scholarly journals Causes of the extensive hypoxia in the Gulf of Riga in 2018

2021 ◽  
Author(s):  
Stella-Theresa Stoicescu ◽  
Jaan Laanemets ◽  
Taavi Liblik ◽  
Māris Skudra ◽  
Oliver Samlas ◽  
...  
Keyword(s):  
Bottom Layer ◽  
Oxygen Depletion ◽  
Phosphorus Release ◽  
Meteorological Conditions ◽  
Mitigation Measures ◽  
Sediment Surface ◽  
Water Volume ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. The Gulf of Riga is a relatively shallow bay connected to the deeper central Baltic Sea (Baltic Proper) via straits with sills. The decrease in the near-bottom oxygen levels from spring to autumn is a common feature in the gulf, but in 2018, hypoxia was exceptional. We analyzed temperature, salinity, oxygen, and nutrient data collected in 2018 and historical data available from environmental databases. Forcing data from the study year were compared with their long-term means and variability. The year 2018 was exceptional due to occasionally dominating north-easterly winds supporting the inflow of saltier waters from the Baltic Proper and meteorological conditions causing fast development of thermal stratification in spring. Existing stratification hindered vertical transport between the near-bottom layer (NBL) and the water layers above it. The estimated oxygen consumption rate at the sediment surface in spring-summer 2018 was about 1.7 mmol O2 m−2 h−1 that exceeded the oxygen input to the NBL due to advection and mixing. We suggest that the observed pronounced oxygen depletion was magnified by the prolonged stratified season and haline stratification in the deep layer that maintained a decreased water volume between the seabed and the pycnocline. The observed increase in phosphate concentrations in the NBL in summer 2018 suggests a significant sediment phosphorus release in hypoxic conditions counteracting the mitigation measures to combat eutrophication. We conclude, if similar meteorological conditions as in 2018 could occur more frequently in the future, such extensive hypoxia would be more common in the Gulf of Riga and other coastal basins with similar morphology and human-induced elevated input of nutrients.

Physical drivers of oxygen depletion in the Central and Eastern Baltic Sea

2020 ◽  
Author(s):  
Taavi Liblik ◽  
Stella-Theresa Stoicescu ◽  
Jaan Laanemets ◽  
Oliver Samlas ◽  
Kai Salm ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Deep Layer ◽  
Oxygen Depletion ◽  
Estuarine Circulation ◽  
Gulf Of Finland ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
The Gulf Of Finland

<p>Eutrophication and consequent increase in biomass production and sedimentation of organic material cause oxygen depletion of the deep layers and an increase in hypoxic bottom areas in the Baltic Sea.</p><p>The Baltic Sea – a semi-enclosed brackish sea – has restricted water exchange with the North Sea. High fresh water runoff and sporadic inflows of saline water through the Danish Straits maintain stratification. Seasonal thermocline and quasi-permanent halocline, their vertical location, shape and strength are sensitive to atmospheric forcing and influence the oxygen depletion in the near-bottom layer. Physical processes altering deoxygenation in the three sub-basins of the Baltic Sea (Baltic Proper, Gulf of Finland and Gulf of Riga) are under scope of the present overview. Permanent halocline is present in the deep Baltic Proper, while in the Gulf of Finland, it occasionally vanishes during winter. Complete mixing occurs in each winter in the shallow Gulf of Riga separated from the Baltic Proper by the sill. We show that the bathymetry, combined with physical drivers, causes distinct spatial and temporal patterns of oxygen depletion in the basins. The results presented here are a summary of in-situ measurement campaigns conducted by the research vessel, underwater glider, autonomous vertical profiler and bottom moorings in 2011–2020.</p><p>Large barotropic inflows from the North Sea temporarily ventilate the deep layer of the Central Baltic Proper, but rather intensify hypoxia in the Northern Baltic Proper and the Gulf of Finland. Wind-driven estuarine circulation alterations shape the hypoxic area and volume in the Gulf of Finland considerably. Seaward winds support estuarine circulation and the advection of hypoxic saltier water of the Northern Baltic Proper into the gulf deep layer. The landward wind can reverse estuarine circulation, the collapse of stratification and mixing of the whole water column in winter (when the seasonal thermocline is absent), thus, temporarily improving oxygen conditions in the deep layer of the gulf. Intrusion of cold saltier water of the Baltic Proper over the sill into the Gulf of Riga deep layer strengthens water column stratification and supports hypoxia formation in summer. Such a water exchange regime is related to the northerly wind forced upwelling along the eastern coast of the Baltic Proper. The role of submesoscale processes on vertical mixing and deep layer ventilation is still unclear, and the data of high-resolution in situ measurements in the Baltic Sea is limited yet. Preliminary results from the dedicated underwater glider surveys conducted at the coastal slope of Eastern Baltic Proper in 2019-2020 will be presented.</p>

