1. The Effects of Various Aquaculture Biodeposits on Nutrient Flux at the Sediment-Water Interface in Maine
Libby Gorse, Aria Amirbahman
Department of Civil and Environmental Engineering, University of Maine, Orono, ME
Preliminary Results and Discussion
Introduction: In order to establish the carrying capacity of a given ecosystem with respect to aquaculture, the rate at which organic biodeposits resulting from these operations can safely be added to an ecosystem must be determined. This is an experimental study to determine the influence of biodeposits from various aquaculture operations on nitrogen and phosphorus species flux at the sediment-water interface. The flux will be measured by analyzing the water above sediment at different time intervals. The knowledge gained from this study will help to locate the areas best suited to raising bivalve and fish species, and enable safe scale-up of aquaculture operations.
Hypotheses to be tested:
Biodeposits high in carbon and nitrogen content increase nutrient flux to the water column.
Fine-grained sediments inhibit the diffusion of oxygen and support lower mineralization rates of organic matter than coarse-grained sediments.
Methods: To study nutrient flux at the sediment-water interface under environmental conditions, specially designed flux chambers are used. These chambers contain sediment cores with overlying seawater for the production and collection of samples. There are well-defined processes that control the cycling of nitrogen and phosphorus. To quantify the cycling of these nutrients their concentrations and fluxes will be tracked over time. The various sediment types that exist in Maine will be examined for aquaculture suitability, and extrapolation of our data based on the bottom-type of possible lease sites will help future aquaculturists and the Department of Marine Resources (DMR) to make informed decisions.
The Schmidt stability index determines the energy necessary to mix lake water. It is calculated by using lake morphometry (area of 1-m thick slices of the water column) and vertical temperature distribution among the slices.
Sed results Al:Fe epi P X schmidt index maine distribution mapX
Cumulative frequency curve vs depth X
surface area X
Schmidt X
WA:LA-linear ? colin (LEAs) X
residence time (1/flushs per year) (get all on same map) (log of surface area)
MOI? Also lea
Colin from LEA
Revise Al:Fe ratio X
3 data sets
Sequenctial extractions
Concept after Kopacek on Al:Fe, Al:P
Epilim CHLA to Schmidt- way to calc schmidt, lakes may change according to mix, go to zero in dimictic lakes twice
Greatest changes are observed in ammonium (NH4+) concentration, whereas nitrate (NO3-), nitrite (NO2-) and phosphorus (P) remain relatively unchanged.
NH4+ is initially generated in the cores amended by biodeposits, but taken up by the unamended cores.
In cores incubated for five days under oxygenated seawater, NH4+ concentrations decrease sharply in amended and unamended cores, due to uptake by sediment. No observable difference in the trends of other species between amended and unamended cores has been found.