USGS

 

Occurrence, Distribution, Instantaneous Loads, and Yields of Dissolved Pesticides in the San Joaquin River Basin, California, During Summer Conditions, 1994 and 2001

By Larry R. Brown, Sandra Y. Panshin, Charles R. Kratzer, Celia Zamora, and JoAnn M. Gronberg

 

U.S. GEOLOGICAL SURVEY

Scientific Investigations Report 2004-5083

Sacramento, California 2004

 

Prepared in cooperation with the
Central Valley Regional Water Quality Control Board




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Abstract

Water samples were collected from 22 drainage basins for analysis of 48 dissolved pesticides during summer flow conditions in 1994 and 2001. Of the 48 pesticides, 31 were reported applied in the basin in the 28 days preceding the June 1994 sampling, 25 in the 28 days preceding the June 2001 sampling, and 24 in the 28 days preceding the August 2001 sampling. The number of dissolved pesticides detected was similar among sampling periods: 26 were detected in June 1994, 28 in June 2001, and 27 in August 2001. Concentrations of chlorpyrifos exceeded the California criterion for the protection of aquatic life from acute exposure at six sites in June 1994 and at five sites in June 2001. There was a single exceedance of the criterion for diazinon in June 1994. The number of pesticides applied in tributary basins was highly correlated with basin area during each sampling period (Spearman's r = 0.85, 0.70, and 0.84 in June 1994, June 2001, and August 2001, respectively, and p < 0.01 in all cases). Larger areas likely include a wider variety of crops, resulting in more varied pesticide use. Jaccard's similarities, cluster analysis, principal components analysis, and instantaneous load calculations generally indicate that west-side tributary basins were different from east-side tributary basins. In general, west-side basins had higher concentrations, instantaneous loads, and instantaneous yields of dissolved pesticides than east-side basins, although there were a number of exceptions. These differences may be related to a number of factors, including differences in basin size, soil texture, land use, irrigation practices, and stream discharge.

Contents

Abstract

Introduction

Purpose and Scope

Study Area

Methods

Sampling Design

Field Method and Sample Processing

Analytical Methods

Quality Control Proceedures

Field Blank Samples

Replicate Samples

Spiked Samples

Assessment of Quality Assurance

Statistical Methods for Assessing Patterns in Application, Occurrence, and Distribution of Pesticides

Instantaneous Pesticide Loads

Results and Discussion

Patterns in Application

Patterns in Occurrence and Distribution

Instantaneous Loads

Summary and Conclusion

References Cited


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