Tuesday 15 March 2022

There should be a name for this season. It warms, and things melt during the day, and then it refreezes at night. The lake is still iced over, but during the day clear pools of water mirror the sky; yet some people still venture boldly onto the ice – I hope they know what they’re doing.

Ice Algae

Regardless, I wonder about the ecodynamics of this time of year. The trees are looking feathery, their buds swelling. I wonder what sort of microbial action is going on in the pools of melt, and how it is that it survives the ice. I suppose I don’t know that there is life there, but it seems a safe presumption. I do notice the change earlier in the year, when I run along Minihaha creek, when the ice becomes cloudy and takes on the faintest of green hues: this is, I am told, due to algae taking advantage of increasing sun as winter eases towards its close.

Doing a little searching on the web turns up this

Winter ice cover is a fundamental feature of north temperate aquatic systems and is associated with the least productive months of the year. Here we describe a previously unknown freshwater habitat for algal and microbial communities in the ice cover of the freshwater St. Lawrence River, Quebec, Canada. Sampling performed during winter 2005 revealed the presence of viable algal cells, such as Aulacoseira islandica (O. Müll.) Simonsen (Bacillariophyceae), and microbial assemblage growing in the ice and at the ice–water interface. Vertical channels (1–5 mm wide) containing algae were also observed. Concentrations of chl a ranged between 0.5 and 169 μg · L⁻¹ of melted ice, with maximal concentrations found in the lower part of the ice cores. These algae have the potential to survive when ice breakup occurs and reproduce rapidly in spring/summer conditions. Freshwater ice algae can thus contribute to in situ primary production, biodiversity, and annual carbon budget in various habitats of riverine communities.
PRESENCE OF ALGAE IN FRESHWATER ICE COVER OF FLUVIAL LAC SAINT-PIERRE (ST. LAWRENCE RIVER, CANADA). https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1529-8817.2008.00481.x

Other sources note that algae can grow in 39° water under the ice and plays an important role in producing oxygen in ice-bound lakes that might otherwise undergo a deficit. Of course, there needs to be enough sun – and little snow on the ice – for photosynthesis to occur below.