Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

N2 fixation rates for several Virginia salt marshes were determined using in situ acetylene-reduction assays. A control and a chronically polluted oil marsh of the mesohaline Mobjack Bay area were sampled over a 1975-76 annual cycle. N2 fixation occurred in all transects which extended from upper mudflat to the Spartina patens zone. An isolated blue-green algal mat exhibited some of the highest N2 fixation rates. Intertidal sediment N2 fixation was patchy, both spatially and seasonally. However average rates (91.45 μg N/m2/h) compared to the estimated N requirement of the graminoid vegetation indicated a significant contribution to the N budget. Vegetation associated nitrogen fixation yielded higher average rates. N2 fixation rates for Wachapreague high salinity and Yorktown relic low salinity marshes were similar to the mesohaline marshes although blue-green algae fixation seemed to be more significant. The seasonal pattern of mesohaline marsh N2 fixation was positively related to temperature. Light-dark and anaerobic-aerobic experiments support the hypothesis that heterotrophic bacteria are the predominant N2 fixers and that availability of oxidizable substrates contribute to the seasonal pattern. Chronic oil treatment showed little effect on fixation rates with the possible exception of median tidal elevation sediments where summer rates were considerably higher than those of the control. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

This project investigated the feasibility of using the brackish water clam Rangia cuneata as a heavy metal pollution indicator, and further investigated the state of heavy metal pollution in the James River. Rangia cuneata were sampled in the fall of 1972 from the Rappahannock and James Rivers , and meats were analyzed by atomic absorption spectrophotometry for wet weight concentrations of copper, zinc, cadmium and lead. Levels of copper and zinc in Rangia cuneata were shown to be unaffected by clam size, spawning differences, salinity or distance upriver, and substrate grain size. Heavy metal concentrations in the oxidized channel sediments, determined from other studies conducted at the same time, were compared to levels in Rangia cuneata, but no relationships were found. Lead was below detection limits (0.2 ppm) in Rangia cuneata at all stations, and cadmium levels appeared to be consistent in both rivers. Copper was found to increase upriver in the James, indicating an upstream source, and zinc concentrations were found to peak at the mouth of the Chickahominy River. A number of possible causes were cited. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

A study of the biogeography of Peromyscus maniculatus was undertaken in order to ascertain a few of the environmental parameters important in defining the distribution of this species and how the species in turn has adapted to these parameters. The Columbia Gorge was chosen as it presents a climatic gradient from maritime to continental with very little elevation gain. Changes along this gradient in topography, soils and vegetation community structure are discussed.

Benthic communities in the estuarine portion of the James River are controlled mainly by salinity. Pollution effects are localized and difficult to assess because of the rigorous physical environment. Mesohaline and oligohaline communities were very similar to those in other east coast estuaries. except for the dominance of Rangia cuneata in the oligohaline zone. Communities of the tidal freshwater zone are most affected by pollution. In the areas of Richmond and Hopewell, where the major portion of the pollution load enters the river, communities are most severely depressed. Separate multivariate analyses of species distributional patterns, and pollution and physical parameters produced similar results dividing the river into mesohaline, oligohaline, and upper and lower tidal freshwater zones. Further analysis of only the tidal freshwater portion, to eliminate the effect of salinity, indicated that the distribution of benthic communities reflected the location and concentration of pollution sources along the river. The communities were dominated·by the introduced Asiatic clam, Corbicula manilensis, tubificids of the genus Limnodrilus and the chironomid larva Coelotanypus scapularis. The fauna of the freshwater zones was very eurytopic and adapted to the silty habitats that characterize the tidal freshwater James River and had great resemblance to the fauna of eutrophic lakes. The classical concept that a sharp increase in the number species occurs from the oligohaline to freshwater zones was found to be misleading. The increase does not occur until nontidal freshwater areas of greater habitat diversity are reached. Various aspects of the ecology of the poorly known tidal freshwater habitat are also discussed. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

No description available.

Turtles are important components of ecosystems around the world, with diverse ecological niches and adaptations. However, there are few detailed studies of how turtle community structure reflects local environments. This project applied techniques of community structure analysis to sites across the United States to infer past ecosystem and environmental conditions of the early Pliocene Gray Fossil Site (GFS) in northeastern Tennessee based on the ancient turtle community. Results indicate extant turtle community structure closely reflects environmental conditions, and that ancient turtle communities can be used to infer climate and habitat conditions of past ecosystems. Application to the GFS turtle community shows similarity to modern communities of the southern Gulf Coast and subtropical southeastern United States. These findings are consistent with previous interpretations of the GFS environment as warmer and wetter than the southern Appalachian climate of today, and demonstrate the utility of fossil turtle assemblage data in determining past environmental conditions.

