UNDERWATER RADIATION MEASUREMENTS: CONSEQUENCES OF AN INCREASED UV-B RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 191

Penetration of UV into this fjord varied during the year within one order of
magnitude. This means that the composition and quantity of absorbing and scattering
matter and particles are of great importance for the UV doses relevant for life in the
water.
UV transparency in the Fjord depended on the natural environmental cycle
during the year. This can be due to snow melting and fresh water flowing into the Fjord
containing large amounts of CDOM. From supplementary measurements done at the
different depths. Salinity profiles were taken and chlorophyll TOC was measured at 3 m
and 10 m depths, as well as chlorophyll measurements. The annual variability of all
these factors was compared at different depths. In Figure 6 samples from 3 m depth are
shown. Salinity varied between 26 and 32 ppm with a minimum in early July (day
number 190, Figure 6) and maximum in winter. TOC varied from 110 PM in winter to
maximum 210 PM in late June correlating well with low salinity and low UV
penetration (correlation coefficients 0.84 and 0.88, respectively). k d at 340 nm and 3 m
depth increased during spring. The highest values were in early July (k d = 4.6) when
salinity was lowest.
Figure 6. Annual variability at 3 m depth at one location in Trondheim Fjord for salinity (open
squares, [ppm]), chlorophyll (closed circles,[Pg/A]), total organic carbon (open diamonds, [PM]) and
diffuse attenuation coefficients at 340 nm (closed triangles, [m -1 ] ).
There was a high correlation between TOC and diffuse attenuation coefficients in
UV. In this Fjord system a high correlation between TOC and salinity were found as
well, indicating that organic carbon brought with river water was an important source
for the TOC.