1.1 MB pdf - Bolsa Chica Lowlands Restoration Project
1.1 MB pdf - Bolsa Chica Lowlands Restoration Project 1.1 MB pdf - Bolsa Chica Lowlands Restoration Project
SECTION 3: ANALYSIS with samples sizes >15 for amphipods and >40 for Mytilus, for which regression slopes were negative with significant (i.e., p 0.5) and the largest sample sizes, followed by LC and EC values based on models with high r 2 and small sample sizes. Moderate uncertainty is associated with LC and EC values based on models where 0.2< r 2 < 0.5. Due to the small amount of variation they describe, LC and EC values based on models with r 2 < 0.2, regardless of sample size, are not recommended for use in remedial decision-making. The LC and EC values with the least amount of uncertainty were carried forward into the stressor-response profile and are presented with other selected effects levels in Section 3.2.2. Although only 20 and 50 percent effects levels were estimated, the simple linear regression analyses and associated figures may also be used to estimate concentrations associated with less severe effects on the test organisms. Additional levels (e.g., EC 10 ) also could be calculated, but time constraints precluded including them in this draft. The chemical data that had been used for the regression was then screened using as the derived EC 20 s and EC 50 s and LC 20 s or LC 50 s to determine the final COPECs. The results of the screening are presented in Table F-3 for sediment and Table F-4 for pore water. 3.2.1.4 Chemical Correlation Evaluation Additional regression analyses were conducted to evaluate chemical factors that could potentially affect the cumulative toxicity of COPECs to ecological receptors. These factors, described in the following subsections, consisted of the following: • Relationship of COPEC concentrations in pore water to those in sediment • Co-occurrence of COPECs in sediment • Principal components analyses in sediment COPEC Concentration Relationship Between Sediment and Pore Water For pore water bioassay data to aid in screening potential toxicity from sediments at Bolsa Chica, the relationship between concentrations of COPECs in sediment to those in pore water must be known. If pore water concentrations can be estimated based on sediment SAC/143368(003.DOC) 3-35 ERA REPORT 7/31/02
SECTION 3: ANALYSIS concentrations, potential toxicity that may result following inundation of sediments that are currently dry may be estimated, and remedial actions to mitigate this toxicity may be planned. Simple linear regression analyses of COPEC concentrations in pore water on those in sediment were performed using SAS (1994) PROC REG. All models were considered significant if p#0.05. The results of these analyses (scatterplots and associated regression analyses) for all chemicals and data transformations are presented in Appendix H. Of 70 chemicals considered, significant regressions based on untransformed data were obtained for only seven chemicals (aldrin, arsenic, beryllium, alpha chlordane, endosulfan sulfate, mercury, and phenanthrene). The highest r 2 for these chemicals was 0.28. Significant regression models were obtained for 10 of 70 chemicals (acenaphthene, aldrin, arsenic, beryllium, alpha chlordane, copper, endosulfan I, endrin aldehyde, total DDT, and thallium) based on natural-log-transformed data. The highest r 2 from these data was 0.24. Because significant relationships between concentrations of COPECs in pore water to those in sediment were observed for few chemicals, and these relationships generally accounted for less that 25 percent of variation, the pore water bioassay results cannot be used to predict potential toxicity from pore water associated with the sediments. The pore water bioassays may, however, be used to evaluate potential toxicity at locations where pore water already exists. Correlations Between COPECs in Sediment Many COPECs have been detected in sediment from throughout the Bolsa Chica Lowlands (using the entire ERA Sampling and Analyses dataset). To aid in streamlining future data collection, correlation analyses were performed among analytes detected in sediment to determine which chemicals were consistently detected in association with each other. Analyses for chemicals whose occurrence is highly correlated may be reduced, such that only those chemicals that are the best indicators are analyzed for. Correlation analyses were performed using SAS (1994) PROC CORR. The resulting correlation matrix is presented in Table 3-22. Principal Components Analyses for COPECs in Sediment Principal components analyses (PCA), a multivariate statistical technique, is another approach to reduce the dimensionality (i.e., number of variables) associated with COPECs in sediment. PCA is a statistical technique that linearly transforms the original numerical variables to a substantially smaller set of uncorrelated variables that represent most of the information in the original dataset (Dunteman, 1989). These uncorrelated variables, known as principal components, are a linear combination of the original variables and are sorted in decreasing order of the amount of variability in the original dataset they explain. Backcorrelation of the principal component scores with the original data provides an indication of which parameters each principal component represents. PCA is generally a data evaluation method used to explore underlying relationships among variables in a large dataset. PCA was performed on the sediment data previously used for correlation analyses using SAS (1994) PROC PRINCOMP. (Note: the complete output from the principal components analyses is included in Appendix H.) A total of 47 principal components was generated, of which the first 9 accounted for 79.5 percent of the variance in the sediment data (Table 3-23). ERA REPORT 3-36 SAC/143368(003.DOC) 7/31/02
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SECTION 3: ANALYSIS<br />
with samples sizes >15 for amphipods and >40 for Mytilus, for which regression slopes were<br />
negative with significant (i.e., p 0.5)<br />
and the largest sample sizes, followed by LC and EC values based on models with high r 2<br />
and small sample sizes. Moderate uncertainty is associated with LC and EC values based on<br />
models where 0.2< r 2 < 0.5. Due to the small amount of variation they describe, LC and EC<br />
values based on models with r 2 < 0.2, regardless of sample size, are not recommended for<br />
use in remedial decision-making.<br />
The LC and EC values with the least amount of uncertainty were carried forward into the<br />
stressor-response profile and are presented with other selected effects levels in Section 3.2.2.<br />
Although only 20 and 50 percent effects levels were estimated, the simple linear regression<br />
analyses and associated figures may also be used to estimate concentrations associated with<br />
less severe effects on the test organisms. Additional levels (e.g., EC 10 ) also could be<br />
calculated, but time constraints precluded including them in this draft. The chemical data<br />
that had been used for the regression was then screened using as the derived EC 20 s and<br />
EC 50 s and LC 20 s or LC 50 s to determine the final COPECs. The results of the screening are<br />
presented in Table F-3 for sediment and Table F-4 for pore water.<br />
3.2.1.4 Chemical Correlation Evaluation<br />
Additional regression analyses were conducted to evaluate chemical factors that could<br />
potentially affect the cumulative toxicity of COPECs to ecological receptors. These factors,<br />
described in the following subsections, consisted of the following:<br />
• Relationship of COPEC concentrations in pore water to those in sediment<br />
• Co-occurrence of COPECs in sediment<br />
• Principal components analyses in sediment<br />
COPEC Concentration Relationship Between Sediment and Pore Water<br />
For pore water bioassay data to aid in screening potential toxicity from sediments at <strong>Bolsa</strong><br />
<strong>Chica</strong>, the relationship between concentrations of COPECs in sediment to those in pore<br />
water must be known. If pore water concentrations can be estimated based on sediment<br />
SAC/143368(003.DOC) 3-35 ERA REPORT<br />
7/31/02
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