Fungicide Runoff & Stream Ecotoxicity Simulator

Fungicide & Field

Fungicide class Triazole

Application rate 2.0 kg/ha

Rainfall intensity 25 mm/h

Buffer strip width 6 m

Downstream Monitoring Station

Peak conc. seen

0.00 mg/L

Hazard quotient

0.00×

Buffer retention

Sim. elapsed

0.0 h

How it works

Concentration C(x,t) in the stream follows the 1-D advection–dispersion–reaction equation used for surface-water solute transport:

∂C/∂t = -u·∂C/∂x + D·∂²C/∂x² - k·C

u = stream velocity, D = dispersion coefficient
k = first-order degradation/removal rate

Rain that falls on the treated field washes a fraction of the applied dose into surface runoff. Only some of that mass reaches the channel — a vegetative buffer strip intercepts and infiltrates the rest, following a saturating exponential:

f_runoff = clamp(rain/50, 0, 1) × 0.15
Retention(w) = 1 - e^(-w / 10 m)
Mass entering stream = applied mass × f_runoff × (1 - Retention)

That mass is injected as a loading pulse at the field edge (x=0) and solved forward explicitly on a 60-cell grid, then advected and spread downstream while decaying at each fungicide class's own rate. Risk to aquatic life is read as a Hazard Quotient against a 72 h algal LC50:

HQ = C_peak / LC50
HQ ≥ 1  →  acutely toxic exposure at the monitoring station

Triazoles degrade slowly (weeks-scale half-life) but are only moderately toxic to algae.
Strobilurins degrade faster but are markedly more algicidal per unit concentration.
Copper-based fungicides don't biodegrade — they're removed mainly by binding to sediment — and are toxic to algae at very low concentrations, since copper is itself an algicide.

Safe (HQ < 0.3) Elevated (HQ < 1) Toxic (HQ ≥ 1)

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