Northern Baltic Sea Research Articles

Impact of Farming System on Potato Yield and Tuber Quality in Northern Baltic Sea Climate Conditions

For finding more sustainable cropping systems, this study on how the farming system influences the yield and quality of potato tubers was carried out with long-term crop rotation experiment. The long-term five-field crop rotation field trial was established with the following farming system treatments: organic farming system treatments: Org I (organic control), Org II (organic crop rotation with winter cover crops) and Org III (organic crop rotation with winter cover crops and the addition of composted cattle manure); conventional farming system treatments: N0 (conventional system without fertilizers), N50 (conventional system with fertilization, N50P25K95), N100 (conventional system, N100P25K95) and N150 (conventional system, N150P25K95). The average yield (based on 3 trial years) of conventional systems was 25% higher, compared to organic systems. However, in organic systems, the yield was the most stable. The most fluctuating cropping system was the most intensively managed N150. In each trial year, the yield differed statistically and it varied from 4.7 t ha−1 up to 10.9 t ha−1. Org I had the same dry matter yield as the N0 system, where chemicals were used, meaning that using chemicals for plant protection but no fertilizer for growth improvement had no positive effect. In each year, the yield in Org III system was similar to N50 system. Regarding the tubers per plant, there were no differences between farming systems but there was a significant difference between the trial years. The tubers in conventional systems had a lower starch content than the organic systems. It is possible to conclude that if cover crops and manure are used, organic farming practices provide just as good results as the conventional farming with low nitrogen level.

Release mortality of wild Atlantic salmon in coastal pontoon-trap fishery in the northern Baltic Sea

The survival and injuries of wild Atlantic salmon released by coastal fishers from pontoon traps was examined in the early summer of 2020 in the Gulf of Bothnia in the northern Baltic Sea. A total of 491 salmon caught with pontoon traps was tagged with dart tags. By the end of December 2020, a total of 62 tag recoveries (13%) were received. Sixty-two per cent of the tag recoveries were obtained from the sea area, mainly from the commercial fishers in the Bay of Bothnia near northern river mouths. The remaining tags were received from river fishers. It took an average of 22 days from tagging to the capture (range 1–91 days), and the longest distance a tagged salmon travelled was more than 700 km. The mortality of salmon caused by capture and release was estimated to be a maximum of 25–31% for multi-sea-winter (MSW) salmon and a maximum of 24% for one-sea-winter (1SW) salmon. Most of the tagged fish were visually in good condition, although some injuries were observed. When two trap emptying techniques were compared, salmon caught in the Bothnian Sea with an emptying chute showed more injuries than salmon caught in the Bay of Bothnia with a lifting bag. Our results suggest relatively low release mortality for Baltic salmon. Furthermore, we show that disentangling release mortality from combined tagging and handling mortality is crucial in tagging studies.

Correlation of wind waves and sea level variations on the coast of the seasonally ice-covered Gulf of Finland

Abstract. Both sea level variations and wind-generated waves affect coastal flooding risks. The correlation of these two phenomena complicates the estimates of their joint effect on the exceedance levels for the continuous water mass. In the northern Baltic Sea the seasonal occurrence of sea ice further influences the situation. We analysed this correlation with 28 years (1992–2019) of sea level data, and 4 years (2016–2019) of wave buoy measurements from a coastal location outside the City of Helsinki, Gulf of Finland in the Baltic Sea. The wave observations were complemented by 28 years of simulations with a parametric wave model. The sea levels and significant wave heights at this location show the strongest positive correlation (τ=0.5) for southwesterly winds, while for northeasterly winds the correlation is negative (−0.3). The results were qualitatively similar when only the open water period was considered, or when the ice season was included either with zero wave heights or hypothetical no-ice wave heights. We calculated the observed probability distribution of the sum of the sea level and the highest individual wave crest from the simultaneous time series. Compared to this, a probability distribution of the sum calculated by assuming that the two variables are independent underestimates the exceedance frequencies of high total water levels. We tested nine different copulas for their ability to account for the mutual dependence between the two variables.

