Climate change and drinking water from Scottish peatlands: Where increasing DOC is an issue?

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

Drinking water is becoming more difficult to treat, especially in the UK, due to the changing concentration and composition of aquatic dissolved organic matter (DOM). The spatial and temporal variations in the DOM composition are not well understood. This study investigated how DOM composition varies along a north/south gradient in the UK, over four years, and between headwaters and reservoirs. There were trends in DOM composition metrics from north to south; carbohydrate and peptide-like compounds were lower in northern sites, while lipid-like compounds were lower further south, suggesting different sources of DOM in north/south catchments. DOM collected in Autumn 2021, after a Summer of low rainfall, was more aromatic, less oxidized, and more diverse than DOM collected in 2018-2020. Decreased lipid content and increased oxy-aromatic content occurred in Autumn, at the end of the plant growing season, when increased rainfall rewets catchments and mobilizes soil OM into surface waters. These seasonal changes in DOM composition coincide with increased DOM concentrations in raw drinking water, leading to more challenges for drinking water treatment, especially as climate change alters rainfall distribution in the UK.

Identifying and understanding how critical landscapes for carbon sequestration respond to development for low carbon energy production: Insight to inform optimal land planning and management strategies

Wind farms can mitigate increasing CO2 emissions by fossil-fuel free energy generation. However, landscape disturbance during development must not have lasting impacts on C sequestration, an ecosystem service. To understand how a critical carbon landscape responds to wind farm development, we monitored for 10 years dissolved organic carbon (DOC) export in five catchments draining Europe's second largest onshore wind farm, Whitelee, UK. The DOC flux trend and seasonality were modelled using Generalised Additive and Mixed Models, novelly using first derivatives of trends to identify responses to wind farm development. Unlike a nearby, minimally-disturbed catchment, Whitelee catchment DOC fluxes increased over the decade, tracking successive phases of wind farm development, particularly forest felling to enable turbine location. Inter-catchment differences in the rate of DOC flux, where slowing suggests recovery (not always evident), reflect differing intensity (timing and spatial reach) of catchment disturbance. However, increased DOC flux approximated 3.5 % maximum of C likely sequestered and therefore soil C sequestration is unlikely to be compromised unless the soils are highly degraded and close to not being a C sink. For the greenest energy transition, responsible planning should minimise C losses, even when small, and in a critical landscape may require consideration of impact on other ecosystem services. For example, deterioration in quality of potable water supply occurred within the observation period. Ongoing provisioning of multiple ecosystem services from critical carbon landscapes requires planning. We demonstrate an example of such an approach for wind farm development considering in priority order carbon storage, forest products, potable water supply. Our findings are relevant to integrated landscape planning and management in temperate and high latitude/altitude peatlands globally that are subject to wind energy development and/or forest felling.

Clusters of composition: Elemental content of aquatic organic matter in UK and Faroe peatlands

Water supply companies with reservoirs in peatland areas need to know how land use and vegetation cover in their supply catchments impact the amount and composition of aquatic organic matter in raw waters. Drinking water treatment processes remove organic matter from potable supplies, but recent increases in concentration and changes in composition have made this more difficult. This study analysed the composition of aquatic organic matter from peatland catchments in the UK and Faroe Islands. Both dissolved organic matter (DOM) and particulate organic matter (POM) compositions varied spatially, but these differences were not consistent as water moved through catchments, from headwaters and peatland pools to lake and reservoir outlets. These data showed that lakes and reservoirs are acting as flocculation hotspots, processing OM, releasing carbon (C), hydrogen (H) and oxygen (O) compounds to the atmosphere, and resulting in OM with higher N content. DOM compositions could be grouped into five clusters, showing that water treatment processes can be maximised to target 'envelopes' or clusters of DOM compositions. Catchment factors such as land use, vegetation cover, percentage peat cover and catchment area are good indicators of OM compositions likely to be present in a reservoir, and can guide water companies to maximise efficiency of their raw water treatment processes.

Climate change and future water demand: Implications for chlorine and trihalomethanes management in water distribution systems

The global change in surface water quality calls for increased preparedness of drinking water utilities. The increasing frequency of extreme climatic events combined with global warming can impact source and treated water characteristics such as temperature and natural organic matter. On the other hand, water saving policies in response to water and energy crisis in some countries can aggravate the situation by increasing the water residence time in the drinking water distribution system (DWDS). This study investigates the individual and combined effect of increased dissolved organic carbon (DOC), increased temperature, and reduced water demand on fate and transport of chlorine and trihalomethanes (THMs) within a full-scale DWDS in Canada. Chlorine and THM prediction models were calibrated with laboratory experiments and implemented in EPANET-MATLAB toolkit for prediction in the DWDS under different combinations of DOC, temperature, and demand. The duration of low chlorine residuals (<0.2 mg/L) and high THM (>80 μg/L) periods within a day in each scenario was reported using a reliability index. Low-reliability zones prone to microbial regrowth or high THM exposure were then delineated geographically on the city DWDS. Results revealed that water demand reduction primarily affects chlorine availability, with less concern for THM formation. The reduction in nodal chlorine reliability was gradual with rising temperature and DOC of the treated water and reducing water demand. Nodal THM reliability remained unchanged until certain thresholds were reached, i.e., temperature >25 °C for waters with DOC <1.52 mg/L, and DOC >2.2 mg/L for waters with temperature = 17 °C. At these critical thresholds, an abrupt network-wide THM exceedance of 80 μg/L occurred. Under higher DOC and temperature levels in future, employing the proposed approach revealed that increasing the applied chlorine dosage (which is a conventional method used to ensure sufficient chlorine coverage) results in elevated exposure toTHMs and is not recommended. This approach aids water utilities in assessing the effectiveness of different intervention measures to solve water quality problems, identify site-specific thresholds leading to major decreases in system reliability, and integrate climate adaptation into water safety management.

Amino Acids as Potential Precursors to Odorous Compounds in Tap Water during Spring Runoff Events

The onset of spring runoff in northern climates and tap water odor events are difficult to predict because common water quality parameters cannot fully explain the intermittent odor events that occurred over past decades. Studies have shown that small polar water-soluble compounds, such as amino acids (AAs), leach first from ice/snowmelt. AAs are known to produce odorous compounds, such as aldehydes and chloroaldimines, upon chlorination. Therefore, we proposed that AAs may serve as markers for small and soluble organics that contribute to the odor of chlorinated tap water. Here, we studied the occurrence of AAs in source water collected at two water treatment plants and the odor profiles of tap water at >300 homes during the 2021 and 2022 spring runoff events. AA concentrations were at baseline levels (<100 ng/L) during the 2021 runoff but much higher (up to 5500 ng/L) in 2022 and associated with an escalation in odor complaints. AA concentrations peaked at the onset of the 2022 spring runoff and corresponded with the strongest reported odor intensities in tap water. We obtained high resolution MS and MS/MS spectra of chloroaldimines and confirmed the formation of chloroaldimines under chlorination of the six AAs detected in source water. The results indicate that AAs signal the onset of spring runoff and represent small polar water-soluble compounds that may contribute to tap water odor problems.