scholarly journals Can the heterogeneity in stream dissolved organic carbon be explained by contributing landscape elements?

2014 ◽  
Vol 11 (4) ◽  
pp. 1199-1213 ◽  
Author(s):  
A. M. Ågren ◽  
I. Buffam ◽  
D. M. Cooper ◽  
T. Tiwari ◽  
C. D. Evans ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Model Development ◽  
Field Measurements ◽  
Mixing Model ◽  
Residual Analysis ◽  
Residence Times ◽  
Stream Network ◽  
Landscape Elements ◽  
Modelling Studies

Abstract. The controls on stream dissolved organic carbon (DOC) concentrations were investigated in a 68 km2 catchment by applying a landscape-mixing model to test if downstream concentrations could be predicted from contributing landscape elements. The landscape-mixing model reproduced the DOC concentration well throughout the stream network during times of high and intermediate discharge. The landscape-mixing model approach is conceptually simple and easy to apply, requiring relatively few field measurements and minimal parameterisation. Our interpretation is that the higher degree of hydrological connectivity during high flows, combined with shorter stream residence times, increased the predictive power of this whole watershed-based mixing model. The model was also useful for providing a baseline for residual analysis, which highlighted areas for further conceptual model development. The residual analysis indicated areas of the stream network that were not well represented by simple mixing of headwaters, as well as flow conditions during which simple mixing based on headwater watershed characteristics did not apply. Specifically, we found that during periods of baseflow the larger valley streams had much lower DOC concentrations than would be predicted by simple mixing. Longer stream residence times during baseflow and changing hydrological flow paths were suggested as potential reasons for this pattern. This study highlights how a simple landscape-mixing model can be used for predictions as well as providing a baseline for residual analysis, which suggest potential mechanisms to be further explored using more focused field and process-based modelling studies.

scholarly journals Can the heterogeneity in stream dissolved organic carbon be explained by contributing landscape elements?

2013 ◽  
Vol 10 (10) ◽  
pp. 15913-15949 ◽  
Author(s):  
A. M. Ågren ◽  
I. Buffam ◽  
D. M. Cooper ◽  
T. Tiwari ◽  
C. D. Evans ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Model Development ◽  
Field Measurements ◽  
Mixing Model ◽  
Residual Analysis ◽  
Base Flow ◽  
Stream Network ◽  
Landscape Elements ◽  
High Discharge

Abstract. The controls on stream dissolved organic carbon (DOC) concentrations were investigated in a 68 km2 catchment by applying a landscape-mixing model to test if downstream concentrations could be predicted from contributing landscape elements. The landscape-mixing model reproduced the DOC concentration well throughout the stream network during times of high discharge, but was even more useful for providing a baseline for residual analysis, which highlighted areas for further conceptual model development. The landscape-mixing model approach is conceptually simple and easy to apply, requiring relatively few field measurements and minimal parameterization. The residual analysis highlighted areas of the stream network that were not well represented by simple mixing of headwaters, as well as flow conditions during which simple mixing based on headwater watershed characteristics did not apply. Specifically, we found that during periods of base flow the larger valley streams underlain by fine sorted sediments had much lower DOC concentrations than would be predicted by simple mixing; while peatland streams had higher DOC than predicted. During periods of intermediate and high flow the model made more accurate predictions of downstream DOC. Our interpretation is that the higher degree of hydrological connectivity during high flows, possibly combined with shorter stream residence times, increased the predictive power of this whole-watershed based mixing model. However, there was still a clear pattern during high discharge periods, with peatland streams having lower DOC than would be predicted by simple mixing while forested streams had higher DOC. These observations suggest several potential mechanisms to be further explored using more focused field and process-based modeling studies, especially on the role of changing hydrological pathways.

scholarly journals Modeling dissolved organic carbon in temperate forest soils: TRIPLEX-DOC model development and validation

