Safety and evidence boundary
Use public system diagrams and aggregate environmental data. Field observations must remain non-contact and safe. Do not enter hazardous water, drains, industrial sites, disaster areas, or collect protected materials. Distinguish measured fluxes from arrows drawn in a model.
Explicit science instruction
A reservoir stores matter; a flux is a rate of transfer between reservoirs. Residence time can be approximated as reservoir amount divided by outgoing flux under steady assumptions. Fast biological cycles and slow geological cycles interact.
Vocabulary: reservoir; flux; residence time; pool; steady state; source; sink; cycle.
Worked example with reasoning
A reservoir contains 1,000 units and loses 100 units per year while approximately balanced by inputs. Approximate residence time is 10 years. If outputs change, the steady-state estimate may no longer apply.
Guided question
Why is a large reservoir not necessarily a fast-moving part of a cycle?
Independent work
- Label reservoirs and fluxes in a supplied system.
- Calculate three residence times.
- Identify one steady-state assumption.
- Separate stored amount from transfer rate.
Misconception check
A wide arrow can represent a large flux while a large box represents a large reservoir; these are different quantities.
Formative understanding check
Reservoir 500 units, output 25/year. Approximate residence time?
Worked response
20 years under the simple steady-state approximation.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to challenge your systems model, quantitative interpretation, alternative explanations, and boundary conditions.
Open ArchaemenesTeacher guidance
Foundation: use box-arrow diagrams. Core: calculate and interpret timescale. Extended: analyze changing reservoirs when inputs and outputs are unequal.
Preserve learning evidence
Keep models, calculations, graphs, corrections and uncertainty notes in the matching Week 32 evidence field.