Temporal and spatial changes in DOM revealed by FT-ICR MS

DOM from peatlands is a collection of complex molecules, but also a significant source of carbon to aquatic pathways. It has a wide impact on aquatic ecosystems, providing an energy source for microbes and buffering capacity for water chemistry changes. The composition of DOM in drinking water reservoirs also impacts on chemical and energy demands of treatment processes, and is an area of growing concern for UK drinking water providers.

DOM was extracted from water collected from peatland headwater streams and reservoirs in the UK. The DOM was analysed with elemental analysis and FT-ICR MS to determine how the composition changes as water moves through the catchment. A combination of spatial and temporal sampling strategies allowed seasonal and catchment characteristics to be investigated (from 2018-2021, and 53-61°N).

There were significant trends in DOM composition metrics across a north/south gradient, with higher lipid content, and lower carbohydrate and peptide content in northern sites than southern sites. Samples collected in 2021 had several significant composition differences to other years. Monthly sampling showed the largest changes in DOM composition coincided with the end of the growing season (September in the UK).

These results show variable DOM in headwaters can be, and how reservoirs act to buffer the most extreme changes, resulting in more stable DOM compositions in reservoirs. Understanding how DOM composition is impacted by season, climate and catchment characteristics will have important ramifications for drinking water providers, and will help catchment managers plan land use changes and timing of water draw-off from peatland reservoirs.