Author(s): Alban Kuriqi; Rui M. L. Ferreira; Joana Pereira; Nelson Abrantes; Moises Brito; Ana M. Ricardo
Linked Author(s): Moisés Brito, Ana M. Ricardo
Keywords: Climate change; Lake management; Numerical modeling; Nutrient availability; Water quality
Abstract: Water motions in lakes vary broadly and include up-and-downwelling currents, turbulent mixing, and wind-generated surface waves. Their combined effect significantly controls how water quality and the lake ecosystem evolve in space and time. Particularly, wind alters the lake surface, which can cause considerable water level fluctuation at specific sections or areas of the lake by maintaining good ecological conditions. Although wind plays a critical role in aquatic ecosystems' function, its influence on the shallow lakes remains scarcely investigated. Therefore, this study investigates the influence of a long-term decrease in wind speed magnitudes on the current density of a shallow eutrophic lake, considering several point source pollutions due to agriculture activities. The annual mean wind speed showed a significant decreasing trend. The maximum continuous days with wind speed < 3 m/s increased significantly from 1981 to 2021. The high-frequency monitoring data showed that bottom water hypoxia occasionally occurred in summer and autumn because of the lake's decreasing water level and high concretion. The numerical results show that lower to medium wind speeds with frequent directional switching toward shore areas developed higher mixing scenarios, which helped reduce water temperatures, distribution, and colony formation of phytoplankton. The onshore winds were the most frequent winds with low wind speeds, whereas; offshore winds have been observed with medium to higher wind speeds. This provides valuable insights in helping policy-makers and water managers to develop appropriate adaptation and protection measures to ensure the good ecological status of the shallow lakes following the European water framework directive.