Understanding how climate change influences mountain lakes both directly and indirectly by modifying catchment processes is central to ongoing and future research. Special emphasis is now placed on problems associated with the interactions between climate change, the melting mountain permafrost, enhanced pollutant release, and ecosystem health. The general objective of the project is to reconstruct the changes in ecotoxicological state of a high-alpine lake ecosystem over the last ca. 10,000 years caused by warming-related increases in trace metal inputs into a lake from an active rock glacier. This goal will be achieved by means of chironomid analysis (Diptera: Chironomidae) of the Holocene sediment records from a lake with a rock glacier and a pond without a rock glacier in the catchment situated in a periglacial environment in the Ã-tztal Alps, South Tyrol, Italy. The general Holocene trend in summer temperature and the major warming events responsible for the past elevated mountain permafrost discharges in the study area will be identified based on a chironomid record obtained from the water body not affected by the rock glacier and on other climatic inferences in the region. The study of morphological mentum abnormalities in chironomid subfossils for the assessment of past environmental toxicity associated with metal influx from melting alpine permafrost will be innovative for the Alpine region. Special attention will be placed on studying the trace metal bioaccumulation in living chironomids and the metal biomagnification through the contemporary benthic food chain in a lake affected by recent metal fluxes from mountain permafrost.
1 Introduction and state of the art
1.1 Mountain glacial and periglacial environments
Climate changes and the High Alps
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Perennially frozen and glacierized high mountain areas react very sensitively to changes in atmospheric temperature (Haeberli & Beniston, 1998). As a consequence, since the middle of 19th century, i.e. since the end of the Little Ice Age, the glaciers in the European Alps have lost about 30 to 40% of surface area and ca. 50% of their original volume (Haeberli & Hölzle, 1995). Since 1980, an additional loss of this remaining ice volume was ca. 25% (Haeberli, 2005). Less visible but also very significant are changes in Alpine permafrost. During 20th century century, it has warmed by about 0.5 to 0.8Â°C in the upper tens of meters (Harris et al., 2003; Harris & Haeberli, 2003). The most direct information about the climate-related changes in mountain permafrost derives from borehole temperature measurements. The longest, high-resolution time series of borehole temperatures in the European Alps is available from permafrost in the active rock glacier Murtèl, Grisons Alps, Switzerland (Haeberli & Gruber, 2009). The general trend observed there since 1987 is permafrost warming by ca. 0.4Â°C per decade at 10 m depth, and roughly twice as much for the summer temperatures in the active layer (Haeberli & Gruber, 2009). Since the end of the Little Ice Age, the lower permafrost limit in the European Alps is estimated to have risen vertically by about 1 m per year (Frauenfelder, 2005).
Permafrost, or permanently frozen ground, consists of lithospheric material (soil, sediment, or rock) that remains at or below 0Â°C for at least two years (van Everdingen, 2005). By definition, glaciers are not permafrost. In the European Alps, a mean annual air temperature below -3Â°C can be used for first-order classification of altitudinal belts that have significant amounts of permafrost (Gruber & Haeberli, 2009). Permafrost exists in different forms, such as steep bedrock, rock glaciers, and debris deposited by glaciers, and can contain over 50% ice (French, 2007). Most permafrost areas experience seasonal thaw, during which surface temperatures rise above the melting point and a certain volume of material directly beneath the surface ('active layer') thaws. A thickness of active layer is usually in the range of 0.5-8 m (Haeberli et al., 2006). Discharge measurements suggest that meltwater from areas underlain by permafrost represents an important share (up to ca. 30%) of the river discharge during summer (Schrott, 1996).
Permafrost is invisible because it is a thermal phenomenon. It usually lies beneath an active layer and its reliable detection requires temperature measurements at greater depths using core drilling into permafrost. The difficulty in detecting permafrost and expensive access hamper the progress in permafrost research in mountain areas. As a consequence, the warming-related changes of perennially frozen mountain slopes have been studied for little more than a decade only (Haeberli & Gruber, 2009).
Alpine rock glaciers as a form of mountain permafrost
Always on Time
Marked to Standard
Rock glaciers and other creep phenomena often visually indicate the presence of permafrost in mountain areas: they form distinct landforms caused by the slow deformation of cohesive, ice-rich sediments (Haeberli et al., 2006). Rock glaciers can be categorized into three types depending on activity and ice content: (1) active, (2) inactive, and (3) relict (Barsch, 1977). Active rock glaciers show actual movement due to interstitial ice and/or core ice. Inactive rock glaciers show no movement but still contain ice. Relict rock glaciers are free of ice; they sometimes show collapse structures but no evidence of movement. In many catchments of high mountain regions where permafrost occurs, rock glaciers cover larger areas than that of glacier ice. Rock glaciers are one of the most widespread forms of permafrost in the European Alps. For example, results of a preliminary inventory showed that there are 1 594 rock glaciers in the Italian Alps (Guglielmin & Smiraglia, 1998). Later, a comprehensive inventory of rock glaciers in South Tyrol resulted in 1 778 only in the eastern sector of the Italian Alps (Monreal & Stötter, 2010).
