UV Radiation and Arctic Ecosystems

328 Pages·2002·2.74 MB·English

by  A. Dahlback (auth.)

Ecological Studies,Vol. 153
Analysis and Synthesis
Edited by
I.T.Baldwin,Jena,Germany
M.M.Caldwell,Logan,USA
G.Heldmaier,Marburg,Germany
O.L.Lange,Würzburg,Germany
H.A.Mooney,Stanford,USA
E.-D.Schulze,Jena,Germany
U.Sommer,Kiel,Germany
Ecological Studies
Volumes published since 1996 are listed at the end ofthis book.
Springer-Verlag Berlin Heidelberg GmbH
D.O.Hessen (Ed.)
UV Radiation
and Arctic Ecosystems
With 105 Figures and 9 Tables
123
Prof.Dr.Dag O.Hessen
University ofOslo
Department ofBiology
P.O.Box 1027 Blindern
0316 Oslo
Norway
Cover illustration:Seal resting on an ice floe in Kongsfjorden near Ny-Ålesund,79 °N
at Svalbard.Many of the results presented in this book are based on research in this
area.Photo:Dag O.Hessen
ISSN 0070-8356
ISBN 978-3-642-62655-5
Library ofCongress Cataloging-in-Publication Data.
UV radiation and Arctic ecosystems / D.O Hessen (ed.).
p.cm.– (Ecological studies ;v.153)
Includes bibliographical references (p.).
ISBN 978-3-642-62655-5 ISBN 978-3-642-56075-0 (eBook)
DOI 10.1007/978-3-642-56075-0
1.Ultraviolet radiation – Environmental aspects – Arctic regions.2.Ecology – Arctic
regions.I.Hessen,D.O.(Dag Olav),1956- II.Series.
QH543.95 .U8 2001
577.27'7'0998–dc21 2001049874
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Preface
Life is supported and constrained by a multitude ofabiotic factors,and access
to water, mineral nutrients and solar energy are key parameters for life in
general.The Arctic environment poses particular challenges to life owing to
low inputs oflight,low temperatures and for most Arctic ecosystems also low
levels of mineral nutrients. This holds particularly for the terrestrial and
freshwater systems where the harsh conditions cause low productivity and
low complexity,and few species are present.These are attributes that indicate
a high vulnerability to additional stress and environmental changes.While
light limitation also constrains marine primary production for most of the
year,Arctic marine waters are,in contrast to most terrestrial and freshwater
systems, highly productive and sustain a high diversity of life forms from
bacteria and phytoplankton to marine mammals as well as fish stocks ofgreat
commercial interest.Thus Arctic marine areas are also vulnerable to environ-
mental stress, yet for somewhat different reasons than the terrestrial and
freshwater systems.
There is an almost paradoxical relationship between light and life in the
Arctic;while photosynthetic active radiation (PAR,380–700nm) is probably
the major limiting factor for Arctic life in general, shortwave ultraviolet
radiation (UV-R, <380 nm) is a potential constraint on ecosystem pro-
ductivity.Since UV-R susceptibility may vary among species and taxa,it may
also be a determinant of community structure and a regulator of food web
dynamics.
Realizing that present-day UV-R may be one of the more important,yet
least known,factors influencing terrestrial or pelagic communities,one ofthe
main motivations behind this volume is to explore and discuss the role ofthis
“natural” UV-R on different Arctic and sub-Arctic ecosystems. Needless to
say, however, the signs of increased stratospheric ozone depletion, and the
corresponding increase in ground levels ofUV-B,are another motivation for
reviewing its potential role for Arctic communities – from bacteria to
humans.
VI Preface
Shortwave radiation is not necessarily a hazard to biology.In fact,there are
several processes that either directly (like D-vitamin synthesis) or indirectly
(lysis ofvirus or bacterial pathogens) may support life.Some organisms may
also benefit due to a release from competitors or predators that are more
prone to UV-mediated damage.Nevertheless,most organisms are stressed in
various ways by UV-R.When exposed to “natural”UV-R,there is an array of
cellular damages that can, and most often do, occur: DNA damage, intra-
cellular production offree radicals or strong oxidants,lipid peroxidation and
other kinds of membrane damage, general protein damage etc. There are
three major aspects that determine the net effect of UV-R: the threshold
where damage exceeds repair capacities, the costs of UV-R protection and
repair and the potential for short-term (physiological) or long-term
(evolutionary) adaptation to increased UV-R.
