Oder Estuary Research Articles

Brown trout in Oder estuary tributaries: genetic structure, stocking, and admixture.

Several rivers that are tributaries of the Oder estuary are inhabited by Salmo trutta L, the most important of which are Ina, Gowienica, and Wołczenica. Both forms of the species, sea trout and resident brown trout, are present. All rivers are traditionally stocked with either sea trout from the neighboring Pomeranian river Rega basin or resident brown trout from various locations. To examine populations in these rivers in terms of genetic structure, genetic diversity, and origin, they were analyzed using 13 microsatellite loci. Relatedness was also assessed for fish stocked in the same year. The obtained genotypes were compared with breeding stocks used for stocking in Poland. The analyses revealed a significant genetic distance between adult individuals from Ina and Rega Rivers and fish caught during electrofishing. Strong kinship relationships were identified in the sampled areas, with high proportions of fish originating from stocking and their dominance in numbers over wild juveniles, primarily in smaller tributaries. Additionally, clear separation in the origin of stocked individuals was observed. Adult trout from Ina and Rega are genetically closer to northern brown trout lineages, providing crucial information for the management and biodiversity conservation of Polish Salmo trutta populations.

Effects of contamination and warming on ragworms Hediste diversicolor: A laboratory experiment with Oder estuary sediments

Knowledge about the effects of sediment contamination on estuarine benthos has come mainly from observational studies and spiking experiments. There is a lack of experimental studies with field-contaminated sediments, especially those assessing the combined effects of contamination and other environmental stressors. Here we investigated the biomarker responses of ragworms Hediste diversicolor to contaminated sediments and warming. Ragworms were exposed to sediments with different contamination levels from the Oder estuary (German-Polish border) at 10 and 20 °C for three weeks. The most contaminated sediments induced dicarbonyl stress, but did not result in enhanced detoxification, significant oxidative stress, or impaired energy balance. Warming altered antioxidant defense in ragworms and increased their energy reserves. The effects of contamination and warming were generally mild, and the interactive effects were absent. This study suggests the relatively high resilience of H. diversicolor to multiple stressors.

Morphometrics, Growth and Condition of the Invasive Bivalve Rangia cuneata during Colonisation of the Oder Estuary (North-Western Poland)

The aim of this study was to determine the biological, morphometric, and shape characteristics of the bivalve Rangia cuneata in the initial phase of colonisation. A total of 504 specimens were caught for the study. Their average length was 31.06 mm (range 12.7–43.2 mm) and weight 6.0 g (0.5–15.3 g). The population was dominated by individuals of 25–30 mm and 30–35 mm in length and the age of 3+ and 4+. The standard major axis regression for measurable traits describing shell cross-section indicate the allometric nature of growth for most parameters. Elongation and convexity indices by age group indicate a change in the shell shape as it becomes more elongated and convex in individuals that have already reached sexual maturity. The collected specimens were of larger sizes compared to other Baltic populations of the species, and similar in size to populations found in the neighboring Pomeranian Bay. The increase in length of R. cuneata in the Oder estuary is smaller compared to the species native sites, probably due to the lower water temperature in the study area. Considering the invasive potential of R. cuneata, it seems necessary to monitor closely its population and distribution in the estuary of Western Baltic.

Habitat Conditions of the Microbiota in Ballast Water of Ships Entering the Oder Estuary.

Ballast water is a vector for the transfer of microorganisms between ecospheres that can subsequently have a negative impact on native species of aquatic fauna. In this study, we determined the microbiota and selected physicochemical properties of ballast water from long- and short-range ships entering a southern Baltic port within a large estuary in autumn and winter (Police, Poland). Microbiological tests of the ballast water samples were carried out according to ISO 6887-1, and physicochemical tests were performed according to standard methods. Low amounts of oxygen (1.6-3.10 mg/dm3 in autumn and 0.60-2.10 mg/dm3 in winter) were recorded in all ship ballast water samples, with pH (above 7.90) and PSU (above 1.20) were higher than in the port waters. Yeast, mold, Pseudomonas bacteria (including Pseudomonas fluorescens), and halophilic bacteria as well as lipolytic, amylolytic, and proteolytic bacteria were found in the ballast water samples. Heterotrophic bacteria and mold fungi (log. 2.45-3.26) dominated in the autumn period, while Pseudomonas bacteria (log. 3.32-4.40) dominated in the winter period. In addition, the ballast water samples taken during the autumn period were characterized by a statistically significantly higher (p < 0.1) abundance of microorganisms (log 1.97-2.55) than in the winter period (log 1.39-2.27).

