Miller, W.L. and M.A. Moran. 1997. Interaction of photochemical and microbial processes in the degradation of refractory dissolved organic matter from a coastal marine environment. Limnol. Oceanogr. 42:1317-1324.
         The interaction between photochemical and biological processes in the
    degradation of marine dissolved organic matter (DOM) was investigated with
    seawater from a coastal Southeastern U.S. salt marsh.  Seawater supplemented
    with humic substances was exposed to alternating cycles of sunlight
    (equivalent to 8 hr of midday sun) and dark incubations with natural
    bacterial populations (1-2 weeks in length).  Photochemical degradation of
    the DOM was monitored during sunlight exposure by direct measurements of
    dissolved inorganic carbon (DIC) and carbon monoxide (CO) formation in
    0.2-um filtered seawater.  Bacterial degradation was monitored during dark
    incubations by tritiated leucine uptake and changes in bacterial numbers in
    bacterivore-free incubations and by direct measurements of DOM loss.  The
    alternating cycles of sunlight and microbial activity resulted in more
    complete degradation of bulk DOM and marine humic substances than was found
    for non-irradiated controls (i.e. with microbial activity alone) by a factor
    of up to 3-fold.  Increased decomposition was due both to direct losses of
    carbon gas photoproducts (DIC and CO in a 15:1 ratio) and to enhanced
    microbial degradation of photodegraded DOM, with approximately equal
    contributions from each pathway.  Mass balance calculations indicated that
    low molecular weight carbon photoproducts, currently considered to be the
    compounds responsible for stimulating bacterial activity following
    photodegradation of DOM, were insufficient to account for the enhanced
    bacterial production observed.  Thus higher molecular weight, chemically
    uncharacterized fractions of DOM may also be modified to more biologically
    available forms during exposure to natural sunlight.