Environmental Engineering Reference
In-Depth Information
within the water body and vary with depth and solar altitude (Kirk
1984
; Belzile
et al.
2002
). The vertical attenuation coefficient (
K
d
PAR) has been found to vary
from 0.40 to 47 m
−
1
in sixteen Argentinean shallow lakes. High
K
d
PAR values
(>13 m
−
1
) have been detected in highly turbid lakes, medium
K
d
PAR values
(<10 m
−
1
) in clear-vegetated lakes, and very low
K
d
PAR values in Patagonian
lakes (<2.5 m
−
1
) (Pérez et al.
2010
). Depending on the occurrence of key absorb-
ance variables such as high CDOM, particulate material and chlorophyll, the
absorption of water can vary considerably. Light attenuation by water contributes
on average 0.3-9 % in UV and PAR, although it is highly variable between clear
and turbid waters (Belzile et al.
2002
; Lund-Hansen
2004
).
3.1.8 Snow and Ice in Arctic and Antarctic Regions
Absorption and scattering by snow and ice significantly affect the UV and PAR
attenuation, particularly in the Arctic and Antarctic region (Belzile et al.
2000
;
Warren et al.
2006
; Grenfell and Perovich
1984
; Buckley and Trodahl
1987
;
Perovich
1993
; Trodahl and Buckley
1990
; Arrigo et al.
1991
; Perovich et al.
1998
; Norman et al.
2011
). Snow is a scattering-dominated medium, the scattering
of which is independent of wavelength between 350 and 600 nm. The attenuation
of solar radiation in snow can be used to infer the spectral absorption coefficient of
pure ice, by reference to a known value at 600 nm (Warren et al.
2006
). The spec-
tral downwelling diffuse attenuation coefficient is caused by both scattering and
absorption within the medium. Scattering by snow depends on grain size, snow
density and water content, whilst scattering by ice depends on ice structure and
particle back-scattering (Buckley and Trodahl
1987
; Trodahl and Buckley
1990
;
Arrigo et al.
1991
; Perovich et al.
1998
).
It has been shown that the UV-B transmittance through 1.7 m-thick first-year
ice decreases from 2-1 to 0.2-0.1 % from the end of October to mid-November
in McMurdo Sound (Trodahl and Buckley
1990
). The decrease in transmittance is
the effect of the formation of a highly scattering layer, subsequent to ice-surface
drainage. UV-B transmittance at 320 nm for 1.6 m of snow-covered first-year ice
also decreases by an order of magnitude from 0.3 % in April to 0.03 % in June
in the Chukchi Sea (Perovich et al.
1998
). A bloom of ice algae at the bottom
of the ice can also reduce the UV radiation transmittance (Perovich et al.
1998
).
Belzile et al. (
2000
) report that about 2-13 % of incident UV-B irradiance is trans-
mitted through snow, ice and ice algae biomass, whilst transmittance increases
to 5-19 % for UV-A and to 5-12 % for PAR. An influence of ice algae on PAR
transmission is also observed (Belzile et al.
2000
; Arrigo et al.
1991
; Palmisano
et al.
1987
). The absorption of irradiance depends on the absoprtion by pure ice
and brine, CDOM and particulate organic matter (POM) (Belzile et al.
2000
;
Uusikivi et al.
2010
; Fritsen et al.
2011
; Grenfell and Perovich
1984
; Perovich
et al.
1998
; Norman et al.
2011
; Warren et al.
1993
). In Baltic Sea ice organic
matter, both particulate and dissolved, influences the optical properties of sea ice
and strongly modifies the UV radiation exposure of biological communities in and
