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QUATERNARY RESEARCH 46, 270±280 (1996) ARTICLE NO. 0066 Alluvial Pollen on the North Plain

XU QINGHAI,YANG XIAOLAN,WUCHEN,MENG LINGYAO, AND WANG ZIHUI Institute of Geography, Academy of Sciences, 050011, China

Received August 31, 1995

mm (up to 800±900 mm). The mean annual precipitation is Mordern alluvial pollen varies with geomorphic setting and de- 500±600 mm in the plain itself. By contrast the mean annual positional facies in sediments of the Yellow, Hutuo, and Luan evaporation is about 2500 mm. All rivers on the North China rivers and in Baiyangdian and Hengshuihu lakes. Most of the Plain rise abruptly during heavy rains and fall, or even dry arboreal pollen is derived from the mountains, whereas most of up, between storms. the nonarboreal pollen is derived from the plain itself. Alluvium Most vascular plants on the plain have been introduced dominated by Pinus pollen and Selaginella spores was deposited by people. The main crops are Triticum aestivum, Zea mays, during a flood. Hydrodynamic sorting of alluvial pollen exists in the sediments of floodplain, central bar, natural levees, and point Oryza sativa, Sorghum, Gossypium, Arachis, Brassica peki- bar. In reconstructing the ancient vegetation and past climate nensis, Apium graveolens var. dulce, Phaseolus, Spinacia based on pollen in alluvium, it is important to consider sedimen- oleracea, and Allium ®stulosum. Trees of Robinia, Ailanthus, tary facies and geomorphologic setting. ᭧ 1996 University of Washington. Ulmus, Populus, Salix, and Paulownia grow in cities, on road sides, and along river banks. Some herbs, such as Digitaria, Imperata cylindrica var. major, Aster, Artemisia, Cheno- INTRODUCTION podium glaucum, Xanthium, and Salsola collina, can be found on farm ®elds, road sides, and river banks. Aquatic Alluvial sediments are frequently used in Quaternary pol- plants, such as Phragmites, Sparganium, Typha, Cypera- len studies in the semiarid and semihumid ceae, Nelumbo, Myriophyllum, and Potamogeton can be where lacustrine and peat deposits are rare. However, owing found in depressions and lakes. Tamarix, Suaeda salsa, Sali- to the lack of adequate understanding of alluvial pollen, past cornia europaea, and Artemisia balodendron are dominant studies (Tong et al., 1983; Xu and Wu, 1985) treated alluvial in the coastal plain area. pollen as having been continuously deposited, as if it accu- Forests are present in the Taihang and Yanshan moun- mulated in a lake. However, pollen in alluvium on the North tains. A forest of Quercus, that includes Pinus tabulaeformis, China Plain varies with depositional facies as well as with Ulmus, Carpinus, Beltula, Tilia, Acer, and Juglans, grows changes in vegetation. at elevations below 1200 m. Betula and Populus forests grow between 1200 and 1700 m elevation. Between 1700 and STUDY AREA 2500 m, the forests are dominated by Picea and Larix. Subal- pine meadows dominated by Poaceae, Cyperaceae, and The North China Plain is bounded by the Taihang Moun- Asteraceae families are found above 2500 m. tains on the west, the Yanshan Mountains on the north, and 2 on the east (Fig. 1). Covering 136,000 km ,it SITES AND METHODS was formed by the , the , and tribu- taries of the . The plain can be divided into a Pollen samples were collected along the Yellow, Hutuo, piedmont and fan zone, a ¯uvial plain zone, and a coastal and Luan rivers and from Baiyangdian and Hengshuihu zone (Wu et al., 1991). lakes. Samples were collected along three transects each The North China Plain has a continental monsoon climate. across the Yellow and Luan rivers, ®ve sections on the Hutuo Under the in¯uence of Mongolian high pressure in winter, River, and one section each at Baiyangdian and Hengshuihu temperature and precipitation are low. Continental low pres- lakes (Fig. 1). Several samples were collected from several sure in summer allows warm Paci®c air to raise temperature different sedimentary facies at each section. All but the river- and produce abundant precipitation. Precipitation in July, bed samples were collected subaerially. Samples at the sur- August, and September makes up 70% of the total annual face and 2±3 cm under the surface were collected at each rainfall. Mountain front regions and hills receive the greatest site to compare the in¯uence of the airborne pollen rain and rainfall, with mean annual precipitation being more than 600 the local pollen. Both the surface and the underlying samples

