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LSM3254 Ecology of Aquatic Environments
Freshwater habitats
Darren Yeo
Dept of Biological Sciences
Objectives
To learn about:
Selected freshwater habitats and associated limnologicalconcepts
Freshwater habitats in Singapore
Scope Watershed
Lentic habitat lakes, swamps
Lotic habitat streams
Freshwater habitats in Singapore
References:
Dodson, S. 2005.Introduction to Limnology. McGraw-Hill Chapters 2, 11
Watershed
Area of land that supplies water to a lake or stream
= Area of land drainedby a lake or stream
Also known as catchment ordrainage
Note: Surface watershed maynot correspond withgroundwater watershed
Lentic environments
Standing water bodies
Lake Large body of water, depth>3m, area >1-10 ha
Often shows thermalstratification
Pond Small body of water, area
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Lakes
Most of the worlds freshwater resides in a few large lakes
~60% of the worlds freshwater in three areas
Lake parameters
Lake morphometrics
Shape, area, volume Shore length (=perimeter)
Varies with shoreline development (human shoreline development)
E.g., for given area,
- More elongate, with rough, folded shoreline longer shore length
- More circular, with smooth, simple shoreline shorter shore length
Measured shore length of lake
Index of shoreline development of lake = ---------------------------------------------------------------
Shore length of a circular lake with same area
Minimum index value = 1
Higher index value increased shoreline development
Water budget: lake inputs and outputs
Residence time: amount of time water spends in lake (yr)= Lake volume/discharge rate
Discharge rate: rate of water output from lake (m3 yr-1)
Flushing rate: rate of lake volume output (yr-1)= 1 / residence time
Lake parameters
6%
Lowest salinity,
nutrients,
productivity,
biodiversity
Highest salinity,
nutrients,
productivity,
biodiversity
Waterru
nsdown
hill-accu
mulates
and
concentr
ates(by
evapora
tion)che
micals
Lake position determines water input/output of lake
influences chemical and biological characteristics of
lake
Seepage lakes: no surface inlets; ground water only (-2, -1)
Drainage lakes: have surface outlets (-1, 1, 2, 3)
Lake position in landscape
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Vertical stratification in lakes: Thermal, oxygen, light,biological, primary production
Thermal stratification: vertical pattern of temperaturedifferences along a depth gradient
Water column divided into layers that resist mixing > 4 deg C: warmer water floats on top of cooler water
< 4 deg C: cooler water floats on top of warmer water
4 deg C: max density water sinks to lake bottom
Mixing of the water column - breakdown of stratification Wind-driven
Ecologically important
Oxygenation of bottom waters
Replenish nutrients in surface waters
Stratified lakes - oxygenation/temp regulation of upper layers
Vertical temperature profile
Graph of lake depth vs temperature
Depth plotted on y axis (vertical)
More diagrammatic representation
Fundamental to limnological
understanding
Thermal stratification gives rise to
other forms of stratification
(chemical, light, biological)
Vertical temperature profile
Vertical temperature profile
Summer stratification Epilimnion
Warm, bright, less dense upper layer
Oxygen rich higher concentration of fauna
Wind-driven mixing
Metalimnion Transition zone
Includes thermocline where temperaturechanges most rapidly with depth
Hypolimnion Cool, dark, denser lower layer
Oxygen-poor lower concentration of fauna
Winter stratification Very weak stratifiction
Reverse of summer Cooler, less dense epilimnion
Warmer, denser hypolimnion Mixing prevented by ice cover
Isothermal lake Spring, autumn
No temperature change with depth
No layers
Mixed
Vertical temperature profile
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Heterograde
Just below thermocline peak[O2] (oxygen anomaly)
Low production lakes deep
light penetration
Growth of hypolimnion algae
(Algal plate)
Vertical oxygen profile Vertical light profile
Euphotic zone
Upper layer with sufficient light fornet primary production byalgae From surface (100% light penetration) to 1% surface light
penetration depth
Compensation zone Just enough light for photosynthesis to support algae
Net primary production = 0
Aphotic zone Insufficient light for photosynthesis to support growth
