Fertilizer Runoff Lab
Investigate the eutrophication cascade from fertilizer application to dead zone formation. Adjust fertilizer rates, soil type, rainfall, slope, and buffer strip width, then watch the 30-day simulation unfold as nitrogen enters waterways, fuels algal blooms, and depletes dissolved oxygen.
Guided Experiment: How Buffer Strips Reduce Nutrient Runoff
If you increase the width of a vegetative buffer strip between a farm field and a stream, how will the nitrogen concentration in the stream change?
Write your hypothesis in the Lab Report panel, then click Next.
Controls
Water Quality Metrics
Data Table
(0 rows)| # | Day | Fertilizer Applied(kg/ha) | Runoff N(mg/L) | Algae(μg/L chl-a) | Dissolved O₂(mg/L) | Water Quality |
|---|
Reference Guide
Eutrophication Process
Eutrophication is the process where excess nutrients (mainly nitrogen and phosphorus) enter a water body, causing a chain reaction. The sequence unfolds over days to weeks.
First, nutrients fuel rapid algal growth (algal bloom). When the algae die, bacteria decompose the organic matter, consuming dissolved oxygen. If oxygen drops below critical thresholds, fish and invertebrates suffocate, creating a dead zone.
Dissolved Oxygen and Aquatic Life
Dissolved oxygen (DO) is the amount of oxygen gas dissolved in water. Aquatic organisms depend on it for respiration. Warm water holds less oxygen than cold water, with saturation around 9.2 mg/L at 20°C.
Most fish species need at least 5-6 mg/L to thrive. Below 4 mg/L, many species experience stress. Below 2 mg/L, most fish and invertebrates cannot survive, creating hypoxic or anoxic conditions known as dead zones.
Buffer Strips
Vegetative buffer strips (also called riparian buffers) are bands of trees, shrubs, or grasses planted between agricultural fields and water bodies. They slow runoff, trap sediment, and absorb nutrients before they reach streams.
A well-maintained 10-meter buffer strip can remove 50-85% of nitrogen from surface runoff. Wider buffers (20-30 meters) provide even more protection and also support wildlife habitat, bank stabilization, and shade for stream temperature regulation.
Nutrient Management
The 4R Nutrient Stewardship framework guides fertilizer best practices: apply the Right source, at the Right rate, at the Right time, in the Right place. Following these principles can reduce N runoff by 30-50% without significantly reducing yields.
Soil testing helps determine exactly how much fertilizer a crop needs. Split applications (applying fertilizer in multiple smaller doses rather than all at once) improve uptake efficiency and reduce the amount available for runoff during rain events.