Environmental impact of removal of a large-scale sluice gate on Nakaumi Lagoon and adjacent coastal waters, southwest Japan: Evidence from long-term foraminiferal monitoring

• Published in: Marine environmental research Vol. 182; p. 105767
• Main Authors: Nomura, Ritsuo, Tsujimoto, Akira, Takata, Hiroyuki
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2022
• Subjects: 210Pb dating; Anthropogenic impact; Environmental assessment; Foraminiferal dispersion; Restoration; Sea-level rise; Environmental assessment; Anthropogenic impact; Foraminiferal dispersion; Restoration; 210Pb dating; Sea-level rise
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2022.105767

A large-scale sluice gate, which was built in southwest Japan as a national project to reclaim and desalinate lagoon water in 1974, was removed between 2005 and 2009. To examine the impact of this removal on both Nakaumi Lagoon and the nearby coastal waters, we analyzed the foraminiferal assemblages of a coastal sediment core and of samples obtained during 10 years of lagoon monitoring (2001–2010). Detailed 210Pb(ex) dating of the sediment core revealed an increased sediment accumulation rate in the coastal waters, implying that discharge of fine-grained materials, including organic matter, was facilitated by removal of the sluice gate. The observed increase in agglutinated foraminifera and decrease in calcareous species was related to the sediment accumulation rate, and these changes occurred close to 2005, when sluice-gate removal began. In Nakaumi Lagoon, the sporadic presence of the coastal species Quinqueloculina seminula within the 6-m water column and the decline in the lagoon-adapted Ammonia “beccarii” have occurred since 2005. The removal of the sluice gate, plus the sea-level rise, allowed greater seawater inflow and stabilized the monthly deep-water salinity fluctuations in Nakaumi Lagoon. •Removal of sluice gate influenced the dynamics of coastal and lagoon waters.•Removal of sluice gate increased the sedimentation rate in coastal waters.•Seasonal fluctuations of deep-water salinity in the lagoon stabilized.•Benthic foraminiferal mobility can be utilized as a new environmental monitoring method.