Environmental systems, feedback and perspectives
Diperkenalkan| English | Makna |
|---|---|
| stock/stɒk/ | cadangan |
| flow/fləʊ/ | aliran |
What would explain this observation?
- A lake can respond to the same nutrient input differently depending on its current state. Environmental outcomes depend on stocks 储量, flows 流量 and feedback.
Build the model
- A system model has a boundary, stores and flows.
- Negative feedback counteracts change; positive feedback amplifies it.
- An environmental perspective shapes what people value and which management outcomes they prioritize.
- stock: An amount held within a system.
- flow: Transfer of an amount per unit time.
What makes a reservoir budget incomplete?
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A budget is incomplete if any real flow is missing: an unmeasured outflow means the books balance only because something was ignored. Consistent units and an explicit boundary are features of a good budget, not defects.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Separate physical evidence from value judgements.
- A stock is an amount at a time; a flow is an amount per time.
- Sustainability decisions require ecological, social and economic evidence and a stated scale.
In the lab: Draw the system boundary before calculating a budget. Identify inflows, outflows and possible unmeasured terms. Compare stakeholder claims using the same evidence, then explain where values lead to different choices.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a reservoir begins with 800 units, receives 120 and loses 90 during a week.
- Change in storage = inflow-outflow = 120-90 = 30.
- Final storage = 800+30 = 830 units.
- The model assumes no omitted flow.
Your turn: A stock starts at 600, receives 80 and loses 110. Find final stock.
A stock starts at 600, receives 80 and loses 110. Find final stock.
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The result is 570 . Known: stock 600; inflow 80; outflow 110. Use change in stock = inflow - outflow. Change = 80 - 110 = -30. Final stock = 600 - 30 = 570 units. The negative change signals a shrinking store.
Check the conclusion and its limits
- A balance that closes mathematically can still omit a real process if terms were estimated to fit.
- Positive feedback does not mean a socially desirable result.
Not true: Positive feedback always produces a socially beneficial outcome. "Positive" in positive feedback means the change is AMPLIFIED, not that the outcome is good. Melting permafrost releasing methane is positive feedback with harmful consequences; desirability is a separate judgement.
- A system model has a boundary, stores and flows.
- Separate physical evidence from value judgements.
- Watch for: A balance that closes mathematically can still omit a real process if terms were estimated to fit.
Write from a final stock of 475
- A store starts at 450 units, receives 60 and loses 35.
- Find the final stock. Positive feedback means a change is amplified, not that the outcome is good.
"Positive" in positive feedback means the change is AMPLIFIED, not that the outcome is good.
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True. "Positive" in positive feedback means the change is AMPLIFIED, not that the outcome is good. Melting permafrost releasing methane is positive feedback with harmful consequences; desirability is a separate judgement.
An amount held within a system: write the technical term.
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stock means An amount held within a system.
A store starts at 450 units, receives 60 and loses 35. What is the final stock, and what does positive feedback not mean?
Final stock is the start plus inflow minus outflow. The word positive does not judge the outcome.
What is the final stock?
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450 plus 60 minus 35 is 475. The start and the inflow are inputs. Other options — 450 units (the starting stock); 60 units (the inflow alone).