Academic journal article Estonian Journal of Ecology

Linking Diatom Community Dynamics to Changes in Terrestrial Vegetation: A Palaeolimnological Case Study of Lake Kuzi, Vidzeme Heights (Central Latvia)/Diatomee- Ja Oietolmuprofiilide Dunaamika Ning Nende Omavahelised Korrelatsioonid Holotseenis Kuzi Jarve (Vidzeme Korgustikul Latis) Naitel

Academic journal article Estonian Journal of Ecology

Linking Diatom Community Dynamics to Changes in Terrestrial Vegetation: A Palaeolimnological Case Study of Lake Kuzi, Vidzeme Heights (Central Latvia)/Diatomee- Ja Oietolmuprofiilide Dunaamika Ning Nende Omavahelised Korrelatsioonid Holotseenis Kuzi Jarve (Vidzeme Korgustikul Latis) Naitel

Article excerpt

INTRODUCTION

Palaeolimnological studies offer an opportunity to improve our knowledge about the past environmental conditions as the physical, chemical, and biological information preserved in lake sediments provides an insight into past events that have occurred within the catchment and their effects on the lake environment.

Due to their ability to colonize new habitats quickly and their sensitivity to environmental factors, diatoms (Bacillariophyceae) can be used to trace changes in a lake, such as water depth, aquatic pH, nutrient availability, salinity, and current conditions. They are preserved well in many types of sediment because of the siliceous composition of their cell walls (Stoermer & Smol, 1999; Battarbee et al., 2001). These features make diatoms ideal for reconstructing environmental changes in lake ecosystems.

As diatoms primarily reflect conditions in a waterbody, palynological analysis is needed to describe the development of its surroundings. Pollen-based palaeoecological studies can provide an essential long-term perspective, not available from the instrumental record or modern ecological studies, on the development of vegetation and its response to past climate change and human impact (Moore et al., 1991; Galloway et al., 2007).

Although palaeoecological records of terrestrial (pollen) and aquatic (diatoms) biota are important in assessing past environmental conditions in a lake and its surroundings, these proxies are frequently observed separately. Palaeolimnological studies quite often focus solely on a lake and its changes while the catchment of the lake is just a background. The reason for this is that the interpretation of patterns in proxy records can be challenging because different components of an ecosystem responding to different aspects of environmental variability have different sensitivities and thresholds to the environmental changes influencing the lake and its catchment system.

The general assumption is that diatoms reflect the development of an aquatic ecosystem and the pollen profile indicates the dynamics of vegetation on the catchment. At the same time processes inside a lake are closely related to the changes in the terrestrial ecosystem, especially to those taking place on the lake catchment. Using pollen and macrofossil data, Kangur et al. (2009) described the Holocene stratigraphy and palaeogeography of a paludified near-shore area of Lake Kuzi (Vidzeme Heights, Central Latvia). They distinguished two terrestrial periods (first from ca. 11 400 cal. BP up to 10 900 cal. BP and the second from 700 cal. BP until present) when the water level was below or around the sediment limit and a lacustrine period between these two when the water level was mainly above the sediment surface. The relatively stable water level after 10 900 cal. BP suggests that the changes in diatom and pollen profiles were mainly caused by other factors than lake-level fluctuations. Therefore we find that this lake is a suitable object for examining lake-catchment interactions and for comparing the dynamics of diatom and pollen sequences, which was the first aim of this study. The overall purpose was to improve the reconstruction of the environmental history of the small Lake Kuzi and the vegetation in its surroundings during the Holocene based on diatom and pollen data.

STUDY SITE

Lake Kuzi (57[degrees]2' N, 25[degrees]20' E; altitude 191.5 m a.s.l.) is situated in the western part of the Vidzeme Heights, Central Latvia (Fig. la). The Vidzeme Heights is located distally from the ice marginal formations of the Luga (North Lithuanian) stage. The most impressive formations of this ice advance were formed about 13 200-13 000 BP (Raukas et al., 1995). The topography of the Vidzeme Heights is varied and complex, with the dominance of subglacial landforms. The elevations of the area vary from 180 to 240 m. Small depressions between hillocks were formed following the withdrawal of glaciers. …

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