Transcript Item 4 Acidification and eutrophication

ITEM 4
Acidification and
eutrophication
ICP Waters
ECE/EB.AIR/WG.1/2010/6
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
1
Effects of atmospheric N
deposition on biology in
oligotrophic surface waters
ICP Waters report 101/2010
• Has atmospheric N deposition contributed
to nutrient enrichment of lakes and rivers?
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
2
Background-1: is algal growth limited
by phosphorus, nitrogen, CO2?
• Debate on causes of
eutrophication in
1970s
• Schindler’s ‘whole lake
fertilization
experiments’ in
Experimental Lake
Area in Canada
• Conclusion: P controls
primary productivity
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
3
Background-2
• P-limitation of algal growth in freshwaters is
textbook knowledge
• Effects of N deposition studied in relation to
acidification
• Recent studies indicate that N supply affects algal
growth
• ICP Waters report:
– to give overview of literature on effects of reactive N in
freshwaters
– to improve/extend critical loads for nutrient nitrogen for
freshwaters
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
4
Effects of atmospheric N
deposition on N leaching
• N deposition leads to increased leaching of nitrate
to surface waters in natural ecosystems
• Leaching of N highly dependent on catchment
type
350
European sites (N=54)
1993
Runoff NO3 + NH4, µeq L-1
300
250
1999
200
150
2005
1990-93
1996-99
100
2002-05
50
0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
-2
1,4
1,6
-1
Total inorganic N deposition (wet), g m yr
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
Kaste ea 2008
5
Effects of N in freshwaters
• Experimental evidence
– Whole-lake experiments
– Smaller scale in-situ experiments
– Laboratory studies
• Historical records:
– Lake sediment studies (paleolimnology)
• Monitoring studies
– Region-wide lake surveys
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
6
Lake ecosystem
Water
plants
Free-floating
algae
Benthic
algae
Lake
sediments
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
7
Experimental evidence
• ’Whole-lake’ experiments
– Expensive, but high ecological
realism
– Additions with P and N show changes
in algal growth and algal species
– N can be a limiting factor
• Mesocosm experiments
– Less expensive and less realistic
– Pelagic (”free-floating”) algae can
respond to N addition only
– Benthic (”rock-dwelling”) algae can
also respond but less clearly
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
8
Experimental evidence
• Nitrogen is (co)limiting factor for growth
of phytoplankton and benthic algae
• No direct link between response to N and
N deposition
• Critical loads need a relation between N
deposition and a certain biological
response
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
9
Historical records:
paleolimnological evidence
• Most studies from arctic and alpine
lakes
• N deposition below 5 kg N/ha/yr
• Types of response:
– Sediments enrichment with 15N which
indicates an atmospheric source
– Changes in algal community structure
(species diversity)
– Statistical correlations between species
diversity and N enrichment
– Climate change is also partly
responsible for observed changes
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
10
Monitoring: lake surveys
• Strength:
– data from many regions
– Possible to relate N deposition to a response
• Weakness:
– other factors than N deposition may control the
response
Bergstrøm and Jansson 2006
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
11
• More NO3 at higher N
deposition
• Higher algal
production where N
deposition was high
[NO3]
• Clearest effect at N
dep < 5 kg N/ha/yr
Algal biomass
Higher productivity with higher
N deposition
(corrected for P)
N deposition ----
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
Bergstrøm
and
12
Jansson 2006
Nitrogen enrichment effects on water
plants (macrophytes)
• Worldwide loss of typical acid-sensitive
communities adapted to low N availability
(isoetides)
• Increased growth of more nitrophilous
species
• Especially well-documented in the
Netherlands
• Related to N-availability and –form
• Also related to alkalinity and nutrients in
sediments
• Critical load 5-10 kg N/ha/yr (Bobbink ea
1995 WASP)
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
13
Conclusions
•
•
Atmospheric N deposition leads to N-enrichment
of oligotrophic lakes in arctic, alpine and boreal
regions
Evidence from paleolimnology, whole-lake and
smaller scale experiments, regional surveys
– increased productivity
– shifts in algal communities
– loss of rare macrophyte species, increase of other
(nuisance) species
– data scarcity on effects on benthic algae and effects at
higher trophic levels
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
14
Empirical CLs
EUNIS description
C1.1
Oligotrophic
softwater lakes
catchment
type
arctic
Alpine,
boreal
C1.4
Regions
Response
Europe,
Canada,
Greenland
USA,
Europe
1. Phytoplankton community shift at N
deposition <1-1.5
Critical load
1. Phytoplankton community shift at N
deposition 3-5
2. Higher phytoplankton productivity at N
deposition < 5
Temperate, Canada,
1. Phytoplankton community shift at N
boreal
USA, UK,
deposition 2-9
Scandinavia, 2. Higher phytoplankton productivity at N
Netherlands deposition < 5
3. Shift of N to P limitation of benthic algae
at N deposition 2-12
4. Productivity of benthic algae increases at
N deposition 2-12
5. Macrophytes: loss of key isoetid species,
increase of species like juncus bulbosus and
sphagnum (Bobbink and Roelofs, 1995)
dunes
Netherlands 1. Increased biomass and rate of succession
(Bobbink et al., 2003)
Dystrophic lakes Temperate, Sweden,
1. Higher phytoplankton productivity,
boreal
Canada
especially at N deposition < 5
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
1
3-5
5-10
10-20
3-5
15
Suggestions for further development
CLs for nutrient-N for freshwaters
• Catchment characteristics determine catchment
N retention capacity
• FAB model is presently used to model critical
loads for acidity by simulation of NO3 leaching
as a function of catchment characteristics
• Use FAB model also in modelling of nutrient-N
CLs for freshwaters?
Brit Lisa Skjelkvåle
WGE 29th session,
September 2010
16