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Vertical mixing and oxygen flux caused by daily sea breezes in a shallow stratified lake

Authors :
Eiji Masunaga
Sachihiko Itoh
Tatsumi Kitamura
Source :
Limnology. 24:95-109
Publication Year :
2022
Publisher :
Springer Science and Business Media LLC, 2022.

Abstract

Vertical transport caused by mixing is essential for understanding physical processes in lakes. However, mixing processes in shallow lakes are not well understood because of the lack of turbulence measurements. This study presents observations of vertical mixing and oxygen flux in a shallow lake, Lake Kitaura of the Lake Kasumigaura continuous lake system, which is located along the central eastern coast of the Japanese mainland. Mooring and microstructure surveys were conducted in August 2020. The vertical eddy diffusivity was estimated from the Ellison scale using high-frequency sampled temperature data from the mooring location, and the estimations were consistent with those observed from the microstructure profiler. The estimated eddy diffusivity revealed a mixing structure and oxygen flux in the lake during the study period. The daily cycle of stratification and mixing was caused by daily heating due to solar radiation and by winds from daily sea breezes, respectively. The daily stratification maximum occurred around noon, which suppressed vertical mixing. Vertical mixing was intensified due to sea breezes in the afternoon, which led to movement of oxygen from the surface layer to the bottom layer. The maximum vertical mixing was observed at 18:00. The oxygen concentration did not increase during nighttime when the negative surface heat flux was observed; thus, nighttime cooling may not primarily contribute to the vertical oxygen supply.

Details

ISSN :
1439863X and 14398621
Volume :
24
Database :
OpenAIRE
Journal :
Limnology
Accession number :
edsair.doi...........f83d557cc8cc85cab50369ed1fae2bf9
Full Text :
https://doi.org/10.1007/s10201-022-00707-0