The influence of macrophytes on diurnal pH variability in subtropical estuaries: A mesocosm study

Coastal ecosystems are increasingly threatened by anthropogenic impacts, particularly from land-based activities that drive eutrophication. This research investigated eutrophication and the unique challenges facing southern hemisphere coastal ecosystems. We used a mesocosm study to measure the influence of a macroalga ( Rhizoclonium riparium ) and a floating macrophyte ( Pistia stratiotes ), on diurnal pH variability. Diurnal pH variability was more pronounced in the presence of macroalgae due to the direct release of metabolic byproducts into the water column during photosynthesis and respiration. In contrast, floating macrophyte treatments had lower diurnal pH variability, as metabolic byproducts are released into the atmosphere through floating foliage. Floating macrophytes influenced overall water column pH levels, resulting in an acidification effect, becoming more pronounced as macrophyte biomass increased. The study highlighted the importance of nutrient management and its association with macrophytes, to preserve the delicate balance of estuaries, and ensure the sustainable functioning of these critical ecosystems. Further in situ research is recommended to validate and expand on the mesocosm findings. • Macrophytes influence estuary water column pH levels. • Floating macrophytes decrease pH and submerged macrophytes increase pH. • Diurnal pH variability is more pronounced in submerged macroalgae. • Floating macrophytes exhibit lower diurnal variability.