Assessment of climate change effects on mountain ecosystems through a cross-site analysis in the Alps and Apennines
Rogora M., Frate L., Carranza M.L., Freppaz M., Stanisci A., Bertani I., Bottarin R., Brambilla A., Canullo R., Carbognani M., Cerrato C., Chelli S., Cremonese E., Cutini M., DiMusciano M., Erschbamer B., Gogone D., Iocchi M., Isabellon M., Magnani A., Mazzola L., Morra di Cella U., Pauli H., Petey M., Petriccione B., Porro F., Psenner R., Rossetti G., Scotti A., Sommaruga R., Tappeiner U., Theurillat J.-P., Tomaselli M., Viglietti D., Viterbi R., Vittoz P., Winkler M., and Matteucci G.
Summarized by Agnes Wasielewski, who is an MAT Earth Science Graduate student at Binghamton University. She loves Geology so much that she decided to share her passion with middle and high school students by becoming a teacher. When she’s not studying Geology or the psychology of teenagers; she spends a lot of time with her husband, three children, and three dogs. When free time becomes available, she loves to read, hike, drink tea, and take naps with her dogs.
What data were used? Researchers collected data from twenty research sites across the Alps (Italy, Switzerland, and Austria) and Apennines Mountains (Italy). All sites were located between 1300 and 3212 meters above sea level. Fourteen sites are in forests, grasslands, alpine tundra, and snow-covered areas. Six sites are in lakes and rivers. All sites considered for the paper experienced an increase in air temperature over the past two decades (1991-2015) compared to a base period of 1961-1990. A combination of data analysis on already existing datasets, projects, and new collection of data to determine results.
Methods: Temperatures taken in June were used to determine snow melting rates, the timing of the beginning of the growing season, and timing of ice-break in lakes and rivers. To analyze regional snow cover duration, data loggers combined with thermistors (special resistors used for temperature measurements) were placed at a soil depth of 10 cm and measured hourly. If the temperatures measured remained within a certain range, the day was considered a “snow cover day”. On days where the daily mean soil temperature dropped below and rose above 0 degrees Celsius, they were labeled as a freeze/thaw cycle. The snow melting date is identified by counting the days since October 1st to the start of the freeze/thaw cycle or melting period. Soil samples were collected in September at the end of the growing season and tests are run to determine water content, carbon content, and nitrate concentrations.
Changes in vegetation cover were calculated by estimating the percentage of each plant species in permanent grids over time. These estimates are used as a proxy for above-ground biomass. Biomass is positive when vegetation cover increases and negative when cover decreases.
Surface water samples for chemical analysis were obtained from lakes in late summer/early autumn. May to October is considered open water season, and water temperatures combined with chlorophyll-a concentrations and zooplankton abundance are recorded. Weather stations were used to collect average air temperatures. Biologic samples were analyzed from rivers at varying distances downriver of melting glaciers to correlate community composition and diversity.
Results: At lower altitudes (~1500 meters above sea level) and latitudes (Lat. 41 degrees N), there are shorter snow cover duration (less than 100 days/year) and snow starts to melt earlier in the year. At higher altitudes (~2800 meters above sea level) and latitudes (Lat. 46 degrees N), there are longer snow cover duration periods (~250 days) and snow starts to melt later in the year. Less snow-covered days allow for increased soil temperatures and more areas for plants to grow and thrive. When more plants can grow and thrive, there are more resources available to local wildlife such as the Alpine ibex (mountain goat) and helps support their population growth. Overall, increased air temperatures and soil temperatures showed a general tendency towards increased vegetation cover for treeline, subalpine, and alpine belts but not in the snow (nival) belts. Over the last fifteen years, it is noted that plant species have been migrating from lower elevations to higher elevations in a process called thermophilization.
An increase in nitrogen deposition has positive effects on tree growth and promotes carbon sequestration (the process of capturing and storing atmospheric carbon dioxide). However, reduction in rainfall can override the positive effects. In the forests tested, a significant increase in the growing season length and a general increase in the annual net carbon sequestration was detected.
During warm and dry years, alpine streams transport concentrated solutes into the lakes and in the runoff water. Over the past decade, there has been a common trend in decreasing nitrate concentrations. Nitrogen uptake in the lake catchments has increased due to the increase in primary productivity (algae and vegetation growth). There has an overall negative trend in NO3 concentration level in rivers and lakes due to decreasing Nitrogen deposition.
Changes in water mineral and chemical concentrations also affect the diversity and population of algae and plankton that live and thrive in mountain lakes and streams.
Why is this study important? Climate warming effects, changes in rainfall seasonality, and water availability have proven to be important for ecosystem productivity. Snow cover duration affects soil carbon and nitrogen cycling and Alpine ibex population dynamics. Warming climate change has shown to lead to an increase in vegetation cover in grasslands and carbon uptake in forests which helps remove CO2 from the atmosphere. Climate drives changes in water chemistry, lake thermal dynamics and plankton phenology can inform us of the health of the water ecosystems. High-elevation ecosystems may also be affected by extreme climatic events such as heat waves, droughts, heavy rainfall, and floods. Both long-term and short-term (extreme) events can affect mountain ecosystems. Mountain ecosystems, if properly studied and monitored, can serve as early indicators of global changes.
The big picture: Global warming affects high mountain ecosystems by increases in temperature, early snowmelt, and a prolonged growing season. With ecosystem productivity, more plant growth helps reduce global climate change by reducing the amount of carbon dioxide in the atmosphere. In mountain ecosystems, carbon sequestration depends on both water availability (precipitation) and air temperature. The understanding of hydro-ecological relationships is essential for the development of effective conservation strategies for alpine rivers. Long-term observations on benthic communities help with the assessment of the potential impacts of global change on stream ecosystems. There is a great need for strong partnerships in mountain ecosystem observation and research for multidisciplinary approaches, encompassing the distinction between different types of ecosystems. There is great potential for further scientific advances that rely on international collaboration and integration.
Citation: Rogora, M., Frate, L., Carranza, M. L., Freppaz, M., Stanisci, A., Bertani, I., Bottarin, R., Brambilla, A., Canullo, R., Carbognani, M., Cerrato, C., Chelli, S., Cremonese, E., Cutini, M., Di Musciano, M., Erschbamer, B., Godone, D., Iocchi, M., Isabellon, M., … Matteucci, G. (2018). Assessment of climate change effects on mountain ecosystems through a cross-site analysis in the Alps and Apennines. The Science of the Total Environment, 624, 1429–1442. https://doi.org/10.1016/j.scitotenv.2017.12.155