Szczecin Lagoon Research Articles

Coastal bathing water quality and climate change – A new information and simulation system for new challenges

Human pathogenic micro-organisms in coastal waters receive increasing attention. Climate change with its multiple effects on micro-organisms is one major reason. Changing survival rates, sources and new invasive species are a challenge for bathing water quality management. We present a new online bathing water information system. It includes an alerting system, software to supports communication between authorities, local municipalities and the public as well as simulation tools, based on a 3D-flow and particle tracking model. In scenario simulations with focus on enterococci and Escherichia coli bacteria we show the potential impact of climate change on bathing water quality and the potential relevance as a decision support system in the large, shallow Szczecin lagoon. Szczecin lagoon in the Baltic at the German/Polish border is a pollution hot-spot and frequent bathing prohibitions hamper tourism development.Because of climate change, the risk of river floods is supposed to increase in future. Higher discharge causes an increased transport velocity in the river flow. At the same time, run-off from city surfaces and agricultural land along the river can cause increased E. coli concentrations in all surface waters. As a consequence E. coli and especially Enterococci are transported far into the lagoon and high concentrations can cause bathing water quality problems even on distant beaches. Especially heavy lasting rain in the river basin together with local rain events are a serious threat for bathing water quality in the lagoon and will very likely require a closing of beaches for swimming. Similar to other coastal waters, a wide range of other potentially human pathogenic micro-organisms might create a threat for the lagoon in future.

Heavy Metals in Water German-Polish Szczecin (Oder-) Lagoon and Their Potentiality in Health Risk Assessment

Heavy Metals in Water German-Polish Szczecin (Oder-) Lagoon and Their Potentiality in Health Risk Assessment

Organotin compounds in surface sediments of the Southern Baltic coastal zone: a study on the main factors for their accumulation and degradation

Sediment samples were collected in the Gulf of Gdańsk, and the Vistula and Szczecin Lagoons—all located in the coastal zone of the Southern Baltic Sea—just after the total ban on using harmful organotins in antifouling paints on ships came into force, to assess their butyltin and phenyltin contamination extent. Altogether, 26 sampling stations were chosen to account for different potential exposure to organotin pollution and environmental conditions: from shallow and well-oxygenated waters, shipping routes and river mouths, to deep and anoxic sites. Additionally, the organic carbon content, pigment content, and grain size of all the sediment samples were determined, and some parameters of the near-bottom water (oxygen content, salinity, temperature) were measured as well. Total concentrations of butyltin compounds ranged between 2 and 182 ng Sn g−1 d.w., whereas phenyltins were below the detection limit. Sediments from the Gulf of Gdańsk and Vistula Lagoon were found moderately contaminated with tributyltin, whereas those from the Szczecin Lagoon were ranked as highly contaminated. Butyltin degradation indices prove a recent tributyltin input into the sediments adjacent to sites used for dumping for dredged harbor materials and for anchorage in the Gulf of Gdańsk (where two big international ports are located), and into those collected in the Szczecin Lagoon. Essential factors affecting the degradation and distribution of organotins, based on significant correlations between butyltins and environmental variables, were found in the study area.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-013-2115-x) contains supplementary material, which is available to authorized users.

Variation in the susceptibility of humic acids from the sediments of water reservoirs to oxidation

AbstractThe aim of this study was to determine whether, and to what extent, structures of pigment‐origin affect the susceptibility of humic acids (HAs) to oxidation, with the primary focus on derivatives of chlorophyll. The sediment samples were collected from lakes with different catchment management, and the Szczecin Lagoon, which is the estuary of the Odra River. HAs were extracted from sediments using 0.5 M NaOH solution. Sediments differed in their contents of total organic carbon (3.8–456.0 g kg−1) and total nitrogen (0.8–33.7 g kg−1). HAs extracted from sediments were characterized by the highly diverse composition of chemical elements and spectrometric properties regarding the visible‐light spectrum and ultraviolet radiation. HAs extracted from the sediments of lakes situated in the Chodzież and Wałcz Lake Districts (ChWLD) with forest catchment areas, were most susceptible to oxidation, indicating that the processes that occur during oxidation are affected by the content of pigment‐originated structures (the derivatives of chlorophyll) in the molecules of HAs. These structures are relatively resistant to oxidation, because they are present in the spectra of alkaline solutions of HAs after oxidation. The conducted studies also proved that the susceptibility of HAs of sediment origin to oxidation cannot be interpreted in the standard way applied to values obtained for soil HAs.

