Photochemical reactions play a complex role in the turnover of dissolved organic matter (DOM) in aquatic systems. While processes leading to the production or destruction of defined chemical species (i.e., CO, CO₂, DMS) are relatively straightforward to quantify, photochemical reactions also lead to broad scale oxidation of the DOM pool and can alter its biological lability which can be challenging to to assess.The balance between photochemical enhancement and photochemical reduction of the lability of the DOM pool is a balance between the activity of photons and the activity of microbes. Experimental conditions that preclude the inclusion of microbes directly require high resolution and low photon doses in order to provide accurate assessments of the effect photochemistry has on biological substrates.  Apparent quantum yields (AQYs) for the transformation of biologically labile DOM were calculated for three different total photon doses on a coastal water sample (Newfoundland, Canada). Samples were irradiated in a custom broadband irradiation set-up in quadruplicate 40-mL amber glass vials with 7 different long-pass cutoff filters. After irradiation, the samples were spiked with inorganic nutrients to induce carbon limitation, and an aliquot of the original microbial community was added. Biologically labile DOM was quantified as biological oxygen demand (BOD) over 14-days incubation using Winkler titrations. Results show the importance of high-resolution photon dose experiments with variable effects on spectral AQYs and total BOD as photon-dose increased.

Primary Presenter: Heather Reader, Memorial University of Newfoundland (hereader@gmail.com)

Authors:

Heather Reader, Memorial University of Newfoundland and Labrador  (hreader@mun.ca)

Kailee Clarke, Memorial University of Newfoundland and Labrador  (kgclarke@mun.ca)