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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.

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Underwater noise properties in waterway areas of the South Baltic Sea

Jaśniewicz D., Klusek Z., Neves S.

Hydroacoustics

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2016

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Vol. 19

173--184

EN

Results of underwater noise records completed with single and multi-hydrophone systems performed in the shallow water in the close vicinity of shipping lanes to the Gdansk/Gdynia and Świnoujście/Szczecin harbours are presented. Due to the fact that the bottom properties, bathymetry, and temporally varying sea surface alter the original sound spectra and reduce the acoustic energy, the sound transmission losses have been modelled, and an attempt to predict source levels of ships was performed. The KRAKEN sound propagation model illustrates the problems of the recognition of sources noise spectra on the basis of observations in a far zone from the sources. On the basis of the observed noise data, jointly with the AIS system the potential ecological effects of anthropogenic underwater noise on marine organisms are given for the Pomeranian Bight. In the paper, some examples of algorithms of ship noise recognition are given.

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Experimental studies of low-frequency acoustic fields in a shallow sea

Luchinin A. G.

Hydroacoustics

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2009

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Vol. 12

117-126

EN

The results of the studies of excitation and propagation of low-frequency acoustic fields in a shallow sea, which have been carried out at the IAP RAS for several years, are discussed. A novel equipment complex designed specially for these experiments and intended for the selective excitation and reception of waveguide modes is described. Examples of measurements of various characteristics of low-order mode acoustic signals are given, which demonstrate high efficiency of the applied equipment and measurement technique.

4

The use of the time reverse acoustics in a shallow sea

Stromkov A. A.

Hydroacoustics

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2008

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Vol. 11

353-363

EN

In this report the results of theoretical, numerical and experimental analysis of TRM in a shallow sea are submitted. It is shown that in shallow sea the characteristics of focusing depend first of all on the sizes of the array of imaginary sources which essentially exceeds the sizes of any real array. The method of an experimental research of characteristics of TRM is founded only on the receiving elements and a probe sources is offered. The spatial sizes and the form of focal area of TRM are measuired. It is experimentally confirmed the identity of focal area of TRM with one element and the vertical arrays. The estimation of efficiency of such systems is executed.