engleski

Spatial and seasonal distribution of carbohydrates as related to hydrographic and nutrient conditions in the northern Adriatic

Carbohydrates (CHO) comprise about 20 % of DOC present in surface waters of the world oceans. Their importance in highly productive estuarine and coastal waters is even greater, particularly during the periods of enhanced phytoplankton activity. It was suggested that diatom blooms could be an important source of carbohydrates that eventually lead to hypertrophic formation of gelatinous aggregates in the northern Adriatic. However, the knowledge about the spatial and temporal variability of CHO in the northern Adriatic, especially about their relation to phytoplankton dynamics, is still very limited. This study describes the distribution of carbohydrates and phytoplankton biomass as related to hydrological regime of the Po River and the resulting hydrographic and nutrient conditions in the period March-September 1994. Samples from different depths (0, 5, 10, 20, 30 and 35 m) were collected on 6 stations along the profile Po River mouth-Rovinj using the standard Niskin bottles. The total carbohydrates (TCHO) were determined using the MBTH-method, while an HPLC method was used for the determination photosynthetic pigments and their degradation products to assess the dynamics of phytoplankton biomass and its physiological status. The concentration of TCHO varied from 72 ľg C/l to 580 ľg C/l with the largest percentage being in the form of polysaccharides. Significantly enhanced values of TCHO (300-580 ľg C/l) were observed in the surface low-salinity layer (0-5 m), while the concentration in deeper layers was rather low (<200 ľg C/l) throughout the whole time period. The concentration of TCHO in the upper layer (0-10 m) of the more eutrophic western part of the basin was higher than in the eastern part, which suggested a strong link to the phytoplankton crop. However, the concentration of TCHO during the summer months was higher than in early spring despite comparatively lower levels of phytoplankton biomass, indicating a significant bioaccumulation of organic-rich carbon in the summer period.

carbohydrates ; nutrients ; distribution ; seawater ; N. Adriatic

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