Growing season variability of nitrate along a trophic gradient - contrasting patterns between lakes and streams

We studied the growing season (May to October) variability of NO(3)-N across Swedish lakes and streams. We found that NO(3)-N concentrations showed the highest growing season variability among all water chemical variables tested, both in lakes and in streams. However, the growing season variability of NO(3)-N increased with increasing trophic status in lakes while it decreased in streams. We attributed the contrasting pattern between lakes and streams to the relative importance of biological uptake and denitrification with increasing trophic status. Our results highlight the relation between growing season NO(3)-N variability and trophic status, which is positive in lakes but negative in streams. The findings of this study have important ramifications for ecosystem studies as well as water management. We suggest that the assessment of growing season variability of NO(3)-N in aquatic systems can be improved by considering the effect of trophic status.