The Speaker Editors

Montana State University environmental scientists have found conclusive evidence that hailstones originate in biological material. MSU researcher Alex Michaud turned travesty into understanding by peeling back the onionlike layers of the crystalline compositions he collected from the Bozeman and two other Rocky Mountain hailstorms, and the results promise to increase our understanding of the role of aerosol particles in atmospheric condensation and, as a part of the bigger picture, improve our model inputs to the Earth’s energy balance.

“A hailstone is a very complex weather phenomenon, Alex Michaud, MSU doctoral student and first author of the paper, told The Speaker. “It can tell us a lot about the properties of the clouds in which it was formed.”

Michaud, who normally studies Antarctic microorganisms, took up the subject of hailstones after storms pummeled Bozeman and other parts of southwest Montana in 2010.

“While they cause lots of damage there are many things to be learned from hailstones. They’re more than just a clump of ice falling from the sky,” Michaud told us.

“This is the first paper to really show that biological material makes hailstones,” commented John Priscu, a polar scientist and professor at MSU’s Department of Land Resources and Environmental Sciences, with whom Michaud regularly works and who coauthored the report. “Despite the millions in dollars of damage the storm caused in Bozeman, the damaging hailstones provided us with a better understanding of hailstone formation, which will help us understand the role of aerosol particles in the formation of precipitation.”

After the Montana storm, Michaud collected and stored hailstones–averaging 1.5 inches in diameter. He also collected hailstones from two other local storms that year and the next.

Michaud peeled back the crystalline layers of the hailstones and found that they had formed around a biological embryo.

“We can assume–quite safely, except maybe in the dead of winter–that biological material is constantly being taken up into the air,” said Michaud. “Many surfaces give off biological material such as leaf surfaces, lakes, oceans, animals, my dandruff, etc. They are emitting bacteria, fungal spores, detritus, and so forth.”

Michaud elaborated to explain that biological material in the air was not the only thing required to create hailstones.

“Certainly the atmospheric and meteorological conditions need to fit a certain set of conditions in order for a hailstorm to occur and produce hailstones. These particular conditions are best answered by a meteorologist, but suffice it to say that you need a very strong thunderstorm conditions to generate a hailstorm. So not all biological material turns into hail because meteorological conditions need to be appropriate to support hailstone formation.”

In his research, Michaud was also able to gauge the temperatures at which the hailstone embryos formed by analyzing stable isotopes in water. The temperatures at which hail froze were warm, Michaud found.

“Warm freezing temperatures–warm, sub-zero temperatures–is indicative of ice nuclei that are efficient at catalyzing ice nucleation. Water needs a template or a nucleus in order to form an ice crystal, only once water reaches ~-40C does it spontaneously freeze. So for something to freeze at warm subzero temperatures means that it provides a good template of an ice crystal, which is found in biological material much more often than abiotic–dust, minerals, etc–material.”

The study builds on previous findings that warm temperature ice nucleation indicated that biological material was likely the nuclei of hailstones.

Among past researchers in hailstones was Tina Santl Temkiv, a postdoctoral researcher at Aarhus University in Denmark, with whom Michaud consulted.

“It was very coincidental that she published two hailstone microbiology papers two years before me and we ended up at the same university for a few month,” said Michaud. “Plus, we are the only ones to work on hailstone microbiology since a 1973 paper in Nature.”

Michaud also said that hailstones were a nice model for studying atmospheric ice nucleation and cloud processes because of the way hailstones grow.

“Hail is a good model system for understanding precipitation formation and nucleation,” said Michaud. “We can trace the life history of a hailstone all the back to the part of the hailstone that was present when it was first started, the embryo. This ability to trace a hailstones life back to its beginnings, and those life history stages are layers of ice that can be peeled away–sort of like an onion–we can be more definitive in saying what was present when the embryo of the hailstone formed.”

Michaud explained to us how the new evidence could contribute to our understanding of the role of aerosol particles in the formation of precipitation.

“Aerosols are a broad term for any particle that is aloft in the atmosphere. These aerosol particles play a large role in reflecting solar energy and in cloud formation–which also reflects solar energy. So understanding how aerosols form precipitation and/or clouds will help with meteorological models and the earth’s energy balance.

“Certainly the last one is a bit of a stretch for my work, but knowing that biological ice nuclei are active in forming clouds and precipitation–rain, snow, and, now, hail–will improve the model inputs to earth’s energy balance. It’s a piece to a much bigger puzzle.”

Michaud was uncertain if the results would have any immediate practical implications.

“On improving our use of aerosol particles, I’m not too sure. In California they are trying to perform cloud seeding to increase snowpack in the Sierras to decrease drought conditions, which is through the use of particular aerosols. I don’t think I am qualified to speak to how we–the royal we, humans–can improve our use of aerosol particles.”

The report, “Biological ice nucleation initiates hailstone formation,” was authored by Alexander B. Michaud, John E. Dore, Deborah Leslie, W. Berry Lyons, David C. Sands andJohn C. Priscu, and was published in the Journal of Geophysical Research: Atmospheres.

