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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 Experiment: Compare 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.

Controls

Measurement Noise10%
Current Sample Readings
pH7.2
DO9.5 mg/L
NO₃⁻0.8 mg/L
PO₄³⁻0.03 mg/L
Turbidity5 NTU
Temp15.0 °C
95
Water Quality Index
Excellent

Parameter Scores

pH
97
Dissolved Oxygen
94
Nitrate
96
Phosphate
94
Turbidity
90
Temperature
100
EPA Compliance Indicators
pH (6.5-8.5)
Dissolved Oxygen (> 5 mg/L)
Nitrate (< 10 mg/L)
Phosphate (< 0.1 mg/L)
Turbidity (< 25 NTU)
WQI=∑i=1nwi⋅qi\mathrm{WQI} = \sum_{i=1}^{n} w_i \cdot q_i(weighted sum of sub-index scores)

WQI Parameter Scores

Data Table

(0 rows)
#TrialSitepHDO(mg/L)NO₃⁻(mg/L)PO₄³⁻(mg/L)Turbidity(NTU)Temp(°C)WQI
0 / 500
0 / 500
0 / 500

Reference Guide

Water Quality Index

The WQI condenses multiple water parameters into a single score from 0 to 100.

WQI=∑i=1nwi⋅qi\mathrm{WQI} = \sum_{i=1}^{n} w_i \cdot q_i

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.

90-100 Excellent
70-89 Good
50-69 Fair
25-49 Poor
0-24 Very Poor

Dissolved Oxygen

Dissolved oxygen (DO) is the amount of oxygen gas dissolved in water, essential for aquatic organisms.

DOsat≈14.6−0.39T+0.007T2\mathrm{DO_{sat}} \approx 14.6 - 0.39T + 0.007T^2

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

Eutrophication is the process where excess nutrients (nitrogen and phosphorus) cause rapid algae growth in water bodies.

Nutrients→Algal Bloom→Die-off→Decomposition→O2 Depletion\text{Nutrients} \rightarrow \text{Algal Bloom} \rightarrow \text{Die-off} \rightarrow \text{Decomposition} \rightarrow \text{O}_2 \text{ Depletion}

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.

EPA Water Quality Standards

The U.S. Environmental Protection Agency sets guidelines for safe water quality parameters.

Parameter Standard
pH 6.5 - 8.5
Dissolved Oxygen > 5.0 mg/L (warm water)
Nitrate (NO₃⁻) < 10.0 mg/L (drinking water)
Phosphate (PO₄³⁻) < 0.1 mg/L (to prevent eutrophication)
Turbidity < 25 NTU (surface water)