Abstract

Organic matter is a cornerstone of sustainable agriculture: it improves soil fertility, enhances water retention, supports microbial diversity, and underpins long-term productivity. Yet, when mobilised into water systems, organic matter (specifically Fluorescent Dissolved Organic Matter (FDOM)) can become a pollutant. FDOM reduces light penetration in aquatic environments, limiting photosynthesis, lowering primary productivity, and disrupting food webs. It can also fuel microbial activity, leading to harmful bacterial blooms, and enhance the downstream transport of toxic metals, threatening water quality and ecosystem health.

This presentation explores how different farming practices influence FDOM build-up in freshwater systems, drawing on long-term data from the North Wyke Farm Platform in Devon, UK. This unique experimental facility comprises 15 hydrologically isolated catchments managed under different farming systems, including pasture and arable. Each catchment has a unique land-use history, including past transitions between different land-use types (livestock and arable) and periods of management. We used high-frequency monitoring of runoff (15-minute intervals once flow exceeds 0.2 L s⁻¹) combined with robust outlier detection and linear mixed modelling to disentangle the effects of farm management, land use, precipitation, and seasonality on FDOM dynamics (2016–2024).

By linking farming systems to water quality outcomes, this research addressed the central question: Do modern agricultural practices increase FDOM in local water supplies, and what are the consequences for aquatic ecosystem health? Specifically:

1. How does agricultural land use and field treatment affect FDOM build-up?
2. Which farming practices contribute most to FDOM accumulation?
3. How do FDOM trends change over time, with land-use transitions, and with climatic variability?

The results provide not only new insights into the environmental costs of different agricultural systems but also evidence to inform farm design, land-use management, and policy aimed at reconciling food production with water quality and ecosystem protection.