Xu Y Jun, Xu Zhen, Potter Lee
School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA 70803, USA; Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 70803, USA.
School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA 70803, USA; Department of Watershed Sciences, Utah State University, Logan, UT 84322, USA.
Sci Total Environ. 2024 May 10;924:171604. doi: 10.1016/j.scitotenv.2024.171604. Epub 2024 Mar 8.
Rivers not only function as a conduit for the delivery of terrestrial constituents to oceans, but they also serve as an essential medium for biogeochemical processing of the constituents. While extensive research has been conducted on carbon transport in many rivers, little is known about carbon transformation in engineered rivers reconnected with their floodplain network. Being the largest distributary of the levee-confined Mississippi River (MR), the Atchafalaya River (AR) carries 25 % of the MR water, flowing through North America's largest freshwater swamp basin and emptying into the Gulf of Mexico. Previous studies reported that this 200-km long, 5-30-km wide river basin can remove a substantial amount of riverine nutrients and organic carbon. This study aimed to test the hypothesis that the AR emits significantly higher CO into the atmosphere as it flows through its extensive floodplain network than the levee-confined MR does. From January 2019 to December 2021, we conducted biweekly - monthly in-situ measurements in the lower AR at Morgan City and in the lower Mississippi River at Baton Rouge. Field measurements included partial pressure of dissolved CO (pCO), water temperature, chlorophyll a, colored dissolved organic matter, dissolved oxygen, pH, and turbidity. During each field sampling, water samples were collected and analyzed for concentrations of dissolved organic and inorganic carbon (DOC and DIC). Mass transport of DOC and DIC and outgassing of CO were quantified for the two rivers. We found that pCO levels were significantly higher in the AR (mean: 3563 μatm; min-max: 1130-8650 μatm) than those in the MR (1931 μatm, 836-3501 μatm), resulting in a doubled CO outgassing rate in the AR (486 mmol m d) than in the MR (241 mmol m d). The AR had higher DOC (8.5 mg L) but lower chlorophyll a (153.9 AFU) when compared with the MR (7.5 mg L and 164.0 AFU). Water temperature was constantly higher in the AR than in the MR, especially during the wintertime. Since the Mississippi-Atchafalaya River system is among the world's largest and most engineered river systems, our assessment offers a field case study to inform on the potential implications of reconnecting rivers with their floodplains networks.
河流不仅是将陆地成分输送到海洋的通道，也是这些成分进行生物地球化学处理的重要介质。虽然对许多河流中的碳运输进行了广泛研究，但对于与洪泛平原网络重新连通的人工河流中的碳转化却知之甚少。阿查法拉亚河（AR）是被堤坝限制的密西西比河（MR）的最大支流，承载着密西西比河25%的水量，流经北美最大的淡水沼泽盆地，最终注入墨西哥湾。此前的研究表明，这条长200公里、宽5 - 30公里的流域能够去除大量的河流养分和有机碳。本研究旨在验证以下假设：与被堤坝限制的密西西比河相比，阿查法拉亚河流经其广阔的洪泛平原网络时向大气中排放的二氧化碳显著更多。从2019年1月到2021年12月，我们在摩根城的阿查法拉亚河下游和巴吞鲁日的密西西比河下游进行了每两周至每月一次的现场测量。现场测量包括溶解二氧化碳的分压（pCO₂）、水温、叶绿素a、有色溶解有机物、溶解氧、pH值和浊度。在每次现场采样期间，采集水样并分析溶解有机碳和无机碳（DOC和DIC）的浓度。对两条河流的DOC和DIC的质量传输以及二氧化碳的脱气情况进行了量化。我们发现，阿查法拉亚河的pCO₂水平（平均值：3563 μatm；最小值 - 最大值：1130 - 8650 μatm）显著高于密西西比河（1931 μatm，836 - 3501 μatm），导致阿查法拉亚河的二氧化碳脱气速率（486 mmol m⁻² d⁻¹）是密西西比河（241 mmol m⁻² d⁻¹）的两倍。与密西西比河（7.5 mg L⁻¹和164.0 AFU）相比，阿查法拉亚河的DOC含量更高（8.5 mg L⁻¹），但叶绿素a含量更低（153.9 AFU）。阿查法拉亚河的水温一直高于密西西比河，尤其是在冬季。由于密西西比 - 阿查法拉亚河水系是世界上最大且工程化程度最高的水系之一，我们的评估提供了一个实地案例研究，以了解河流与洪泛平原网络重新连通的潜在影响。
