27 pages covering all 12 lectures in this module. Goes over: properties of water, algae, nutrients, the microbial loop, macroinvertebrates and organic pollution in rivers, zooplankton in lakes, estuaries, global warming and vertebrates in Antarctica.
L1 – Water Characteristics
Mixing Regime:
Lotic water: running, moving + turbulent water e.g. river
• Organisms attached to each other + sediment
Lentic water: standing water + strong currents beneath. Currents go around the sides of body
• Organisms need floating ability
• Some organisms attached
Temperature + Density:
• Water more viscous + dense > air
o Plants don’t need to invest energy into structural tissues as upthrust helps them
stand up with increased SA for photosynthesis
-> aquatic plants reproduce faster than terrestrial plants
• Water higher heat capacity > air
o Water retains heat + is a more stable environment
• As temperature increases, mass of freshwater decreases
o Freshwater most dense at 4 degrees + freezes at 0 degrees
o Seawater most dense at 1.062 degrees + freezes at -1.93 degrees
• Ice less dense < water
o Aquatic system ice forms a barrier over the water surface, water
Light:
Vertical Structures:
1. Shallow Lakes < 3m: sunlight increases temperature of surface water = decreases mass ->
single circular motion
2. Deep Lakes > 3m: Homothermal = temperature same at top + bottom -> deeper water
doesn’t mix with surface water -> stratification: 2 separate bodies with own circulating
system e.g. lakes, estuaries + coastal waters
Stratification Layers:
1. Epilimnion: warm top layer + least nutrients
2. Thermocline: most life = most food – nutrients from hypolimnion diffuse upwards
3. Hypolimnion: cold bottom layer + most nutrients
Stratification Types:
1. Amictic: permanently stratifies = oceans + Antarctic lakes
2. Holomictic: never stratifies = shallow lakes, coastal waters, rivers
3. Monomictic: stratifies once a year = deep lakes
High T in summer -> increases depth of top layer = thermocline is deeper
In autumn -> circulation breaks down stratification = overturn
4. Oligomictic: stratifies but not every year
5. Dimictic: stratifies 2x a year
6. Polymictic: stratifies + mixes frequently
7. Meromictic: partially stratified
Light Attenuation: absorption
Euphotic zone: where algae can photosynthesise
, 1. Deep euphotic zone = low nutrients + more humic material = brown
2. Shallow euphotic zone = high nutrients + less humic material = clear
Blue light has highest light attenuation = is best water penetration
Catchment:
Space around water body, altitude, size, utilisation, geology
Freshwater = influenced by catchments
Open ocean = has no catchment
Oxygen Availability:
Less O2 availability in water > air
Warm blooded mammals = breath air
Cold blooded vertebrates + some invertebrates = gills
Microbes + some invertebrates = diffusion
O2 availability: Air = 210mg O2/L > water = 10mg O2/L
Air O2 diffusion coefficient = 0.198 Water O2 diffusion coefficient = 0.000025
• Gases more soluble in cold water
Trophic Saturation:
1. Ultra-oligotrophic: 90% O2 saturation, <4ug/L TP, <1 ug/L Chl a
2. Oligotrophic: 80-90% O2 saturation, 4-10ug/L TP, 1-2.5ug/L Chl a
3. Mesotrophic: 40-80% O2 saturation, 10-35ug/L TP, 2.5-8ug/L Chla
4. Eutrophic: 0-40% O2 saturation, 35-100ug/L TP, 8-25ug/L Chl a
5. Hyper-eutrophic: 0% O2 saturation, >100ug/L TP, >25ug/L Chl a
L2 – Algae + Nutrients
Plankton: microbe floating/drifting
Algae: functional guild
Guild: group of species = exploit same class of environmental resources in a similar way
• Primary producers
• Prokaryotes + eukaryotes
1. Marine = macroscopic algae + microscopic algae
2. Freshwater = macroscopic algae
Deep chlorophyll maxima: region in body with highest chlorophyll concentration
• Algae need 1% light penetration
Major Resources:
- don’t use organic elements
• Inorganic carbon = CO2
• Inorganic nitrogen = NO4, NO3, N2
• Inorganic phosphorous = PO4
• Sunlight
Redfield Ratio = C:N:P = 106:16:1
Algal Carbon Acquisition: photosynthesis fixes inorganic carbon using blue + red sunlight energy and
chlorophyll a
Photosynthetically Active Radiation: PAR = 400-700nm
Chl a concentration = directly proportional to algal concentration
Algal Nutrient Acquisition: concentration + ratio
• C never limiting
, • Diffusion -> N+P
1. Marine = N limited – N:P < 16
2. Freshwater = P limited – N:P > 16
Algal Groups:
Prokaryotes
1. Cyanobacteria:
• Filamentous + < 3um
• Single celled
• Colonial
• Accessory pigments:
a. Phycoerythrin: dominant in marine = pink
b. Phycocyanin: dominant in freshwater = blue/green
• Specialised cells = heterocyst: fixes N2
o Anaerobic + rest of filament = aerobic
o Excel at high nutrient concentrations -> toxic
Eukaryotes:
2. Diatoms:
• Silica frustule: hard cell wall = silicic acid
• Mostly attached + can release mucus -> movement
• Brown chloroplasts
• 23% of global carbon fixation
• 2 shapes:
a. Centric: 2 chloroplasts in line + gap in middle = Planktonic
b. Pennate: 2 parallel chloroplasts along length of cell = Attached
3. Green Algae:
a. Chlorophytes:
• Non-motile
• Mostly planktonic
• Mostly colonial
b. Autotrophic Flagellates:
• Flagella -> movement in 1 direction
• Mostly planktonic
• Eugelena has lipid rich eye spots – detect light -> uses flagella to swim towards
optimum light -> euglena found in distinct layer in water column
• E.g. volvox, synura, euglena
c. Dinoflagellates:
• 2 flagella
o 1 around waist = spin
o 1 at base = propulsion
• Mostly planktonic
• Prevalent in summer
• Marine dinoflagellates produce neurotoxins
Algae in Thermocline + Epilimnion:
Algae normally found in thermocline as more nutrients
If thermocline = brown water -> algae move towards epilimnion
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