No abstract

Two distinct hypoxic patterns were revealed from high-frequency dissolved oxygen (DO) data collected from North Branch of Onancock Creek, a shallow coastal estuary of the Chesapeake Bay, from July to October 2004. Diurnal hypoxia developed associated with large DO swings during fair weather and hypoxia/anoxia developed for prolonged 2-5-day periods following rainfall events. A simplified diagnostic DO-algae model was used to investigate DO dynamics in the creek. The model results show that the modeling approach enables important features of the DO dynamics in the creek to be captured and analyzed. Large anthropogenic inputs of nutrients to the creek stimulated macroalgae blooms in the embayment. High DO production resulted in supersaturated DO in daytime, whereas DO was depleted at night as the high respiration overwhelmed the DO supply, leading to hypoxia. Unlike deep-water environments, in this shallow-water system, biological processes dominate DO variations. High macroalgae biomass interacting with low light and high temperature trigger the development of prolonged hypoxic/anoxic postrainfall events.

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The production of reproductive shoots, vegetative shoots, and seeds was characterized for Ruppia maritima populations in the Virginia portion of Chesapeake Bay in 1988 and 1989. The study locations included two previously unvegetated sites recently colonized by R. maritima in the Rappahannock River and an established site and an in'egularly flooded marsh panue site, both in the York River. A corer was used to collect plant material, which was then separated into reproductive shoots, vegetalive shoots, and seeds. Sampling took place at approximately 2-week intervals from the time of first observation of flowering shoots until reproductive senescence. Reproductive shoot and seed production were high for all sites, particularly the previously unvegetated sites. The percent of reproductive shoots ranged from less than one percent to 52 percent. One previously unvegetated site produced 23,390 seeds m--" in 1988, the highest level of seed production measured during this study. Dramatic decreases in production from 1988 to 1989 at two of the study locations, the salt pannc and one previously unvegetated site, are attributable to the effects of drought and cownose ray (Rhinoptera bonasus) activity, respectively. High levels of seed production, frequently above 20,000 seeds m ~' , and their eventual dispersal may account for the rapid colonization in cerlain areas of Chesapeake Bay by R. mar#ima.

No abstract