In a mosaic landscape moderately affected by agriculture and tourism, such as found in the Masurian Lakeland (north-eastern Poland) external input of nutrients (TP, TN, NNO3) and their retention were compared in a cascade of shallow in-river lakes, between several years of different weather conditions. The average and maximum air temperature in the summer and winter months and that of the freshet (April) tended to be higher in the late 90s than the late 70s. The annual summer precipitation was lower in some years of the 90s than the 70s. This combination of dry and warm conditions (especially in summer) resulted in the water discharge, renewal rate of lake water and nutrient loads to the lakes becoming drastically reduced and more differentiated between freshet and other periods. This imbalance resulted in the occasional higher concentration of nutrients (due to internal loading) in lake outflows and lower retention of nutrients in the lake systems. Downstream exports of TP or TN took place occasionally from the lakes, although N-NO3 was usually retained. Speculations are made about how frequently this situation may affect surface-fed, shallow lakes in the light of global warming (already detected in the region) and how important this could become for future eutrophication in shallow, temperate lakes generally.
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