Hydrological significance of mountain glacial and periglacial environments
Mountains play a central role in collecting and storing the most vital element - fresh water. The streams and rivers that flow from mountain slopes are living bonds connecting mountain and lowland communities. More than half the world's population relies on the fresh water that flows from mountains. The European Alps form the watershed of the Mediterranean Sea, the North Sea, and the Black Sea and are often called the "water towers" of Europe (Schwaiger, 2007). The Alps provide not only enormous quantities of water but also water of excellent quality. Glaciers play an important role in the hydrologic system of the Alps by storing water during cold and wet periods and releasing water in hot and dry phases. The hydrological contribution of rock glacier ice melt is considerably lower, because ice loss in a rock glacier is orders of magnitude slower than from a glacier (Arenson & Jakob, 2010). Rock glacier ice can be old (hundreds to several thousands of years), in contrast to glacier ice, where a continuous mass exchange occurs at much shorter temporal scales (French, 2007). In the current period of marked glacier recession and permafrost degradation, in spite of the differences in hydrological contribution, meltwater discharge from both glaciers and rock glaciers can sometimes cause serious poisoning of freshwater ecosystems by inorganic and organic pollutants.
High-alpine lakes: glacial meltwater input and ecotoxicological risk
Continued, if not accelerated, warming causes enhanced water exchange of high-alpine lakes due to a strong meltwater influx from glaciers and permafrost. In a situation like this, glaciers and glacial meltwater accordingly may represent a secondary source of airborne anthropogenic pollutants deposited to glaciers in earlier time (Schwikowski & Eichler, 2010). For instance, persistent organic pollutants (POPs) are known to accumulate in cold environments because of progressive volatilization from warm source regions and condensation in colder regions (Kallenborn, 2006; Westgate & Wania, 2010). Palaeoecological studies in the Swiss Alps have shown that melting glaciers may represent a secondary source of POPs that were previously deposited to and incorporated into glaciers and are now discharged into high-alpine lakes due to the accelerated melting of glaciers (Bogdal et al., 2009, 2010; Schmid et al., 2011).
In contrast to these examples of organic pollutants of definitely anthropogenic origin, a study in the Italian Alps has shown that pronounced changes in water chemistry of high-alpine lakes may also be caused by meltwater discharge from active rock glaciers into the lakes (Thies et al., 2007). In, Rasass See, a high-alpine lake with an active rock glacier in the catchment, concentrations of the most abundant ions magnesium, sulfate and calcium have reached the 68-fold, 26- and 13-fold values, respectively, during the last two decades. In addition, unexpected high nickel concentrations exceeding the limit for drinking water by more than one order of magnitude have been found in this lake recently. Nickel and other heavy metals are amongst the toxic contaminants that may concentrate through the food chains at its top; high concentrations of heavy metals in water and/or sediments can lead to a number of disorders in aquatic ecosystems (Moore & Ramamoorthy, 1983). Since the adjacent pond, not affected by the rock glacier, has negligible metal concentrations, the current high value of nickel in Rasass See cannot be attributed to catchment geology but rather to meltwaters from an active rock glacier (Thies et al., 2007). These high-alpine water bodies, Rasass See and the adjacent pond, are the study sites of the present project and will be discussed in detail below.
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Climate modellers predict that under different global warming scenarios, by 2100 the near-surface permafrost area will shrink by ca. 90% in the Northern Hemisphere (Lawrence & Slater, 2005). Despite the extent and speed of these changes, very little is known about how melting permafrost will affect global geochemical cycles and freshwater ecosystems. Zones of high ion concentration in areas of ice-rich permafrost are a reservoir of chemicals that can potentially be transferred to fresh waters during thawing. A recent study of arctic lakes (Kokelj et al., 2005, 2009; Mesquita et al., 2008, 2010) has shown that lakes disturbed by retrogressive permafrost thaw slumps have sediments richer in calcium, magnesium and strontium, and greater transparency of the water column than undisturbed lakes. Interestingly, a massive increase calcium and magnesium concentrations has also been observed in two alpine lakes in Italy (Rasass See) and Austria (Schwarzsee ob Sölden) under the influence of melting rock glaciers (Thies et al., 2007). In addition, the results suggest that retrogressive permafrost slumping can significantly affect food webs in lakes through an increase in lake's water clarity and a subsequent increase in biomass of submerged macrophytes (especially aquatic mosses) and benthic invertebrates (Mesquita et al., 2008, 2010).
1.2 Trace metals: their fates and effects in freshwater environment
Trace metals (Ni, Zn, Mn, etc) play an important role in various biological processes as essential cofactors. However, when their concentration exceeds metabolic requirements, they become harmful. Weathering of minerals, industrial effluents, atmospheric precipitation and nonpoint discharges are important sources of high concentrations of trace elements in aquatic ecosystems. In aquatic environments, sediments have the capacity to accumulate and integrate low concentrations of trace elements in water, and can store toxicants after the original sources of contamination are eliminated. Further, metals can enter the food chain and increase in concentration from the environment to the first consumer (bioaccumulation). Some metals become more concentrated in successive trophic levels of a food web (biomagnification). Benthic macroinvertebrates feeding on sediments, algae, macrophyte tissues, and other invertebrates show great bioaccumulation and biomagnification rates (Markert & Friese, 2000).
