Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


The oxygen metabolism and exchange of nutrients between sediment and water were studied on a submerged sandy shoal in the York River, Virginia from March to December 1983. Particular emphasis was placed on the variability in metabolic estimates over different time scales. Variation in oxygen metabolism was examined over the photoperiod, between successive sampling days, between tidal condition (mid-day high vs. low tide), and among seasons. Morning NP was significantly greater than afternoon NP over the study. Mean hourly NP and R were significantly different between successive days in 4 of 6 tests, and 2 of 6 tests respectively. R was significantly higher on days with mid-day low tides (noon (+OR-) 2 hours). Mean hourly NP was 49% greater on days with mid-day low tides and R was 70% greater. Hourly NP and R were significantly different among seasons. R peaked in summer and NP in fall. Plots of mean hourly NP and R by month were made using all data for a given month and compared to plots made by randomly selecting a single measurement for each month. The latter plots are based on 12 data points, the former on 185 points. The two types of plots produced very similar annual rate estimates but differed radically in their depiction of seasonal changes. Within dark domes, hourly fluxes of ammonium and phosphate ranged from -21 (uptake) to 364 ug-at N m('-2) and -3 to 76 ug-at P m('-2). Nitrate + nitrite fluxes were generally small and erratic, comprising an average of only 15% of the total dissolved inorganic nitrogen flow. Releases of ammonium and phosphate peaked in summer, were an exponential function of temperature, and a linear function of respiration. Average ammonium release within transparent domes was only 25% of the average release in the dark domes, but phosphate fluxes were nearly identical to those in the dark domes. Nitrate + nitrite fluxes comprised an average of 17% of the total dissolved inorganic nitrogen flux of the transparent domes. Ammonium fluxes were significantly different between dome treatments, fluxes of the other nutrients were not significantly different.



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