Can the heterogeneity in stream dissolved organic carbon be explained by contributing landscape elements?

Abstract

Abstract. The controls on stream dissolved organic carbon (DOC) concentrations were investigated in a 68 km 2 catchment by applying a landscape-mixing model to test if downstream concentrations could be predicted from contributing landscape elements. The landscape-mixing model reproduced the DOC concentration well throughout the stream network during times of high and intermediate discharge.The landscape-mixing model approach is conceptually simple and easy to apply, requiring relatively few field measurements and minimal parameterisation. Our interpretation is that the higher degree of hydrological connectivity during high flows, combined with shorter stream residence times, increased the predictive power of this whole watershed-based mixing model. The model was also useful for providing a baseline for residual analysis, which highlighted areas for further conceptual model development. The residual analysis indicated areas of the stream network that were not well represented by simple mixing of headwaters, as well as flow conditions during which simple mixing based on headwater watershed characteristics did not apply. Specifically, we found that during periods of baseflow the larger valley streams had much lower DOC concentrations than would be predicted by simple mixing. Longer stream residence times during baseflow and changing hydrological flow paths were suggested as potential reasons for this pattern. This study highlights how a simple landscape-mixing model can be used for predictions as well as providing a baseline for residual analysis, which suggest potential mechanisms to be further explored using more focused field and process-based modelling studies.

The assumption of uniform specific discharge: unsafe at any time?

“…This indicates that there was a change in the spatial structure of Q sp depending on the wetness state of the system. These results are analogous to other studies that have also revealed seasonal and wetness dependency of hydrological and biogeochemical processes (Grayson et al, 1997;Buffam et al, 2007;Payn et al, 2012;Ågren et al, 2014).…”

Modelling landscape controls on dissolved organic carbon sources and fluxes to streams

“…The dominance of near-surface hydrological flow paths in such soils results in episodic transport of DOC to streams during storm events, that is highly nonlinear (Buffam et al 2007;Laudon et al 2011;Å gren et al 2014;. In many areas, increasing DOC in surface waters has been reported and variously ascribed to the effects of reduced acid precipitation, changes in land management, climate change and increased drought frequency (Laudon et al 2012).…”

Hydrologic control of dissolved organic matter concentration and quality in a semiarid artificially drained agricultural catchment

“…Additionally, the DOC flux-runoff relationship for this site is very similar to what has been observed in agricultural watersheds in the U.S. at a range of scales, and for large watersheds globally ( Figure 5). While this study isolates the DOC flux from soil in a homogenous agricultural catchment, which is a poorly quantified flux in the context of watershed carbon budgets [Regnier et al, 2013], inputs from other land cover types and in-stream processing would be expected to alter this relationship at larger scales [Dalzell et al, 2011;Ågren et al, 2014;Vidon et al, 2014].…”