Bio2129 topic 6
what is a trophic status
the nutrient concentration and primary productivity in lakes
what factors vary in aquatic ecosystems
density of water ( temperature, salinity and verical stratification) and chemical proporties ( nutrients, ph, dissolved O2, conductivity)
aquatic ecosystems are classified into what categories
Oligotrophic, Mesotrophic and eutrophic
what is Oligotrophic
low nutrient concentration (P, N), clear water, deep with high O2, low primary productivity (few algae)
what is mesotrophic
moderate nutrient levels (N, P), medium primary productivity.
what is eutrophic
High nutrient levels (N, P), murky water, often shallow, high primary productivity with frequent algal blooms, low O2 in deeper layers due to decomposition
what are the most common causes of variation in lake trophics status
Substrate (natrual cause) and human activities (agriculture and water use)
how can agriculture cause variation in lake trophic status
Rain runoff carries fertilizers rich in nitrogen and phosphorus into waterways, which increases nutrient levels and leads to eutrophication. (when it rains on a farm)
what is an example of how water use varies lake trophic status
Sewage outflows add nutrients and pollutants to lakes and alters their trophic status.
what is eutrophication
process where lakes become nutrient-rich and more productive over time
differences in trophic levels lead to variation in
PP, photosynthesis and ecological structure in lakes
there are significant biotic differences between lakes
depending on trophic status ( oligotrophic, mesotrophic, eutrophic)
what is subsrate
composition of surrounding rocks and soils that affect nutrient availability
what are soluble substrates
more nutrient-rich runoff (ex. sedimentary rocks)
What are insoluble substrates
nutrient-poor runoff (ex., granite) is common in oligotrophic lakes
what subrate example is Dunedin, New zealand
eroded sedimentry rock, nutrient rich runoff
What substrate example is La Maurice Notional park, Canada
granite rock, nutrient-poor runoff (oligotrophic)
circulation of water and mixing affects
The distribution of nutrients in the water column
water density varies
with temperature and reaches peak density at 4C
belwo 4C, water becomes
less dense
why does ice float
because it is less dense than liquid water, and the molecular structure expands when it freezes
when water colls and solidifies
Its density decreases because of the hydrogen bond expanding
density differences cause
Stratification in lakes affects seasonal mixing
what is stratification
the layering of water in a body of water due to differences in temperature and density.
soluble substrates are associated with
eutrophic and mesotrophic conditions
soluble substrates releases
minerals and nutrients into water. easily eroded by runoff and vegetation
insoluble substrates have
little dissolved material, are poorly eroded and nutrient poor
What is thermal stratification
The formation of specific layers in a lake due to the differences in water density
what are the layers in thermal stratification
Epilimnion, metalimnion (thermocline) and hypolimnion
what is the epilimnion layer
warm, well-mixed surface layer exposed to sunlight
what is the metalimnion (thermocline)
middle layers where temperature changes with depth
what is the hypolimnion layer
cold, dense bottom layer that is isolated from surface mixing
seasonal patterns for turnover periods in thermal stratification is important because
They are essential for redistributing O2 and nutrients
stratification is good because it
limits O2 transfer between layers
decomposition at the bottom of thermal stratification layers
consumes o2
As T decreases or increases away from 4C
desnity decrases
desnity difference causes
Vertical stratification in lakes
oxygen solubility increases at
low temperatures
salt solubility decreases at
low temperatures
cold water holds more
dissolved oxygen than warm water
warm stagnant conditions = less
dissolved oxygen and stress for aquatic organisms
oligotrophic lakes have low nutrient levels and therefore
low GPP and NPP
Eutrophic lakes have high nutrient levels and therefore
high GPP and NPP
eutrophic zones =
NPP > 0
compensation depth =
NPP=0
Aphotic zone
GPP=0
What is light attenuation
light is absorbed, scattered and reflected as it travels downward through the water column
the rate of light decreases with
depth depends on turbidity and dissolved substrates
what is morphometry
the basic physical dimensions of a lake and its catchment (land it drains into)
what does morphometry influence
circulation, nutrient deposition and physical properties of the water body
examples of morphometric factors
1) Euphotic zone: how far light penetrates (affects photosynthesis). 2) Watershed size: determines how much material (nutrients & sediment) enters the lake from runoff. 3) Fetch: the longest distance that wind blows across a lake ( influences wave height, mixing oxygen distribution and depth thermocline)
what are prevailing winds
winds move surface water from one side of the lake to the other from windward to leeward side)
prevailing winds causes
upwelling and downwelling
what is upwelling
cold nutrient-rich water rises to the surface
what is down welling
warm surface water is pushed downward
downwelling and upwelling create
variation in temperature and nutrient levels across the lake
what are the ecological effects of prevailing winds
In large lakes ( like the great lakes), prevailing winds play a major role in circulation and productivity.
how do prevailing winds play a major role in circulation and productivity in large lakes
They cause surface currents that mix water, which helps distribute heat, oxygen and nutrients throughout the water column. upwelling brings nutrient-rich water from the bottom to the surface which promotes algal growth increasing the lake's productivity and supporting aquatic life
The vertical distribution of plants is determined by
light penetration, nutrient availability and substrate type
what are some consequences of physical factors in lakes
vertical distrobution of plants, vertical distrobution of fish ans geographic distrobution of phyloplanlton
what are macrophytes
rooted aquatic plants that grow in shallow zones with lots of available light
what is phytoplankton
floating microscopic algae, dominant in open water and stay on the upper levels where there's lots of light
how is the vertical distrobution of fish determined
by temperature, oxygen, and food availability, with warm-water species (like bass) remaining in the epilimnion and cold-water species (like trout) inhabiting the cooler, oxygen-rich hypolimnion, though stratification can limit movement when deep layers become oxygen-depleted.
how does the geographic distrobution affect phytoplankton
in freshwater species composition depends on the nutrient level. in the ocean, distribution is influenced by light, nutrients and temperature. upwelling zones ( nutrient-rich cold water) support high phytoplankton productivity