scholarly journals Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

2017 ◽  
Vol 14 (8) ◽  
pp. 2113-2131 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Cross Sections ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Long-term oxygen and nutrient transports in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations with and without data assimilation covering the period 1970–1999 are carried out. Here, the weakly coupled scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate observed profiles in the reanalysis system. The reanalysis shows considerable improvement in the simulation of both oxygen and nutrient concentrations relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen-dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between sub-basins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections are calculated. Further, the spatial distributions of regions with nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net transport (export minus import) of nutrients from the Baltic proper into the surrounding sub-basins (except the net phosphorus import from the Gulf of Riga and the net nitrogen import from the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are retained in this sub-basin. For the calculation of sub-basin budgets, the location of the lateral borders of the sub-basins is crucial, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

2021 ◽  
Vol 18 (9) ◽  
pp. 2981-3004
Author(s):  
Astrid Hylén ◽  
Sebastiaan J. van de Velde ◽  
Mikhail Kononets ◽  
Mingyue Luo ◽  
Elin Almroth-Rosell ◽  
...  
Keyword(s):  
Organic Matter ◽  
Deep Water ◽  
Oxygen Depletion ◽  
Inorganic Phosphorus ◽  
Phosphorus Release ◽  
Water Inflow ◽  
Low Oxygen ◽  
In Situ Experiment ◽  
Inflow Event ◽  
The Baltic

Abstract. Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under low-oxygen bottom water conditions, phosphorus release from the sediment is elevated, which further stimulates primary production. It is commonly assumed that re-oxygenation could break this “vicious cycle” by increasing the sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this 3-year study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment, likely due to an increase in organic matter supply to the deeper basins, potentially combined with a transient stimulation of the mineralisation efficiency. As a result, the net sedimentary DIP release per m2 was 56 %–112 % higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release.

scholarly journals Nutrient cycling in the Baltic Sea – results from a 30-year physical-biogeochemical reanalysis

2016 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
Phosphorus Transport ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. The long-term oxygen and nutrient cycles in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations covering the period 1970–1999 are carried out with and without data assimilation, respectively. Here, the "weakly coupled" scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate the observed profiles in the reanalysis system. The simulation results show considerable improvements in both oxygen and nutrient concentrations in the reanalysis relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between subbasins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections, are calculated. Further, bottom areas of nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net exports of nutrients into the surrounding subbasins (except the phosphorus transport into the Gulf of Riga and the nitrogen transports into the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are buried in this subbasin. For the calculation of subbasin budgets, it is crucial where the lateral borders of the subbasins are located, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals Non-stationary analysis of water level extremes in Latvian waters, Baltic Sea, during 1961–2018

2020 ◽  
Author(s):  
Nadezhda Kudryavtseva ◽  
Tarmo Soomere ◽  
Rain Männikus
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Water Level ◽  
Shape Parameter ◽  
Extreme Value Distribution ◽  
Scale Parameters ◽  
Stationary Analysis ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Analysis and prediction of water level extremes in the eastern Baltic Sea is a difficult task because of the contribution of various drivers to the water level, the presence of outliers in time series and possibly non-stationarity of the extremes owing to the changes in the atmospheric forcing. Non-stationary modelling of extremes was performed to the block maxima of water level derived from the time series at six locations in the Gulf of Riga and one location in the Baltic proper, Baltic Sea, during 1961–2018. Several parameters of the Generalised Extreme Value distribution of the measured water maxima both in the Baltic proper and in the interior of the Gulf of Riga exhibit statistically significant changes over these years. The most considerable changes occur to the shape parameter ξ. All stations in the interior of the Gulf of Riga experienced a regime shift: a drastic abrupt drop of the shape parameter from ξ ≈ 0.03 ± 0.02 to ξ ≈ −0.36 ± 0.04 around 1986 followed by an increase of a similar magnitude around 1990. This means a sudden switch from a Fréchet distribution to a three-parameter Weibull distribution and back. The water level extremes at Liepaja in the Baltic proper and Kolka at the entrance to the Gulf of Riga reveal significant linear trends in the location and scale parameters. This pattern indicates a different course of the water level extremes in the Baltic proper and the interior of the Gulf of Riga. The described changes may lead to greatly different projections for long-term behaviour of water level extremes and their return periods based on data from different intervals.

