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Francis Parcheso

Publications and source records attributed to Francis Parcheso.

23 records · Page 2Linked to original sources
USGS2002

Near field receiving water monitoring of benthic community near the Palo Alto Water Quality Control Plant in south San Francisco Bay: February 1974 through December 2000

Analyses of the benthic community structure over a 26-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinal clam Macoma balthica from the same area. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that could be indicative of a more stable community that is subjected to less stress. 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. Heteromastus filiformis, a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. Analysis of the reproductive activity of Macoma balthica shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissue of this organism. Reproductive activity is presently stable with almost all animals reproducing during the two reproductive seasons (spring and fall) of most years.

California↗
USGS2001

Benthic flux of dissolved nickel into the water column of south San Francisco Bay

Field and laboratory studies were conducted between April, 1998 and May, 1999 to provide the first direct measurements of the benthic flux of dissolved (0.2-micron filtered) nickel between the bottom sediment and water column at three sites in the southern component of San Francisco Bay (South Bay), California. Dissolved nickel and predominant ligands (represented by dissolved organic carbon, and sulfides) were the solutes of primary interest, although a variety of ancillary measurements were also performed to provide a framework for interpretation. Results described herein integrate information needs identified by the State Water Resources Control Board and local stakeholders with fundamental research associated with the U.S. Geological Survey Toxic Substances Hydrology Program. Dissolved-Ni concentrations in the bottom water over the three sampling dates ranged from 34 to 43 nanomoles per liter. Dissolved-macronutrient concentrations in the bottom water were consistently higher (frequently by orders of magnitude) than surface-water determinations reported for similar times and locations (Regional Monitoring Program, 2001). This is consistent with measured positive benthic fluxes for the macronutrients. Benthic-flux estimates for dissolved nickel from core-incubations, when areally averaged over the South Bay, were significant (that is, of equivalent or greater order of magnitude) relative to previously reported freshwater point and non-point sources. This observation is consistent with previous determinations for other metals, and with the potential remobilization of sediment-associated metals that have been ubiquitously distributed in the South Bay. Similar to dissolved-nickel results, benthic flux of macronutrients was also consistently significant relative to surface-water inputs. These results add to a growing body of knowledge that strongly suggests a need to consider contaminant transport across the sediment-water interface when establishing future management strategies for the watershed.

California↗