Naturally there is a tremendous variability in UV-R tolerance, not only
between taxa or species,but also between individuals.The net effects on the
community level may be rather intricate due to the fact that although two
competitors are both negatively influenced by UV-R, one will be less
susceptible and thus may benefit from UV-R in relative terms,the net effect
on prey species may be positive iftheir predator is more susceptible etc.Also,
there may be quite subtle food web effects that may rely not only on direct
species interactions, but on UV-R-mediated changes in food biochemistry
and quality.
To these effects acting directly on the biota we may add a number of
indirect effects since UV-R also strongly affects the physico-chemical
environment.It is well known that UV-R produces free radicals,oxidants and
may liberate inorganic nutrients on trace metals in surface waters. These
processes are supported by the presence oforganic matter,notably dissolved
humic substances, in water. Humic substances are, however, also prone to
photo-degradation that may turn rather recalcitrant complex molecules into
substances that are more accessible to biota (heterotropic bacteria).Again,the
balance of these processes will determine the net effect on the biota.These
processes are all covered in this volume in more detail.Although there is no
doubt that UV-R affects the environment in various ways,the entangled bank
of ecosystems frequently makes prediction of effects a difficult task.
Nevertheless,it is imperative to our understanding ofthe threat ofcontinued
ozone depletion to gain insight into the role of“natural”UV-R on ecosystem
components.
There has been an ongoing debate whether there really was a decrease in the
stratospheric ozone layer over the Arctic.Mostly,the discussion reflected the
major,natural fluctuations in the stratospheric ozone that are due to seasonal
and meteorological conditions.These natural oscillations demand long-term
series from various stations to identify real trends in ozone concentrations.
During the past years,however,a number of analyses from different stations
Preface VII
and with different methodology have clearly revealed a downward trend for
stratospheric ozone over Antarctic areas,yet not as dramatic as for the long-
lasting “ozone-hole” that has been a regular phenomenon in the Antarctic
spring for years.There are signs ofan increasing rate ofozone losses over the
Arctic.During the winter of1999–2000,the largest local ozone losses yet seen
in the Arctic occurred with over 60% observed in the altitude range of
18–20 km. Integrated total ozone column losses amounted to 20–25% less
ozone than previously observed.Release of chlorine-containing compounds
(CFCs) into the stratosphere has clearly decreased due to the Montreal
Protocol.Stratospheric chlorine concentrations are currently so high,however,
that it could take 50years or more for chlorine to return to 1980 levels even with
a total cut in halocarbon emissions. Also, due to the long half-life of
halocarbons in the atmosphere, ozone concentrations over the Arctic and
elsewhere are predicted to decline further for the coming two decades.To this
add the somewhat counterintuitive effect of global warming. A continued
warming ofthe troposphere may lead to cooling ofthe stratosphere which,in
turn,will enhance the formation of polar stratospheric clouds that facilitate
chemical reactions that lead to ozone destruction.
A tempting question might be:Why study the effects of decreased ozone
and increased UV-R in the Arctic when there is a more than 10-year record on
potential effects from the Antarctic? The obvious reply is that except from
being the coldest places on earth with some physical similarities, the Ant-
arctic and Arctic environments differ in several regards. First, the Arctic
includes large terrestrial circumpolar areas;second,there is a vast number of
freshwater ponds and lakes in the Arctic; and third,the are major physico-
chemical and biological differences between Antarctic and Arctic marine
areas that make effect predictions in the Arctic based on Antarctic experience
largely irrelevant.The Arctic areas also house large stocks of commercially
important fish species,species that spawn and spend part of their fry period
in surface waters just during spring-time ozone minima.
The following chapters deal with both the physical and biological aspects
of UV-R,although,in line with the series title,the focus is on the ecological
effects. Starting with a chapter that explains and explores the relationship
between ozone depletion and UV-R,we proceed to chapters discussing the
actual penetration of shortwave radiation into Arctic marine and freshwater
systems, as well as ice and snow of different quality. To which depths can
biologically relevant radiation be traced,and what are the key regulators of
UV attenuation in these systems? Then the ecosystems and their biological
members are examined in detail.First,we present a review on the terrestrial
systems, focusing on plants and their general responses to UV-R with
examples from high Arctic and sub-Arctic systems. Then there is a more
specific look at the key terrestrial invertebrates of the high Arctic, the
evolutionary ancient group Collembola,which bears some striking similar-
VIII Preface
ities with Arctic crustacean plankton in pigmentation and behaviour as a
consequence of UV stress. The chapters on freshwaters deal with phyto-
plankton and microbial communities,zooplankton and food-web responses
in three separate reviews.For the marine systems,separate presentations are
devoted to the planktonic micro-algae and benthic macro-algae.Both are key
players,representing the base of the food web,and the planktonic algae also
constitute an important sink of atmospheric CO . Then there is a compre-
2
hensive presentation of UV-R and effects on high latitude marine zoo-
plankton and fish.Realizing that man is also a natural member ofecosystems,
the book closes with a review of the potential hazards of increased UV-R on
humans in the Arctic.
