Unravelling the Relative Contribution of Dissolved Carbon by the Red River to the Atchafalaya River

Xu, Y. Jun; DelDuco, E.

doi:10.3390/w9110871

Cited by 9 publications

(5 citation statements)

References 51 publications

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“…This study was conducted in the Lower Mississippi River at Baton Rouge, Louisiana, USA (30 • 26 16.6 N, 91 • 11 31.6 W, Figure 1), approximately 369 river km upstream of the river's outlet to the Gulf of Mexico. The Mississippi is the largest river in North America, draining 3.2 million km 2 of land and discharging approximately 680 km 3 of freshwater into the Gulf annually, in combination with the Atchafalaya River [24]. Due to the vast drainage size and diverse land use, the Mississippi River carries dissolved inorganic and organic carbon (DIC and DOC) from various sources, with an average DIC and DOC flux rate of 12.6 Tg yr −1 and 4.1 Tg yr −1 , respectively, at Baton Rouge during the past three years [25].…”

Section: Methodsmentioning

confidence: 99%

Diel Variability of pCO2 and CO2 Outgassing from the Lower Mississippi River: Implications for Riverine CO2 Outgassing Estimation

Reiman

2018

Water

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Carbon dioxide (CO2) outgassing from river surface waters is an important component of the global carbon cycle currently not well constrained. To test the hypothesis that riverine partial pressure of CO2 (pCO2) and CO2 outgassing rates differ between daylight and darkness, we conducted in-situ pCO2 and ambient water measurements over four 24-h periods in the spring and summer of 2018 in the Lower Mississippi River under varying flow regimes. We hypothesized that diel pCO2 variation will correlate inversely with solar radiation due to light-induced photosynthesis. Despite differing ambient conditions between seasons, we found a consistent diel cycle of riverine pCO2, with highest values before sunset and lowest values during peak daylight. Recorded pCO2 measurements varied by 206–607 µatm in spring and 344–377 µatm in summer, with significantly lower records during daylight in summer. CO2 outgassing was significantly lower during daylight in both seasons, with diel variation ranging between 1.5–4.4 mmol m−2 h−1 in spring and 1.9–2.1 mmol m−2 h−1 in summer. Daily outgassing rates calculated incorporating diel variation resulted in significantly greater rates (26.2 ± std. 12.7 mmol m−2 d−1) than calculations using a single daily pCO2 value. This study suggests a likely substantial underestimation of carbon outgassed from higher order rivers that make up a majority of the global river water surface. The findings highlight the need for high temporal resolution data and further research on diel CO2 outgassing in different climate regions to constrain uncertainties in riverine flux estimation.

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Section: Methodsmentioning

confidence: 99%

Diel Variability of pCO2 and CO2 Outgassing from the Lower Mississippi River: Implications for Riverine CO2 Outgassing Estimation

Reiman

2018

Water

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“…The focus of this study was on the lowermost Atchafalaya River and its two outlets to the Northern Gulf of Mexico: The ARMC and the artificially bifurcated Wax Lake outlet channel (WLOC) (Figure 1c). The Atchafalaya River is the largest distributary of the Mississippi River, carrying approximately 25% of the Mississippi River water and the total flow of the Red River and discharging a combined flow of about 200 km 3 annually (Xu & DelDuco, 2017). The river begins at the confluence of the Red River and the Mississippi River diversion channel, also known as the Outflow Channel, and travels southward for about 220 km before entering the Gulf of Mexico (Figure 1b).…”

Section: The Lowermost Atchafalaya Rivermentioning

confidence: 99%

Artificial bifurcation effect on downstream channel dynamics of a large lowland river, the Atchafalaya

