Assessment of Eutrophication Status Based on Sub-Surface Oxygen Conditions in the Gulf of Finland (Baltic Sea)

Stoicescu, Stella-Theresa; Lips, Urmas; Liblik, Taavi

doi:10.3389/fmars.2019.00054

Cited by 18 publications

(11 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A way to describe the level of eutrophication is to estimate the amount of oxygen consumed by organic material degradation (Carstensen et al, 2014;Stoicescu et al, 2019). Because the inflowing saltier Baltic Proper waters have higher oxygen concentration than oxygen concentrations in the central Gulf of Riga near-bottom layer, hypoxia has to be locally developed.…”

Section: Discussionmentioning

confidence: 99%

“…2 ( 1) is salinity of the "new" water defined as salinity in the NBL at station G1 at time step t2. To account for the changes in the NBL salinity and oxygen concentration due to vertical mixing between the NBL and upper water layers, we used a similar approach as by Stoicescu et al (2019). Diffusive flux through the border between the NBL and the water column above can be estimated based on the vertical gradient of salinity = * ⁄ or oxygen 2 = * 2 ⁄ , where the vertical diffusivity coefficient is calculated as = ⁄ , α is the empirical intensity factor of turbulence (we applied a constant value α = 1.5 * 10 -7 m 2 s -2 ) and N is the Brunt-Väisälä frequency defined by the vertical density gradient.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Stoicescu

Laanemets

Liblik

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Stoicescu

Laanemets

Liblik

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…The gulf is impacted by estuarine circulation reversals caused by westerly wind impulses (Elken et al, 2003), which considerably weaken the halocline and lower salinity in deep layers (Elken et al, 2003;Lilover et al, 2016;Stoicescu et al, 2019). In the case of long-lasting, strong westerly winds, circulation reversals can lead to the vanishing of the stratification in large areas of the gulf in winter (Liblik et al, 2013;Lips et al, 2017).…”

Section: Salinity Dynamics Of the Gulf Of Finlandmentioning

confidence: 99%

Salinity dynamics of the Baltic Sea

Lehmann

Myrberg

Post

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. In the Baltic Sea, salinity and its large variability, both horizontal and vertical, are key physical factors in determining the overall stratification conditions. In addition to that, salinity and its changes also have large effects on various ecosystem processes. Several factors determine the observed two-layer vertical structure of salinity. Due to the excess of river runoff to the sea, there is a continuous outflow of water masses in the surface layer with a compensating inflow to the Baltic in the lower layer. Also, the net precipitation plays a role in the water balance and consequently in the salinity dynamics. The salinity conditions in the sea are also coupled with the changes in the meteorological conditions. The ecosystem is adapted to the current salinity level: a change in the salinity balance would lead to ecological stress of flora and fauna, and related negative effects on possibilities to carry on sustainable development of the ecosystem. The Baltic Sea salinity regime has been studied for more than 100 years. In spite of that, there are still gaps in our knowledge of the changes of salinity in space and time. An important part of our understanding of salinity are its long-term changes. However, the available scenarios for the future development of salinity are still inaccurate. We still need more studies on various factors related to salinity dynamics. Among others more knowledge is needed, e.g. from meteorological patterns in various space and time scales and mesoscale variability in precipitation. Also, updated information on river runoff and inflows of saline water is needed to close the water budget. We still do not understand accurately enough the water mass exchange between North Sea and Baltic Sea and within its sub-basins. Scientific investigations of the complicated vertical mixing processes are additionally required. This paper is a continuation and update of the BACC II book which was published in 2015, including information from articles issued until 2012. After that, there have been many new publications on the salinity dynamics, not least because of the Major Baltic Inflow which took place in December 2014. Several key topics have been investigated, including the coupling of long-term variations of climate with the observed salinity changes. Here the focus is on observing and indicating the role of climate change for salinity dynamics. New results of MBI-dynamics and related water mass interchange between the Baltic Sea and the North Sea have been published. Those studies also included results from the MBI-related meteorological conditions, variability in salinity and exchange of water masses between various scales. All these processes are in turn coupled with changes in the Baltic Sea circulation dynamics.

show abstract

“…The focus on MBIs only is not sufficient to quantify the oxygen supply to the deep Baltic Sea waters. An example for hypoxia dynamics in the Gulf of Finland was given in an observational study by Stoicescu et al (2019). This region shows a strong seasonality due to a temporal pycnocline.…”

Section: Organic Matter Remineralizationmentioning

confidence: 99%

Baltic Earth Assessment Report on the biogeochemistry of the Baltic Sea

Kuliński

Rehder

Asmala

et al. 2021

Preprint

View full text Add to dashboard Cite

Abstract. Location, specific topography and hydrographic setting together with climate change and strong anthropogenic pressure are the main factors shaping the biogeochemical functioning and thus also the ecological status of the Baltic Sea. The recent decades have brought significant changes in the Baltic Sea. First, the rising nutrient loads from land in the second half of the 20th century led to eutrophication and spreading of hypoxic and anoxic areas, for which permanent stratification of the water column and limited ventilation of deep water layers made favourable conditions. Since the 1980s the nutrient loads to the Baltic Sea have been continuously decreasing. This, however, has so far not resulted in significant improvements in oxygen availability in the deep regions, which has revealed a slow response time of the system to the reduction of the land-derived nutrient loads. Responsible for that is the low burial efficiency of phosphorus at anoxic conditions and its remobilization from sediments when conditions change from oxic to anoxic. This results in a stoichiometric excess of phosphorus available for organic matter production, which promotes the growth of N2-fixing cyanobacteria and in turn supports eutrophication. This assessment reviews the available and published knowledge on the biogeochemical functioning of the Baltic Sea. In its content, the paper covers the aspects related to changes in carbon, nitrogen and phosphorus (C, N and P) external loads, their transformations in the coastal zone, changes in organic matter production (eutrophication) and remineralization (oxygen availability), and the role of sediments in burial and turnover of C, N and P. In addition to that, this paper focuses also on changes in the marine CO2 system, structure and functioning of the microbial community and the role of contaminants for biogeochemical processes. This comprehensive assessment allowed also for identifying knowledge gaps and future research needs in the field of marine biogeochemistry in the Baltic Sea.

show abstract

Assessment of Eutrophication Status Based on Sub-Surface Oxygen Conditions in the Gulf of Finland (Baltic Sea)

Cited by 18 publications

References 32 publications

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

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

Salinity dynamics of the Baltic Sea

Baltic Earth Assessment Report on the biogeochemistry of the Baltic Sea

Contact Info

Product

Resources

About