Groundwater flow paths drive longitudinal patterns of stream dissolved organic carbon (DOC) concentrations in boreal landscapes

[摘要] Preferential groundwater flow paths can influence dissolved organic carbon (DOC) concentration and export in the fluvial network because theyfacilitate the inflow of terrestrial DOC from large upslope contributingareas to discrete sections of the stream, referred to as discrete riparian inflow points  (DRIPs). However, the mechanisms by which DRIPs influence longitudinal patterns of stream DOC concentrations are still poorly understood. In this study, we ask how DRIPs affect longitudinal patterns of stream DOC concentrations under different hydrologic conditions, as they can simultaneously act as major sources of terrestrial DOC and important locations for in-stream processes. To answer this question, we tested four model structures that account for different representations of hydrology (distributed inflows of DRIPs vs. diffuse groundwater inflow) and in-stream processes (no DOC uptake vs. in-stream DOC uptake downstream of DRIPs) to simulate stream DOC concentrations along a 1.5 km headwater reach for 14 sampling campaigns with flow conditionsranging from droughts to floods. Despite the magnitude and longitudinalpatterns of stream DOC concentration varying across campaigns, at least onemodel structure was able to capture longitudinal trends during eachcampaign. Specifically, our results showed that during snowmelt periods or high-flow conditions ( >50  L s −1 ), accounting for distributedinputs of DRIPs improved simulations of stream DOC concentrations along thereach, because groundwater inputs from DRIPs diluted the DOC in transport.Moreover, accounting for in-stream DOC uptake immediately downstream ofDRIPs improved simulations during five sampling campaigns that were performed during spring and summer, indicating that these locations servedas a resource of DOC for aquatic biota. These results show that the role ofDRIPs in modulating DOC concentration, cycling, and export varies over time and depends strongly on catchment hydrology. Therefore, accounting for DRIPs can improve stream biogeochemistry frameworks and help inform management of riparian areas under current and future climatic conditions.

[学科分类] 妇产科学