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

100%

Luchinin A. G.

tom Vol. 12

117-126

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.

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

88%

Liblik T. , Buschmann F. , Siht E. , Kuprijanov I. , Väli G. , Lipp M. , Erm A. , Laanemets J. , Eschbaum R. , Verliin A. , Saks L. , Zekker I.

tom Vol. 66 (1)

9--25

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.

Consltruction of a numerical model of storm surges with a refined grid

63%

Chilicka Z. , Kowalik Z. , Wierzbicki Z.

tom 16

On the resistance law in a shallow sea

63%

Lewandowicz R.

tom 22