Geology topics

Elizabeth Wells

Publications and source records attributed to Elizabeth Wells.

3 recordsLinked to original sources

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 .

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USGS2016

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

Executive Summary Phytoplankton is an important and limiting food source in the Sacramento-San Joaquin Delta (the Delta) and San Francisco Bay; the decline of phytoplankton biomass is one possible factor in the pelagic organism decline and specifically in the decline of the protected delta smelt. The bivalves Corbicula fluminea and Potamocorbula amurensis have been shown to control phytoplankton biomass in several locations throughout the system, and their distribution and population dynamics are therefore of great interest. We were able to describe the distribution and dynamics of bivalve biomass through use of samples collected by the California Department of Water Resources (DWR) as part of a monitoring program from 1977 to 2013. As one element of DWR’s and the Bureau of Reclamation’s Environmental Monitoring Program (EMP), the DWR benthic monitoring program examines the impact of water project operations on the estuary as prescribed by a series of Water Rights Decisions mandated by the State Water Resources Control Board (SWRCB). The availability of multidecade samples allowed us to examine long-term trends in biomass, recruitment, and size of bivalves at the 15 stations sampled. Biomass and grazing rate had the same basic trends, and the conclusions that we apply to biomass can be applied to grazing rate data. During winter of most years, Potamocorbula biomass was low at all locations and was near zero in the shallow San Pablo Bay station. The Potamocorbula biomass at shallow stations consistently peaked during summer and fall, but there was no consistent peak season in the deep stations. Corbicula had a much less consistent seasonal biomass pattern than Potamocorbula . However, some interannual patterns were consistent between stations. Corbicula biomass at three stations declined after 2003 (C9, D16, and D28). The Franks Tract (D19) Corbicula biomass had a baseline shift up (that is, all values were > 0) in 1985 until DWR ceased sampling at the station in 1995. Two other stations showed a similar increase in baseline but at different times; D24 shifted up after 2007 and D11 shifted up in 1991. Potamocorbula recruitment (any bivalve ≤ 2.5 millimeters [mm] in length) occurred anytime between spring and fall, with bivalves at the most downstream stations in San Pablo Bay recruiting in spring and animals at the most upstream stations recruiting in fall. The bivalves at the stations between these endpoints recruited in (1) spring or (2) summer and fall (Carquinez Strait), or in some combination of two of those three seasons in Grizzly Bay. The few locations where Potamocorbula and Corbicula overlapped showed recruitment abundance opposing each other, with Potamocorbula recruits peaking during the more saline time of year and Corbicula recruits peaking during periods of lower salinities. Corbicula recruits were present throughout most of the year with some peaks in abundance, but the patterns were not seasonally consistent at any station. Mean size peaked in both bivalves in late summer and early fall and never got above a certain size; maximum size depended on location. The mean size of both bivalves has decreased over the years, with the size distributions throughout the Delta now skewed toward smaller, younger Corbicula (< 10 mm). The mean size of Potamocorbula has also become skewed toward the small, younger bivalves, with sizes in the range of 2 – 8 mm. The mean size of Potamocorbula increased from spring to fall and decreased in winter. A similar generalization is not possible with Corbicula because seasonal patterns in size varied depending on station location. Station D24 on the Sacramento River was the only location with an increase in Corbicula mean size over the sampling period. The largest mean sized Potamocorbula were seen in the channel areas, where sizes of 15 mm were common at stations D41C, 8.1, and D6; sizes in excess of 15 mm were observed at all three D4 stations during the mid 1990s. The mean size of Potamocorbula in the shoals was ≈5 – 7 mm in most years in Grizzly Bay (D7) and San Pablo Bay (D41A), with an increase to > 10 mm at D7 in the wet years. The largest mean sized Corbicula were in the southern Delta (C9 ≈25 mm during 1996 – 97 and 2012 – 2013), and the smallest average sizes were in the San Joaquin River (P8 and D16). Corbicula at the upstream Sacramento River station (D24) and in the southern Delta (C9) showed similar interannual patterns in average size although the animals at C9 were consistently larger than those at D24 were. Corbicula in Franks Tract (D19) and the Old River (D28A) south of Franks Tract were also similar in size and in interannual patterns. At the few stations where Potamocorbula and Corbicula co-occur, it appears that they did not hinder each other’s growth. Both bivalves had large animals at D4, where Corbicula size increased coincident with the presence of Potamocorbula in 1987. Corbicula were observed in wet years prior to Potamocorbula’s invasion at D7 (Grizzly Bay) and were capable of growing to significant size in wet years (> 20 mm in 1986).

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