aquatic ecology i
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Aquatic Ecology I. Ann Zimmerman [email protected] 402 Ramsay Wright. Ramsay Wright. Ramsay Wright (402). Lash Miller. 2. Ecosystem perspective on aquatic systems. Emphasizing relationships among: - PowerPoint PPT PresentationTRANSCRIPT
Aquatic Ecology IAnn Zimmerman
[email protected] Ramsay Wright
Ramsay Wright
Lash Miller
Ramsay Wright(402)
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Ecosystem perspective on aquatic systems
Emphasizing relationships among: the physical aquatic habitat (temperature, morphometry, hydrology, light etc.) chemical milieuand biological community structure
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Watershed - area of land draining to a particular lake, wetland or stream
Everything that happens on the watershed affects stream/lake water quality
Aquatic ecologists think of watersheds as systems and advocate ecosystem based, adaptive management
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Individual lakes can also be thought of as ecosystems
amenable to adaptive management
However just as timber interests can operate independently from the rest of the forest ecosystem (at least for awhile), there are resource managers/commercial fisherman interested in lakes (or oceans) only for their fisheries or other commercial interests focused solely on water itself (drinking water, irrigation, hydroelectric generation).
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So…. not surprisingly, just as humans eventually get themselves into trouble when they try to divorce timber production from the rest of the forest ecosystem, we get ourselves into serious difficulties when we forget that water and fish are intimately connected to each other and to other components of the aquatic ecosystem.
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Given an ecosystem perspective, what kinds of
questions might limnologists ask
(and what might you expect to understand when we’re finished!)?
Three-spined stickleback (Gasterosteus aculeatus aculeatus)
What accounts for variance in growth rates of lake trout among
lakes?
43-46 cm35-38 cm
Lake Louisa 7 yr old
Redrock Lake 7 yr old
lake size/shape?
transparency?nutrients?
forage?
temperature?
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Is water quality more likely to respond to watershed phosphorus control or in
situ rehabilitation of piscivore populations?
Northern Pike Esox lucius
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Can we do anything to reduce loss of the Aral Sea: once the world’s 4th
largest freshwater lake?The "virtual water" trade: poor countries growing water-intensive crops for export to countries then able to conserve their own water supplies.
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The nature of Canada’s coming water “crisis”?
Alberta: dry to start with The Great Lakes Basin:
billions of dollars in lost shipping, unprecedented nuisance and/or toxic blooms of algae
Pressures for export: the American situation
www.inkcinct.com.au/
What are the likely consequences of diverting
water from James Bay?
climate change?
massive loss of wetlands?
habitat fragmentation?
exotic invasions?
eutrophication?
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Rather than trying to take detailed notes, use the slide printouts and
reference theLimnological Facts of Life
ENV234homepage and follow the links
env.chass.utoronto.ca/env234y/bht
13Rainbow darter (Etheostoma caeruleum)
14http://env.chass.utoronto.ca/env234y/bht
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http://env.chass.utoronto.ca/env234y/bht
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The limnological facts of life
Not quite everything you always wanted to know about aquatic ecosystems in four lectures.
http://env.chass.utoronto.ca/env234y/bhtor
ENV234Y homepage and follow the links
17http://env.chass.utoronto.ca/env234y/bht
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What?
stratification morphometry light regimes hydrologic regimes nutrient chemistry primary producers secondary producers tri-trophic relationships
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When? Today: physical limnology (temperature, morphometry, light)Wed: hydrology and chemical limnology (the bioassay lab)Mon: primary/secondary producers, tri-trophic interactionsWed: Case studies: ecosystem ecology (Scavia et al.), the Aral Sea, the Grand Canal
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Limnological Facts of Life
I. Temperature/Density Relationships
maximum density of water does not occur at its freezing point
change in density of water as a function of temperature is not linear
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Density as a function oftemperature
oC Density0.0 0.99986791.0 0.99992672.0 0.99996793.0 0.99999224.0 1.00000005.0 0.9999919
oC Density10.0 0.999727712.0 0.999524714.0 0.999271216.0 0.998970118.0 0.998623220.0 0.9982323
Density (g.mL-1) of water as a function of
temperature
Maximum density not 0o CLFoL: I
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Comparison of density (g.L-1) differences
18o and 20o
(998.6232) - (998.2323)= 0.3909 g
Change in density wrt temperature is not a linear function
12o and 14o
(999.7277) - (999.5247)= 0.203 g
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Take -home message As water at the surface of a lake changes temperature (e.g. warming in response to incoming solar radiation or cooling as a result of convective losses), it will change its density.
As it cools, it will sink (and be mixed into the underlying water)
As it warms, it will float as a lens on top of underlying water unless/until wind energy is sufficient to mix adjacent layers.
