Aquatic environments Flashcards
Oxygen and carbon cycle
Photosynthesis and respiration controls the oxygen and carbon cycles
Phtoplankton
Oxygenic phototrophs suspended freely in water; include algae and cyanobacteria
Benthic species
They are attached to the bottom or sides of a lake or stream
Misbalance in productivity and consumption
If rate of productivity in a pond exceeds the rate of consumption of organic matter, it will stimulate heterotrophs to increase dramatically.
this results in O2 consumption being greater than production which will cause the pond to be anoxic
heterotrophs and autotrophs
Activity of hetero is highly dependant on activity of primary producers; oxygenic phototrophs produce organic matter and oxygen
Oxygen stratification
Oxygen has limited solubility in water, the deep layers of freshwater can become anoxic once oxygen is consumed
O2 concentrations are dependant on amount of organic matter present and physical mixing of the system
Temporal variation
In day: Photoautotrophs photosynthesise and O2 is produced
At night: No photosynthesis occurs and O2 decreases
Spatial variation
Lake is stratified according to the season.
epilimnion
Warmer, less dense surface water of lake
hypolimnion
it is the cooler, denser water at the bottom of lake or pond
Thermocline
Seperates epilimnion and hypolimnion
Aeration of epilimnion
-Production of O2 by phototrophs
-Diffusion of O2 by air into water
chemicals in hypolimnion
There are chemorganotrophs in hypolimnion that break down organic matter produced by epilimnion anaerobically and produce H2S, Ammonia and Methane
Summer stratification
Epilimnion is seperate from hypolimnion where Ep has O2 and organic nutrients and Hypo contains some organic matter but no O2
Spring and Winter stratification
Water at top gets colder than water below
-Cooler water sinks which causes mixing of layers
-This causes the hypolimnion to become oxygenated, which affects microbe diversity and abundance in each layer.
Strom effect on lake stratification
It causes mixing of layers which causes toxic substances found in bottom layers to mix with upper layers which causes many organisms to die
River stratification
May be well mixed because of rapid water flow
-Can still suffer from oxygen deficiences because of high inputs of agricultural and industrial pollution
Biochemical oxygen demand
-The microbial oxygen-consuming capacity of a body of water
-Increases with the influx of organic material and then decreases over time
Effect pf input of organic rich waste waters into aquatic systems
-Sudden influx in sewage causes an increase in organic matter present
-This causes a sudden accumulation in heterotrophs
-This causes a decrease in autotrophs as oxygen and organic matter is used up
-When O2 is depleted, heterotrophs decrease which allows autotrophs and hence O2 to increase
Autrophs outcompeted by heterotrophs
Heterotrophs can always respire and utilise the available energy while autotrophs only respire at night
Phylogenetic sampling of lakes
Molecular studies such as 16S rRNA sequence is used as a culture-independant method.
-High microbial diversity reflects dynamic character of lake
-Seasonally variable inputs of endogenous and exogenous nutrients sustains a phylogenetically and metabolically complex community of Bacteria and a few groups of Archaea