So, are there any genuine conclusions that may be drawn from these
presentations? Do we face an environmental disaster as some newspapers put
it a few years ago,or will not only present-day UV-R but also predicted UV-R
be masked by natural ecosystem fluctuations induced by climate and season?
A vague answer will be thatit depends.It surely depends on which ecosystem
components are considered,on the time scales,and not the least on defini-
tions of such concepts as significant harmful effects.What will be clear after
reading these chapters is that ecosystems will indeed be affected by increased
UV-R, some taxa or species substantially, other less, and some will benefit
from reduced competition and predation.Strong conclusions on overall food-
web effects are still premature for most systems,however.
Our belief is that we do not face a catastrophe,but a serious problem if
ozone depletion continues.And for reasons given above (as well as in the
chapters), ecosystems are complex and ecological responses may thus
sometimes be hard to predict.Another book on UV-R and Arctic ecosystems
in 20 years (I am sure there will be some in this time span...) may probably
reach more conclusive,and in some cases also different,predictions than we
do.Nevertheless,our hope is that this book not only presents an overview of
present-day knowledge,but also a state-of-the-art review that future research
can build on.
Oslo,August 2001 Dag O.Hessen
Contents
Part I Ozone Depletion and UV Radiation in the Arctic
1 Recent Changes in Surface UV Radiation
and Stratospheric Ozone at a High Arctic Site . . . . . . . . 1
A.Dahlback
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Atmospheric Ozone . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Natural Variations . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.2 Long-Term Ozone Changes at High Latitudes . . . . . . . . 6
1.3 UV Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.1 Spectral Distribution and UV Controlling Factors . . . . . . 9
1.3.2 Arctic UV Radiation . . . . . . . . . . . . . . . . . . . . . . 12
1.3.3 UV Radiation Model . . . . . . . . . . . . . . . . . . . . . . 19
1.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2 Spectral Properties and UV Attenuation
in Arctic Marine Waters . . . . . . . . . . . . . . . . . . . . 23
E.Aas,J.Høkedal,N.K.Højerslev,R.Sandvik,E.Sakshaug
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Factors Determining the Vertical Attenuation
ofIrradiance in the Sea . . . . . . . . . . . . . . . . . . . . . 25
2.2.1 Transmission ofIrradiance Through the Surface ofthe Sea . 25
2.2.2 Vertical Attenuation Coefficient ofDownward Irradiance . . 26
2.3 Spectral Properties ofMarine Optical Components . . . . . 27
2.3.1 Pure Seawater . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.2 Yellow Substance . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.3 Phytoplankton and Associated Detritus . . . . . . . . . . . . 31
2.3.4 Minerogenic Particles . . . . . . . . . . . . . . . . . . . . . . 33
2.3.5 Sea Ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4 Relations Between Spectral Vertical Attenuation Coefficients 35
X Contents
2.5 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.5.1 Representation ofUV Daylight Transparency . . . . . . . . 38
2.5.2 Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.6 Regional Transparency ofUV Daylight . . . . . . . . . . . . 40
2.6.1 Characteristics ofArctic Marine Waters . . . . . . . . . . . . 40
2.6.2 Nordic and Barents Seas . . . . . . . . . . . . . . . . . . . . 42
2.6.3 Kara Sea and Davis Strait . . . . . . . . . . . . . . . . . . . . 48
2.7 Summary and Conclusions . . . . . . . . . . . . . . . . . . . 51
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3 Spectral Properties and UV Attenuation
in Arctic Freshwater Systems . . . . . . . . . . . . . . . . . . 57
J.B.Ørbæk,T.Svenøe,and D.O.Hessen
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.2 Optical Properties ofArctic Lakes . . . . . . . . . . . . . . . 59
3.3 UV Scenarios for Arctic Lakes . . . . . . . . . . . . . . . . . 67
3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4 UV and the Optical Properties ofSea Ice and Snow . . . . . 73
D.K.Perovich
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.2 Sea Ice Structure and Morphology . . . . . . . . . . . . . . . 74
4.3 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.4 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.5 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Part II UV Radiation and Arctic Terrestrial Systems
5 Effects ofUV-B Radiation on Terrestrial Organisms
and Ecosystems with Special Reference to the Arctic . . . . 93
L.O.Björn
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 Terrestrial Arctic Conditions and UV-B Effects . . . . . . . 94