Shell morphology, growth and longevity of Unio tumidus (Bivalvia: Unionidae) from an archaeological site and contemporary population inhabiting the Oder estuary

Mussel shells are often found in archaeological excavations and can provide information useful for ecological reconstruction and assessment of anthropogenic impact on waters. In this study, two sample groups of swollen river mussel (Unio tumidus) which occurred during the Early Middle Ages (EMS) and currently (MS) in the Oder river estuary (Baltic basin) were compared. Allometric shell growth, morphological characteristics of the shell (length, width, height and thickness), age structure and growth of mussels were analysed using the von Bertalanffy equation. All three types of allometric growth (isometry and both positive and negative allometry) were observed in the studied mussels. In both groups, typical values of shell length, width, height and thickness were recorded. However, higher values of these morphological characteristics were recorded in the EMS group. Moreover, the EMS group, compared with the MS group of U. tumidus, was characterised by a higher longevity (12 and 10 years, respectively) and asymmetric length (L∞) (93.09 and 83.23 mm, respectively). Both groups of mussels had a similar growth rate (k). Larger shell sizes in the EMS group were probably caused by differential preservation and/or differential archaeological recovery, and resulted from differences in the age structure, especially higher mortality rate amongst individuals older than 6 years in the MS group.

Species richness and the diversity of parasite communities of eelpout Zoarces viviparus (Linnaeus, 1758) in the Oder River estuary, Poland

Abstract A parasitological study was carried out on 330 eelpouts from two fishing grounds of the Polish fishing zone off the Oder estuary (Pomeranian Bay and Dziwna Mouth). A total of 11 species and genera of parasites from six higher taxa were recorded: 1 monogenean, 1 digenean, 5 nematodes (eelpout was a new host for Ascarophis morhuae and Capillaria gracilis), 2 acanthocephalans, 1 mollusk and 1 protist (a fungus-related pathogen). A total of 4284 autogenic countable parasites were identified. These included parasites of eight species and two genera (six higher taxa) from Pomeranian Bay, and five species (two higher taxa) from the Dziwna Mouth. The abundance of parasites per host was higher in fish from the Dziwna Mouth, while the parasitic biodiversity index was almost two times lower than in Pomeranian Bay. Pomphorhynchus laevis dominated among the eelpout parasites in both fishing grounds, but the parasite communities from the Dziwna Mouth consisted of a larger number of dominating classes. The high intensity of infection of Hysterothylacium auctum and the relative density affect more the dimensions of the dominant parasite (P. laevis) in the Dziwna Mouth than the crowding of parasites. Infection by more abundant large parasites have an important influence on the value of Fulton’s coefficient.

PHYSIOGRAPHIC EVALUATION OF SESSILE AND MOBILE FAUNA IN THE ODER ESTUARY

An attempt was made initial classification of invertebrate fauna habitats in the Oder estuary. Comprehensive analysis of differences in taxonomic composition and physicochemical factors permitted delineating three characteristic zones: brackish waters; fresh lotic lagoon waters; bay-lake waters. In the first zone of brackish waters, the epiphyte assemblages were characterized by the highest biocenotic index values, which is evidence of high biodiversity that is influenced by the occurrence of both brackish-water and freshwater species. The freshwater lotic lagoon sites were characterized by the greatest number of taxons, especially by representatives of Insecta and Gastropoda. Amphipoda also occurred abundantly, and

First record of the round goby Neogobius melanostomus (Pallas, 1814) in the lower River Oder, Germany

In September 2013, the non-native round goby Neogobius melanostomus was found for the first time in the River Oder, Germany, about 58 km upstream of the Szczecin Lagoon (Zalew Szczecinski). Seven specimens were caught at river kilometre 703.5 near Friedrichsthal (53°08'24.29N, 14°23'03.59E) during the regular fish monitoring program for the Water Framework Directive. This record is especially important because i) it represents a very early stage of the invasion process, a round goby invasion front, and ii) it potentially reflects the natural dispersal ability of the species. The latter was concluded from the time lag of about 15 years between the first occurrence of round goby in the Baltic Sea in front of the River Oder estuary in 1998, in the German part of the Szczecin Lagoon (River Oder estuary) in 2003, its subsequent establishment in the Szczecin Lagoon in 2006, and its upstream migration observed in 2013. The slow average migration speed of 3.9 km per year might correspond to natural dispersal.

