Ulrike Nickus

The Impact of Climate Change on Lakes in Central Europe

◦by 2071‐2100. The associated projections for the rainfall give even more cause for concern with the reductions in some areas approaching 50% in summer. In this chapter we analyse impacts of changing weather conditions on lakes in Central Europe. Long-term data sets from a number of lakes are used to link measured variables to climate signals. Particular attention is paid to the lakes in the perialpine region which are known to be very sensitive to short-term changes in the weather (Psenner, 2003; Thompson et al., 2005). Here, the topography and the steep orography enhance the water cycle, and result in flooding, debris flows, avalanches, vertical plant migration etc. The Alps also form a barrier to the mass movement of air and are responsible for the sharp climatic divide between Atlantic, Continental and Mediterranean influences. Central Europe is a variously and vaguely defined region. Rather than a physical entity, it is more a reflection of a shared history. The results summarized here are based on the analysis of long-term climatological and limnological data from the countries shown in Fig. 20.1. These include Germany (DE), Poland (PL), the Czech Republic (CZ), Slovakia (SK), Switzerland (CH), Lichtenstein (LI), Austria (AT) and Hungary (HU). The Central European countries are geographically diverse with landforms ranging from the North-German Lowlands, through the Alps to the Hungarian plain. The pannonian plain in the eastern part is also a major climatic ‘crossing point’ and is affected by the Eastern-European continental, the WesternEuropean oceanic and the Mediterranean influence.

Seasonal development of ion concentration in a high alpine snow pack

With samples taken from 49 snow pits on a glacier in the Tyrolean Alps the seasonal development of concentration and total deposition of sulfate, nitrate, ammonium, chloride, sodium and calcium was studied. Concentrations are of the order of a few microequivalents per liter in the winter months including March and rise sharply during April. It is shown that this increase is connected to the intensity of atmospheric convection. All ions were eluted from the snow pack at a rapid rate when snow melt set in, leading to June concentrations comparable to those of early winter. With this general background common to all, the behavior of individual ions, notably ammonium and calcium, is discussed.

TRENDS IN THE WATER CHEMISTRY OF HIGH ALTITUDE LAKES IN EUROPE

Here we present the chemical trends of seven high altitude lakes, analysed within the AL:PE and MOLAR Projects of the EU (1999) and selected on the basis of the availability of complete and reliable data for the period 1984–1999. The lakes are representative of the Scandinavian Alps, the Cairngorm Mountains in Scotland, the Alps and the Pyrenees. Significant trends were identified for some indicators of acidification, for instance pH and alkalinity, but not all lakes reacted similarly to decreasing depositions of sulphate and base cations. Differences in lake response are discussed in relation to recent variations of atmospheric deposition chemistry and associated changes in climatic conditions. Beside individual variations of the studied lakes, depending, among other things, on altitude and morphology, catchment characteristics and climate trends play a major role for the reaction of high altitude lakes on changes in atmospheric depositions.

Major element chemistry in alpine snow along a north-south transect in the Eastern Alps

The regional distribution of ion concentration and ionic load along a meridional transect in the Eastern Alps was investigated in 1993 and 1994 taking samples of the high alpine snow pack at six sites. High concentrations of atmospheric trace substances seemed to be related to high rates of snow accumulation. Zugspitze at the northern, and Careser Glacier at the southern margin of the Alps and Hintereisferner at the main divide had higher concentrations of sulfate and nitrate than adjacent sites. The pattern found in the ion concentrations was accentuated in the deposition rates with maximum ionic loads up to three times higher than the minima at the dry sites. Sulfate concentrations and sulfate to nitrate ratios were higher in the southern part of the transect.

Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake

Piburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication in the 1990s with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend from the early 2000s onwards. We hypothesize that recent changes in phytoplankton biomass and functional structure are triggered by changes in lake nitrogen and silica concentrations, and we expect climate-related factors to modulate the trophic status of Piburger See. Phytoplankton data were analyzed by non-metric multidimensional scaling (NMDS) applied on biovolume of morpho-functional groups, combined with correlation analyses of environmental variables. Since the 2000s, short-term changes in phytoplankton of Piburger See were explained by varying concentrations and ratios of nitrogen and silica, while the inter-annual variability in phytoplankton species composition was rather attributed to superimposed rising water temperature and lake thermal stability. Our results underline the co-dominant role of phosphorus and nitrogen as phytoplankton drivers in lakes that experience periods of nitrogen limitation. The combined impact of nutrients and climate on phytoplankton development can thus mimic short-term increases in the trophic level of less productive lakes.

