Figure 1.
Conceptual diagram describing two causal mechanisms through which watershed urbanization might alter denitrification rates in streams.
The first mechanism (pathway A) focuses on the direct effect of urbanization on denitrification through changes to nitrate and organic carbon concentrations. The second mechanism (pathway B) focuses on the indirect effect of urbanization on denitrification through changes to denitrifier community composition.
Table 1.
Study streams, ranked in order of percent impervious cover in the watershed.
Figure 2.
Non-metric multidimensional scaling (NMS) ordination of overall bacterial and nirK and nosZ denitrifier communities based on presence-absence TRFLP (terminal restriction fragment length polymorphism) data.
Each point represents the community in a study stream on a particular sampling date. Black circles are streams in watersheds with high percent impervious cover (% IC). Green triangles are streams in watersheds with intermediate % IC. Blue squares are streams in watersheds with low % IC. Values given in parentheses following axes titles are estimated R2 values for individual axes. All three NMS ordinations had a final solution with three dimensions. Total R2 values for overall bacterial, nirK, and nosZ ordinations were 0.70, 0.55, and 0.59, respectively.
Figure 3.
Linear regressions of NMS ordination axes scores against arcsine square root transformed percent impervious cover.
Table 2.
Results from an ANOVA conducted to determine the significance of fixed effects on the final linear mixed-effects model (without interactions) of log-denitrification.
Table 3.
Results from an ANOVA conducted to determine the significance of fixed effects on the final linear mixed-effects model (with interactions) of log-denitrification.