Hydrometeorological parameters and aquatic chemistry of Lake Engure: Trends of changes due to human impact and natural variability

Lake Engure, located in Latvia, is the largest shallow coastal lake that developed after retreat of the Littorina Sea. It supports high biodiversity and has national and international importance. Engure is a hardwater lake with abundant macrophyte and charophyte vegetation. The present study determined the impact of the main meteorological indicators related to global warming, and also indicators of climate extremes. The lake water level is regulated by hydrotechnical constructions. In the the warm period (April-October) of the year the lake level tends to increase. However, from a perspective of long-term changes, there was a good relationship between the Western type of Atmospheric Circulation Index and water level in general, and also between NAO index in March and lake water level in April. Regarding water chemical composition, there has been a decrease of phosphorus concentration while ammonium and nitrate concentrations have not changed. Ionic composition of Lake Engure is characterised by dominance of hydrocarbonates, calcium and magnesium ions.