| Summary |
Sediment-water material fluxes of O₂, NH₄+ , and CO₂ were measured in core incubations and a microcosm experiment. Through testing of 4 hypotheses, using general linear models with statistical control, I examined relationships of material fluxes and community structure. Fluxes were determined from light and dark core incubations of 1-m and 2-m sediments from Masonboro Island and Currituck Banks, NC, and Goodwin Islands and Hog Island, VA. From the same cores, Chl a concentrations [mu]g cc ̄¹ sediment), bacterial densities (# cc ̄¹ sediment), and faunal densities (# 10 cc ̄¹ sediment) were quantified. Chi a concentration contributed to the models that explained O₂ (p= 0.0001) and NH₄+ (p= 0.01) fluxes in light incubated sediments, while microfauna contributed significantly to the model of O₂ fluxes (p = 0.0001 ). Site and depth variables helped explain variances of both O₂ and NH₄+ fluxes. Site differences reflect edaphic, water-column, or metabolic characteristics of organism species and sizes indigenous to study locations. Depth may represent long-term differences in the light history of benthic sediments. In the microcosm experiment, light and nutrient treatments were imposed in intermediate terms (days) to study effects on material fluxes and community structure of the sediments. O₂ fluxes were significantly affected by light and day but not nutrient enrichments. NH₄+ models were not significant. When organisms were included, bacterial and faunal densities contributed significantly to the model of O₂ flux in the dark. Chl a and light contributed significantly to the model of NCR O₂ fluxes. O₂ and NH₄+ fluxes from microcosm experiments were better explained by community structure than fluxes measured in field experiments. This inconsistency in effects of organisms may be from uncontrolled factors in field experiments. Alternatively, there may be lack of a natural redox-potential discontinuity layer in the microcosm experiments, which may decrease chemical oxygen demand. This may greatly affect sediment-water material fluxes in the field. |
