphorus and high phytoplankton biomass, turbid water and occasionally undesired biological changes such as a loss of biodiversity and eutrophication (Corell, 1998).
As the proportion of P increased throughout the collected core from the Nino lake, the possibility of a shift of the aquatic state from a mesotrophic to a eutrophic environment is a plausible scenario. With the increased P-input, the richness of the biodiversity, nowadays still present, could be reduced due to the simultaneous oxygen depletion (Corell, 1998). As an increase in primary production goes along with an increase in algal presence, oxygen in the water column will be depleted faster with a higher amount of algae due to cellular respiration leading to hypoxic or anoxic conditions. The presence of horses, wild pigs and an increasing amount of tourists every day as the main cause of this P increase is questioned. Eutrophication of lake Nino is also a natural aging process as older lakes become nutrient rich. This process is affected by the biophysical, chemical characteristics as well as the hydrogeology and land use pattern of the watershed.
Because the lake is situated in the center of the watershed, surrounded by the slopes of mountains, erosional patterns trigger the faster increase in P concentration as soil in the surrounding area is likely to end up inside the lake. The age of the lake, together with the land use pattern and the geomorphology of the basin are all favorable for an increase in P over time.
Fig. 16. Conceptualization of freshwater eutrophication (Corell, 1998).
As visualized in figure 16, whenever the P-input surpasses a certain threshold, the primary production rate is suppressing the richness of biodiversity within the lake altogether with an inevitable decrease in dissolved oxygen levels, therefore leading to an eutrophic environment. Observations made in the field allowed to draw conclusions concerning the representativeness of the shallow pozzines as an advanced state of the lake. The pozzines, some isolated from the lake, showed several signs of eutrophic environments with low levels of dissolved oxygen and therefore less species than in the lake itself. If temperatures in Corsica continue to rise in the upcoming decade due to global warming, the water level of lake Nino is expected to drop slowly as a result of evaporation and also due to the lack of water input as all glaciers disappeared (Rivier & Dumont, 1988). Therefore, the sediment cores taken from the pozzines could draw a trend for forthcoming evolution of the lake from sediment cores sampled in the middle of the lake. Nevertheless, due to a
Fig. 16. Eutrophic, almost hypoxic, state of pozzine, lake
lack of time, this study will not focus on the chemical composition of the other collected pozzines and lacustrine cores.
4.2.2 C:N ratio
The C:N ratio of organic matter is widely used to distinguish algal and terrestrial origins of sedimentary matter. The high content of proteins (nitrogen rich) in plankton and the cellulose and lignin (nitrogen poor) in terrestrial plants and macrophytic vegetation explains the possible C:N variations (Meyers, 2003). Elemental chemical compositions in sediments can be modified by partial degradation of organic matter during diagenesis and thus influence the C:N ratio within lacustrine sediments. Therefore, the C:N ratio provides a sensitive measure of nutrient status in a lake and the sources of sedimentary organic matter.
C:N ratios are preserved in subaqueous sediments over time to such an extent that the sediment retains reliable source information (Meyers, 2003). Concerning the C:N ratio within the lake sediments, when the contribution of organic matter from vascular plants is small in comparison to the level of the water column, the C:N ratio in the sediment tends to be lower than the C:N ratio of lakes receiving significant quantities of plant debris. According to Gray & Middelstone, C:N ratios higher than 10 have terrestrial origins and lower derive from marine sources. Fresh plant litter may have ratios above 100 (Schlesinger, 1997).
Variations within the C:N ratio can reflect shifts in organic source material. According to Hecky et al. (1993), C:N values between 8.3-14.6 indicate moderate nitrogen deficiency and values above 14.6 extreme nitrogen deficiency. C:N ratio that has a value of approximately 13-14 for surface sediments suggest a sub equal mixture of algal and vascular plant contributions (Meyer & Lellier-Verges, 1999).
Through the first 5 cm of sediment, the C:N ratios had approximate values of 13-14. The C:N ratios along the sediment core showed some significant variabilities. Whenever the C:N value was not above 10, it approached the values around 0. This designates that a lot of measurements
indicated that the source of organic matter was quite variable. This is due to erosional and anthropogenic patterns changing sedimentation rates over the last decade also shown in figure 15, where the historical Google Earth images indicate the sediment infilling of the water basin.