Distribution and species composition of red algal communities in the northern Baltic Sea

Red algae are an important component of the Baltic Sea rocky shores. Within the Finnish marine area, in the northern Baltic Sea, red algal communities (on habitat level) are currently listed as endangered, due to eutrophication effects and potential future decrease in salinity. At species level, Rhodomela confervoides and Ceramium virgatum are red-listed. Despite their common use in different management contexts within the Baltic Sea, e.g. their depth distribution used as an indicator of the status of the sea areas, we know little about the commonness and more detailed distribution patterns of the red algal species. This limits the reliability of algae-based assessments. The aim of this study was to describe the general occurrence patterns, abundance and prevalence of erect perennial and annual red algae, based on extensive scuba-diving inventories within the Finnish marine area. Furthermore, the most representative areas for the red algal communities were identified. The results show high variation in depth distribution and prevalence across environmental gradients for many red algal species, e.g. for the relatively common perennial species Furcellaria lumbricalis and Vertebrata fucoides. In comparison to older data, reductions in depth penetration and occurrence were identified especially for deep-occurring species such as Rhodomela confervoides. With improved knowledge on the occurrence patterns of red algal species in relation to environmental variation, our results enable more reliable use of red algae as indicators of the status of the sea areas. By identifying areas where red algal communities are currently most representative, the results also allow better targeting of management efforts aiming to improve their status, such as areal protection measures or reducing nutrient input from point sources.

The “Seili-index” for the Prediction of Chlorophyll-α Levels in the Archipelago Sea of the northern Baltic Sea, southwest Finland

To build a forecasting tool for the state of eutrophication in the Archipelago Sea, we fitted a Generalized Additive Mixed Model (GAMM) to marine environmental monitoring data, which were collected over the years 2011–2019 by an automated profiling buoy at the Seili ODAS-station. The resulting “Seili-index” can be used to predict the chlorophyll-α (chl-a) concentration in the seawater a number of days ahead by using the temperature forecast as a covariate. An array of test predictions with two separate models on the 2019 data set showed that the index is adept at predicting the amount of chl-a especially in the upper water layer. The visualization with 10 days of chl-a level predictions is presented online at https://saaristomeri.utu.fi/seili-index/. We also applied GAMMs to predict abrupt blooms of cyanobacteria on the basis of temperature and wind conditions and found the model to be feasible for short-term predictions. The use of automated monitoring data and the presented GAMM model in assessing the effects of natural resource management and pollution risks is discussed.

Seawater browning alters community composition and reduces nutritional quality of plankton in a subarctic marine ecosystem

Inflows of coloured terrestrial organic matter cause seawater browning and reduced phytoplankton production in subarctic coastal ecosystems, potentially deteriorating the nutritional quality of marine food webs. We analyzed the fatty-acid (FA) compositions of seston and the zooplankton taxa Eurytemora affinis and cladocerans at three locations of the northern Baltic Sea. At the coastal and northerly locations, salinity and phosphorus concentrations were low, while concentrations of humic substances (i.e., terrestrial organic matter) were high. The southerly location showed the opposite trend. The ratio between alga-specific ω3 polyunsaturated FA and terrigenous monounsaturated FA (MUFA) in Eurytemora decreased from south to north, as did the ratio between the alga-specific docosahexaenoic acid (DHA) and terrigenous MUFA in cladocerans. With increasing humic substances, the biomass of DHA-rich phytoplankton decreased and the zooplankton MUFA content increased. Our results indicate that coloured terrestrial organic matter alters the phytoplankton composition, consequently affecting the zooplankton nutritional quality.

