A method to combine observations and an ensemble of ecological models is suggested to produce a eutrophication assessment. Using threshold values and methodology from the Oslo and Paris Commissions (OSPAR) and the Helsinki Commission (HELCOM), four models are combined to assess eutrophication for the Baltic and North Seas for the year 2006. The assessment indicates that the entire southeastern part of the North Sea, the Kattegat, the Danish Straits, the Gulf of Finland, and the Gulf of Riga as well as parts of the Arkona Basin, the Bornholm Basin, and the Baltic proper may be classified as problem areas. The Bothnian Bay and parts of the Baltic proper, the Bornholm Basin, and the Arkona Basin are classified as potential problem areas. This method is a useful tool for the classification of eutrophication; however, the results depend on the threshold values, and further work is needed within both OSPAR and HELCOM to harmonize these values.

Climate change is likely to have large effects on the Baltic Sea ecosystem. Simulations indicate 2-4 degrees C warming and 50-80 % decrease in ice cover by 2100. Precipitation may increase similar to 30 % in the north, causing increased land runoff of allochthonous organic matter (AOM) and organic pollutants and decreased salinity. Coupled physical-biogeochemical models indicate that, in the south, bottom-water anoxia may spread, reducing cod recruitment and increasing sediment phosphorus release, thus promoting cyanobacterial blooms. In the north, heterotrophic bacteria will be favored by AOM, while phytoplankton production may be reduced. Extra trophic levels in the food web may increase energy losses and consequently reduce fish production. Future management of the Baltic Sea must consider the effects of climate change on the ecosystem dynamics and functions, as well as the effects of anthropogenic nutrient and pollutant load. Monitoring should have a holistic approach, encompassing both autotrophic (phytoplankton) and heterotrophic (e.g., bacterial) processes.

The dynamic catchment model HBV-N has been further developed by adding routines for phosphorus transport and is now called the HBV-NP model. The model was shown to satisfactorily simulate nutrient dynamics in the Ronnea catchment (1 900 km(2)). Its sensitivity to input data was tested, and results demonstrated the increased sensitivity to the selection of input data on a subcatchment scale when compared with the catchment scale. Selection of soil and land use databases was found to be critical in some subcatchments but did not have a significant impact on a catchment scale. Although acceptable on a catchment scale, using templates and generalization, with regards to emissions from point sources and rural households, significantly decreased model performance in certain subcatchments when compared with using more detailed local information. A division into 64 subcatchments resulted in similar model performance at the catchment outlet when compared with a lumped approach. Adjusting the imported matrixes of the regional leaching of nitrogen, from agricultural land, against mean subcatchment water percolation did not have a significant impact on the model performance.

Climate change resulting from the enhanced greenhouse effect is expected to give rise to changes in hydrological systems. This hydrological change, as with the change in climate variables, will vary regionally around the globe. Impact studies at local and regional scales are needed to assess how different regions will be affected. This study focuses on assessment of hydrological impacts of climate change over a wide range of Swedish basins. Different methods of transferring the signal of climate change from climate models to hydrological models were used. Several hydrological model simulations using regional climate model scenarios from Swedish Regional Climate Modelling Programme (SWECLIM) are presented. A principal conclusion is that subregional impacts to river flow vary considerably according to whether a basin is in northern or southern Sweden. Furthermore, projected hydrological change is just as dependent on the choice of the global climate model used for regional climate model boundary conditions as the choice of anthropogenic emissions scenario.

Starting from six regional climate change scenarios, nitrogen leaching from arable-soil, water discharge, and nitrogen retention was modeled in the Ronnea catchment. Additionally, biological response was modeled in the eutrophic Lake Ringsjon. The results are compared with similar studies on other catchments. All scenarios gave similar impact on water quality but varied in quantities. However, one scenario resulted in a different transport pattern due to less-pronounced seasonal variations in the hydrology. On average, the study shows that, in a future climate, we might expect: i) increased concentrations of nitrogen in the arable root zone (+50%) and in the river (+13%); ii) increased annual load of nitrogen from land to sea (+22%) due to more pronounced winter high flow; moreover, remote areas in the catchment may start to contribute to the outlet load; iii) radical changes in lake biochemistry with increased concentrations of total phosphorus (+50%), total nitrogen (+20%), and planktonic algae such as cyanobacteria (+80%).