Vertical light profile
Log
Light penetration Estimated using Secchi disk
Affected by:
Suspended particles (e.g.,phytoplankton, sediment)
Dissolved pigments (e.g.,tannins)
Depth/differentialabsorbance of colours(wavelengths) by water
Most strongly absorbed:IR, red, UV
Least absorbed: blue,green (most reflected)
Biological vertical profiles
Examples
Algae (phytoplankton) affected by light penetration
Bacteria and zoobenthos (bottom-dwelling
invertebrates) vertical profiles in the sediment
affected by [O2]
Zooplankton and fishes affected by physical (e.g.,
[O2]) and biological factors (e.g., predation)
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Diel Vertical Migration (DVM)
Daily pattern observed in zooplankton (small pelagicanimals)
Day migration to deeper waters avoid predation from visual
predators
Depth limited by [O2]
Night migration to shallow waters faster growth and
reproduction
Also observed in larval fishes
Biological vertical profiles Primary production vertical profiles
Net primary production (NPP): Energy in lake
ecosystem (from photosynthesis) excludingmetabolic requirements (for respiration) of algaeand plants
Highest NPP surface waters (epilimnion) inagricultural and urban watersheds Higher temperature
High light High inorganic nutrients
Primary production vertical profiles
Lake classification based on primary production
Eutrophic lake: High 1 production
Nutrient-rich Abundant phytoplankton
Poor light penetration turbid water due to phytoplankton
Photic zone upper epilimnion
Oxygen depleted (anoxic) hypolimnion
Oligotrophic lake: Low 1 production Nutrient-poor
Low in phytoplankton
Good light penetration clear water
Photic zone epilimnion to hypolimnion Well oxygenated hypolimnion
Primary production vertical profiles
Lake classification based on primary production
Mesotrophic lake: Intermediate 1 production Intermediate nutrient availability - between oligotrophic toeutrophic conditions
Dystrophic lake: Very low 1 production
Nutrient-poor abundant predacious plants
Low in phytoplankton
Low light penetration dark water dissolved organic
pigments
Oxygen depleted anoxic hypolimnion
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Lake types and origins
Glacial lakes Glaciation - a major process
at higher latitudes
Deposited sediments(glacial till) moraines,alluvial dams
Deposited icebergskettle ponds
Depressions/basins plunge basins, glacialscouring, proglacial lakes
Lake types and origins
Non-glacial lakes Oxbow lakes (billabongs, bayous)
erosion/sedimentation along streammeanders
Sinkholes dissolved limestone in karstareas
Frost polygons thawed permafrost
Beaver ponds biological activity
Lake types and origins
Crater lakes volcanicactivity
Rift lakes tectonicactivity along fault lines
Lake Pinatubo Lake Toba
Lake Baikal Lake Poso African Rift Lakes
Lakes types and origins
Inland, shallow wetlands
Coastal wetlands - part brackish
Tonle Sap
ChilkaLake
Lake Songkhla
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Natural lakes in
tropical SE Asia- Inland, shallow wetlands
- Coastal wetlands: part brackish
- Volcanic and tectonic lakes
Tasik Bera (Malaysia)
Tonle Sap (Cambodia)
Inle Lake (Myanmar)
Lake Songkhla (Thailand)
Lake Toba (Sumatra)
Lake Poso (Sulawesi)
Lake Pinatubo (Luzon)
Lake development Lakes have finite life spans
Gradually become shallower
Lakes
wetlands Key process: sedimentation particles dropped bymoving water
Inorganic sediment (e.g., clay,silt, sand, etc.) in drainage lakes
Basins often deeper thanwater depth
Lake Baikal: 1741m water +>3000m of sediment
Organic sediment (e.g., peat compressed, very slowlydecomposing plant material)
Artificial Lakes
Reservoir
Artificial pond or lake
Created by construction of
a dam or barrage across a Valley
Depression
River mouth
River basin
Morphology and hydrology
distinct from natural ponds
or lakes
Artificial Lakes
Reservoirs Often characterised by
dendritic shorelines
Different from natural lakes
Tasik
Temenggor
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Swamps
Wetland
Soil saturated withwater
Shallow standing water
(up to 1m depth)
Extensively vegetated
Grasses marsh or bog
Trees - swamp
Swamps Lentic environment
Low-lying area relative to surrounding topography
Water table at or close to the surface; prone to flooding
Substratum includes spongy, slowly rotting vegetation
