Journal Article

Hydrodynamic Modeling of Stratification and Mixing in a Shallow, Tropical Floodplain Lake

Melack, John M., Amaral, Joao H. F., Zhou, Wencai, MacIntyre, Sally, Cortés, Alicia, Barbosa, Pedro M.

2024

Overview

Floodplain lakes are widespread and ecologically important throughout tropical river systems, however data are rare that describe how temporal variations in hydrological, meteorological and optical conditions moderate stratification and mixing in these shallow lakes. Using time series measurements of meteorology and water‐column temperatures from 17 several day campaigns spanning two hydrological years in a representative Amazon floodplain lake, we calculated surface energy fluxes and thermal stratification, and applied and evaluated a 3‐dimensional hydrodynamic model. The model successfully simulated diel cycles in thermal structure characterized by buoyancy frequency, depth of the actively mixing layer, and other terms associated with the surface energy budget. Diurnal heating with strong stratification and nocturnal mixing were common; despite considerable heat loss at night, the strong stratification during the day meant that mixing only infrequently extended to the bottom at night. Simulations indicated that the diurnal thermocline up and downwelled creating lake‐wide differences in near‐surface temperatures and mixing depths. Infrequent full mixing creates conditions conducive to anoxia in these shallow lakes given their warm temperatures. Key Points Diel thermal structure in a tropical floodplain lake was characterized by high‐resolution field measurements over two hydrological years State and process evaluation show that diel and seasonal stratification and mixing were simulated well by a 3‐D hydrodynamic model Diurnal heating with strong stratification and nocturnal mixing were common while mixing to the bottom was intermittent

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU),Wiley
• Subject: Amazon floodplain / Anoxia / Brunt-vaisala frequency / buoyancy frequency / Diurnal / Diurnal thermocline / energy / Energy budget / Environmental Sciences & Ecology / Floodplains / heat / Heat loss / high‐resolution temperature measurements / Hydrodynamic models / Hydrodynamics / hydrologic models / Hydrology / hypoxia / Lakes / Marine & Freshwater Biology / meteorological measurements / Meteorology / Mixed layer / Night / River systems / rivers / Surface energy / Surface properties / Surface temperature / temperature profiles / Temporal variability / Temporal variations / Thermal stratification / Thermal structure / Thermocline / three‐dimensional hydrodynamic modeling / time series analysis / water / Water Resources