engleski

Coastal phytoplankton response to nutrient enrichment: an experimental system

The approach of a model system was chosen to simulate the natural nutrient status, the biological processes of the Gulf of Trieste (Adriatic Sea) and the effects of nutrient addition. Nutrient enrichment experiments were conducted in June 1994 and April 1995 to estimate the effects of different nutrient concentrations and ratios on coastal plankton dynamics and the production of organic matter. Natural phytoplankton were incubated in situ with the addition of four artificial nutrient sources (phosphate, nitrogen as nitrate+ammonium, silicate, a mixture of all nutrients) and natural nutrient sources (rain water and river water). In both experiments additions of phosphate and the mixture of all nutrients had the most profound effect on biomass increase and on production of particulate and dissolved organic matter. Bacterial biomass and production increased shortly after nutrient addition while phytoplankton passed over a 2-3 day lag phase. Size-fractionated primary production showed the largest enhancement in the >10 ľm and 2-10 ľm size fractions, while picoplanktonic cyanobacteri were outcompeted. The rates of released extracellular organic carbon (EOC) and the percentage of extracellular release (PER) were higher in the first experiment. Our results indicate that the effects on nutrients’ pulses depended not only on different nutrient ratio but also on the initial structure of the biotic component in the marine system.

phytoplankton; coastal waters; nutrient enrichment

nije evidentirano