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Francis Parchaso

Publications and source records attributed to Francis Parchaso.

25 records · Page 2Linked to original sources
USGS2015

Benthic response to water quality and biotic pressures in lower south San Francisco Bay, Alviso Slough, and Coyote Creek

Benthic invertebrate communities are monitored because the composition of those communities can effect and be affected by the water quality of an aquatic system. Benthic communities use and sometimes regulate the cycling of essential elements (for example, carbon). Benthic invertebrate taxa may also indicate acutely and chronically stressful environments because they are mostly sessile, accumulate contaminants, and sometimes respond dramatically to oligotrophic as well as eutrophic conditions. Benthic communities can in turn affect water quality by grazing pelagic food resources and increasing the rate of nutrient regeneration through feeding and bioturbating the sediment. South San Francisco Bay is a system dependent on phytoplankton as the base to the food web. Despite abundant nutrients, south San Francisco Bay has had limited phytoplankton production in the last several decades owning to poor light conditions and high grazing losses from the water column by benthic invertebrates. The south San Francisco Bay achieves a balance of biogeochemical conditions in most springs to accommodate a short phytoplankton bloom. This balance has maintained the phytoplankton in south San Francisco Bay at low biomass levels relative to other high-nutrient urban estuaries. The role that benthic invertebrates play in this balance, in these episodic spring events, and in other seasons within the estuary remains of great interest to water-quality and biological resource managers. Our primary objective in this study is to quantify current (2014) benthic-community structure and function in the south San Francisco Bay sloughs and to compare those communities temporally over decadal time scales with a unique long-term dataset. The study area (fig. 1) is inclusive of the area south of the Dumbarton Bridge (DB) including Alviso and Guadalupe Sloughs and Coyote Creek. The following are results highlighted in this report: The benthic communities of Coyote Creek and Alviso, Guadalupe, and Artesian Sloughs were dominated by different organisms but similar functional groups in March, June, and September 2014. Coyote Creek stations (D3 and CC1) had a similar increase in Potamocorbula amurensis biomass followed by a decline in 2014, as was observed annually in the south San Francisco Bay since 1999. The lack of grazing pressure owing to the observed declines in these taxa in 2014 may allow the sloughs to become sources of phytoplankton in spring. Bivalve biomass is elevated in summer and fall relative to the spring and winter except in Artesian Slough, where bivalves did not establish a signifcant presence. Presence of certain species contributes to the prey value of the community to predators. Potamocorbula amurensis is a shallow-burrowing bivalve and hence is easy prey for bottom-feeding predators. In contrast, Macoma petalum is a deposit feeder and can burrow deeper into the substrate than Potamocorbula amurensis , making it harder to be preyed upon. The quantitative importance of such predator-prey relationships on phytoplankton dynamics requires further investigation. There were also more amphipods in the sloughs in March 2014; this group is another potential contributor to the benthic-pelagic biomass balance. There is no observed reason for Artesian Slough to have low bivalve biomass values and high amphipod abundances.

California↗
USGS2010

The transition of benthic nutrient sources after planned levee breaches adjacent to upper Klamath and Agency Lakes, Oregon

Four sampling trips were coordinated after planned levee breaches that hydrologically reconnected both Upper Klamath Lake and Agency Lake, Oregon, to adjacent wetlands. Sets of nonmetallic pore-water profilers were deployed during these trips in November 2007, June 2008, May 2009, and July 2009. Deployments temporally spanned the annual cyanophyte bloom of Aphanizomenon flos-aquae (AFA) and spatially involved three lake and four wetland sites. Profilers, typically deployed in triplicate at each lake or wetland site, provided high-resolution (centimeter-scale) estimates of the vertical concentration gradients for diffusive-flux determinations. Estimates based on molecular diffusion may underestimate benthic flux because solute transport across the sediment-water interface can be enhanced by processes including bioturbation, bioirrigation and groundwater advection. Water-column and benthic samples were also collected to help interpret spatial and temporal trends in diffusive-flux estimates. Data from these samples complement taxonomic and geochemical analyses of bottom-sediments taken from Upper Klamath Lake (UKL) in prior studies. This ongoing study provides information necessary for developing process-interdependent solute-transport models for the watershed (that is, models integrating physical, geochemical, and biological processes) and supports efforts to evaluate remediation or load-allocation strategies. To augment studies funded by the U.S. Bureau of Reclamation (USBR), the Department of the Interior supported an additional full deployment of pore-water profilers in November 2007 and July 2009, immediately following the levee breaches and after the crash of the annual summer AFA bloom. As observed consistently since 2006, benthic flux of 0.2-micron filtered, soluble reactive phosphorus (that is, biologically available phosphorus, primarily as orthophosphate; SRP) was consistently positive (that is, out of the sediment into the overlying water column) and ranged from a negligible value (-0.19?0.91 milligrams per square meter per day; mg m-2 d-1) within wetlands of the Upper Klamath National Wildlife Refuge to 74?48 mg m-2 d-1 at the newly restored wetland site removed from the levee breach (TNC1); both observed in May 2009 before the annual AFA bloom. When areally averaged (13 km2 for the newly restored wetlands), an SRP flux to the overlying water column is determined of approximately 87,000 kilograms (kg) over the 3-month AFA bloom season that exceeds the magnitude of riverine inputs (42,000 kg for the season). Elevated SRP benthic flux at TNC1 relative to all other lake and wetland sites (including TNC2 near the breached levee) in 2009 suggests that the restored wetlands, at least chemically, remain in a transition period after engineered blasts on October 30, 2007, restored hydrologic connectivity between lake and wetland environments. As reported in previous lake studies, ammonium fluxes to the water column were consistently positive, with the exception of two measurements at the restored wetland sites (TNC1 and TNC2) immediately following the levee breaches in November 2007. The flux of ammonia, particularly at elevated pH in the overlying water column, has toxicological implications for endangered fish populations in both lake and wetland environments. For dissolved nitrate, with the exception of a single positive flux measurement at TNC1 in June 2008 (0.16?0.02 mg m-2 d-1), consistently negative (consumed by the sediment) or undetectable nitrate-flux values were observed (-21?12 mg m-2 d-1 to undetectable fluxes due to concentrations for dissolved nitrate <0.03 milligrams per liter (mg L-1) in both porewaters and overlying waters near the sediment-water interface). Such negative fluxes for dissolved nitrate are typical of microbial transformations, such as dinitrification (dissimilatory nitrate reduction), that benthically consume nitrate from the water column. The diffusive-flux measurements reported herei