In Europe, nickel is listed on the European Commission List II (Dangerous Substances Directive) and regulated through the Council of European Communities because of its toxicity, persistence, affinity for bioaccumulation, and potential for biomagnification. The World Health Organization classifies nickel compounds in Group 1 (human carcinogens) (Eisler, 2008). Nickel is also the metal that causes most frequent allergic reactions in humans. Some metals have been reported to produce synergistic and antagonistic interactions whenever in a mixture (Sprague, 1985). Zinc can interact with numerous chemicals, sometimes producing altered patterns of accumulation, metabolism, and toxicity. For example, nickel-zinc mixtures were additive in toxicity to marine copepods (Verriopoulos & Dimas, 1988). Besides, zinc bioavailability and toxicity to aquatic organisms are highest under conditions of low pH, low alkalinity, low dissolved oxygen, and elevated temperatures (Eisler, 2008).
1.3 Chironomids as bioindicators of environmental changes
The dipteran family Chironomidae (non-biting midges; Insecta: Diptera) is one of the most widely distributed insect groups in the world. Chironomids undergo four distinct stages during their life cycle. The larval stage is the longest part in their life cycle (Oliver, 1971). In lake environments, chironomid larvae often represent a major component of the benthic fauna and play an important role in key processes such as food chain dynamics, bioturbation, productivity, nutrient cycling and decomposition (Reice & Wohlenberg, 1993). The taxonomic composition and survival of chironomid larvae depends on a number of different environmental parameters, including temperature, water and sediment chemistry, habitat and food availability. Chironomids respond sensitively to a number of human impacts and are frequently used as bioindicators of ecosystem health (Rosenberg, 1992; Rosenberg & Resh, 1993). Some of these responses are at the population level, for example, loss of sensitive species and changes in the taxonomic composition. Other responses take the form of physical deformities induced by exposure of individuals to toxic environmental pollutants (Warwick, 1991).
The most common deformities of chironomid larvae are the abnormalities in head capsule structures, mainly, in mouthparts and antennae. The incidences of morphological deformities in chironomid populations and/or communities can be related to various sources of anthropogenic stressors and can be used to assess sublethal water and sediment toxicity associated with heavy metals, and other xenobiotics (Vermeulen, 1995). A practice of using larval chironomid deformities as an index of the toxicological contamination of freshwater ecosystems has been established by Warwick (1985, 1988), after initial observations by Sæther (1970) and Hamilton and Sæther (1971) on severely deformed chironomid larvae in Canadian lakes polluted by agricultural and industrial chemicals. Generally, deformities in chironomids are relatively rare; the incidences of deformities at uncontaminated reference sites (background level) have been reported to be commonly less than 1% (Wiederholm, 1984; Swansburg et al., 2002) or completely absent (Bird, 1994). The frequency of deformities in areas contaminated by heavy metals (Ni, Pb, Cd, Zn, Cu, Hg etc.) can range from 1% to about 50% (Martinez et al., 2002; Ilyashuk et al., 2003; Bhattacharyay et al., 2005; Al-Shami et al., 2010), or may be as high as 30-80% in environments extremely polluted by radionuc1ides (Warwick et al., 1987; Williams et al., 2001). Swansburg et al. (2002) and Ochieng et al. (2008) have shown that the occurrence of deformities in chironomid larvae is a sufficiently sensitive proxy measurement to indicate rather low heavy metal contamination. The wide range of frequency morphological deformities observed in chironomid larvae make them a useful tool for impact assessment and the biomonitoring of polluted freshwater ecosystems (Ochieng et al., 2008; Williams et al., 2001).
In Western Europe, the deformities in chironomid larvae have been found in Swedish lakes polluted by heavy metals (Wiederholm, 1984), in Belgian lowland rivers containing high trace metal concentrations (Janssens de Bisthoven et al., 1998), in a wastewater polluted river in northwest Spain (Servia et al., 2000), in streams polluted by acid mine drainage in South Portugal (Janssens de Bisthoven et al., 2005), in a metal contaminated lake in Central Italy (Di Veroli et al., 2010). Up to now, however, reports about mouthpart deformities of chironomids from alpine lakes do not exist.
Remains of chironomid larvae, namely the strongly sclerotized head capsules, are well preserved in lake sediments, and can generally be readily identified. Analysis of subfossil chironomid remains can be used to reconstruct the past chironomid fauna of lakes and to infer past environmental conditions (Walker, 2001). Subfossil chironomid analyses have been used to address questions such as the effects of human-induced eutrophication (e.g., Langdon et al., 2006; Brodersen & Quinlan, 2006), acidification (e.g., Henrikson et al., 1982; Brodin & Gransberg, 1993), and long-term metal contamination (e.g., Ilyashuk & Ilyashuk, 2001; Ilyashuk et al., 2003) on lake ecosystems. The frequency of morphological deformities in chironomid head capsules as a measure of toxic stress of various pollutants in freshwater ecosystems has been successfully used in palaeoecological studies as well (Warwick, 1980a, 1980b; Wiederholm, 1984; Ilyashuk et al., 2003). In addition, chironomids are widely recognized as useful indicators of the natural, undisturbed development of lakes, past climates and environments (e.g., Porinchu & MacDonald, 2003; Walker & Cwynar, 2006).
