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Recent phytoplankton changes in a restored mountain lake as a response to nutrients and climate
Full text linkSedimente von vier Hochgebirgsseen unter unterschiedlichem Einfluß von Permafrost
Full text linkA paleolimnological survey of high mountain lakes in North- and South-Tyrol was conducted within the Interreg project Permaqua (permafrost and its effects on water balance and mountain water ecology) aiming at econstructing the ecological evolution of lakes in permafrost regions since the end of the Little ice Age (~1850), and to investigate possible effects of permafrost thawing on lake geochemistry and biology. Sediment
cores from four lakes located above ~2500 m a.s.l. on crystalline bedrock were radioistopically dated (210Pb, 226Ra, 137Cs and 241Am and 14C) and analyzed for lithological (wet density, water and organic content), geochemical (principal elements and heavy metals), and biological (diatom abundance and speceis composition) proxies. All the cores studied showed lithological and biological changes between the end of the Little Ice
Age and the first decades of the 20th century. Concentrations of heavy metals increased in the studied cores during the last ~ 150 years and reached highest values after the 1990s. On the contray, changes in diatom species composition which typically characterize many lower lakes of the northern hemisphere after the economic development in the 1960s were not recorded in the lakes investigated. However, it is not possible to explain these changes as completely related to the presence of active rock glaciers in the lake catchments. The long-term changes of biological and chemical indicators observed in the studied sediment cores appear to be the results of a set of combined factors, such as geochemistry, weathering, or catchment characteristics
Gli archivi ambientali nei rock glacier, nelle paludi e nei sedimenti lacustri
Full text linkSono definiti archivi ambientali i depositi di materiale che possono essere datati permettendo così una ricostruzione
delle condizioni ambientali in determinati periodi del passato. I sedimenti lacustri e i depositi di torba, ad esempio,
sono archivi ambientali ad alta risoluzione che ci forniscono informazioni molto dettagliate sulle condizioni climatiche
nel periodo della loro formazione. I rock glacier attivi ci forniscono informazioni sulle condizioni del permafros
Evidence of rock glacier melt impacts on water chemistry and diatoms in high mountain streams
No full textA first study of high alpine freshwaters at Hochebenkar and Krumgampen (Oetztal Alps, Tyrol, Austria) revealed pronounced differences in the concentration of major ions, heavy metals, species composition and
biodiversity of epilithic diatoms in streams emerging from two active (i.e. ice containing) rock glaciers and in adjacent unaffected reference streams. The clear-water streams impacted by active rock glaciers are characterized by high electrical conductivity (EC) values, but differ in acidity, heavy metal concentrations and by the proportion of circumneutral and acidobiontic diatoms. On the contrary, all reference streams exhibit low EC and circumneutral to slightly acidic pH values characteristic for surface waters on bedrock composed of paragneiss and micaschist, with no detectable heavy metals and a diatom composition typical for high altitude softwater streams. The high ion concentrations in streams emerging from rock glaciers are attributed to a seasonally increasing release of melt waters from active rock glacier
Sediments of high mountain lakes as records of long-term environmental changes
No full textA limnological and paleolimnological survey of high mountain lakes in North- and South-
Tyrol was conducted within the Interreg Project Permaqua (Permafrost and its effects on
water balance and mountain water ecology) aiming at reconstructing the ecological
evolution of lakes in permafrost regions since the end of the Little Ice Age (~1850), and
investigating potential effects of permafrost thawing on lake geochemistry and biology. In
fact, recent studies conducted in the Central Alps outlined potential effects of rock glacier
thawing on the ecological quality of headwaters. Sediment cores from four lakes located
above ~2500 m a.s.l. on crystalline bedrock were radioisotopically dated, and analysed for
lithological, geochemical, and biological proxies. All cores studied showed major lithological
and biological changes between the end of the Little Ice Age and the first decades of the
20th century. Concentrations of heavy metals increased in the studied cores during the last
~150 years and reached highest values after the 1990s. On the contrary, changes in diatom
species composition which typically characterize many low-land lakes of the northern
hemisphere after the economic development in the 1960s were not recorded in the lakes
investigated. Although it is not possible to explain the observed changes as directly related
to the presence of active rock glaciers in the lake catchments, it seems likely that long-term
changes of biological and chemical indicators observed in the studied sediment cores are
due to a combination of factors, such as geochemistry, weathering, or catchment
characteristics
Temperature modulated effects of nutrients on phytooplankton changes in a mountain lake
No full textPiburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend appeared since the early 2000s. We hypothesize that recent phytoplankton changes 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 lake
Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake
No full textPiburger 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 lake
Blockgletscherabflüsse im Äußeren Hochebenkar: Hydrologie, Wasserchemie und Kieselalgen
Full text linkHochebenkar rock glacier is one of the most
intensively investigated active rock glaciers of the Austrian Alps with first measurements of flow velocities by Pillewizer in 1938. Since 2007 the discharge of the rock glacier outflows has been studied quantitatively by automatic gauges and chemical analysis is used to determine the water quality of the discharge. Runoff of an active rock glacier reveals a high
seasonal variability with varying contributions of snowmelt, precipitation events, groundwater and melting of the internal ice body. Peak values of runoff generally occur in late spring caused by the melting of the seasonal winter snow pack. The major melt phase is characterised
by a high daily course of runoff values
with maxima at night and minima in the late
morning. Cold spells generally interrupt the
melt phase several times a year causing runoff and its daily course to decrease. Secondary peaks are linked to summer precipitation events when quickflow causes runoff to increase. By late summer or fall, runoff generally decreases and often ceases in November when air temperatures fall below zero.Solute concentrations tend to increase between the onset of major snowmelt and fall.
