Trends Analysis of Simultaneously Extracted Metal Copper Sediment Concentrations from a California Agricultural Waterbody including Historical Comparisons with Other Agricultural Waterbodies

The objectives of this study were to: (1) assess annual, seasonal and spatial trends in simultaneously extracted metal copper (SEM copper) sediment concentrations in an agricultural California waterbody (Cache Slough) sampled over three years and two seasons (spring and fall); (2) determine the relationship between SEM copper sediment concentrations and precipitation; (3) compare the SEM copper sediment concentrations from Cache Slough with other agricultural streams and (4) compare trends in SEM copper with total copper sediment concentrations previously reported from this waterbody. Sediment samples for SEM copper analysis were collected by boat. Regression analysis, Analysis of Variance, T-test procedure and the Fisher LDS method were used for statistical analysis of data. The results from this study showed that mean seasonal SEM copper sediment concentrations from Cache Slough ranged from 18.6 to 30.1 µg/g dw. SEM copper sediment concentrations were not reported to increase over time in this agricultural waterbody where copper was used as a fungicide, although some spatial differences in SEM copper sediment concentrations were reported. Seasonal analysis showed no significant differences in SEM copper sediment concentrations for both spring and fall for two years, but spring concentrations were statistically higher than fall concentrations for the last year of the study. There were no statistically significant relationships between SEM copper sediment concentrations and precipitation for the three-year period, based on an analysis by year and season. A comparative analysis of total copper and SEM copper from Cache Slough showed that the range of mean seasonal concentrations of SEM copper was much lower, and more sites showed declining trends for SEM copper than for total copper. Increasing trends were not reported at any of the sites for either SEM copper or total copper. A comparison of SEM copper data from Cache Slough was reported to be similar to concentrations reported for other water bodies influenced by agricultural use. Additional multiple year studies in other geographic areas assessing trends in SEM copper sediment concentrations with a comprehensive spatial scale are recommended.