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.

SHORT COMMUNICATION. Rapid establishment of the alien crabRhithropanopeus harrisii(Gould) in the Gulf of Riga

INTRODUCTION Owing to its low salinity and short evolutionary history, the Baltic Sea virtually lacks native top predatory crabs. This contrasts to true oceanic waters where crabs constitute an essential element of the nearshore benthic ecosystems (e.g. Lee, 1998). To date, the only 'iconic' species in the Baltic Sea range is the Chinese mitten crab Eriocheir sinensis (H. Milne-Edwards). Despite occasional findings of this invasive species all over the coastal Baltic Sea, the reproduction of the mitten crab in the central, northern, and eastern Baltic regions is considered unlikely due to the low salinity, and the individuals caught are assumed to have actively migrated into the region over 1500 km distance (Ojaveer et al., 2007). However, the Baltic Sea also hosts the Harris mud crab Rhithropanopeus harrisii (Gould) (Fig. 1). This species has a native distribution from New Brunswick (Canada) to Veracruz (Mexico). In Europe the invasive species was first found in 1874 in the Netherlands, in the Baltic Sea area it was first observed in 1936 (Nikolaev, 1951). In contrast to E. sinensis, the mud crab is capable of reproducing in the diluted Baltic Sea and can form high-density populations (Maiju Lehtiniemi, pers. comm.); thus, it may exert strong pressure on the local benthic macrophyte and invertebrate communities. Despite its long invasion history, until very recently the distribution of R. harrisii was confined to Mecklenburg Bay, the Oder Estuary, the Gulf of Gdansk, and the Curonian Lagoon only (Jazdzewski & Konopacka, 1993; Bacevicius & Gasiunaite, 2008; Czerniejewski, 2009; Jazdzewski & Grabowski, 2011). Seemingly, R. harrisii has a large between population variability in Europe with more recent populations showing a tendency for increased genetic diversity (Projecto-Garcia et al., 2010). This suggests that R. harrisii is still in the process of expansion in Europe and its sudden northwards expansion seems to be a result of new introductions. In this study we report the sudden expansion of this alien invasive species over 500 km northwards and provide information on its distribution. [FIGURE 1 OMITTED] MATERIAL AND METHODS Crabs are not systematically monitored in the Estonian coastal sea. Nevertheless, since 1995 the Estonian National Monitoring Programme surveys benthic macrophytes and the associated invertebrates around the whole Estonian coastal range. In addition, the programme also surveys pelagic communities. The phytobenthos and zooplankton sampling and sample analysis follow the guidelines developed for the HELCOM COMBINE programme (HELCOM, 2012). Although not specifically targeted towards large and mobile invertebrates, the national monitoring programme is potentially capable of sighting the mud crab both in benthic and pelagic ecosystems. In addition, there is another local long-term activity that provides semiquantitative data on crabs. Specifically, this is done through the provision of artificial spawning substrata for the commercially valuable fish pike-perch in Parnu Bay. This activity was started already in the late 1980s and has been done every year since then. Most of these artificial spawning substrata consist of linen gillnets of small mesh size. Such substratum may also provide a suitable habitat for the Harris mud crab and, therefore, may provide occurrence information on the species. These artificial spawning substrata were checked for the mud crab occurrence in 2011-2012, also with SCUBA diving, which was also performed in several additional localities in Parnu Bay to map the distribution of the species. Finally, owing to good long-term relations with local professional fishermen, several occurrence data on the crab were obtained from them. RESULTS AND DISCUSSION The Harris mud crab R. harrisii was first found in the Estonian waters in August 2011. Seven individuals were found in three deployed lines of pike-perch artificial spawning substrata at the northern coast of Parnu Bay (NE Gulf of Riga) (Fig. …

