The 1997 (dry year) biplots obtained using CANOCO (Fig. 6a) showed a significant positive correlation between DO and Axis 1 (r ¼ 0:669; po0:01), and a significant negative correlation between BOD and Axis 2 (r ¼ 0:735; po0:01). On the biplots, both these determinants have long arrows, indicating the importance of DO and BOD in the community that year.