Nitrogen turnover during the spring outflows of the nitrate-rich Curonian and Szczecin lagoons using dual nitrate isotopes

Coastal zones that receive high nitrogen loads from rivers often suffer from intense eutrophication. This is the case in the Baltic Sea, where nutrient concentrations decrease rapidly offshore, but uptake and turnover processes in the highly eutrophic near-shore areas are not well understood. The Oder and Nemunas Rivers, the second and third largest nitrogen contributors (70 and 45ktNy−1), drain into the Szczecin and Curonian lagoons, respectively, and thus into the coastal waters of the Baltic. In this study, nitrate turnover processes in the coastal zones of the Baltic Sea were determined in March 2009 by measuring nutrient concentrations, nitrate uptake rates, and dual isotopes in nitrate (δ15N-NO3− and δ18O-NO3−) in the lagoon outflows. While mixing processes dominated in the outflow of the Curonian lagoon, a phytoplankton spring bloom largely accounted for the nitrogen processes in the outflow of the Szczecin lagoon. Here, nitrate assimilation in the surface waters was evidenced by a parallel enrichment of 15N and 18O. In the near-bottom waters of the Szczecin lagoon, a deviation from the 1:1 relationship between δ18O-NO3− and δ15N-NO3−, typical of denitrification, suggested the coupling of nitrification and denitrification, triggered by the presence of organic material from the spring bloom. The particulate material may be rapidly sequestered in the sandy sediments off the outflow and generate the isotope signal of nitrate. The highly enriched δ15N-NO3− and δ18O-NO3− values (up to 28‰) in the near-bottom layer implied that the impact of isotopic enrichment from sediment processes in the water column is higher in sandy than in muddy sediments.

ENVIRONMENTAL STUDY OF THE SEASONAL SUCCESSION OF MESOZOOPLANKTON IN A BRACKISH WATER ODRA RIVER ESTUARY DURING 2003–2005

The entire estuary water is dominated by the discharge of the River Odra into the Szczecin Lagoon. The water body is brackish and the salinity in the central part ranges 0.5 and 2 PSU. The Lagoon has a long eutrophication history; usually, two phytoplankton biomass peaks are observed: Diatoms in spring and blue-green algae in summer. The recent data on zooplankton is limited. Rotifers and Cladocerans supply the bulk of the zooplankton biomass. The ichtiofauna is composed of fresh and brackish water, migratory and marine species. Zooplankton and water samples were collected during 2003–2005. The results suggest that during 10 season’s climate in Odra River estuary, Cladocera were the dominant group, large impact on the density of mesozooplankton were: Daphnia cucullata and Daphnia longispina, Copepoda played a lesser role in the Odra River estuary than Cladocera. Biomass of mesozooplankton from the Lagoon was significantly higher compared with the biomass of mesozooplankton from Odra River estuary, which could be related to a greater inflow of nutrients into the Lagoon and the increased growth of phytoplankton, which forms an excellent first stage food web for herbivorous and carnivorous zooplankton, and fish and consequently cormorants.

Variability in the concentrations of Ca, Mg, Sr, Na, and K in the opercula of perch (Perca fluviatilis L.) in relation to the salinity of waters of the Oder Estuary (Poland)

Abstract Macro-ionic composition of fish opercula may be an indicator of the fish stock identity. This is especially interesting in river estuaries, where individual sections of the estuary may differ in terms of their hydrochemical regimes. Diversified macro-ionic tissue composition is likely to provide clues not only about the origin of an individual fish, but also about its possible migration routes. The current study researched this aspect of the chemical composition of perch collected from different sections of the Oder River estuary. A total of 60 European perch, Perca fluviatilis L., were obtained from 3 sampling sites located in the river at Widuchowa, Szczecin Lagoon, and Pomeranian Bay, where waters are subject to dynamic macro-ionic transformations. Fish length ranged from 20 to 25 cm. Opercula of the fish were examined for their content of calcium, magnesium, strontium, sodium, and potassium, with the aid of the flame method using a Perkin-Elmer 3100 atomic absorption spectrophotometer. Perch inhabiting the waters of the Oder River between Widuchowa and Szczecin Lagoon had their opercula composed predominantly of calcium. Calcium was also the predominant ion dissolved in the water in this area; Ca represented 83.6% of all cations in the water and 41.6% of those present in the bones of the perch operculum. The increased levels of salinity near the sea were associated with the replacement of calcium in bones by other, more readily available elements (magnesium or strontium). Differences in the observed macro-ion composition of the opercula were sufficient to assign the perch studied to two distinct groups inhabiting fresh and brackish waters.