The duration of all stages of chironomids is strongly dependent on temperature (Pinder, 1986). Many chironomid taxa have temperature-dependent species distributions (e.g., Walker et al., 1991), reflecting the effects of air and water temperatures on all stages of their life cycles. Due to recent advances in multivariate numerical techniques and approaches, quantitative chironomid-temperature inference models have been developed based upon the modern distribution of chironomid species along climatic gradients (e.g., Walker et al., 1997; Brooks and Birks, 2001; Larocque et al., 2006; Heiri et al., 2003; Langdon et al., 2008; Luoto 2009). Chironomid-based temperature reconstruction has received increasing attention in recent years (Velle et al., 2010) and a large number of chironomid-based temperature records are now available from formerly glaciated regions in Europe and North America (e.g., Larocque-Tobler et al., 2010; Axford et al., 2011).
In the Alpine region, most chironomid-based temperature reconstructions are restricted to temperature variations at the northern and western parts of the Alps (e.g., Heiri & Lotter, 2005; Ilyashuk et al., 2009; Larocque-Tobler et al., 2010). The first quantitative Holocene summer temperature reconstruction derived from the chironomid assemblages of a high-mountain lake has recently been published also for the Eastern Alps, Austria (Ilyashuk et al., 2011). The scarcity of quantitative long-term high-resolution climate reconstructions in the Eastern Alps, however, limits our comprehension of climatic patterns and of the biotic response to climatic changes in the region.
2. Project aims
2.1 Main aim of the research project:
By means of chironomid analysis to test the hypothesis that elevated trace metal inputs into high-alpine lakes and relevant ecotoxicological stress in the Holocene were caused by warming-related increases in meltwater discharge from mountain permafrost
2.2 Sub-goals of the project:
comparison of the coincidence of morphological abnormalities and trace metal bioaccumulation in contemporary chironomid populations from two alpine lakes, one with and one without a rock glacier in the catchment;
analysis of trace metal biomagnification through the benthic food chain in the lake affected by metal inputs from the melting rock glacier;
estimation of the causal relationship between the incidence of mentum deformities in living chironomid larvae and the frequency of chironomid mentum abnormalities in subfossils from surface sediments of the lake affected by meltwater from the active rock glacier;
identification of the general Holocene trend in summer temperature and the major warming events in the region by means of chironomid analysis of the sediment sequence recovered from the alpine water body with no permafrost in its catchment;
reconstruction of the changes in chironomid assemblages and the incidence of chironomid mentum deformities throughout the Holocene in the lake affected by discharge of the rock glacier;
study of the cause-and-effect relationships between the Holocene warming events and the incidence of chironomid mentum deformities through elevated discharge of metals from the rock glacier.
3 Study site and background
3.1 Study site
The major focus of the research will be on the study of contemporary and subfossil chironomid assemblages from two water bodies, with and without a rock glacier in the catchment, and situated in a periglacial environment (2682 m a.s.l.) in the Ã-tztal Alps (the Central Eastern Alps) in South Tyrol, Italy, near the Swiss and Austrian borders (Fig. 1). Both water bodies, Rasass See (RAS) and the adjacent pond (RP), are remote, located above the actual and historical timberline and unaffected by direct human disturbance.
Rasass See (RAS)
The lake (46Â°44'50''N, 10Â°27'23''E) has a maximum depth of ca. 9 m and a surface area of 0.015 kmÂ² (max. width is 120 m; max. length is 200 m). Its topographic catchment area is 0.22 kmÂ² and the maximal catchment altitude is 2870 m a.s.l. An active rock glacier occupies 0.038 kmÂ² (17%) of the catchment area and extends on a slope rising above the lake in the south (Thies et al., 2007). The bedrock in the catchment consists of metamorphic bare rocks and talus (paragneisses, micaschists, and orthogneisses). The soil coverage is sparse (ca. 10% of catchment area) and characterized by alpine grass vegetation. Snow accounts for most of the annual precipitation. There is an inflow at the southwest and a well-developed outflow at the northeast of the lake. The present mean lake-water pH is 5.7. Submerged macrophytes represented by mosses occur at the deeper area of the lake. At present, the lake is fishless.
Pond adjacent to the lake (RP)
Next to RAS, just 50 m northwest of the lake, lies a small pond (RP; ca. 45 m Ã- 25 m). It has a maximum depth of ca. 1 m and a surface area of 0.0008 km2 (Thies et al., 2007). The pond lacks well-developed inflows, but has a well-developed outflow. The present mean pond-water pH is 7.5. Water chemistry of RP suggests that the pond is not affected by meltwater and solute fluxes from the active rock glacier (Thies et al., 2007; Koinig et al., unpublished).
