Geological, geochemical and bacteriological conditions in a post- dredging pit in Puck Bay (Southern Baltic, Poland)
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The paper presents the results of geological and geochemical studies carried out in an artificial pit which was formed after dredging the sediments up from the bottom of Puck Bay in 1991. It was found out that fine-grained classic sediments (d50 = 0.2 - 0.08 mm) as well as a great amount of organic matter (Pilayella littoralis) were deposited in the pit. The proc-esses of organic matter mineralization brought about reducing conditions. Ammonia concen-trations in near-bottom waters were higher than in the areas surrounding the pit 191.0 mmol?dm-3 compared to 3.97 mmol?dm-3. Phosphate concentrations in the waters and sedi-ments were elevated and reached values up to 1 mmol?dm-3. Intensive processes of organic matter mineralization caused both the temporary decline in sulphate concentration in near-bottom waters down to the value of 272 mg?dm3 (almost twice lower than the average concen-tration in Puck Bay waters) as well as sulphate deficiency in interstitial water. Below the 5 - metre isobath, the concentration of hydrogen sulphide varied between 0.11 and 0.49 mmol?kg-1w.w. The total number of bacteria in 1 cm3 of near-bottom water amounted to 107 and the number of sulphate-reducing bacteria ranged from 240-46000. The number of sulphate-reducing bacteria in 1 g d.w. of surface bottom sediments was estimated as 104 to 106.
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J. Bolalek Institute of Oceanography, University of Gdansk, Al. Marszalka Pilsudskiego 46, 81-378 Gdynia, Poland