Stream epilithic, epipelic and epiphytic diatoms: habitat fidelity and use in biomonitoring

We compared the use of epilithic, epiphytic, and epipelic diatom communities in stream biomonitoring by investigating species composition and relationships with measured water quality variables in two tributaries of the Grand River, Ontario, Canada. Although ordination showed some separation of the epilithon from other habitats, clear habitat preferences and seasonality were not identified. Canonical correspondence analysis showed that measured water quality variables explained the major gradients in the diatom data for all three habitats. The diatoms from each habitat were strongly related to alkalinity, suspended solids, biological oxygen demand and conductivity, and in addition, epipelic and epiphytic diatoms showed significant relationships with total phosphorus. It was concluded that although some species were more abundant in one habitat than the others, the community structure of the epilithic, epiphytic and epipelic habitats from these streams was not consistently different. The results indicate no apparent benefit to sampling discrete habitats for water quality monitoring using diatoms, however, the best relationship are obtained using the sum of the diatom data from all three habitats.