Abstract:

This study explored the relationship between pollen and vegetation in the Luanhe River Basin and surrounding areas (39°00′-42°00′ N and 115°40′-119°50′ E) at elevations that ranged from 0 m at the Bohai Sea to 2 082 m in the Yanshan Mountains. Airborne pollen samples were collected for two years by 2 permanent weather-vane-pollen-collectors in Caiyuan, Qian'an County. Pollen samples in the surface soil were collected from 53 locations at about 100 m elevational intervals in the Yanshan Mountains and at about 20 km intervals across the level plains between the Yanshan Mountains and the Bohai Sea. Vegetation surveys were conducted simultaneously where pollen samples were collected. Alluvial pollen samples were collected from fresh sediments in the riverbed, and, at the same time, water samples were collected from the river during the low, flood, and mean water periods. Airborne pollen assemblages generally reflected the local vegetation and corresponded with flowering patterns of the vegetation over the course of the year. Most trees flowered in the spring whereas most herbs flowered in the summer and autumn. Because no plants bloom during the winter in this region, the airborne pollen in winter was wind dispersed pollen from the soil surface and some foreign pollen. From the mountain peak to seashore, five successive palynoflora zones were identified: montane meadow, coniferous-broad-leaf mixed forest or coniferous-broad-leaf mixed forest mainly composed of coniferous trees, montane brush, alluvial plain meadow and seaside meadow or saline meadow. Correspondingly, five pollen assemblages were identified: Artemisia-Thalictrum-Pinus-Betula pollen assemblage, Pinus-Betula-Quercus-Artemisia pollen assemblage, Chenopodiaceae-Artemisia-Gramineae-Selaginella sinensis pollen assemblage, Chenopodiaceae-Artemisia-Compositae-Typha pollen assemblage and Chenopodiaceae- Artemisia -Cyperaceae- Gramineae pollen assemblage. Arboreal pollen grains were dominated by Pinus that were transported a long distance, and herbaceous pollen grains were dominated by Artemisia and Chenopodiaceae that were transported a short distance. Pollen assemblages from the river water and alluvial deposits reflected the vegetation of the river basin near where the samples were collected and the genera and proportion of pollen were related to the blooming period of the different plants. The pollen concentration in river water was positively correlated with the proportion of sand in the river water indicating that the pollen grains were carried as sedimentary particles in river. The pollen in alluvial deposits came from the vegetation in the river basin, and the pollen assemblages reflected the vegetation of the whole river basin instead of partial area. Because pollen was transported in the river water by sediment suspension, pollen sorting in the river was not apparent during low and mean water flow periods but was evident during flood periods. The alluvial pollen assemblages varied among different river flow periods.

Key words: Airborne pollen, Surface pollen, Alluvial pollen, Luan River Basin