| Popis: |
Physical and chemical characteristics of the water column and sediment at sea bass / sea bream farm located in the middle Adriatic island of Brač were investigated during 2001-2006 period. Measurements and samplings were performed at the stations inside the farm area and at the reference station, approximately 1 km distanced away from the farm. Investigated parameters in the water column were temperature, salinity, transparency, suspended matter concentration, oxygen saturation and nutrient concentrations. Parameters measured in the sediments were granulometric composition, redox-potential, organic matter, organic carbon and total nitrogen content, inorganic phosphorus (P) species concentration (biogenic apatite P, authigenic apatite P, detrital apatite P and P bound on to iron oxides and hydroxides) and organic P. Transparency in the water column at all stations followed natural seasonal course, although constantly lower values at the farm station relative to reference site indicate certain impact of fish farming on this parameter. Impact on chemical parameters was moderately expressed in the surface and middle layer of the water column through the deficiency of oxygen and increased concentrations of dissolved inorganic nitrogen, orthophosphate and urea due to fish excretion and degradation of their metabolic products. Sediment inorganic P concentrations were enhanced under the cages compared to reference site, while organic P was mainly in range of “ natural” middle Adriatic concentrations. Sequential analysis of inorganic P species showed increased portion of biogenic apatite P and decreased detrital apatite P at the farm stations related to inorganic P pool at reference station as a direct consequence of fish farming. Sediment redox-potential, granulometric composition, organic matter content, carbonates as well as organic carbon and total nitrogen content reflected natural sediment characteristics rather than fish farm influence. |