In the upper layers of the sediment core, many variations in C:N were distinguished. The values approaching 0, thus algal sources, indicate that there was more N available than C. This excess in N nutrients in several periods can increase the primary production rate which goes along with algal blooms. The excessive increase in primary production on a short term will produce eutrophic conditions. This is exemplified by degraded water conditions. This chain reaction is an indicator for slow eutrophication of the lake in the last years as the C:N ratio shows an interesting amount of variabilities. The increase of N in the lake can be related to the increased tourism and husbandry in the surroundings of the catchment. It is clearly visible that the variations indicate a fragile state of the lake as it can easily be influenced and affected by external, anthropogenic factors. The deeper, more ancient, layers of the sediment core had significantly higher C:N ratio values. Those higher values designated more terrestrial origins of the sedimentary matter than present day. Nevertheless, the extreme last value could have been measured on a piece of fresh plant litter.
The simultaneous increase in P content altogether with the reducing C:N ratio over the last years suggested that the measured values of both proxies are coherent. Therefore, with this double argumentation, the out coming results indicate the progressive shift of a mesotrophic towards an eutrophic environment at lake Nino. This will on the long-term affect the biodiversity on a local scale at the Nino lake. In addition to this, the progressive sediment infilling of the water basin will result in a lower water level, favorable for eutrophication as oxygen will be consumed even faster by algal blooms. Therefore, it is assumed that the
16 Fig. 17. Distinctive source combinations of atomic C:N and organic 13-C values (Meyers, 1994).
surrounding pozzines, characterized by shallow and oxygen poor waters, can be considered as an advanced state of the Nino lake.
5.0
Conclusion
The analysis of the sediment core allowed to reconstruct paleoenvironmental and paleoclimatic changes for lake Nino and its surrounding watershed. The isotopic compositions of the lake demonstrated the climatic and anthropogenic related changes in the catchment primarily affected the stable isotopes in the lacustrine sediments over the last decades. The source of organic matter in the lacustrine sediments in the Nino lake has been evaluated using C and N stable isotopes ratios in conjunction with C:N ratios. The increasing C:N ratio and increase in P were likely attributed to the continuous, increasing, input of nutrients linked to the development of the surrounding landscape. The increased input of P and soil erosion altogether with a significant increase in anthropogenic related impacts suggests, despite the remote location of lake Nino, human disturbances by tourism triggering eutrophication of the lake. The ongoing marketing on hiking activities on Corsica makes the lake a tourist attraction and is therefore likely to become even more disturbed in the near future. Improved monitoring will enable better protection and management of this high-altitude ecosystem.
This research allowed to develop several findings concerning former climatic regimes and the impact of anthropogenic influences in terms of eutrophication. Further elaboration is needed in order to provide accurate dating of the sediment core in addition to multiple, longer, core sampling through a spatial distribution grid which will provide more ancient information concerning environmental conditions in the past. The collection of more past climatic conditions will allow this research to extent its scope and more connections could be drawn between climate, anthropogenic activities and eutrophication in the studied area.
6.0 References
Adatte, T., Stinnesbeck, W., Keller, G., 1996. Lithostratigraphical and mineralogic correlations of near K/T boundary clastic sediments in northeastern Mexico: implications for origin and nature of deposition. Geological Society of America Special Paper 307, 211–226. Antonioli, F., Silenzi, S., Gabellini, M., Mucedda, M. (2003). High resolution climate trend over the last 1000 years from a stalgmite in
Sardinia (Italy). Quat. Nova 7, 1-5.
Avramidis, P., Nikolaou, K., & Bekiari, V. (2015). Total organic carbon and total nitrogen in sediments and soils: a comparison of the wet oxidation–titration method with the combustion-infrared method. Agriculture and Agricultural Science Procedia, 4, 425-430. Birck, C., Domaizon, I., & Rimet, F. (2013). Monitoring of French altitude lakes in multi-stressors situations: Focus on 5 lakes in
Haute-Savoie. In 5th Symposium for Research in Protected Areas (pp. 59-64).
Blott, S. J., & Pye, K. (2001). GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth surface processes and Landforms, 26(11), 1237-1248.
Cazaubon, A. 2006. Études des algues de cinq lacs d’altitude de Corse (Nino, Melo, Maggiore, Bastani, Cavacciole). Étude réalisée dans le cadre de l’appel d’offre de l’Office de l’Environnement de la Corse.
