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Limnology Midterm

Terms in this set (60)

What are nine classes of geological processes that form lakes?
glacial processes, tectonic processes, volcanic processes, landslide processes, Fluvial (riverine) processes, aeolin (wind) processes, solution processes, coastal processes, and biotic processes
What are the influences of surface area on lakes?
1. amount of sunlight
2. quantity of evaporation from surface
3. effect of wind on the lake (fetch)
4. gas exchange with the atmosphere
What are the influences of volume on lakes?
1. the mass of water and other materials
2. how long water and other materials remain in the lake (ie. residence time)
3. the potential for sediment/water interactions
What are the influences of depth on lakes?
1. thermal structure and lake vertical mixing processes
2. vertical distribution of biota and biotic processes
What are the influences of light on aquatic ecosystems?
1. physical features
2. amount and distribution of primary production
3. the spatial distribution of organisms
What are the different components of light extinction coefficients in lakes?
1. natural attenuation of water
2. particulates (DOC)
3. color
What are the four causes of density differences?
1. Temperature
2. Pressure
3. Solutes
4. Suspended particulates
Holomixis
Lakes where wind driven circulation mixes the entire water column
What is the most common form of vertical structure in lakes (ie. kind of stratification)?
Thermal stratification
Amictic
lakes that never mix, ice-capped lakes
Dimictic
mix twice a year; lakes circulate in spring and fall, thermally stratify in summer, usually inversely stratified when lakes are frozen in winter
Warm monomictic
Circulate freely in winter and above 3.98°C and stratify in the summer
Oligomictic
circulate rarely and infrequently mostly lakes in tropical areas where waters temp are more than 3.98°C
ex. amazon oxbow lakes
Polymictic
mixes several times a year or circulate almost continously
Meromictic
lakes that almost never circulate top-to-bottom because of density differences owing to salinity differences (mixolimnion on top and moninmolimnion on bottom separated by chemocline)
Ectogenic meromixis
results when an external source causes a change in salinity of a proportion of the water column (ex. saltwater intrusion into freshwater lake)
crenogenic meromixis
Saline springs can deliver dense water to the bottom of a lake
biogenic meromixis
salts are liberated by decomposition in the sediments and collect in the the monimolimnion (usually very deep lakes with little fetch)
What are the forces acting on a water bodies?
1. wind
2. atmospheric pressure
3. gravity
4. Coriolis (earth rotation)
5. inflowing rivers and streams
What factors determine whether flow is laminar or turbulent?
1. average density
2. density gradient
3. gravity
4. velocity
What does Richardson's number tell you about a lake?
High Richardson's number means that there is primarily laminar flow (little mixing).
Low Richardson's number means that turbulent flow dominates and there is mixing of the two fluids.
surface currents
formed from the frictional forces of wind on the water surface; angle of deflection from the wind is maximized in large lakes and decreases with size
Ekman spirals
coriolis forces cause surface currents to spiral to the right in the northern hemisphere and to the left in the southern hemisphere
Langmuir circulation
develops with high wind speeds and causes streaking on the water surface that is due to the convergence and divergence of helical circulation cells
surface seiche
forms at air-water interface; wind causes water to accumulate at one end of the lake and then stops or changes direction and causes standing waves that oscillate; fast and low amplitude
internal seiche
formed at interfaces of layers of different densities; oscillating movement in the thermocline and rocking of the hypolimnion while the surface of epilimnion stays still; slow and high amplitude
Internal Progressive Waves
created when turbulent flow results from internal seiching activity and mixes heat and water between the epi and hyplimnion; combined tilting from internal seiche and twisting from Coriolis effect
metalimnetic entrainment
occurs when turbulent flow from an internal seiche erodes the metalimnion, deepening epilimnion; important for nutrient mixing with surface water
What affects the solubility of oxygen in water?
temperature, pressure, and salinity
biological oxygen demand (BOD)
the rate at which a volume of water consumes oxygen through respiration (positively affected by temperature and amount of organic material available)
Winterkill
Seen in very productive but shallow lakes during ice-cover; snow-covered ice prevents light from penetrating to the water column and planktonic respiration depletes oxygen, killing fish
Summerkill
Seen in very productive stratified lakes during the summer; after spring stratification, hypolimnion of productive lakes loses oxygen to respiration of sediments and organic material falling from the epilimnion which can lead to a depletion of oxygen in the hypolimnion by the end of summer, killing off fish that cannot survive in the water epilimnion
Trophogenic zone vs. Tropholytic zone
Trophogenic- where organic matter is produced and photosynthesis >> respiration
Tropholytic- where organic matter is consumed and respiration >> photosynthesis (no O2 produce, usually hypolimnion)
What is the most significant form of organic phosphorus in lakes and where does it come from naturally?
Orthophosphate (PO4 3-) & comes from igneous rocks containing apatite (Ca5(PO4)3+) attached to Cl-, OH-, or Fl-
What are ways that phosphorus gets to lakes?