Wang

et al. 2021

Earth Surf Processes Landf

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Artificial river bifurcations have been widely created for different purposes. Yet, long‐term dynamics in the bifurcated channels and natural channels downstream of the artificial bifurcation nodes are not well investigated. Herein, we employed an approach combining three decades (1977–2006) of bathymetric survey records, geographic information system (GIS) application, and bed material transport modeling to investigate riverbed dynamics in an artificially bifurcated channel and the downstream natural channel of the Atchafalaya River, the largest distributary of the Mississippi River. Decadal changes in the riverbed volume were determined, and erosion/deposition patterns in these channels were assessed. Hydraulic properties under low, medium, and high flow conditions were quantified to analyze main factors affecting the long‐term trend of channel dynamics. Our study found that flow from the Atchafalaya River into the artificially bifurcated Wax Lake outlet channel (WLOC) steadily increased. Hydraulic gradient, stream power, and shear stress under all flow conditions of the WLOC were greater than those of the Atchafalaya River natural mainstem channel (ARMC) downstream of the artificial bifurcation. On average, 52% of the total bed material loads (BMLs) from the Atchafalaya entered the steeper and straight WLOC with 41% of the river's flow from 1977 to 2006. Despite the higher sediment inflow, the WLOC degraded with an average rate of −0.12 × 105 m3 km−1 yr−1, while the ARMC downstream of the bifurcation aggraded substantially with an average rate of 0.38 × 105 m3 km−1 yr−1 over the three decades. The disproportional flow–sediment ratio and channel erosion‐aggradation patterns below the artificial bifurcation were apparently a reflection of the difference in the river hydraulic properties. These findings imply that lowland alluvial river diversions for introducing sediment to build new land in world's sinking deltas need to develop sustainable solutions in order to avoid causing severe bed scouring in one but excessive deposition in the other channel downstream of the bifurcation.

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“…DIC production is more likely occurring largely in soils and floodplain ecosystems using fresher and more reactive sources of organic material produced within the AR Basin. A recent study indicated the Red River may contribute bioavailable DOC to the AR [71], which may explain some of the labile organic material present. Leaf litter from within the basin may provide further source of less degraded organic carbon for respiration; leaf leachates as well as the breakdown of large organic materials to DOC by bacteria and fungi are major sources of DOC to waters [72][73][74].…”

Section: Dissolved Organic Carbon Dynamicsmentioning

confidence: 99%

“…Leaf litter from within the basin may provide further source of less degraded organic carbon for respiration; leaf leachates as well as the breakdown of large organic materials to DOC by bacteria and fungi are major sources of DOC to waters [72][73][74]. Organic material in the AR are compositionally different from that of the MR, indicating significant leaf litter inputs from its landscape as well as the Red River [29,71]. The timing of leaf litter input within this basin corresponds with the only months where DOC mass loads increased from origin to outlet (August-October).…”

Section: Dissolved Organic Carbon Dynamicsmentioning

confidence: 99%

Dissolved Carbon Transport and Processing in North America’s Largest Swamp River Entering the Northern Gulf of Mexico

DelDuco

2019

Water

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Transport and transformation of riverine dissolved carbon is an important component of global carbon cycling. The Atchafalaya River (AR) flows 189 kilometers through the largest bottomland swamp in North America and discharges ~25% of the flow of the Mississippi River into the Gulf of Mexico annually, providing a unique opportunity to study the floodplain/wetland impacts on dissolved carbon. The aim of this study is to determine how dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the AR change spatially and seasonally, and to elucidate which processes control the carbon cycling in this intricate swamp-river system. From May 2015 to May 2016, we conducted monthly river sampling from the river’s inflow to its outflow, analyzing samples for concentrations and δ13C stable isotope composition of DOC and DIC. We found that DIC concentrations in the AR were three times higher than the DOC concentrations on average, and showed more pronounced downstream changes than the DOC. During the study period, the river discharged a total of 5.35 Tg DIC and a total of 2.34 Tg DOC into the Gulf of Mexico. Based on the mass inflow–outflow balance, approximately 0.53 Tg (~10%) of the total DIC exported was produced within the floodplain/wetland system, while 0.24 Tg (~10%) of the DOC entering the basin was removed. The AR’s water was consistently oversaturated with CO2 partial pressure (pCO2) above the atmospheric pCO2 (with pCO2 varying from 551 µatm to 6922 µatm), indicating a large source of DIC from river waters to the atmosphere as well as to the coastal margins. Largest changes in carbon constituents occurred during periods of greatest inundation of the swamp-river basin and corresponded with shifts in isotopic composition. This effect was particularly pronounced during the initial flood stages, supporting the hypothesis that subtropical floodplains can act as effective enhancers of the biogeochemical cycling of dissolved carbon.

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Unravelling the Relative Contribution of Dissolved Carbon by the Red River to the Atchafalaya River

Cited by 9 publications

References 51 publications

Diel Variability of pCO2 and CO2 Outgassing from the Lower Mississippi River: Implications for Riverine CO2 Outgassing Estimation

Diel Variability of pCO2 and CO2 Outgassing from the Lower Mississippi River: Implications for Riverine CO2 Outgassing Estimation

Artificial bifurcation effect on downstream channel dynamics of a large lowland river, the Atchafalaya

Dissolved Carbon Transport and Processing in North America’s Largest Swamp River Entering the Northern Gulf of Mexico

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