Conchon, O. (1988). Manifestation et chronologie de la déglaciation fini-würmiennne en Corse. Bulletin de l'Association française pour l'étude du quaternaire, 25(2), 91-96.
Correll, D. L. (1998). The role of phosphorus in the eutrophication of receiving waters: A review. Journal of Environmental Quality, 27(2), 261-266.
Dresch, J. (1941). Anciens glaciers corses. Bulletin de l'Association de géographes français, 18(140-141), 115-120.
Eaton, A.D., Clesceri, L.S., Greenberg, A.E., 1995. Standard Methods for examination of Water and Waste Water IXI, 4113–4114.
Folk, R. L., & Ward, W. C. (1957). Brazos River bar: a study in the significance of grain size parameters. Journal of Sedimentary Research,27(1).
Friedman, G. M. (1962). On sorting, sorting coefficients, and the lognormality of the grain-size distribution of sandstones. The Journal of Geology, 737-753.
Fritz, S. C. (2008). Deciphering climatic history from lake sediments. Journal of Paleolimnology, 39(1), 5-16.
Garçon, M., Chauvel, C., Chapron, E., Faïn, X., Lin, M., Campillo, S., ... & Charlet, L. (2012). Silver and lead in high-altitude lake sediments: Proxies for climate changes and human activities. Applied Geochemistry, 27(3), 760-773.
Hecky, R. E., Campbell, P. & Hendzel, L.L. 1993. The stoichiometry of carbon, nitrogen, and phosphorus in particulate matter of lakes and oceans. Limnol. Oceanogr. 38: 709–724.
Ishiwatari, R., N. Takamatsu, and T. Ishibashi. "Separation of autochthonous and allochthonous materials in lacustrine sediments by density differences."Japanese Journal of Limnology 38 (1977)
Jones, B. F., & Bowser, C. J. (1978). The mineralogy and related chemistry of lake sediments. In Lakes (pp. 179-235). Springer New York. Kagalou, I., Papastergiadou, E., & Leonardos, I. (2008). Long term changes in the eutrophication process in a shallow Mediterranean lake
ecosystem of W. Greece: Response after the reduction of external load. Journal of Environmental Management, 87(3), 497-506. Kaplan, M. R., Wolfe, A. P., & Miller, G. H. (2002). Holocene environmental variability in southern Greenland inferred from lake sediments.
Quaternary Research, 58(2), 149-159.
Klump, J. V., Weckerly, K., Edgington, D., Anderson, P., Szmania, D., Waples, J., & Eadie, J. D. (2006, February). Historical sedimentation rate determinations in lake Erie. In Lake Erie Millennium Network Conference, Windsor, ON (Vol. 28).)
Kuhlemann, J., Frisch, W., Székely, B., Dunkl, I., Danišik, M., & Krumrei, I. (2005). Würmian maximum glaciation in Corsica. Austrian Journal of Earth Sciences, 97, 68-81.
Kübler, B., 1987. Cristallinité de l'illite, méthodes normalisées de préparations, méthodes normalisées de mesures. Cahiers Institut Géologie de Neuchâtel, Suisse, série AD.
Last, W. M., & Smol, J. P. (Eds.). (2006). Tracking environmental change using lake sediments: volume 2: physical and geochemical methods (Vol. 2). Springer Science & Business Media.
Leroux, A., Bichet, V., Walter-Simonnet, A. V., Magny, M., Adatte, T., Gauthier, É., ... & Baltzer, A. (2008). Late Glacial-Holocene sequence of Lake Saint-Point (Jura Mountains, France): Detrital inputs as records of climate change and anthropic impact. Comptes Rendus Geoscience, 340(12), 883-892.
Magny, M, Vannière, B, Calo, C, et al. (2011). Holocene hydrological changes in south-western Mediterranean as recorded by lake-level fluctuations at Lago Preola, a coastal lake in southern Sicily, Italy. Quaternary Science Reviews 30: 2459–2475.
Magny, M., de Beaulieu, J.L., Drescher-Schneider, R., Vannière, B., Walter-Simonnet, A.V., Miras, Y., Millet, L., Bossuet, G., Peyron, O., Brugiapaglia, E., Leroux, A. (2007). Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany, Italy). Quaternary Science Reviews 26, 1736-1758.
