Near-Field Receiving-Water Monitoring of Trace Metals and a Benthic Community Near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California—2019

Open-File Report 2021-1079
Prepared in cooperation with the City of Palo Alto, California
By: , and 

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  • Related Works:
    • Open-File Report 2019-1084 - Near-Field Receiving-Water Monitoring of Trace Metals and a Benthic Community Near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California—2018
    • Open-File Report 2018-1107 - Near-Field Receiving-Water Monitoring of Trace Metals and a Benthic Community Near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California—2017
    • Open-File Report 2017-1135 - Near-Field Receiving-Water Monitoring of Trace Metals and a Benthic Community Near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California; 2016
    • Open-File Report 2016-1118 - Near-Field Receiving-Water Monitoring of Trace Metals and a Benthic Community Near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California; 2015
  • Data Release: Data Release - Data for monitoring trace metal and benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California
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Abstract

Trace-metal concentrations in sediment and in the clam Limecola petalum (formerly reported as Macoma balthica and M. petalum), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, Calif. This report includes the data collected by the U.S. Geological Survey (USGS) for the period January 2019 to December 2019. These data append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2019 data within the context of the longer, multidecadal dataset. This dataset supports the City of Palo Alto’s Near-Field Receiving-Water Monitoring Program, initiated in 1994.

Significant reductions in silver and copper contamination occurred at the site in the 1980s following the implementation by PARWQCP of advanced wastewater treatment and source control measures. Since the 1990s, concentrations of these elements in surface sediments have continued to decrease, although more slowly. Silver appears to have stabilized at concentrations about twice the regional background concentration. Presently, sediment copper concentrations appear to be near the regional background level. Over the same period (1994–2019), sedimentary iron and zinc also exhibited modest declines. Sedimentary aluminum, chromium, mercury, nickel, and selenium have not exhibited any trend. Since 1994, concentrations of silver and copper in L. petalum have varied seasonally, apparently in response to a combination of site-specific metal exposures and cyclic growth and reproduction, as reported previously. Seasonal patterns for other elements, including chromium, mercury, nickel, selenium, and zinc, were generally similar in timing and magnitude as those for silver and copper. The annual growth and reproductive cycle explained a small amount of the variance in annual silver and zinc tissue metal concentrations. However, interannual trends are not apparent for any element.

Biological effects of elevated silver and copper contamination at the Palo Alto site have been interpreted from data collected during and after the recession of these contaminants. Concentrations of both elements in the soft tissues of L. petalum declined with sedimentary copper and silver. This pattern was associated with changes in the reproductive activity of L. petalum, as well as the structure of the benthic invertebrate community. Reproductive activity of L. petalum increased as metal concentrations in L. petalum declined and presently is stable with almost all animals initiating reproduction in the fall and spawning the following spring. Analyses of the benthic community structure indicate that the infaunal invertebrate community has shifted from one dominated by several opportunistic species when silver and copper exposures were highest to one in which the species abundance is more evenly distributed, a pattern that indicates a more stable community that is subjected to fewer stressors. Importantly, this long-term change is unrelated to other metals and other measured environmental factors, including salinity and sediment composition. In addition, two of the opportunistic species (Ampelisca abdita and Streblospio benedicti) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2019. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2019.

An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for deep-dwelling animals like L. petalum. However, within two months of this event, animals returned to the mudflat. The resilience of the community suggested that the disturbance was not caused by a persistent toxin or anoxia. The reproductive mode of most species that were present in 2019 was indicative of species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2019 benthic community data, which showed that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of species that consume the sediment, or filter feed, those that have pelagic larvae that must survive landing on the sediment, and those that brood their young. USGS scientists view the 2008 disturbance event as a response by the infaunal community to an episodic natural stressor (possibly sediment accretion or a pulse of freshwater), in contrast to the long-term recovery from metal contamination. We will compare this recovery to the long-term recovery observed after the 1970s when the decline in sediment pollutants was the dominating factor.

Suggested Citation

Cain, D.J., Croteau, M.-N., Thompson, J.K., Parchaso, F., Stewart, R., Shrader, K.H., Zierdt Smith, E.L., and Luoma, S.N., 2021, Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2019: U.S. Geological Survey Open-File Report 2021–1079, 59 p., https://doi.org/10.3133/ofr20211079.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments  
  • Executive Summary of Past Findings  
  • Abstract  
  • Introduction  
  • Methods  
  • Results  
  • Summary  
  • References Cited  
  • Appendix 1. Certified Concentrations and Recovery Percentages of Inorganic Elements in National Institute of Science and Technology Standard Reference Materials 2709a and 2711a, Prepared in 2019  
  • Appendix 2. Certified Concentrations and Recovery Percentages of Inorganic Elements in National Research Council Canada Certified Reference Material TORT-3 and National Institute of Science and Technology Standard Reference Material 1566b, Prepared in 2019  
  • Appendix 3. Mercury and Selenium Concentrations Determined in Sample Splits of Surface Sediments and Clam Limecola petalum Collected at Palo Alto, Calif., Site in 2019  
  • Appendix 4. Recovery Percentages (±Standard Deviation) of Mercury and Selenium in Standard Reference Materials  
  • Appendix 5. Method Detection Limits and Method Reporting Levels for Inductively Coupled Plasma Optical Emission Spectrophotometry Methods  
  • Appendix 6. Statistical Summary of Silver and Copper Concentrations in Sediment and Clam Limecola petalum Collected at Palo Alto, Calif., Site in 2019 and in 1977–2019  
  • Appendix 7. Reproduction Data for Clam Limecola petalum Collected at Palo Alto, Calif., Site in 2015–2019  
  • Appendix 8. Complete List of Benthic Species Found at Palo Alto, Calif., Site in 2019  
  • Appendix 9. Benthic Species Name Changes as of 2019
Publication type Report
Publication Subtype USGS Numbered Series
Title Near-field receiving-water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in south San Francisco Bay, California—2019
Series title Open-File Report
Series number 2021-1079
DOI 10.3133/ofr20211079
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) WMA - Earth System Processes Division
Description Report: viii, 59 p.; Data Release
Country United States
State California
Other Geospatial South San Francisco Bay
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details