The fate of sediment, wood, and organic carbon eroded during an extreme flood, Colorado Front Range, USA

Rathburn, Sara L.; Bennett, Georgina L.; Wohl, Ellen; Briles, Christy E.; McElroy, Brandon; Sutfin, Nicholas A.

doi:10.1130/g38935.1

Cited by 46 publications

(63 citation statements)

References 16 publications

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“…Sediment yields from steep, mountainous basins are highly sensitive to climatic changes, as well as to tectonic activity (Farnsworth and Milliman, 2003;Draut et al, 2009;Warrick and Mertes, 2009;Hovius et al, 2011;Lee et al, 2015;Chen et al, 2016). Most sediment flux from such watersheds occurs during rare, extreme discharge events in response to high rainfall rates (Griggs, 1987;Inman and Jenkins, 1999;Warrick et al, 2015;Rathburn et al, 2017). The magnitude and frequency of major storms are expected to change and, in many regions, increase under 21st century climatic change (Emanuel, 2005;Allan and Soden, 2008;Warner et al, 2015;Burt et al, 2016;Shields and Kiehl, 2016;Swain et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Pitlick (1993) observed that sediment yield in a Colorado stream decreased exponentially after a dam-break flood, returning to background levels in about 5 years. Such examples provide an imperfect comparison with the San Lorenzo because a single catastrophic flood creates new sediment sources that did not form in the San Lorenzo floods of 2017, such as large debris-flow deposits or new, high-elevation fluvial bars (Coats et al, 1985;Griggs, 1988;Pitlick, 1993;Anderson et al, 2015;Rathburn et al, 2017). Such examples provide an imperfect comparison with the San Lorenzo because a single catastrophic flood creates new sediment sources that did not form in the San Lorenzo floods of 2017, such as large debris-flow deposits or new, high-elevation fluvial bars (Coats et al, 1985;Griggs, 1988;Pitlick, 1993;Anderson et al, 2015;Rathburn et al, 2017).…”

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confidence: 99%

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A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

East

Stevens

Ritchie

et al. 2018

Earth Surf Processes Landf

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Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

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Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

East

Stevens

Ritchie

et al. 2018

Earth Surf Processes Landf

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“…, Wohl and Ogden ), floods (Sutfin ), or wildfires influence inputs of OC to the river corridor, storage of OC within the river corridor, or transport downstream over periods of days to a few years. Storms and floods, in particular, typically result in greater DOC, POC, and LW inputs to rivers, which can be stored in depositional areas within the river corridor, or exported downstream to a reservoir or the ocean (Rathburn et al., in press ). More sustained changes such as droughts or land use can influence OC dynamics over periods of 10 1 –10 2 yr (e.g., Worrall and Burt ).…”

Section: Carbon Dynamics In Natural River Corridorsmentioning

confidence: 99%

Carbon dynamics of river corridors and the effects of human alterations

Wohl

Hall

Lininger

et al. 2017

Ecological Monographs

106

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Research in stream metabolism, gas exchange, and sediment dynamics indicates that rivers are an active component of the global carbon cycle and that river form and process can influence partitioning of terrestrially derived carbon among the atmosphere, geosphere, and ocean. Here we develop a conceptual model of carbon dynamics (inputs, outputs, and storage of organic carbon) within a river corridor, which includes the active channel and the riparian zone. The exchange of carbon from the channel to the riparian zone represents potential for storage of transported carbon not included in the “active pipe” model of organic carbon (OC) dynamics in freshwater systems. The active pipe model recognizes that river processes influence carbon dynamics, but focuses on CO2 emissions from the channel and eventual delivery to the ocean. We also review how human activities directly and indirectly alter carbon dynamics within river corridors. We propose that dams create the most significant alteration of carbon dynamics within a channel, but that alteration of riparian zones, including the reduction of lateral connectivity between the channel and riparian zone, constitutes the most substantial change of carbon dynamics in river corridors. We argue that the morphology and processes of a river corridor regulate the ability to store, transform, and transport OC, and that people are pervasive modifiers of river morphology and processes. The net effect of most human activities, with the notable exception of reservoir construction, appears to be that of reducing the ability of river corridors to store OC within biota and sediment, which effectively converts river corridors to OC sources rather than OC sinks. We conclude by summarizing knowledge gaps in OC dynamics and the implications of our findings for managing OC dynamics within river corridors.

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“…However, the more heterogeneous upper facies are poorly represented in the available data and rely on literature estimates from similar systems. Additionally, woody debris is not explicitly accounted for our estimates of carbon burial, suggesting that actual values may be significantly higher (cf., Rathburn et al, ). Our estimates of deposition in heterogeneous regions are thus subject to a great deal of uncertainty; however, we believe our literature‐based carbon concentrations to represent relatively conservative values.…”

Section: Discussionmentioning

confidence: 99%

The Importance of Coarse Organic Matter and Depositional Environment to Carbon Burial Behind Dams in Mountainous Environments

2019

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The relationship between carbon burial and sedimentation in reservoirs is unknown, contributing to uncertainty in our understanding of the net impact of dams to the global carbon budget and exposing gaps in our fundamental understanding of the transport, processing, and deposition of organic matter in fluvial and lacustrine systems. Taking opportunistic advantage of the removal of two high‐head dams, we investigate this relationship by developing a stratigraphic, process‐based framework to estimate total carbon accumulation as a function of depositional environment in the sediments of two former ~1‐km2 reservoirs on the Elwha River, Washington, USA. Former Lake Mills (upstream; completed 1927) accumulated ~330 Gg, with depositional zone average accumulation rates from 229 to 9,262 gCm2/year, while Former Lake Aldwell (downstream; completed 1913) accumulated ~91 Gg (263 to 2,414 gCm2/year). Carbon storage in both reservoirs was dominated by heterogeneous, coarse organic matter and woody debris in the coarse‐grained delta slope and relatively coarse‐grained prodelta regions of the reservoirs, with little in the gravel‐dominated, subaerial delta plains. Carbon accumulation in fine‐grained lacustrine and prodelta sediments was relatively homogeneous, but turbidity flows from the Gilbert‐style delta slope in former Lake Mills delivered significantly more carbon to the prodelta than the mouth bar‐style delta of former Lake Aldwell. C:N ratios support interpretation of most organic matter in both reservoirs as allochthonous. Sampling schemes based only on lacustrine and/or prodelta would underestimate total carbon accumulation by up to 30% in former Lake Aldwell but overestimate carbon by up to 47% in former Lake Mills.

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The fate of sediment, wood, and organic carbon eroded during an extreme flood, Colorado Front Range, USA

Cited by 46 publications

References 16 publications

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

Carbon dynamics of river corridors and the effects of human alterations

The Importance of Coarse Organic Matter and Depositional Environment to Carbon Burial Behind Dams in Mountainous Environments

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