LFoL Figure 1: Temporal changes in lake temperature
profilesCheck LFoL• epilimnion• metalimnion• hypolimnion• What’s
happening wrt time 7?• epilimnion cools• thermocline degrades
Z
0
10
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Temperature
5 10 15 20 25 30
epilimnion
metalimnion
hypolimnion
times
1 2 3 4 5 6
times:1 = under ice
2 = turnover
3 = May
6 = Aug
thermocline
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Lakes at our latitude are dimictic: they “turn-over” twice a year (once in the fall and once in the spring). Depending on latitude/altitude, lakes may turn-over only once a year (monomictic) or never (amictic) Depending on depth, lakes may turn-over periodically (polymictic)
thermocline
inverse or- stratification
isothermy + stratification isothermy
While most Ontario lakes are dimictic . . .
lakes can also stratify chemicallye.g. Crawford Lake 26
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Salinity(ppt)
Density at4o
0 1.000001 1.000852 1.001693 1.0025110 1.0081835 1.02822
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Density as a function of salinity (kg.L-1)
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Density differences due to temp and salinity
(g.L-1)
0% and 35% salinity
(1000.00) - (1028.22)= 28.22 g
4o and 1o
(1000.0000) - (999.9267)= 0.033 g
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Lakes that are chemically stratified are called meromictic
lakes
mixolimnion
monimolimnion
chemocline
From Wetzel 2002 Limnology
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Meromictic Lakes
ideal for paleolimnological studies • lack of bioturbation in sediments • highly predictable deposition characteristics
chemically interesting (speciation of redox-sensitive elements)
biologically interesting because diversity microbial fauna across the chemocline
most notorious, however, for releases of dissolved carbon dioxide and methane, such as at Lake Nyos in Cameroon, West Africa where 1800 people died of asphyxiation due to a CO2 emission
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2000
-1900
-1950
-1750
turbidites
Charcoal rich(Clark and Royall 1995)
Ca
na
dia
n Z
on
e
Fossil rotifer loricaFossil maize smut spore
Fossil pollen from Iroquoian Zone
Portulaca
Cucurbita
Crawford Lake
JOHN H. McANDREWS, University of TorontoJANE L. TERANES, Scripps Institute of OceanographyCHARLES L. TURTON, Royal Ontario MuseumCHAD A. WITTKOP, University of MinnesotaERIK J. EKDAHL, University of Michigan
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Changes in the density of seawater as a function of temperature (and
salinity) also lead to stratification in the oceans . . .
,
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. . .and rising sea levels as the oceans warm due to climate change
The vast volumes of water in the oceans and the increases in ocean temperatures associated with climate change are leading to rising sea levels from thermal expansion (increases of 57 mm since 1993)
Thermal expansion is currently the most significant element in increasing sea levelsWalsh, J.E. 2005. Chapter 6: Cryosphere and Hydrology. ACIA
Scientific Report.
Temporal variations in global mean sea level (MSL) computed from TOPEX/POSEIDON measurements between Dec 92 and Jul 02
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IBID
Projected global sea-level rise between 1990 and 2100 from both
thermal expansion and land ice changes for each of seven AOGCMs
(11 to 43 cm)
Water at 10oC = 0.9999919 gm.cm-3 or a space 1 x 1 x
1.00002724 cm
Water at 12oC = 0.9995247 gm.cm-3 or a space 1 x 1 x
1.0000455 cm
Sea level is not affected by melting sea ice as that simply displaces a volume ofocean water equivalent to its mass
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Remain skeptical Local sea level is a
surprisingly complicated function of wind, currents and temperature and globally sea levels can vary by up to 2 metres
http://www.exitmundi.nl/images/sealevelamericaMap.jpgglobalclimatechange.jpl.nasa.gov
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Changes in (salinity derived) density may also impact THC
(MOC)
Currently it remains uncertain as to what might happen: Some
models project a weakening or even collapse of the THC; others suggest its trajectory will shift either north or south; still others project no change (AR4 predicts
slowing)
1000 year residence time
The whirlwind tour stratification morphometry light regimes hydrologic regimes nutrient chemistry primary producers secondary producers tri-trophic relationships
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http://www.gen.umn.edu/research/fish
Largemouth bass (Micropterus salmoides)
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Layer on morphometric effects
(in 2 slides)!
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Morphometric descriptors(II: Lake Shape) mean depth m
(V in m3/A in m2) shoreline
development (Plake:Pcircle
of similar area)
Low values of mean depth: small volumes relative to
surface area
High values of mean depth: large volumes relative to surface area
Increasing influence of sediment chemistry on water column chemistry
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Watershed: Lake Surface Area Ratio
HighLow
How big is the watershed compared to the lake?
Ratio = Watershed Area = Aw:Ao
Lake Area
Higher ratio = higher levels of nutrient loading; higher productivity; often reduced water quality
The whirlwind tour stratification morphometry light regimes hydrologic regimes nutrient chemistry primary producers secondary producers tri-trophic relationships
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What happens to light (EMR) when it reachesEarth’s atmosphere?
Reflection Transmission Scatter (proportional
to 1/λ4 - short scatter more)
Absorption (H2O, CO2 O2, O3, etc.)As EMR moves through the
atmosphere, scattering and absorption change both its intensity
and its spectral composition.
Why is the sky blue?
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latent/sensible heat = 30%
Fig 6.1-5
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EMR that reaches the surface of a lake depends
upon
Latitude Season Time of day Elevation of the lake Meteorological conditions
(ice cover, wave disturbance, suspended materials)
III. Light in Lakes