The application of a Biopollution Index in German Baltic estuarine and lagoon waters

This paper assesses the status of three German Baltic estuarine and lagoon waters with respect to invasive species (macrozoobenthos) and their impact. A Biological Pollution Index was applied and evaluated. Overall 130 macrozoobenthic species were identified, 17 of which were aquatic alien species. The Szczecin Lagoon had the highest number of invasive species (13). Most species were of Pontocaspian origin; inland waterways are likely to play a significant role in their migration. According to the Biological Pollution Index Level (BPL) this lagoon was ‘moderately influenced’ by invasive species. Warnow Estuary had 11 invasive species; their origin noted generally from North-America, suggesting shipping traffic as the major distribution vector; invasive species had the same BPL as in the Szczecin Lagoon. In the Dars-Zingst-Bodden-Chain only 6 invasive species were observed, having the highest relative abundance (9–71%). Furthermore, this area had the highest BPL of all three areas, i.e. a strong negative impact. The BPL required a lot of data (including historical) and some ratings were subjective and comparisons with other areas assessed were difficult and often impossible. Due to these limitations, it is suggested that the BPL should only be used with restrictions as a universal assessment tool for invasive species in the estuarine and lagoon waters of the Baltic Sea.

Ecology of the Szczecin Lagoon diatom flora with reference to the utility of diatom indices in assessing water quality

Abstract The study focuses on applying the diatom flora to evaluate environmental conditions of the Szczecin Lagoon. A total of 521 taxa (diatom species and varieties) of 74 genera were identified in the samples. Light microscope (LM) counts were processed with OM-NIDIA software to yield diatom indices. The diatom flora structure and relations between assemblages at individual sites were explored with multivariate analyses. Applicability of diatom indices in assessing the state of the Szczecin Lagoon was confirmed. The infer- ences produced by diatom indices were compared with those derivedfrom directly meas- uring physico-chemical water parameters and from using the diatom bioindicative charac-teristics. Diatom indices produced conclusions similar to those resulting from conventional application of diatom bioindicative potential. Both methods showed the Szczecin Lagoon to be eutrophic and moderately polluted. Key index words : Baltic Sea, bioindication, diatom indices, diatoms (Bacillariophyceae), Szczecin Lagoon Introduction Diatoms are commonly believed to be highly sensitive microorganisms, useful in environmental assessment. The presence or absence of certain taxa as well as their development allows to draw conclusions regarding the state of the water mi-lieu. The bioindicative potential of diatoms was explored in numerous studies in which salinity, eutrophication or saprobity was assessed (e.g. Geissler 1982, Geissler & Jahn 1984, Patrick 1984, Cox 1991, Fritz et al. 1991, Dixit et al. 1992, Round 1993, Hofmann 1994). A number of diatom-based environment assessment methods have been developed in recent decades. The methods involve matching certain diatom species of known indicative value to calculate the so-called diatom indices (Descy 1979, Lenoir & Coste 1996, SladeCek 1986, Prygiel et al. 1996, Dell'Uomo 1996, Kelly & Whitton 1995, Watan- abe 1986, Coste & Ayphassorho 1991). As the benthic diatom-based indices are now a major tool in riverine water quality assessment, it

Critical reflections on a systems approach application in practice: a Baltic lagoon case study

This paper contributes to our understanding of the challenges faced when seeking to apply systemic, integration concepts in ‘arenas of practice’. It takes a critical look at the application of the systems-based SPICOSA Project in the region of the Oder (Szczecin) Lagoon, which forms the border between Germany and Poland. The paper highlights a range of place-based and temporal-based factors, which need careful consideration when adopting systems-based approaches to Integrated Coastal Zone Management and makes a series of recommendations for how such approaches might be approved. The experience within the study site was that challenges relating to scale, in one of its many facets, strongly influenced abilities to integrate within the systemic approach. Our view is that cross-scale issues and multi-level challenges can be thought of as one of the dominant factors controlling the successfulness of system approaches to managing complex environments.

