Lesson 2: Capacity and Load: Understanding System Limits
Duration of Days: 3
Lesson Objective
Students will analyze the relationship between bioload, bacterial processing capacity, and plant biomass to determine how system limits influence stability and carrying capacity.
What determines how much life a system can support?
How does bioload relate to bacterial capacity?
What role does plant biomass play in nitrogen removal?
What happens when input exceeds processing capacity?
How can carrying capacity shift over time?
Bioload
Carrying capacity
Processing capacity
Colonization time
Surface area
Biomass
Nutrient uptake
Limiting factor
Scaling
HS LS2 1
Use mathematical and computational representations to support explanations of factors that affect carrying capacity of ecosystems at different scales.
HS LS2 4
Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
Science and Engineering Practice, Analyzing and Interpreting Data
Science and Engineering Practice, Constructing Explanations
Crosscutting Concept, Stability and Change
Crosscutting Concept, Systems and System Models
Crosscutting Concept, Cause and Effect
Students interpret quantitative relationships.
Students analyze proportional reasoning.
Students evaluate how increasing one variable affects another.
Description and Purpose
Day 1: Quantifying Bioload
Students estimate fish biomass and feeding rate.
They calculate approximate daily input of waste based on feeding amounts.
Students compare this input to observed ammonia levels.
They discuss:
Did we increase input faster than the system could process?
The goal is to connect numbers to ecological consequence.
Day 2: Processing Capacity
Students analyze:
Available surface area for bacteria
Plant biomass relative to nitrate production
Oxygen availability
They identify limiting factors in the system.
Students construct a short explanation:
Identify the primary limiting factor in our system and justify using evidence.
Day 3: Dynamic Carrying Capacity
Students examine how carrying capacity is not fixed.
They consider:
How increasing plant mass could raise nitrate processing capacity
How adding filtration media increases bacterial colonization
How reducing feeding lowers input
Students refine their system model to include load versus capacity balance.
The purpose is to shift thinking from “what went wrong” to “what exceeded limits.”
DOK 1
Recall components of the nitrogen cycle, ammonia, nitrite, nitrate, bacteria.
DOK 2
Explain relationships between ammonia, nitrite, and nitrate.
Interpret water testing data in relation to the cycle.
DOK 3
Construct a system specific nitrogen cycle model using actual tank data.
Explain how disruption at one stage affects the entire system.
Aquaculture facilities must carefully balance fish stocking density with filtration capacity.
Wastewater treatment plants rely on bacterial communities to convert toxic compounds.
Overstocked ponds and lakes experience nutrient overload leading to ecological collapse.
Students recognize that natural and engineered systems operate under capacity constraints.
Bacteria are harmful rather than essential.
More feeding always helps fish grow without consequences.
Nitrate is dangerous at all levels.
The nitrogen cycle happens instantly.
If ammonia is zero once, the system is permanently stable.
https://docs.google.com/document/d/1siFIsOAs45CxuUlyJt9dNRdT70eTva14fJMeE1qXHPk/edit?usp=sharing%20
Limiting Factor Statement
Students submit a brief written explanation identifying the key limiting factor that contributed to imbalance.