Quantifying rapid spatial and temporal variations of CO2 fluxes from small, lowland freshwater ponds

Hydrobiologia, Jun 2016

Small ponds comprise a substantial portion of the total area of the Earth’s inland waters. They can be powerful carbon sinks or sources, potentially significant processors of organic carbon. Our understanding of their role is constrained by the absence of information regarding their CO2 fluxes (F CO2) and how these change with wet or dry phases and across distinct pond plant communities. We monitored the F CO2 from 26 neighbouring small ponds over a 2-week drying period in late summer in 2014. The mean F CO2 on day 1 (−641 ± 1490 mg m−2 day−1) represented a net intake across the site. As ponds dried they switched to becoming CO2 sources resulting in a net site emission of CO2 by day 12 (3792 ± 2755 mg m−2 day−1) although flux rates did not vary systematically between plant communities. Significant variability in the F CO2 was observed amongst adjacent ponds on individual sampling days, resulting in marked spatial heterogeneity in CO2 processing. This large degree of temporal and spatial heterogeneity across short time periods and small distances highlights the variability in the F CO2 from temporary systems, making it hard to generalize their role in carbon cycle models.

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Quantifying rapid spatial and temporal variations of CO2 fluxes from small, lowland freshwater ponds

Quantifying rapid spatial and temporal variations of CO2 fluxes from small, lowland freshwater ponds 0 P. J. Gilbert D. A. Cooke M. Deary S. Taylor M. J. Jeffries (&) Northumbria University , Ellison Building, Newcastle upon Tyne NE1 8ST , UK 1 Guest editors: Mary Kelly-Quinn, Jeremy Biggs & Stefanie von Fumetti / The Importance of Small Water Bodies: Insights from Research Small ponds comprise a substantial portion of the total area of the Earth's inland waters. They can be powerful carbon sinks or sources, potentially significant processors of organic carbon. Our understanding of their role is constrained by the absence of information regarding their CO2 fluxes (F CO2) and how these change with wet or dry phases and across distinct pond plant communities. We monitored the F CO2 from 26 neighbouring small ponds over a 2-week drying period in late summer in 2014. The mean F CO2 on day 1 (-641 ± 1490 mg m-2 day-1) represented a net intake across the site. As ponds dried they switched to becoming CO2 sources resulting in a net site emission of CO2 by day 12 (3792 ± 2755 mg m-2 day-1) although flux rates did not vary systematically between plant communities. Significant variability in the F CO2 was observed amongst adjacent ponds on individual sampling days, resulting in marked spatial heterogeneity in CO2 processing. This large degree of temporal and spatial heterogeneity across short time periods and small distances highlights the variability in the F CO2 from wetland Introduction temporary systems, making it hard to generalize their role in carbon cycle models. Carbon flux Temporary pond Small In recent years, the role that small ponds play in global geochemical processes has received increasing interest (Cole et al., 2007; Battin et al., 2009; Downing, 2010) . Estimations of their cumulative global coverage have suggested that they are comparable in area to the Earth’s largest lakes (Downing et al., 2006) , although more recent estimates have been more conservative (Seekell & Pace, 2011; Verpoorter et al., 2014) . Equally these systems support disproportionately intense processes for their size, when compared to larger water bodies (Torgersen & Branco, 2008; Downing, 2010; Catala´n et al., 2014) . This makes them ideal cyclers of atmospheric carbon (here after C), accounting for a substantial portion of the missing C budget from which small ponds and wetlands are frequently omitted. The absence of small ponds from C budgets is in part due to a lack of robust data quantifying their rates and processes. Biogeochemical processing in ponds remained relatively understudied until the late twentieth century as limnological research focused on larger lakes and river systems, where it was assumed that the dominant inland aquatic processing of C occurred (Downing, 2010) . However, just as ponds were once overlooked as wildlife habitats but are now known to be disproportionately rich in species and rarities compared to streams, rivers and lakes (Williams et al., 2004; Davies et al., 2008) , their potential significance for ecosystem services, such as C sequestration, is being increasingly recognized (Cole et al., 2007; Tranvik et al., 2009; Downing, 2010; Cereghino et al., 2014; Gilbert et al., 2014) . The number of studies on C cycling within ponds is rapidly increasing (Downing, 2010; Boix et al., 2012; Ewald et al., 2012) . Within this overall biome of ponds, temporary systems are receiving increasing interest (Torgersen & Branco, 2008; Fromin et al., 2010; Catala´n et al. 2014; von Schiller et al., 2014) . Temporary ponds are known by a range of diverse regional names or technical definitions: e.g. seasonal, ephemeral, playa or vernal (Keeley & Zedler, 1998) . Recognized as ecologically valuable they support a specialist flora and fauna, which adds a significant contribution to c biodiversity on the landscape scale, that is able to withstand drought through resistant propagules or by rapid re-colonization (Collinson et al., 1995; Jeffries, 1998, 2010) . They are internationally important terrestrial habitats, ubiquitous in all climatic zones across the globe including extreme desert and polar environments, including thaw ponds in Arctic Tundra (Gallagher & Huissteden, 2011) , temporal pools in Mediterranean and desert biomes (Catala´n et al., 2014) , constructed rice paddies in equatorial tropics (Jonai & Takeuchi, 2014) , to melt pools in Antarctica (Allende & Mataloni, 2013) . They are also typical of temperate biomes such as south American grasslands (e.g. mallines, Kutschker et al., 2014) , prairie potholes and woodland vernal ponds in North America (Batzer et al., 2005; Gala & Melesse, 2012) , across the riverine plains of Europe (e.g. tributaries of the Danube in Hungary; Boven et al., 2008) , through into the Asian steppes (Mozley, 1937; an unusual example of a rare early appreciation of their value) . Temporary habitats can also be historically long-lived fea (...truncated)


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Peter J. Gilbert, David A. Cooke, Michael Deary, Scott Taylor, Michael J. Jeffries. Quantifying rapid spatial and temporal variations of CO2 fluxes from small, lowland freshwater ponds, Hydrobiologia, 2017, pp. 83-93, Volume 793, Issue 1, DOI: 10.1007/s10750-016-2855-y