The Baltic Sea is suffering from eutrophication and attempts are being made to reduce nutrient loads. This article focuses on nitrogen transport from southern Sweden (145 000 km(2)), and presents a model approach (HBV-N) that has been used in the national decision-making process for best management practices. Calculations of nitrogen leaching, retention in the freshwater system, net transport to the sea, and source apportionment are presented for the period 1985-1994. Input data were handled in GIS, including results from SOIL-N and MATCH. Daily simulations were made in 3725 subbasins with calibration against measured time series at 722 sites. Diffuse source pollution was normally retained by 10-25% before entering the river network. Lakes normally reduced nitrogen transport by 30-40 kg ha(-1) yr(-1) of lake area. On average, 45% of the annual gross load was reduced during transport, but temporal and spatial variations were great. 75 000 tonnes N yr(-1) reached the sea.

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.

A hydrological-based model (HBV-NP) was applied to a catchment (1900 km(2)) in the southern part of Sweden. Careful characterization of the present load situation and the potential for improved treatment or reduced soil leaching were analyzed. Several scenarios were modeled to find strategies to reach the Swedish environmental goals of reducing anthropogenic nitrogen load by 30% and phosphorus load by 20%. It was stated that the goals could be reached by different approaches that would affect different polluters and social sectors. However, no single measure was enough by itself. Instead, a combination of measures was necessary to achieve the goals. The nitrogen goal was the most difficult to attain. In order to be cost-effective, these measures should be applied to areas contributing the most to the net loading of the sea. This strategy could reduce the costs by 70%-80% when compared with implementing the measures in the entire catchment. Integrated catchment models may thus be helpful tools for reducing costs in environmental control programs.

Created wetlands have been suggested as a method to reduce nitrogen transport to the Baltic Sea. This paper presents a dynamic conceptual model for simulation of the hypothetical effect of wetlands on nitrogen export to the coastal zone. The study was performed in the Soder-kopingsan drainage basin (882 km(2)) in southeastern Sweden, discharging into the Baltic Sea. An empirically based routine for wetland retention was calibrated separately and incorporated in the model. Scenarios with different location and size of wetlands were analyzed. It was estimated that conversion of 1% (8.8 km(2)) of this basin into wetlands would reduce the nitrogen transport by 10-16% and that more than 5% (45 km(2)) conversion to wetlands is required to reduce the transport by 50%. It was concluded that creation of wetlands should be considered, primarily, downstream from major lakes, in coastal areas, and where the summer load is a significant portion of the annual load. Some further conclusions from the study were that: i) the net reduction of nitrogen transport per unit area of wetland decreases with increasing total area of wetlands in a drainage basin; ii) the wetland retention efficiency obtained in studies of individual wetlands can not be extrapolated in a linear fashion to estimate the net reduction of nitrogen transport at the mouth of a whole drainage basin; iii) the seasonal hydrological and hydrochemical dynamics are of fundamental importance for wetland retention efficiency, which complicates comparison and extrapolation of results from one region to another.

A database of monthly inflow of fresh water from rivers and land to the Baltic Sea and its subbasins is created. The database covers the period 1950-1990 and is based on observations from the national hydrological services of the surrounding countries. The main features of the database are presented including river flow of selected rivers and total inflow to the Baltic Sea and its subbasins. Long term, seasonal and short-term variabilities are analyzed and the effects of hydropower development are identified. An earlier database by Mikulski is used for comparison and extension of the record to cover the period 1921-1990. It is concluded that the variability of inflow is great and that the decade 1981-1990 was the wettest in 70 years. Wet years are also found in the 1920s. The increase in runoff is mainly due to increasing river flow during the cold seasons. The effects of hydropower development are noticeable in the records for the Bothnian Bay and the Bothnian Sea.

The goals for water-quality and ecosystem integrity are often defined relative to "natural" reference conditions in many water-management systems, including the European Union Water Framework Directive. This paper examines the difficulties created for water management by using "natural" as the goal. These difficulties are articulated from different perspectives in an informal (fictional) conversation that takes place after a workshop on reference conditions in water-resources management. The difficulties include defining the natural state and modeling how a system might be progressed toward the natural, as well as the feasibility and desirability of restoring a natural state. The paper also considers the appropriateness for developing countries to adopt the use of natural as the goal for water management. We conclude that failure to critically examine the complexities of having "natural" as the goal will compromise the ability to manage the issues that arise in real basins by not making the ambiguities associated with this "natural" goal explicit. This is unfortunate both for the western world that has embraced this model of "natural as the goal" and for the developing world in so far as they are encouraged to adopt this model.

