Characterizing optical and chemical properties of dissolved organic matter under changing environments

Organic matter is the largest reservoir of carbon-based compounds on Earth. The transformation of organic matter between land, water, the atmosphere, and the biosphere maintains the balance of the global carbon cycle. In aquatic environments, dissolved organic matter (DOM) transforms into dissolved inorganic carbon (DIC) through photomineralization and decomposition, thereby regulating carbon dioxide levels from water to the atmosphere. The subset of DOM that absorbs solar radiation, chromophoric DOM (CDOM), affects the penetration of solar radiation into the water column, influencing water color, photosynthesis, and overall aquatic ecosystem health.

DOM in aquatic environments is a complex mixture of organic compounds derived from various sources, such as terrestrial vegetation, algae, and microbial activity. Further study on the behavior of DOM is needed to assess water quality, track its sources and sinks, and comprehend its role in biogeochemical cycles and the impacts of climate change on aquatic ecosystems. Understanding the mechanisms and dynamics of DOM requires the integration of chemical, physical, biological, and geological processes. Its characteristics are influenced by environmental factors and other dissolved substances. Additionally, the composition and properties of DOM vary across different water bodies and change over time due to factors like seasonality, hydrological events, and human activities. Among the main environmental factors, solar radiation drives various photochemical reactions affecting DOM, and the abundant presence of iron in water further influences these light-induced processes, impacting DOM.

The thesis investigates the influence of visible light and ferric ions on the complex chemical degradation process of DOM and elucidates its impact on the spectrometric properties. We opt for a multiscale interdisciplinary approach that combines chemical analyses with spectroscopic and colorimetric measurements. The results contribute to water quality monitoring, remote sensing, and citizen observations of DOM. In pursuit of investigating how initial material composition and environmental conditions influence the transformation process of organic matter and the optical properties of CDOM, we conducted laboratory-scale controlled experiments to investigate the variations in their chemical composition and optical properties of representative CDOM precursors. We analyzed several key spectrometric parameters and correlated these with CDOM’s chemical composition indices like the hydrogen-to-carbon and oxygen-to-carbon ratios.