1. Inflowing from streams/rivers
2. sediments recycling P back into the water column (via RedOx)
3. mobile biota
4. humans
What are the key features of the Lake Washington case study? (what was happening in the 50s, how did they fix it, what were the ecological consequences?)
City was dumping sewage into the lake --> high phosphorus/nutrients causing blue-green algal blooms
Diverting sewage caused water to clear and daphnia to increase in size because there were more phytoplankton that they could actually consume (which was previously outcompeted by inconsumable blue-green algae) AND predator Neomysis decreased due to increased longfin smelt fish
Longfin smelt increased when the dredging of the Cedar river stopped because it allowed them to spawn upstream
What are the main sources of nitrogen to aquatic ecosystems?
1. atmosphere (not usable, has to be fixed by prokaryotes)
2. dry fall and precipitation (acid rain)
3. surface and groundwater inflows
4. excretion by terrestrial and aquatic consumers
What are the four nitrogen transformations and what do they require to occur?
1. Fixation - done by cyanobacteria or bacteria using high amounts of energy and enzyme nitrogenase
2. Ammonification - organic carbon is converted to ammonia as a waste product of aquatic animals or bacterial decay of material in an anoxic hypolimnion (both aerobic and anaerobic bacteria)
3. Nitrification - requires oxygen because goes from more reduced to oxidized state and done by two kinds bacteria together; decreases in acidic conditions
4. Denitrification - nitrate converted back to N2; requires anaerobic conditions and decreases in acidic conditions
What is the greatest source of carbon dioxide to lakes?
Primarily from respiration of organic carbon that flows in from the watershed
Secondarily, very productive lakes draw CO2 from the atmosphere (although the major of global lakes emit CO2 not consume)
Buffering capacity
the ability of waters to resist changes in pH when acids like CO2 are added
What is ANC and how is it measured?
Acid neutralizing capacity- refers to the ability of solution to resist changes in pH with the addition of acids or bases; due to the presence of weak anions that can absorb H+ ions (HCO3-, CO3 2-, OH-)
What forms is iron found in in lakes and in what conditions?
Either in soluble form (Fe++) in anoxic conditions or in its insoluble form (Fe+++) as colloidial or particulate in oxidized conditions
Can bind with Phosphorus in the presence of oxygen --> ferrous wheel!
What is the most common form of sulfur in lakes and where does it come from?
Sulfate (SO4 2-) is the most common and usually comes from precipitation (fossil fuel emissions have increased the amount of atmospheric carbon significantly)
Can also be from old marine sediments (CaSO4) and pyrite (FeS2) in watersheds
Where would you find sulfides as opposed to sulfates?
Sulfides (H2S, FeS) are present in anoxic conditions and are reduced
Sulfates (SO4-) are present in oxygenated water and are oxidized
What is the most common form of silica in lakes and where does it come from?
Usually SiO2 when dissolved in water and most of it comes from weathering feldspar rocks (second most abundant element in the lithosphere)
Lost with diatom blooms (diatoms use it up to create their structure and cannot grow more without it)
isostatic rebound
earth's crust rebounding from being so far depressed from glaciers 1000s of years ago
glacial scour lakes
grinding and weight of glacier against the earth's crust depressed it and carved out depression where lake formed (glaciers moving around)
EX: Lake WA and Sammamish
glacial moraine lake
Any lake left behind by the movement of a large glacier.
Glacier sitting traps water behind it
glacial kettle lake
typically small lakes, what used to be huge ice cube buried in gravel as continental glacier receded and left behind pit
often round like an ice cube
EX: lakes in N. WI
Paternoster lakes
A chain or series of lakes in a glacial valley
tectonic (rift) lakes
two plates come together and through slippage of lakes, develop basin that collects water
OLDER than glacier lakes (relatively old) --> much higher biodiversity and many endemic species
EX: famous African rift lake (like lake Malawi)
crater lakes
formed in volcanic craters and calderas which fill up with precipitation more rapidly then they empty
may be able to see old crater rim
Most water in Crater lake rained directly into the lake b/c very small watershed (little algae b/c little nutrients w/o runoff and chemistry reflects atmosphere)
landslide
geological activity forms lake
flavial (oxbow) lake
as river moving, migrates back and forth but every now and then storm comes through & one of bends cut off from rest of river --> forms lake b/c water is stagnant
aeloian (wind) lakes
blowing sand around causes dunes to form and forms depression
solution lakes
water actively dissolving rocks (has to have water soluble rocks such as limestone)
Cenote- type of spring found in Florida, water is dissolving limestone and little pond formed
coastal processes
wave action can form ponds that are isolated from larger main bodies of water
biotic formations
biological processes forming lakes
EX: beaver dam flooding valley upstream of it OR humans damming a river
extraterrestrial lakes
divets in Earth's surface caused by meteor big enough to form depression which then fills up with water
hypsographic curve
shows relationship between height of land and depth of ocean; describes physical shape of lake
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