The Role of Fe and pH in the Photolytic Decomposition of Dissolved Organic Carbon in Boreal Lakes

Jennifer L Mead1, Sherry L Schiff1, Jason J Venkiteswaran2, Richard J Elgood1, Ryan H.S. Hutchins3, Pieter Aukes1 and John Spoelstra1,4, (1)University of Waterloo, Earth and Environmental Sciences, Waterloo, ON, Canada, (2)Wilfrid Laurier University, Department of Geography and Environmental Studies, Waterloo, Canada, (3)University of Waterloo, Department of Earth and Environmental Sciences, Waterloo, ON, Canada, (4)Environment Canada, Burlington, ON, Canada

Contact First Author: Jennifer L Mead; jmead@uwaterloo.ca

Previously Published Material: Preliminary results from experiments that will be presented at AGU were first presented at the CCFFR/SCL Conference in Ottawa, January, 2015.

Abstract ID#: 34312

 

English Abstract:
Dissolved organic carbon (DOC) is the largest input of carbon to northern shield lakes but retention of DOC within lakes is large. Photodegradation of DOC is an important abiotic process for DOC loss. Products of DOC photodegradation including particulate organic carbon (POC), dissolved inorganic carbon (DIC), and photolytically altered DOC affect the size of carbon pools in lakes. Concomitantly, lake parameters such as pH and Fe concentrations can influence the rates of carbon transformation, yet these influences are poorly understood. Stable isotope analysis has been used to provide insight into the fate of allochthonous DOC and the accumulation of POC in lake sediments. In laboratory experiments, pH and Fe concentrations of three boreal streams (2 sites from The Experimental Lakes Area, Kenora, ON and one site from Dorset, ON) were manipulated to observe the impact on DOC photodegradation and POC formation. Measurement of carbon pools before, during and after photolysis allows the determination of DOC loss (production of DIC and POC formation) and carbon mass and isotopic mass balances. A novel size exclusion method, LC-OCD, was used in conjunction with other measures of quality to identify changes in DOC composition resulting from photodegradation. Changes in 13C/12C from photolysis were measured in the DOC before and after the experiment while the evolved CO2 was measured throughout the experiment. The data will provide insight into the mechanisms controlling the partitioning of terrestrial carbon between the atmosphere and lake sediments.
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