Long-term eutrophication history and ecosystem changes in a large Baltic river basin - estuarine system

1 - We apply a spatial integrative approach to analyse the eutrophication history and functional changes of the Odra river basin, the Szczecin Lagoon and its coastal waters in the southern Baltic region (area of about 150,000 km²) between early 1960s and 2000s. For this purpose, a river basin model was linked to a coastal and marine 3D-hydrodynamic ecosystem model. 2 - Annual riverine nutrient loads increase from the 1960s until the mid 1980s to 110,000 t nitrogen (N) and 15,000 t phosphorus (P) and decrease afterwards, but show a strong inter-annual variability. The contribution and location of emission sources in the catchment change significantly during the investigated 40 years. 3 - Nutrient and chlorophyll concentrations in the estuary follow changes in riverine loads quickly. Strong spatial gradients in the estuary are maintained. Nutrient availability, N/P ratios as well as processes like denitrification and N fixation show spatial and temporal changes. 4 - In the lagoon, N fixation does not play an important role and riverine N load reductions are not compensated by increased N fixation. 5 - The lagoon’s quantitative N retention is stable over the 40 years. However, in the early 1960s, about 26% of the total N load into the lagoon is removed by denitrification, compared to only about 15% during 1999–2002. 6 - River basin management measures should focus on a load reduction of P and on N.

Infection of European eel, Anguilla anguilla (L.), with the nematode Anguillicoloides crassus (Kuwahara, Niimi et Itagaki, 1974) in Polish waters

The aim of this study was to determine the degree of Anguillicoloides crassus infection in European eel inhabiting Polish waters based on selected parasitic descriptors and on anatomical pathology of the swimbladder using macroscopic methods. In all, 154 European eel specimens were sampled from eleven sites in Poland and A. crassus was present in the swimbladder of 114 fish. The intensity of A. crassus infection in all the eel specimens ranged from 1 to 62 parasites at a mean value of 7.5. High values of mean infection intensity were noted in samples from Pomeranian lakes Bukowo, Łebsko, and Jamno. The health of the swimbladder was evaluated using the swimbladder degenerative index (SDI). The mean value of the SDI for all of the eel examined was 3.3, and extensively degenerated swimbladders were observed mainly in samples in the Szczecin Lagoon and from lakes. According to the individual SDI ratings, 9.1% of the eel specimens did not exhibit pathological symptoms of the swimbladder (SDI-0) and an extremely damaged (SDI-6) swimbladder was noted in 11.7% of the fish examined. In the case of eel infected with A. crassus, higher SDI values were reflected in initially increasing shares in subsequent categories. In fish that were not infected with the nematode, only 20% (8 individuals) of the swimbladders showed no symptoms of pathology (SDI-0).

Simulation tools to support bathing water quality management: Escherichia coli bacteria in a Baltic lagoon

Insufficient hygienic water quality and bathing prohibitions are still a serious problem in the Szczecin Lagoon (southern Baltic). In our study we focus on the southern lagoon coast and analyse the causes and consequences of high Escherichia coli bacteria concentrations. For this purpose we carry out laboratory experiments on the behaviour of E.coli in the lagoon, a literature review and apply a three-dimensional flow model together with a Lagrangian particle tracking routine. Three major E.coli sources, the Uecker river, the wetlands with cattle as well as sea gulls with bathing and fisheries were allocated, quantified and compiled into an emission scenario. This serves as input for transport simulations under different wind conditions and for the development of a spatial contamination map. Reasons for high E.coli concentrations in the lagoon are a permanent supply from different sources and the special environmental situation in the lagoon. The availability of organic matter, either in form of reed stems or as muddy sediments, has a positive effect on bacteria survival. Very important, too, are the prevailing wind and flow conditions, which cause water and organism transport in narrow ribbons along the coastline and promote near-shore accumulations. Even in our shallow lagoon, the application of a 3D-model is beneficial. Heavy rains are, very likely, responsible for the outstanding high total-coliform concentrations of 11,000 cfu/100 ml on August 21, 2006. The model system proved to be a valuable tool for spatial analysis and is suitable to support the development of bathing water profiles according to the EU Bathing Water Directive (2006/7/EC).

