Simulating water temperature in Lake Vättern in Sweden using a 3D lake model

إنجليزي. Lake ecosystems are increasingly affected by climate change, leading to prolonged periods of elevated water temperatures. This warming reduces surface water density, intensifying thermal stratification and trapping cold water in deeper layers. Consequently, cold-water fish and other organisms are confined to limited deep-water habitats. Understanding lake thermal structure is crucial for effective fish management and ecosystem conservation. However, the lack of in-situ temperature measurements across full depth gradients necessitates the use of three-dimensional hydro thermodynamic models. While these models are valuable, they require reliable in-situ data for validation, presenting a significant challenge. This study simulates the three-dimensional water temperature distribution in Lake Vättern, Sweden, using the Delft3D Flexible Mesh Suite 2D3D and evaluates the model performance. Additionally, the study explores the potential and limitations of telemetry temperature data, a previously unexamined in-situ data source for hydro-thermodynamic model calibration and validation. Using telemetry data from 2023 provided by Swedish University of Agricultural Sciences (SLU), this study investigates the temperature lag in transmitter instruments, an element acknowledged as a major source of uncertainty in temperature measurements. Meteorological forcing was supplied by ERA5-Land hourly data from the Copernicus Climate Change Service, while boundary conditions and bathymetric data from SLU and the Swedish Land Survey supported the creation of the model’s computational grid. Validation of transmitter temperatures showed promising accuracy with a one-hour depth residence threshold, though limited observations hindered statistical reliability. Consequently, only stationary telemetry receiver temperatures were used for model validation. The simulated water temperatures showed moderate accuracy, presumably due to the absence of turbulence parameter calibration. However, the most significant errors likely stemmed from validation data limitations, particularly the absence of telemetry receivers at critical depths. While challenges remain, telemetry emerges as a promising in-situ data source for lake water temperatures that justifies continued research efforts.

إنجليزي. As our climate warms, lakes around the world are feeling the heat, literally. In Lake Vättern, Sweden, rising air temperatures lead to warmer waters in the upper parts of the lake. This results in cold water getting trapped in the deeper layers, creating a squeeze from above for species like cold-water fish that need those lower, cooler zones to survive. Understanding how temperature shifts in a lake isn’t just interesting, it’s vital for protecting biodiversity and retain stable ecosystems. But getting detailed temperature data throughout an entire lake is no easy task. To fill in the gaps, this study used a high-tech simulation tool called Delft3D Flexible Mesh, which models how water temperatures move and change in three dimensions. To check the accuracy of the model, the study turned to an unexpected data source: tiny sensors surgically implanted into fish. These sensors measure the temperature of the water the fish swim through and transmit the data via acoustic signals to stationary receivers, a method known as telemetry. By comparing these measurements with the model’s output, the study could evaluate where the simulation succeeded and where it fell short. It wasn’t perfect. The sensors showed considerable uncertainty in the reliability of the temperature readings, and there were few receivers available at certain depths. The comparisons performed indicated that the model could be improved by refining how it simulates water mixing processes. Still, the results revealed real promise: telemetry may be a viable tool in some lakes for validating simulation models, and in turn help monitor lake conditions in a warming world. This study is a step toward smarter lake management and greater climate resilience. What happens beneath the surface may be invisible to the naked eye, but it holds crucial insights for the future of aquatic life, entire ecosystems, and humanity’s ability to keep food on the table.