Geology topics

Kelly H. Shrader

Publications and source records attributed to Kelly H. Shrader.

7 recordsLinked to original sources

USGS2023

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

Trace-metal concentrations in sediment and in the clam Limecola petalum (World Register of Marine Species, 2020; formerly reported as Macoma balthica and M. petalum ), clam reproductive activity, and benthic macroinvertebrate community structure were investigated in a mudflat 1 kilometer (km) south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in south San Francisco Bay, California. This report includes the data collected by the U.S. Geological Survey (USGS) for January 2020–December 2020 (Cain and others, 2022). These data append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2020 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. Silver and copper contamination substantially decreased 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. For example, from 1994 to 2020, the minimum annual mean silver concentration—0.20 milligram per kilogram (mg/kg)—was observed in multiple years. In 2020, silver concentrations ranged from 0.18 to 0.28 mg/kg. These concentrations are 2 to 3 times higher than the regional background concentration. Presently (2020), sediment-copper concentrations appear to be near the regional background level. Over the same period (1994–2020), sedimentary iron and zinc exhibited modest decreases. Sedimentary aluminum, chromium, mercury, nickel, and selenium have not exhibited any trend. Since 1994, silver and copper concentrations 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, generally were similar in timing and magnitude as those for silver and copper. Downward trends in the silver and zinc concentrations in L. petalum during 1994–2020 were evident and appeared to be related to the general physiological condition of the clam, indicated by a condition index. 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 decreased 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 decreased (Hornberger and others, 2000), 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 decrease in dominance coincident with the decrease in metals. Both species had short-lived rebounds in abundance in 2008, 2009, and 2010 and showed signs of increasing abundance in 2020. 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 from 2011 to 2012 and returned to pre-2011 numbers in 2020. The reproductive mode of most species that were present in 2020 was indicative of species that were capable of movement 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 2020 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. The long-term recovery observed after the 1970s can be ascribed to the decrease in sediment pollutants.

California↗

USGS2023

Bivalve effects on the food web supporting delta smelt—A long-term study of bivalve recruitment, biomass, and grazing rate patterns with varying freshwater outflow

Phytoplankton are an important and limiting food source in the Sacramento-San Joaquin Delta and San Francisco Bay in California. Decreasing phytoplankton biomass is one possible factor for the pelagic organism decline and the decline of the protected Hypomesus transpacificus (delta smelt). Bivalves Corbicula fluminea and Potamocorbula amurensis (hereafter C. fluminea and P. amurensis , respectively) have been shown to control phytoplankton biomass throughout San Francisco Bay and the Sacramento-San Joaquin Delta; therefore, their distribution and population dynamics are of great interest. We describe the distribution and dynamics of bivalve biomass using samples from California Department of Water Resources’ (DWR) 2019 benthic monitoring program. As one element of DWR’s and the Bureau of Reclamation’s Environmental Monitoring Program (EMP), the DWR benthic monitoring program examines the effect of water project operations on the estuary as prescribed by a series of Water Rights Decisions mandated by the California State Water Resources Control Board (SWRCB). The biomass and grazing rate values of both bivalves had similar patterns, therefore, comments on biomass distribution can be applied to grazing rate data. Biomass and recruitment values of C. fluminea were too low at station C9 (Old River upstream from Clift on Court Forebay Intake) to describe a temporal pattern. Corbicula fluminea biomass values were consistently high at station D24 (Sacramento River). Station D4L (confluence of San Joaquin and Sacramento Rivers) biomass values were low during the first half of the year and high the rest of the year. Corbicula fluminea biomass values at station P8 (San Joaquin River) were the highest and most consistent on that river. Station D16 (San Joaquin River) and station D28A (central delta) biomass values were near zero with a small peak in May. Potamocorbula amurensis biomass values were near zero at station D4L (confluence of San Joaquin and Sacramento Rivers). Biomass values were strongly seasonal at station D6 (Suisun Bay). Station D41 (San Pablo Bay) had the highest P. amurensis biomass values. Station D7 (Grizzly Bay) and station D41A (San Pablo Bay) had low biomass values in January-June or July and maximum biomass values in August. Corbicula fluminea recruits in the Sacramento River stations peaked twice, from January to June and from September to December. At the San Joaquin River stations, C. fluminea recruitment peaked from May to July or August and from November to December. Peak recruit abundance was higher on the Sacramento River than the San Joaquin River. Potamocorbula amurensis recruitment was more seasonal than C. fluminea , with a high number of recruits followed by periods with no recruits. Station D4L had few recruits except in January. Station D6 had low recruitment from January to February, increased in August, and peaked from November to December. Station D7 had fewer recruits than station D6 but had a similar temporal pattern, although winter recruits continued into April instead of February. Station D41 recruits were sparce and present only from May to July. Station D41A had the most recruits from January to July, and again in September.