The physical state of the Baltic Sea in possible future climates is approached by numerical model experiments with a regional coupled ocean-atmosphere model driven by different global simulations. Scenarios and recent climate simulations are compared to estimate changes. The sea surface is clearly warmer by 2.9degreesC in the ensemble mean. The horizontal pattern of average annual mean warming can largely be explained in terms of ice-cover reduction. The transfer of heat from the atmosphere to the Baltic Sea shows a changed seasonal cycle: a reduced heat loss in fall, increased heat uptake in spring, and reduced heat uptake in summer. The interannual variability of surface temperature is generally increased. This is associated with a smoothed frequency distribution in northern basins. The overall heat budget shows increased solar radiation to the sea surface, which is balanced by changes of the other heat flux components.

A study of the water-mass circulation of the Baltic has been undertaken by making use of a three dimensional Baltic Sea model simulation. The saline water from the North Atlantic is traced through the Danish Sounds into the Baltic where it upwells and mixes with the fresh water inflow from the rivers forming a Baltic haline conveyor belt. The mixing of the saline water from the Great Belt and Oresund with the fresh water is investigated making use of overturning stream functions and Lagrangian trajectories. The overturning stream function was calculated as a function of four different vertical coordinates (depth, salinity, temperature and density) in order to understand the path of the water and where it upwells and mixes. Evidence of a fictive depth overturning cell similar to the Deacon Cell in the Southern Ocean was found in the Baltic proper corresponding to the gyre circulation around Gotland, which vanishes when the overturning stream function is projected on density layers. A Lagrangian trajectory study was performed to obtain a better view of the circulation and mixing of the saline and fresh waters. The residence time of the water masses in the Baltic is calculated to be 26-29 years and the Lagrangian dispersion reaches basin saturation after 5 years.

We quantified horizontal transport patterns and the net exchange of nutrients between shallow regions and the open sea in the Baltic proper. A coupled biogeochemical-physical circulation model was used for transient simulations 1961-2100. The model was driven by regional downscaling of the IPCC climate change scenario A1B from two global General Circulation Models in combination with two nutrient load scenarios. Modeled nutrient transports followed mainly the large-scale internal water circulation and showed only small circulation changes in the future projections. The internal nutrient cycling and exchanges between shallow and deeper waters became intensified, and the internal removal of phosphorus became weaker in the warmer future climate. These effects counteracted the impact from nutrient load reductions according to the Baltic Sea Action Plan. The net effect of climate change and nutrient reductions was an increased net import of dissolved inorganic phosphorus to shallow areas in the Baltic proper.

We used an off-line, regional, model of atmospheric transport and chemistry to investigate current and future levels of near-surface ozone and accumulated ozone exposure over a threshold of 40 ppb(v) (AOT40) in Europe. To describe the current situation and enable an evaluation of the model's performance we simulated a number of years around 2000. To assess changes in ozone concentrations due to possible emission changes in Europe, the model was run with the meteorology of the early 2000s and precursor emissions from a set of Clean Air for Europe (CAFE) emissions scenarios. By extrapolation of the observed increase in near-surface O(3) at coastal locations in northwest Europe we constructed model boundaries that were used to simulate the impact of increasing hemispheric background in 2020. To assess changes in ozone concentrations due to climate change, the model was run with recent (2000) emissions but using meteorology from a regional climate model simulating a control (1961-1990) and a future (2021-2050) climate. The results indicate that climate change will have a small impact on ozone concentrations and AOT40 in the Nordic countries. Changes in hemispheric background concentrations and changes in precursor emissions in Europe will have a larger effect on ozone in Northern Europe. The situation is quite different in southern Europe, where climate change is expected to result in a very large increase in near-surface ozone concentrations.

