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

2. Objectives 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

3. Common Variables A common subset of variables of sediment description and contamination

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

5. Study Locations

6. Methods Pearsons 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

7. Principal Components Analysis Contaminant mixtures

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

9. Summary of Analyses Contaminants Grain size Salinity TOC

10. Future Steps - Establish Linkages 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 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 Conclusions