United States Environmental Protection Agency Chesapeake Bay Program Annapolis MD 21401 Research and Development EPA-600/S3-83-052 Aug. 1983 Project Summary Stratigraphic Evidence of Human Disturbance in Some Chesapeake Bay Tributaries Grace S. Brush and Frank W. Davis Response of diatom (algal) and sub- merged macrophyte (angiospermous) populations to disturbance in some Chesapeake Bay tributaries over the last few centuries is interpreted from abundance of diatom frustules and presence of macrophyte seeds pre- served in dated estuarine sediments. The historical record of disturbance during the time period considered in- cludes land clearance and urbanization of the watershed resulting from human activity, as well as from periodic storms. The stratigraphic record indicates that both the diatom and submerged macro- phyte populations were stable prior to European settlement. With the onset of land clearance, dramatic changes are registered that include shifts in total numbers of cells and seeds as well as in species composition. The kind of re- sponse appears to be unique for a particular type of disturbance. This Project Summary was developed by EPA's Chesapeake Bay Program, Annapolis, MD, to announce key find- ings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Biostratigraphy is a tool scientists use to analyze layers of fossil remains of seeds, pollen grains, and diatoms in order to gain a long-term perspective of change. The method used here describes the changes in submerged aquatic vegetation (SAV) and diatom populations and corre- lates these changes with historical rec- ords of land use as well as with the stratigraphic record of sediment accumu- lation. Little historical data are available concerning the biological and chemical conditions of Chesapeake Bay. Thus, the stratigraphic method is important be- cause sediments contain records of popu- lations as they occurred both before and after human occupation of the surround- ing area. In any stratigraphic study, the fossils used as indicators must be care- fully selected with respect to their ability to preserve and their sensitivity to envi- ronmental factors. The variability of the populations in the sediment must be analyzed for natural factors induced by competition and predation. Core locations must be selected in areas of undisturbed deposition. Though the stratigraphic meth- od is used in lake and open ocean studies, it has not been utilized in the estuarine environment as extensively because it has been assumed that mixing of sedi- ments by physical processes and biotur- bation would have erased or distorted the records preserved therein. The stratigraphic method was used in this study to demonstrate the feasibility of the approach in identifying trends of SAV and changes in eutrophication and sedi- mentation rates in Chesapeake Bay by developing sampling methods that would avoid the above-mentioned problems. Procedure and Methodology Thirteen sediment cores were gathered at six locations [Furnace Bay, Patuxent River (Jug Bay, Eagle Harbor, St. Leonard Creek), and Ware River] using a piston corer which extracts samples up to 180 cm long. Cores analyzed for pollen and diatoms were divided into 2 cm intervals. Pollen and diatoms were then extracted from sediment, identified, and counted. ------- Cores analyzed for SAV were divided into 4 cm intervals and SAV seeds were extracted, identified, and recorded as either present or absent. Time lines were drawn, based on changes in the vertical pollen profiles that reflect major changes in regional vegeta- tion that can be dated from the historical record. These changes include land clear- ance, recognized in the sediments by a large increase in ragweed pollen; urban- ization, recognized by an increase in the density of pollen; and the demise of chestnut, by the chestnut blight, recog- nized by the absence of chestnut pollen in the sediments after the chestnuts had died. Results and Conclusions Prior to human occupation, diatom and macrophyte populations were fairly uni- form in Chesapeake Bay estuaries. After a human settlement, both populations underwent changes that are correlated with changes in land and water use. Presence or absence of seeds from multiple cores at a location indicates trends in SAV. One layer void of SAV seeds has been dated as the time of Tropical Storm Agnes (1972) when the SAV population of the upper Bay was nearly destroyed. The Bay-grass beds have not yet recovered from the storm. The rate of sediment accumulation increases greatly after land clearance and the accumulation of sediment is greater in the upper tributaries than at the mouths. A change in the number of diatoms present at a particular level indicates changes in water turbidity and water quality. Like sedimentation rates, water quality is governed by watershed use. During times of land clearance when siltation was high, diatom populations decreased. This may be due to the reduc- tion of light available for photosynthesis. The amount of diatoms found may also indicate changes in water quality; dia- toms are sensitive to the chemical, phys- ical, and biological properties of their environments. With increased human occupation of the surrounding land (about 1820) came enrichment of the Bay from inorganic fertilizers and sewage runoff. Certain species of diatoms that prefer nutrient rich water were found in sedi- ment deposited after fertilizers had been added to the watershed and after sewage was discharged into the tributaries. Con- versely, species which are known to occur only in clear water disappeared at the time of land clearance and have not returned. Many benthic species were replaced by planktonic species. Recommendations Historical links exist between changes in pollen grain types, diatom populations, the disappearance of SAV seeds, and the condition of the Bay. Past regional conditions can be inferred by careful observation of changes in core samples. Effects of human activities and nature on the environmental quality of the Bay can be analyzed and, where necessary, corrected. The stratigraphic method can be useful in defining future management plans for the preservation of Chesapeake Bay because it provides a long-term perspective of the variability of some populations and allows a compar- ison of conditions before and after human occupation of the region. Grace S. Brush and Frank W. Davis are with The Johns Hopkins University, Baltimore, MD 21218. David A. Flemer is the EPA Project Officer (see below). The complete report, entitled "Stratigraphic Evidence of Human Disturbance in Some Chesapeake Bay Tributaries," (Order No. PB 83-225 292; Cost: $8.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Chesapeake Bay~Program U.S. Environmental Protection Agency 2083 West Street, Suite 5G Annapolis, MD 21401 «US GOVERNMENT PRINTING OFFICE 1983-659-017/7145 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 PS 0000329 U S ENVIR PROTECTION AGENCY REGION 5 LIBRARY 230 S DtARBORN STREET CHICAGO IL 60604 f.fi..11....!!..!!....!..!.i..if ------- |