Spatial Distribution and Long-Term Trends of Water Transparency in Lake Ladoga

M. A. Naumenko

Based on the analysis of the surface water transparency (the depth of the Secchi disk disappearance), a seasonal trend of transparency for the entire lake water area was derived for the largest European lake, Lake Ladoga, on an equidistant grid and for limnetic regions. A spatial distribution of monthly mean water transparency of Lake Ladoga is considered from May to October. Climatic trends of transparency are assessed for the period from 1905 to 2003. The climatic trends are analyzed with a linear model used for each month from May to September. The areas with significant negative trends are singled out. A mean trend value is 0.02 m/year. The character of a spatial trend distribution changes depending on the month. In summer, the area with significant trends increases and covers about half of the lake water area. In the spring and in the fall, this area is much smaller and coincides with the southern regions of the lake.