2014 ◽  
Vol 7 (3) ◽  
pp. 867-881 ◽  
Author(s):  
H. Wu ◽  
C. Peng ◽  
T. R. Moore ◽  
D. Hua ◽  
C. Li ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Forest Soils ◽  
Model Development ◽  
Terrestrial Ecosystems ◽  
Forest Harvesting ◽  
Biogeochemical Model ◽  
White Pine ◽  
C Cycling ◽  
Development And Validation

Abstract. Even though dissolved organic carbon (DOC) is the most active carbon (C) cycling in soil organic carbon (SOC) pools, it receives little attention from the global C budget. DOC fluxes are critical to aquatic ecosystem inputs and contribute to the C balance of terrestrial ecosystems, but few ecosystem models have attempted to integrate DOC dynamics into terrestrial C cycling. This study introduces a new process-based model, TRIPLEX-DOC, that is capable of estimating DOC dynamics in forest soils by incorporating both ecological drivers and biogeochemical processes. TRIPLEX-DOC was developed from Forest-DNDC, a biogeochemical model simulating C and nitrogen (N) dynamics, coupled with a new DOC process module that predicts metabolic transformations, sorption/desorption, and DOC leaching in forest soils. The model was validated against field observations of DOC concentrations and fluxes at white pine forest stands located in southern Ontario, Canada. The model was able to simulate seasonal dynamics of DOC concentrations and the magnitudes observed within different soil layers, as well as DOC leaching in the age sequence of these forests. Additionally, TRIPLEX-DOC estimated the effect of forest harvesting on DOC leaching, with a significant increase following harvesting, illustrating that land use change is of critical importance in regulating DOC leaching in temperate forests as an important source of C input to aquatic ecosystems.

scholarly journals Modeling dissolved organic carbon in temperate forest soils: TRIPLEX-DOC model development and validation

2013 ◽  
Vol 6 (2) ◽  
pp. 3473-3508 ◽  
Author(s):  
H. Wu ◽  
C. Peng ◽  
T. R. Moore ◽  
D. Hua ◽  
C. Li ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Forest Soils ◽  
Model Development ◽  
Terrestrial Ecosystems ◽  
Forest Harvesting ◽  
Biogeochemical Model ◽  
White Pine ◽  
C Cycling ◽  
Development And Validation

Abstract. Even though dissolved organic carbon (DOC) is the most active carbon (C) cycling that takes place in soil organic carbon (SOC) pools, it is missing from the global C budget. Fluxes in DOC are critical to aquatic ecosystem inputs and contribute to C balances of terrestrial ecosystems. Only a few ecosystem models have attempted to integrate DOC dynamics into terrestrial C cycling. This study introduces a new process-based model, TRIPLEX-DOC that is capable of estimating DOC dynamics in forest soils by incorporating both ecological drivers and biogeochemical processes. TRIPLEX-DOC was developed from Forest-DNDC, a biogeochemical model simulating C and nitrogen (N) dynamics, coupled with a new DOC process module that predicts metabolic transformations, sorption/desorption, and DOC leaching in forest soils. The model was validated against field observations of DOC concentrations and fluxes at white pine forest stands located in southern Ontario, Canada. The model was able to simulate seasonal dynamics of DOC concentrations and the magnitudes observed within different soil layers, as well as DOC leaching in the age-sequence of these forests. Additionally, TRIPLEX-DOC estimated the effect of forest harvesting on DOC leaching, with a significant increase following harvesting, illustrating that change in land use is of critical importance in regulating DOC leaching in temperate forests as an important source of C input to aquatic ecosystems.

scholarly journals Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands

2017 ◽  
Vol 14 (7) ◽  
pp. 1793-1809 ◽  
Author(s):  
Amy E. Pickard ◽  
Kate V. Heal ◽  
Andrew R. McLeod ◽  
Kerry J. Dinsmore
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Water Samples ◽  
Stream Water ◽  
Direct Conversion ◽  
Aquatic Systems ◽  
Residence Times ◽  
Terrestrial Environment ◽  
Rainfall Events ◽  
Fluorescence Characteristics

