French floating solar study examines changes in crayfish and fish behavior

Here, a trap has caught a creature that does not belong in this French lake.

In it is a Louisiana crayfish, an invasive species whose feeding may transport carbon within the aquatic food chain.

Over it, solar panels float on the surface, covering approximately half of the area of this gravel pit lake located in Peyssies, Haute-Garonne.

Towards the end of the experiment, there was one year of data on pre-installed observations and two years after for its impact monitoring lakes.

Now, the scientists are studying the crayfish, fish, insects, plankton, and water itself to find an answer to a rather complex question.

What happens below when the sun’s energy turns into electrical energy before reaching the lake?

Half the lake has a roof

The floating photovoltaic system is built by the company Urbasolar and occupies an area of approximately 50% of the lake called Peyssies.

This leads to two different aquatic zones within the same water body.

One zone is exposed to light and wind.

Another zone is under the cover of floaters and photovoltaic panels that block out some amount of light and shade.

These differences may go beyond shading.

The entire concept of the ECLIPSE research project is based on the premise that floating solar systems can change light, temperature, oxygenation, water mixing, and gas exchange, which will further propagate to the ecosystem.

The crayfish is a carbon detective

Scientists from Peyssies employ baited traps placed in the lake to collect samples of the Louisiana crayfish.

It is important because it recycles carbon and is an important link in the food chain.

These scientists are examining whether the presence of the floating plant has any effect on the diet or habitat use of this crayfish.

The difference between these two is critical.

The discovery of a crayfish underneath a solar panel does not mean that the panel attracts the crayfish.

The significant question is whether the animals have a different diet or habitat underneath covered water than anywhere else.

Fish sit higher in the same chain

They are also fishing for fish by dropping gill nets below the buoy array.

These species include European perch and northern pike and are some of the most important predators in these ecosystems. Therefore, any changes lower in the food web will eventually affect them.

Scientists are collecting samples that are even smaller than the fish.

Macroinvertebrates that have been collected in Peyssies are stored separately in order to analyze them using the stable isotope technique, which will help to understand how organisms feed, not just based on netting.

This project also analyzes phytoplankton, periphyton, zooplankton, nutrients, light, temperature, decomposition, greenhouse gases, and whole lake metabolism, according to the European Commission CORDIS.

The food web is being traced from the sun down.

Less light can change the whole lake

This is the initial step in the process.

Photosynthetic algae and other photosynthetic organisms capture energy from light and convert it into organic matter, and this is what sustains higher-level organisms.

Covering part of the lake causes some light to be lost on its way to the lake.

There are also temperature changes.

Another whole-lake study within the same research project has compared three floating solar lakes with three control lakes and found that average water temperatures have decreased by 1.2°C annually since their installation.

On the hottest days of spring and summer, reductions have been larger, more than 3°C.

This does not prove what happened with the crayfish and fish at Peyssies.

It proves why scientists think that there might be biological effects.

The answer is still being assembled

The ECLIPSE project used a design that compared lakes using floating solar to lakes without by collecting data before and after implementation.

Towards the end of the experiment, there was one year of data on pre-installed observations and two years after for its impact monitoring lakes.

Controlled experiments with 0%, 25%, 45%, and 65% floating solar coverage were conducted while modeling the possibility that open spaces (“light islands”) between the panels could minimize any ecological effects.

It means that the crayfish traps in Peyssies will not be used to draw any conclusion on the positive or negative impact of the floating solar on the animal population.

These traps are part of a much bigger puzzle.

The floating panels will affect the amount of sunlight entering the lake.

It is time for scientists to find out where this light goes from there.