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CHINESE ALLUVIAL POLLEN 271

FIG. 1. Map of North China Plain showing geomorphic setting of sampled sections. are modern alluvial analogs. As a river ¯ows along a very the surface, it re¯ects the in¯uence of both airborne pollen small trough, all sedimentary facies but the river bed are and local pollen. Sampling was done in the September and subaerial at the time of sampling. Pollen in alluvium at the October 1990 during a time of low river ¯ow. At that time, surface may be in¯uenced by airborne pollen and the local the average ¯ow of the Yellow River at Lijin station was pollen. If the surface pollen, especially the pollen concentra- about 200±400 m3/sec (Cheng, 1991); the Luan River at tion, is more than that of samples collected 2±3 cm beneath Luanxian station ¯owed at about 108 m3/sec (Yu et al.,

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1994). The Hutuo River was drying up, with no water on zone and the ¯uvial plain zone mainly comprise pollen from the river bed. drought-tolerant grasses and mesothermal herbs. Chenopodi- Most of the samples collected in the river channels were aceae pollen, probably from salt-tolerant species, is domi- deposited in 1990. The samples collected on the alluvial nant in the coastal plain sediments. Much aquatic pollen plain (outside the river bank) or higher on the ¯oodplain collects in lakes. These pollen assemblages essentially re¯ect were deposited after the exceptional ¯oods in 1963 and 1964. the main characteristics of nearby vegetation, which in turn During the two ¯oods, almost all rivers on the North China re¯ects the local geomorphic setting. Plain over¯owed their banks and deposited a layer of ¯ood sediment on the plain (Department of Hydrology, Hebei ALLUVIAL POLLEN IN DIFFERENT Province, unpublished data of 1991). SEDIMENTARY FACIES Samples of river water were collected from the surface in a plastic pail (2.5 liters). In the laboratory, 80 g of sediment from each sample was We illustrate here the effects of sedimentary facies at the placed in 10% HCl. Tracers of Lycodium spores were added Huangbizhuang section (Figs. 3 and 4), in the piedmont and to permit calculation of pollen concentration (Li, 1985). Sam- fan zone of the Hutuo River, and at the Pinyin section (Figs. ples were then treated with 10% KOH to remove humates. All 5 and 6) in the ¯uvial plain zone of the Yellow River. From water sampled in plastic pails was poured into a 3000-ml bea- these sections we make several quali®cations: ker, and the sediment was then allowed to settle. After concen- (1) River bed: The river bed usually has less pollen, fewer tration, the samples were transfered to glycerol. At least 300 pollen taxa, and lower pollen concentration than the other pollen and spore grains were identi®ed for each sample. facies. (2) Central bar, ¯oodplain, and natural levees: The abun- dant pollen in these ¯ood-water facies is characterized by GENERAL FEATURES OF ALLUVIAL POLLEN Selaginella spores and Pinus pollen (Figs. 3 and 5). Fall ON THE NORTH CHINA PLAIN (1987) also found high percentages and concentrations of Pinus in such environments. We infer that Selaginella spores Alluvial pollen of the North China Plain is composed of and Pinus pollen grains, being larger and heavier than other plants growing both on the plain and in nearby mountains. pollen, were deposited by ¯oods that carried other pollen Most of the arboreal pollen is derived from such mountain trees away. In that case, high percentages of Selaginella spores as Pinus, Picea, Quercus, Betula, Tilia, Castanea, Juglans, and and Pinus pollen can be used as an indicator of ¯ooding. Alnus. The appearance of their pollen in alluvium, especially (3) Point bar: Point bars have low pollen concentrations, 2±3 cm under the surface, indicates that they were transported typically less than 200 grains/g. Pollen concentrations in- by rivers from the mountains to the plain. By contrast, we treat crease toward the river banks (Fig. 6). Populus, Salix, Ulmus, and Ailanthus as plain trees, because (4) Alluvial plain (outside the river bank): Pollen assem- of their dominance in the plain. Ferns, which grow only in the blages are dominated by pollen from upstream or from the mountains, are represented by spores that were also moved by local area. The greater the distance from the river (over 10's rivers from the mountains to the plain. of kilometers), the more abundant the local pollen is (Xu et Nonarboreal pollen taxa are mainly Artemisia, Cheno- al., 1994a). podiaceae, Poaceae, Xanthium, and Polygonum. They are Pollen assemblages also vary with geomorphic setting produced by plants which are common both in the mountains along the Yellow River. From Figure 7 it is clear that both and on the plain. This distribution makes it dif®cult to deter- surface pollen concentration and pollen concentration 2±3 mine their provenance. cm under the surface are high in the piedmont and fan zone The abundance of arboreal pollen derived from the moun- and in the coastal zone, but low in the ¯uvial plain zone. tains decreases with distance from the mountains. Figure 2 The total pollen concentration is mostly more than 6000 shows three percentage diagrams of mountain arboreal pol- grains/g (up to 32,900 grains/g) in the piedmont and fan len in alluvium in different geomorphic zones of the Luan area, more than 2000 grains/g in the coastal area, and less River. It is clear that mountain tree pollen is relatively high than 1000 grains/g (to as little as 200 grains/g) in the ¯uvial (20±30 %) at the Luanxian and Dingliuhe sections of the plain area. This is also the case for the Hutuo and Luan piedmont and fan zone but is relatively low (2.8±13.4 %) rivers. Although the total pollen concentrations in the pied- in the coastal zone. Similar pollen percentages of mountain mont and fan zone are lower than that along the Yellow trees can also be seen in the different geomorphic zones River, they are still more than 1000 grains/g. along the Yellow and Hutuo rivers. Baiyangdian Lake has the highest total pollen concentra- Alluvial pollen assemblages in the North China Plain are tions, more than 40,000 grains/g in most sediments (Xu et dominated by herbs. Sediments from the piedmont and fan al., 1994b).

