Long-term Hydrochemical Changes and “harmful Algal Blooms” in the Arctic Lake Imandra

The large arctic Imandra Lake is located in the industrial Murmansk region, Russia. Since the 2000s it has regular Harmful Algal Blooms. Significant changes in hydrochemical indices were recorded in 1985—2017. The ratio of the main ions has changed, the pH and alkalinity have increased. The indicators of water salinity, the total content of P and N, and their mineral forms have decreased. The concentrations of Zn, Cu, Ni и SO42– have decreased as well. The decrease trends in the content of macronutrients in waters contradict traditional concepts and the role of mineral P and N in the development of HAB. This indicates more complex mechanisms of flowering in this arctic reservoir, which are being discussed.