An integrated river basin-coast-sea modelling scenario for nitrogen management in coastal waters

Linked river basin and coastal water models were applied to analyse the effects of an optimal nitrogen management scenario in the Oder/Odra river basin on water quality in the Oder (Szczecin) Lagoon and the Pomeranian Bay (Baltic Sea). This scenario would reduce nitrogen loads into the coastal waters by about 35%, a level which is similar to the load of the late 1960’s. During summer the primary production and algae biomass in the Oder estuary is limited by nitrogen, which makes a nitrogen management reasonable. The comparison of the late 1960’s and the mid 1990’s shows that an optimal nitrogen management has positive effects on coastal water quality and algae biomass. However, this realistic nitrogen reduction scenario would not ensure a good coastal water quality according to the European Water Framework Directive. A good water quality in the river will not be sufficient to ensure a good water quality in the lagoon. Nitrogen load reductions bear the risk of increased potentially toxic, blue-green algae blooms, especially in the Baltic coastal sea. However, to reach water quality improvements in lagoons and inner coastal waters, nitrogen cuts are necessary. A mere focus on phosphorus is not sufficient.

Heavy-metal pollution of sediments from the Polish exclusive economic zone, southern Baltic Sea

Analysis of 59 surface sediment samples from the Polish exclusive economic zone (EEZ) shows that Szczecin Lagoon sediments are the most polluted by heavy metals and that the degree of heavy-metal pollution decreases substantially on passing from the Szczecin Lagoon to the Pomeranian Bay and the inner shelf area and then on passing to the Bornholm Deep and Slupsk Furrow. Heavy-metal pollution in the sediments of the western part of the Polish EEZ therefore appears to follow the dispersion of the Oder River. Fluffy material from the Oder estuary appears to be the main source of heavy metals in the muddy sediments of the Bornholm Deep. The formation of sulphides is therefore not the principal factor controlling the enrichment of heavy metals in the sediments of this anoxic basin, although it may be responsible for the uptake of Mo, Sb and As. Two main factors control the distribution of the rare earth elements (REE) in sediments of the Polish EEZ: the input of Fe-organic colloids from rivers and the presence of detrital material in the sediments.

Silicon dynamics in the Oder estuary, Baltic Sea

Studies on dissolved silicate (DSi) and biogenic silica (BSi) dynamics were carried out in the Oder estuary, Baltic Sea in 2000–2005. The Oder estuary proved to be an important component of the Oder River–Baltic Sea continuum where very intensive seasonal DSi uptake during spring and autumn, but also BSi regeneration during summer take place. Owing to the regeneration process annual DSi patterns in the river and the estuary distinctly differed; the annual patterns of DSi in the estuary showed two maxima and two minima in contrast to one maximum- and one minimum-pattern in the Oder River. DSi concentrations in the river and in the estuary were highest in winter (200–250 μmol dm − 3 ) and lowest (often less than 1 μmol dm − 3 ) in spring, concomitant with diatom growth; such low values are known to be limiting for new diatom growth. Secondary DSi summer peaks at the estuary exit exceeded 100 μmol dm − 3 , and these maxima were followed by autumn minima coinciding with the autumn diatom bloom. Seasonal peaks in BSi concentrations (ca. 100 μmol dm − 3 ) occurred during the spring diatom bloom in the Oder River. Mass balance calculations of DSi and BSi showed that DSi + BSi import to the estuary over a two year period was 103.2 kt and that can be compared with the DSi export of 98.5 kt. The difference between these numbers gives room for ca. 2.5 kt BSi to be annually exported to the Baltic Sea. Sediment cores studies point to BSi annual accumulation on the level of 2.5 kt BSi. BSi import to the estuary is on the level of ca. 10.5 kt, thus ca. 5 kt of BSi is annually converted into the DSi, increasing the pool of DSi that leaves the system. BSi concentrations being ca. 2 times higher at the estuary entrance than at its exit remain in a good agreement with the DSi and BSi budgeting presented in the paper.

