Biofilm phosphorus uptake capacity as a tool for the assessment of pollutant effects in river ecosystems

Abstract

Biofilms are a key component in the nutrient removal from the water column. However, nutrient uptake by biofilms may be hampered by the occurrence of pollutants or other stressors. This study aimed: (i) to investigate the biofilm phosphorus (P) uptake capacity as a relevant process for the maintenance of fluvial water quality and (ii) to explore the sensitivity of this process to different chemical and environmental stressors. We conducted chamber experiments to test for the relevance of biofilm P uptake capacity (PUC) as a tool to detect effects of pollutants on river self-depuration. PUC was calculated by measuring P temporal decay after performing controlled P-spikes in chambers with biofilm-colonized tiles. Four different experiments were conducted to evaluate the response of PUC to: (a) several river waters from increasing polluted sites; (b) the effect of the bactericide triclosan (TCS); (c) the combined effect of TCS and grazers; and (d) the effect of TCS after a drought episode that affected the biofilms. These experiments showed that biofilms decreased their PUC along the pollution gradient. The biofilm PUC was significantly reduced after receiving high TCS concentrations, though lower TCS concentrations also affected the biofilm when this was submitted to grazing pressure. PUC decrease was induced by flow interruption which further enhanced the TCS negative effects. Overall, PUC was sensitive to the effects of pollutants like TCS as well as to the action of biological (grazing) and environmental (drought) factors. The study also showed that multiple stressors enhance the negative effects of pollutants on the PUC of biofilms. Our study values the use of biofilms' PUC as a sensitive ecological-based tool to assess the effects of chemicals on freshwater communities and their derived functioning in river ecosystems.

Priming of leaf litter decomposition by algae seems of minor importance in natural streams during autumn

“…In general, the metabolic activity of stream biofilm depends on its biomass [ 44 ], whereas the uptake per unit biomass tends to be greatest at oligotrophic, nutrient-poor reaches [ 45 ]. Nevertheless, internal phosphorus recycling at the biofilm level gains importance in nutrient-rich reaches [ 46 ], which usually reduces uptake rate [ 47 ] and results in our bioassay yielding highest uptake rate in moderately enriched streams (Arturo Elosegi, unpublished data). The small differences we found in P uptake rate per unit of chlorophyll a suggest a part of the algal biomass to be not very active, probably as a consequence of the senescence of algal mats by the end of autumn, which reduces the biological activity even if the biomass is large [ 48 ].…”

Priming of leaf litter decomposition by algae seems of minor importance in natural streams during autumn

“…Nevertheless, internal phosphorus recycling at the biofilm level gains importance 321 in nutrient-rich reaches (Mulholland et al, 1995), which usually reduces uptake 322 rate (Proia, Romaní & Sabater, 2017) and results in our bioassay yielding highest 323 uptake rate in moderately enriched streams (Arturo Elosegi, unpublished data).…”

Water Flow and Light Availability Influence on Intracellular Geosmin Production in River Biofilms

“…The nutrients uptake capacity of biofilms was estimated considering the difference in nutrients concentrations between the input and the outflow of each flume taking into account the area colonized by biofilms (Proia et al, 2017). The uptake capacity (U, mg/m 2 ) (Eq.…”