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Environmental impact of water exchange blocking in a strait – a multidisciplinary study in the Baltic Sea

Liblik Taavi, Buschmann Fred, Siht Enriko, Kuprijanov Ivan, Väli Germo, Lipp Maarja, Erm Ants, Laanemets Jaan, Eschbaum Redik, Verliin Aare, Saks Lauri, Zekker Ivar

Oceanologia

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2024

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Vol. 66 (1)

9--25

EN

In this study, we report the environmental impact of water exchange blocking by a 3 km road dam built in 1896 in the shallow Väike Strait, north-eastern Baltic Sea. Using a multidisciplinary measurement campaign and numerical simulations, we show ecological conditions in the strait have considerably altered; the previously free-flowing strait now comprises two bays with separate circulation systems. Water exchange in the area close to the dam has decreased 10–12-fold. Since advection is weakened, exchange with the atmosphere and sediments has a relatively greater role in shaping water characteristics. Consequently, occasional very high sea surface temperature, salinity, and total nitrogen, and strong diurnal cycles in water temperature (>4°C) and dissolved oxygen (>4 mg l−1) were observed near the dam in summer. Oxygen levels are continuously below saturation in winter and concentration occasionally drops to hypoxic levels with ice cover. Nitrogen content in sediments near the dam is 3–4 times higher than in neighboring areas. The dam also modifies sea level, wind wave and suspended matter patterns in the strait. Sediments near the dam show elevated content of hazardous substances likely associated with traffic on the dam road. The phytobenthos community near the dam is dominated by annual green algae, which massively decompose during winter. The dam likely impedes fish migration between suitable feeding and spawning areas, also there have been fish kills caused by rapid fluctuations in sea levels, amplified by dam. The construction of new openings would alleviate negative impacts of the dam.

2

On the buoyant sub-surface salinity maxima in the Gulf of Riga

Liblik T., Skudra M., Lips U.

Oceanologia

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2017

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No. 59 (2)

113--128

EN

Thermohaline structure in the Gulf of Riga (GoR) was investigated by a multi-platform measurement campaign in summer 2015. Stratification of the water column was mainly controlled by the temperature while salinity had only a minor contribution. Buoyant salinity maxima with variable strength were observed in the intermediate layer of the Gulf of Riga. The salinity maxima were likely formed by a simultaneous upwelling–downwelling event at the two opposite sides of the Irbe strait. The inflowing salty water did not reach the deeper (> 35 m) parts of the gulf and, therefore, the near-bottom layer of the gulf remained isolated throughout the summer. Thus, the lateral water exchange regime in the near bottom layer of the Gulf of Riga is more complicated than it was thought previously. We suggest that the occurrence of this type of water exchange resulting in a buoyant inflow and lack of lateral transport into the near-bottom layers might contribute to the rapid seasonal oxygen decline in the Gulf of Riga.

3

Currents and waves in the northern Gulf of Riga: measurement and long-term hindcast

Suursaar Ű., Kullas T., Aps R.

Oceanologia

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2012

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No. 54 (3)

421-447

EN

Based on measurements of waves and currents obtained for a period of 302 days with a bottom-mounted RDCP (Recording Doppler Current Profiler) at two differently exposed locations, a model for significant wave height was calibrated separately for those locations; in addition, the Gulf of Riga-Väinameri 2D model was validated, and the hydrodynamic conditions were studied. Using wind forcing data from the Kihnu meteorological station, a set of current, water exchange and wave hindcasts were obtained for the period 1966-2011. Current patterns in the Gulf and in the straits were wind-dependent with characteristic wind switch directions. The Matsi coast was prone to upwelling in persistent northerly wind conditions. During the hindcast period, currents increased along the Ko~iguste coast and in the Suur Strait, waves decreased noticeably off Ko~iguste but fluctuated without a clear linear trend near Matsi. The spatially contrasting results for differently exposed coasts were related to the corresponding variations in local wind conditions and to changes in atmospheric circulation patterns over northern Europe.

4

Flow, waves and water exchange in the Suur Strait, Gulf of Riga, in 2008

Raudsepp U., Laanemets J., Haran G., Alari V., Pavelson J., Köuts T.