scholarly journals Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

2021 ◽  
Author(s):  
Astrid Hylén ◽  
Sebastiaan J. van de Velde ◽  
Mikhail Kononets ◽  
Mingyue Luo ◽  
Elin Almroth-Rosell ◽  
...  
Keyword(s):  
Deep Water ◽  
Oxygen Depletion ◽  
Inorganic Phosphorus ◽  
Phosphorus Release ◽  
Water Inflow ◽  
Low Oxygen ◽  
In Situ Experiment ◽  
Inflow Event ◽  
Bottom Waters ◽  
The Baltic

Abstract. Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under low-oxygen bottom-water conditions, phosphorus release from the sediment is elevated which further stimulates primary production. It is commonly assumed that re-oxygenation could break this ‘vicious cycle’ by increasing sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in-situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this three-year-long study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment. As a result, the net sedimentary DIP release per m2 was 35–70 % higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release.

scholarly journals Interannual and Seasonal Temperature and Salinity Variations in the Gulf of Riga and Corresponding Saline Water Inflow From the Baltic Proper

2001 ◽  
Vol 32 (2) ◽  
pp. 135-160 ◽  
Author(s):  
Urmas Raudsepp
Keyword(s):  
Baltic Sea ◽  
River Flow ◽  
Saline Water ◽  
Seasonal Temperature ◽  
The Baltic Sea ◽  
Increasing Trend ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
Salinity Variations

Salinity and temperature data from the Gulf of Riga, a semi-enclosed sub-basin of the Baltic Sea, were analyzed with a focus on interannual and seasonal variability. The data were compiled from measurements taken from 1973 to 1995, a period which includes the stagnation period in the Baltic Sea. Interannual and seasonal variations in the net inflow of saline water from the Baltic Proper were estimated from volume and salt conservation equations for the period 1973-90. The basic decreasing trend, superimposed interannual variations in salinity, and interannual and seasonal temperature variations in the Gulf of Riga coincided with corresponding changes above the halocline in the Baltic Proper. Seasonal salinity variations were notable in the Gulf of Riga as compared to the Baltic Proper, where variations were negligible. Estimated annual mean inflow varied between 2,000 and 5,000 m3/s (average 3,200 m3/s), with a notable increasing trend. A simultaneous increasing trend was extracted from annual mean river flow data. Short-term fluctuations (over 4-6 years) of annual mean inflow ran opposite to the fluctuations of the magnitude of river flow. The average salinity in the Gulf of Riga increased during strong inflow and weak river flow and decreased when inflow was weak and river flow was strong. Variations in the inflow of water salinity had a minor effect on salinity variations in the Gulf of Riga. Seasonal inflow was strongest in spring and autumn and weak in winter.

scholarly journals Non-stationary analysis of water level extremes in Latvian waters, Baltic Sea, during 1961–2018

2021 ◽  
Vol 21 (4) ◽  
pp. 1279-1296
Author(s):  
Nadezhda Kudryavtseva ◽  
Tarmo Soomere ◽  
Rain Männikus
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Water Level ◽  
Shape Parameter ◽  
Linear Trend ◽  
Significant Linear Trend ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
Eastern Baltic

Abstract. Analysis and prediction of water level extremes in the eastern Baltic Sea are difficult tasks because of the contribution of various drivers to the water level, the presence of outliers in time series, and possibly non-stationarity of the extremes. Non-stationary modeling of extremes was performed to the block maxima of water level derived from the time series at six locations in the Gulf of Riga and one location in the Baltic proper, Baltic Sea, during 1961–2018. Several parameters of the generalized-extreme-value (GEV) distribution of the measured water level maxima both in the Baltic proper and in the interior of the Gulf of Riga exhibit statistically significant changes over these years. The most considerable changes occur to the shape parameter ξ. All stations in the interior of the Gulf of Riga experienced a regime shift: a drastic abrupt drop in the shape parameter from ξ≈0.03±0.02 to ξ≈-0.36±0.04 around 1986 followed by an increase of a similar magnitude around 1990. This means a sudden switch from a Fréchet distribution to a three-parameter Weibull distribution and back. The period of an abrupt shift (1986–1990) in the shape parameters of GEV distribution in the interior of the Gulf of Riga coincides with the significant weakening of correlation between the water level extremes and the North Atlantic Oscillation (NAO). The water level extremes at Kolka at the entrance to the Gulf of Riga reveal a significant linear trend in shape parameter following the ξ≈-0.44+0.01(t-1961) relation. There is evidence of a different course of the water level extremes in the Baltic proper and the interior of the Gulf of Riga. The described changes may lead to greatly different projections for long-term behavior of water level extremes and their return periods based on data from different intervals. Highlights. Water level extremes in the eastern Baltic Sea and the Gulf of Riga are analyzed for 1961–2018. Significant changes in parameters of generalized-extreme-value distribution are identified. Significant linear trend in shape parameter is established at Kolka. The shape parameter changes in a step-like manner. The shape parameter of GEV has regime shifts around 1986 and 1990 in the gulf.

