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• The F yw (young streamflow fraction) is determined by seasonal isotope cycles. • Landscape metrics have close relationships with multiple water quality parameters. • FRAC and SHDI followed by CONTAG were most correlated to water quality. • Water quality parameters associated with landscapes did not correlate with F yw. • The F yw has the potential for nitrogen modeling across multiple spatial scales. Landscape patterns and water age are considered to play similar roles in influencing water quality, as human-caused landscape fragmentation usually leads to complex hydrological pathways and older water ages. The young streamflow fraction (F yw), which can significantly alter water age, is believed to disproportionately impact water quality. Landscape and F yw thus may play different roles in streamwater quality, but this assumption has not been examined. Here we examined the roles of F yw (estimated by the amplitudes of seasonal cycles of oxygen isotope ratios in precipitation (A p) and streamwater (A s)) and landscape pattern (reflected by common landscape metrics) in streamwater quality over 7 forest-dominated catchments in eastern China. Landscape metrics, indicating land use arrangement, were closely related to multiple water quality parameters, suggesting a close association between stream water quality (sinks) and land use (sources). The F yw had a positive relationship with ammonia nitrogen (R2 = 0.51, P = 0.044) and a negative relationship with nitrate nitrogen (R2 = 0.62, P = 0.022). The F yw , determined by the heterogeneous-independent A s /A p , offers the possibility of modeling nitrogen compounds across multiple spatial scales. Importantly, the water quality parameters that significantly correlated with F yw did not correlate with the landscape metrics. Differences in correlations of landscape and F yw to water quality parameters imply that landscape and F yw differed in their roles in water quality parameters, as well as the consideration for different water quality management strategies for different contaminants. [Display omitted] [ABSTRACT FROM AUTHOR]