Oceanographic regional climate projections for the Baltic Sea until 2100

Abstract. The Baltic Sea, located in northern Europe, is a semi-enclosed, shallow and tideless sea with seasonal sea-ice cover in its northern sub-basins. Its long water residence time contributes to oxygen depletion in the bottom water of its southern sub-basins. In this study, recently performed scenario simulations for the Baltic Sea including marine biogeochemistry were analysed and compared with earlier published projections. Specifically, dynamical downscaling using a regionally coupled atmosphere–ocean climate model was used to regionalise four global Earth system models. However, as the regional climate model does not include components representing terrestrial and marine biogeochemistry, an additional catchment and a coupled physical–biogeochemical model for the Baltic Sea were included. The scenario simulations take the impact of various global sea level rise scenarios into account. According to the projections, compared to the present climate, higher water temperatures, a shallower mixed layer with a sharper thermocline during summer, less sea-ice cover and greater mixing in the northern Baltic Sea during winter can be expected. Both the frequency and the duration of marine heat waves will increase significantly, in particular in the coastal zone of the southern Baltic Sea (except in regions with frequent upwellings). Nonetheless, due to the uncertainties in the projections regarding regional winds, the water cycle and the global sea level rise, robust and statistically significant salinity changes could not be identified. The impact of a changing climate on biogeochemical cycling is predicted to be considerable but still smaller than that of plausible nutrient input changes. Implementing the proposed Baltic Sea Action Plan, a nutrient input abatement plan for the entire catchment area, would result in a significantly improved ecological status of the Baltic Sea, including reductions in the size of the hypoxic area also in a future climate, which in turn would increase the resilience of the Baltic Sea against anticipated climate change. While our findings regarding changes in heat-cycle variables mainly confirm earlier scenario simulations, they differ substantially from earlier projections of salinity and biogeochemical cycles, due to differences in experimental setups and in input scenarios for bioavailable nutrients.

Trends in Salinity and Bottom Temperature in the Northern Baltic Sea Over the Past Six Decades

Trends in Salinity and Bottom Temperature in the Northern Baltic Sea Over the Past Six Decades

Distribution and ecology of the recently introduced tanaidacean crustacean Sinelobus vanhaareni Bamber, 2014 in the northern Baltic Sea

Distribution and ecology of the recently introduced tanaidacean crustacean Sinelobus vanhaareni Bamber, 2014 in the northern Baltic Sea

Cormorant predation mortality of perch (Perca fluviatilis) in coastal and archipelago areas, northern Baltic Sea

Abstract Perch (Perca fluviatilis) is an important prey species of the great cormorant (Phalacrocorax carbo sinensis) in the coastal waters of the northern Baltic Sea. The annual predation mortality caused by cormorants was estimated based on the consumed numbers of perch in relation to the abundance of perch in vulnerable age groups in the sea. We used existing stock assessment data (Archipelago Sea) or a simple population model in other areas (Gulf of Finland, Bothnian Sea, and Quark), based on commercial and recreational perch catches, and estimated fishing and natural mortalities, with distributions describing our understanding about the likelihood of different values for every variable. The median predation mortality was 4–10% annually, depending on the sea area. The area-specific 80% likelihood limits ranged from 3 to 21% annually. Compared to a recent perch tagging study in the Quark, the cormorant-induced mortality estimates were considerably lower, but the likelihood distributions partly overlapped. The results were sensitive to the estimated number of vulnerable perch in the population, which in turn largely depends on the natural mortality in young perch age groups.

Comparison of cold season sedimentation dynamics in the non-tidal estuary of the Northern Baltic Sea

In this study, we investigated sedimentation differences between two distinctive cold seasons, in terms of hydrometeorological and hydrodynamic conditions, in a coastal area of the Northern Baltic Sea in 2018–2020. A combination of sediment trap data, hydrometeorological data and hydrodynamic modelling provided a unique set-up to discover differences in sedimentation rates and compositions. Our study shows that the averaged sedimentation accumulation rate (SAR) was nearly three times higher during warmer cold season (30.9 g m−2 day−1), characterised by higher precipitation, especially rain and discharge, as well as snowless and open water conditions, compared to regular cold season (10.6 g m−2 day−1). While sedimentation was higher during the warmer season, the mean sediment grain size (D50) was higher during the regular cold season with permanent snow and ice cover. Similarly, while sediments of the regular cold season were organically rich, the total amount of organic matter accumulation was larger during the warmer cold season. Sediments consisted mostly of clastic matter (85–89%), of which the mean grain size varied from clay to fine silt (0.3–3.0 μm). Sedimentation differences between the cold seasons can be explained by differences in precipitation, river flow, wind-induced resuspension and a low air pressure system forcing sea level changes. Sedimentation differences along the study bay were found to be connected to channel cross-sectional area and flow conditions caused by river input and sea level changes.

Phytoplankton Morpho-Functional Trait Variability along Coastal Environmental Gradients.

