Abstract
AbstractPeatland reservoirs are global hotspots for drinking water provision and are likely to become more important as demand per capita rises and the climate changes. Dissolved organic carbon (DOC) is associated with harmful disinfection byproducts and reduced aesthetic quality, and its removal is the major treatment cost. Littoral zones are known to be disproportionately important for DOC production through macrophyte inputs, and such communities are predicted to expand with warming in northern regions. However, little is known about autochthonous DOC contributions and their response to climatic change. Here we exposed mesocosms to elevated CO2 (eCO2), warming and a combined treatment across a trophic gradient. Regression analysis indicated that while sediments, macrophytes, and phytoplankton are important DOC sources (P < 0.05), benthic algal biomass showed the strongest relationship with DOC (P < 0.05), suggesting it is an underestimated source. DOC removal indicators, namely phenol oxidase (depolymerization) and respiration (mineralization) were inversely related to DOC concentration in oligohumic (P < 0.05) and oligotrophic (P < 0.1) systems, suggesting heterotrophic processes are important in DOC removal. DOC concentrations increased across all systems (P < 0.05), irrespective of trophic status, due to increased photoautotrophic inputs (macrophyte, pelagic, and benthic algae) under eCO2, warming, and combined scenarios, with inhibited depolymerization and mineralization under eCO2, even when combined with warming (P < 0.05 and P < 0.05 excepting the oligo‐mesotrophic reservoir P < 0.1 respectively). Increased DOC loads of all fractions, regardless of provenance, are predicted in a future climate and, thus, investment in techniques to remove a greater range of DOC fractions is proposed to help “future proof” drinking water supplies.
Highlights
Dissolved organic carbon (DOC) has numerous effects on aquatic ecosystem properties (e.g., Evans et al, 2005) and ecosystem goods and services (e.g., Lapierre et al, 2013; Winterdahl et al, 2014), including drinking water quality (Bull et al, 1995), feedbacks to climate change and mitigation strategies (Wallin et al, 2013)
Using site water only, in the oligohumic pool the elevated CO2 (eCO2) treatment led to a 25% rise in pCO2 (F = 7.59, P = 0.014), warming induced a fall of 4% and there was no significant interaction between these factors in the combined treatment (14%; Figure 3b)
Relationships between phytoplankton biomass and wDOC were significant across nutrient-poor systems, suggesting that pelagic algae may be more important in these low productivity systems than expected
Summary
Dissolved organic carbon (DOC) has numerous effects on aquatic ecosystem properties (e.g., Evans et al, 2005) and ecosystem goods and services (e.g., Lapierre et al, 2013; Winterdahl et al, 2014), including drinking water quality (Bull et al, 1995), feedbacks to climate change and mitigation strategies (Wallin et al, 2013). While trends are not necessarily universal (Winterdahl et al, 2014; Worrall et al, 2018), increased DOC concentrations across North America and Europe have been reported as a result of climatic changes (e.g., Fenner, Freeman, et al, 2007; Fenner, Ostle, et al, 2007; Freeman et al, 2004; Freeman, Evans, et al, 2001; Freeman, Ostle, & Kang, 2001; Larsen et al, 2011), increased solubility due to pH changes FENNER ET AL. Understanding drivers of changes in DOC concentration is important, not least because terrestrial biomes where peatlands are abundant are global hotspots for drinking water provision (Xu et al, 2018) and DOC is becoming increasingly difficult to treat using conventional coagulation processes, due to changes in composition and increased concentration (Worrall & Burt, 2009). DOC acts as a precursor during chlorination for harmful carbonaceous (C-), and nitrogenous (N-) disinfection byproducts (DBP) (WHO, 2011)
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