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.
The model applies a one-hour storm each day to one hectare. Runoff water stays within the rainfall budget, and mobilized nitrogen is divided between export and buffer retention. Algae and oxygen curves illustrate possible responses rather than predict a stream.
Guided ExperimentHow 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.
This classroom model applies a one-hour storm each day to one hectare. Runoff water cannot exceed rainfall. Mobilized nitrogen is divided between buffer retention and export. Algae and oxygen responses are illustrative and do not predict a real stream. Reset keeps recorded observations. Reset All clears the table and report.
Controls
Water Quality Metrics
Data Table
(0 rows)| # | Runoff water(L/ha) | Exported N(kg N/ha) | Buffer retained N(kg N/ha) | Trial fertilizer(kg N/ha) | Rainfall(mm/hr) | Soil | Slope(°) | Buffer(m) | 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.
The percentages below come from this lab's assumed exponential retention curve. They illustrate how increasing buffer width can change nutrient export. Actual retention depends on soil, plants, water flow and maintenance.
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. These principles help farmers plan nutrient applications for local conditions. This lab does not model crop uptake or yield.
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.
Compare management choices under the same model conditions. Treat the resulting differences as classroom examples rather than field estimates.