We utilized the trait-based approach in a novel way to examine how specific phytoplankton traits are related to physical features connected to global change, water quality features connected to catchment change, and nutrient availability connected to nutrient loading. For the analyses, we used summertime monitoring data originating from the coastal northern Baltic Sea and generalized additive mixed modeling (GAMM). Of the physical features connected to global climate change, temperature was the most important affecting several studied traits. Nitrogen-fixing, buoyant, non-motile, and autotrophic phytoplankton, as well as harmful cyanobacteria, benefited from a higher temperature. Salinity and stratification did not have clear effects on the traits. Water transparency, which in the Baltic Sea is connected to catchment change, had a mostly negative relation to the studied traits. Harmfulness was negatively correlated with transparency, while the share of non-harmful and large-sized phytoplankton was positively related to it. We used nutrient loading source type and total phosphorus (TP) as proxies for nutrient availability connected to anthropogenic eutrophication. The nutrient loading source type did not relate to any of the traits. Our result showing that N-fixing was not related to TP is discussed. The regionality analysis demonstrated that traits should be calculated in both absolute terms (biomass) and proportions (share of total biomass) to get a better view of community changes and to potentially supplement the environmental status assessments.

Landfast sea ice in the Bothnian Bay (Baltic Sea) as a temporary storage compartment for greenhouse gases

Although studies of biogeochemical processes in polar sea ice have been increasing, similar research on relatively warm low-salinity sea ice remains sparse. In this study, we investigated biogeochemical properties of the landfast sea ice cover in the brackish Bothnian Bay (Northern Baltic Sea) and the possible role of this sea ice in mediating the exchange of greenhouse gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) across the water column–sea ice–atmosphere interface. Observations of total alkalinity and dissolved inorganic carbon in both landfast sea ice and the water column suggest that the carbonate system is mainly driven by salinity. While high CH4 and N2O concentrations were observed in both the water column (up to 14.3 and 17.5 nmol L–1, respectively) and the sea ice (up to 143.6 and 22.4 nmol L–1, respectively), these gases appear to be enriched in sea ice compared to the water column. This enrichment may be attributable to the sea ice formation process, which concentrates impurities within brine. As sea ice temperature and brine volume decrease, gas solubility decreases as well, promoting the formation of bubbles. Gas bubbles originating from underlying sediments may also be incorporated within the ice cover and contribute to the enrichment in sea ice. The fate of these greenhouse gases within the ice merits further research, as storage in this low-salinity seasonal sea ice is temporary.

Cultural influences on the castration age of cattle in the northern Baltic Sea region during the medieval and post-medieval periods

Oxen – castrated male cattle (Bos taurus) – were used as draught animals in Finland, Estonia and Sweden for centuries. From the medieval period onwards, the wider phenomenon of oxen culture is evidenced by zooarchaeological material and historical documents, which reflect, among other things, the castration age. When males were castrated at a young age – a method used in Sweden, according to the ethnological sources – it affected the growth of the metacarpal bones; thus, the metacarpals of these oxen should be distinct from those of cows and bulls. However, when males were castrated as adults – a method used in Estonia – it had less effect on the bones, so the metacarpals of these oxen are more likely to resemble those of bulls. Documents from the early modern period indicate that in Finland, cattle were castrated as calves (as they were in Sweden), but some medieval bone finds indicate that they were castrated in adulthood (as they were in Estonia). To resolve this apparent contradiction between the zooarchaeological data and the written evidence, and to understand the cultural transitions in farming practices relating to draught oxen in the northern Baltic Sea region, we studied morphometric changes in 621 metacarpals in Finland and Estonia dating from the medieval and post-medieval periods (13th to 20th century) and compared them with previously published contemporaneous data from Sweden. To investigate the size and shape of the individuals and to distinguish oxen from bulls and cows, we applied widely used osteometric criteria, including the maximum breadth of the distal epiphysis and Mennerich indices. For a set of uncertain samples from medieval Turku, Finland, we identified the sex by amplifying the TSPY gene and X and Y chromosome-specific variations in the ancient DNA. Our results confirm that throughout the medieval and post-medieval periods, late castration was practised in Estonia and early castration was practised in Sweden. In Finland, however, we detected a temporal change in the castration age: cattle were castrated as adults in the medieval period and at a young age in the post-medieval period.

