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Abstract Most terrestrial allochthonous organic matter enters river networks through headwater streams during high flow events. In headwaters, allochthonous inputs are substantial and variable, but become less important in streams and rivers with larger watersheds. As allochthonous dissolved organic matter (DOM) moves downstream, the proportion of less aromatic organic matter with autochthonous characteristics increases. How environmental factors converge to control this transformation of DOM at a continental scale is less certain. We hypothesized that the amount of time water has spent travelling through surface waters of inland systems (streams, rivers, lakes, and reservoirs) is correlated to DOM composition. To test this hypothesis, we used established river network scaling relationships to predict relative river network flow‐weighted travel time (FWTT) of water for 60 stream and river sites across the contiguous United States (3090 discrete samples over 10 water years). We estimated lentic contribution to travel times with upstream in‐network lake and reservoir volume. DOM composition was quantified using ultraviolet and visible absorption and fluorescence spectroscopy. A combination of FWTT and lake and reservoir volume was the best overall predictor of DOM composition among models that also incorporated discharge, specific discharge, watershed area, and upstream channel length. DOM spectral slope ratio (R2 = 0.77) and Freshness Index (R2 = 0.78) increased and specific ultraviolet absorbance at 254 nm (R2 = 0.68) and Humification Index (R2 = 0.44) decreased across sites as a function of FWTT and upstream lake volume. This indicates autochthonous‐like DOM becomes continually more dominant in waters with greater FWTT. We assert that river FWTT can be used as a metric of the continuum of DOM composition from headwaters to rivers. The nature of the changes to DOM composition detected suggest this continuum is driven by a combination of photo‐oxidation, biological processes, hydrologically varying terrestrial subsidies, and aged groundwater inputs.
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This content will become publicly available on September 10, 2026
Sediment Storage Behind Low‐Head Dams: Assessing Potential Contribution to Reservoir Sedimentation in Kansas, USA
Low-head dams (LHDs) are widespread in river systems, yet the volume of sediment impounded behind them remains largely unquantified. Failure or planned removal of these often-aging structures can mobilize stored sediment, posing added risk to reservoirs already losing capacity to sedimentation. In Kansas, the failure of an LHD in May 2018 released sediment equivalent to ~25% of the downstream reservoir's annual accumulation and motivated a broader assessment of storage behind other LHDs. Addressing this knowledge gap, this study quantifies sediment storage behind LHDs located upstream of three federal reservoirs: Tuttle Creek Lake, Perry Lake, and Kanopolis Lake. An integrated approach was employed, combining remote sensing for LHD identification with field-based bathymetric surveys and sediment analysis to directly measure accumulated sediment volumes (VLHD) at representative sites and to estimate VLHD at remotely sensed sites. The relative storage for individual LHDs, expressed as a fraction of downstream annual reservoir sedimentation (fARS), ranged from 0.005 to 0.659, with a median fARS of 0.025. Storage volume (VLHD) was more closely related to local physical properties of LHDs—such as dam height and width—than watershed-scale drivers, such as precipitation and drainage area. Bathymetric maps revealed scour holes immediately upstream of LHDs, typically centered 20–50 m upstream and up to ~1.3 m deep, indicating partial sediment continuity and dynamic equilibrium. This research provides crucial data to inform regional sediment management and enhance reservoir sustainability in Kansas and offers a transferable methodology for quantifying the contribution of LHDs in other watersheds.
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- Award ID(s):
- 2500251
- PAR ID:
- 10635653
- Publisher / Repository:
- John Wiley & Sons Ltd
- Date Published:
- Journal Name:
- River Research and Applications
- ISSN:
- 1535-1459
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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