The phytoplankton photochemical efficiency of photosystem II (PSII) is a good indicator in environmental monitoring?
Year: 2025
Type: dissertation
Abstract: The photochemical efficiency of photosystem II (PSII) is widely used in marine and estuarine environments to assess the physiological state of phytoplankton, yet its application in freshwater monitoring remains limited. This study aims to evaluate the short-term (within a day), medium-term (daily), and long-term (monthly) temporal variation of PSII photochemical efficiency in an artificial tropical freshwater lake to determine its potential use as a parameter in environmental monitoring. Water samples were collected over five consecutive days per month and five times throughout the day from April 2023 to June 2024 to measure PSII photochemical efficiency (Fv'/Fm'), along with environmental variables such as dissolved oxygen (DO), pH, oxidation-reduction potential (ORP), water temperature, salinity, conductivity, turbidity, and pigments (chlorophyll and phycoerythrin). The composition and density of the phytoplankton community were also assessed through quantitative subsurface sampling. A linear mixed-effects model (LMM) was applied to determine which environmental factors influenced photochemical efficiency, and redundancy analysis (RDA) was used to explore temporal patterns in phytoplankton composition. The results indicate that photochemical efficiency is more effective for long-term monitoring, showing significant variation between months but no clear daily pattern. Low efficiency values were associated with excessive light and temperature exposure, leading to photoinhibition and ultimately reducing phytoplankton diversity and evenness. The combination of high phytoplankton density, elevated pH and dissolved oxygen levels, and increased chlorophyll and phycoerythrin concentrations suggests an advanced stage of eutrophication, reinforced by the dominance of the class Cyanophyceae, as eutrophic environments generally favor opportunistic species. The LMM revealed that PSII photochemical efficiency was significantly negatively influenced by photosynthetically active radiation (PAR) and pH, while it was positively influenced by dissolved oxygen. This study highlights the importance of photochemical efficiency (Fv'/Fm') as a key tool for ecological monitoring in freshwater environments, particularly in eutrophic systems. The correlations between photochemical efficiency and environmental factors such as PAR, dissolved oxygen, and pH underscore the complex interactions between available light, oxidative stress, and water chemistry in regulating photosynthesis. The low Fv'/Fm' values observed during the study suggest chronic photoinhibition caused by excessive light exposure and high temperatures, associated with the dominance of Cyanophyceae, reflecting the effects of eutrophication. These findings reinforce the potential of Fv'/Fm' as an early indicator of ecosystem changes, making it valuable for freshwater monitoring programs. Future research should further investigate its applicability across different trophic states and environmental conditions to enhance its use in ecological health assessments and conservation strategies.
Author: Alvarenga, Brener Freitas de
Language: Portuguese
Subfield: Environmental Chemistry
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7213993245