Benthic diatoms are beneficial organisms whose activity supports ecosystems and improves water quality. The pennate diatom Nitzschia palea is an important diatom species, as it has a potential to control cyanobacterial blooms. Several studies have attempted to restore lakes by using artificially produced substrates that remove nutrients or harmful substances. Although substrates provide attachment sites, they may adversely affect the growth of diatoms by removing nutrients. In this study, we investigated a suitable substrate for N. palea growth. Substrates such as glass beads, activated carbon, and oyster shells, which can be used for lake water or ecosystem restoration, were selected. The most suitable substrate was determined from the perspective of nutrient adsorption, elution, and availability of adhesion sites. N. palea was cultivated with substrates until the stationary growth phase was attained, and N. palea growth and the change in nutrient content of the medium were investigated. Silicate eluted from small glass beads considerably increased the maximum cell yield of N. palea (7.03 × 106 cells mL−1). Activated carbon absorbed nitrate from the medium and decreased the specific growth rate of N. palea from 0.47 d−1 (without substrate) to 0.24 d−1 while providing attachment sites and increasing the maximum cell yield compared to the control (1.49 × 106 and 1.01 × 106 cells mL−1 under activated carbon and control treatments, respectively). Oyster shells absorbed phosphate and did not increase the maximum cell yield. Our results suggest that submerged substrates that absorb nutrients may negatively affect the growth of attached diatoms. Therefore, when using the substrates for lake water restoration, attention must be paid to the growth of attached diatoms.
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