Abstract. Aquatic systems draining peatland catchments receive a high loading of dissolved organic carbon (DOC) from the surrounding terrestrial environment. Whilst photo-processing is known to be an important process in the transformation of aquatic DOC, the drivers of temporal variability in this pathway are less well understood. In this study, 8 h laboratory irradiation experiments were conducted on water samples collected from two contrasting peatland aquatic systems in Scotland: a peatland stream and a reservoir in a catchment with high percentage peat cover. Samples were collected monthly at both sites from May 2014 to May 2015 and from the stream system during two rainfall events. DOC concentrations, absorbance properties and fluorescence characteristics were measured to investigate characteristics of the photochemically labile fraction of DOC. CO2 and CO produced by irradiation were also measured to determine gaseous photoproduction and intrinsic sample photoreactivity. Significant variation was seen in the photoreactivity of DOC between the two systems, with total irradiation-induced changes typically 2 orders of magnitude greater at the high-DOC stream site. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. During the experimental irradiation, 7 % of DOC in the stream water samples was photochemically reactive and direct conversion to CO2 accounted for 46 % of the measured DOC loss. Rainfall events were identified as important in replenishing photoreactive material in the stream, with lignin phenol data indicating mobilisation of fresh DOC derived from woody vegetation in the upper catchment. This study shows that peatland catchments produce significant volumes of aromatic DOC and that photoreactivity of this DOC is greatest in headwater streams; however, an improved understanding of water residence times and DOC input–output along the source to sea aquatic pathway is required to determine the fate of peatland carbon.

scholarly journals Sources and fate of terrestrial dissolved organic carbon in lakes of a Boreal Plains region recently affected by wildfire

2013 ◽  
Vol 10 (10) ◽  
pp. 6247-6265 ◽  
Author(s):  
D. Olefeldt ◽  
K. J. Devito ◽  
M. R. Turetsky
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Mineral Soil ◽  
Terrestrial Ecosystems ◽  
Fulvic Acids ◽  
Mixing Model ◽  
Selective Removal ◽  
Boreal Plains ◽  
Peat Pore Water ◽  
Surface Geology

Abstract. Downstream mineralization and sedimentation of terrestrial dissolved organic carbon (DOC) render lakes important for landscape carbon cycling in the boreal region. The chemical composition of terrestrial DOC, the downstream delivery of terrestrial DOC and its processing within aquatic ecosystem may all be influenced by climate change, including increased occurrence of wildfire. Here, we assessed composition and lability (during both dark- and UV incubations) of DOC from peatland groundwater and mineral soil groundwater, and from shallow lakes within a peatland-rich region on the Boreal Plains of western Canada that was recently affected by wildfire. Wildfire was found to increase aromaticity of DOC in peat pore water above the water table, but had no effect on the concentrations or composition of peatland groundwater DOC or mineral soil DOC. Using a mixing model we estimated that on average 98 and 78% of terrestrial DOC inputs to the lakes in fine- and coarse-textured settings, respectively, originated from peatland groundwater sources. Accordingly, lake DOC composition reflected primarily a mixing of peatland and mineral soil groundwater sources, with no detectable influence of the recent wildfire. Lake and peatland DOC had low biodegradability, lower than that of mineral soil DOC. However, both mineralization and sedimentation of peatland DOC increased substantially during UV incubations through selective removal of aromatic humic and fulvic acids. Similar shifts in DOC composition as observed during the UV incubations were also observed across lakes with longer water residence times. The mixing model estimated that on average 54% (95% confidence interval: 36–64%) of terrestrial DOC had been removed in lakes as a result of mineralization and sedimentation. Meanwhile, the reduction in absorbance at 254 nm was 71% (58–76%), which suggests selective removal of aromatic DOC. Hence, incubation results, patterns of DOC composition among lakes and mixing model results were consistent with significant within-lake removal of terrestrial DOC through UV-mediated processes. Selective removal of highly aromatic DOC through UV-mediated processes implies that organic sources that are considered stabile in terrestrial ecosystems can be readily mineralized once entering aquatic ecosystems. Together, our results suggest that regional characteristics (climate, surface geology and lake morphometry) can prevent wildfire from causing pulse perturbations to the linkages between terrestrial and aquatic C cycling and also regulate the processes that dominate within-lake removal of terrestrial DOC.

