Sunday, June 12, 2011


How to complete this activity and what you can get out of it.

The following paper was developed for teachers and their students to have an example of the type of research that can be completed with the sediment samples obtained at Milford Point. Students can copy some of the laboratory methods or devised new ways to interpret the data. I have also included some optional reading that will help students understand the Long Island Sound Geology and its sedimentation since the last glacier event.


Methods and Materials
A sediment sample was taken on 5/4/2011 from Milford Point in Milford, Connecticut to be analyzed for sedimentation rate and diatom content. This sediment was extracted from the muddy shore right in front of the Audubon Coastal Center using a PCV home made sediment core sampler. Latitude and Longitude was 41.17615 and -73.10107.
Sediment samples contain a percentage composition of sand, silt, clay and other organic and mineral components at sedimentation rates through out time.

Based on studied completed by the University of Connecticut, at Every Point by Frank W. Bohlen (personal communications) sedimentation rate in Connecticut shores can be about one centimeter per year. The total core extracted was 35 centimeter in length. So based on that rate the oldest part of the core is about 35 years old.

Sediment sample was taken using a home made core sampler shown on the picture. This PCV pipe contains an inner plastic tube. Core was captured by this tube. Once on the laboratory, the plastic tube was cut and the sample exposed for experimentation.

In this exercise, I wanted to compare the oldest section of the core against the most recent section, so samples were taken from both ends of the core. The one referred as "the top" is the most recent one, sedimentation dated to be from the last 5 years, and the one referred as "the bottom" would be the oldest section of the core that I have estimated to be 35 years old.

Sediment size, silt and clay content, and diatom diversity was assess from both end and the results were analyzed.

Sediment Rate

Sediment analysis
The sediment was assessed for sand vs. silt and clay and particle size content using the same methods recommended by Howard M. Weiss and Michael W. Dorsey on their Project Oceanology teacher manual Investigating The Marine Environment: Source book. 1979. Methods are reproduced in the Project Periphyton Manual.

Diatom Biodiversity
Diatom biodiversity was assessed using the methods recommended by Alberto F. Mimo in my manual "Project Periphyton" 2011. . Methods are reproduced in the Project Periphyton Manual.

Sediment Composition
To asses the sediment composition of the core section, a small piece of core was cut using a knife, dried using a convention oven and weighted to +/- 0.1 grams.
Sediment then separated by using a Mini Sieve set. The Mini-Sieve set comes with 8 sieve sizes. Numbers 230, 170, 120, 80, 60, 45, 35 and 25. Sand particles include any particle that would be retained by anyone of these sieves. Anything smaller that .063 mm would be considered silt or clay.

For our experimentation I only used sieves number 25, 35, 45 and 60 corresponding to particle size .71 mm, .5 mm. , .355 mm. and .25 mm. Smaller sieves are impractical to use, so anything that pass through my smaller filter was consider < .25 mm. Water was used to force particles through the filters. At the end all particles captured were dried and weighted. Two samples were selected, one from the top of the core, corresponding to new sediments and one from the bottom of the core corresponding to about 35 years ago. Results Sediment dry weight and percentage 35 years old T W Size 25 Size 35 Size 45 Size 60 Size >60
Weight (gr.) 16.6 2.1 1.7 2.1 2.3 8.4
% 12.6506 10.24096 12.6506 13.85542 50.60241
New Sample 11.9 1.1 1.4 1 2.9 5.5
% 9.243697 11.76471 8.403361 24.36975 46.21849

See Graph.

During the last 35 years there has been very little change in the sediment composition left on the shore of Milford Point. Composition of sediment sizes are very similar. During that time, the most significant change has been on sediment size corresponding to .25 mm. in size with a negative change of 10.51 percent. Small particle size of < .25 mm which includes some sand, sit and clay have a positive change of 4.39 percent during the last 35 years. See graph.

Science Education is not about answers but about questions. Our objective is to provide students with materials that will bring up their interest and curiosity. In this sedimentation rate exercise we know that there has been sedimentation changes through the 35 years. The questions are why and how this changes have affected the shore and the environment. Our job now will be to ask the students to come up with theories based of additional readings that can answer some of their questions. I have included some materials that will help students have a better understanding of sedimentation in the Long Island Sound.

