Atmospheric Nutrient Input to the Baltic Sea from 1850 to 2006: A Reconstruction from Modeling Results and Historical Data

In this study, a consistent basin-wise monthly time series of the atmospheric nutrient load to the Baltic Sea during 1850-2006 was compiled. Due to the lack of a long time series (1850-1960) of nutrient deposition to the Baltic Sea, the data set was compiled by combining a time series of deposition data at the Baltic Nest Institute from 1970 to 2006, published historical monitoring data and deposition estimates, as well as recent modeled Representative Concentration Pathways (RCP) emission estimates. The procedure for nitrogen compounds included estimation of the deposition in a few intermediate reference years, linear interpolation between them, and the decomposition of annual deposition into a seasonal deposition pattern. As no reliable monitoring results were found for the atmospheric deposition of phosphorus during the early period of our study, we used published estimates for the temporal and spatial pattern of the phosphorus load.     

Impact of Climate Change on Ecological Quality Indicators and Biogeochemical Fluxes in the Baltic Sea: A Multi-Model Ensemble Study

Multi-model ensemble simulations using three coupled physical-biogeochemical models were performed to calculate the combined impact of projected future climate change and plausible nutrient load changes on biogeochemical cycles in the Baltic Sea. Climate projections for 1961-2099 were combined with four nutrient load scenarios ranging from a pessimistic business-as-usual to a more optimistic case following the Helsinki Commission's (HELCOM) Baltic Sea Action Plan (BSAP). The model results suggest that in a future climate, water quality, characterized by ecological quality indicators like winter nutrient, summer bottom oxygen, and annual mean phytoplankton concentrations as well as annual mean Secchi depth (water transparency), will be deteriorated compared to present conditions. In case of nutrient load reductions required by the BSAP, water quality is only slightly improved. Based on the analysis of biogeochemical fluxes, we find that in warmer and more anoxic waters, internal feedbacks could be reinforced. Increased phosphorus fluxes out of the sediments, reduced denitrification efficiency and increased nitrogen fixation may partly counteract nutrient load abatement strategies.     

Climate Change Impact on Riverine Nutrient Load and Land-Based Remedial Measures of the Baltic Sea Action Plan

To reduce eutrophication of the Baltic Sea, all nine surrounding countries have agreed upon reduction targets in the HELCOM Baltic Sea Action Plan (BSAP). Yet, monitoring sites and model concepts for decision support are few. To provide one more tool for analysis of water and nutrient fluxes in the Baltic Sea basin, the HYPE model has been applied to the region (called Balt-HYPE). It was used here for experimenting with land-based remedial measures and future climate projections to quantify the impacts of these on water and nutrient loads to the sea. The results suggest that there is a possibility to reach the BSAP nutrient reduction targets by 2100, and that climate change may both aggravate and help in some aspects. Uncertainties in the model results are large, mainly due to the spread of the climate model projections, but also due to the hydrological model.     

Reconstructing the Development of Baltic Sea Eutrophication 1850–2006

A comprehensive reconstruction of the Baltic Sea state from 1850 to 2006 is presented: driving forces are reconstructed and the evolution of the hydrography and biogeochemical cycles is simulated using the model BALTSEM. Driven by high resolution atmospheric forcing fields (HiResAFF), BALTSEM reproduces dynamics of salinity, temperature, and maximum ice extent. Nutrient loads have been increasing with a noteworthy acceleration from the 1950s until peak values around 1980 followed by a decrease continuing up to present. BALTSEM shows a delayed response to the massive load increase with most eutrophic conditions occurring only at the end of the simulation. This is accompanied by an intensification of the pelagic cycling driven by a shift from spring to summer primary production. The simulation indicates that no improvement in water quality of the Baltic Sea compared to its present state can be expected from the decrease in nutrient loads in recent decades.     

Echoes from the Past: A Healthy Baltic Sea Requires More Effort

Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change.     

The Governance of the Mitigation of the Baltic Sea Eutrophication: Exploring the Challenges of the Formal Governing System

This article focuses on the governing system of the mitigation of eutrophication in the Baltic Sea. Policies and measures of the Baltic Sea coastal countries, the macro--regional (HELCOM) level, and the level of the European Union are described and governance challenges explicated. We found that the main challenges at different governance levels include: differences between coastal countries in terms of environmental conditions including environmental awareness, overlaps of policies between different levels, the lack of adequate spatial and temporal specification of policies, and the lack of policy integration. To help to meet these challenges, we suggest closer involvement of stakeholders and the public, the improvement of the interplay of institutions, and the introduction of a “primus motor” for the governance of the mitigation of eutrophication in the Baltic Sea.     

