61 research outputs found
L\ue4\ue4nemere eutrofeerumise indikaatorite pikaajalised muutused. Long-term Changes of the Eutrophication Indicators of the Baltic Sea
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Oxygen in the gulf of Finland and the role of major Baltic inflows: a modelling experiment
No full textDuring recent decades near-bottom hypoxia and anoxia became common in the Gulf of Finland (GoF), even though nutrient discharge from land has declined. Since the beginning of the 1990s, after a long stagnant period, several strong saline water inflows to the Baltic Sea occurred. Consequences of these events on oxygen dynamics in the GoF were studied with the aid of a coupled hydrodynamic-biogeochemical model. After the model was set up to reproduce ecohydrodynamic conditions in the Baltic Sea since 1990, an experimental run was performed, without sea-level variations at the open boundary. This does exclude one of the most important factors causing barotropic inflows to the Baltic Sea. Our main results showed that in the absence of inflows vertical salinity stratification in the GoF decreases, which improves oxygenation of deep layers. On the other hand, in case of inflows from the Baltic Proper to the GoF, less salty, but anoxic water is brought in. However, due to a weaker stratification, oxic conditions in the GoF restore rather quickly. Mechanisms responsible for the exchange between Baltic Proper and the GoF are further analysed. The results confirm that during recent decades the major Baltic inflows had a distinct influence on the near-bottom oxygen dynamics in the GoF. This raises a question of the potential impact of inflows on the GoF environment in the future, especially in combination with ecosystem management actions and climate change.JRC.H.1 - Water Resource
Water quality assessment using integrated modeling and monitoring in Narva Bay, Gulf of Finland
No full textModeling of eutrophication processes in the Gulf of Finland during 1991-2010
No full textThe hydrodynamic model GETM coupled with the ecosystem model ERGOM was applied to the Baltic Sea area for the period 1991-2010. The first part of the modeled period is characterized by considerable socioeconomic changes in the area that are generally considered favorable for the status of coastal marine ecosystems due to a decrease in external nutrient loads. Model results were used to describe and analyze changes in salinity, nutrient (nitrate and phosphate) and oxygen dynamics in the central part of the Gulf of Finland, the most eutrophied sub-basin of the Baltic Sea, over the last two decades. Model validation showed very good agreement between modeled and measured parameters in the Gulf. In the surface layer nitrates were slightly underestimated, while phosphates were overestimated during the second half of the modeled period. Near-bottom parameters were generally accurately reproduced. Model results show that in fact the eutrophication status of the Gulf of Finland has worsened during the last two decades, especially during the latter part of the modeled period. This is reflected in an increased frequency of anoxic events and consecutive high phosphate loading and decrease of near-bottom nitrate concentrations. Stronger stratification favors anoxic conditions in the near-bottom, while a decrease in salinity induced by mixing processes allows for oxygenation of deep areas. However, the effect of these mixing events is short-term and deep water quickly returns to the anoxic state.JRC.H.1 - Water Resource
Modeling the Response of the Gulf of Finland Ecosystem to Changing Climate
No full textDirect and indirect effects of changing meteorological conditions include alterations in nutrient cycling, timing and extent of algal blooms, species composition and oxygen dynamics of the Baltic coastal ecosystems. In this study the one-dimensional water column model GOTM coupled with a modified version of the biogeochemical model ERGOM was implemented to study the effects of changes in meteorological forcing associated with climate change on dynamics of nutrients, phytoplankton and dissolved oxygen in the central part of the Gulf of Finland. The modeling period from 1997 to 2008 (11 years) was chosen. Initial distributions of salinity, temperature and biogeochemical parameters from available measurement data were prescribed. As a reference run representing the present conditions of the ecosystem, model results with real atmospheric forcing were used. The model results were validated using observational data from the HELCOM monitoring program. The first three years of the simulation were used as a spin-up period. For the rest of the period modeled ecosystem sensitivity to variations in wind speed, air temperature, cloud cover and precipitation were analyzed separately and in a combination. The ranges of variations were chosen in agreement with recent publications on the assessment of climate change in the Baltic Sea region. Results have shown that increase in precipitation does not have any remarkable effect on the ecosystem. Increase in wind speed intensifies water mixing thus providing more nutrients for phytoplankton, but also slightly decreases water temperature. Change in cloud cover negatively affects phytoplankton growth due to decrease in light availability during biologically active period. Increased air temperature influences phytoplankton growth rates, leading to enhanced sedimentation of organic matter and near-bottom oxygen consumption. The scenario which combined all the previous, showed similar results as change in air temperature only, but slightly closer to the reference run due to action of wind speed and cloud cover. The study has shown that regardless of known limitations of one-dimensional models, they are a valuable tool in the investigation of marine ecosystem properties and their sensitivity to changes in the forcing parameters.JRC.DDG.H.3 - Global environement monitorin
Modelling the spatial distribution of phytoplankton and inorganic nitrogen in Narva Bay, southeastern Gulf of Finland, in the biologically active period
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