The Sources of Carbon and Nitrogen in Mountain Lakes and the Role of Human Activity in Their Modification Determined by Tracking Stable Isotope Composition.

We also found that a clear trend of isotopic curves toward lower values of δ 13 C and δ 15 N (both ~3 ‰) began in the 1960s.

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In both lakes, a slight trend toward the heavier C isotopes is observed since the 1980s.

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The steady decline of the C/N ratio in the SME during the eighteenth century changed into an increasing trend in the nineteenth century and again into a decline in the twentieth century (Fig. 4 ).

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