DEPOSITION AND STORAGE OF SPHEROIDAL CARBONACEOUS FLY-ASH PARTICLES IN EUROPEAN MOUNTAIN LAKE SEDIMENTS AND CATCHMENT SOILS

Spheroidal carbonaceous particles(SCPs) are produced only from high temperaturecombustion of fossil-fuels. In mountain lakesystems, they provide an unambiguous indicator ofatmospheric deposition. In order to comparedepositional fluxes of SCPs between mountainareas experiencing various pollutant regimes,intensive bulk deposition sampling was undertakenat five sites across Europe. Catchment soil coresand lake sediment cores were also taken at eachsite to compare SCP storage over the post-industrial period. Atmospheric, sediment and soilSCP data showed similar patterns. Highestcontamination was found in Scotland, Slovakia andSpain with the Austrian site intermediate and themid-Norwegian site least contaminated. A highproportion of accumulated SCPs were found to bestored in catchment soils at each site.Therefore, a significant increase in soilerosion, possibly as a result of future climatechange, could lead to the input of largequantities of catchment stored SCPs and, byimplication, other atmospherically depositedcontaminants to the lake ecosystem.

Application of static critical load models for acidity to high mountain lakes in Europe

Critical load models for acidityprovide a measure of the sensitivity of surfacewaters to acid deposition, and can be used todetermine critical load exceedance and potentiallong-term harmful effects. Three static models,the Steady-State Water Chemistry model, diatommodel and First-order Acidity Balance model, arehere applied to 11 high mountain lakes in Norway,Scotland, the Alps, the Pyrenees and the Tatras.Between five and seven of the lakes show criticalload exceedance, depending on the model used.Nitrogen as well as sulphur deposition isimportant in causing exceedance. Since soil andvegetation cover are generally sparse, geologyand lake retention time appear to be key factorsin the determination of critical load. Retentionof nitrogen is observed, but it is unclearwhether this occurs within the lake or theterrestrial part of the catchment.

The redox speciation of iron in two lakes

The redox speciation of iron was determined by voltammetry in two lakes (Blelham Tarn, a lowland lake, and Gossenkollesee (GKS), a mountain lake). The reactive iron (FeR) concentration was ~40 nM in the epilimnion of Blelham Tarn, and up to 37% of this occurred as iron(II). In contrast, the FeR concentration in GKS was much lower at ~1 nM, similar to concentrations found in the open ocean. Under ice cover the iron(II) concentration peaked in GKS just below the Chl-a maximum, amounting to 50% of FeR. In July, the Chl-a concentration was lower, and iron(II) was present throughout the water column at ~30% of FeR. This work has demonstrated that iron occurs to a large extent as iron(II) in lake waters, of greatly differing conditions, in spite of the presence of oxygen; the main cause for this is not clear because the iron(II) may have been produced biologically or photochemically (or both). This, and the unexpectedly low reactive-iron concentrations in the transparent mountain-lake waters, warrant further work to evaluate their importance to the microorganisms in the lakes.

Ion chromatographic determination of anions and cations at ultra-low concentrations in Alpine snow

Abstract As part of the international project ALPTRAC the acid deposition at high Alpine sites was investigated. This paper reports on experiences with ion chromatography in the μg/kg range that was characteristic for the samples, and on the sample contamination and its sources. Particular emphasis is given to a drop of ionic concentration from the first to the second injection drawn from the vials of the automated sampler. This drop was observed at detection ranges of 3 μS/cm and less and amounted to 17 μg/kg for sodium, 14 μg/kg for chloride and 1 to 4 μg/kg for magnesium, calcium and sulphate.

Ion chromatographic determination of lithium at trace level concentrations. Application to a tracer experiment in a high-mountain lake.

The water residence time of a high-mountain seepage lake in the Austrian Alps was derived from the flushing rate of a tracer substance. A diluted lithium chloride solution was injected into the lake during holomictic conditions in order to favour the homogeneous distribution of the tracer. The exponential decline of the mass of lithium in the lake revealed a water residence time of 1.5 to 3 months for summer and almost no lake water exchange during winter. Lithium concentrations ranged from background values of 0.06 microg l(-1) to about 3 microg l(-1) immediately after the tracer injection. Lake water samples were analyzed with ion-exchange chromatography using a Dionex device with a CS 12A separation column. The method detection limit determined according to the definition of the US Envirinmental Protection Agency amounted to 0.009 microg l(-1).