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Lake Temperatures in the Time of Climate Change

People depend on lakes for many ecosystem services such as water, food, transportation, and recreation, but these services are at an unknown level of risk because we do not understand how lakes are affected by climate change. A network of 39 scientists from 20 countries on five continents are collaborating to put long-term and high-frequency data to work to understand, predict, and communicate the role and response of lakes in our changing global environment. This work was partly funded by the John Wesley Powell from U.S. Geological Survey and the Foundation for Research on Biodiversity (FRB), through the research projects GEISHA of the FRB’s Center for Biodiversity Synthesis and Analysis (CESAB).

 

Many of the scientists hypothesized that storms would have strong impacts on water temperature and water column mixing, based on a prior synthesis studyHowever, the team’s most recent study found that wind- and rainstorms do not cause major temperature changes in lakes.

 

They examined how wind- and rainstorms affected lake temperature across 18 lakes and 11 countries using meteorological and water column temperature data and found minimal changes to lake temperature from storms. In fact, they found that day-to-day changes in lake temperature during non-storm periods were often more extreme than storm-induced temperature changes. As expected, storms impacted the temperature of deep lakes less than shallow lakes because more energy is needed to mix layers of water with different temperatures in deep lakes than in shallow lakes. For example, storm-induced temperature changes in Lake Superior (average depth almost 500 feet) will be smaller than in Lake Okeechobee (average depth about 10 feet).

 

 

A storm rolls over Lake Superior. Photo credit: Jessica Wesolek, Lake Superior State University’s Center for Freshwater Research and Education

 

Because storm-induced changes to lake temperature were minimal overall, storm-induced changes in other environmental conditions such as nutrient concentrations or light may have larger impacts on lake animals and plants,” said Jonathan Doubek, Assistant Professor at Lake Superior State University in the School of Natural Resources & Environment and the Center for Freshwater Research and Education, who joined the network while at the University of Vermont. These findings represent concrete progress in understanding how lakes are weathering storms.

 

“Professor Doubek’s study highlights the usefulness of high-frequency data: we were able to discover that the effect of storms on lake temperatures may not be as strong as we previously believed,” said Dr. Jason Stockwell, Professor and Director of the Rubenstein Ecosystem Science Laboratory at the University of Vermont.

 

The team of scientists has begun analyzing the impact of storm-related changes in nutrient concentrations and light availability on organisms using the same global dataset and has recently had a proposal funded to help continue this work into the future. “The power of global collaborative teamwork to pool data and ideas is improving our understanding about how our planet functions and may function in the future,” Stockwell said. “We need this information to protect ecosystem and human health.”

The polecat, this big outsider

Its bad reputation precedes it. It is accused of smelling, of “screaming loudly”, and more recently of sexism through the character of Pepe the Polecat. But, the polecat, this small mustelid, we know little or nothing about it. This is the observation made by researcher Sébastien Devillard and his team, who received the Barbault and Weber “Involved Ecology” grant in 2021 to fill this knowledge gap: “The polecat is a species that is difficult to observe and study because it is a cryptic and nocturnal animal. It lives in low density territories where males and females only cross paths during reproduction”, explains the researcher.

 

The Curriculum of the polecat is therefore quite short. As an adult, this small mustelid weighs between 600 grams and 1.5 kg, has the diet of an omnivore, mainly meat, and lives in open and wooded areas, often near wetlands. “However,”, continues Sébastien Devillard, “we have noticed that for the past 30 or 40 years, the wetlands, and riparian forests, which are its preferred habitat, have been steadily deteriorating. In all likelihood, that this had and continues to have an impact on the populations of this species.”

 

If its conservation status is not considered to be at risk by IUCN, it is once again due to a lack of knowledge on this topic according to the researcher: “When IUCN does not have the exact number of individuals living in a territory to monitor its temporal evolution, it looks to see if the distribution area of this species has decreased independently of the population densities. However, the polecat is still present in Europe over a distribution area that seems stable, which is why IUCN has not classified it as a threatened species. “However, local studies carried out by naturalists using photographic traps, or by national organizations responsible for collecting signs of presence, such as visual observations or roadside kills, suggest that the number of such signs of presence has been steadily declining for the last twenty years, particularly in wetlands.” To change its conservation status and justify the implementation of in situ conservation programmers, scientists will have to adopt a conservation biology approach that will study the polecat’s space use and population size.

 

The research team is therefore committed to understanding how this small mustelid uses and selects its habitat, in particular its dependence on wetlands and protected areas. At the Pierre Vérots Foundation estate in Ain, the research team plans to fit three polecats with GPS collars to track their movements and identify the determinants of their use of space. “This is a world first, stresses the researcher. For a long time, we were limited by the size of GPS collars, which required large batteries to operate and ensure sufficiently long tracking to obtain useful information. “In ecology, the rule is that animals cannot be fitted with collars that exceed 3 to 5% of their weight. Until then, only larger mammals, from a few kilograms up to giraffes or elephants, benefited from this type of tracking to respect the ethical and animal welfare dimension. The miniaturization of batteries has changed the situation: “Once the polecats are fitted with the equipment, we will be able to go out into the field every week to download the data, which will give us extremely detailed and unprecedented information on the use of space by this species.”

 

The technique is revolutionary in many ways. Previously, the data collected came from VHF radio collars. To locate the individuals studied, the scientists had to visit the area several times a week and triangulate by positioning themselves at three different locations to pick up the signal from the radio collars. “This classic radio-tracking technique did not allow for more than two or three locations per week. Thanks to the GPS collars, this team of scientists will now be able to obtain data on the polecat’s occupation of space and on its pace of activity throughout the day.

 

This project is only the first step in a larger ambition: “If we manage to show that this device works, we will be able to expand our study area and fit more animals.” The goal? To obtain more data and carry out survival analyses, which will then enable demographic models to estimate the size of the population locally and the rate of population growth. At the same time, researchers want to deploy a photo-trapping protocol to estimate local polecat density. Scientists will thus be able to propose new arguments for the study of its conservation status and perhaps also change the way our society looks at this small, discreet mustelid.

Le réchauffement climatique, un bouleversement pour les écosystèmes et les scientifiques

Le changement climatique n’est pas un état problématique passager, mais bien une situation pérenne qu’il va falloir considérer dans sa globalité. Il nécessite une adaptation importante des écosystèmes et de ceux qui les étudient. Sous nos latitudes tempérées, ces changements prennent une signification particulière en modifiant la longueur relative des saisons. Or, l’arrivée du printemps rythme le cycle annuel de toute la biodiversité. La remontée printanière des températures s’accompagne d’une reprise explosive de la végétation. Les jeunes feuilles fournissent une nourriture de qualité pour une multitude d’invertébrés herbivores, aux premiers rangs desquels, les chenilles de papillons. Eux-mêmes sont alors consommés par des carnivores. Ce formidable accroissement de la biomasse va, en particulier, permettre aux prédateurs de se reproduire. Ce phénomène est cependant éphémère : les jeunes pousses tendres se chargent rapidement de tanin et deviennent indigestes. On assiste ainsi à un pic d’abondance de nourriture et chaque niveau de la chaîne alimentaire tente de se synchroniser sur le pic dont il dépend.