Bivalve Monitoring: Figure 4.31

Tables

Figure 4.31. Total DDT accumulation or depuration in parts per billion dry weight (ppb) in three species of transplanted bivalves for eleven sampling periods from 1993-1998 (mean of all stations). Note different y-axis scales. * In 1996, the reference population of "clean" Corbicula fluminea at Lake Isabella crashed and disappeared. Despite exploring several other potential reference sites, field staff was unable to find sufficiently large populations suitable for transplantation into the Estuary. Beginning with the 1996 data, C. fluminea bioaccumulation could no longer be compared with previous years due to the initial high concentrations of some contaminants, particularly trace organics, which biases bioaccumulation estimates toward the low end. ** Specimen were collected for analysis from the native population in the Sacramento and the San Joaquin Rivers. This resident clam is not comparable with the ones from Lake Isabella and therefore not included in the same chart.

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