Kamilla Kurucz

and 5 more

Despite the growing use of Aquatic Ecosystem Models (AEMs) for lake modelling, there is currently no widely applicable framework for their configuration, calibration, and evaluation. To date, calibration is generally based on direct data comparison of observed vs. modelled state variables using standard statistical techniques, however, this approach may not give a complete picture of the model’s ability to capture system-scale behaviour that is not prevalent in the state observations, but which may be important for resource management. The aim of this study is to compare the performance of ‘naïve’ calibration and a ‘system-inspired’ calibration, a new approach that augments the standard state-based calibration with a range of system-inspired metrics (e.g. thermocline depth, metalimnetic oxygen minima), in an effort to increase the coherence between the simulated and natural ecosystems. This was achieved by applying a coupled physical-biogeochemical model to a focal site to simulate temperature and dissolved oxygen. The model was calibrated according to the new system-inspired modelling convention, using formal calibration techniques. There was a clear improvement in the simulation using parameters optimised on the additional metrics, which helped to focus calibration on aspects of the system relevant to reservoir management, such as the metalimnetic oxygen minima. Extending the use of system-inspired metrics for the calibration of models of nutrient cycling, algal blooms, and greenhouse gas emissions has the potential to greatly improve the prediction of complex ecosystem dynamics.

Keisuke Nakayama

and 10 more

Aquatic models used for both freshwater and marine systems frequently need to account for submerged aquatic vegetation (SAV) due to its influence on flow and water quality. Despite its importance, simplified parameterizations are generally adopted that simplify feedbacks between flow, canopy properties (e.g., considering the deflected vegetation height) and the bulk friction coefficient. This study reports the development of a fine-scale non-hydrostatic model that demonstrates the two-way effects of SAV motion interaction with the flow. An object-oriented approach is used to capture the multiphase phenomena, whereby a leaf-scale SAV model based on a discrete element method is combined with a flow-dynamics model able to resolve stresses from currents and waves. The model is verified through application to a laboratory-scale seagrass bed. A force balance analysis revealed that leaf elasticity and buoyancy are the most significant components influencing the horizontal and vertical momentum equations, respectively. The sensitivity of canopy-scale bulk friction coefficients to water depth, current speeds and vegetation density of seagrass was explored. Deeper water was also shown to lead to larger deflection of vegetation height. The model approach can contribute to improved assessment of processes influencing, water quality, sediment stabilization, carbon sequestration, and SAV restoration, thereby supporting understanding of how waterways and coasts will respond to changes brought about by development and a changing climate.