3.2 Previous, ongoing and coming studies at the study area: overview
The Biological Laboratory of the Province of South Tyrol, Italy, has been monitoring the RAS limnochemistry since 1985. The Institute of Ecology, University of Innsbruck, also participates in the lake monitoring program.
Pronounced changes in limnochemistry have been registered over the last two decades (1985-2005). The electrical conductivity has increased by from 24 to 450 Î¼S cm-1 (18-fold). The increase in concentration of the most abundant ions was 68-fold for magnesium (from 40 to >2700 Âµequiv L-1), more than 26-fold for sulfate (from 167 to >4400 Âµequiv L-1), and more than 13-fold for calcium (from 133 to >1700 Âµequiv L-1) (Thies et al., 2007). Unexpected high concentrations of nickel, manganese, aluminum, and zinc in lake water have been detected in recent years (Table 1). Unfortunately, long time-series data for trace elements in the lake are absent.
The distinct changes in the water chemistry of RAS can not be explained by an increase of bedrock weathering due to recent climate warming but is attributed to the solute release from the active rock glacier into the lake (Thies et al., 2007). Melt water draining into the lake has caused solute concentrations to increase since the 1990's, while the effects of bedrock weathering and atmospheric deposition on lake water chemistry are considered to be insignificant (Nickus et al., 2010).
Although both RAS and RP catchments are located directly adjacent to each other and are characterized by the same lithology, RP exhibits strikingly different water chemistry when compared to RAS (Table 1). In September 2005, the water conductivity in RP was 110 Î¼S cm-1, i.e. four times less than in RAS. The concentrations of magnesium and calcium were significantly lower than in RAS in 2005 and 2010. The nickel, manganese and zinc concentrations in RP were below the detection limit (<1 Âµg L-1) in the monitoring periods. A striking difference in water chemistry of RAS and RP can be explained only by the fact that RP is not influenced by the RAS rock glacier.
Chemical, diatom, and pollen records were studied from a short sediment core retrieved from RAS in the beginning of the 1990's, within the palaeolimnological study of high-alpine lakes.
This study showed for the first time that the pH of remote alpine lakes is mainly controlled by climate (Psenner & Schmidt, 1992).
Coring of short sediment cores from RAS, covering the last some centuries, and a study of modern benthic communities in RAS and RP were carried out in 2010 within the ongoing Melting project of the Austrian Academy of Sciences (2010-2012; project leader - K.A. Koinig, Institute of Ecology, University of Innsbruck) to investigate changes in geochemistry, and diatom and chironomid species over the last centuries.
This study revealed that the benthic invertebrate fauna of both water bodies includes the typical elements of mountain oligotrophic lakes: Chironomidae, Oligochaeta, and Tipulidae. Two taxa, Micropsectra radialis-type and Pseudodiamesa nivosa, dominate the contemporary chironomid assemblages in both water bodies. In addition, a rather large population of the beetle Agabus sp. (Coleoptera: Dytiscidae) was recorded in RAS. Under fishless and clear-water conditions, this large-bodied invertebrate predator feeding on smaller-bodied chironomids and oligochaetes is at the top of the benthic food chain in the lake.
A pilot analysis of RAS sediment samples revealed a relatively high incidence of mentum deformities in Pseudodiamesa nivosa head capsules. At least two types of mentum deformities, bifid teeth and mentum gap, were found (Fig. 2). These finding give evidence of the toxic effect of nickel and/or other trace elements to chironomids in RAS. It is notable that both types of mentum deformities were also observed in the head capsules of Chironomus sp., the dominant chironomid species in a Russian subarctic lake that received wastewaters from a copper-nickel smelter during six decades (Ilyashuk et al., 2003).
Coring of a long sediment core (covering the Holocene) is planned in summer 2011 within the future project Nickel Control (Project of the Autonomous Province Bolzano/Bozen, 2011-2015; project leader - K.A. Koinig, Institute of Ecology, University of Innsbruck) to investigate changes in geochemistry, mineralogy, and diatoms over the Holocene. Note: Chironomid analysis is not funded within this project.
4.1 General research questions and methodology
The general research questions and main objectives of this study can be summarized as follows:
Are there substantial differences in concentrations of trace metals in sediments and bioaccumulations of these elements by chironomids between RAS, which is strongly influenced by the rock glacier, and RP, which has no rock glacier in its catchment?
Concentrations of trace elements will be measured and compared in samples of surface sediments and living chironomid larvae collected from both water bodies. Calculating the bioaccumulation factors of trace elements in chironomids will allow me to determine and compare the extent to what elements are concentrated in invertebrate tissues in these water bodies.
Does trace metal biomagnification occur through the benthic food chain in the lake affected by permafrost discharge?
Concentrations of trace metals will be measured in the population of the beetle Agabus sp. from RAS, the top predator of the benthic food chain in this lake. A comparison of trace metals measured in chironomid and beetle tissues from RAS will be used to assess the biomagnification factor of trace metals through the benthic food chain.
What are the differences in the incidence of mentum deformities in contemporary chironomid larvae between the water bodies with and without a rock glacier in catchments? How is the incidence of mentum deformities in living chironomid larvae reflected in their subfossil assemblages?
