Derron L. LaBrake, PWS, CED, MWS

Wetlands & Ecology, Inc.



Ecological Risk Assessment in a Salt Marsh – Designing an Effective Sampling Plan for Contaminant Delineation and Assessment of Ecological Risks


The Where, What, How and Why of the Sampling Plan:


Selecting Appropriate Sample Locations and Density for Delineation: 

·       Sample Location is dictated by the Site Conceptual Model-Ecological, contaminant transport mechanisms that are based on the pathway from source to receptor.

·       The expected gradient determines how far from the source you may will need to go.

·       Using doubling the distance or a fixed distance, pros and cons.

·       Salt marshes have habitat variables that may warrant different sampling techniques; differentiating between vegetated marsh and unvegetated channels.

·       Determining the appropriate sample density, considering investigation costs and the potential cost of remediation.  Both should be considered when selecting a sampling density.

·       Where and what is an appropriate background location and how many background samples should be collected.


Contaminant Transport dictates sample locations: 

·       Salt marshes are large organic carbon sinks so the presence of an abundance of organic carbon plays a significant role in the sampling decision making process.

·       Marshes are constantly consolidating and subsiding as new organic and inorganic material are transported into the marsh.


Sampling Depth: 

·       Dictated by where the biological activity is.

·       Defining the oxic/anoxic line.

·       Agencies may require deeper delineation sampling.


Sampling Methods for Marsh and Marsh Channels: 

·       Russian peat corer;

·       Ekman or Ponar dredge;

·       Direct fill, they all have their place.


Pre-stake the sample locations:

·       The sample locations are more efficiently selected when you are not trying to fill jars and coordinate other sampling crews.

·       Stake them all at once and don’t hesitate to go back and move some (before sampling of course) if later you decide that different locations need to be sampled as you become familiar with the site.

·       When you stake the locations use a GPS to map their locations.

·       Use different colored stakes for different types of samples (marsh/channel), number them as you go, on the days you come back to fill the jars it will go much faster

·       Pick a numbering sequence that will prevent confusion later and can be easily added to if you are delineating, to avoid adding confusion, if more sampling is required


Tides present unique set of issues:

·       Low tide is the easiest time to sample it avoids pulling samples through a column of water.

·       Remember that you can’t sample during a low tide that is after the sun goes down.


Take a salinity meter with you, salt marshes have a gradient of salinity and if you later need to run bio-assay tests, different organisms have different salinity tolerances.  You don’t want to change the salinity of your sample to accommodate an organism because then you are changing the chemistry of your sample – it may enhance or mast toxicity…


Laboratory Considerations and Coordination:


Talk to your lab!

·       Maximizing the field days – Collect all your samples at once and have the lab freeze the ones you can.  Maximizes the efficiency of the field effort.

·       Difficulties caused by the percent solids calculation.

o   You can overcome this by air drying, or

o   by running the percent solids first and add that percentage to the aliquot.

·       This removes uncertainty from the percent solids correction factor.

·       Use a larger sample aliquot based on the % solids to remove the percent solids estimate from the result


The Importance of Total Organic Carbon:

·       Normalizing for organic carbon when your COCs are non-polar organics (pesticides, PCBs, PAHs, etc.)

·       Oven determination vs. Lloyd Kahn Extraction

·       What is the difference and why is it important?


Grain Size:

·       When is it important?

·       What do you do with it?


Acid-Volatile Sulfides:

·       Acid Volatile Sulfide-Sequential Extraction Method

·       Be careful of O2

·       When is this useful data to have?


Data Analysis for Screening:



·       Average vs. Geometric Mean

·       Number of Detections

·       Average, Minimum and Maximum

·       Normalizing to 1% TOC for screening

·       Acid Volatile Sulfide (AVS-SEM)

·       90% UCL

·       Appropriate Screening Values – drill a little deeper, always



·       Concentration Delineation

·       Using some of GIS’ tools

·       Is the delineation complete?


Case Study:


·       Sampling outlined above was executed

·       Review of findings

·       Skeet Range issues to overcome

·       Restoration Test Plots