Rivers play an important role in the carbon cycle, as sites of carbon transport, storage, and transformation. Two of the largest organic carbon (OC) stocks in river corridors (channels and floodplains) are soil OC and dead, downed large wood (LW) in rivers. Human modifications of river corridors, such as damming and floodplain land-use change, have likely modified floodplain OC storage and retention. However, we lack data that provide insight into the influence of human alterations on floodplain OC. We measured floodplain soil OC and downed LW loads on three rivers in northern Sweden that represent a gradient in human alteration of river corridors. The Muddus River is located in a national park, is free-flowing, and the floodplain has never been logged. The Vindel River is also free-flowing but has been modified via logging and other land-use changes within the floodplain. The Ume River is dammed along its length and has also experienced floodplain logging and land-use change. These three floodplains provide a gradient of human alteration in a similar climate and biome, allowing for assessing the influence of human alteration. We use statistical models to determine significant differences among rivers with different degrees of human alteration, accounting for variations in land-use type and geomorphic position within the catchment. We find that the highest soil OC concentrations occur in the unaltered Muddus River (mean = 3.70%; median = 3.81%), with lower soil OC along the Vindel (mean = 1.44%; median = 0.72%) and Ume (mean = 2.47%; median = 1.12%) Rivers. The Muddus River also has the highest downed LW loads (mean = 22.25 m3 ha-1) compared to the Vindel (mean = 3.10 m3 ha-1) and Ume (mean = 7.26 m3 ha-1) Rivers. Average soil OC stocks calculated to a depth of 1 m are 43.55, 68.64, and 71.46 Mg C ha-1 for the Muddus, Vindel, and Ume Rivers, respectively. Variations in soil OC and downed large wood loads indicate that damming may reduce floodplain soil OC in these boreal systems through reducing inputs of organic matter, water, and sediment. In addition, logging and other land-use changes likely reduce OC inputs to the floodplain surface through removal of organic matter and LW. Further research is needed to elucidate the impact of human modifications on floodplain OC across diverse regions.
Lininger, K. B., & Polvi, L. E. (2019). Data associated with Evaluating floodplain organic carbon stocks across a gradient of human alteration in the boreal zone. University of Colorado Boulder. https://doi.org/10.25810/NHXB-FT27
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