The river as a chemostat: fresh perspectives on dissolved organic matter flowing down the river continuum

Creed, Irena F.; McKnight, Diane M.; Pellerin, Brian A.; Green, Mark B.; Bergamaschi, Brian A.; Aiken, George R.; Burns, Douglas A.; Findlay, Stuart E. G.; Shanley, J. B.; Striegl, Rob; Aulenbach, Brent T.; Clow, David W.; Laudon, Hjalmar; McGlynn, B. L.; McGuire, K. J.; Smith, Richard A.; Stackpoole, S. M.

doi:10.1139/cjfas-2014-0400

Cited by 276 publications

(326 citation statements)

References 73 publications

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“…Meanwhile, we also found that contributions from tributary dilutions on DOC decreases were all positively correlated with water discharge in both river sections (Figures 4A,B). This relationship matched well with the fact that DOC concentrations and water discharge are generally positively correlated in most tributaries of the Mississippi watershed (Irena et al, 2015). Using the above mass balance approach, our results showed that tributary inputs are the primary control on riverine DOC longitudinal changes, while in situ processing play a secondary role.…”

Section: Tributary Inputs As a Dominant Control On The Doc Longitudinsupporting

confidence: 83%

Impact of Wetland Decline on Decreasing Dissolved Organic Carbon Concentrations along the Mississippi River Continuum

Duan

Kaushal

et al. 2017

Front. Mar. Sci.

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Prior to discharging to the ocean, large rivers constantly receive inputs of dissolved organic carbon (DOC) from tributaries or fringing floodplains and lose DOC via continuous in situ processing along distances that span thousands of kilometers. Current concepts predicting longitudinal changes in DOC mainly focus on in situ processing or exchange with fringing floodplain wetlands, while effects of heterogeneous watershed characteristics are generally ignored. We analyzed results from a 17-year time-series of DOC measurements made at seven sites and three expeditions along the entire Mississippi River main channel with DOC measurements made every 17 km. The results show a clear downstream decrease in DOC concentrations that was consistent throughout the entire study period. Downstream DOC decreases were primarily (∼63-71%) a result of constant dilutions by low-DOC tributary water controlled by watershed wetland distribution, while in situ processing played a secondary role. We estimate that from 1780 to 1980 wetland loss due to land-use alterations caused a ca. 58% decrease in in DOC concentrations in the tributaries of the Mississippi River. DOC reductions caused by watershed wetland loss likely impacted the capacity for the river to effectively remove nitrogen via denitrification, which can further exacerbate coastal hypoxia. These findings highlight the importance of watershed wetlands in regulating DOC longitudinally along the headland to ocean continuum of major rivers.

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Section: Tributary Inputs As a Dominant Control On The Doc Longitudinsupporting

confidence: 83%

Impact of Wetland Decline on Decreasing Dissolved Organic Carbon Concentrations along the Mississippi River Continuum

Duan

Kaushal

et al. 2017

Front. Mar. Sci.

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“…Our analyses, based on the extensive USGS observational dataset, provide a systematic examination of DOC variability and the associated environmental controls at regional and national scales. We observed substantial changes in the role of different environmental factors for explaining variations in DOC concentrations across different water resource regions in the U.S., which testifies to the complexity of coupled-terrestrial aquatic carbon cycling [49,54]. Significant spatial variability in environmental factors resulted in region-specific environmental controls on DOC concentrations [53].…”

Section: Environmental Controls On Doc Concentrationssupporting

confidence: 52%

“…The high litter inputs combined with high decomposition rates favor the generation of DOC and explain the relatively high average DOC concentrations in the 2nd order rivers (Figure 3). For large rivers, terrestrial sources tend to be outweighed by instream processes due to differences in water depth, land cover types, and nutrient conditions, as compared with small streams [49]. The standard deviation for stations on 6th and higher order rivers is smaller than that for low order (order < 5) rivers, which may be caused by the relatively balanced DOC input and removal in downstream regions [50].…”

Section: Spatial Patterns Of Doc Concentrationsmentioning

confidence: 98%

“…Changes in DOC concentrations by river order reflect the sources of carbon inputs and varied removal rates from headwaters to large rivers [49]. Due to dense riparian plant canopy, litter fall provides the majority of organic carbon loads to headwaters, which is characterized by high bioavailability and decomposition rates.…”

Section: Spatial Patterns Of Doc Concentrationsmentioning

confidence: 99%

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

Yang

Zhang

et al. 2017

Water

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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.

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“…While Swedish rivers have substantial water renewal along watercourses from the Scandes to the Baltic Sea (Muller et al, 2013), at such broad scales several environmental factors may modify element bioavailability through modification and differential uptake and remineralisation of C, N, and P. For example, bacterial processing (Creed et al, 2015), photodegradation (Bushaw et al, 1996) and reactive oxygen (Gao and Zepp, 1998) may influence organic matter degradation and changes in bioavailability over the long timescales encompassed by large river systems. In this regard, it is interesting to note that our estimates of short-term macro-nutrient bioavailability were similar for lakes and rivers, which suggest that possible differences in long-term macronutrient bioavailability across these very different sites did not seem to impact on the results determined under our specific laboratory conditions.…”

Section: Broad-scale Riverine Bdoc Bdn and Bdp Patternsmentioning

confidence: 99%

New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton

et al. 2017

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Abstract. Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on "total pools", yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105-693 µg C L −1 for BDOC (2 % of initial total DOC), 24-288 µg N L −1 for BDN (31 % of initial total dissolved nitrogen), and 0.2-17 µg P L −1 for BDP (49 % of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80 % of BDN and 61 % of BDP. In addition, we demonstrate that total C : N and C : P ratios are as much as 13-fold higher than C : N and C : P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich freshwaters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.

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The river as a chemostat: fresh perspectives on dissolved organic matter flowing down the river continuum

Cited by 276 publications

References 73 publications

Impact of Wetland Decline on Decreasing Dissolved Organic Carbon Concentrations along the Mississippi River Continuum

Impact of Wetland Decline on Decreasing Dissolved Organic Carbon Concentrations along the Mississippi River Continuum

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

New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton

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