Our Students and Their Research

Cultures of the marine diatom Skeletonema costatum, the major diatom species in the Delaware Bay estuary, were grown in f/2 culture medium at a salinity of 20 ppt. DOM was collected and ultrafiltrated to obtain two fractions (>lkDa and

The effect of UV-B radiation, on the morphology and physiology of marsh vegetation was studied in situ. Plots of Spartina intermixed with Salicornia were covered by screens with selective absorption in the UV-B range. Results were compared to control plots (without screens and screens transmitting all UV-B). The screened plots transmitted less ambient light leading to decrease concentration of UV pigments in Salicornia virginica and Spartina alterniflora. Also, S. alterniflora showed morphological change when covered. However, the effects of decreased UV radiation on marsh vegetation are unclear from the data of this study.

An investigation of the nutrient cycling, particularly denitrification, of a tidal freshwater marsh was conducted using flux core experiments. Sediment cores were collected from the Jug Bay Wetlands Sanctuary on the Patuxent River, MD, and incubated in a controlled environment chamber. A recently developed Membrane Inlet Mass Spectrometer (MIMS) technique was used to measure denitrification rates in the sediment core flux chambers. Denitrification rates ranged from 45 µmol N m^-2hr^-1 to 165 µmol N m^-2hr^-1 in early summer and from 27 µmol N m^-2hr^-1 to 160 µmol N m^-2hr^-1 during late summer. Although large spatial and temporal variation was seen, there was strong evidence for the importance of coupled nitrification and denitrification, as decreases in the concentration of nitrate accounted for 35-90 % of the total denitrification in early summer, and 1-8 % during late summer. Methanogenesis rates in the marsh were also substantial, and methane ebullition represents a possible vector for the removal of nitrogen during the tidal cycle. These summer denitrification rates, which were comparable to spring rates in bottom sediments of the Patuxent River, demonstrate that the marsh represents an important sink for combined nitrogen in the ecosystem.