Aquatic Ecology IAnn Zimmerman

ann.zimmerman@utoronto.ca402 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