Photochemical dissolution of organic matter from resuspended sediments: Impact of source and diagenetic state on photorelease

Tuesday, 15 December 2015
Poster Hall (Moscone South)
John R Helms1, Donna A Glinski2, Ralph N Mead3, Melissa Southwell4, Gene B Avery Jr5, Robert J Kieber5 and Stephen Andrew Skrabal6, (1)Morningside College, Biology and Chemistry Department, Sioux City, IA, United States, (2)Environmental Protection Agency Athens, National Exposure Research Laboratory, Athens, GA, United States, (3)University of North Carolina Wilmington, Wilmington, NC, United States, (4)Flagler College, Natural Sciences, Saint Augustine, FL, United States, (5)University of North Carolina Wilmington, Chemistry and Biochemistry, Wilmington, NC, United States, (6)Univ North Carolina Wilmington, Wilmington, NC, United States
Resuspended sediments exposed to simulated solar radiation release dissolved organic carbon (DOC). However, it is

unclear how the provenance of sedimentary organic matter (OM) impacts this photorelease. In the first

geographically extensive study of this phenomenon, twenty three size fractionated, fine grained sediments (< ca.

10–20 μm) from a variety of drainage basins were resuspended (at suspended solid loading of 29–

255 mg/l) and exhibited a net photochemical DOC release ranging from 2 to 178 μmol/g/h. There was

a logarithmic increase in photoreleased DOC vs. the proportion of sedimentary OC (%), most likely due

to photon limitation at high sedimentary OC loading (i.e. high mass-specific absorption limiting

light penetration). Sediment source and quality – determined using lipid biomarkers – had a significant effect

on DOC photorelease. The fatty acid terrestrial aquatic ratio (TARFA) indicated that terrestrially derived

sediments exhibited relatively greater DOC photorelease. The long chain carbon preference index

(CPI24–34) indicated that diagenetically unaltered terrestrial OM photoreleased more DOC than diagenetically

altered terrestrial OM. The short chain carbon preference index (CPI14–22) demonstrated that sediments

containing diagenetically altered planktonic or algal derived OM had a greater photorelease rate

of DOC than fresh algal OM. This suggests that humic substances (humus and/or adsorbed humic and fulvic

acids) play an important role in the photochemical dissolution of OC regardless of whether or not they

are imported from upstream (i.e. terrestrial humics) or generated within the depositional or sedimentary

environment (i.e. humification of algal dissolved OM).