Photo: Alex Michaud, Andrew Slaughter and Kelly Gorham, MSU

New understanding has been gained into how densities within populations can affect outcomes for the species as a whole. Answers to how species populations can be manipulated to increase and properly manage fish yields, better eliminate unwanted pests, and other species-wide effects have been demonstrated by Princeton University researcher Anieke van Leeuwen and two European colleagues who asked, “Can less really be more?”

“When we think about dynamics in ecological systems, either in one population or through interactions between populations (for example predator-prey dynamics or competition) or in entire ecosystems (food webs), we have to consider the fact that individual organisms differ within a population (or stock or species),” Dr Anieke van Leeuwen, postdoctoral research associate at Princeton University’s Department of Ecology and Evolutionary Biology and one of the three authors of the report, told The Speaker.

There was a significant benefit to understanding how differences among individuals within a species population affect outcomes for the whole, van Leeuwen told us.

“There are differences in sizes, and individuals need to grow and develop, which costs energy. In other words, we cannot think in terms of numbers of individuals (and therewith average all biological characteristics, such as size, over all individuals). We will have to count the biomass per individual organism and account for the energy that it takes to grow to that size and maintain that biomass.”

Van Leeuwen explained how this could be done.

“Consider a herring population that has grown to the maximum ‘capacity’ of its resource environment. In such a setting we would predict that all individuals in the population experience harsh competition for resources, resulting in slow growth and a population size-distribution that is hump-shaped. Or in other words, the population is stunted.

“When we are interested in harvesting in particular the large individuals, the presence of such large, mature individuals could be boosted by some source of mortality on this herring population. Through increased mortality the intra-specific (i.e. intra-population) competition can be released, which would allow individuals in the population to attain higher growth rates and reach larger individual sizes. In the scenario accounting for some source of mortality (which may be imposed by fisheries or caused by predatory marine species, such as cod) the population size-distribution would become bimodal (at least to a much stronger extent than in the previous scenario) and large individuals are present (at all, or in higher densities than before).”

Van Leeuwen pointed to an earlier research paper, “How cod shapes its world,” which provided illustrations of the overcompensation phenomenon as well as the collapsing pattern that can result from overfishing in a more complex species system. In this research, the scientists reviewed existing studies that showed positive population level impacts of mortality, and explained how this has been looked at in theoretical models: classically (i.e. mostly non-size-structured populations) vs when accounting for population size structure, and compared the essential assumptions and processes of such models with what is reported in empirical studies.

Logically extending their understanding, the researchers concluded that species could be decimated if imposed mortality surpassed a certain point.

“If fishing pressure in such a setting steadily increases, observations show and models predict that there is a maximum, above which the herring population collapses,” van Leeuwen explained. She offered an illustration from the world of art: Pieter Bruegel the Elder’s “Big Fish Eat Little Fish” (1557).

“It shows the importance of size-structure and differentiation so beautifully, while at the same time pointing out that humans are overexploiting natural systems,” commented van Leeuwen.

In seeking to understand species dynamics, many ecological models have ignored differences in body size in development while predicting that modest gains in total species numbers could be achieved by imposing mortality. Considering these theories, in addition to research that has shown that mortality of individuals from certain life stages or size classes can have a positive effect, the researchers concluded that the overlap of these data showed that it was a division along lines of developmental stages that was key to understanding mortality benefits.

“Only theory predicting the life stage specific positive mortality effects accounts for fundamental aspects of individuals,” the researchers found. “Mortality-induced density increases that are specific to life-history stage are common in nature.”

We asked van Leeuwen about whether their findings could be applied to human populations to understand the world’s various demographics. The comparison of humans to other animal species was complicated, she said, because human existence involves much more complicated social relationships than the animal settings in the study systems the researchers looked at allow for (for example, laboratory settings or the simplifying assumptions made in mathematical models).

“This question is extremely hard to answer from our context,” said van Leeuwen. “I think it is reasonable to say that in general human populations are limited in a different fashion or by different kinds of resources than the simplified ‘one-resource’ by which consumers are limited in the studies we refer to.

“Moreover, the structure in human populations is very much determined by certain social constructs and social configurations. These would influence populations to a large extent, while the research we review discounts any such social structure.”

Van Leeuwen offered an alternative starting point.

“I think with respect to potential applications for human interest, we should rather think about how the concept of culling has been known and used for ages in forestry and agriculture; and also in recreative or sports fisheries this is a familiar phenomenon.”

The report, “When less is more: positive population-level effects of mortality,” was completed by first author Arne Schröder, a postdoctoral research fellow at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin and first author, and Tom Cameron, a lecturer in aquatic community ecology at the University of Essex in the United Kingdom, in addition to van Leeuwen, and was supported by the Journal of Experimental Biology, the Swedish Research Council and the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, the University of Leeds, the National Environment Research Council and the European Commission Intra-European Fellowship, and the National Science Foundation.

By Day Blakely Donaldson
Photos: the research team, Jørgen Schyberg, and The Speaker