Browsing by Subject "browning"

Aims of this study. Previous studies have shown cyanobacterial dominance and harmful cyanobacterial blooms to increase due to recent climate warming. The increase of aggressively blooming species and toxin-producing strains of cyanobacteria has been predicted to further increase in the future. However, information on the response of cyanobacteria communities to environmental forcing in the Arctic region – which is experiencing warming at over twice the rate compared to the global average – has been insufficient. Thus, it is crucial to study how algal and cyanobacterial communities have developed after industrialization to better understand and predict future trends of subarctic algal communities as well as changes within cyanobacteria communities experiencing environmental forcing. This study aims to provide information on the effect of recent climate warming and lake browning on algal communities in subarctic lakes, with a special focus on cyanobacteria and cyanotoxins. Materials and methods. Modern and historical primary producer group abundances of 23 subarctic lakes located on an ideal temperature and vegetation gradient were studied using sedimentary algal pigments as a proxy. The top-bottom method was used to study both changes within algal communities during the last ca. 150 years and the broader trends in algal communities of subarctic lakes. Pigment data was analyzed together with environmental data using ordination analyses (principal component analysis (PCA) and redundancy analysis (RDA)) as well as other statistical analyses in order to determine possible trends of change and to reveal the environmental variables that have the strongest impact on cyanobacterial abundance. Results and conclusions. Algal communities have changed during the last ca. 150 years and show a general trend of increased primary production as well as lake browning in the spruce, pine and birch (SPB) vegetation zone. Siliceous algae generally dominate modern algal communities, and relative abundances of cyanobacteria have declined throughout the vegetation gradient. Within the Barren (Ba)- and mountain birch woodland (MBW) vegetation zones, cyanobacteria communities show a marked decline in the abundance of assumed benthic species based on pigment data, and low abundances of planktic picocyanobacteria. However, due to climate warming and lake browning, abundances of cyanobacteria have increased in several sites within the SPB vegetation zone and are suspected to indicate an increase of harmful planktic species. The most significant environmental variables controlling the abundance of cyanobacteria were total phosphorus, temperature and the amount of organic matter. The results highlight the urgent need to mitigate climate warming in order to preserve the unique biota and characteristics of Arctic and subarctic lake ecosystems, and to prevent the possible harmful increase of cyanotoxins in these sensitive ecosystems.