Multimodel simulation of vertical gas transfer in a temperate lake

Victor Stepanenko,Huaxia Yao,Sofya Guseva,Wim Thiery,Qianlai Zhuang,Zeli Tan,Andreas Lorke,Tobias Bleninger,Bruna Arcie Polli,James Anthony Rusak,Klaus Jöhnk

doi:10.5194/hess-24-697-2020

Abstract

Abstract. In recent decades, several lake models of varying complexity have been developed and incorporated into numerical weather prediction systems and climate models. To foster enhanced forecasting ability and verification, improvement of these lake models remains essential. This especially applies to the limited simulation capabilities of biogeochemical processes in lakes and greenhouse gas exchanges with the atmosphere. Here we present multi-model simulations of physical variables and dissolved gas dynamics in a temperate lake (Harp Lake, Canada). The five models (ALBM, FLake, LAKE, LAKEoneD, MTCR-1) considered within this most recent round of the Lake Model Intercomparison Project (LakeMIP) all captured the seasonal temperature variability well. In contrast, none of the models is able to reproduce the exact dates of ice cover and ice off, leading to considerable errors in the simulation of eddy diffusivity around those dates. We then conducted an additional modeling experiment with a diffusing passive tracer to isolate the effect of the eddy diffusivity on gas concentration. Remarkably, sophisticated k−ε models do not demonstrate a significant difference in the vertical diffusion of a passive tracer compared to models with much simpler turbulence closures. All the models simulate less intensive spring overturn compared to autumn. Reduced mixing in the models consequently leads to the accumulation of the passive tracer distribution in the water column. The lake models with a comprehensive biogeochemical module, such as the ALBM and LAKE, predict dissolved oxygen dynamics adequate to the observed data. However, for the surface carbon dioxide concentration the correlation between modeled (ALBM, LAKE) and observed data is weak (∼0.3). Overall our results indicate the need to improve the representation of physical and biogeochemical processes in lake models, thereby contributing to enhanced weather prediction and climate projection capabilities.

Highlights

The past 2 decades have seen a renewed interest in lake modeling
All the lake models simulate seasonal water temperature dynamics adequately (Fig. 2): the epilimnion is warming throughout the first half of summer, accompanied by thermocline deepening, eventually leading to overturn in autumn
The ice formation and ice melt dates play a key role in various processes: the interaction of the lake surface with the atmosphere, the overturning during spring, biogeochemical processes, and release of gases that have accumulated during wintertime, e.g., CO2 or CH4

Summary

Introduction

The past 2 decades have seen a renewed interest in lake modeling. Due to the ever-increasing spatial resolution in numerical weather prediction systems and climate models, manyPublished by Copernicus Publications on behalf of the European Geosciences Union.S. Lakes are increasingly recognized as a considerable source of greenhouse gases, such as carbon dioxide (CO2) and methane (CH4), to the atmosphere (Tranvik et al, 2009; Bastviken et al, 2011; Raymond et al, 2013; Tan and Zhuang, 2015; Wik et al, 2016)

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Results

Conclusion