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Network Connectivity and Local Hydrology Drive DOM Composition in a Nonperennial Stream.

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Title: Network Connectivity and Local Hydrology Drive DOM Composition in a Nonperennial Stream.
Authors: Flynn, Sarah M.1,2 (AUTHOR) s.m.flynn@ku.edu, Hale, Rebecca L.3 (AUTHOR), Seybold, Erin2,4 (AUTHOR), Plont, Stephen5 (AUTHOR), Busch, Michelle2 (AUTHOR), Sommerville, Alexi2,4 (AUTHOR), Brown, Connor L.2,4 (AUTHOR), Burgin, Amy J.6 (AUTHOR) burginam@iastate.edu
Source: Journal of Geophysical Research. Biogeosciences. May2026, Vol. 131 Issue 5, p1-19. 19p.
Subject Terms: *Dissolved organic matter, *Hydrology, *Carbon cycle, *Biogeochemistry, *Streamflow, Fluorescence spectroscopy, Ephemeral streams
Abstract: Nonperennial streams are dynamic sites of biogeochemical processing, yet much remains to be learned about how hydrologic connectivity at different spatial and temporal scales impacts the composition of dissolved organic matter (DOM). We characterized spatial and temporal patterns of DOM composition in a nonperennial prairie stream network using 3 years of hydrologic data and fluorescence spectroscopy of surface water. Principal component analyses revealed that humic, terrestrial components explained the most variance in DOM composition. These components were highest at sites in the headwaters. In contrast, autochthonous DOM was relatively greater at sites with persistent local‐scale surface water and flowing conditions. Network and local controls (i.e., the degree to which surface water is connected across the network and site‐level water persistence and flow metrics, respectively) interacted to alter DOM composition, with their combined influence depending on the hydrologic phase. High connectivity promoted mixing and transport that diluted local autochthonous signals, whereas low or transitional flows enhanced retention, autochthonous activity, and microbial processing. These findings suggest that hydrologic fragmentation in nonperennial systems modulates not only DOM source and transformation but also its downstream bioavailability, with implications for carbon cycling under shifting climate and flow regimes. Plain Language Summary: Nonperennial streams dry at some point in time or space. They are widespread and increasingly common with climate change, but we know relatively little about how they affect water quality and carbon cycling. We examined the types of dissolved organic matter found in stream water across a nonperennial prairie watershed in Kansas. We collected water samples throughout the watershed over 3 years during both wet and dry conditions. Our results showed that when the stream was fully connected and flowing, the composition of DOM was relatively well mixed and uniform across the network. However, when water levels were lower and the stream became fragmented, the types of DOM varied depending on whether the site had flowing water, was an isolated pool, or had recently dried. Sites with continuous water had more autochthonous and microbially degraded DOM, whereas sites that had recently dried or contained isolated pools had DOM primarily derived from leaching of soil and plant material. This study highlights that organic matter composition can alter significantly across drying stream networks, especially at sites where water persists throughout time through microbial processing. Understanding these dynamics is important for predicting how carbon and nutrients move through freshwater systems in a changing climate. Key Points: Network connectivity transports dissolved organic matter, while local hydrology governs the transformation of dissolved organic matterNetwork‐scale dry downs increased the humic and terrestrial components of dissolved organic matterAutochthonous dissolved organic matter increased with local water persistence [ABSTRACT FROM AUTHOR]
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Database: GreenFILE
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Abstract:Nonperennial streams are dynamic sites of biogeochemical processing, yet much remains to be learned about how hydrologic connectivity at different spatial and temporal scales impacts the composition of dissolved organic matter (DOM). We characterized spatial and temporal patterns of DOM composition in a nonperennial prairie stream network using 3 years of hydrologic data and fluorescence spectroscopy of surface water. Principal component analyses revealed that humic, terrestrial components explained the most variance in DOM composition. These components were highest at sites in the headwaters. In contrast, autochthonous DOM was relatively greater at sites with persistent local‐scale surface water and flowing conditions. Network and local controls (i.e., the degree to which surface water is connected across the network and site‐level water persistence and flow metrics, respectively) interacted to alter DOM composition, with their combined influence depending on the hydrologic phase. High connectivity promoted mixing and transport that diluted local autochthonous signals, whereas low or transitional flows enhanced retention, autochthonous activity, and microbial processing. These findings suggest that hydrologic fragmentation in nonperennial systems modulates not only DOM source and transformation but also its downstream bioavailability, with implications for carbon cycling under shifting climate and flow regimes. Plain Language Summary: Nonperennial streams dry at some point in time or space. They are widespread and increasingly common with climate change, but we know relatively little about how they affect water quality and carbon cycling. We examined the types of dissolved organic matter found in stream water across a nonperennial prairie watershed in Kansas. We collected water samples throughout the watershed over 3 years during both wet and dry conditions. Our results showed that when the stream was fully connected and flowing, the composition of DOM was relatively well mixed and uniform across the network. However, when water levels were lower and the stream became fragmented, the types of DOM varied depending on whether the site had flowing water, was an isolated pool, or had recently dried. Sites with continuous water had more autochthonous and microbially degraded DOM, whereas sites that had recently dried or contained isolated pools had DOM primarily derived from leaching of soil and plant material. This study highlights that organic matter composition can alter significantly across drying stream networks, especially at sites where water persists throughout time through microbial processing. Understanding these dynamics is important for predicting how carbon and nutrients move through freshwater systems in a changing climate. Key Points: Network connectivity transports dissolved organic matter, while local hydrology governs the transformation of dissolved organic matterNetwork‐scale dry downs increased the humic and terrestrial components of dissolved organic matterAutochthonous dissolved organic matter increased with local water persistence [ABSTRACT FROM AUTHOR]
ISSN:21698953
DOI:10.1029/2025JG009568