Trace element diagenesis in pyrite-rich sediments of the Achterwasser lagoon, SW Baltic Sea

The early diagenesis of trace elements (V, Cr, Co, Cu, Zn, As, Cd, Ba, U) in anoxic sediments of the Achterwasser, a shallow lagoon in the non-tidal Oder estuary in the Baltic Sea, was investigated in the context of pyrite formation. The dissolved major redox parameters show a two-tier distribution with transient signals in the occasionally re-suspended fluid mud layer (FM) and a permanently established diagenetic sequence in the sediment below. Intense microbial respiration leads to rapid depletion of O 2 within the uppermost mm of the FM. The reduction zones of Mn, Fe and sulfate overlap in the FM and in the permanently anoxic sediment section which appears to be a typical feature of estuarine sediments, under low-sulfate conditions. Degrees of pyritization (DOP) range from 50% in the FM to remarkably high values > 90% at 50 cm depth. Pyrite formation at the sediment surface is attributed to the reaction of Fe-monosulfides with intermediate sulfur species via the polysulfide pathway. By contrast, intense pyritization in the permanently anoxic sediment below is attributed to mineral growth via adsorption of aqueous Fe-sulfide complexes onto pyrite crystals which had originally formed in the surface layer. The studied trace elements show differential behavior patterns which are closely coupled to the diagenetic processes described above: (i) Zn, Cu and Cd are liberated from organic matter in the thin oxic layer of the sediment and diffuse both upwards across the sediment/water boundary and downwards to be trapped as monosulfides, (ii) V, Cr, Co and As are released during reductive dissolution of Mn- and Fe-oxyhydroxides, (iii) U removal from pore water occurs concomitantly to Fe reduction in the FM and is attributed to reduction of U(VI) to U(IV), (iv) the Ba distribution is controlled by reductive dissolution of authigenic barite in the sulfate reduction zone coupled with upward diffusion and re-precipitation. The incorporation of trace elements into pyrite is most intense for Co, Mn and As, intermediate for Cu and Cr and little to negligible for U, Zn, Cd, V and Ba. The observed trend is largely in agreement with previous studies and may be explained with differing rates for ligand exchange. Slow and fast ligand exchange and thus precipitation kinetics are also displayed by downcore increasing (Mn, Cr, Co and As) or constantly low (Zn, Cu, Cd) pore water concentrations. The downward increasing degrees of trace metal pyritization (DTMP) for Co, Cu, Zn and As are, in analogy to pyrite growth, assigned to adsorption of sulfide complexes or As oxyanions onto preexisting pyrite minerals.

Hydrological Forecasting in the Oder Estuary using a Three- Dimensional Hydrodynamic Model

A three-dimensional operational hydrodynamic model, developed at the Institute of Oceanography, University of Gdansk was used to forecast hydrological conditions in the Oder Estuary. The model was based on the coastal ocean circulation model known as the Princeton Ocean Model (POM). Because of wind-driven water backup in the Oder mouth, a simplified operational model of river discharge, based on water budget in a stream channel, was developed. Linking these two models into a single system made it possible to forecast water levels, currents, water temperature, and salinity in the estuary. A good fit between the observed and computed data allowed to consider the model as a reliable environmental tool. Obtaining a hydrological forecast via a quick website access gives potential users an opportunity to predict the day-by-day course of processes that may affect different areas of human life and activities, e.g., navigation, port operations, flood protection of coastal areas; the predictions may also be used in studies of coastal processes in the estuary.

Operational hydrodynamic model for forecasting extreme hydrographic events in the Oder Estuary

A 3D operational hydrodynamic model, developed at the Institute of Oceanography, University of Gdansk, was used to forecast extreme hydrographic events in the Oder Estuary. The model was based on the coastal ocean circulation model known as the Princeton Ocean Model (POM); it was adapted to Baltic conditions and to a 48-h numerical meteorological forecast. Wind-driven water backup in the Oder mouth necessitated working out a simplified operational model of river discharge, based on water budget in a stream channel. The model generates 60-h forecasts of water levels, currents, water temperature and salinity in the estuary. As the model adequately approximates hydrographic variability in the estuary, it can be regarded as a reliable tool for storm surges forecasting and for the assessment of Oder water spread in the Baltic. The forecast is rapidly accessed on its designated website, thereby providing assistance in decision-making by emergency situation centres and bodies that are responsible for navigation safety, port operation and environmental and flood protection of coastal areas. It is intended to fine-tune the model so that a better fit between the observed and computed data is obtained.