River flow to the Baltic Sea originates under a range of different climate regimes in a drainage basin covering some 1 600 000 km(2). Changes to the climate in the Baltic Basin will not only affect the total amount of freshwater flowing into the sea, but also the distribution of the origin of these flows. Using hydrological modeling, the effects of future climate change on river runoff to the Baltic Sea have been analyzed. Four different climate change scenarios from the Swedish Regional Climate Modelling Programme (SWECLIM) were used. The resulting change to total mean annual river flow to the Baltic Sea ranges from -2% to +15% of present-day flow according to the different climate scenarios. The magnitude of changes within different subregions of the basin varies considerably, with the most severe mean annual changes ranging from -30% to +40%. However, common to all of the scenarios evaluated is a general trend of reduced river flow from the south of the Baltic Basin together with increased river flow from the north.

A large-scale hydrologic model of macroscale dimension for total daily runoff to the Baltic Sea has been developed using 25 subbasins ranging from 21000 to 144000 km(2). Daily synoptic input was calibrated against monthly recorded river flows. Reasonable model results for the water balance were obtained while keeping the level of detail to a minimum with a proven conceptual modeling approach. Important elements of the modeled water balance are presented for the five main Baltic Sea drainage basins. The model is used for cooperative research with both meteorological and oceanographic modeling within the Baltic Sea Experiment (BALTEX) and the Swedish Regional Climate Modelling Programme (SWECLIM). It provides off-line analysis for coupled model development and fills a needed role until truly coupled models become available. Furthermore, the model is suitable for operational applications and will be used to extend runoff records, fill in missing data, and perform quality checks on new observations.

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.

Global climate change is expected to have an effect on the physical and ecological characteristics of the Baltic Sea. Estimates of future climate on the regional scale can be obtained by using either statistical or dynamical downscaling methods of global AOGCM scenario results. In this paper, we use 2 different coupled ice-ocean models of the Baltic Sea to simulate present and future ice conditions around 100 years from present. Two 10-year time slice experiments have been performed using the results of atmospheric climate model simulations as forcing, one representing pre-industrial climate conditions (control simulation), and the other global warming with a 150% increase in CO2 greenhouse gas concentration (scenario simulation). Present-day climatological ice conditions and interannual variability are realistically reproduced by the models. The simulated range of the maximum annual ice extent in the Baltic in both models together is 180 to 420.10(3) km(2) in the control simulation and 45 to 270.10(3) km(2) in the scenario simulation. The range of the maximum annual ice thickness is from 32 to 96 cm and from 11 to 60 cm in the control and scenario simulations, respectively. In contrast to earlier estimates, sea ice is still formed every winter in the Northern Bothnian Bay and in the most Eastern parts of the Gulf of Finland. Overall, the simulated changes of quantities such as ice extent and ice thickness, as well as their interannual variations are relatively similar in both models, which is remarkable, because the 2 coupled ice-ocean model systems have been. developed independently. This increases the reliability of future projections of ice conditions in the Baltic Sea.

Bathymetry, the underwater topography, is a fundamental property of oceans, seas, and lakes. As such it is important for a wide range of applications, like physical oceanography, marine geology, geophysics and biology or the administration of marine resources. The exact requirements users may have regarding bathymetric data are, however, unclear. Here, the results of a questionnaire survey and a literature review are presented, concerning the use of Baltic Sea bathymetric data in research and for societal needs. It is demonstrated that there is a great need for detailed bathymetric data. Despite the abundance of high-quality bathymetric data that are produced for safety of navigation purposes, the digital bathymetric models publicly available to date cannot satisfy this need. Our study shows that DBMs based on data collected for safety of navigation could substantially improve the base data for administrative decision making as well as the possibilities for marine research in the Baltic Sea.

A high-resolution chemical transport model, driven by meteorology representing current and future climate, was used to investigate the effects of possible future changes in climate on nitrogen deposition in northwestern Europe. The model system was able to resolve the climatology of precipitation and chemical properties observed in northern Europe during the 1980s, albeit with some underestimation of the temporal and spatial variability of meteorological parameters and chemical components. The results point toward a substantial increase (30% or more) in nitrogen deposition over western Norway as a consequence of increasing precipitation but more moderate changes for other areas. Deposition of oxidized nitrogen will increase more than the deposition of reduced nitrogen. Over Sweden, oxidized nitrogen will increase only marginally and reduced nitrogen will decrease, although annual precipitation is expected to increase here as well. This is probably because more reduced nitrogen will be removed further west in Scandinavia because of the strong increase in precipitation along the Norwegian coast. The total deposition of oxidized nitrogen over Norway is expected to increase from 96 Gg N y(-1) during the current climate to 107 Gg N y(-1) by 2100 due only to changes in climate. The corresponding values for Sweden are more modest, from 137 Gg N y(-1) to 139 Gg N y(-1).

