March 4, 2009
Time = distance
1 dimensional cross section
classical succession description
2 D - mosaic
dynamic models such as for forest fire disturbance
cellular automata -http://www.eddaardvark.co.uk/fivecell/forest.html
multiple processes
Oxygen consumption and reaeration in a stream
some organic pollutant is injected into the stream
process 1 - biological activity degrades the organic and uses up available dissolved O2
process 2 - oxygen from the air gets mixed and diffuses back into the stream
process 1 > process 2 you will get a sag in the dissolved O2 downstream
There is a simple set of equations that can be used to model this situation
rate of process 1 = kr * BOD
kr is the rate constant for respiration/consumption of BOD (2.0 day^-1)
BOD is the amount of oxygen that a particular amount of organic would consume in mg L^-1 of O2
rate of process 2 = kd * (oxygen_deficit)
kd is the rate constant for reaeration (0.4 day^-1)
oxygen_deficit is the difference between saturation DO and the current DO (saturation DO at 21 deg C is 8.9 mg L^-1)
the rate of change of DO is the rate of process 1 - the rate of process 2
d (DO)/dt = kr * BOD - kd * (oxygen_deficit)
courses/STELLA/stream-dilution-decay.stm