Aroon R. Melwani and Bruce Thompson San Francisco Estuary Institute

The Influence of Chemical and Physical Factors on Macrobenthos in the San Francisco EstuaryA Stressor Identification Method Aroon R. Melwani and Bruce Thompson San Francisco Estuary Institute

Test a method for benthic stressor identification in the San Francisco Estuary Use the method to determine which sediment contaminant(s) have the highest association with benthic impacts observed in the Estuary Objectives

Common Variables • A common subset of variables of sediment description and contamination

Individual benthic metrics identified by Thompson and Lowe (2004) as representative indicators of Estuary benthos were used as dependant variables Benthos Data

Study Locations

Pearson’s Correlation Analysis of chemistry and sediment variables Step 1: multiple regression of sediment variables and mERMq Principal Components Analysis (PCA) of chemical variables Step 2: multiple regression of PCA factors and sediment variables Methods

Principal Components Analysis • Contaminant mixtures

Step 2 Multiple Regression • Contaminant factors, salinity and sediment-type

Summary of Analyses Contaminants Grain size Salinity TOC

Link benthos, toxicity, and sediment contamination Assess benthic samples from locations identified as toxic in Causes of Sediment Toxicity Study Determine linkages between laboratory toxicity tests and benthic impacts Five Year Plan Conclusions Future Steps - Establish Linkages • Different physical and chemical sediment factors appear to influence • benthos in different areas of the Estuary • Contaminant mixtures always contributed to changes in benthos • Testable hypotheses may be generated by analyses

Aroon R. Melwani and Bruce Thompson San Francisco Estuary Institute