Effects of long term nutrient and climate variability on subfossil Cladocera in a deep, subalpine lake (Lake Garda, northern Italy)

• While subfossil Cladocera remains are considered to be a reliable proxy for tracking historical lake development, they have hardly been studied in large and deep lakes. In this study, subfossil Cladocera remains from Lake Garda in northern Italy were analyzed to track environmental changes since the Middle Ages. One core was retrieved from the largest sub-basin of Lake Garda (Brenzone, 350 m deep) and another two were retrieved from the profundal and littoral zones of a smaller sub-basin (Bardolino; 80 and 40 m deep, respectively). The species distribution of Cladocera remains in recent sediment layers was similar to that of the contemporary assemblages observed in the water column. The deepest sections of the three cores were characterized by species sensitive to water temperature, suggesting a lake response to the major climatic events that occurred during the late Holocene. A common and evident change in Cladocera assemblages was observed in the studied cores during the 1960s, when planktonic taxa such as Daphnia spp. and Bosmina spp. became the dominant group at the expense of littoral taxa. Despite the highly coherent general pattern within Cladocera assemblages, the cores showed minor differences, which were attributed to different morphological and hydrological features of the two basins forming Lake Garda. Multivariate analysis revealed a clear response of Cladocera to climate variability during periods of low lake nutrient levels (i.e. before the 1960s). This stands in contrast to conclusions drawn previously based on data for diatoms and pigments, which did not fully capture effects of climate change during these periods. Since the beginning of the lake’s nutrient enrichment phase (i.e. after the 1960s), diatoms and Cladocera exhibited concomitant shifts in assemblage composition due to a pronounced increase and then a less pronounced decrease in nutrient concentrations. During this period, the response of the Cladocera to climate shifts was overridden by shifting nutrient levels. This work highlights the value of a multi-proxy approach for disentangling the multifaceted biological responses to multiple environmental stressors in large and deep lakes.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

Cladocera

Paleoecology

Sediment

Climate change

Trophy

Lake Garda

Publikations- och innehållstyp

vet (ämneskategori)

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