Environmental Engineering Reference
In-Depth Information
INFLUENCE OF ULTRAVIOLET RADIATION ON THE CHROMOPHORIC
DISSOLVED ORGANIC MATTER IN NATURAL WATERS
R. DEL VECCHIO AND N. V. BLOUGH
Department of Chemistry and Biochemistry, University of Maryland,
College Park, 20742, MD, USA.
1. Abstract
Colored or chromophoric dissolved organic matter (CDOM) is by definition that
portion of the dissolved organic matter (DOM) capable of absorbing light (i.e. contains
chromophores). It represents a dominant absorbing species in natural waters and
therefore it plays a critical role in controlling the light distribution in aquatic
environments. CDOM shows a featureless absorption spectrum that increases
exponentially with decreasing wavelength. Under light exposure CDOM loses its
optical properties (photobleaching), altering the aquatic light field. Field and laboratory
studies indicate that the CDOM photobleaching can represent a quite significant sink of
this material over a short time scale.
2. Introduction
Dissolved organic matter (DOM) represents one of the largest reservoirs of
organic carbon on the earth 1 . The amount of dissolved organic carbon (DOC) in aquatic
environments is comparable to that of carbon (as CO 2 ) in the atmosphere. DOM has
therefore the potential to influence the global carbon cycle and climate change 2 .
CDOM, also referred to as Gelbstoff, yellow substances or humic substances, is a
complex mixture of species originating from the decay of photosynthetically produced
organic matter and found ubiquitously in the environment. Because CDOM is one of the
primary absorbing species in aquatic environment, its light absorption is important in
determining the aquatic light field. Due to its strong absorption in the ultraviolet (UV)
spectral range, CDOM limits the penetration of biologically damaging UV-B radiation
in the water column, so shielding the living organisms. At higher levels, CDOM
absorption extends well into the visible regime, affecting the quality and quantity of
UV-B and photosynthetically active radiation (PAR) available to the phytoplankton,
with potentially very important impacts on the ecosystems 3-10 .
3. Optical properties
Because CDOM absorbs and emits light in the ultraviolet and visible, studies on
this material often employ absorbance and fluorescence spectroscopy. The featureless
Search WWH ::




Custom Search