Water Quality & Eutrophication Lab
Sample water from different environments, calculate a Water Quality Index, and simulate how excess nutrients cause algal blooms, oxygen depletion, and ecological damage through eutrophication.
Guided ExperimentCompare Upstream vs Downstream Water Quality
How do you think water quality will differ between an upstream pristine site and a downstream site that receives runoff? Which parameters will change most?
Write your hypothesis in the Lab Report panel, then click Next.
Nitrate is reported as nitrate-N in mg N/L. This classroom WQI uses illustrative scoring curves. The eutrophication model applies a ten-day nutrient pulse, then stops loading so a bloom can decline. Fixed light, temperature, biomass quota and decomposition rates illustrate a process rather than predict a lake.
Controls
Parameter Scores
These teaching thresholds compare raw readings. They do not establish drinking-water safety or regulatory compliance.
WQI Parameter Scores
Data Table
(0 rows)| # | Experiment | Trial | Site | pH | DO(mg/L) | Nitrate-N(mg N/L) | PO₄³⁻(mg/L) | Turbidity(NTU) | Temp(°C) | WQI | Day | Available N(mg N/L) | Algae Density(cells/mL) | Fish Stress |
|---|
Reference Guide
Water Quality Index
The WQI condenses multiple water parameters into a single score from 0 to 100.
Where w is the weight and q is the sub-index score for each parameter. Scores above 90 indicate excellent water quality; below 25 indicates very poor quality unsuitable for most aquatic life.
Dissolved Oxygen
Dissolved oxygen (DO) is the amount of oxygen gas dissolved in water, essential for aquatic organisms.
DO saturation decreases with temperature. Most fish require DO above 5 mg/L. Below 2 mg/L creates hypoxic "dead zones" where most organisms cannot survive.
- Above 8 mg/L - Healthy for all species
- 5-8 mg/L - Adequate for most fish
- 2-4 mg/L - Fish stress, sensitive species die
- Below 2 mg/L - Hypoxia, dead zone
Eutrophication
The simulation applies a nutrient pulse during the first ten days, then stops loading. Its fixed rates illustrate bloom growth and decomposition in a closed classroom model.
Eutrophication is the process where excess nutrients (nitrogen and phosphorus) cause rapid algae growth in water bodies.
The cycle proceeds as follows. Fertilizer runoff adds nitrogen and phosphorus. Algae multiply rapidly (bloom). When algae die, bacteria decompose them, consuming dissolved oxygen. Oxygen depletion kills fish and other organisms.
Classroom Comparison Thresholds
These thresholds support comparisons in this lab. They combine teaching choices for different purposes and do not establish water safety or regulatory compliance.
Nitrate is measured as nitrogen throughout this lab. EPA's drinking-water nitrate limit uses the same mass basis. EPA drinking-water standards explain that separate regulatory context.
| Parameter | Threshold |
|---|---|
| pH | 6.5 - 8.5 |
| Dissolved Oxygen | > 5.0 mg/L (classroom threshold) |
| Nitrate-N | < 10.0 mg N/L |
| Phosphate (PO₄³⁻) | < 0.1 mg/L (classroom threshold) |
| Turbidity | < 25 NTU (classroom threshold) |
