DOC sources and DOC transport pathways in a small headwater catchment as revealed by carbon isotope fluctuation during storm events

Abstract

International audienceMonitoring the isotopic composition ( 13CDOC) of dissolved organic carbon (DOC) during flood events can be helpful for locating DOC sources in catchments and quantifying their relative contribution to stream DOC flux. Highresolution (< hourly basis) 13CDOC data were obtained during six successive storm events occurring during the highflow period in a small headwater catchment in western France. Intra-storm 13CDOC values exhibit a marked temporal variability, with some storms showing large variations (> 2 ‰), and others yielding a very restricted range of values (< 1 ‰). Comparison of these results with previously published data shows that the range of intra-storm 13CDOC values closely reflects the temporal and spatial variation in 13CDOC observed in the riparian soils of this catchment during the same period. Using 13CDOC data in conjunction with hydrometric monitoring and an end-member mixing approach (EMMA), we show that (i) > 80% of the stream DOC flux flows through the most superficial soil horizons of the riparian domain and (ii) the riparian soil DOC flux is comprised of DOC coming ultimately from both riparian and upland domains. Based on its 13C fingerprint, we find that the upland DOC contribution decreases from ca. 30% of the stream DOC flux at the beginning of the high-flow period to < 10% later in this period. Overall, upland domains contribute significantly to stream DOC export, but act as a sizelimited reservoir, whereas soils in the wetland domains act as a near-infinite reservoir. Through this study, we show that 13CDOC provides a powerful tool for tracing DOC sources and DOC transport mechanisms in headwater catchments, having a high-resolution assessment of temporal and spatial variability

Effects of human land use on the terrestrial and aquatic sources of fluvial organic matter in a temperate river basin (The Meuse River, Belgium)

“…The seasonal variability in stream DOC concentrations contrasts with the more common pattern reported in other temperate streams whereby stream DOC typically increases with stream discharge, resulting in higher concentrations during high flow periods compared to low flow periods (Lambert et al 2014;Raymond and Saiers 2010;Sanderman et al 2009). In the Meuse River, increases in DOC concentrations at peak discharge are consistent with greater inputs of terrestrial DOM during rainfall events (Lambert et al 2014;Sanderman et al 2009) but stable levels of F Max of terrestrial humic-and microbial-like components along the entire hydrological cycle means that terrestrial inputs are relatively constant and hydrologically independent in-between rainfall episodes.…”

“…In the Meuse River, increases in DOC concentrations at peak discharge are consistent with greater inputs of terrestrial DOM during rainfall events (Lambert et al 2014;Sanderman et al 2009) but stable levels of F Max of terrestrial humic-and microbial-like components along the entire hydrological cycle means that terrestrial inputs are relatively constant and hydrologically independent in-between rainfall episodes. A similar pattern was observed at the scale of the Meuse basin whereby F Max of terrestrial components were slightly higher during S2 (summer period, low specific discharge) relative to S1 (winter period, high specific discharge).…”

“…The terrestrial (allochthonous) or aquatic (autochthonous) origin of OM determines its composition that in turn drives its reactivity and its impact on stream metabolism (Strauss and Lamberti 2002;Tranvik and Bertilsson 2001). Terrestrial inputs as well as autochthonous primary production of OM are the result of the interplay of several catchment attributes such as soil properties (Autio et al 2016;Nelson et al 1992), land cover (Giling et al 2014;Wilson and Xenopoulos 2009), hydrology and water residence time (Lambert et al 2014;Sanderman et al 2009) and nutrient availability (Reche et al 1998), all of these basic drivers being altered by human activities (Carpenter et al 2011;Stanley et al 2012). The conversion of natural landscapes for human use has thus been shown to alter the sources, composition and reactivity of fluvial OM with significant effects on carbon cycling in freshwaters (Parr et al 2015;Petrone et al 2011;Rosemond et al 2015;Wilson and Xenopoulos 2009).…”

New molecular evidence for surface and sub-surface soil erosion controls on the composition of stream DOM during storm events

“…The use of chemical components such as these is common in order to trace the contribution of sources to the stream Lambert et al, 2014;Morel et al, 2009). The soil solution analysis revealed variable concentrations during the event (Fig.…”

“…With the establishment of storm flow, the transfer of DOM from the soil solution is assumed to be made conservatively via a pistonlike effect, as used for the endmember mixing analysis and isotopic studies (Bazemore et al, 1994;Klaus and McDonnell, 2013;Lambert et al, 2014). However, recent studies have demonstrated that this assumption about the conservative transport of DOM could be impacted by production mechanisms activated during storm flow which could possibly induce a modification of the DOM composition (Dalzell et al, 2005;Hernes et al, 2008).…”