Electrical conductivity – as a measure of the
total ion content of a solution – varies from
about 100 μS/cm in early summer to some 400 μS/cm in fall at the automatic gauge run by the Hydrographic Service of Tyrol (2,220 m). Conductivity values may even be higher and reach > 500 μS/cm when measured directly
at the rock glacier outflow. Heavy summer
precipitation events cause a dilution of
the highly concentrated rock glacier streams,
and secondary runoff peaks coincide with
conductivity minima. The same accounts for
those ions that dominate the ion content of
the brooks, i.e. sulfate, calcium and magnesium. The seasonal course of the solute concentrations reflects the varying contributions of snowmelt, precipitation, groundwater and melting of the internal ice body. So called reference brooks, i.e. brooks without any impact of an active rock glacier revealed substance concentrations that ranged one order of magnitude below values found in rock glacier impacted brooks.
Epilithic diatom assemblages were investigated in rock glacier impacted and not impacted streams at two sites (Hochebenkar and Krummgampen) with varying chemical properties. First results indicated that rock glacier outflows may affect species composition and abundance of epilithic diatoms. In particular, increasing acidity caused the substitution of circumneutral taxa by acidophilous and acidobiontic tax
Die Kieselalgen (Diatomeen) in Blockgletscher-beeinflussten Hochgebirgsbächen/Diatoms in high altitude creeks affected by rock glaciers
No full textPermafrost ist in Südtiroler Höhenlagen ober 2500 m relativ stark verbreitet. Ein typisches Landschaftelement des alpinen Permafrosts sind die Blockgletscher. Sie reagieren empfindlich auf die Klimaerwärmung und ihr Schmelzwasser enthält oft erhöhte Werte von Schwermetallen. Ziel dieser Studie ist es festzustellen, ob sich die Zusammensetzung der Kieselalgen in blockgletscherbeeinflussten Bächen von unbeeinflussten Bächen, so genannten Referenzbächen, unterscheidet.
Im Rahmen des Interreg IV Projektes PERMAQUA erfolgten 2012 in drei Projekt-Untersuchungsgebieten, und zwar im Ultental (Rossbänke), Schnalstal (Lazaun) und Reintal (Napfengletscher) die Beprobungen von Blockgletscherquellen und Blockgletscherbächen sowie von unbeeinflussten Referenzbächen.
Temperatur, Leitfähigkeit und Sauerstoffgehalt wurden vor Ort gemessen. Zusätzlich wurden im Labor pH-Wert, Hauptionen und Nährstoffe, sowie die Konzentration von Schwermetallen untersucht. Für die biologische Charakterisierung der Quellen und Bäche wurden Kieselalgen sowie Makro- und Meiozoobenthos untersucht.
Die untersuchten Gewässer sind aufgrund ihrer Höhenlage keiner direkten anthropogenen Belastung ausgesetzt. Die permafrost-beeinflussten Bäche unterscheiden sich jedoch sowohl in der Zusammensetzung der Kieselalgen als auch in ihren chemisch-physikalischen Eigenschaften von den Referenzgewässern
Coherent response of Alpine lakes to combined global warming and airborne contamination as revealed by sediment records
No full textAlpine lakes are considered as sentinels of climate change and ideal research-objects to investigate the ecological effects of global warming combined with anthropogenic airborne contamination. Nonetheless, the evaluation of long- term environmental and ecological lake evolution is hampered by scarce monitoring data and must rely on the palaeolimnological approach. We present the results of a sediment study, conducted on a set of mountain lakes of the southern Central-Eastern Alps, aimed at investigating the effects of the current Alpine deglaciation on lake habitat and biodiversity, and at revealing signs of airborne contamination. Radiometrically dated short cores were analysed for lithological (water and organic content), biogeochemical (C and N stable isotopes and CN content of bulk organic matter) and biological (subfossil diatoms) proxies. Lake productivity and biodiversity show clear responses to the end of the Little Ice Age and to the warming acceleration since the 1980s. The isotopic signature of sediment organic matter outlines a coherent increase in nitrogen atmospheric deposition during the last 100-150 years, in agreement with results from many lakes in the northern hemisphere. The results suggest a possible synergy between global warming and nitrogen enrichment in driving the biological changes recently observed in all the study lakes
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