Diatoms in ponds and small lakes of the Kathmandu Valley, Nepal – relationships with chemical and habitat characteristics

Diatoms were examined in twelve ponds and four small lakes of the Kathmandu Valley, Nepal, to assess their biodiversity, response to environmental conditions and potential use as bioindicators for water quality. They were investigated from different substrates and relationships with water chemistry and habitat character were assessed. In total 212 diatom species were found with 98 taxa at relative abundances > 1 %. The most species-rich genera were Navicula (42), Gomphonema (39), Achnanthes sensu lato (27), Nitzschia (27) and Fragilaria sensu lato (20). Species diversity was low (mean 0.95 ± 0.17 sd) and most assemblages were dominated by 1-3 taxa. Thirty percent of the taxa found could not be identified using relevant literature. Species richness, diversity and evenness were not related to water chemistry or habitat character, but varied significantly on different substrate types and were higher in the sediment compared to stones and macrophytes. At five of seven sites, where several substrates were collected, the most abundant species occurred on all substrates. Canonical correspondence analysis (CCA) revealed that changes in species composition were most strongly correlated with gradients in water chemistry. Achnanthidium minutissimum was characteristic at sites with higher Ca concentrations, while Eolimna minima, Nitzschia palea, Nitzschia palea cf. var. debilis and Gomphonema parvulum indicated higher concentrations of K, Cl, Na, As, Ni, Fe and Al. E. minima and N. palea were also typical at sites with higher concentration of SO 4 2- , Sr and Al. Assemblage composition was also significantly correlated with habitat character such as aquatic vegetation, substrate composition, bank character and land use.