Dissolved carbon export and CO2 outgassing from the lower Mississippi River – Implications of future river carbon fluxes
Dissolved carbon export and CO2 outgassing from the lower Mississippi River – Implications of future river carbon fluxes
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DOI：
10.1016/j.jhydrol.2019.124093
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发表时间：
2019-11
影响因子：
6.4
通讯作者：
J. Reiman;Y. Xu
中科院分区：
文献类型：
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作者：
J. Reiman;Y. Xu
在过去的一个世纪里，许多河流流域的气温、降水和河流流量一直在稳步增加。尤其是北美最大的河流流域，320万公里的密西西比河流域，占美国陆地总面积的41%以上。然而，我们对这些变化将如何影响通过河流系统向沿海水域和大气输出陆源碳缺乏了解。本研究调查了2015-2018年密西西比河下游DOC、DIC和co2的浓度和质量通量。我们发现，DOC和DIC每年向墨西哥湾的河流出口量分别为3.95 Tg C和12.25 Tg C，其中75%和67%的负荷分别在1月至7月的雨季排放。来自密西西比河流域的河流质量输出通量率为1.4 g DOC-C m - 2和4.2 g DIC-C - 2，远远高于其他河流流域的报告。下游密西西比河的地表水不断被溶解的CO2过饱和，其分压（pCO2）范围为526 ~ 3961 µatm，平均放气速率为654 g C m−2yr−1。输出的DOC和pco2测量值大大大于十年前报告的估计值，同时河流流量和空气温度显著增加。这些发现有力地表明，由于生物生产力的提高以及在排放和气温升高的情况下随后向河流的碳输出，未来从密西西比河流域进入沿海水域和大气的DOC和co2通量很可能会增加。
Air temperatures, precipitation, and river discharge have been steadily increasing in many river basins over the last century. This is especially the case with North America’s largest river basin, the 3.2-million-km2Mississippi River Basin, which comprises over 41% of the total land surface area in the contiguous USA. Yet we lack an understanding of how these changes will influence the export of terrigenous carbon through river systems into coastal waters and the atmosphere. This study investigated concentrations and mass fluxes of DOC, DIC, and CO2during 2015–2018 in the Lower Mississippi River. We found an annual riverine export of 3.95 Tg C and 12.25 Tg C for DOC and DIC into the Gulf of Mexico, with 75 and 67% of their respective loads discharged during the wet season from January through July. The riverine mass exports represent a flux rate of 1.4 g DOC–C m−2and 4.2 g DIC–C−2from the Mississippi River Basin, which are considerably higher than those reported for other river basins. Surface water of the Lower Mississippi River was constantly supersaturated by dissolved CO2, with its partial pressure (pCO2) ranging from 526 to 3961 µatm and an average outgassing rate of 654 g C m−2yr−1. Export of DOC andpCO2measurements were substantially greater than estimates reported over ten years prior, accompanied by significant increases in river discharge and air temperatures. These findings strongly suggest that DOC and CO2fluxes from the Mississippi River Basin into coastal waters and the atmosphere will very likely increase in the future due to increasing biological productivity and subsequent carbon export to rivers under increasing discharge and air temperatures.