Logger reveals just how cold it gets in a pond at 3 300 m asl
In March 2021, the MeaseyLab visited the Lesotho highlands as the final stop in an altitudinal transect for Laurie's study of African clawed frog physiology (see blog post here). A year later, I went to retrieve the temperature loggers (see blog post here), but the Lesotho logger had disappeared in a flood. Happily, we have friends in Lesotho, and Bongani Ntloko agreed to deploy a logger in a pond where Xenopus laevis occur in the highest areas of Lesotho.
In this first picture, you can see the pond where the logger was deployed in March 2022. Note the string that snakes into the middle of the pond which has the logger on the end of it.
In the next picture, taken in July 2022, you can clearly see the ice on the pond and the snow on the hill. The skies are still very blue!
In the graph below you can see how the temperature of the water has decreased from March to July. We would not expect temperatures to go below zero, but the logger shows that it gets very close to freezing in this pond. In the height of summer, maximum temperatures are all below 18 C, and the pond returns to temperatures below 10 C at night. These temperatures are very different from those recorded at sea-level where the temperature did not go below 10 C (see here).
From October to march it appears as if the logger has dried out, but in fact this is when Lesotho receives its rains. The dramatic swings in temperature during this period are likely because of the addition of rainwater into the pool. This appears to allow a continuing trend to increase water temperature during the day but the addition of rainwater cools it right down. During this period the frogs need to be able to adapt to a 14° C change from 4 to 18°! Below you can see an image of the pond taken on 4 April 2023 soon after the logger was removed - looking much as it did in March 2022.
Thanks very much to Bongani and his team for their help with obtaining this data. It will be invaluable together with Laurie's results in her work on the physiology of this population.
