Statement of Work

Patuxent River Damage Assessment of the Chalk Point 

Oil Spill on Shallow Water and Intertidal Benthos

The Academy of Natural Sciences

Estuarine Research Center

10545 Mackall Road

St. Leonard, Maryland 20685

Telephone: 410-586-9700

 Fax: 410-586-9705

Principal Investigator

Richard W. Osman, Curator

Benthic Ecology
Patuxent River Damage Assessment of the Chalk Point Oil Spill

on Shallow Water and Intertidal Benthos

The proposed study will survey three Patuxent River sites to assess whether any oilrelated impacts could be found from the April 2000 oil spill. The sites have been chosen 

to represent exposure to different quantities of the oil released at PEPCO’s Chalk Point 

facility. 

STUDY DESIGN

Sites. We will contrast samples from 3 sites, each in a different tributary or creek 

entering the Patuxent River (Figure 1). The sites were chosen based on the advice of a 

representative of the Trustees and differ in the degree of their exposure to oil. The most 

heavily-oiled site is in Swanson's Creek, the moderately-oiled site is in Trent Hall Creek, 

and the reference or control site that received no oil is in Hunting Creek.

Every effort was made to choose specific locations within the creeks that share 

similar environmental characteristics other than their exposure to oil. Based on field 

examination, sites were chosen that had significant amounts of sands and muds (sandy 

muds to muddy sands), were located in areas close to or adjacent to marshes, and had 

similar wave exposure.

Sampling Design. All 3 sites will be sampled on the same day. Samples will be 

collected from the lower intertidal to shallow subtidal zone immediately adjacent to the 

shore. Samples will be collected during the time period between mid and low tide and 

taken in water < 0.3 m depth. Every effort will be made to sample from the same tidal 

height or water depth at all 3 sites.

Sample Number. Ten replicate samples of each type will be collected at each of the 

3 sites. Sampling locations will be at least 1 m apart and chosen randomly (see below).

Sample Types. The proposed sampling program concentrates on the intertidal to 

shallow subtidal fauna that inhabits the sediments. Two types of samples will be taken at 

each creek site:

a. Core Samples. At each of the 3 field sites a 20-m transect line marked at 1 m 

intervals will be placed parallel to the shore. Samples will be taken at 10 of the 1-m 

marked locations along the transect. These 10 locations will be chosen randomly. At 

each of the 10 locations a meter stick will be centered perpendicular to the transect line 

and parallel to the surface of the water, and the actual sample location will be randomly 

marked at either end of the stick. Thus the 10 replicate samples will be collected at 10 

random locations along a 20-m transect with each sample randomly collected 0.5 m above 

or below the transect.
Each sample will be collected as a core sample. These cores will be approximately 

15 cm in diameter and 20 cm in depth. Approximately 3.5 l of sediment will be sampled by 

each core. The sediment collected from each replicate core will be placed in a separate 

plastic lidded container, returned to the laboratory and refrigerated. Initial processing of 

the cores, consisting of sub-sample collection and sieving of the bulk of the sediment for 

macroinvertebrates, will be done within 24 h of collection. Sub-samples will taken after the 

mixed core sediments in each container. Sub-sampling will include the collection of 100 g 

of the sediment for grain size analysis and 20 ml that will be frozen for subsequent analysis 

of organic matter content. 

1. Macroinvertebrate Samples. The remaining bulk of the sediment will be sieved 

using a 500 μm screen. All material retained on the sieve will be fixed in 

formalin and stained with Rose Bengal. After approximately 1 wk samples 

will be transferred into alcohol. Subsequently, samples will be examined 

using a dissecting microscope and all macroinvertebrate organisms will be 

identified and counted.

2. Sediment Grain Size Analysis. The 100 g sample will be sieved using a series 

of stacked screens with mesh sizes of 1.000, 0.500, 0.250, 0.125 and 0.062 

mm (Butler and McManus 1979, Buchanan 1984). The sediment will be 

sieved wet to avoid aggregation of the finer particles as a consequence of 

drying. All water and sediment passing through the 0.062 mm sieve will be 

retained and filtered to retrieve the fine silt - clay sediments (Butler and 

McManus 1979). The proportion of the sample in each of the 6 size classes 

will be determined by volume and dry weight and used to characterize the 

sediment and any differences within and among the 3 field sites. 

3. Organic Matter Content. The 20-ml frozen samples will be analyzed using the 

ignition method (McCave 1979, Rosa et al. 1991) for organic matter content. 

Each sample will be dried at 60° C, weighed, combusted at 450° C, and 

then re-weighed. The difference in weight before and after combustion will 

be used to estimate the proportion of organic matter in each sample. 

Combustion will be at 450° C to avoid the combustion of any shell 

(carbonate) material in the samples (Rosa et al. 1991).

b. Chemistry Samples. A 200-g sediment sample from the top 5-10 cm of the 

bottom will be collected adjacent to each core sample. Each sample will be collected by 

hand-scooping a sample with the hand covered by a new disposable glove for each 

sample. Each sample will be placed in a collection jar supplied by Entrix and sealed. 

Samples will be conveyed at the sampling site to a representative of the NRDA Trustees 

or Entrix for disposition.

Environmental Data. We will take a variety of background environmental data each 

time a site is sampled. These data will include salinity, water temperature, field 

observations on the presence of oil, sampling time, and the water depth of each core 

sampling site. 
Data Analysis. Differences in the composition and structure of the communities at 

the three sites will be compared. As appropriate, these analyzes will include standard 

classification and ordination analyzes. Populations of key species will also be contrasted 

among the sites. In general a one-way analysis of variance will be used to compare 

abundances at the 3 sites. However, if environmental variables such as oil contamination 

or sediment grain size varies significantly within a site, then regression analyzes will be 

used.

References

Buchanan, J. B. 1984. Sediment analysis. Pp. 41-65 in N. A. Holme and A. D. McIntyre, 

ed., Methods for the study of marine benthos. Blackwell Scientific Publishers, 

Boston.

Butler, A. T. and J. McManus. 1979. Sediment sampling and analysis. Pp. 87-130 in K. 

Dyer, ed., Estuarine hydrography and sedimentation, a handbook. Cambridge 

University Press, New York.

McCave, I. N. 1979. Suspended sediments. Pp. 131-185 in K. Dyer, ed., Estuarine 

hydrography and sedimentation, a handbook. Cambridge University Press, New 

York.

Rosa, F, J. Bloesch, and D. E. Rathke. 1991. Sampling the settling and suspended 

particulate matter (SPM). Pp. 97-130 in A. Murdoch and S. D. MacKnight, ed. , 

CRC Handbook of Techniques for Aquatic Sampling. CRC Press, Boston.