11:30 AM - 11:45 AM
[ACC25-10] Seasonal and altitudinal variations in snow algal bloomings in Mt. Gassan in Yamagata prefecture, Japan
Keywords:Snow algae, Bloomings of snow algae
Snow algae are photosynthetic microbes growing on melting snow surface. Bloomings of snow algae can be commonly observed on alpine snow in Japan during melting season and vary in color such as red, green and yellow. Previous studies showed that red snow appears under oligotrophic conditions with strong sunlight, and green snow appears under eutrophic conditions with weak sunlight (Thomas and Duval, 1995). In Mount Gassan in Yamagata Prefecture, Japan, green and yellow snow appears every year on the snow surface of the floor of broad-leaved forests. However, it is not known how the algal bloomings are distributed in alpine snow and changes with seasons. It is necessary to understand their distribution and seasonal changes in order to understand the conditions of snow algal blooming. Therefore, we aim to describe the seasonal and altitudinal variations of this bloomings and to determine the factors to induce them.
In this study, we collected colored snow from the lower deciduous forest to the upper alpine area above tree line in the period from May to July of 2019 at Mt. Gassan in Yamagata prefecture, Japan. From the collected snow, we measured the chlorophyll a concentration, the cell volume biomass (biovolume) of snow algae, and the absorption spectra of the algal pigment extracted from the samples. In addition, in order to determine the cause of the algal blooming, we analyzed the nutrient concentration and calculated the coverage of the forest using aerial images of satellite and drones.
Chlorophyll a concentration in the colored snow continuously increased at all of the sites from May to July, especially significant increase occurred at the lower area in the forest. Chlorophyll a in the alpine area increased in July, but it was significantly lower than the forest site. Multiple snow algal cells with different morphologies were observed by microscopic analyses. The composition of morphological types of snow algae differs between the alpine area and the forest area. In addition, as the season progressed, the dominant algal types changed at the all of sites. The absorption spectra of algal pigments extracted from the samples can be mainly divided into three types (red, green, and orange types) according to their spectral curve. These types are likely to be due to different pigment composition contained in algal cells. The snow type changed with altitude, red type appeared only in the alpine area, and the green type predominated in the forest area. As the season progressed, red type increased in the alpine area, and green type increased in the forest area. The orange type appeared only at low altitudes in the forest area in the early melting season.
We compared the altitudinal distribution of chlorophyll a concentration, cell type composition, nutrient concentration and the coverage of the forest leave above the snowy floor. Results showed that the nutrients are likely to be sufficiently supplied to the snow surface at all of the sites, but the vegetation changed with the altitude. The light conditions appear to differ significantly between above and below the tree line in the study area. Solar radiation was more intense on the snow surface in the alpine area than in the forest. The difference of dominant type of snow algae between alpine and forest areas is probably due to such light condition. In the alpine area, the production of red pigments was promoted against the intense radiation. On the contrary, in the forest area, the light conditions may be suitable for algal growth and thus the red pigment may not have been produced. Furthermore, the increase of chlorophyll a concentration in the forest area may be due to coming into leaf of trees, which shade and reduce the solar radiation on the snow surface at the forest floor. These results suggest that the presence of trees and their timing of coming into leaf are largely control the appearance of colored snow in this area.
In this study, we collected colored snow from the lower deciduous forest to the upper alpine area above tree line in the period from May to July of 2019 at Mt. Gassan in Yamagata prefecture, Japan. From the collected snow, we measured the chlorophyll a concentration, the cell volume biomass (biovolume) of snow algae, and the absorption spectra of the algal pigment extracted from the samples. In addition, in order to determine the cause of the algal blooming, we analyzed the nutrient concentration and calculated the coverage of the forest using aerial images of satellite and drones.
Chlorophyll a concentration in the colored snow continuously increased at all of the sites from May to July, especially significant increase occurred at the lower area in the forest. Chlorophyll a in the alpine area increased in July, but it was significantly lower than the forest site. Multiple snow algal cells with different morphologies were observed by microscopic analyses. The composition of morphological types of snow algae differs between the alpine area and the forest area. In addition, as the season progressed, the dominant algal types changed at the all of sites. The absorption spectra of algal pigments extracted from the samples can be mainly divided into three types (red, green, and orange types) according to their spectral curve. These types are likely to be due to different pigment composition contained in algal cells. The snow type changed with altitude, red type appeared only in the alpine area, and the green type predominated in the forest area. As the season progressed, red type increased in the alpine area, and green type increased in the forest area. The orange type appeared only at low altitudes in the forest area in the early melting season.
We compared the altitudinal distribution of chlorophyll a concentration, cell type composition, nutrient concentration and the coverage of the forest leave above the snowy floor. Results showed that the nutrients are likely to be sufficiently supplied to the snow surface at all of the sites, but the vegetation changed with the altitude. The light conditions appear to differ significantly between above and below the tree line in the study area. Solar radiation was more intense on the snow surface in the alpine area than in the forest. The difference of dominant type of snow algae between alpine and forest areas is probably due to such light condition. In the alpine area, the production of red pigments was promoted against the intense radiation. On the contrary, in the forest area, the light conditions may be suitable for algal growth and thus the red pigment may not have been produced. Furthermore, the increase of chlorophyll a concentration in the forest area may be due to coming into leaf of trees, which shade and reduce the solar radiation on the snow surface at the forest floor. These results suggest that the presence of trees and their timing of coming into leaf are largely control the appearance of colored snow in this area.