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FIG. 2. Mountain arboreal pollen percentages from sections along the Luan River. Pollen percentages are based on the pollen sum of trees, herbs, and ferns. Mountain arboreal pollen includes Pinus, Abies, Picea, Quercus, Beyula, Tilia, Castanea, Juglans, and Alnus.

POLLEN IN RIVERWATER grass pollen more abundant in the autumn (Table 1). This indicates no obvious sorting in Yellow River water but rather Pollen percentages of the main taxa in water samples from seasonal variation of pollen taxa. The variation of pollen the Yellow River are similar to percentages at different sites percentages at different sampling dates may re¯ect different sampled at the same time, and are little different at different ¯owering seasons. The trees usually ¯ower in the spring, times. Arboreal pollen is more abundant in the spring and and herbs in the summer and autumn. Pollen concentrations

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FIG. 3. Pollen percentage diagram of the Huangbizhuang section, Hutuo River.

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FIG. 4. Pollen concentration diagram of the Huangbizhuang section, Hutuo River.

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FIG. 5. Pollen percentage diagram of the Pinyin section, Yellow River. of the main taxa increase downstream. This reveals that most alluvial plain. Similar ®ndings have been reported by Martin herbaceous pollen deposited in alluvium originates from (1963), Solomon et al. (1982), and Hall (1985). plants growing on the ¯oodplain, central bar, point bars, and All water samples from the Luan River, except the one

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FIG. 6. Pollen concentration diagram of the Pinyin section, Yellow River. sampled in May 1990, contain very little pollen (Table 2). Why River (average 0.3 kg/m3 in suspended load; Yu et al., 1994). does the Luan River water contain fewer pollen than Yellow Suspended sand increases the buoyancy of the river water. River water? This may relate to the sand content of the water. Thus, Yellow River water contains more pollen. However, why In the Yellow River (average 25 kg/m3 in suspended load; does water sampled at Luanxian in May contain much pollen, Cheng, 1991), sand is much more plentiful than in the Luan whereas other rivers do not? This may also relate to the sand

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FIG. 7. Total pollen concentrations at sections along the Yellow River.

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TABLE 1 Pollen Percentages and Concentrations of the Main Pollen Taxa of Yellow River Water

Zhengzhou Fengqiu Pinyin Rivermouth

Pollen taxa Pa Cb PCPCPC

Pinus 11.3 51 4.9 230 2.4 134 4.9 55 Broad-leaves 8.3 37 4.9 231 5.3 291 7.9 900 Total trees 19.6 88 9.8 461 7.7 425 12.8 1458 Artemisia 45.4 204 51.7 2429 62.8 3465 48.9 5587 Chenopodiaceae 11.3 51 14.7 693 14.6 805 14.9 1707 Total herbs 73 330 84.5 3972 89.9 4964 82.3 9402 Ferns 7 33 5.7 266 2.4 134 4.9 559 Sampling dates 4/90 10/90 10/90 10/90

a P, percentages. b C, concentration (grains per liter). content in river ¯ow. A rainstorm occurred in the upper reaches of alluvial pollen, rarely paid attention to the changes related of the Luan River 1 day before the sampling. The rain may to depositional facies. Based on our study of alluvial pollen, increase surface ¯ow and sand content of the riverwater. Pollen there are great differences in pollen assemblages between allu- taxa of the riverwater sampled at Luanxian in May 1990 are vial and lacustrine sediments. Lacustrine sediments are charac- dominated by Pinus. This coincides with the fact that pine terized by a great amount of aquatic pollen and by high pollen ¯owers in May in the Yanshan Mountains, and also suggests concentrations (more than 40,000 grains/g; Xu et al., 1994b). that the pollen abundance in the riverwater is related to the On the other hand, alluvium is characterized by a great amount ¯owering period of plants. of pollen originating from the mountains and also by a great variation in pollen frequency between different depositional DISCUSSION facies. Thus, in conducting alluvial pollen analysis on the North China Plain, it is vital to pay attention to pollen variation associ- Differences among Sedimentary Facies ated with different facies. Although many pollen studies have been carried out on the Sources of Alluvial Pollen North China Plain (Li, 1985; Zhou, 1965; Liu, 1965; Kong et Both Martin (1963) and Solomon et al. (1982) suggested al., 1982; and Xu et al., 1988, 1993), most studies, especially that pollen in modern alluvium is almost entirely derived

