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Abstract

Weather variation and climate fluctuations are the main sources of ecosystem variability in remote mountain lakes.Here we describe the main patterns of seasonal variability in the ecosystems of nine lakes in Europe, and discuss the implications for recording climatic features in their sediments. Despite the diversity in latitude and size, the lakes showed a number of common features. They were ice-covered between 5-9 months, and all but one were dimictic. This particular lake was long and shallow, and wind action episodically mixed the water column throughout the ice-free period. All lakes showed characteristic oxygen depletion during the ice-covered-period, which was greater in the most productive lakes. Two types of lakes were distinguished according to the number of production peaks during the ice-free season. Lakes with longer summer stratification tended to have two productive periods: This is the third of 11 papers published in this special issue on the palaeolimnology of remote mountain lakes in Europe resulting from the MOLAR project funded by the European Union. The guest editor was Richard W. Battarbee. Mountain Lake ResearchMOLAR 26 one at the onset of stratification, and the other during the autumn overturn. Lakes with shorter stratification had a single peak during the ice-free period. All lakes presented deep chlorophyll maxima during summer stratification, and subsurface chlorophyll maxima beneath the ice. Phosphorus limitation was common to all lakes, since nitrogen compounds were significantly more abundant than the requirements for the primary production observed. The major chemical components present in the lakes showed a short but extreme dilution during thawing. Certain lake features may favour the recording of particular climatic fluctuations, for instance: lakes with two distinct productive periods, climatic fluctuations in spring or autumn (e.g., through chrysophycean cysts); lakes with higher oxygen consumption, climatic factors affecting the duration of the ice-cover (e.g., through low-oxygen tolerant chironomids); lakes with higher water retention time; changes in atmospheric deposition (e.g., through carbon or pigment burial); lakes with longer stratification, air temperature changes during summer and autumn (e.g., through all epilimnetic species).

The Late-Glacial and Holocene Marboré Lake sequence (2612 m a.s.l., Central Pyrenees, Spain): Testing high altitude sites sensitivity to millennial scale vegetation and climate variability

“…Mountain vegetation has been shown to be particularly sensitive to climate variability (Birks and Ammann, 2000;González-Sampériz et al, 2006;Magny et al, 2013;Pérez-Sanz et al, 2013;Thöle et al, 2016) and particularly at higher altitudes (Birks and Ammann, 2000). In this sense, remote mountain lakes have high potential as past climate and vegetational change archives (Battarbee et al, 2002;Catalan et al, 2002;Ilyashuk et al, 2011). However, interpreting pollen sequences from high altitude sites has some specific challenges, as pollen percentages do not reflect vegetation cover, some taxa are over-represented (pines) and values are highly influenced by sedimentation rates which are likewise influenced by ice-cover season.…”

Chironomids, temperature and numerical models: a reply to Seppälä

“…Seppälä also casts doubts on our pH determinations, showing that he is not familiar with the chemical limnology of northern lakes. Our longterm monitoring records from several lakes in subarctic Fennoscandia clearly demonstrate that most water-chemistry variables, including pH, are extremely stable throughout the open-water period, except for the shortduration period during spring melt (Rautio, 1998;Blom et al, 1998;2000;MOLAR Water Chemistry Group, 1999;Sorvari et al, 2000;Rautio et al, 2000;Korhola et al, 2001;Catalan et al, 2001). Based on results from the organisms most sensitive to pH, namely diatoms, the transient drop in pH during the spring melt does not affect the organisms (Korhola et al, 1999).…”

Some Mixotrophic Flagellate Species Selectively Graze on Archaea

“…The lake is dimictic, well oxygenated throughout the water column, and usually covered by ice and snow 6 months a year (61). The productivity patterns and seasonal changes in the water column are typical for high mountain lakes (62,63). This lake has been widely studied in the last 30 years.…”