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No description available.

Tidal freshwater wetlands represent a transitional wetland between tidal salt marshes and non-tidal wetlands. as such, they exhibit some of the vegetation characteristics of both systems. If the changes in the vegetation pattern favor the characteristics of one system over the other, the changes may be an indication of changes in the environmental conditions of the estuarine ecosystem that favors that system. Unfortunately, little is known of the temporal and spatial changes that occur in the vegetation patterns of tidal freshwater marshes of the mid-Atlantic coastal region. In 1987 a vegetation analysis was done on a 60 hectare section of Sweet Hall Marsh, a tidal freshwater marsh of Chesapeake Bay. The data was compared with that of a similar study completed in 1974 to determine the changes that may have occurred in the vegetation pattern of the marsh. The results found that there was no significant difference in the species diversity of the two studies. However, further analysis showed that there was a change in the plant species contributing to the diversity. Spartina cynosuroides, an oligohaline species that was not important in the 1974 study, had the fourth highest importance value in this study. The shift in species composition of Sweet Hall Marsh may reflect a shift in the marsh's environment from being historically that of tidal fresh water to one of being more transitional between oligohaline and tidal fresh water.

The community structure and vertical distribution patterns of mesozooplankton in the lower York River, Virginia were examined during August, 1978. Samples were collected in the upper and lower water strata before, during and after destratification of the water column due to tidal mixing. In the stratified pre-mixed water column, distinct zooplankton communities were identified above and below the pycnocline. Pronounced diurnal vertical migrations of Acartia tonsa (all stages) and Pseudodiaptomus coronatus were documented. During the well-mixed hydorgraphic regime, the previously identified communities were not as well defined. There was a greater homogeneity of species assemblages and less pronounced differentiation of the vertical distributions for the dominant species during all light conditions. Following restratification, the species assemblages and diurnal vertical distributions closely resembled those identified in the well-mixed sampling period rather than the communities and patterns observed from the initial stratified environment. The homogeneous nature of the zooplankton communities in the well-mixed environment is attributed to the absence of water column stratification. The inability of the zooplankton to reestablish vertically distinct assemblages following restratification of the water column is proposed to be a result of low oxygen concentrations.

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Surrogate contaminant variables (heavy metals, organics, physical oceanograpic data) can be used to predict the incidence of positive cultures of Acanthamoeba sp. in oceanic sediments. Amoebae data are drawn from five years of study involving stations in Narragansett Bay, Rhode Island, the New York Bight, and the Philadelphia-Camden dumpsite, and associated pollution parameters are drawn from literature sources, computerized marine pollution data bases, and other archives. The Statistics Analysis System (SAS) MAXR('2) improvement technique (stepwise regression) and general linear model procedures are used to generate correlations for surrogate variables and produce final predictive models and tables. Model procedures for the three study areas are most valid for Narragansett Bay and the New York Bight but less valid for the Philadelphia-Camden dumpsite due to the small quantity of relevant data. The Durbin-Watson statistic is used to test for autocorrelation of model residuals and, using this test, the Philadelphia-Camden model is again found to be the least valid, although applicable within limits. The division of contaminant variables into "tactical" (short-term, simple analysis) and "strategic" (long-term, more complex analysis) categories enhances the predictive effort through the introduction of a cost-effective procedure evaluation. Generally, the simple variables predict the incidence of positive Acanthamoeba cultures as well as the more complex data sets. There are sufficient data and applicable computer programs to produce useful results for an investigation involving potentially pathogenic protozoans and public health management decisions may be made using the tables and formulae generated using these procedures.

No description available.

No description available.