Eutrophication of the Baltic Sea is considered a major threat to its ecological status. We present and discuss Polish riverine flow normalized loads of total nitrogen (TN) and total phosphorus (TP) discharged into the Baltic Sea in (i) 1988-2014, (ii) periods of maximum TN (1992-1994), TP (1988-1991) emission, (iii) the reference period (1997-2003) established by the Helsinki Commission (HELCOM), (iv) 2012-2014, last years of our study. Despite considerable nutrient load reductions prior to the HELCOM reference period, Poland is expected to reduce TN and TP loads by 30% and 66%, respectively. In the light of our historical and up-to-date findings defining ecological status of the Baltic Sea, we suggest that the proposed TP load reduction is overestimated and its realization may lead to (i) undesirable consequences for the Baltic ecosystem, (ii) would require a decline in TP concentrations to 0.067 mg P dm(-3) (the Vistula River) and 0.083 mg P dm(-3) (the Oder River), values reported for pre-industrial times. The current nutrient concentrations in the Vistula and Oder safely comply with the requirements of the Water Framework Directive. We also comment on the top-down and bottom-up effect resulting in quantitative and qualitative reorganization of the Baltic ecosystem, a phenomenon already observed in the Baltic Sea.

Lake Simcoe, the largest lake in southern Ontario outside of the Laurentian Great Lakes, is affected by numerous stressors including eutrophication resulting from total phosphorus (TP) loading, climate change, and invasions of exotic species. We synthesized the long-term responses of Lake Simcoe to these stressors by assessing trends in water quality and biological composition over multiple trophic levels. Evidence for climate change included increasing thermal stability of the lake and changes in subfossil diatom communities over time. Although the deep water dissolved oxygen (O-2) minimum has increased significantly since TP load reductions, it is still below estimated historical values and the Lake Simcoe Protection Plan end-of-summer target level of 7 mg O-2 L-1. Low deep water O-2 concentrations corresponded with a decline in coldwater fish abundance. Since 1980, some nutrient concentrations have decreased (spring TP) while others have increased (silica), but many show no obvious changes (ice-free TP, nitrate, ammonium). Increases in water clarity, combined with declines in chlorophyll a and phytoplankton biovolumes in Cook's Bay, were temporally consistent with declines in TP loading and the lake-wide establishment of dreissenid mussels as a major component of the Lake Simcoe ecosystem. Using an investigative tool, we identified 2 periods when abrupt shifts potentially occurred in multiple parameters: 1986 and 1995-1997. Additional ecosystem level changes such as declines in zooplankton, declines in offshore benthic invertebrate abundance, and increased nearshore invertebrate abundance likely reflect the effects of invasive species. The interaction of these multiple stressors have significantly altered the Lake Simcoe ecosystem.

Eutrophication continues to be a major global challenge to water quality scientists. The global demand on water resources due to population increases, economic development, and emerging energy development schemes has created new environmental challenges to global sustainability. Eutrophication, causes, consequences, and control provides a current account of many important aspects of the processes of natural and accelerated eutrophication in major aquatic ecosystems around the world. The connections between accelerated eutrophication and climate change, chemical contamination of surface waters, and major environmental and ecological impacts on aquatic ecosystems are discussed. Water quality changes typical of eutrophication events in major climate zones including temperate, tropical, subtropical, and arid regions are included along with current approaches to treat and control increased eutrophication around the world. The book provides many useful new insights to address the challenges of global increases in eutrophication and the increasing threats to biodiversity and water quality.

This work uses empirical data from the HELCOM database and a new empirically-based model to predict the concentration of cyanobacteria in the Baltic Proper. The aim has been to estimate nitrogen fixation. The inherent variabilities/patchiness in the variables regulating nitrogen fixation are great. This means that different approaches may provide complementary information so that several relatively uncertain estimates may together provide less uncertainty in the estimate for nitrogen fixation in a given system. We show that there is marked variability in nitrogen fixation among different years (a factor of 20 between the year 2001 with the smallest value and 2005 with the highest value of about 900 kt/yr of N-fixation). The mean value for the period from 1997 to 2005 was 190 kt/yr. TN/TP based on median monthly data has been higher than the Redfield ratio of 7.2 since 1994. 6.5% of all individual data (n = 3001) from the surface-water layer (44 m) in the Baltic Proper for samples with temperatures higher than 15°C (when risks of getting cyanobacteria blooms are favoured) have TN/TP lower than 7.2. The mean TN/TP is 20 for surface-water sites with temperatures higher than 15°C, indicating that the average trophic conditions in the Baltic Proper are likely more limited by phosphorus than nitrogen. Nitrogen fixation is an important contributor to the nitrogen concentration and we give overall budgets for nitrogen and phosphorus in the Baltic Proper, including nutrient data from land uplift, which is the most important contributor for nutrients and often neglected in discussions about sources of nutrients to the Baltic Sea.

There are major differences in the bioproduction potential of different coastal areas. The aim of this work is to review and discuss simple, operational criteria related to the bioproduction potential of coastal areas and to present and motivate an Index of Biological Value (IBV) for coastal management. This index is based on two key variables, which can be determined easily from bathymetric maps and data from standard monitoring programs: (1) the bottom area of the coast above the Secchi depth and (2) the topographical openness (or exposure) of the coastal area. The exposure is defined by the ratio between the section area of the coast and the enclosed coastal area. The boundaries of the coastal area should not be defined in an arbitrary manner but according to the topographical bottleneck method so that the exposure attains a minimum value. IBV is meant to be used to identify coastal areas with a high production potential so that preservation plans and remedial actions can be directed to such areas in a cost-efficient manner. Applying the index using a dataset including 478 coastal areas from the Baltic Sea, there were 5 (1%) extremely productive coastal areas (IBV > 50), 43 (9%) very productive coastal areas (25 < IBV < 50), 209 (43.7%) productive coastal areas (10 < IBV < 25), 214 (63.0%) moderately productive coastal areas (1 < IBV < 10) and 7 (1.5%) low-productive coastal areas (IBV < 1).

There are major differences in sensitivity or vulnerability to anthropogenic loading of nutrients (eutrophication) among different coastal areas. The aim of this work is to discuss criteria for coastal area sensitivity and to present a sensitivity index (SI). This index is based on two morphometric parameters, which can be determined from simple bathymetric maps. (1) The topographical openness (or exposure) and (2) the dynamic ratio of the coastal area. The exposure is defined by the ratio between the section area of the coast and the enclosed coastal area. The boundaries of the coastal area should not be defined in an arbitrary manner but according to the topographical bottleneck method so that the exposure attains a minimum value. The exposure regulates the theoretical water retention time, which, in turn, regulates the effects of a given nutrient loading. The dynamic ratio is defined by the ratio between the square root of the coastal area and the mean depth. The dynamic ratio influences many fundamental internal transport processes. Coastal management should focus remedial actions on critical coastal areas which are at hand if the nutrient loading is high and/or the sensitivity is high. Testing the sensitivity index using a comprehensive data set including 478 coastal areas from the Baltic Sea. There were 2 (0.4%) extremely sensitive coastal areas (SI > ; 50), 50 (10.5%) very sensitive coastal areas (10 < , SI < , 50), 121 (25.3%) sensitive coastal areas (5 < , SI < , 10), 301 (63.0%) low sensitive coastal areas (1 < , SI < , 5) and 4 (0.8%) not sensitive coastal areas (SI < , 1).