Stable isotope composition of subfossil Cerastoderma glaucum shells from the Szczecin Bay brackish deposits and its palaeogeographical implications (South Baltic Coast, Poland)

The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have been reconstructed on the basis of the stable carbon and oxygen isotope (18O and 13C) analysis and radiocarbon dates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core were well preserved in their life positions, representing a geochemical record of past temperature variation over the middle Holocene. Three major periods with different thermal conditions have been distinguished in the interval ~6000–4300calyr BP, when the important Littorina regional transgression took place. During the first period, 6000–5250calyr BP, water temperature decreased by 1.4°C, and then remained constant over the second period (5250–4750calyr BP). In contrast, during the third period (4750–4300calyr BP) both δ-values were highly variable and the mean summer temperature (March–November) increased by about 3.5°C. During first two periods, δ18O and δ13C were significantly correlated, indicating stability of the environmental conditions.

Zebra Mussel Farming in the Szczecin (Oder) Lagoon: Water-Quality Objectives and Cost-Effectiveness

The Oder (Szczecin) Lagoon in the southern Baltic Sea is a heavily eutrophicated and degraded coastal ecosystem. We applied a systems approach framework to critically evaluate whether existing water-management measures achieve waterquality objectives for the river and lagoon systems. Our simulations reveal that the existing water-quality objectives for the river and the coastal waters are not sufficiently complementary. We suggest new water-quality threshold concentrations, which are in agreement with the European Water Framework Directive, and we calculate acceptable maximum nutrient loads for the Oder River. These calculations suggest that external nutrient-load reductions in the river basin alone seem insufficient to achieve good water quality in the lagoon. A comprehensive eutrophication management approach should also include internal nutrientretention and nutrient-removal measures in the lagoon. We focus on mussel farming, i.e., that of zebra mussels, Dreissena polymorpha, because they are efficient in removing nutrients and improving water transparency in the Oder Lagoon. For this purpose, the ecosystem model ERGOM is extended by a mussel module and an economic model. The economic model describes costs and benefits of mussel cultivation depending on the the farm size. We included additional potential sources of income such as water-quality tax or emission certificates. The simulations show that mussel farming in the lagoon is a suitable supportive measure and, at a load-reduction target of 50% or more, it is a cost-efficient measure for removing nutrients and for implementing the Baltic Sea Action Plan. In the Oder Lagoon, mussel farming could potentially remove nearly 1000 t of N (70 t of P)/year, or about 2% of the present N and P loads, and it would have the additional benefit of improving water transparency.

Periphyton dry mass, ash content, and chlorophyll content on natural substrata in three water bodies of different trophy

Abstract Periphyton communities were studied on several dominating macrophytes, Phragmites australis, Potamogeton lucens, and Nuphar lutea, in three different types of lakes. In soft-water mesotrophic Lake Mały Borek and in shallow, eutrophic Lake Gardno samples were collected about once every two months from April to November 2009. In eutrophic Szczecin Lagoon (the estuary of the Oder River), samples were only collected once in July. The aim of this paper was to determine the dry mass, the ash content, and the chlorophyll-a content of periphyton on a natural substratum, in order to determine the mass, the inorganicorganic status of periphyton, and the auto-heterotrophic character of this complex. The analyzed periphytic communities exhibited low dry mass at the beginning of the growth season, which increased with colonization period on the aquatic vegetation. The highest (but still low) values were achieved in autumn, which persisted, with small loss, until spring of the subsequent year. The differences in dry mass between each type of lake were small, but in the strongly eutrophic Szczecin Lagoon this index was slightly higher than in the other two water bodies. The highest dry mass was noted for periphyton dominated by Cordylophora caspia colonies overgrowing common reeds and for periphyton on Potamogeton lucens in Szczecin Lagoon. In shallow water bodies, such as Lake Gardno and Szczecin Lagoon, wind causes strong resuspension of sediments. This can explain the relatively high level of inorganic matter in dry mass of the periphyton in both water bodies. However, the small ash content in periphyton in Mały Borek may result from the soft-water character of this lake. The hetero-autotrophic status of the periphytic community prevailed throughout the study period in Gardno and Mały Borek lakes. The auto-heterotrophic status of periphyton was noted only in short periods of time in each lake.