Martinez-Ruiz, F., Kastner, M., Gallego-Torres, D., Rodrigo-Gámiz, M., Nieto-Moreno, V., and Ortega-Huertas, M. (2015). Paleoclimate and paleoceanography over the past 20 000 years in the Mediterranean Sea Basins as indicated by sediment elemental proxies, Quat. Sci. Rev., 107, 25–46.
Melton, M. A. (1965). The geomorphic and paleoclimatic significance of alluvial deposits in southern Arizona. The Journal of Geology, 1-38. Meyers, P.A., (2003). Applications of organic geochemistry to paleolimnoligal reconstructions: a summary of examples from Laurentian
Great Lakes. Organic Geochemistry, 34: 261-289.
Meyers, P. A. (1994). Preservation of elemental and isotopic source identification of sedimentary organic matter. Chemical Geology, 114(3-4), 289-302.
Meyers, P. A., & Lallier-Vergès, E. (1999). Lacustrine sedimentary organic matter records of Late Quaternary paleoclimates. Journal of Paleolimnology,21(3), 345-372.
Meyers, Philip A., and Ryoshi Ishiwatari (1993). "Lacustrine organic geochemistry—an overview of indicators of organic matter sources and diagenesis in lake sediments." Organic geochemistry 20.7: 867-900.
O'sullivan, P. E. (1983). Annually-laminated lake sediments and the study of Quaternary environmental changes—a review. Quaternary Science Reviews,1(4), 245-313.
Regattieri, E. (2014). Coeval dry events in the central and eastern Mediterranean basin at 5.2 and 5.6 ka recorded in Corchia (Italy) and Soreq caves (Israel) speleothems, Global and Planetary Change, Volume 122, 130-139.
Reille, M., Gamisans, J., Beaulieu, J. L., & Andrieu, V. (1997). The late‐glacial at Lac de Creno (Corsica, France): a key site in the western Mediterranean basin. New Phytologist, 135(3), 547-559.
Reille, M., Gamisans, J., Andrieu-Ponel, V., de Beaulieu, J.-L. (1999). The Holocene at Lac de Creno, Corsica, France: a key site for the whole island. New Phytol. 141, 291-307.
Rivier B., Dumont B. (1988). Etude ichtyologique des lacs d’altitude de la Corse, lac de Rotondo, lac de Nino. Rapport Cemagref Aix en Provence. PNRC, 91p.
Rivier, B.(1996). Lacs de haute altitude.Collection Études du Cemagref, série Gestion des milieux aquatiques, 11.
Roche B., Loye – Pilot M.D. (1989). Eutrophisation récente d’un lac de montagne sans occupation humaine (lac de Bastani, Corse) : conséquence d’apports atmosphériques? Revue des Sciences de l’eau, 2 n° 4 pp 681 à 707.
Rodrigo-Gamiz, M., Martinez-Ruiz, F., Jimenez-Espejo, F.J., Gallego-Torres, D., Nieto-Moreno, V., Romero, O., Ariztegui, D. (2011). Impact of climate variability in the western Mediterranean during the last 20,000 years: oceanic and atmospheric responses. Quat. Sci. Rev. 30, 2018-2034.
Schlesinger, W.H., 1997. Biogeochemistry An analysis of global change. Academic Press, San Diego, 588 pp.
Simonneau, A. (2012). Tracking glacial and high altitude Holocene alpine environments fluctuations from clastic and organic markers in proglacial lacustrine archives (Lake Blanc Huez, Grandes Rousses Massif, France).Quaternary International, 279, 451.
Somot, S. (2005). Modélisation climatique du bassin méditerranéen: variabilité et scénarios de changement climatique (Doctoral dissertation, Météo-France).
Toucanne, S., Jouet, G., Ducassou, E., Bassetti, M.-A., Dennielou, B., Angue Minto'o, C.M., Lahmi, M., Touyet, N., Charlier, K., Lericolais, G., Mulder, T. (2012). A 130,000-year record of Levantine Intermediate Water flow variability in the Corsica Trough, western Mediterranean Sea. Quaternary Science Reviews, 33, 55–73.
Wick, L., Lemcke, G., & Sturm, M. (2003). Evidence of Lateglacial and Holocene climatic change and human impact in eastern Anatolia: high-resolution pollen, charcoal, isotopic and geochemical records from the laminated sediments of Lake Van, Turkey. The Holocene, 13(5), 665-675.
