Oxygen exchange and nutrient transformation rates under fluctuating salinity treatments in two subtidal marsh habitats

Charles Norman Farris, University of Rhode Island


The subtidal marsh and creek beds are major sites of nitrogen and phosphorus transformations. However, tidal changes in salinity concentrations may lead to variability in the nutrient contribution of marsh habitats. Characterizing these sources of variation will give a better understanding of the contribution of these habitats to system nutrient budgets. Tidal water exchange processes are a source of natural diurnal variation in the characteristics of the water masses estuaries.^ This research investigated oxygen exchange and nutrient regeneration processes in two subtidal salt marsh habitats. I investigated the changes in exchange rates that the two environments exhibited in response to a change in salinity of the overlying water over a tidal cycle. This was done in order to examine how these habits respond to environmental variability. Oxygen production in both the sediment and macroalgal habitats increased with increasing salinity, demonstrating an inhibition of productivity during low salinity levels. Macroalgal production rates also exhibited peak levels in early July and were associated with salinity, light levels and high levels of algal biomass. Macroalgal respiration rates were associated with temperature and algal biomass levels. Sediment production and respiration rates were much smaller than macroalgal rates, but showed similar trends.^ Nitrogen flux rates for the sediment habitat were comparable to previous studies. Nitrogen uptake and exchange rates indicated that the sediment was a significant source of ammonia in shallow waters. Nitrate + nitrite uptake rates were dependent on nitrate concentration and were driven mainly by nitrogen demand associated with macroalgal productivity. This opportunistic uptake allows the macroalgae to exploit available nitrate.^ Phosphorus uptake and exchange rates were generally low compared to previous studies. Phosphorus release was observed at middle and low salinity in both habitats. At high salinities, sediments both took up and released phosphorus. Macroalgae took up phosphorus during peak productivity periods. Phosphorus uptake was correlated with nitrate concentrations during the early summer at high salinities. This was probably due to increased phosphorus demands by macroalgae whose productivity was partly dependent on nitrate input to the marsh watershed. ^

Subject Area

Biology, Ecology|Biology, Oceanography|Biogeochemistry

Recommended Citation

Charles Norman Farris, "Oxygen exchange and nutrient transformation rates under fluctuating salinity treatments in two subtidal marsh habitats" (1996). Dissertations and Master's Theses (Campus Access). Paper AAI9707383.