Algal Transport Through Saturated Sediments: Implications for Ecosystem Resilience

Sustainable primary producer communities depend on a diverse pool of physiologically active cells surviving transport through sediment pore spaces. However, algal transport through saturated sediments remains a major knowledge gap in surface water–groundwater (SW-GW) interactions. In this study, vertical column experiments used a conservative tracer (NaCl) to establish hydraulic baselines. Three algal groups (green algae, cyanobacteria, and diatoms) were then tested across pH 8, 7, and 6, with recovery measured through biomass quantification, morphological identification, and post-run culturing. Green algae showed the highest mobility, with recovery increasing from 14.42% at pH 8 to 38.39% at pH 6 and retardation factors (R) of 1.33–1.40. Cyanobacteria peaked at neutral pH (29.50%) with higher retardation (1.60–2.31), while diatoms were strongly retained (≤5.72%) with high retardation (1.87–2.31). These differing transport patterns are primarily driven by morphological traits. Small, unicellular green algae are less susceptible to mechanical straining, enabling higher mobility. Conversely, cyanobacteria and diatoms experience stronger retention due to physical straining of their complex morphologies (filaments and chains) and enhanced surface adhesion from extracellular polymeric substances. A permutation-based two-way ANOVA indicated that the algal group significantly affected percent recovery (p = 0.0034), whereas neither pH (p = 0.166) nor the pH × algal group interaction (p = 0.076) was significant. Post-run culturing showed approximately 68% of inoculated genera persisted after passage, suggesting that saturated sediments can function as a biological “seed bank” for algal communities. These results highlight group-specific transport patterns in controlled sand columns and may inform future studies of algal persistence in natural surface water–groundwater systems; however, field-scale transport will also depend on sediment heterogeneity, flow conditions, and changing pore-water chemistry.