title: Spatial patterns and environmental controls of particulate organic carbon in surface waters in the conterminous United States.
abstract: Carbon cycling in inland waters has been identified as an important, but poorly constrained component of the global carbon cycle. In this study, we compile and analyze particulate organic carbon (POC) concentration data from 1145 U.S. Geological Survey (USGS) gauge stations to investigate the spatial variability and environmental controls of POC concentration. We observe substantial spatial variability in POC concentration (1.43 ± 2.56 mg C/L, mean ± one standard deviation), with the Upper Mississippi River basin and the Piedmont region in the eastern U.S. having the highest POC concentration. Further, we employ generalized linear models (GLMs) to analyze the impacts of sediment transport and algae growth as well as twenty-one other environmental factors on the POC variability. Suspended sediment and chlorophyll-a explain 26% and 17% of the variability in POC concentration, respectively. At the national level, the twenty-one environmental factors combined can explain ca. 40% of the spatial variance in POC concentration. At the national scale, urban area and soil clay content show significant negative correlations with POC concentration, whereas soil water content and soil bulk density correlate positively with POC. In addition, total phosphorus concentration and dam density correlate positively with POC concentration. Furthermore, regional scale analyses reveal substantial variation in environmental controls of POC concentration across eighteen major water resource regions in the U.S. The POC concentration and associated environmental controls also vary non-monotonically from headwaters to large rivers. These findings indicate complex interactions among multiple factors in regulating POC concentration over different spatial scales and across various sections of the river networks. This complexity, together with the large unexplained uncertainty, highlights the need for considering non-linear interplays of multiple environmental factors and developing appropriate methodologies to track the transformation and transport of POC along the terrestrial-aquatic interfaces.
authors.affiliation: Joint Global Change Research Institute, Pacific Northwest National Lab, College Park, MD 20740, USA.
authors.forename: Qichun
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Joint Global Change Research Institute, Pacific Northwest National Lab, College Park, MD 20740, USA; Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA. Electronic address: xuesong.zhang@pnnl.gov.
authors.forename: Xuesong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Joint Global Change Research Institute, Pacific Northwest National Lab, College Park, MD 20740, USA; Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Xingya
authors.initials: X
authors.lastname: Xu
authors.affiliation: Joint Global Change Research Institute, Pacific Northwest National Lab, College Park, MD 20740, USA.
authors.forename: Ghassem R
authors.initials: GR
authors.lastname: Asrar
authors.affiliation: US Geological Survey, MS 413 National Center, Reston, VA 20192, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Smith
authors.affiliation: Resources For the Future, 1616 P St., NW Washington, DC 20036, USA.
authors.forename: Jhih-Shyang
authors.initials: JS
authors.lastname: Shih
authors.affiliation: Earth System Science Interdisciplinary Center, University of Maryland, 5825 University Research Court, #4049, College Park, MD 20740, USA.
authors.forename: Shuiwang
authors.initials: S
authors.lastname: Duan
mesh_terms: D002244:Carbon / Q000032:analysis*; D057486:Carbon Cycle; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D014481:United States; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D006812:Humic Substances; D014873:Water Pollutants; D002244:Carbon
keywords: Environmental control; Particulate organic carbon; Spatial variability; Uncertainty