SEDIMENT BALANCE OF THE VISTULA LAGOON

2017 ◽  
Author(s):  
Vladimir Chechko ◽  
Vladimir Chechko ◽  
Boris Chubarenko ◽  
Boris Chubarenko
Keyword(s):  
Baltic Sea ◽  
Field Measurements ◽  
Water Volume ◽  
Critical Element ◽  
Vistula Lagoon ◽  
The Baltic Sea ◽  
Direct Measurements ◽  
Biogenic Components ◽  
The Baltic ◽  
The Vistula Lagoon

Vistula Lagoon is the second largest lagoon in the Baltic Sea with maximum depth 5.2 m and average depth 2.7 m. Water volume and area are 2.3 km3 and 838 km2. Lagoon is connected with the Baltic Sea by single inlet 400 m wide and 10-12 m deep. Sediment budget estimation were made using literature sources, results of field measurements (hydrology, suspended sediment content, upper layer sediment structure, direct measurements of sedimentation in summer and winter conditions). The budget for terrigene and biogenic components of sediments were made, considering their contributions from the rivers, inflow from the Baltic Sea, coastal erosion and aerial flux, biological production within the lagoon, totally - ca. 730 thousands ton per year. Nearly half of total gain is washed out (105 and 244 thousands ton per year of terrigene and biogenic components), another half is dissolved and mineralized (biogenic component), and only 10% is deposited on the bottom, resulting in rather low sedimentation rate - 0.4 mm/year during last 100 years. Paper explain the reason of difference with estimation made in (Chubarenko&Chubarenko, 2002) and concludes that the clarification of estimates of the amounts of sediments transported from the lagoon to the Baltic Sea is a critical element for understanding the evolution of the Vistula Lagoon as a sedimentation system.

Optimization of Nutrient Removal in Stockholm

1991 ◽  
Vol 24 (7) ◽  
pp. 103-111 ◽  
Author(s):  
G. Brattberg ◽  
L.-G. Reinius ◽  
M. Tendaj
Keyword(s):  
Nutrient Removal ◽  
Sewage Treatment ◽  
Water Source ◽  
Chemical Precipitation ◽  
Phosphorus Load ◽  
Sewage Treatment Plants ◽  
Limiting Nutrient ◽  
Baltic Proper ◽  
Mechanical Stage ◽  
The Baltic

Stockholm was founded at the point where the waters of Lake Mälaren emerge into the Baltic Sea. Lake Mälaren is the water source of the water works of Stockholm. The Lake also receives water from one of the sewage treatment plants. The outlet from the two other sewage treatment plants are in the inner part of the archipelago. During 1968-73 the treatment was improved, after which the phosphorus load to the receiving water significantly decreased. The total P concentration in the surface water has decreased since 1970 and phosphorus has replaced nitrogen as the most limiting nutrient throughout the entire archipelago within 50 km from Stockholm. To further reduce the eutrophication a continued reduction of the phosphorus load is most effective. For the Baltic proper as a whole, where primary nitrogen limitation is present, it is important to reduce the supply of nitrogen to the greatest possible extent. The treatment plants in Stockholm are located in subsurface rock-chambers. The treatment includes mechanical, biological and chemical treatment. In the mechanical stage the sewage is treated in screens, grit chambers and primary sedimentation. The biological stage is a conventional activated sludgeprocess. For the chemical precipitation ferroussulphateis added before the screens. The sludge is stabilized in anaerobic digesters and dewatered in centrifuges before disposal on farmland. To meet more stringent requirements on nitrification and nitrogen removal several projects are going on to optimize the nutrient removal. The aim of these investigations is to improve the plants' performance within the existing plant.

Sign in / Sign up

Export Citation Format

Share Document