Volume 36 (2007): Issue 1 (March 2007)

Zooplankton phosphorus excretion was studied in Swarzędzkie Lake in 2000-2002. Phosphorus excretion rates were high from spring through autumn, but low in winter. The highest value, 203.7 μgP 1^-1 d^-1 (vertical profile mean), was recorded in June 2000. The mean rate was 26.6 μgP 1^-1 d^-1 and was 10 times greater for rotifers than for both cladocerans and copepods. In most months, the calculated phosphorus excretion rate was greater than the sum of tributary external phosphorus loading and internal bottom sediment loading. Nevertheless, the influence of the zooplankton phosphorus excretion rate on yearly phytoplankton abundance, biomass and chlorophyll a was not statistically significant. Yearly variance in phytoplankton variables was best explained by a canonical variable composed of internal loading and zooplankton phosphorus excretion (total redundancy 32.8%).

In this study psychrophilic, mesophilic and denitrifying bacterial abundances were studied seasonally (summer, autumn, winter and spring) in the water column and surface sediment layer (0-5 cm) in the post dredging pit Kuźnica II and natural areas of Puck Bay. The research was conducted between VI 2001 and III 2003.

In the pit area an increase in mesophilic bacteria and a decrease in denitrifying bacteria numbers were observed, when compared to the natural areas. In the case of the mesophilic bacteria, the increase was visible in the near-bottom waters and surficial sediments during the period of well developed vegetation - in summer and autumn. In the case of denitrifying bacteria, the decrease of number concerned the sediments. Numbers of psychrophilic bacteria in both the natural and dredged areas did not differ significantly over the course of the study.

These results suggest that deep dredging can cause the self-purification potential of the ecosystem to be diminished and induce strong bacteriological pollution.

This investigation of Pomeranian Bay waters was conducted from March 2001 to August of 2003 from aboard the r/v Nawigator XXI, which is owned by the Maritime Academy in Szczecin. A total of 147 water samples were collected at 15 stations on three transects in the Pomeranian Bay from Świnoujście, Międzyzdroje, and Dziwnów to the Odra Bank. Zooplankton was sampled with a Bongo type planktonometer Ø = 20 cm with a mesh size of 80 μm during 10 min. filtering hauls in the pelagic zone from the bottom to the surface at an average vessel speed of 3 - 4 knots. The method developed and published by Orłowski was used to transform the large amount of seasonal data for the entire study period into isoline illustrations of the spatial structures in the Pomeranian Bay of mesozooplankton and selected species, namely Acartia bifilosa, Acartia longiremis, Pseudocalanus elongatus, and Temora longicornis. The average mesozooplankton aggregations in ten consecutive seasons at the 15 stations investigated from 2001 to 2003 in the entire Odra estuary area fluctuated from 2,442 to 92,200 ind. m^-3. The highest species variety was noted among marine Copepoda, which was the dominant group in virtually every season investigated. Their maximum abundance reached as much as 213,493 ind. m^-3. The euryhaline species A. bifilosa occurred throughout the research period and at all stations at an abundance that reached 210,443 ind. m^-3. The seasonal succession series were as follows: in spring, the dominants were Acartia spp. and Evadne nordmanni; in summer - Keratella cochlearis, Bosmina coregoni maritima, and A. bifilosa; in fall - T. longicornis and Acartia spp.; in winter - T. longicornis and Centropages hamatus.

A three-dimensional operational hydrodynamic model of the Baltic Sea (M3D_UG) developed based on the Princeton Ocean Model (POM) was applied to model water exchange in the Oder River mouth area. Due to wind-driven back flow in the Oder mouth, a simplified operational model of river discharge was also developed based on the water budget in a stream channel. Linking the Oder discharge and Baltic Sea models into a single system allowed simulating hydrodynamic conditions in the Szczecin Lagoon and the Pomeranian Bay. Since the model adequately approximates hydrodynamic variability, it is a reliable tool for modeling water exchange in the Oder River mouth area and for assessing Oder water spread in the Baltic Sea.

The Odra River mouth area is affected by storm surges caused by passages of deep low-pressure systems over the Baltic Sea. The surges are the result of wind action and changes in atmospheric pressure at the sea surface. The two effects may be additive, in which both factors increase or decrease the sea level on the coast, or they may be non-additive, where one factor increases the sea level and the other decreases it. This paper discusses the role of the wind field and changes in atmospheric pressure in the duration and extent of storm surges in the Odra River mouth area.

Sulfur cycling and the sulfurization of humic and fulvic acids were compared in recent sediments from two western European rivers (the heavily polluted River Rupel in Belgium and the pristine River Authie in northern France). The sulfurization of humic and fulvic substrates occurs in both sediments irrespective of organic loading, but the sulfur species added to the organic substrate differ. Some sulphurization of fulvic acid by oxidized S was observed in the strongly reducing sediment of the River Rupel. Humic acids were sulfurized in the sediments of both rivers in these segments with prevailing reducing conditions by reduced S.

The main aim of this study was to determine the size of the load carried by the Reda River that was discharged into the sea and the load distribution on the bottom of the Puck Lagoon. Water exchange with the open sea was limited in this shallow reservoir where the average depth was 3.13 m. The input of material was dominated by river transport, whereas abrasion and aeolian processes were insignificant in the total sediment inflow. The Reda River, one of the main rivers flowing into the lagoon, is 44.9 km long and has a catchment area of 485.2 km². The investigations were conducted between 2001 and 2004 at the Mrzezino hydrological cross-section and at the river mouth in the Puck Lagoon.

The study demonstrated that the Reda River discharged annually approximately 9,900 tons of sediments into the Puck Lagoon, 73% of which was the bed load that in the final course of the river created an underwater accumulation form. The granulometric composition of the deltaic deposits, similar to the bed load, was dominated by coarse-grained sand fractions. The proportion of the aleurolite and pelite fraction was insignificant at less than 1%. The suspended sediment was composed of particles that ranged in size from 0.00045 mm to 0.25 m. Mineral particles were more common than organic ones in the load discharged by the Reda River into the Puck Lagoon and constituted 99% of the bed load.

Nodularia spumigena Mertens, Aphanizomenon flos-aquae (L.) Ralfs and some species of the genus Anabaena are the dominant cyanobacterial taxa occurring in the Gulf of Gdańsk. The heterocystous cyanobacteria use dissolved molecular N₂ as an additional nitrogen source, and this allows them to bloom during the summer when growth of other phytoplankton species is normally nitrogen-limited. Although cyanobacterial blooms have been reported in the Baltic Sea since the mid-19^th century, the extent and intensity of blooms have recently increased due to anthropogenic sources of eutrophication. Increased river phosphorus input and changes in the phosphorus to nitrogen ratio are implicated as causal factors. After us the initial cause of the cyanobacterial bloom is a low N:P ratio, which indicates phosphorus excess, i.e. favourable nutrient conditions for nitrogen-fixing algae. An N:P ratio of 10 has been considered an approximate value for the N:P requirements of Baltic phytoplankton. For several years this ratio has been lower than 10.

The mean annual value of the N:P ratio for the water of the Gulf of Gdańsk ranged from 3 to 7. Differences in the intensity of blooms observed in different years could be linked to temperature. During hot summers, when the seawater temperature increased to 20°C, large blooms were noted. For the cyanobacterial blooms in the Baltic Sea, the low N:P ratio is the primary factor and high temperature is a starting point.