| dc.description.abstract | The nutrients phosphorus and nitrogen are necessary for phytoplankton growth, but nutrient enrichment (eutrophication) can be of global and national concern. Lake Årungen is a eutrophic lake that has been plagued by visible cyanobacteria blooms, which can be toxic. This thesis examined the succession in the phytoplankton community and investigated if there were any connections between phytoplankton growth and nutrient dynamics in Lake Årungen. Data was collected as water samples and in situ measurements on biweekly field trips, where the water samples were later analysed at the lab for nutrients and phytoplankton pigments.
Diatoms dominated at the beginning and end of the season, and were also present during the peaks of other phytoplankton groups. In August a visible cyanobacteria bloom began to form on the lake surface. Principal component analysis (PCA) found a correlation between total phosphorus (TP) and chlorophyll a, indicating a relationship between the two. Total nitrogen (TN) and nitrate correlated with the TN and nitrate for the outlet, but not to any of the pigments.
The main findings in this study were the domination of diatoms, the succession of phytoplankton groups in Lake Årungen, and the coupling between TP and phytoplankton growth. Another important finding is that Lake Årungen was feeding the outlet with nitrogen, with possible adverse effects further down in the river system. This study challenges the assumption that all eutrophic lakes are dominated by cyanobacteria and highlights the need for more understanding of phytoplankton dynamics throughout the summer. | |