The Gulf of Bothnia contains about 29% of the whole water volume of the Baltic Sea. The water exchange between the Baltic proper and the Gulf is good, which results in a water renewal time of about 4 to 5 yrs. The dynamics and thermodynamics of the Gulf of Bothnia are guided by hydrological, meteorological and, partly, topographical factors, such as freshwater supply, wind over sea, sun radiation, sea ice and sill depth between the sub-basins, The water mass is vertically divided into two layers with a halocline at 50 to 60 m depth. The deep water, below 60 m, mainly originates from the upper layer of the Baltic proper and has a salinity of 6-7 psu. In the surface layer, a thermocline develops each summer. This upper well-mixed layer is, on average, 15 m deep. The north to south water transport mainly occurs in this surface layer along the coasts, with a tendency to cyclonic circulation. It is, however, strongly wind-dependent and thus intermittent in time, On a long time scale, pulse-like wind events produce on average an eastbound current drift in the open sea. The river runoff causes a slow southbound current drift of diluted freshwater along the western region of the Bothnian Sea. Distribution and deposition of dissolved and particulate matter occurs with several types of transport mechanisms. Our measurements during 1991 show that in the surface water, substances can be distributed right across the Bothnian Sea in about one to two weeks, but perhaps more normally in about one month, The geographical extension of the accumulation bottoms is most often limited to areas deeper than 40 m. Transport of particulate matter can however also occur below this critical depth especially during periods of strong winds, forcing wind waves of sufficient wave length and amplitude to erode bottom particulate matter.

The Rossby Centre Atmospheric Regional Climate Model (RCA2) is described and simulation results, for the present climate over Europe, are evaluated against available observations. Systematic biases in the models mean climate and climate variability are documented and key parameterization weaknesses identified. The quality of near-surface parameters is investigated in some detail, particularly temperature, precipitation, the surface energy budget and cloud cover. The model simulates the recent, observed climate and variability with a high degree of realism. Compensating errors in the components of the surface radiation budget are highlighted and the fundamental causes of these biases are traced to the relevant aspects of the cloud, precipitation and radiation parameterizations. The model has a tendency to precipitate too frequently at small rates, this has a direct impact on the simulation of cloud-radiation interaction and surface temperatures. Great care must be taken in the use of observations to evaluate high resolution RCMs, when they are forced by analyzed boundary conditions. This is particularly true with respect to precipitation and cloudiness, where observational uncertainty is often larger than the RCM bias.

The Rossby Centre regional climate model (RCA2) has been integrated over the Arctic Ocean as part of the international ARCMIP project. Results have been compared to observations derived from the SHEBA data set. The standard RCA2 model overpredicts cloud cover and downwelling longwave radiation, during the Arctic winter. This error was improved by introducing a new cloud parameterization, which significantly improves the annual cycle of cloud cover. Compensating biases between clear sky downwelling longwave radiation and longwave radiation emitted from cloud base were identified. Modifications have been introduced to the model radiation scheme that more accurately treat solar radiation interaction with ice crystals. This leads to a more realistic representation of cloud-solar radiation interaction. The clear sky portion of the model radiation code transmits too much solar radiation through the atmosphere, producing a positive bias at the top of the frequent boundary layer clouds. A realistic treatment of the temporally evolving albedo, of both sea-ice and snow, appears crucial for an accurate simulation of the net surface energy budget. Likewise, inclusion of a prognostic snow-surface temperature seems necessary, to accurately simulate near-surface thermodynamic processes in the Arctic.

