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

• Published in: Oceanologia Vol. 66; no. 1; pp. 9 - 25
• Main Authors: Liblik, Taavi, Buschmann, Fred, Siht, Enriko, Kuprijanov, Ivan, Väli, Germo, Lipp, Maarja, Erm, Ants, Laanemets, Jaan, Eschbaum, Redik, Verliin, Aare, Saks, Lauri, Zekker, Ivar
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2024
• Subjects: Baltic Sea; Environmental impact of marine structures; Fish migration; Shallow sea; Water exchange; Shallow sea; Fish migration; Water exchange; Baltic Sea; Environmental impact of marine structures
• ISSN: 0078-3234
• DOI: 10.1016/j.oceano.2023.06.002

•Water exchange is blocked by a 3 km road dam in the shallow strait in the Baltic.•Ecological conditions in the strait have considerably deteriorated.•Water exchange in the area close to the dam has decreased 10–12-fold.•Extreme temperature, oxygen and total nitrogen occur near the dam.•Bottom sediment structure, benthos and fish are impacted by the dam. 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.