An official website of the United States government
Streams and rivers integrate and transport particulate organic carbon (POC) from an array of aquatic and terrestrial sources. Storm events greatly accelerate the transport of POC. The sequences by which individual POC inputs are mobilized and transported are not well-documented but are predicted to be temporally transient and spatially dependent because of changes in forcing functions, such as precipitation, discharge, and watershed morphology. In this study, the 3rd−4th order agricultural stream network, Clear Creek in Iowa, U.S.A., was sampled at a nested series of stations through storm events to determine how suspended POC changes over time and with distance downstream. Carbon and nitrogen stable isotope ratios were used to identify changes in POC. A temporal sequence of inputs was identified: in-channel algal production prior to heavy precipitation, row crop surface soils mobilized during peak precipitation, and material associated with the peak hydrograph that is hypothesized to be an integrated product from upstream. Tile drains delivered relatively 13 C- and 15 N-depleted particulate organic carbon that is a small contribution to the total POC inventory in the return to baseflow. The storm POC signal evolved with passage downstream, the principal transformation being the diminution of the early flush surface soil peak in response to a loss of connectivity between the hillslope and channel. Bank erosion is hypothesized to become increasingly important as the signal propagates downstream. The longitudinal evolution of the POC signal has implications for C-budgets associated with soil erosion and for interpreting the organic geochemical sedimentary record.
more »
« less
This content will become publicly available on February 1, 2026
Molecular-level exploration of spatiotemporal dynamics of fluvial particulate organic carbon sources during storm events: Using a high-temporal resolution multi-biomarker approach
Identifying the origins of storm fluvial particulate organic carbon (POC) provides information about the hydrological connectivity within the river corridor and the roles of the land-stream interface in the carbon cycle. However, current understanding of storm-induced POC source dynamics is constrained by observations limited in space and time. This study presents a unique approach integrating higher spatial and temporal resolution sampling with a multi-biomarker analysis to better understand POC source dynamics across scales. Storm POC samples were collected at ~2 h intervals at three locations along the flow trajectory of an agricultural stream during six storm events with varied storm characteristics and seasonality, and characterized for their concentrations, C and N contents, stable C isotopes, and biomarker contents. Our results showed a source transition from in-stream algal production during early storm stages to surface soils with vascular plant signatures during peak precipitation and discharge across events and stations. Biomarkers further resolved the terrestrial signature into one likely from bank vegetation and another from row crop soils. This additional separation appeared conditionally, with the magnitude and sequence influenced by environmental factors such as storm trajectory, antecedent conditions, and management/vegetation cover. Source transitions were less distinctive in the lower reaches due to the greater integration of inputs, although one storm with localized precipitation showed the opposite pattern. Both scenarios align with the expected lower hydrological connectivity downstream. With the employed approach, the evolution of the storm pulse POC as it responds to river corridor processes could be visualized both temporally and spatially.
more »
« less
- Award ID(s):
- 2012850
- PAR ID:
- 10630778
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Science of The Total Environment
- Volume:
- 963
- Issue:
- C
- ISSN:
- 0048-9697
- Page Range / eLocation ID:
- 178447
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Beddoe, Riley; Karunaratne, Kumari (Ed.)Permafrost holds more than twice the amount of carbon currently in the atmosphere, but this large carbon reservoir is vulnerable to thaw and erosion under a rapidly changing Arctic climate. Convective storms are becoming increasingly common during Arctic summers and can amplify runoff and erosion. These extreme events, in concert with active layer deepening, may accelerate carbon loss from the Arctic landscape. However, we lack measurements of carbon fluxes during these events. Rivers are sensitive to physical, chemical, and hydrological perturbations, and thus are excellent systems for studying landscape responses to thunderstorms. We present observations from the Canning River, Alaska, which drains the northern Brooks Range and flows across a continuous permafrost landscape to the Beaufort Sea. During summer 2022 and 2023 field campaigns, we opportunistically monitored river discharge, sediment, and organic carbon fluxes during several thunderstorms. During one notable storm, river discharge nearly doubled from ~130 m3/s to ~240 m3/s, suspended sediment flux increased 70-fold, and the particulate organic carbon (POC) flux increased 90-fold relative to non-storm conditions. Taken together, the river exported ~16 metric tons of POC over one hour of this sustained event, not including the additional flux of woody debris. Furthermore, the dissolved organic carbon (DOC) flux nearly doubled. Although these thunderstorm-driven fluxes are short-lived (hours to days), they play an outsized role in exporting organic carbon from Arctic rivers. Understanding how these extreme events impact river water, sediment, and carbon dynamics will help predict how Arctic climate change will modify the global carbon cycle.more » « less
-
Concentration-discharge (C-Q) relationships of total suspended solids (TSS), total dissolved solids (TDS), particulate organic carbon (POC), and dissolved organic carbon (DOC) were investigated in the tributaries and main-stems of two mountainous river systems with distinct watershed characteristics (Eel and Umpqua rivers) in Northern California and central Oregon (USA). Power-law (C = a × Q b) fits to the data showed strong transport-limited behavior (b > 1) by TSS and POC, moderate transport limitation of DOC (b > 0.3) and chemostatic behavior (b < 0) by TDS in most streams. These contrasts led to significant compositional differences at varying discharge levels, with particle-bound constituents becoming increasingly important (relative abundances of 50% to >90%) at high-flow conditions. Organic carbon contents of TSS displayed marked decreases with discharge whereas they increased in TDS during high-flow conditions. Daily and cumulative material fluxes for different coastal streams were calculated using the C-Q relationships and showed that the delivery of transport-limited constituents, such as TSS and POC (and DOC to a lesser degree), was closely tied to high-discharge events and occurred primarily during the winter season. The coherence between winter fluxes and high wave-southerly wind conditions along the coast highlights how seasonal and inter-annual differences in fluvial discharge patterns affect the fate of land-derived materials delivered to coastal regions.more » « less
-
Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon ( 14 C) ages on two groups of molecular tracers of plant-derived carbon—leaf-wax lipids and lignin phenols—from a globally distributed suite of rivers. We find significant negative relationships between the 14 C age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil 14 C ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change–induced perturbations of soil OC turnover and stocks.more » « less
-
Wymore, A.S. (Ed.)The loss of organic carbon (OC) from soils because of agriculture is well established. Where that carbon goes, far less so. Accelerated oxidation could lead to a net source of CO2 to the atmosphere. However eroded soil OC sequestered in alluvia and reservoirs could create a net sink for atmospheric CO2. The Intensively Managed Landscape—Critical Zone Observatory (IML-CZO) has provided an opportunity to study the fate of the eroded soil OC. A preliminary inventory of post-settlement sediment and associated OC accumulation has been made in the IML-CZO site in the Sangamon River Basin of Illinois. Significant stores of OC were found in downslope depressions, floodplain sedimentary deposits and a reservoir at the terminus of the Upper Sangamon Basin, Lake Decatur. Approximately 90% of the OC was trapped by the landscape. Carbon isotopic (δ13C) measurements of bank exposures and Lake Decatur sediments indicate that row crop soils with corn (C4 plant) isotopic signatures contribute to the sequestered C pools but are not the sole sources of OC. C-isotope and biomarker measurements of Lake Decatur sediments reveal the episodic nature of row crop soil OC transport, which appears to be facilitated by sequences of storm events.more » « less