Clouds play an important role in the climate system, and strongly modify radiation conditions in the atmosphere and at the earth's surface. Present estimations show that the net impact of clouds in the atmosphere results in a cooling several times larger than the expected warming that would result from a doubling of the CO2-concentration in the atmosphere. Regional and global monitoring of cloud conditions is therefore necessary for studying the role of clouds in possible climate feedback mechanisms. This paper presents a method to estimate cloud conditions (cloud cover) in the Nordic region, from multispectral satellite data. A cloud classification scheme, based on high-resolution imagery data from polar orbiting NOAA-satellites, was used to produce monthly cloud frequencies for the summer of 1993. Comparisons with existing surface observations have shown very good agreement. Cloud conditions are shown to be highly sensitive to characteristics of the earth's surface. Large differences between land and sea areas were found, especially in the beginning of summer. Cloud frequencies were significantly lower over the Baltic Sea compared to surrounding land areas. Mountainous areas showed, on the contrary, much higher cloud frequencies than surrounding areas.

A set of six regional climate model experiments is investigated for future changes in daily temperature and precipitation in Europe. Changes in the probability distributions for these variables are studied. It is found that the asymmetry of these distributions change differently depending on location and season. Large summertime changes in extremely high temperatures in central, eastern and southern Europe are followed by higher than average temperature increases on warm days in general. Likewise, temperatures on cold days increase much more than the average temperature increase during winter in eastern and northern Europe. A comparison with historical data on wintertime temperature shows that the model simulated and observed daily variability are similar. In particular, the much stronger increase in temperatures on cold days, compared to the average temperature increase as observed in warm compared to cold historical periods, is simulated also by the model. The contribution from heavy precipitation events is simulated to increase over most parts of Europe in all seasons.

This article reviews interactions and health impacts of physical, chemical, and biological weather. Interactions and synergistic effects between the three types of weather call for integrated assessment, forecasting, and communication of air quality. Today's air quality legislation falls short of addressing air quality degradation by biological weather, despite increasing evidence for the feasibility of both mitigation and adaptation policy options. In comparison with the existing capabilities for physical and chemical weather, the monitoring of biological weather is lacking stable operational agreements and resources. Furthermore, integrated effects of physical, chemical, and biological weather suggest a critical review of air quality management practices. Additional research is required to improve the coupled modeling of physical, chemical, and biological weather as well as the assessment and communication of integrated air quality. Findings from several recent COST Actions underline the importance of an increased dialog between scientists from the fields of meteorology, air quality, aerobiology, health, and policy makers.

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.

Long-term trends in the Secchi depth of the Baltic Sea have been interpreted in terms of eutrophication (1, 2). The spectral attenuation coefficient K-d (490) can be estimated from remote sensing data (3). Given the empirical and theoretical relationships between diffuse attenuation and Secchi depth, it is therefore possible to estimate the trophic state from remote sensing data. This paper considers relationships among remotely sensed and in-water measured K-d (490), and Secchi depth data obtained during dedicated sea-truthing campaigns in the eastern Baltic Proper in 1999 (4) and in the western Baltic Proper/Himmerfjarden area during 2001 and 2002. In-water measurements are used to establish the relationship between the PAR and the spectral attenuation coefficient in the Baltic Sea via regression analysis. The analysis showed that in the area of investigation K-d(490) is about 1.48 times higher than K-d(PAR). This relationship is then used to define the link between the photic zone depth and the remote sensing optical depth, K-d (490)(-1). The results show that the depth of the euphotic zone is about 6.8 times K-d (490)(-1). The regression analysis between K-d (PAR) and Secchi depth confirmed previous work that K-d (PAR) is about 1.7 of the inverse Secchi depth. Furthermore, an in-water algorithm between Secchi depth and K-d (490) is used to simulate a Secchi depth map of the Bartic sea from seaWiFS K-d (490) data. This map is verified against sea-truthing data. K-d (490) data derived from satellite is compared to in situ Kd (490), and the sources of error are discussed.

Recent mild and wet years in Sweden were compared with long observation series of temperature, precipitation and runoff. Spatial average series for northern and southern Sweden were constructed and analyzed for the period 1901-2002. Precipitation increased considerably during the period, whereas temperature and runoff increases were weaker. On average, for the whole country, the differences between the period 1991-2002 and 1901-1990 were +0.7degreesC for temperature, +11% in precipitation and +7% in runoff. The differences in temperature and precipitation, but not runoff, were significant at the 5% level. However, the 1930s were equally mild, and the runoff was almost as high in the 1920s. The characteristic feature of the past decade is the combination of high temperature, precipitation and runoff. The deviation between the most recent decade and the preceding years is consistent with climate scenario projections for Sweden, but there are also differences in the seasonal pattern.

