Rain Pattern and Soil Moisture Content Effects on Atrazine and Metolachlor Losses in Runoff

Abstract

Herbicide concentration in runoff varies dramatically within a storm, therefore storm pattern is postulated to have a significant impact on herbicide loss. We evaluated the effects of storm pattern and soil moisture content on herbicide loss in runoff, and used our data to validate the uniform mixing concept for modeling herbicide transfer to runoff. Atrazine and metolachlor were surface applied to air‐dried soil at rates of 1.12 and 2.24 kg/ha, respectively. Two soils (Cecil sandy loam and Miami silty loam), four storm patterns (uniform, advanced peak, intermediate peak, and delayed peak), and two moisture levels (wet and dry) were used. Dissolved herbicide losses from the advanced peak were twice those from the other patterns for both herbicides for Cecil soil. The significance of rain pattern effects was reduced for Miami soil, but metolachlor loss from the advanced peak was 1.9 times that from the delayed peak. Rain pattern affected sediment‐bound herbicide loss, but no consistent trend was shown for both soils. Under wet conditions a greater potential for dissolved and sediment‐bound herbicide losses was shown for both herbicides on Miami soil than on Cecil soil. Measured herbicide concentrations in runoff decreased exponentially with cumulative rainfall depth, and were adequately described by the uniform mixing model. Results show that information on intensity distribution and transient infiltration rate is needed to better predict both instantaneous and total herbicide losses during a storm.

Modeling and Risk Analysis of Nonpoint-Source Pollution Caused by Atrazine Using Swat

“…This proportion agrees with values reported by other researchers (Huber, 1993;Zhang et al, 1997;Christensen and Ziegler, 1998).…”

“…A loss of up to 15% of applied atrazine has been determined in Miami silt loam soil, 95.4% of which occurred in the dissolved phase (Zhang et al, 1997). Christensen and Ziegler (1998) found that approximately 1% of the atrazine applied in the Little Arkansas River watershed, in Kansas, was transported annually in surface runoff to the river in the period 1995-1997.…”

Modeling the effect of rainfall intermittency on the variability of solute persistence at the soil surface

“…These include transient variations in water content and temperature and their effects on sorption and degradation [Walker, 1974]; upward solute transport due to evaporation, diffusion and raindrop impact [Ahuja et al, 1981;Zhang et al, 1997]; and rate limited transport which may depend upon rainfall intensity [Zhang et al, 1997]. While the anticipated effects on the results are mixed, generally, neglecting these processes may tend to underpredict the mean and variance of solute persistence which we derive here.…”

“…[12] The conceptual model for solute dissipation considers the chemical to reside in a thin surface layer, which fully mixes with water from intermittent rainfall events [Leonard, 1990;Steenhuis et al, 1994;Zhang et al, 1997]. This thin layer is the depth over which rapid flows interact.…”

Sampling strategies based on sets of behavioural parameters. Application to a simple pesticide fate model

“…A instead of s, which is somewhat arbitrary and requires no new parameter; prop is assumed to be constant, at least for an event. This part of the model is able to yield increasing concentration with decreasing discharge, a behaviour attributed to far from equilibrium desorption by Zhang et al (1997).…”