Literature Reviews

Frank W. Bohlen. Phd. MIT Woods Hole
University of Connecticut, Avery Point Campus, Groton, CT.
From his website:
My research program is designed to increase our understanding of the dynamics governing the transport of fine-grained sediments in coastal and estuarine waters. In broad outline, this program consists of three principal components: field and laboratory experimental studies, instrument design and development, and numerical computer modeling. The field and laboratory investigations seek primarily to document the response of the sediment-water interface to both long-term persistent and short-term aperiodic, storm related factors. Many of the instrument systems required to obtain these observations have been designed and constructed at the University of Connecticut. Data provided by the deployment of these arrays in a variety of coastal environments has shown the interfacial response to be highly non-linear and significantly variable in both space and time. Such variability complicates specification of transport algorithms in numerical predictive models. Ongoing work seeks to extend and refine these observations to permit resolution of the specific factors governing transport non-linearities including consideration of biologically mediated variations in sediment fabric, particulate associated alterations in boundary shear stress, and advective effects associated with variations in the local flow field.
The experimental work will require continuing redesign and modification of the available instrument arrays. Existing optical systems, presently used to monitor suspended material concentrations, are to be improved and supplemented by a variety of acoustic systems in order to increase both spatial and temporal resolution. In addition, the field arrays are to be supplemented by a series of sensors intended to detail the fabric of the sediment column in the immediate vicinity of the sediment-water interface. A number of systems are to be tested including radioactive probes, acoustic and electromagnetic systems and simple mechanical probes with ultimate selection based on simplicity of operation and reliability and the potential to yield vertical resolution over scales of 1 mm or less.Patterns of recruitment, abundance and dominance within several subtidal communities in southern New England have been found to persist year after year over large areas of the bottom. This long-term persistence is not expected in such an open system with disturbances continually creating open patches for recruiting larvae whose identity and abundances change both temporally and spatially. Present research suggests that the persistence results from strong local control of recruitment that overrides any variability in larval production and dispersal of species from outside a site. We have been testing this hypothesis by conducting manipulative field experiments which delineate abiotic and biotic controls of local recruitment and how these affect community establishment and development.The variety of experimental work is being complemented by concurrent continuing development of a series of numerical models intended to incorporate the laboratory and field data for calibration purposes and to permit the extension of these data in space and time for predictive purposes.
Fredette, T.J., W.F. Bohlen and D.C. Rhoads. 1988. Erosion and resuspension effects of Hurricane Gloria at Long Island Sound dredged material disposal sites. Proc. Of Water Quality 1988. U.S. Army Corps of Engineers, Hydraulic Engineering Center, Davis, CA. Fenster, M.S., D.M. Fitzgerald, W.F. Bohlen, R.S. Lewis and C.T. Baldwin. 1990. Stability of giant sand waves in eastern Long Island Sound. U.S.A. Marine Geol. 91: 207-225.Bohlen, W.F. 1990. Ocean disposal of particulate wastes: practices, properties and processes. In: K.R. Demars and R.C. Cheney (eds.). Geotechnical Aspects Of Ocean Waste Disposal. Amer. Soc. for Testing and Materials, Spec. Pub.Bohlen, W.F., D.R. Cohen and M.M. Howard-Strobel. 1992. An Investigation of Sedimentation Induced by Gas Pipeline Laying Operations in the Vicinity of the Oyster Bed Lease Areas, Milford, CT. Prepared for Iroquois Gas Transmission System. Shelton, CT. 40 pp. & Figs.Bohlen, W.F., D.R. Cohen and M.M. Howard-Strobel. 1992. An Investigation of Water Column Currents and Suspended Sediment Dispersion Associated with Dredged Material Disposal Operations, Cornfield Shoals Disposal Site, Eastern Long Island Sound. Prepared for Science Applications international Corporation. Newport, RI. 49 pp. & Figs.Lissner, A., C. Phillips, E. Waddell, P. Hamilton, A. Barnett, D. Diener, P. Raimondi and W.F. Bohlen. 1995. Monitoring Assessment of Long-term Changes in Biological Communities in the Santa Maria Basin: Phase III. Report submitted to US Department of Interior Minerals Management Service/National Biological Service. Cont. No. 14-35-0001-30584.Bohlen, W.F., M.M. Howard-Strobel, D.R. Cohen and E.T. Morton. 1996. An Investigation of the Dispersion of the Sediments Resuspended by Dredging Operations in New Haven Harbor. Submitted to New England Division, US Army Corps of Engineers. Waltham, MA.

Charles W Ellis
Marine Sedimentary Environmnets in the Vicinity of the Norwalk Islands, CT. 1962
State Geological and Natural History Survey of Connecticut, 1962. Bulletin Number 94.

S. Jeffress Williams
Geological Framework Data from Long Island Sound, 1981-1990
USGS Digital Data Release, U.S Geological Suvey Open-File Report 02-002

Diatom Diversity

Diatom Analysis

I have compared the diatom composition of both sides of the core, the newest end probably no more than 5 years old and the bottom of the core which we presume to be 35 years old.
Small piece of sediment was taken using a spatula and dissolved in a small amount of water. This sediment can be clean using paleontology methods, but for the purpose of this exercise, I have just look at the sediment with a compound microscope at X400 magnification and sometimes at x1000.

Sample diatom

Diatoms are covered with silica and they are practically indestructible, so one can find diatoms on the sample. I have placed a small drop of sediment/water on a regular microscope slide and pan through the slide in search for diatoms. When I have found a diatom I have made a drawing of the specimen and take a picture with my microscope camera. Pictures are not necessary. My objective was to find as many different diatoms as possible. I am not looking at the abundance, just at the diversity. I also have compared the diatoms to pictures found in several diatom keys and identified the organisms as much as it was possible.


I was able to identify a total of 9 different taxa from the bottom of the core, the old sediment, and 13 different taxa from the new sediment. There was higher diversity and much more abundance of organism in my new sediment.
Here are some of the picture I took.




Correct identification of Diatoms is very difficult. But trying is a great exercise and will provide your students with a challenge.
Diatom diversity will be a direct outcome of a better and less polluted environment. Thirty five years ago would have been somwhere in 1975, the very beginning of the environmental movement and the establishment of the Clean Water Act. I can see that we may have had some improvement over this past 35 years that would be reflected on our samples.

Additional Reading from websites

The Diatoms: Biology and Morphology of the General F. E Round. Cambrige University Press.

Monitoring Coastal Environments Using Foraminifera and Thecamoebia Indicators. David B. Scott, Franco S. Medioli and Charles T. Schafer. Cambridge University Press.

The Ecology of Fresh Water Phytoplankton. C.S Reynolds. Cambridge University Press.