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USGS2023

Bivalve effects on the food web supporting delta smelt—A spatially intensive study of bivalve recruitment, biomass, and grazing rate patterns with varying freshwater outflow in 2019

Phytoplankton are an important and limiting food source in the Sacramento-San Joaquin Delta and San Francisco Bay. The decline of phytoplankton biomass is one potential factor in the decline of the protected Hypomesus transpacificus (delta smelt) and other pelagic organisms. The bivalves Corbicula fluminea and Potamocorbula amurensis (hereafter C. fluminea and P. amurensis , respectively) have been shown to control phytoplankton biomass in several locations throughout the San Francisco Bay and the Sacramento-San Joaquin Delta; therefore, knowledge of their distribution and population dynamics are of great interest. Here, we describe the distribution and dynamics of bivalve biomass using samples collected by the California Department of Water Resources (DWR) as part of the benthic monitoring program in 2019. One element of DWR’s and the Bureau of Reclamation’s Environmental Monitoring Program—the Generalized Random Tessellation Stratified (GRTS) program—examines the spatial and temporal extent of C. fluminea and P. amurensis control on phytoplankton. Historically, the GRTS program sampled 175 benthic stations (50 stations that are monitored every year and 125 randomly selected new stations that are changed yearly) throughout the Sacramento-San Joaquin Delta and northern San Francisco Bay (San Pablo and Suisun Bays) during one week in May and October. In 2019, only the 50 annually replicated stations were sampled. Corbicula fluminea and P. amurensis biomass and grazing rates had similar trends; therefore, the conclusions regarding biomass are applied to grazing rate data as well. Corbicula fluminea biomass decreased from May to October, whereas P. amurensis average biomass (reported increased from May (1 g ash-free-dry-tissue mass/square meter (g AFDM/m 2 ) to October (2 g AFDM/m 2 ). Although C. fluminea ’s average biomass was lower in October (10 gAFDM/m 2 ) than in May (20 gAFDM/m 2 ), the highest single biomass value was also observed in October (300 gAFDM/m 2 ). In both May and October, most stations that recorded high C. fluminea biomass values were located in the deep water (≥3 m of depth between the surface of the water and the surface of the substrate on the bottom) and were sampled in either rivers or sloughs. A relation between depth and biomass was not observed for P. amurensis . Both C. fluminea and P. amurensis recruitment (recruits are considered animals ≤2.5mm in length in this study and recruitment is the process of recruits successfully settled to the bottom) increased from May to October. The total number of C. fluminea recruits more than doubled from May to October, whereas P. amurensis total recruitment increased by 8-fold during the same period. Most P. amurensis recruits in May can be attributed to one station, whereas the recruits in October were found at 14 stations. A relation between number of recruits and station depth was not evident for either C. fluminea or P. amurensis .

California↗

USGS2021

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

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.

California↗

USGS2021

If you give a clam an estuary: The story of potamocorbula

When you look at San Francisco Bay, what animals do you see? You may see lots of fish swimming around and birds flying above. What you DON’T see is Potamocorbula, a little clam that has had a big impact. Many years ago, ships accidentally brought Potamocorbula into the Bay. Pretty soon, Potamocorbula spread out all over in large numbers! Clams pump water over their gills and eat small particles of food, like phytoplankton, that pass through with the water. Potamocorbula can pump water much faster than other clams that live in the Bay, and they can eat more than their share of phytoplankton. Sometimes Potamocorbula eats phytoplankton faster than phytoplankton can grow! What problems does that cause for other animals, like birds and fish, that also need phytoplankton? Does Potamocorbula’s invasion only have negative impacts? In this article, we dive to the bottom of the Bay to find some answers. Book series publishing the chapter: https://kids.frontiersin.org/collection/13528/where-the-river-meets-the-ocean-stories-from-san-francisco-estuary

California↗

USGS2019

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

Trace-metal concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica ), 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 U.S. Geological Survey (USGS) scientists for the period January 2018 to December 2018. These append to long-term datasets extending back to 1974. A major focus of the report is an integrated description of the 2018 data within the context of the longer, multi-decadal 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 concentrations in both sediment and M. petalum 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 appear to have stabilized at concentrations somewhat above (silver [Ag]) or near (copper [Cu]) regional background concentrations. Data for other metals, including chromium (Cr), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn), have been collected since 1994. Over this period, concentrations of these elements have remained relatively constant, aside from seasonal variation that is common to all elements. In 2018, concentrations of silver and copper in M. petalum varied seasonally in response to a combination of site-specific metal exposures and annual growth and reproduction, as reported previously. Seasonal patterns for other elements, including Cr, Ni, Zn, Hg, and Se, were generally similar in timing and magnitude as those for Ag and Cu. This record suggests that legacy contamination and regional-scale factors now largely control sedimentary and bioavailable concentrations of silver and copper, as well as other elements of regulatory interest, at the Palo Alto site.

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USGS2019

Benthic community dynamics in Coyote Creek and Artesian Slough, southern San Francisco Bay, California, May 2016 to March 2018

The primary objective of this study is to quantify current (2016–18) benthic-community structure and function in the southern San Francisco Bay, and to compare those communities to the communities in the neighboring sloughs. The study area is inclusive of the area south of the Dumbarton Bridge including Coyote Creek and Artesian Slough. The southern San Francisco Bay is a system dependent on phytoplankton as the base to the food web. Despite abundant nutrients, southern San Francisco Bay has had limited phytoplankton production in the last several decades owing to poor light conditions caused by high turbidities, and high grazing losses from the water column by benthic invertebrates and zooplankton. However, the balance of biogeochemical conditions during spring of most years accommodates a short phytoplankton bloom in the southern San Francisco Bay. This balance between available light, nutrients, and grazing has maintained the phytoplankton biomass in the southern San Francisco Bay at low levels relative to other high-nutrient urban estuaries. The role of benthic invertebrates during episodic spring events, as well as in other seasons, remains of great interest to water-quality and biological resource managers.

California↗