The HBV-NP model is a newly developed water quality model that describes the turnover and fluxes of both nitrogen and phosphorous. It is based on the conceptual precipitation/runoff HBV model. The HBV-NP model was applied for simulation of nitrogen for the Ronnea catchment in southern Sweden. The catchment was divided into 64 subcatchments in the model. Discharge measurements from six stations and nitrogen measurements from 12 stations were used in the calibration of parameters in the model. Eight automatic calibrations were performed with different combinations of time periods, objective functions, and levels of the nitrogen load in the model. A regionally extended interpretation of the Nash-Sutcliffe R-2 criterion was used in the calibration. In the evaluation of the criterion, the errors were summed over both time steps and sampling points. Scenario simulations of combined measures for reduction of nitrogen load into the sea by 30% were thereafter performed with the eight sets of parameters established by calibration. The model parameters were not uniquely defined by the calibration. However, the simulated relative reduction of nitrogen load into the sea was relatively insensitive to the choice of parameter set, given the available input sources, variables, and data.

Understanding how climate change, exploitation and eutrophication will affect populations and ecosystems of the Baltic Sea can be facilitated with models which realistically combine these forcings into common frameworks. Here, we evaluate sensitivity of fish recruitment and population dynamics to past and future environmental forcings provided by three ocean-biogeochemical models of the Baltic Sea. Modeled temperature explained nearly as much variability in reproductive success of sprat (Sprattus sprattus; Clupeidae) as measured temperatures during 1973-2005, and both the spawner biomass and the temperature have influenced recruitment for at least 50 years. The three Baltic Sea models estimate relatively similar developments (increases) in biomass and fishery yield during twenty-first century climate change (ca. 28 % range among models). However, this uncertainty is exceeded by the one associated with the fish population model, and by the source of global climate data used by regional models. Knowledge of processes and biases could reduce these uncertainties.

We present a multi-model ensemble study for the Baltic Sea, and investigate the combined impact of changing climate, external nutrient supply, and fisheries on the marine ecosystem. The applied regional climate system model contains state-of-the-art component models for the atmosphere, sea ice, ocean, land surface, terrestrial and marine biogeochemistry, and marine food-web. Time-dependent scenario simulations for the period 1960-2100 are performed and uncertainties of future projections are estimated. In addition, reconstructions since 1850 are carried out to evaluate the models sensitivity to external stressors on long time scales. Information from scenario simulations are used to support decision-makers and stakeholders and to raise awareness of climate change, environmental problems, and possible abatement strategies among the general public using geovisualization. It is concluded that the study results are relevant for the Baltic Sea Action Plan of the Helsinki Commission.

Sea-ice in the Baltic Sea in present and future climates is investigated. The Rossby Centre Regional Atmosphere-Ocean model was used to perform a set of 30-year-long time slice experiments. For each of the two driving global models HadAM3H and ECHAM4/OPYC3, one control run (1961-1990) and two scenario runs (2071-2100) based upon the SIRES A2 and B2 emission scenarios were conducted. The future sea-ice volume in the Baltic Sea is reduced by 83% on average. The Bothnian Sea, large areas of the Gulf of Finland and Gulf of Riga, and the outer parts of the southwestern archipelago of Finland will become ice-free in the mean. The presented scenarios are used to study the impact of climate change on the Baltic ringed seal (Phoca hispida botnica). Climate change seems to be a major threat to all southern populations. The only fairly good winter sea-ice habitat is found to be confined to the Bay of Bothnia.

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.

In the future, the Baltic Sea ecosystem will be impacted both by climate change and by riverine and atmospheric nutrient inputs. Multi-model ensemble simulations comprising one IPCC scenario (A1B), two global climate models, two regional climate models, and three Baltic Sea ecosystem models were performed to elucidate the combined effect of climate change and changes in nutrient inputs. This study focuses on the occurrence of extreme events in the projected future climate. Results suggest that the number of days favoring cyanobacteria blooms could increase, anoxic events may become more frequent and last longer, and salinity may tend to decrease. Nutrient load reductions following the Baltic Sea Action Plan can reduce the deterioration of oxygen conditions.