Chapter 1 - Núria BONADA

Chapter 7
headwaters at high altitude from lowland reaches. Second axis is positively related to chemical
variables, discharge, basin area, channel width and others, whereas it is negatively associated
with high values of riparian and biological quality, several habitat characteristics and
temporality (Table 4). Finally, the third axis is associated to temperature, stream order and
sedimentary geology in a positive direction and to riparian and habitat characteristics in the
negative one (Table 4). According to Figure 3, a gradient of caddisfly species appear from left to
right side of the graph and three groups may be differentiated. Headwaters and high altitude
samples with a high substrate diversity, located in the left, are associated with Glossosoma
sp., A. chauviniana, M. longulum, H. tesselatus, Rh. cf. occidentalis and H. tibialis whereas
lowland rivers in the right present H. exocellata, P. pusilla, P. cf. ctenophora and H. brevis. In
the middle, a group of midstream samples associated with several Hydropsychids,
Philopotamids, Polycentropodids and Psychomiids are present. Second axis in Figure 3
appears to differentiate between small temporary streams from middle and large streams. Few
taxa is associated to positive values of second axes, as Rh. fasciata, Rh. dorsalis, Ecnomus
sp. and several Hydropsychids, characteristic from middle reaches.
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