Oceanologia

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2011

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No. 53 (1)

35-56

EN

Wind, flow and wave measurements were performed in November-December in 2008 in the relatively narrow and shallow Suur Strait connecting the waters of the Väinameri and the Gulf of Riga. During the measurement period wind conditions were extremely variable, including a severe storm on 23 November. The flow speed along the strait varied between ±0.2 m s-1, except for the 0.4 m s-1 that occurred after the storm as a result of the sea level gradient. The mean and maximum significant wave heights were 0.53 m and 1.6 m respectively. Because of their longer fetch, southerly winds generated higher waves in the strait than winds from the north. All wave events caused by the stronger southerly winds induced sediment resuspension, whereas the current-induced shear velocity slightly exceeded the critical value for resuspension only when the current speed was 0.4 m s-1. A triple-nested two-dimensional high resolution (100 m in the Suur Strait) circulation model and the SWAN wave model were used to simulate water exchange in 2008 and the wave-induced shear velocity field in the Suur Strait respectively. Circulation model simulations demonstrated that water exchange was highly variable, that cumulative transport followed an evident seasonal cycle, and that there was an gross annual outflow of 23 km3 from the Gulf of Riga. The horizontal distribution of wave-induced shear velocity during the strong southerly wind event indicated large shear velocities and substantial horizontal variability. The shear velocities were less than the critical value for resuspension in the deep area of the Suur Strait.

5

Modeling water exchange in the Oder River mouth area

Kowalewska-Kalkowska H., Kowalewski M.

Oceanological and Hydrobiological Studies

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2007

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Vol. 36, No.1

55-67

EN

A three-dimensional operational hydrodynamic model of the Baltic Sea (M3D_UG) developed based on the Princeton Ocean Model (POM) was applied to model water exchange in the Oder River mouth area. Due to wind-driven back flow in the Oder mouth, a simplified operational model of river discharge was also developed based on the water budget in a stream channel. Linking the Oder discharge and Baltic Sea models into a single system allowed simulating hydrodynamic conditions in the Szczecin Lagoon and the Pomeranian Bay. Since the model adequately approximates hydrodynamic variability, it is a reliable tool for modeling water exchange in the Oder River mouth area and for assessing Oder water spread in the Baltic Sea.

6

Periodic variability of currents induced by topographically trapped waves in the coastal zone in the Gulf of Finland

Talpsepp L.

Oceanologia

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2006

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No. 48 (S)

75-90

EN

The aim of this paper is to examine the water exchange regime between the bays of northern Estonia (Pakri Bay, Ihasalu Bay and Muuga Bay) and the open part of the Gulf of Finland. To this end, the current measurements and CTD-castings performed at the border of the bays and the open part of the Gulf of Finland in summer 1994, 1995-96 and 1997 are analysed. All the current measurements displayed one feature in common: the existence of periodic variability with a current amplitude of between 5 and 25 cm s-1 and a variability period of 3-4 days (68 hours in Pakri Bay, 72 hours in Muuga Bay and 78 hours in Ihasalu Bay). The amplitudes of this variability differed during different time periods of the experiment and in different parts of the southern Gulf of Finland. The hypothesis was propounded that this variability is the result of bottom-trapped waves, as had been found in many other regions of the Baltic Sea (Aitsam & Talpsepp 1982, Talpsepp 1983). To interpret the results of the measurements, a model of bottom-trapped waves for this region was used. This was the short-wave version of Huthnance's (1978) numerical model of coastal-trapped waves, according to which the wave parameters for the experimental regions were calculated. Comparison of the model and the measurements implies that coastal-trapped waves do exist off the southern coast of the Gulf of Finland.

7

Modelling of the circulation, water exchange and water age properties of the Gulf of Bothnia

Myrberg K., Andrejev O.

Oceanologia

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2006

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No. 48 (S)

55-74

EN

To estimate the mean circulation, water exchange and water age in the Gulf of Bothnia a ten-year simulation using a three-dimensional numerical model was carried out. The results confirmed the early findings by Witting (1912) and Palmén (1930) that a mean cyclonic circulation takes place both in the Bothnian Sea and in the Bothnian Bay. However, the modelling results showed clearly that there exist meso-scale circulation features including coastal "jets", not reported in the Witting-Palmén results. The simulated mean currents were also higher than those found earlier, while the persistency of this circulation is typically between 20 and 60%, which is similar to the earlier results. There is a large difference between the various model-based water-exchange estimates: these are strictly dependent on the time-averaging used. Water age proved to reflect properties of the mean circulation system, and the highest water age (of around 7.4 years) was found in the central part of the Bothnian Bay. The water age was found to be rather high also in the entire Gulf of Bothnia, which provides evidence of the rather slow water exchange between the Gulf and the Baltic Sea. This leads to the conclusion that, from the physical point of view, the Gulf of Bothnia is vulnerable to eutrophication.