The incidence of mentum deformities will be quantified in living and subfossil chironomid assemblages from surface sediments of both water bodies; this will yield a robust basis to analyze historical changes in the occurrence and frequency of mentum deformities.
How are the differences in feeding strategy and food spectrum of chironomid taxa reflected in their bioaccumulation of trace elements and the incidence of mentum deformities?
The contemporary chironomid assemblages of both water bodies are dominated by two taxa, Micropsectra radialis-type and Pseudodiamesa nivosa. Larvae of these chironomid taxa differ in feeding strategies and food spectra (Pagast, 1947). M. radialis-type larvae are collectors, feeding on fine organic detritus particles whereas P. nivosa larvae are omnivorous, i.e. feeding on detritus and/or on smaller chironomids and other small aquatic invertebrates. The working hypothesis for this investigation is that the bioaccumulation of trace elements and the incidence of mentum deformities are higher in the omnivorous P. nivosa larvae than in the detritivorous M. radialis-type.
Which periods of the Holocene can be associated with the warming events causing elevated permafrost discharges in the region?
The Holocene chironomid-based temperature will be reconstructed from a long sediment core taken in the deepest part of RP, the water body where chironomid responses to climatic changes have not been affected by meltwater fluxes from the active rock glacier. This reconstruction as well as other climatic inferences from the region will allow me to define the general Holocene trend in summer temperature and the major warming events in the past
Are the Holocene climate shifts the major driving force for changes in the sediment trace metal concentrations and the incidence of chironomid mentum deformities in the lake affected by permafrost discharge?
A long sediment core covering the Holocene history of RAS, subsequent geochemical analyses and diatom-based pH inferences will be provided by the project Nickel Control of the Autonomous Province Bolzano/Bozen (2011-2015; project leader - K.A. Koinig). Analysis of changes in the chironomid assemblages and the incidence of chironomid mentum deformities during the Holocene from this core will allow me to define periods of unfavorable ecotoxicological situations in the lake. Applying nonlinear structural equation modelling, I will analyse the cause-and-effect relationships between the past warming events, the diatom-inferred pH values, increases in the sediment trace metal concentrations and the incidence of chironomid mentum deformities caused by elevated permafrost discharges into the lake.
4.2 Laboratory and numeric methods
Invertebrate and sediment sampling
Qualitative samples of living chironomid larvae for the measurement of trace elements and the incidence of mentum deformities will be collected using a biological bottom dredge with a mesh size of 250 Î¼m. A Surber Sampler with a mesh size of 500 Î¼m will be applied for collection of beetles in RP. Surface sediment samples (0-1 cm depth) will be retrieved at the deepest part of both water bodies with a modified Kajak corer (UWITEC; http://www.uwitec.at/). A long sediment core will be taken in the deepest part of RP with a Russian peat corer and transported to the Institute of Ecology, University of Innsbruck. The uppermost loose sediments will be sampled with a modified Kajak corer and subsampled in the field. The Holocene sediment core from RAS will be provided by the above cited Nickel Control project.
Trace metals in surface sediments and invertebrates: sample preparation and analysis
In the laboratory, the collected chironomid larvae, predominantly 3rd and 4th instars, will be sorted and the dominant species (presumably M. radialis-type and P. nivosa) will be separated and counted under a stereomicroscope. All invertebrates, the separated chironomid larvae of dominant species from RAS and RP, and beetles Agabus sp. (also counted) from RAS, will be cleaned with distilled water, placed in Petri dishes and kept at 4Â°C for 24h in order to purge the guts. Thereafter they will be removed and rinsed slightly with distilled water and then frozen pending analysis.
In preparing the samples of invertebrates and surface sediments for total metal analysis, a procedure by Lynch et al. (1988) will be applied. The samples will be oven-dried for 24h and ca. 0.5 g DW from every sample (done in triplicates) will be used for the analyses. The samples will be dissolved with concentrated nitric acid using microwave digestion technique and metal concentrations will be then measured via inductively-coupled plasma optical emission spectrometry (ICP-OES) at the Institute of Mineralogy and Petrography, University of Innsbruck. The detection limits for many metals will be of ca. 0.5 Âµg g-1.
The sediment bioaccumulation factor (BAF) of trace metals in aquatic invertebrates, according to Harraby and Clements (1997), will be used to determine the extent to which metals are concentrated in tissues of invertebrates. The bioaccumulation factor will be calculated as:
where Morg is the element mass fraction in the organism, Î¼g g-1 DW),
and Msediment is the element concentration in the sediment, Î¼g g-1 DW.
Bioaccumulation will be considered efficient for cases where bioaccumulation factors are >1. The same approach will be applied to estimate the trace metal biomagnification through the benthic food chain in RP.
Chironomid taxonomy and incidence of mentum deformities
Taxonomic identification of the contemporary and subfossil chironomids will be primarily based on descriptions of genera and species groups provided in Wiederholm (1983), Schmid (1993) and Brooks et al. (2007).
