FIG. 4.

Triplot of RDA for bacterial phyla from the 36 stream sediments at six sites located on or near the Oak Ridge Reservation, with forward selection of predictor variables followed by Monte Carlo permutations. Solid arrows represent predictor (geochemical) variables significantly associated (P < 0.05) with the variation in the bacterial community structure. Dashed arrows represent individual phyla (r > 0.6) significantly associated with the variation among samples. The length of each arrow is correlated with the degree of relationship between the response variables. The arrows point in the direction of the maximum change for the associated variable. Open symbols represent midchannel samples, and closed symbols represent near-bank samples.