Oregon↗
USGS2003

Assessing toxicant effects in a complex estuary--A case study of effects of silver on reproduction in the bivalve, Potamocurbula amurensis, in San Francisco Bay

Contaminant exposures in natural systems can be highly variable. This variability is superimposed upon cyclic variability in biological processes. Together, these factors can confound determination of contaminant effects. Long term, multidisciplined studies with high frequency sampling can be effective in overcoming such obstacles. While studying trace metal contamination in the tissues of the clam, Potamocorbula amurensis , in the northern reach of San Francisco Bay, an episode of high Ag concentrations was identified (maximum of 5.5 µg g −1 ) at two mid-estuary sites. High concentrations were not seen in clams up-estuary (maximum of 1.92 µg g −1 ) from these sites and were reduced down-estuary (maximum of 2.67 µg g −1 ). Silver is not common naturally in the environment, so its elevated presence is usually indicative of anthropogenic influences such as municipal and industrial discharge. Monthly sampling of reproductive status of clams characterized the reproductive cycle and differences in the patterns of reproductive activity that corresponded to changes in Ag tissue concentrations. The proportion of reproductive clams was less than 60% during periods when tissue concentrations were high (generally >2 µg g −1 ). When tissue concentrations of Ag decreased (≤1 µg g −1 ), the proportion of reproductive clams was 80 to 100%. A comparison between the annual proportion of reproductive clams and annual Ag tissue concentrations showed a significant negative correlation. No other measured environmental variables were correlated with reproductive impairment. The weight-of-evidence approach strongly supports a cause and effect relationship between Ag contamination and reduced reproductive activity in P. amurensis .

California↗
USGS2002

Influence of hydrologic processes on reproduction of the introduced bivalve Potamocorbula amurensis in northern San Francisco Bay, California

Monthly censusing of reproductive condition of the Asian clam Potamocorbula amurensis at four sites in northern San Francisco Bay over a 9-yr period revealed year-to-year differences in local reproductive activity that are associated with patterns of hydrologic variability. Between 1989 and 1992, Northern California experienced a drought, whereas the period between 1993 and 1998 was marked by a mix of wet and dry years. We took advantage of the extreme year-to-year differences to examine reproductive responses to river inflow patterns. Populations of P. amurensis at the upstream sites in Suisun Bay and Carquinez Strait were more reproductively active during wet years than dry years. Conversely, at the downstream site in San Pablo Bay, the population was more reproductively active during dry years than wet years. We suggest that the different reproductive patterns observed reflect the clam's response to different sources of food. During wet years, organic matter from the rivers augments food supplies in Suisun Bay. During dry years, when inflow into the San Francisco Bay Estuary from the rivers is reduced, water transported from the adjacent ocean into the estuary as far as San Pablo Bay provides a supplemental food supply for the local production. The populations take advantage of these spatially distinct food supplies by initiating and maintaining local reproductive activity. We conclude that the ability of P. amurensis to consume and use various types of food to regulate its reproductive activity is part of the reason for its success as an invasive species.

California↗
USGS2001

Behind the energetics of the asiatic clam, Potamocorbula amurensis, in San Francisco Bay

The Asian clam (Potamocorbula amurensis) has played a key role in the food web of northern San Francisco Bay since its invasion in the fall of 1986. It has been associated with a dramatic decline in primary production, loss of a zooplankton species and a native mysid shrimp, the probable decline in striped bass, and has introduced alternative pathways for contaminant cycling in the bay food web.

Interagency Ecological Program Newsletter↗