Phytoplankton account for at least half of all primary production in estuarine waters and are at the center of biogeochemical cycles and material budgets. Environmental managers use water column chlorophyll-a (chl-a) concentrations as a basic water quality indictor, as the problems of eutrophication and hypoxia are intrinsically linked to excessive phytoplankton growth. Evidence suggests that the distribution and frequency of harmful algal blooms may be increasing worldwide. For the most part, phytoplankton communities follow a standard seasonal pattern, with specific groups dominating the assemblage during the time of year when environmental conditions correspond to their requisites for growth. However, climate change will result in incremental but consistent shifts in some environmental factors known to affect phytoplankton production and biomass accumulation. Mean surface temperatures in North American mid-Atlantic coastal and estuarine regions are steadily rising, and the frequency and severity of drought and storm events are projected to fluctuate, potentially increasing the severity of extreme weather events. Anthropogenically-induced nutrient loading, especially from non-point sources, is one of the largest consistent contributors to coastal marine eutrophication. The consequences of changes in these environmental factors to estuarine ecosystems and phytoplankton community dynamics are unclear. Because different phytoplankton groups respond to environmental changes in distinctive ways, some classes thrive during periods of environmental stability and others at times of temporary or sustained disturbance. to predict how phytoplankton and therefore water quality might respond to changes in climate and land use, we built mathematical phytoplankton kinetics sub-models that differentiate phytoplankton groups using taxonomic classes with well-defined functional characteristics. Then we integrated them into a reduced-complexity estuarine ecosystem model. The sub-models were designed to simulate daily biomass of diatoms, dinoflagellates, cyanobacteria, and raphidophytes in the New River Estuary, NC. We calibrated and validated the model using data collected from 2007 – 2012 through the Aquatic Estuarine monitoring module of the Defense Coastal/Estuarine Research Program. The model was a relatively good predictor of total chl-a and primary production, and a fair predictor of group dynamics. The model was employed in heuristic simulations of changes in temperature, nutrient loading, and freshwater delivery to predict their effects on overall phytoplankton biomass, productivity, and community composition. Increases in temperature had a modest effect on mean daily simulated phytoplankton production and chl-a, but considerably decreased the relative abundance of diatoms and simultaneously increased the relative abundance of cyanobacteria. The seasonal phenology of phytoplankton abundance also shifted in response to increased temperatures: chl-a concentrations were larger in the winter and spring and smaller in the summer and fall. The model was most sensitive to changes in the watershed nutrient load. Nutrient influx had a dramatic effect on the temporal and spatial extent of phytoplankton blooms. The relative abundance of dinoflagellates and raphidophytes increased in response to elevated nutrient loading, regardless of whether load was increased directly as in nutrient simulations or indirectly as in freshwater simulations. Initially, greater freshwater discharge increased total chl-a, productivity, and the frequency of phytoplankton blooms. However, these relationships leveled off or were reversed as flow continued to increase due to greater rates of flushing and light attenuation. Results demonstrated how models like this can be important tools for both heuristic understanding and environmental management. A benefit of this model is how easy it is to update to other estuarine systems through the re-parameterization of the phytoplankton groups.

Habitats of Chesapeake Bay have been altered due to anthropogenic impacts and climate change. Due to these human disturbances, seagrasses have been extirpated from many areas in lower Chesapeake Bay and persisting beds face future losses as water temperatures continue to rise. Further loss of seagrass habitat will negatively impact juvenile blue crabs (Callinectes sapidus) that use seagrass beds as nursery grounds. Habitat degradation allows for more successful introductions of exotic species, and the communities formed from the mixing of native and exotic species are known as emerging ecosystems. Gracilaria vermiculophylla, an exotic macroalga, may be an emerging nursery habitat for juvenile blue crabs in Chesapeake Bay; however the extent to which the alga is present and used as a nursery by juvenile blue crabs are largely unknown. I investigated algal distribution in the shallow littoral areas of the York River, a subestuary of Chesapeake Bay, over two years (2013 – 2014) and found that G. vermiculophylla presence correlated with salinity and that algal presence and biomass increased with seagrass presence, although biomass was generally low. The alga was present in areas where seagrasses have been lost, and is therefore likely providing nursery habitat in these areas of high megalopal recruitment. Benthic epifaunal communities had lower species richness and were less abundant in G. vermiculophylla relative to seagrass, while benthic infaunal communities had lower species richness but similar abundance in the alga relative to seagrass. Juvenile blue crab densities were similar in the alga and seagrass, although seagrass supported about 3 times as many first and second instar crabs than G. vermiculophylla. Young juvenile blue crabs preferred seagrass, which may be due to epifaunal prey preference, and G. vermiculophylla likely represents a secondary nursery habitat. Juvenile blue crab growth rates of crabs 15 – 50 mm carapace width were similar in the alga, native seagrass, and unvegetated habitat, indicating that growth does not drive ontogenetic shifts in habitat use by larger (20 – 30 mm carapace width) juveniles. Similar growth rates also suggest that G. vermiculophylla performs similarly to seagrass as a nursery habitat in terms of providing resources for growth. Simulations of density-dependent migration of young juvenile blue crabs between habitat types suggest that G. vermiculophylla may mediate continued seagrass loss, at least in part. Together, these results increase our understanding of an emerging Chesapeake Bay ecosystem and the impacts that changes to nursery habitats have on the juvenile component of the blue crab population.

The finfish communities using the intertidal surfaces of a bay-exposed marsh and a sheltered, channel marsh of the Goodwin Islands, York River, Virginia were studied from May to November 1994. Samples were taken approximately twice monthly using a flume weir at three stations in each marsh. Species composition, abundance and biomass were estimated, and growth patterns and production rates were described for the dominant species. A total of 3001 fish were collected from 11 species and 8 families. Fundulus heteroclitus dominated both marshes and accounted for 83.07% of the total number of fish caught, and 84.83% of the total biomass collected. Menidia menidia was the second most abundant species at 9.00% of the total number of fish, but F. majalis was second in the total biomass at 7.51 % of the total. Abundance first peaked in June, and a second peak occurred in November. Biomass had a small peak in the beginning of August, and a large peak in late September. Analysis of variance showed the number of species captured did not differ significantly between the marshes. However, both the number of individuals and biomass were significantly higher in the protected marsh. Correspondence analysis showed that species composition in the protected marsh was mostly cyprinodontids, but in the open marsh species composition varied more throughout the sampling season. Species densities were highest at 9.8 ± 3.3 fish/m2 for F. heteroclitus in the protected marsh. Production for F. heteroclitus over the summer in the protected marsh was high at 10.1 g dry wt.fm2 due to the large number of rapidly growing larval and juvenile fish.