Extensive root mats and macrophytes
Regulates water flow and quality - functions like a giant,landscape level sponge Absorbs and holds excess water during rainy periods flood control
Slow release of trapped water during dry period maintain water flow
Natural filter for polluted runoff traps/absorbs pollutants and nutrients
Important habitat E.g., Singapores Nee Soon Swamp Forest
Lotic environments
Running or flowing waters(cf. lentic - standing waters) Rivers
Streams (creek, crick, branch,rivulet, trace, brook )
Springs
Estuary
Stream parameters
Stream morphometrics
Velocity: rate of downstreammovement
Gradient: decrease inelevation over fixed distance
Cross-sectional area ~1.5 x (depth x width)
Discharge: volume of water
carried per unit time Spates: Small pulses Floods: major peaks
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Classification of habitats in Singapore
Natural habitats Tree-country forest streams (primary,
secondary forest)
Freshwater swamp
Tend to be refuges for native aquaticspecies
Urban habitats (artificial of modified) Open-country rural streams
Concrete canals, drains
Reservoirs (inland, coastal)
Park/garden/landscape ponds
Artificial or modified ecosystems
Tend to have more exotic species
Ephemeral habitats In natural areas, e.g., pools, temporary
streams in forests
In artificial areas, e.g., marshland?
Natural freshwater ecosystems
Rivers and streams Absence of large rivers
Original large natural freshwater ecosystems - small rivers e.g., Sungei Kranji, Sungei Seletar, Sungei Kallang, Singapore River
But now almost all drowned or heavily modified
Absence of native large river species
Natural freshwater ecosystems Forest streams
Primary/secondary rain-forests Bukit Timah and Central Catchment Nature
Reserves
Mostly flowing into inland reservoirs
Few, if any, torrent streams
Natural/unmodified environmental conditions Shallow (
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Natural freshwater ecosystems
Nee Soon Swamp Forest (contd) Natural/unmodified environmental conditions
Slow-flowing streams draining into shallow, oftenflooded, valleys
Saturated, waterlogged soils - unstable and anaerobicsubstratum
Plants with some similar adaptations to mangrove plants stilt or prop roots breathing roots (pneumatophores)
Clear, stained (by tannins from decaying vegetation),soft, acidic (typically 28 deg C
Little any leaf litter or woody debris
Algae and macrophytes
Different environmental conditions (cf.forest streams) Open, deeper, less acidic waters
Few robust, adaptable native aquaticspecies
More exotic species better adapted tomodified conditions. E.g.,
Small species Species associated with higher pH and
temperature waters
Guppy (Poecilia reticulata)
Name that reservoir
http://www.pub.gov.sg/water/Pages/LocalCatchment.aspx
Artificial/modified freshwater ecosystems
Reservoirs 17 reservoirs for domestic/industrial use Artificial equivalents of natural lentic habitats (i.e. lakes),
which are absent
Damming natural river drainages or river basins Protected and Urban/Unprotected catchments
Inland reservoirs and coastal (estuarine) reservoirs Inland reservoirs dams at headwaters/upper reaches Coastal (estuarine) reservoirs barrages at river mouth or across
common basin Take years to flush out salt water
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Artificial/modified freshwater ecosystems
Different environmental conditions (cf. forest
streams) Open, deeper, less acidic, sluggish to standing waters
Few robust, adaptable native aquatic species
More exotic species better adapted to modified conditions.E.g.,
Large river/lentic species
Species associated with higher pH and temperature waters
Artificial/modified freshwater
ecosystems
Ponds Small, mostly isolated in parks, golf courses and
disused granite quarries
Canals Heavily modified rivers/streams, especially those
flowing through urban areas
Canalisation - straightening, deepening, widening,and cementing of the banks and substrates
Canalised for: Flood control
Mosquito control
Exposed to urban runoff and pollution
Harsh, exposed environmental conditions Warm, hard, often polluted, shallow waters
Bare concrete substratum Frequent and severe flash flooding
Few robust, adaptable natives
More exotic species. E.g., Species associated with hard, high pH and temperature
waters