Effects of regulated dam discharge on plants and migratory waterfowl are mediated by salinity changes in estuaries

Abstract

The rapid increase in dam construction has resulted in a worldwide loss of natural river flows. Regulated dam discharge into estuaries can interrupt the spatiotemporal occurrence of brackish communities adapted to optimal salinity ranges, further threatening biodiversity and ecosystem function in the affected regions. We used annual survey records from the Nakdong River Estuary from 2009 to 2018 to identify the indirect effect of regulated dam discharge on plants and migratory waterfowl. Increased mean salinity during the spring season negatively influenced the area covered by plants and the number of days on which swans were present during winter. Moreover, the mean salinity during the early growing periods of plants providing food to waterfowl was regulated by the amount of freshwater discharge from the estuarine barrage rather than by the direct effect of precipitation. Conservation managers should consider the amount of dam discharge and the salinity conditions during spring to maintain sufficient food resources and supporting functions for migratory waterfowl in the estuary. Our study highlights the need for a comprehensive assessment of time‐lag effects to minimize the negative impacts resulting from regulated dam discharge.

Extreme changes in salinity drive population dynamics of Catostylus mosaicus medusae in a modified estuary

“…Barrages are commonly constructed to regulate freshwater flows in estuaries (Lehner et al, 2011;Mulligan et al, 2020). How barrages modify both the physical characters of estuaries (Ma et al, 2019;Kang and Lee, 2020), and population dynamics of estuarine animals (Gillanders and Kingsford, 2002;Amorim et al, 2018;Kim and Kim, 2020), is a key research focus with the aim of balancing societal needs with ecological impacts.…”

“…Salinity tolerances normally constrain estuarine inhabitants to specific areas of the natural salinity gradient in an estuary (Gillanders and Kingsford, 2002). Construction of a barrage greatly narrows, and in some cases, eliminates the gradient from fresh to saltwater as these constructions primarily act as a physical barrier separating fresh river water from the marine saltwater (Kim and Kim, 2020). In the Fitzroy River, the construction of a barrage greatly shortened the extent of the estuary, reducing the available habitat for medusae (Margvelashvili et al, 2003).…”

Influence of Seasonal Abiotic Factors and Co-Existing Salt Marsh Plants on the Growth and Reproduction of Zostera japonica in Fluctuating Estuarine Environments

“…Within the Nakdong River estuary, 32 vascular hydrophytes were identified, including various seagrass and salt marsh species such as Zostera marina, Z. japonica, Ruppia maritima, B. planiculmis, and Phragmites australis [3,5]. This highly productive vegetation in the Nakdong River estuary serves as a critical habitat and food source for overwintering migratory birds, making it a key stopover along the East Asia-Australia flyway [3,5,6]. However, the construction of the Nakdong River Estuary Barrage in 1987 triggered a significant ecological shift [3,6,7].…”

“…This highly productive vegetation in the Nakdong River estuary serves as a critical habitat and food source for overwintering migratory birds, making it a key stopover along the East Asia-Australia flyway [3,5,6]. However, the construction of the Nakdong River Estuary Barrage in 1987 triggered a significant ecological shift [3,6,7]. This human-made barrier disrupts the natural exchange of water between the freshwater river and the estuarine saltwater Sustainability 2023, 15, 16065 2 of 17 regions [6], leading to the prolonged retention of pollutants, increased nutrient concentrations, and substantial changes in the predominant vegetation of the Nakdong River estuary [3,4,[7][8][9].…”

“…However, the construction of the Nakdong River Estuary Barrage in 1987 triggered a significant ecological shift [3,6,7]. This human-made barrier disrupts the natural exchange of water between the freshwater river and the estuarine saltwater Sustainability 2023, 15, 16065 2 of 17 regions [6], leading to the prolonged retention of pollutants, increased nutrient concentrations, and substantial changes in the predominant vegetation of the Nakdong River estuary [3,4,[7][8][9]. This underscores the urgent need for enhanced protective measures and sustainable management to preserve the ecological richness of the Nakdong River estuary.…”