April 2011 (est.) article: “Comparison of Two Parametric Methods to Estimate Pesticide Mass Loads in California’s Central Valley,” by Dina K. Saleh, David L. Lorenz, Joseph L. Domagalski.
Agricultural pesticides are applied at very specific times of the year, with the temporal pattern depending on the particular pesticide. Modelers often have simulated the annual seasonal pattern of pesticides in streams with (to simplify) a sine function. This article presents an alternative, the Seasonal Wave model (SeaWave), in which a pulse signal is used to describe the annual cycle of pesticide occurrence in a stream.
The authors test both models with four pesticides in California. They conclude, “… in watersheds with variable and intermittent pesticide applications, the SeaWave model would be more suitable to use, due to its robust capability of describing seasonal variation of pesticides concentrations in the watershed.”
[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]