Political upheaval, external influences and domestic traditions: The emergence of the nineteenth-century Ålandic yacht

This article examines the emergence of the nineteenth-century Ålandic peasant yacht within the larger political, economic and social context of the central and northern Baltic Sea region. Through an analysis of the region's fluctuating and changing trading environment following the Finnish War of 1808–1809, it is demonstrated that the increasing uncertainty, as well as decreasing profitability, of previously stable trading relations provided the necessary impetus to change the traditional vessel design. Avenues for both foreign and domestic innovations are examined. In addition to exogenous influences, wherein the role of the Ålandic peasant sailors’ involvement in the Swedish navy is accentuated, the effects of the increasing smuggling activities of the archipelago's inhabitants and the competitive sailing environment that emerged during trading journeys are considered as factors that possibly affected shipbuilding. The results highlight the complex networks and processes through which innovations are generated, transmitted and adopted.

Anthropogenic Inputs of Terrestrial Organic Matter Influence Carbon Loading and Methanogenesis in Coastal Baltic Sea Sediments

Coastal regions globally have experienced widespread anthropogenic eutrophication in recent decades. Loading of autochthonous carbon to coastal sediments enhances the demand for electron acceptors for microbial remineralization, often leading to rearrangement of the sediment diagenetic zonation and potentially enhancing fluxes of methane and hydrogen sulfide from the seafloor. However, the role of anthropogenic inputs of terrestrial organic matter (OMterr.) in modulating diagenesis in coastal sediments is often overlooked, despite being of potential importance in regions of land-use and industrial change. Here we present a dated 4-m sediment and porewater geochemistry record from a eutrophic coastal location in the northern Baltic Sea, to investigate sources of recent carbon loading and their impact on modern diagenetic processes. Based on an end-member mixing model of sediment N/C ratios, we observe that a significant fraction of the late-20th century carbon loading at this location was contributed by OMterr.. Furthermore, analysis of lignin in this material shows depleted ratios of syringyl/vanillyl (S/V) and cinnamyl/vanillyl (C/V) phenols, indicative of enhanced inputs of woody gymnosperm tissue likely from forest industries. The rapid loading of organic matter from combined terrestrial and autochthonous sources during the late 20th century has stimulated methanogenesis in the sediment column, and shoaled the sulfate-methane transition zone (SMTZ) to a depth of 5–20 cm. Optical parameters of colored dissolved organic matter confirm that OMterr. is actively degrading in the methanogenic layer, implying a role for this material in diagenetic processes. Porewater CH4, SO42− δ13C-DIC, and ∑S2− data suggest that the modern SMTZ is a broad zone in which organoclastic sulfate reduction, methanogenesis and anaerobic oxidation of methane (AOM) co-occur. However, fluxes of CH4 and SO42− show that rates of these processes are similar to other marine locations with a comparably shallow SMTZ. We suggest that the shallow depth of the modern SMTZ is the principal reason for high observed diffusive and ebullitive methane fluxes from sediments in this area. Our results highlight that anthropogenic activities lead to multiple pathways of carbon loading to coastal sediments, and that forest industry impacts on sedimentation in the northern Baltic Sea may be more widespread than previously acknowledged.

The role of marinas in the establishment and spread of non-indigenous species in Baltic Sea fouling communities

The study included the sampling of 12 marinas across six areas of the Baltic Sea with settlement plates and scraping of submerged structures to assess the role of marinas in the spread of non-indigenous species (NIS) via biofouling. 15 NIS were detected in the marinas and secondary spread of previously introduced NIS was detected in five out of six sea areas. Salinity and sea area significantly affected the composition of the fouling assemblages. Settlement plates appeared as the more efficient sampling method over scraping, while the seasonal analyses revealed that the monitoring effort should span over the summer and early autumn in the south-eastern, central, and northern Baltic Sea. The present findings indicate that marinas contribute to the spread of non-indigenous fouling organisms, and there is an increasing demand for the monitoring of marinas and stricter regulations regarding the biofouling management of leisure boats in the Baltic Sea.

