Periphyton efficiency in phosphorus accumulation affected by phytoplankton dynamics in reservoir for water supply

Most of methods for phosphorus harvesting from affected aquatic ecosystems are proven to be effective predominantly when performed under controlled conditions. The efficiency of phosphorus accumulation by short- and long-term exposed periphyton developed on polyacrilic substrates was estimated in two basins of the reservoir for water supply - Lake Ćelije (Serbia), to examine the effectiveness of this biological method for phosphorus harvesting in situ. The dynamics of phytoplankton abundance in both basins was also assessed during periphyton exposure. Maximal phosphorus accumulation in both basins was achieved in one-month, two-month and four-month exposed periphyton, each harvested in October, which accumulated 1695, 2897 and 6058 mgTP/m2 in eutrophic and 1845, 3064 and 5405 mgTP/m2 in mesotrophic basin, respectively. The most abundant phytoplankton was detected in the August (132,900 in eutrophic and 28,953 cell/ml in mesotrophic basin), while the sparsest community was recorded in October in both basins (4600 in eutrophic and 117 cell/ml in mesotrophic basin). Inhabiting the same niche and exploiting the same resources, periphyton and phytoplankton compete fiercely for phosphorus. Phytoplankton occurred to be competitively dominant in assimilating this nutrient from the water column allowing periphyton to increase phosphorus accumulation only during the periods of very low phytoplankton abundance. The results also suggest that the efficiency of phosphorus accumulation by periphyton is more closely related to phytoplankton abundance during the exposure period than to the exposure duration. If this method potentially is employed at large scale during the remediation process, the harvesting of substrates exposed during scarce phytoplankton development would be most effective.