Mountain aquatic Isoetes populations reflect millennial-scale environmental changes in the Bohemian Forest Ecosystem, Central Europe
Abstract
In this study we aim to investigate millennial-scale dynamics of Isoetes, a type of macrophyte well adapted to oligotrophic and clear-water lakes. Despite its wide distribution during the Early Holocene, nowadays Isoetes is considered as vulnerable or critically endangered in many Central European countries.
Using a multi-proxy palaeoecological reconstruction involving Isoetes micro- and megaspores, pollen, plant macrofossils, macro-charcoal, diatoms and chironomids from four lakes (Prasilske jezero, Plesne jezero, Cerne jezero, Rachelsee) located in the Bohemian Forest Ecosystem mountain region in Central Europe, we reconstruct Isoetes dynamics and discuss how local environmental factors impacted its distribution and abundance during the Holocene. Our results show regionally concurrent patterns of Isoetes colonisation across all lakes beginning 10,300-9300 cal yr BP, and substantially declining around 6400 cal yr BP.
Results from Prasilske jezero imply that Isoetes decline and collapse in this lake reflect gradual dystrophication that led to the browning of lake water. This is evidenced by a shift in diatom assemblages towards more acidophilous taxa dominated by Asterionella ralfsii and by a decrease in total chironomid abundance and taxa sensitive to low oxygen levels.
Dystrophication of Prasilske jezero was linked with the immigration of the late-successional tree taxa (Picea abies and later Fagus sylvatica and Abies alba), peatland expansion, and decreasing fire activity. Multi-site comparison of pollen records suggest that these vegetation-related environmental changes were common for the whole region.
Our study demonstrates the sensitivity of Isoetes to millennial-scale natural environmental changes within the surrounding lake catchment.