Biogeochemical and mineralogical effects of Fe-P-S dynamics in sediments of continental shelf sea: Impact of salinity, oxygen conditions, and catchment area characteristics

In this study, we investigate how salinity, oxygen concentration and catchment area characteristics impact the dynamics of Fe-P-S cycling in the continental shelf sea sediments. Samples were collected from three sites representing different environmental conditions: Gdańsk Deep (southern Baltic Sea), Gotland Deep (central Baltic Sea) and Bothnian Sea (northern Baltic Sea). Sediments were analysed for their mineral composition and speciation of iron and phosphorus. The main groups of Prokaryota involved in Fe-P-S cycling in sediments were indicated. Concentrations of sulphate, hydrogen sulphide, alkalinity, chloride, calcium, phosphate and iron were measured in pore waters. We demonstrated that in the eutrophicated southern region with moderate salinity and oxygen deficit in bottom water, sediments had high potential for retaining Fe and releasing P as indicated by high concentrations of pyrite and labile forms of phosphorus, respectively. Strong salinity stratification and intermittent pelagic redoxcline in the central Baltic Sea resulted in a clearly higher rate of pyrite deposition. Sediment was enriched with Mn due to the formation of Ca-Mn carbonates driven by intensive Mn redox cycling and sulphate reduction. Because of high availability of Mn oxides connected with episodic inflows of oxic seawater from the North Sea, sulphate was present in the entire profile of the studied sediments in the Gotland Deep. Sediments in the well-oxygenated, virtually fresh and rich in land-derived iron northern Baltic Sea retained significant amounts of P in authigenic minerals. Organic matter mineralisation in the surface sediment of this area was dominated by iron reduction. The variability of environmental conditions and consequent availability of electron acceptors were the cause of regional differences in the composition of Prokaryota communities – the number of sulphate reducers in the Gdańsk and Gotland Deeps was greater than in the Bothnian Sea, where there were more Fe reducers and bacteria that oxidise Fe and S.

The ms Estonia Shipwreck Revisited: New Developments in the Protection of Underwater Cultural Heritage in the Northern Baltic Sea

Abstract It is widely believed that international law does not enable to protect effectively the wreck of the ms Estonia against looting. The protection regime established under the 1995 ms Estonia Treaty is binding and violations against it can be effectively sanctioned in respect of only the nationals of its few States Parties, resulting in numerous jurisdictional gaps. This study argues that the law of the sea and administrative law provide the means for safeguarding the ms Estonia wreck against pilferers. Estonia has repeatedly designated tiny buffer zones around relatively modern shipwrecks outside its territorial sea. Finland can follow this practice in relation to the ms Estonia wreck that lies less than 19 nm from its baselines. In effect, Finland would be entitled to regulate and authorize activities directed at the shipwreck with the right to exercise its enforcement jurisdiction against persons that disturb the peace of the mass grave.

Physical drivers of epi- and infauna communities related to dominating macrophytes in shallow bays in the Northern Baltic Sea

Shallow coastal bays with dense aquatic phytobenthic communities are important but vulnerable habitats and nursery areas for fish and invertebrates in the Baltic Sea. These habitats are under increasing anthropogenic stress, and understanding their dynamics is a prerequisite for management and conservation. In this study, we examined the effects of isolation of the bay from the sea, water and sediment characteristics, and macrophyte species on the invertebrate communities. In each bay, both epifauna and infauna were sampled in pairs of monospecific patches of dominating habitat-forming macrophytes (Stuckenia pectinata, Chara tomentosa and Ceratophyllum demersum). We found that the invertebrate community was mainly affected by bay isolation, which correlated with other environmental variables, and thus likely drives many processes in the bays. Further, the epifauna community responded to both the median grainsize and geometric standard deviation across both the isolation gradient (S. pectinata alone) and in the S. pectinata - C. demersum macrophyte pair, whereas the median grainsize affected the epifauna in the S. pectinata - C. tomentosa macrophyte pair. The infauna community responded to either the median grainsize or the geometric standard deviation across the isolation gradient and in both macrophyte pairs. Only minor differences between the dominating macrophyte species were seen regarding invertebrate abundance, taxon richness and diversity, although the more structurally complex C. demersum supported the highest epifauna diversity and lowest infauna abundance. However, at local, within bay scale, epifauna communities varied between most pairs of macrophyte species, suggesting that habitat-forming macrophytes have important roles in structuring local invertebrate community patterns. This study emphasizes the complexity of biotic and abiotic interactions within and among shallow coastal bays, and the challenges with studying and comparing processes in these unique ecosystems.