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22-01-2025

Optical properties of water: a new vision of aquatic biodiversity

Picture Laura Carrau (https://www.lauracarrau.com/, Mileva Films). 

Continental aquatic ecosystems are fundamental to the biodiversity and biogeochemical cycles of the planet. One of the most innovative fields in the study of these systems is the analysis of the optical properties of water, both in situ and through remote sensing, a methodology that allows us to understand the composition of water and the processes that take place in it. 

Camille Minaudo, a researcher of IRBio at the University of Barcelona, studies the physical and biogeochemical mechanisms that determine the trajectories of water quality in continental aquatic ecosystems affected by human activities. A specialist in the biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P), he combines long-term monitoring data, optical properties of water and remote sensing products to address his research questions and better understand the dynamics of freshwater ecosystems from Pyrenean lakes to large rivers, such as the Gambia. 

This approach combines spatial and temporal observation, key to understanding the variability within the aquatic ecosystems he studies. By studying how light interacts with water and its components, scientists can track key variables, often from specific signatures measured in situ or by remote sensing (drones, satellites). 

Studying the composition of water 

Phytoplankton and micro-algae, as primary producers, play a crucial role in these environments. Their biomass, detectable thanks to their light-absorbing capacity, is a key indicator of environmental conditions, reflecting the health of aquatic ecosystems. 

Particles composed of sediments as well as altered organic or inorganic materials, contribute to water turbidity and significantly influence biogeochemical cycles. Added to this is colored dissolved organic matter (CDOM), often originating from organic-rich systems such as peatlands, which stains the water a characteristic brown and reflects the presence of dissolved organic compounds. Together, these elements illustrate the complexity of the biological, chemical and physical interactions that shape the dynamics of aquatic ecosystems. In recent studies, this approach, little explored in limnology, has allowed Dr. Minaudo to identify significant episodes of calcite precipitation in the Sau reservoir, such as an event in 2017 that even impacted the Susqueda reservoir. 

Optical properties of water to protect aquatic biodiversity 

Finally, the optical properties of water can be used to quantify phytoplankton biomasses by in situ measurements or by remote sensing, providing an additional tool for monitoring water masses. The optical properties of water are not limited to scientific understanding: they are a tool to monitor, restore and protect our aquatic ecosystems. Discoveries in hydrodynamics, chemistry and remote sensing offer new perspectives for managing and protecting aquatic ecosystems in an increasingly changing world.