Exploring Ecological Responses Associated with Silica-Adsorbed Micronutrient Formulation Dosing in Aquatic Systems

Improving water quality through the support of natural biological and biogeochemical processes has attracted increasing interest in aquatic system management. It is hypothesised that phytoplankton community restructuring intervention using amorphous silica and adsorbed micronutrients could support biological processes involved in nutrient uptake and transformation. This study evaluated ecological responses following silica-adsorbed micronutrient formulation (SAMF) dosing at two field sites in Australia and New Zealand using nutrient and phytoplankton indicators. Site A comprised a reservoir monitored across pre-dosing, dosing, and post-dosing phases, whereas Site B comprised a constructed wetland with treated and untreated monitoring locations. Temporal and regression analyses were used to examine nutrient dynamics and phytoplankton responses. At Site A, the full-dosing period coincided with lower cyanobacterial abundance, increased diatom abundance, and generally lower total nitrogen concentrations relative to pre-dosing conditions. Regression analyses indicated that, relative to pre-dosing conditions, the full-dosing period was associated with approximately 76% lower cyanobacterial cell counts (95% CI: 43.9–89.9%) and 35% lower cyanobacterial biovolume (95% CI: 16.8–48.6%), while diatom abundance was statistically significantly higher during the full-dosing period. In contrast, Site B exhibited weaker and less consistent responses, with no significant difference in cyanobacterial abundance between treated and control locations in the main model (p = 0.691), despite temporal variation in nutrient and phytoplankton indicators among monitoring locations. Overall, the findings provide field-based evidence that SAMF dosing may be associated with changes in nutrient dynamics and phytoplankton community structure under real-world conditions. However, responses were not consistent across sites, suggesting that treatment performance is likely influenced by local environmental conditions.