Intense pyrite formation under low-sulfate conditions in the Achterwasser lagoon, SW Baltic Sea

In comparison to similar low-sulfate coastal environments with anoxic-sulfidic sediments, the Achterwasser lagoon, which is part of the Oder estuary in the SW Baltic Sea, reveals unexpectedly high pyrite concentrations of up to 7.5 wt%. Pyrite occurs mainly as framboidal grains variable in size with diameters between 1 and 20 μm. Pyritization is not uniform down to the investigated sediment depth of 50 cm. The consumption of reactive-Fe is most efficient in the upper 20 cm of the sediment column, leading to degrees of pyritization (DOP) as high as 80 to 95%. Sediment accumulation in the Achterwasser takes place in high productivity waters. The content of organic carbon reaches values of up to 10 wt%, indicating that pyrite formation is not limited by the availability of organic matter. Although dissolved sulfate concentration is relatively low (<2 mmol/L) in the Achterwasser, the presence of H 2S in the pore water suggests that sulfate is unlikely to limit pyrite authigenesis. The lack of free Fe(II) in the pore waters combined with the possibility of a very efficient transformation of Fe-monosulfides to pyrite near the sediment/water interface suggests that pyrite formation is rather controlled by (i) the availability of reactive-Fe, which limits the FeS formation, and by (ii) the availability of an oxidant, which limits the transformation of FeS into pyrite. The ultimate source for reactive-Fe is the river Oder, which provides a high portion of reactive-Fe (∼65% of the total-Fe) in the form of suspended particulate matter. The surficial sediments of the Achterwasser are reduced, but are subject to oxidation from the overlying water by resuspension. Oxidation of the sediments produces sulfur species with oxidation states intermediate between sulfide and sulfate (e.g., thiosulfate and polysulfides), which transform FeS to FeS 2 at a significant rate. This process of FeS-recycling is suggested to be responsible for the formation of pyrite in high concentrations near the sediment surface, with DOP values between 80 and 95% even under low sulfate conditions. A postdepositional sulfidization takes place in the deeper part of the sediment column, at ∼22 cm depth, where the downward diffusion of H 2S is balanced by the upward migration of Fe(II). The vertical fluctuation of the diffusion front intensifies the pyritization of sediments. We suggest that the processes described may occur preferentially in shallow water lagoons with average net-sedimentation rates close to zero. Such environments are prone to surficial sediment resuspension, initiating oxidation of Fe-sulfides near the sediment/water interface. Subsequent FeS 2 formation as well as postdepositional sulfidization leads to a major pyrite spike at depth within the sediment profile.

Role of the Oder estuary (southern Baltic) in transformation of the riverine nutrient loads

Role of the Oder estuary (lagoon type) in transformation of the nutrient loads was estimated through water, salt, N, and P mass budget calculations made for the period 1993–1998. Annual mean net export to the open Baltic Sea was estimated at 39 kt year − 1 for total nitrogen (TN) and 3.1 kt year − 1 for total phosphorus (TP). That means that nearly half of TN and 1/3 of TP loads reported for the Oder River were retained in the estuary. Nutrient retention was greatly diversified in the Oder estuarine system, with its inland part playing a key role; almost 85% of TN retention and 72% of TP retention took place there. Lack of DIP retention pointed to balanced assimilation and regeneration processes. In consequence, net ecosystem production (NEP) was also close to zero. The major sink for nitrogen was denitrification in excess to nitrogen fixation (Den-Nfix). Den-Nfix, estimated on stoichiometric basis, amounted to 25 kt year − 1 and that constituted 70% of the TN retained. Its intensity was four times higher in the inland (ca. 19 g N m − 2 year − 1 ) than in the marine part of the estuary (ca. 5 g N m − 2 year − 1 ).

