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The intent of this model is to allow students to investigate a dynamic, interconnected system, a stream ecosystem. They can examine how land-use and weather interact to effect water quality and species diversity in the stream.
Students may compare a run using default values to runs where variables are changed systematically. Before running the simulation with a modified parameter value, students predict what dependant variable they think will change and explain their reasoning.
They can continue this process and print out a log of their thinking.
In this way, students procede to generate explanations for the seasonal fluctuations in the stream variables (oxygen, nitrates, sediment, temperature, etc.). Some simple cause and effect relationships need to be reviewed including: the effect of air tempe
rature on water temperature. Less obvious effects of land-use on water temperature, i.e. how stream shading and run-off water from pavement areas and cleared land can effect stream temperatures. The relationship between water temperature and dissolved oxy
gen needs to be understood, as well as the sensitivity of aquatic organisms to oxygen levels. Also essential is the appreciation of the effect of different land-use types on the amount of run-off from a precipitation event, and the associated pollutants w
hich run-off from the different land-use areas, e.g., fertilizer nutrients(nitrates) from agriculture and lawns, sediment from agriculture and construction, toxins from pavement(hydrocarbons), lawns(weed killers), agriculture(pesticides) and industry.
Whenever a model variable is altered, students should describe how they expect or predict stream variables and species diversity to change as a result. After running the model, they can compare the model results with their expectations(hypotheses). Only b
y investigating many scenarios do students begin to construct a mental model of the complex interconnections inherent in a dynamic system.
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