8

Coherent current oscillations and water exchange in the straits of the Gulf of Riga

Talpsepp L.

Oceanologia

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2005

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No. 47 (2)

115-127

EN

The water exchange processes through the Irbe and Virtsu (Suur) Straits were investigated in 1993-1997 within the framework of a five-year study programme - the Gulf of Riga Project. Simultaneous current measurement data from autonomous mooring stations in both straits were available for the analysis in two periods. In addition to the dominant signals - inertial oscillations in the Virtsu Strait and diurnal oscillations in the Irbe Strait - low-frequency oscillations were found in both straits. During the experiment in July-August 1994, 12-14-day oscillations were observed in both straits: the maximum phase lag in the Virtsu Strait was 1 day. The other important low-frequency periodic component in both straits was 88 hours. In this case, the phase lag in the Virtsu Strait was about 20 hours. In the 1995 experiment in the Irbe Strait, 42-hour oscillations were observed with a phase lag of 10-12 hours. The amplitude was about 30 cm -1 in both straits. As in Lilover et al. (1998), where the flow regime in the Irbe Strait was observed, we can interpret these oscillations as being wind-generated. The present work shows the existence of these disturbances also in the Virtsu Strait. The 88-hour oscillations observed in July-August 1994 can be interpreted as the first mode of the basin's eigenoscillations according to the concept of Otsmann et al. (1997) of a basin with two separate outlets. The lowest frequency oscillation with the period of 12-14 days seemed to propagate to the Gulf of Riga from the Baltic Proper, but the generating force could not be established because there was no noticeable variability between depressions and anticyclones during that period. Based on the current measurements, two types of water exchange through the Irbe strait were established: the outflow over the whole cross-section of the strait, and a bidirectional flow with an inflow near the southern shore and increasing inflow in the near-bottom layers and an outflow in the northern part of the strait.

9

Formy występowania oraz właściwości kationów metali w środowisku wodnym

Grzybkowski W.

Chemia i Inżynieria Ekologiczna

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2004

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Vol. 11, nr S2

151-164

PL

Dokonano przeglądu chemicznych, termodynamicznych i kinetycznych właściwości kationów metali w roztworach wodnych. Omówiono współczesne poglądy na strukturę hydratów, wymianę molekuł wody oraz hydrolizę soli. Zwrócono uwagę na kwasowość hydratów. Wskazano istotne związki między stanem koordynacyjnym soli w roztworach wodnych a właściwościami fizykalnymi roztworów. Omówiono formy wystepowania kationów metali w wodzie morskiej.

EN

Chemical, thermodynamic and kinetic properties of metal cations in aqueous solutions are presented and discussed in terms of structural factors controlling physical properties of the systems. Structure of hydrated cations, reaction mechanism of water exchange on the cations, hydrolytic phenomena and acidity of the cations are descibed. Correlations between coordination states of the salts in and bulk properties of the solutions are indicated. Elements of aquatic chemistry are presented.

10

Influence of morphology changes on flow and water exchange in the Odra Estuary

Jasińska E.

Archives of Hydro-Engineering and Environmental Mechanics

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2001

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Vol. 48, nr 3

33-57

EN

Knowledge of the hydrodynamic conditions and the exchange of water in estuaries is important for ecological, navigational and water management reasons. The morpho-logy, river flow, sea level and local winds constitute important factors that influence the water currents and rate and extent of the mixing of salt and fresh water. The influence of the morphology changes on flow conditions, on the penetration of salt into the estuary and on the water exchange in the estuaries in this paper are analysed on the example of the Odra Estuary. The morphology of the Odra Estuary, and specially the Świna Strait, has changed immensely since the beginning of the XVIII century. The analyses were performed on the basis of data from in situ measure-ments and results of calculations. For the calculation the three-dimensional model ESTURO was used, because of the complexity of the hydrodynamic regimes and their three-dimensional character. The calculations were performed for the three different hydro-meteorological conditions for each of the five analysed morphological situations of the Odra Estuary. Some results of calculations have been presented.