An Analysis of Terrestrial and Aquatic Environmental Controls of Riverine Dissolved Organic Carbon in the Conterminous United States

Abstract

Analyses of environmental controls on riverine carbon fluxes are critical for improved understanding of the mechanisms regulating carbon cycling along the terrestrial-aquatic continuum.Here, we compile and analyze riverine dissolved organic carbon (DOC) concentration data from 1402 United States Geological Survey (USGS) gauge stations to examine the spatial variability and environmental controls of DOC concentrations in the United States (U.S.) surface waters. DOC concentrations exhibit high spatial variability in the U.S., with an average of 6.42 ± 6.47 mg C/L (Mean ± Standard Deviation). High DOC concentrations occur in the Upper Mississippi River basin and the southeastern U.S., while low concentrations are mainly distributed in the western U.S. Soil properties such as soil organic matter, soil water content, and soil sand content mainly show positive correlations with DOC concentrations; forest and shrub land have positive correlations with DOC concentrations, but urban area and cropland demonstrate negative impacts; and total instream phosphorus and dam density correlate positively with DOC concentrations. Notably, the relative importance of these environmental controls varies substantially across major U.S. water resource regions. In addition, DOC concentrations and environmental controls also show significant variability from small streams to large rivers. In sum, our results reveal that general multi-linear regression of twenty environmental factors can partially explain (56%) the DOC concentration variability. This study also highlights the complexity of the interactions among these environmental factors in determining DOC concentrations, thus calls for processes-based, non-linear methodologies to constrain uncertainties in riverine DOC cycling.

Sources of dissolved organic carbon (DOC) in a mixed land use catchment (Exe, UK)

“…The comparison of sites in urban areas (Bolham vs. Exe at Tiverton comparison) did not prove to offer significant contributions to DOC concentration, despite the potential for urban runoff and sewage effluent to influence this (Noacco et al, 2017) and inclusion in the ALM results. This is also contrary to the findings of Yang et al, (2017) who noted a significant effect of urban extent on DOC concentrations in their study of 1,402 sites across the USA. This could perhaps be explained by the relatively small size of Tiverton, the main conurbation upstream of the treatment works, which has a population of 21,335 (UK census 2011).…”

“…This provides evidence for hypothesis b), that there are significant sources of Work in nearby catchments in the south-west of England has also suggested that baseflow DOC concentrations can be higher in agricultural catchments than in semi-natural ones (Glendell and Brazier, 2014) due to the addition agricultural amendments to the soil and artificial fertiliser altering the rate of carbon turnover (Chantigny, 2003). These findings agree with other published work suggesting that DOC quantity and quality can be influenced by the extent of riparian wetlands, woodlands and cropland (Wilson and Xenopoulos, 2008;Yang et al, 2017). These data also add weight to the growing need for an understanding of how agriculturally-derived DOC affects catchment carbon budgets, how this may change in the future and how this can be managed for positive water quality outcomes (e.g.…”

“…Although some catchments in the UK drain exclusively peatland areas, there are many which cover a number of land uses with potential influences from agriculture, forestry and urban areas. Studies concerning catchment scale influences on DOC concentration and chemical character often highlight percentage wetland cover in the catchment as a key parameter for predicting the concentration of DOC, however significant associations with DOC concentrations have also been observed for cropland, woodland and urban extent (Noacco et al, 2017;Wilson and Xenopoulos, 2008;Yang et al, 2017). Furthermore, DOC which enters rivers in the headwaters is subject to a number of mechanisms of removal and transformation including photolysis, bacterial utilisation and flocculation/sedimentation .…”

Carbon limitation leads to thermodynamic regulation of aerobic metabolism

“…To test the role OM chemistry as a key regulator of aerobic metabolism, we incubated sediments with thermodynamically distinct N-bearing or N-free OM treatments at concentrations commonly observed in freshwater systems (from 0.3 to 9 mg C L −1 , Supplementary Table 1) 12,24,25 . We inferred carbon limitation at low treatment concentrations (< 3 mg C L −1 ) because sediments were collected from a low carbon area (%C < 0.6 as previously discussed in Graham et al 11 ) with observed C:N < 5 11 which is typically associated with carbon limitation 26,27 .…”

Distribution of Carbon and Nitrogen as Indictors of Environmental Significance in Coastal Sediments of Weizhou Island, Beibu Gulf

“…Continental margin sediments contain more than 90% of the carbon buried in the ocean, and the estuary coastal zone, as a sensitive exchange zone for sea-land carbon pools, effectively indicates that the global carbon cycle process is driven by sea level changes [1,2]. However, as an open system, the biogeochemical signals of coasts are complex due to the influence of multiple natural factors (such as global coastline and paleoclimate changes) and the interference of human activities [3][4][5][6][7].…”