TABLE 2 Pollen Percentages and Concentrations of the Main Taxa of the Luan River

Luanxian Luanxian Dingliuhe Rivermouth Rivermouth

Pollen taxa Pa Cb PCPCPCPC

Pinus 41 287 (2)c (2) Broad loaves 2.2 15 (1) Total trees 43.2 302 Artemisia 6.5 45 (5) (6) Chenopodiaceae 2.2 15 (2) Gramineae 18 126 (6) (2) Other herbs 5.1 35 (2) (1) Total herbs 44 221 Selaginella 11.6 81 (2) (1) Other ferns 13.6 96 Total ferns 25.2 176 Sampling dates 5/90 10/90 10/90 10/90 10/90

a P, percentages. b C Å Concentrations (grains per liter); (2), two grains of pollen.

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280 XU ET AL. from ¯oodplain taxa. Fall (1987) found that mordern allu- Cheng, Guodong (1991). ``Modern Sedimentation and Its Model of the vium is dominated by Pinus pollen throughout Canyon de Yellow River Delta,'' pp. 1±110. Geology Press, Beijung. Chelly, northeastern Arizona, in the semiarid southwestern Fall, P. L. (1987). Pollen taphonomy in a canyon stream. Quaternary Re- United States, re¯ecting not the surrounding ¯oodplain vege- search 28, 393±406. tation, but rather the vegetation in the nearby mountains. Hall, S. A. (1985). Quaternary pollen analysis and vegetational history of Study of the modern alluvium of the North China Plain the southwest. In ``Pollen Records of Late-Quaternary orth American Sediments'' (V. M. Bryant, Jr. and R. G. Holoway, Eds.), pp. 95±123. shows that pollen in alluvium originates from both the sur- American Association of Stratigraphic Palynologists, Dallas. rounding mountains and the plain itself. Most arboreal pollen Hall, S. A. (1989). Letter to the editor. Pollen analysis and palaeoecology in alluvium is carried to the plain by rivers from the Taihang of alluvium. Quaternary Research 31, 435±438. and Yanshan mountains. Most of the nonarboreal pollen is Kong, Zhaochen, Du, Naiqiu, and Zhang, Zibin (1982). Vegetational and derived from the plain itself. Because herbs grow both on climate changes in the Beijing area during the past 10000 years. Acta the plain and in the mountains, it is dif®cult to ascribe herba- Botanica Sinica 24(2), 172±180. ceous pollen to mountain or plain sources. Pollen analysis Liu, Jinling (1965). Pollen assemblages at the south piedmont area of the of riverwater from the Yellow River shows that pollen con- Yanshan Mountain. Quaternary Sciences of Sinica 4(1), 105±117. centrations of major pollen types in the river increase down- Li, Wenyi, and Liang, Yulian (1985). Vegetation and environment of the stream, indicating that most pollen (herbs) in the alluvium hypsi-thermal interval of Holocene in Estern Hebei Plain. Acta Botanica is derived from the ¯oodplain and alluvial plain. Thus, it is Sinica 27(6), 640±651. apparent that alluvial pollen may have multiple sources. Martin, P. S. (1963). ``The Last 10000 Years: A Fossil Pollen Record of the America Southwest.'' Univ. of Arisona Press, Tucson. Sorting of Alluvial Pollen Solomon, A. M., Blasing, T. J., and Solomon, J. A. (1982). Interpretation of ¯oodplain pollen in alluvial sediments from an arid region. Quaternary Brush (1972) and Fall (1987) suggested that alluvial pol- Research 18, 52±71. len is sorted during transport by running water. We ®nd Tong, Guobang, Ke, Manhong, and Yu, Shufeng (1983). Quaternary pollen that the alluvium dominated by Pinus pollen and Selaginella assemblages and their geological signi®cance on the Hebei Plain Marine spores was deposited during a ¯ood. Strong sorting of allu- Geology and Quaternary Geology 3(4), 99±103. vial pollen occurs during a ¯ood, whereas sorting of pollen Wu, Chen, Zhu, Xuanqing, He, Naihua, Xu, Qinghai, Yuan, Wenying, is not obvious during times of low river ¯ow. Weak sorting Wang, Zihui, Shi, Derong, and Zhao, Mingxuan (1991). Ancient channels of alluvial pollen is also seen in the meandering reaches of on the North China Plain. Science in China (Series B) 2, 188±197. the river, but it is not apparent in the ¯uvial plain alluvium Xu, Qinghai, and Wu, Chen (1985). Division of the Holocene strata and (Xu et al., 1994a). vegetation changes in Heilonggang region with pollen analysis. