Mountains stand apart, literally – they’re islands rising high in a sea of lowlands. For many, they’re the place to reconnect to nature, to relax and to enjoy a clean environment and fresh air. The popularity of mountains during the current pandemic clearly showed the need of humans to enjoy nature.
Mountains also provide us with many important goods, including wood, pastures for livestock, drinking water and clean air. All are provided by mountain ecosystems, through complex processes, that are maintained by the community of different species and their interactions between them and with the abiotic environment. Those species are numerous. They comprise invisible microorganisms, tiny plankton species, small plants, trees, cryptic reptiles and amphibians, swift birds, and mammals. Those species produce organic matter, bind CO2, and produce oxygen.
Together, all these species shape, change and rebuild the environment in complex interactions that are difficult to describe. Even the most powerful information systems have not yet been able to simulate a real ecosystem with all of its interactions, functions and processes. Nature humbles our technological and intellectual capacities.
Far and above
Mountains are generally considered to be remote areas, as many are difficult to travel to, as roads are scarce and accessibility limited due to weather conditions. We imagine them little impacted by humans and free of pollution. Unfortunately, human activities like mining, livestock, energy production and tourism impact them. Here, I am referring to the exploitation to serve the civilized world, living in urbanized areas. Humans have exploited the timber, mining and pasturage resources of mountain environments for millennia. These activities and others have impacted mountain ecosystems to varying degrees.
Today, the rapid flux of people and resources into and out of mountains compounds the challenges they face. The activities pollute even remote mountain areas at high altitudes. Pollutants can be transported to mountains by orographic effects and may enrich in lake sediments, peat bogs, and generally in mountain wetlands, driven by patterns of rainfall, snowfall, length of growth season, and wind patterns. Temperature-dependent partitioning between air and atmospheric particles, snow surface, or water droplets determine dry and wet deposition rates that may lead to a fractionation and deposition of different pollution compounds at different altitudes.
The pollution of mountain freshwater with chemical compounds – a key challenge humanity is facing – is therefore closely linked to climate change and climate extremes. Climate extremes play a key role in the redistribution of chemical pollutants and are assumed to enhance release of pollutants stored in ice, soils or sediments through flood events.
Humans’ heavy hand
In addition to these direct impacts, humans have changed the world climate. Mountains are very fragile environments and are among the regions that are most sensitive to climate change and to the impacts of human activities. Climate change is a worldwide threat, but its impact on mountains is particularly strong and troubling. High elevation areas tend to experience intensified climate-change induced warming and weather extremes.
As with high latitudes (our poles), where ice melt is far more rapid than predicted, the rate of warming is also amplified with elevation. That means that high mountains are experiencing more rapid changes in temperature and much higher variations in daily temperatures as compared to lowland regions. Glaciers are melting more and more quickly, snow cover is reduced and highly variable between years. Further, heavy rain events, creating torrents and floods, and periods of no rain, drying out mountain landscapes, have been observed to be more and more common frequent. All this has important implications for nature, for wildlife and for the human society.
High-altitude areas around the world share many characteristic and common features. All of them have in common that, while being considered an extreme environment with short vegetation times, they harbor an important amount of different species, adapted to such a harsh environment.
Climate change puts enormous stress on them, leading to important changes in those biological communities due to changes in abundance of species, loss of species, and range changes of species. Interactions between the species and the environment drive the functioning of ecosystems. Mountains and their biodiversity are sentinels of change. Changes in the mountains will lead to the loss of essential ecosystem services, which poses risks for the well-being of all of us.
These human impacts on mountain ecosystems disturb biodiversity across all trophic levels, from microbes, plankton to higher animals with little understood consequences for the whole ecosystem. For example, microbial communities, comprising the community of fungi, yeasts, bacteria, viruses and protozoans, are all so tiny that we cannot see them with the naked eye are everywhere: in the air, on the surfaces, in the water, the soil, on our skin, in our very bodies. Despite their small size, these communities drive major processes in and on animals, plants as well as in the environment.
Microbial web of life
The community of microorganisms help plants and animals to adapt to the environment, by e.g. increasing temperature tolerance. They form biological barriers against pathogens and parasites by competing with them and by mitigating disease effects. They help their animal or plant host to synthesize vital nutrients, thereby increase energy uptake and growth and hence might have far reaching consequences by increasing reproductive success. Similarly, micro-organisms stabilize whole ecosystems by buffering against change through the maintenance of biodiversity and ecosystem processes.
In ecosystems, micro-organismic communities also represent a barrier against alien species and improve resistance, resilience and tolerance of ecosystems. Most importantly, micro-organismic communities hold important ecosystem functions, such as nutrient cycling, energy fluxes and carbon fixation. For example, the interactions between micro-organisms and plankton constitute the basis of aquatic food web and determine the functioning of biogeochemical cycles, accounting for more than half of the global carbon fixation.
Any kind of disturbance of the community of micro-organisms can therefore have far reaching impacts on species and ecosystems. For example, the influx of pollutants together with other impacts of climate change will disturb biodiversity across all trophic levels, from micro-organism, plankton to higher animals with little understood consequences for the whole ecosystem. The natural equilibrium then is perturbed and can lead to the increase of pathogens, also critical to human well-being, as e.g. plankton would not be able to control the proliferation of zoonotic pathogens, such as the bacterium Escherichia coli and the protozoan genus Giardia, or toxic algae. And pathogens can be easily introduced to mountains through pastoralism, tourism or wind drift and hence the biological barrier the community of micro-organism represent is of high relevance to avoid proliferation of pathogenic micro-organisms.
Changes in mountain ecosystems will lead to eutrophication, loss of biodiversity and reduce availability of clean drinking water, but give also rise to wildlife and human pathogens, leading to increasing probabilities of zoonoses. We are currently only at the beginning of understanding the functional ecology in mountain ecosystems, but international research already suggests that changing the communities will be detrimental to the environment, biodiversity and our life-support system.
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