Biological and land use controls on the isotopic composition of aquatic carbon in the Upper Mississippi River Basin

Global Biogeochemical Cycles
By: , and 

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Abstract

Riverine ecosystems receive organic matter (OM) from terrestrial sources, internally produce new OM, and biogeochemically cycle and modify organic and inorganic carbon. Major gaps remain in the understanding of the relationships between carbon sources and processing in river systems. Here we synthesize isotopic, elemental, and molecular properties of dissolved organic carbon (DOC), particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in the Upper Mississippi River (UMR) system above Wabasha, MN, including the main stem Mississippi River and its four major tributaries (Minnesota, upper Mississippi, St. Croix, and Chippewa Rivers). Our goal was to elucidate how biological processing modifies the chemical and isotopic composition of aquatic carbon pools during transport downstream in a large river system with natural and man-made impoundments. Relationships between land cover and DOC carbon-isotope composition, absorbance, and hydrophobic acid content indicate that DOC retains terrestrial carbon source information, while the terrestrial POC signal is largely replaced by autochthonous organic matter, and DIC integrates the influence of in-stream photosynthesis and respiration of organic matter. The UMR is slightly heterotrophic throughout the year, but pools formed by low-head navigation dams and natural impoundments promote a shift towards autotrophic conditions, altering aquatic ecosystem dynamics and POC and DIC composition. Such changes likely occur in all major river systems affected by low-head dams and need to be incorporated into our understanding of inland water carbon dynamics and processes controlling COemissions from rivers, as new navigation and flood control systems are planned for future river and water resources management.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Biological and land use controls on the isotopic composition of aquatic carbon in the Upper Mississippi River Basin
Series title Global Biogeochemical Cycles
DOI 10.1002/2017GB005699
Volume 31
Issue 8
Year Published 2017
Language English
Publisher American Geophysical Union
Contributing office(s) National Research Program - Central Branch
Description 18 p.
First page 1271
Last page 1288
Country United States
Other Geospatial Upper Mississippi River Basin