Influence of Nutrient Desorbed from Sediments and Density Variations Driven by Organic Matter on Flow Patterns in Closed Water Bodies

Abstract

In enclosed water bodies, water quality deterioration has emerged as a critical environmental issue. Eutrophication contributes to phenomena such as red tides and blue tides, raising concerns about foul odors and adverse impacts on surrounding aquatic ecosystems. Despite efforts to reduce nutrient loading through water quality management measures, reports of stagnant or a worsening water quality persist. One key factor is the accumulation of nutrients in deep layers. Nutrient-rich fluids form density currents along the lakebed, transporting nutrients and organic matter to deeper regions. This study investigates the hydrodynamic properties of a nutrient release from the lakebed in Lake Biwa using hydrodynamic and ecosystem models. The results reveal that a nutrient release triggers plume formation along sloping lakebed surfaces, facilitating the transport of nutrients and dissolved organic matter. Additionally, water circulation driven by density currents and nutrient concentrations along the slopes generate compensatory flows, leading to dynamic variability in Lake Biwa’s hydrodynamics.