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—2020

First posted April 24, 2023 For additional information, contact: Contact Information,Geology, Minerals, Energy, & Geophysics Science CenterMenlo Park, CaliforniaU.S. Geological SurveyBuilding 19, 350 N. Akron Rd.P.O. Box 158Moffett Field, CA 94035 Trace-metal concentrations in sediment and the clam Limecola petalum (World Register of Marine Species, 2020; formerly reported as Macoma balthica M. petalum), reproductive activity, benthic macroinvertebrate community structure were investigated a mudflat 1 kilometer (km) south discharge Palo Alto Regional Water Quality Control Plant (PARWQCP) San Francisco Bay, California. This report includes data collected by U.S. Survey (USGS) for January 2020–December 2020 (Cain others, 2022). These append to long-term datasets extending back 1974. A major focus is an integrated description within context longer, multidecadal dataset. dataset supports City Alto’s Near-Field Receiving- Monitoring Program, initiated 1994.Silver copper contamination substantially decreased at site 1980s following implementation PARWQCP advanced wastewater-treatment source-control measures. Since 1990s, these elements surface sediments have continued decrease, although more slowly. example, from 1994 2020, minimum annual mean silver concentration—0.20 milligram per kilogram (mg/kg)—was observed multiple years. In ranged 0.18 0.28 mg/kg. are 2 3 times higher than regional background concentration. Presently (2020), sediment-copper appear be near level. Over same period (1994–2020), sedimentary iron zinc exhibited modest decreases. Sedimentary aluminum, chromium, mercury, nickel, selenium not any trend. 1994, L. varied seasonally, apparently response combination site-specific metal exposures cyclic growth reproduction, previously. Seasonal patterns other elements, including selenium, zinc, generally similar timing magnitude those copper. Downward trends during 1994–2020 evident appeared related general physiological condition clam, indicated index.Biological effects elevated been interpreted after recession contaminants. Concentrations both soft tissues with silver. pattern was associated changes activity petalum, well invertebrate community. Reproductive increased (Hornberger 2000), presently stable almost all animals initiating reproduction fall spawning spring. Analyses indicate that infaunal has shifted one dominated several opportunistic species when highest which abundance evenly distributed, indicates subjected fewer stressors. Importantly, this change unrelated metals measured environmental factors, salinity composition. addition, two (Ampelisca abdita Streblospio benedicti) brood their young live on tubes shown continual decrease dominance coincident metals. Both had short-lived rebounds 2008, 2009, 2010 showed signs increasing 2020. Heteromastus filiformis (a subsurface polychaete worm lives sediment, consumes organic particles residing reproduces laying its eggs or sediment) concurrent increase and, last years before population. H. slightly 2011 2012 returned pre-2011 numbers 2020.The mode most present indicative capable movement either pelagic larvae mobile adults. Although oviparous lower number group, authors hypothesize will return slowly move into area. The use functional ecology highlighted data, now can respond successfully physical, nontoxic disturbance. Today, show mix consume filter feed, must survive landing young. recovery 1970s ascribed pollutants.