Long-term and seasonal changes in chemical composition of surface waters in Latvia.

The changes of the chemical composition in Latvian inland waters over the last twenty years were determined. based on data of the National Monitoring Programme. Relationships between the water composition were studied. The chemical composition and seasonal change pattern depend a lot on hydrological factors which differed between eastern and western Latvia. Different pattern of long-term changes is found for substances which have different sources and sinks, at first for nutrients (decrease only in the last few years) and inorganic ingredients (commonly increasing trend). An attempt was made to identify the main sources of the major water ingredients and link changes of their concentrations with changes in loading to waters.