Biogeochemical Control of the Coupled CO2–O2 System of the Baltic Sea: A Review of the Results of Baltic-C

Past, present, and possible future changes in the Baltic Sea acid–base and oxygen balances were studied using different numerical experiments and a catchment–sea model system in several scenarios including business as usual, medium scenario, and the Baltic Sea Action Plan. New CO₂ partial pressure data provided guidance for improving the marine biogeochemical model. Continuous CO₂ and nutrient measurements with high temporal resolution helped disentangle the biogeochemical processes. These data and modeling indicate that traditional understandings of the nutrient availability–organic matter production relationship do not necessarily apply to the Baltic Sea. Modeling indicates that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, increased mineralization and biological production will amplify the seasonal surface pH cycle. The direction and magnitude of future pH changes are mainly controlled by atmospheric CO₂ concentration. Apart from decreasing pH, we project a decreasing calcium carbonate saturation state and increasing hypoxic area.     

The Significance of the North Water Polynya to Arctic Top Predators

The North Water polynya (~76°N to 79°N and 70°W to 80°W) is known to be an important habitat for several species of marine mammals and sea birds. For millennia, it has provided the basis for subsistence hunting and human presence in the northernmost part of Baffin Bay. The abundance of air-breathing top predators also represents a potential source of nutrient cycling that maintains primary production. In this study, aerial surveys conducted in 2009 and 2010 were used for the first time to map the distribution and estimate the abundance of top predators during spring in the North Water. Belugas (Delphinapterus leucas) were not detected north of 77°20′N but were found along the coast of West Greenland and offshore in the middle of the North Water with an abundance estimated at 2245 (95 % CI 1811–2783). Narwhals (Monodon monoceros) were widely distributed on the eastern side of the North Water with an estimate of abundance of 7726 (3761–15 870). Walruses (Odobenus rosmarus) were found across the North Water over both shallow and deep (>500 m) water with an estimated abundance of 1499 (1077–2087). Bearded (Erignathus barbatus) and ringed seals (Phoca hispida) used the large floes of ice in the southeastern part of the North Water for hauling out. Most polar bears (Ursus maritimus) were detected in the southern part of the polynya. The abundances of bearded and ringed seals were 6016 (3322–10 893) and 9529 (5460–16 632), respectively, and that of polar bears was 60 (12–292). Three sea bird species were distributed along the Greenland coast (eiders, Somateria spp.), in leads and cracks close to the Greenland coast (little auks, Alle alle) or widely in open water (thick-billed guillemots, Uria lomvia).     

Seasonal and spatial variations of Po and Pb activity concentrations in Mytilus galloprovincialis from Croatian coast of the Adriatic Sea

Results of 2 years monitoring of ²¹⁰Po and ²¹⁰Pb activity concentrations in soft tissue of the species Mytilus galloprovincialis from Croatian part of the Adriatic coast are presented. The samples were collected at thirteen coastal stations (some of which are also a part of the Mediterranean Mussel Watch Project) in spring and autumn of 2010 and 2011. The collected mussels were ranging between 4 cm and 6 cm in shell length. After sample pre-treatment lead and polonium were radiochemically separated on Sr resin. ²¹⁰Po was determined by alpha-particle spectrometry and ²¹⁰Pb was determined, via ²¹⁰Bi, by a low-level gas proportional counter. The results of ²¹⁰Po activity concentrations were found to vary between (104 ± 11) and (1421 ± 81) Bq kg⁻¹ dry weight while ²¹⁰Pb activity concentrations were much lower and in range (8.2 ± 5.3)–(94.1 ± 29.8) Bq kg⁻¹ dry weight. Higher ²¹⁰Po and ²¹⁰Pb activity concentrations were determined in spring period. The inter-site differences seen in their activity concentrations can be due to natural background levels of sites. The ²¹⁰Po/²¹⁰Pb activity concentration ratios in all cases exceeded unity for all mussel samples and ranged between 4.0 and 47.9.     

Visions for the North Sea: The Societal Dilemma Behind Specifying Good Environmental Status

We augment discussions about the Good Environmental Status of the North Sea by developing two extreme visions and assessing their societal benefits. One vision (‘Then’) assumes restoration of benthic functioning; we contend that trawling had already degraded the southern North Sea a century ago. Available information is used to speculate about benthic functioning in a relatively undisturbed southern North Sea. The second vision (‘Now’) draws on recent benthic functioning. The supply of five ecosystem services, supported by benthic functioning, is discussed. ‘Then’ offers confidence in the sustainable supply of diverse services but restoration of past function is uncertain and likely to be paired with costs, notably trawling restraints. ‘Now’ delivers known and valued services but sustained delivery is threatened by, for example, climate change. We do not advocate either vision. Our purpose is to stimulate debate about what society wants, and might receive, from the future southern North Sea.

Electronic supplementary material

The online version of this article (doi:10.1007/s13280-014-0536-5) contains supplementary material, which is available to authorized users.