Schneider, Natalie2025-11-062025-11-062025-11-062025-11-04https://hdl.handle.net/10012/22616Phosphorus (P) loadings to streams often occur in short duration events associated with runoff from human activities. Although it has been shown that stream periphyton can uptake and assimilate event-based P, the role of antecedent P concentrations in modulating P uptake from event-based loadings and resulting effects on periphyton structure and function is not known. To assess effects of antecedent P concentration on stream periphyton response to short-term P loading events, we completed two 26-day artificial stream experiments at the Thames River Experimental Stream Sciences (TRESS) Centre in London, Canada. Experiments consisted of exposing periphyton communities in nine artificial streams to a range of 48-hour P loading event concentrations (15 to 690 μg P/L) under low (10 μg P/L) or high (50 μg P/L) antecedent P concentrations. Periphyton was sampled one day before, one day after and 10 days after P loading events to quantify periphyton structure (ash free dry mass (AFDM), chlorophyll a (chl a), P content) and function (P uptake, benthic metabolism, cellulose decomposition, biomass growth, chl a accumulation). Under low antecedent P conditions one day after the P event, P content and P uptake had a positive linear relationship with event concentration and this was similarly seen in biomass and chl a ten days after the P event. One day after the P event in high antecedent streams, P content and P uptake showed a positive linear response with P event concentration, but this additional P in periphyton did not lead to increases in biomass and chl a. Whereas, a negative linear relationship with event concentration and P uptake was seen ten days after the P event. Measures of periphyton function (benthic metabolism and cellulose decomposition) were unaffected by P event size and regardless of the antecedent condition. These findings suggest that high antecedent P concentrations caused cellular saturation of periphyton limiting the assimilation of P from event-based P loads. Therefore, streams with high antecedent P may deliver reduced water purification benefits with regards to attenuating P transport to downstream ecosystems at risk of eutrophication. Management actions to reduce antecedent P concentrations will be needed to rehabilitate ecosystem service provision in streams chronically enriched in P.enperiphytonphosphoruseutrophicationnutrient loadingMaster Thesis