The 4th and 3rd instars of chironomid larvae from the dredge samples and their remains from the surface sediment samples will be sorted under a stereomicroscope in the laboratory. At least 100 head capsules of every dominant species (presumably M. radialis-type and P. nivosa) in the contemporary and surface subfossil material from both water bodies will be examined for mentum deformities under a compound microscope, generally at 400Ã- magnification. Mouthparts of chironomid larvae damaged during the cleaning and mounting process usually have abrupt breaks that are readily visible and easily distinguishable from deformed structures (Dermott 1991). The incidence of mentum deformities in this study will be evaluated using the toxic score index (TSI) proposed by Lenat (1993). According to Lenat (1993), the mentum deformities can be categorized into three classes: Class I includes slight deformities which are difficult to separate from the "chipped" teeth; Class II consists of larvae with more conspicuous deformities, such as extra teeth, missing teeth, large gaps, and distinct asymmetry; and in Class III are included the larvae that suffer severe deformation, including at least two Class II characters. According to Lenat (1993), the TSI can be computed as follows:
Core subsampling and dating
In order to attain a high temporal resolution, the RP core will be subsampled in 0.5 cm steps. The sediment samples will be stored cool (4Â°C) until further analyses at the Institute of Ecology, University of Innsbruck. The chronology of the sediment sequence will be based on 210Pb and 137Cs dating, eight-ten AMS radiocarbon dates obtained on plant macrofossils and on numerical age-depth model. For 210Pb and 137Cs dating, sediment samples will be submitted to the University of Waterloo, Canada. The AMS radiocarbon dating will be carried out at the Poznan Radiocarbon Laboratory, Poland. Subsampling, dating and age-depth modelling of the Holocene sediment sequence from RAS will be provided by the above cited Nickel Control project.
Chironomid remains will be extracted from the sediment samples following the standard procedure described by Walker (2001). At least 120-150 chironomid head capsules will be counted, identified, and examined for mentum deformities from each subsample. The incidence of mentum deformities in the dominant species will be evaluated as described above. Stratigraphic diagrams will be produced with the software TGView (Grimm, 2004). The stratigraphy will be zoned with the constrained cluster analyses, and the number of statistically significant zones will be determined with the broken-stick approach (Bennett, 1996).
The Holocene climatic pattern at the study site
The chironomid record from the RP sediment core will be used to reconstruct the Holocene mean July air temperature (TJuly) by applying a chironomid temperature transfer function based on subfossil chironomid assemblages in the surface sediments of 100 lakes at altitudes from 409 to 2815m a.s.l. in the Alpine region (Heiri et al., 2003; Heiri & Lotter, 2008). A locally weighted regression smoothing will be used to highlight the major trend in the reconstructed values and to identify the warming events responsible for the elevated meltwater discharge from the RAS rock glacier. In addition, results of the Holocene TJuly inferences from another remote high-mountain lake, Schwarzsee ob Sölden, situated only 45 km apart at similar altitude (Ilyashuk et al., 2011) will be used as well.
Classical and multivariate (e.g., DCA, PCA, CCA, RDA) statistics will be applied to the contemporary and fossil invertebrate assemblage and geochemical data to summarize, compare and interpret the major patterns, differences and trends in the chironomid assemblages and ecotoxicological risks at the study site in space and time. Nonlinear structural equation modelling based on partial least-squares regression will be applied to estimate the cause-and-effect relationships between the past warming events, the diatom-inferred pH values, and increases in the sediment trace metal concentrations and the incidence of chironomid mentum deformities through elevated permafrost discharges in the lake affected by the active rock glacier.
4.3 Dissemination of the results
Results will be published in highly ranked international peer reviewed journals, aimed to reach a broad readership in the limnological, climatological and environmental fields.
Results will be presented as lectures and posters at national and international scientific workshops and conferences.
Given the public interest in climate change, melting permafrost in the Alps and the quality of alpine headwaters, I will furthermore strive to disseminate my scientific results to the public, by meeting with correspondents of newspapers, journals, radio and television.
4.4 Work schedule
The project will be carried out during 24 months. For achievement of the sub-goals and the main goal, the work within the project falls roughly into four parts. First, analysis of contemporary invertebrate assemblages and surface sediment geochemistry from RAS and RP. The second part is dedicated to coring and chironomid analysis of a long sediment sequence from RP (Core RP), and the third part - to chironomid analysis of a long sediment core from RAS (Core RAS), comparison and evaluation of all data. The fourth part is dedicated to dissemination of experience and new knowledge. An overview of the planned work schedule is given in Table 2.
5 Relevance and benefits of the project
In recent years, concern has grown over the increased contamination of remote areas, particularly the Arctic and mountain regions, and the unprecedented level of pollutants observed in areas previously considered to be pristine (Rose et al., 2005). Understanding how climate change influences mountain lakes both directly and indirectly by modifying catchment processes and the behavior of pollutants is central to ongoing and future research (Catalan et al., 2009; Battarbee, 2010; Nickus et al., 2010). Special emphasis is now placed on problems associated with the interactions between climate change, the melting of rock glaciers, enhanced pollutant release, and ecosystem health (Nickus, 2007; Battarbee et al., 2009). Melting mountain permafrost and rock glaciers are regarded to be the source for heavy metals released into alpine aquatic ecosystems under the influence of rapid warming. However, the mechanism behind the interactions and potential ecotoxicological implications remain obscure. In this connection, the proposed study aimed at reconstruction of the climate and environmental history of the alpine lakes will provide insight into natural background variability and contribute to better understanding of climate-related processes influenced mountain lakes. The implementation of the project will bring actual knowledge about warming-related processes of excessive metal release from melting rock glaciers in the Alps and associated ecotoxicological consequences.
