Lake Morphometry and River Network Controls on Evasion of Terrestrially Sourced Headwater CO₂

Abstract

Inland waters play an important role in the global carbon cycle, contributing significant greenhouse gas (GHG) emissions to the atmosphere (Bastviken et al., 2011; Cole et al., 2007; Raymond et al., 2013). River networks are generally conceptualized as active biogeochemical reactors that mix, store, and evade GHGs and constituents transported from upstream together with those generated from in-stream production (Cole et al., 2007; see also; Raymond et al., 2016; Zarnetske et al., 2018). Ultimately, inland waters store, evade, and transport over half of the carbon that they receive from the terrestrial ecosystem before reaching the oceans (Hotchkiss et al., 2015), thereby playing a fundamental role in global carbon processes. Running inland waters (hereafter termed 'rivers') are generally supersaturated with GHGs and exhibit a net evasive flux of these gases from water to air (Cole & Caraco, 2001; Jones et al., 2003). This flux [M/L 2 T] is relatively easy to calculate with in situ knowledge of the gas concentration gradient between the water [gas] water and the air [gas] air [M/L 3 ] and the gas transfer velocity k [L/T] (Equation 1).

Streamflow regime of a lake‐stream system based on long‐term data from a high‐density hydrometric network

“…The potential role of stream-lake network structure on influencing spatiotemporal variability in streamflow regimes could be further evaluated using existing approaches for describing and quantifying the structure of lake-stream networks for a range of geologic and climatic settings (Allerton et al, 2019;Gardner et al, 2019;Goodchild, 1988;Mark & Goodchild, 1982). These topological approaches may provide a means to generalize how hillslopes, lakeless tributaries and lakes interact to influence streamflow regimes at regional and global scales, similar to studies that have considered lake-stream network structure and its influence on nutrient transport (Brinkerhoff et al, 2021;Soranno et al, 2015).…”

Global Controls on DOC Reaction Versus Export in Watersheds: A Damköhler Number Analysis

“…This was partly due to unavailability of global discharge or flow velocity data sets (Lin et al., 2019) that allows for consistent seasonal characterization of surface WRTs over millions of river/stream reaches and across watersheds. While recently modeled for some regional river systems (Brinkerhoff et al., 2021), this lack of a consistent global residence time database, in practice, has impeded a broad‐scale perspective of cross‐region watershed removal or export, given that WRT is a necessary parameter.…”

Does Photomineralization of Dissolved Organics Matter in Temperate Rivers?

“…As a result, rivers of all stream orders are broken into multiple reaches, including first order tributaries (which are frequently segmented by ponds). Discharges (m 3 s −1 ) and hydraulic residence times (HRT, days) were calculated according to the method of Brinkerhoff et al (2021) at four different "characteristic discharges" (Q 2 , Q 15 , Q 50 , Q 98 ), which refer to the streamflows for each reach that exceeds that percent of the time. Q 50 represents median annual flows calculated specifically for each reach, while Q 2 and Q 98 represent extreme flood and low-flow events at the tail ends of the observed record, respectively.…”

“…Transport rates deal primarily with the time available for DOC to be photooxidized within a given river reach, which is dependent on the physical hydrology. Streams with high water velocities tend to have high discharges (flows) and short water residence times, and thus less time is available for reactions to take place (Brinkerhoff et al., 2021; Raymond et al., 2016). Both classical and modern research in inland waters has shown that the relative proportion of a parcel or pulse of a constituent that is transformed or eliminated from the water column is inversely related to the water residence time (Maavara et al., 2020; Vollenweider, 1975).…”