The use of epilithic diatom assemblages in assessing land use in Silago, Southern Leyte, Philippines

Silago is a municipality in Southern Leyte in which logging for high-quality timber and land clearing for agricultural purposes threaten stream ecosystems. The objective of this study was to assess the response of diatom assemblages in relation to land use. Diatoms and water quality sampling was done at 27 sites on two sampling occasions (June and July 2014). Multiple diatom metrics were calculated to measure the response of diatoms to changes in land use. In all, 135 diatom species distributed to 48 genera were recorded. The results showed that diatom species and their attributes gave similar responses to those obtained in environmental variables. Pollution tolerance index classified all sampling sites as oligo-b-mesosaprobic. Meanwhile, Cymbella richness, percent motile taxa, and percent Achnanthidium minutissimum indicated good water quality in forested areas, distinguishing them from other land use types. Contrary to other studies, species richness was found to increase with greater degrees of disturbance, thus giving unreliable evaluation of water quality. Overall, the study suggests that epilithic diatoms can be applied in biomonitoring of freshwater bodies in the country.