Nutrient dynamics in the Pomeranian Bay (southern Baltic): Impact of the Oder River outflow

The Pomeranian Bay is a coastal region fed by the Oder River, one of the seven largest Baltic rivers, whose waters flow through a large and complex estuarine system before entering the bay. Nutrients (NO3−, NO2−, NH4+, Ntot, PO43−, Ptot, DSi), chlorophylla concentrations, oxygen content, salinity, and temperature were measured in the Pomeranian Bay in nine seasonally distributed cruises during 1993–1997. Strong spatial and temporal patterns were observed and they were governed by: the seasonally variable riverine water-nutrient discharges, the seasonally variable uptake of nutrients and their cycling in the river estuary and the Bay, the character of water exchange between the Pomeranian Bay and the Szczecin Lagoon, and the water flow patterns in the Bay that are dominated by wind-driven circulation. Easterly winds resulted in water and nutrient transport along the German coastline, while westerly winds confined the nutrient rich riverine waters to the Polish coast and transported them eastward beyond the study area. Two water masses, coastal and open, characterized by different chemical and physical parameters and chla content were found in the Bay independently of the season. The role of the Oder estuary in nutrient transformation, as well as the role of temperature in transformation processes is stressed in the paper. The DIN:DIP:DSi ratio indicated that phosphorus most probably played a limiting role in phytoplankton production in the Bay in spring, while nitrogen did the same in summer. During the spring bloom, predominated by diatoms, the DSi:DIN ratio dropped to 0.1 in the coastal waters and to 0.6 in the open bay waters, pointing to silicon limitation of diatom growth, similar to what is being observed in other Baltic regions.

Eutrophication Of The Shallow Szczecin Lagoon (Baltic Sea): Modelling,Management And The Impact Of Weather

The Oder estuary, especially the large, shallow Szczecin (Oder) Lagoon (687 km2, average depth 3.8 m) suffers from severe and ongoing eutrophication due to heavy loads, mainly by the Oder river. Poor water quality nowadays is a main obstacle for further touristic development around the lagoon. Long-term nutrient concentrations show a high interannual variability and a decline during recent years. Using a simple eutrophication box model and comparing dry, warm years (1989-1991) with colder, wet years (1986-1988) we analyse the impact of interannual and short-term weather conditions on the eutrophication process. Internal nutrient cycling processes in the lagoon are mainly driven by shortterm weather conditions. During rare and short calm summer periods a stratification and oxygen depletion above the sediment is likely. Coarse model-based estimations indicate an anoxic P-release from sediments of up to 10 μmol P md or up to 400-600 t P for the entire lagoon. These situations are restricted to several days and occur only in a few years. Wind with a daily average velocity above 2-3 m/s cause mixing and put an end to anoxic P-release. Compared to a monthly summer load of 100-150 t P by the Oder river, internal eutrophication in the lagoon is important, but has no pronounced effect on biology. In wet years the P and N load with the Oder river can be up to twice as high compared to dry years. Discharge and load by rivers control the nutrient dynamic in the Szczecin Lagoon, to a high degree. The observed reduction in nutrient concentrations in early 90’s is an effect of the warm, dry years and cannot be attributed to anthropogenic nutrient load reductions. Management implications are discussed. 1 Problems and management challenges in the Oder estuary The large Oder-catchments is located at the German-Polish border. With a surface area of 120,000 km and a population of about 13 Mio inhabitants it is responsible for the heavy nitrogen and phosphorous load of the Oder river. In recent years, about 63,000 t total N/a and 3,500 t total P/a were transported with the Oder towards the Baltic Sea. The river therefore is the most important source of eutrophication and pollution for the south-western Baltic Sea. The respective coastal zones, especially the Szczecin (Oder) Lagoon, suffer from severe eutrophication, heavy algal blooms of potentially toxic species, high water turbidity and even hygienic quality problems [1]. The Szczecin Lagoon is a key element of the Oder river estuary. It is a large (687 km2) and shallow (average depth 3.8 m) coastal flow lake. The lagoon consists of two main parts Kleines Haff on the German side and Wielki Zalew located on Polish territory (Fig. 1). The Wielki Zalew comprises about 60 % of the lagoon area and volume. A theoretical water exchange time of the entire water body is about 2 months, but its western part (Kleines Haff) receives only between 10 % and 20 % of the Oder water [2]. Germany Sweden Finland Poland Germany Poland Dziwna