The proposed project will focus on a reconstruction of changes in the structure of chironomid assemblages and the incidence of morphological deformities in chironomid subfossils over the Holocene at two alpine lakes situated in a periglacial environment. The obtained results will provide essential information about the onset and the degree of metal pollution from melting permafrost during warm periods in the past.
Analysis of the trace metal bioaccumulation in contemporary chironomid populations and biomagnification through the benthic food chain will make it possible to gain independent information about the extent of current metal pollution and relevant ecotoxicological effects in the periglacial water bodies.
Given the scarcity of quantitative long-term high-resolution climate reconstructions in the Eastern Alps, the chironomid-based summer temperature reconstruction performed within the proposed project from an alpine lake not affected by a rock glacier will play a significant part in our comprehension of climatic patterns and the biotic response to climatic changes in the region. The obtained results will provide background knowledge to compare the magnitude of recent climate warming and other warm periods in the past and to predict the effects of possible future climate changes on lake ecosystems in the Alpine region.
In the context that high alpine headwaters are generally regarded as pristine and are widely used as drinking water resources, the results of the proposed research can be very important for freshwater ecosystem management and the administration responsible for drinking water supply in Tyrol.
The project implementation will provide me an opportunity to co-operate with noted scientists from the Institute of Ecology, University of Innsbruck, whose experience and knowledge in the area of limnological and palaeolimnological studies are very valuable. The fact, that the long core from RAS will be provided by another project (Nickel Control, as cited above), is very favorable for this proposal.
6 Research site
6.1 Host scientific expertise in the field
The project will be carried out in the Institute of Ecology, University of Innsbruck. The Institute of Ecology is part of the interdisciplinary research area Alpine Space - Man & Environment, the main purpose of which is to study the interaction between man and environment in alpine regions. The Limnology Unit of the Institute of Ecology has extensive background in limnological research of alpine lakes on a range of time-windows ranging from sub-decadal (modern aspects of limnochemistry and microbial ecology, plankton ecology and photobiology, benthic communities) to geological timescales (palaeoclimatic and palaeolimnological reconstructions). The Research Group Biogeochemistry, Palaeolimnology & Extreme Ecosystems focuses on the biogeochemical cycles of nutrients and pollutants in lakes, on the long-term history of lake ecosystems, on groundwater microbiology, on snow and ice as habitats of active (micro-)organisms, and also on theoretical and philosophical aspects of aquatic ecology. Benthic invertebrate communities as indicators of climate change are intensively studied by the Research Group Alpine Stream Ecology & Invertebrate Biology focused on running waters in alpine and polar regions. Over the last decade, research of the Unit particularly focused on global change impacts on high alpine lakes including the effects of increased air temperature, UV radiation, and shortened duration of the ice- and snow-covered periods (Psenner, 2003; Füreder et al., 2006; Sommaruga, 2007; Psenner et al., 2008). The Unit's recent research efforts also include palaeolimnological reconstruction of past climate and environmental change in the Alps based on lake sediments using proxy-indicators as different as sediment geochemistry, mineralogy, pollen, diatoms, and chironomids (Koinig et al., 2002, 2003, submitted). A full account of Limnology Unit's activities and publications is provided at http://www.uibk.ac.at/ecology/forschung/forschung.html.en
Overall, the Limnology Unit, including technical staff, is a strong research team and this ensures professional advice on a very broad range of neo- and palaeolimnological research issues. The Unit is also well equipped for broad range of neo- and palaeoecological research activities, including obtaining lake sediment records, sampling contemporary benthic invertebrates, and microscopy facilities for chironomid analysis.
6.2 Originality and innovation
Within the proposed project, for the first time, the influence of a rock glacier on a lake ecosystem in the Alps will be studied by mean chironomid analysis from a Holocene sediment record.
The investigation of the incidence of mentum morphological abnormalities in chironomid subfossils at lake affected by an active rock glacier discharge during the Holocene will be innovative for the Alpine region.
Special attention will be placed on studying living chironomid larvae as indicators of ecosystem health, i.e. an assessment of sublethal environment toxicity associated with metal release from melting alpine permafrost.
Assessment of the trace metal bioaccumulation and biomagnification along the benthic food chain will be a new approach for assessing impacts of metals on living organisms in the lake affected by solute fluxes from mountain permafrost in the Alps and for determining the potential ecotoxicological hazards associated with the environmental contaminants.
The investigations of long-term climate-induced changes in alpine headwaters in the vicinity of an active rock glacier by chironomid analysis will be original for the host institute and will help to gain more information about ecotoxicological risks to periglacial lakes caused by melting permafrost. Chironomid-based reconstructions will add and specify knowledge obtained from other single-proxies within other research projects.