B23D-0633
Photochemical dissolution of organic matter from resuspended sediments: Impact of source and diagenetic state on photorelease
Abstract:
Resuspended sediments exposed to simulated solar radiation release dissolved organic carbon (DOC). However, it isunclear 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).