Limnological changes in South Carpathian glacier-formed lakes (Retezat Mountains, Romania) during the Late Glacial and the Holocene: A synthesis

Abstract

Remains of aquatic biota preserved in mountain lake sediments provide an excellent tool to study lake ecosystem responses to past climate change. In the PROLONG project a multiproxy study was performed on sediments of glacier-formed lakes from the Retezat Mountains, Southern Carpathians (Romania). The studied lakes (Lake Brazi and Gales) are situated on the northern slope of the mountain at different altitudes (1740 m and 1990 m a.s.l.). Our main objectives were 1) to describe the main limnological changes in these lakes during the last ca.15,000 years and 2) to summarize the environmental history of the studied lakes based on taxonomical and functional patterns of the biological proxies. For this synthesis we used the results of diatom and chironomid analyses, and indirect biotic and abiotic parameters, including sediment organic matter (LOI) content, geochemical element concentrations (Al, Ca, S, Sr) and biogenic silica content. Using multivariate numerical approaches we analysed changes in the assemblage structure of siliceous algae and chironomids, compared temporal patterns among proxies, examined the relationship between potential driving factors, chironomid and diatom assemblage changes and identified paleolimnological phases of the lake successions. Changes in assemblage composition and aquatic ecosystem state apparently followed summer insolation, local climatic conditions and local productivity changes driven by these. Diatom and chironomid assemblages generally changed in a similar direction and at a similar time within a lake, but differed to some extent between Lake Brazi and Gales. At both lakes the strongest variations were observed in the Late Glacial and the first half of the Holocene. The strongest Holocene assemblage changes took place in the earliest Holocene in Lake Brazi, but extened into the mid-Holocene in Lake Gales, following long-term insolation changes and climatic changes. In addition, three common zone boundaries were identified: at ca. 14,200 and at ca. 6500 cal yr BP for every records and at ca. 3100 cal yr BP for diatom records in both of the lakes and for the chironomid record of Lake Brazi. This multi-proxy synthesis provides comprehensive data that increase our understanding of the past variability of lake ecosystem functioning and biodiversity in East-Central Europe.

Holocene paleoclimate inferred from stable isotope (δ18O and δ13C) values in Sphagnum cellulose, Mohos peat bog, Romania

“…Changes detected in stable isotope records are of similar scale, and changes are also observed in many other proxy climate records, e.g. in pollen, chironomid, diatom and geochemical stratigraphies (Buczkó et al 2012;Braun et al 2013;Tóth et al 2018).…”

Carbon accumulation rates of Holocene peatlands in central-eastern Europe document the driving role of human impact for the past 4000 years

“…This is in agreement with other studies of European peatlands (Ratcliffe et al, 2018), where rapid CARs are reconstructed in the early Holocene as a result of warm temperatures, a reflection of the key role temperature plays in CARs (Charman et al, 2009). Regionally, our data reflect the impact of warmer than present conditions and lower than present precipitation levels and higher seasonality reconstructed from multi-proxy records (Buczkó et al, 2013;Davis et al, 2003;Feurdean et al, 2008;Magyari et al, 2009;Tóth et al, 2018Tóth et al, , 2015 and modelled data which coincided with higher than present (summer) insolation (Berger and Loutre, 1991). During the mid-Holocene (7000 -3000 yr BP), CARs were generally low, with our composite record reconstructing a decreasing trend until 4000 yr BP (Fig.…”

Carbon accumulation rates of Holocene peatlands in central–eastern Europe document the driving role of human impact over the past 4000 years

“…This is in agreement with other studies of European peatlands (Ratcliffe et al, 2018), where rapid CARs are reconstructed in the early Holocene as a result of warm temperatures; this is a reflection of the key role that temperature plays in CARs (Charman et al, 2009). Regionally, our data reflect the impact of warmer-than-present conditions and lower-than-present precipitation levels as well as higher seasonality reconstructed from multi-proxy records (Buczkó et al, 2013;Davis et al, 2003;Feurdean et al, 2008;Magyari et al, 2009;Tóth et al, 2015Tóth et al, , 2018 and modelled data which coincided with higher-than-present (summer) insolation (Berger and Loutre, 1991).…”

“…As such, understanding the history of carbon accumulation in peatlands is important for critically assessing the terrestrial carbon cycle in our anthropogenically altered world (Hugelius et al, 2020;Loisel et al, 2021). Model-derived estimates of future climatic change suggest that peatlands will act as an efficient carbon sink as climate warms (Gallego-Sala et al, 2018), as observed in reconstructions of warm periods in Earth's past (Treat et al, 2019). However, this conclusion is far from certain, as land-use-driven degradation of peat since the 1960s has led to peatlands acting as a net source of carbon (Leifeld et al, 2019).…”

“…For individual peatlands, fire and grazing disturbances negatively impact peatland development (Nieveen et al, 2005;Worrall and Clay, 2012) due to the loss of surface peat or changes to local vegetation (Garnett et al, 2000;Kuhry, 1994). Furthermore, draining of wetlands and the extraction of peat plays a major role in both long-term carbon accumulation in peat and its short-term release back into the atmosphere (Holden et al, 2011;Turetsky et al, 2011), with hydrological shifts potentially altering the ecology of bogs (Tahvanainen, 2011). Furthermore, climate change also influences the stability of the extensive Northern Hemisphere boreal peatlands, potentially resulting in the enhanced release of methane, thereby further exacerbating the effects of rising global temperatures (Schaefer et al, 2014;Schuur et al, 2015).…”