scholarly journals Sample Preparation of Dissolved Organic Carbon in Groundwater for AMS 14C Analysis

Radiocarbon ◽  
2001 ◽  
Vol 43 (2A) ◽  
pp. 183-190 ◽  
Author(s):  
G S Burr ◽  
J M Thomas ◽  
D Reines ◽  
D Jeffrey ◽  
C Courtney ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Organic Carbon ◽  
Sample Preparation ◽  
Dissolved Organic Carbon ◽  
Analytical Procedure ◽  
Preparation Technique ◽  
Residence Times ◽  
Sample Preparation Technique ◽  
Southern Nevada ◽  
Multiple Measurements

This study describes a sample preparation technique used to isolate dissolved organic carbon (DOC) in groundwater for radiocarbon analysis using accelerator mass spectrometry (AMS). The goal of the work is to improve our ability to determine groundwater residence times based on 14C measurements of the DOC fraction in groundwater. Water samples were collected from carbonate and volcanic rock aquifers in southern Nevada. Multiple measurements of total dissolved organic carbon (TDOC) in groundwater from one site are used to demonstrate the reproducibility of the analytical procedure. The reproducibility of the method is about one percent (1σ) for a 0.5 mg sample. The procedural blank for the same size sample contains about 1 percent modern carbon (pMC).

scholarly journals Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands

2016 ◽  
Author(s):  
Amy E. Pickard ◽  
Kate V. Heal ◽  
Andrew R. McLeod ◽  
Kerry J. Dinsmore
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Systems ◽  
Co2 Production ◽  
Residence Times ◽  
Terrestrial Environment ◽  
Rainfall Events ◽  
Fluorescence Characteristics ◽  
Induced Changes ◽  
Study Laboratory

Abstract. Aquatic systems draining peatland catchments receive a high loading of dissolved organic carbon (DOC) from the surrounding terrestrial environment. Whilst photo-processing is known to be an important process in the transformation of aquatic DOC, the drivers of temporal variability in this pathway are less well understood. In this study, laboratory irradiation experiments were conducted on water samples collected from two contrasting peatland aquatic systems in Scotland. The first system was a stream draining the Auchencorth Moss peatland with high DOC concentrations subject to strong seasonal and flow driven variability. The second was the low DOC reservoir, Loch Katrine, also situated in a catchment with a high percentage peat cover. Samples were collected monthly at both sites from May 2014 to May 2015 and from the stream system during two rainfall events. DOC concentrations, absorbance properties and fluorescence characteristics were measured to investigate characteristics of the photochemically labile fraction of DOC. CO2 and CO produced by irradiation were also measured to determine total photoproduction and intrinsic sample photoreactivity. Significant variation was seen in the photoreactivity of DOC between the two systems, with total irradiation induced changes typically two orders of magnitude greater at the high DOC stream site. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. Rainfall events were identified as important in replenishing photoreactive material in the stream, with lignin phenol data (Ad:Alv,s and P:V) indicating mobilisation of fresh DOC derived from woody vegetation in the upper catchment. Using DOC-CO2 conversion data from irradiation experiments, we estimate that the contribution of Auchencorth Moss catchment to photo-induced aquatic CO2 production is up to 3.48 ± 2.02 kg CO2 yr−1. We have shown that peatland catchments produce significant volumes of aromatic DOC and that photoreactivity of this DOC is greatest in the headwaters, however an improved understanding of water residence times and DOC input-output along the source to sea aquatic pathway is required to determine the fate of peatland carbon.

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