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

Abstract

Hydro-morphological alterations in water bodies caused by climate change and human activities affects the ecosystem functioning and generate important water quality problems. Some of these alterations can generate an increase in cyanobacterial blooms, which are associated with the appearance of bad taste and odorous compounds such as geosmin. The factors that trigger their production are still unclear, and this inability to predict geosmin episodes provokes economic problems for water supply companies. This study aims to evaluate the effects of water flow and light availability on biofilm development and intracellular geosmin formation. A mesocosm experiment was performed between February-April, 2019. The mesocosms were a set of 10 outdoor 3 m long flumes, with a continuous water supply from the Ter river (Catalonia, NE Spain). Two light intensities were established: natural light and light reduced to 80%, combined with five gradual water flows from 0.09 to 1.10 L/s. Water samples were taken to analyze nutrients, and biofilm samples, to analyze geosmin concentration, chlorophyll a and the community. Geosmin in biofilm was detected in those treatments in which Oscillatoria sp. appeared. The concentration of intracellular geosmin was higher at lower water flows (0.09 and 0.18 L/s), and the highest (2.12 mg/g) was found in the flume with the lowest water flow (0.09 L/s) and irradiation (20%). This flume was the one that presented a greater concentration of Oscillatoria sp. (21% of the community). It stands out that, when geosmin in biofilm was found, the dissolved inorganic nitrogen and soluble reactive phosphorus ratio decreased, from an average of 417:1 to 14:1. This was mainly due to an increase in inorganic phosphorus concentration generated by a change in the nutrient uptake capacity of the community's biofilm. The results obtained in this study indicated the potential implications for stream ecosystem management to control geosmin appearance. Likewise, they could be used as an early warning system, establishing that in times of drought, which lead to a general decrease in river water flow, the situation could be optimal for the appearance and development of geosmin producing cyanobacteria in low-flow areas near the river banks.

Effects of the interaction between nutrient concentration and DIN:SRP ratio on geosmin production by freshwater biofilms

“…Changes at the structural level were reflected in functional parameters with photosynthetic efficiency (Yeff) being significantly lower under low DIN:SRP ratio. This could be explained by the higher presence of cyanobacteria in these treatments, since some studies have found that cyanobacteria usually show low photosynthetic efficiency values compared with the rest of the algal community (Espinosa et al, 2020;Luimstra et al, 2018).…”

“…The concentration of geosmin in biofilm was quantified following the protocol described by Espinosa et al (2020). Briefly, a headspace solid phase micro-extraction was performed.…”

“…Abundant growth of benthic and planktonic cyanobacteria in freshwaters exploited for drinking water purposes has been correlated with the appearance of secondary metabolites, such as geosmin and 2 -methylisoborneol (MIB) (Espinosa et al, 2020;Lee et al, 2017), affecting the organoleptic characteristics of water and influencing both odor and taste, with a consequent negative impact in the perception of the population about the tap water quality (Ding et al, 2014). Although no health risk has been linked to these Taste and Odor compounds (T&Os), they are perceived by humans at very low levels of concentration (Smith et al, 2009), resulting in consumer complaints and representing a challenge for drinking water companies.…”

Driving Factors of Geosmin Appearance in a Mediterranean River Basin: The Ter River Case

“…After that, each cobble was scrapped in 60 ml of water from the same sampling site to obtain a biofilm suspension. Aliquots of this suspension were used to analyze chlorophyll- a (Chl- a ), performed as described by Jeffrey and Humphrey (1975) , and ash-free dry mass as described in Espinosa et al (2020) . The Margalef index was also calculated as the quotient between the carotenoid/Chl- a ratio, being values obtained from the spectrophotometric reading of the sample at 430 nm (carotenoids and accessory pigments concentration) and 665 nm (Chl-a concentration), to obtain information about the maturity of the populations ( Elosegui and Sabater, 2009 ).…”

Data_Sheet_1.PDF

“…This would agree with our study, where higher geosmin concentration was observed at lower temperatures (close to 10 • C), whereas at higher temperatures (20-25 • C), geosmin levels were below the detection limit (Figure 6B). Moreover, considering that low light conditions have been described to favor intracellular geosmin production in river biofilms (Espinosa et al, 2020), the increased light availability occurring in summer may be an additional limiting factor for microbial geosmin production in the Ter River, as higher light incidence prevents gaseous vacuoles formation and geosmin production (Li et al, 2012). In fact, different studies have shown that at temperatures ≈20-25 • C, higher light intensity hinders the production of geosmin by cyanobacteria (Oh et al, 2017;Alghanmi et al, 2018).…”