Spatial and Temporal Variations in Aquatic Organic Matter Composition in UK Surface Waters.

Area of Science:

• Environmental Chemistry
• Water Quality Science
• Organic Geochemistry

Background:

• Drinking water treatment in the UK faces increasing challenges due to evolving aquatic dissolved organic matter (DOM).
• Spatial and temporal variations in DOM composition significantly impact water treatability but remain poorly understood.
• Climate change and altered rainfall patterns exacerbate these challenges by influencing DOM characteristics.

Purpose of the Study:

• To investigate the spatial (north-south gradient) and temporal (four-year period, seasonal) variations in DOM composition in UK surface waters.
• To identify how DOM sources and characteristics differ between headwaters and reservoirs across the UK.
• To correlate observed DOM compositional changes with raw drinking water quality and treatment implications.

Main Methods:

• Utilized advanced analytical techniques (e.g., Ultrahigh-performance liquid chromatography with high-resolution mass spectrometry) to characterize DOM composition.
• Collected water samples over four years across a north-south transect in the UK, including headwater streams and reservoirs.
• Analyzed DOM for key compositional metrics, including aromaticity, oxidation state, and specific compound classes (carbohydrates, peptides, lipids).

Main Results:

• Significant north-south trends in DOM composition were observed: northern sites had lower carbohydrate and peptide-like compounds, while southern sites had lower lipid-like compounds.
• DOM collected in Autumn 2021 (post-low rainfall summer) exhibited higher aromaticity, lower oxidation, and greater diversity compared to samples from 2018-2020.
• Seasonal shifts, particularly in Autumn, showed decreased lipid content and increased oxy-aromatic compounds, linked to rainfall rewetting and soil organic matter mobilization.

Conclusions:

• DOM composition in UK waters exhibits distinct geographical and seasonal variability, influenced by catchment characteristics and climatic conditions.
• Autumnal DOM profiles, characterized by increased aromaticity and diversity, pose greater challenges for drinking water treatment.
• Understanding these DOM dynamics is crucial for developing resilient water treatment strategies in the face of climate change and evolving water quality.