New and ‘visiting’ fish species collected off the western coast of Poland (Baltic Sea) in 2007–2008 with a description of their parasite fauna

The first occurrence of striped red mullet Mullus surmuletus in the Pomeranian Bay (in 2007) and the occurrence of three very rarely noted species (tub gurnard Chelidonichthys lucerna, Atlantic horse mackerel Trachurus trachurus, thicklip grey mullet Chelon labrosus) collected in 2007–2008 in the Pomeranian Bay, Szczecin Lagoon and Lake Dąbie are reported. Their expansion is probably due to increased sea temperatures resulting from climate change, as well as the inflow of saline water. The ‘visitors’ hosted eight pathogens from four taxonomic groups: Protozoa, Nematoda, Acanthocephala and Mollusca. Nematodes, the most numerous ones, were found in three host species. All the parasite species were new for the hosts examined; only the larvae of the acanthocephalan Corynosoma strumosum had already been recorded in one of the hosts (Chelidonichthys lucerna). The stomachs of almost all the fish examined were empty, but the species composition of the parasite fauna found showed that the fish must have ingested some food in the Pomeranian Bay.

Holocene marine ingressions in the coastal zone of the pomeranian bay based on radiocarbon assays

Abstract In recent years, a team at the Geology and Paleogeography Unit, Marine Sciences Institute, University of Szczecin, has been performing geological, geochronological and paleogeographic surveys in (i) the Szczecin Lagoon and Świna Gate Sandbar and (ii) the estuary section of the Rega river valley near Mrzeżyno. These studies have helped to examine and identify not only the distribution of fossil marine sediments but also their lithological and sedimentological characteristics. The age of marine ingressions and regressions in the coastal zone of the Pomeranian Bay were determined using approximately 170 radiocarbon assays. It was found that the marine ingression associated with the ‘Littorina transgression’ was not synchronous at these two areas. It started earlier in the Mrzeżyno area, ca. 8300-8200 cal BP. In that first phase, marine sediments developed as tightly packed sands containing a few fragments of shells. In several profiles, these deposits were separated from the bottom and top with layers of peat, thus allowing an indirect determination of their age. The next phase of ingression began about 7300 cal BP. These younger marine sediments already contained quite numerous shells of marine malacofauna, especially Cardium glaucum, often found in a life position. In the area of the Szczecin Lagoon and Swina Gate Sandbar, the oldest marine ingression started as early as about 7350 cal BP. The quite clear trace is a considerably thicker series of marine sands with numerous sea shells representing marine and brackish-marine environments, including Cardium glaucum shells in a life position, which made it possible to identify the age and the rate of accumulation of marine sands.

The variability in concentrations of chosen nitrogen and phosphorus forms in the Oder River estuary in 1999-2002

Abstract The Oder River creates one of the largest estuaries in Poland. The estuary can be divided into three zones, each with a different hydrochemical regime: the Pomeranian Bay (salt water habitat), the Szczecin Lagoon (brackish water habitat), the Oder River up to the Widuchowa section (transitional environment - brackish and typical freshwater). The Pomeranian Bay was characterized by the lowest concentration of nutrients throughout the research series in comparison to the other regions. It had a low nitrogen to phosphorus proportion and the highest stability of variability in total nitrogen concentration. The Szczecin Lagoon was characterized by a higher concentration of nutrient loads in comparison to the Pomeranian Bay, by a lower nitrogen and phosphorus proportion than the Oder waters, and by the high stability of variability of concentrations of mineral nitrogen and total nitrogen. As the "nutrient trap" for the Oder estuarine system, the Oder River, with its highest nutrient concentration, is characterized by the highest stability of variability of total nitrogen concentration.

Nitrogen retention in the Szczecin Lagoon, Baltic Sea

Nitrogen (N) retention and transformation in the Szczecin Lagoon, southern Baltic Sea, were studied by means of budget calculations and stable isotope data of dissolved and particulate matter. Two stations, one located at the main outlet of the lagoon (Świna Strait) and the other 100 km to the south, on the Oder River (Widuchowa), were sampled biweekly over the years 2000–2002. The Oder River is one of the five largest rivers draining into the Baltic Sea and the largest one discharging its waters into the western Baltic. According to our data, the Oder River carried approximately 60 kt y−1 total N, of which 7 kt y−1 (<12 %) are particulate organic nitrogen and 46 kt y−1 (77 %) dissolved inorganic nitrogen. Seasonal patterns of particulate nitrogen and nitrate concentrations were similar at Widuchowa and Świna Strait station, but nitrate concentrations in the Świna Strait were much lower, pointing not only to the dilution effect but also to considerable nutrient removal capacity (especially of nitrate) in the lagoon. The loss of nitrate suggests that denitrification is the major N-removal process, whereas primary production was only a minor contributor, due to the very low particle load. Combining budget calculations with stable isotope measurements reveal unique information about nitrogen turnover processes in the lagoon.