General Objectives (for CEP & RMP) Build understanding of ecosystem characteristics and processes… To provide sufficient (better) basis for deciding among possible management alternatives
Specific Objectives (for this Study) Estimate future loads from eroding buried contaminants Estimate historic loadings of contaminants (especially recent decades) Characterize contamination with depth to assess current status and likely future changes Provide data for parameterization and evaluation of the multi-box model
If ~20 Cores Budgeted: Random sampling –Pros: aim to be representative of studied system –Cons: muddy signal, may need many samples before important factors IDd Deterministic sampling –Pros: build process with relatively few samples –Cons: selected samples often not characteristic of larger system (e.g. USGS depositional cores)
Sediment Core Sampling Strategy Hybrid Approach –Some samples specifically to understand loading history (deposition only zones) –Remainder of sites to begin representative characterization of Bay sediments
Initial Effort Timeline One cruise 1 year (not 2 years) –Relatively few stations spaced widely apart –Long lived isotopes, pollutants, ~1 yr storage not too bad if stored properly –Not enough samples (e.g. 10 in yr 1) for info to change stratification midstream
Sampling Effort Distribution Use general Bay segmentation scheme –Suisun, San Pablo, South, Lower South Bay Areas with bathymetric change history mapped Different sediment and pollutant loading quantities and sources Cores from each segment –1 depositional (wetland or deep Bay?) –1 erosional –2 more characteristic of that segment Depositional, neutral, or erosional
Modeling & Other Needs Hybrid approach seeks some of each –Assumes near 0 possibility that any model can do without verification of loading histories or process outcomes ? Is how much of each ? –~20 samples not a large number –Numbers likely not definitive of loading or representativeness –Collect excess samples of each type? Will we be able to get around to analyses soon enough?
Example Stratification + 0 -
Distribution of Sites
Future loads from erosion Unmixed buried sediments become mixed Pollutant profiles at depth mixed layer? –Introduced and averaged into mixed layer –Widespread characterization preferred Rate of erosion –Extrapolate recent history (Jaffe rates) –Predicted from model (calibrated to Jaffe?)
Future Loads w/ no More Cores Assume a range of profiles from existing data? –Pollutant profiles at depth mixed layer –How much higher or lower is reasonable? –Trend is likely depth > or = surface USGS cores depth > surface Many others suggest depth ~ surface –Guessing time scale of change much harder
Historic Contaminant Loadings Depositional cores reflect past conditions Potential limitations: –Ambiguous chronology: multiple tracers? –Natural or manmade disturbances: choose sites carefully? –Not representative of Bay: what does it reflect? Deep bay or wetland?
Historic Contaminant Loadings Deep bay cores –Pros:likely less hot spot influence, more representative of segment conditions –Cons: integrate more processes = more degrees of freedom (mixing w/ other seds, long response time), location history uncertain Wetland cores –Pros:respond more quickly to changes, reflective of local sources (hotspot, effluent or tributary), better mapped, history –Cons: more reflective of local sources, slow accretion
Alternatives Historic Loadings Assume Breivik close enough? Revise Breivik with upper and lower bounds? –How low/high is reasonable? Monitor current loads with time series Guadalupe river, Mallard Island Representative enough? –Project trends backward for hindcast?
Contaminant Profiles w/ Depth System status not just in surface 5cm sediments Dominant sedimentation regimes in each segment sampled ( sedimentation) Spatially variable but representative in long term –(must start somewhere) Alternatives (?) –Assume concentration surface sediments Even larger uncertainties
Data for Model (Multi box or other) Past & future loads, current system status are needed to model –(input parameters, initial or final conditions) Loads and status data needed independent of model –Relative priority somewhat model dependent –Which is more important?
Comments on Plan to Date Too expensive (much of CEP budget) Underfunded for objectives Too little of budget for interpretation/reporting Any geologic cores for sediment transport perspective? Why not Cs137 or mix of other tracers? Can cores be collected and stored for later analysis? Why wetland cores (not in model)?
Comments on Plan to Date Expect high % of useless cores Use screening analyses Need more sections per core for temporal trends (fewer cores more sections)
Regional Board Wish List Some Central Bay sites Trade OC pesticides for other organics in some samples? –Selenium (for a background baseline?) –PCDD/Fs –Background PCB levels