Henryk Renk, STANISŁAW Ochocki, Mariusz Zalewski and Henryk Chmielowski
Sea Fisheries Institute, ul. Kołłątaja 1, 81-332 Gdynia, Poland

Key words: nutrients, chlorophyll a, transparency of water, primary production, photosynthetic light curves, Vistula Lagoon

Abstract.
This work presents the characteristics of some environmental factors influencing primary production and chlorophyll a distribution of the Polish part of the Vistula Lagoon based on investigations that were carried out between April and November 1999. Due to the significant temporal and spatial variability of nutrient concentrations, the average values of particular parameters were derived in order to describe the hydrochemical conditions. The highest nutrient concentrations occurred near the outlets of the Nogat River and the Elbl�g Canal. The highest N/P ratio, on average about 20, was also observed in these areas, whereas the average N/P ratio for the entire Polish part of the Vistula Lagoon is about 6. A significant decrease in nutrient concentration, especially of nitrates and ammonia nitrogen, was observed when the results of the current investigations were compared with those from 1975-1978. The transparency of the lagoon waters has also decreased. The average chlorophyll concentrations were estimated to be about 43.5 mg � m^-3. The chlorophyll distribution in the Vistula Lagoon was described, and the primary production rate was determined. Additionally, the monthly primary production was derived. The average annual production was estimated to be 303.8 gC m^-2 � y^-1. A dependence between the photosynthetic rate and the phosphate concentration was noted.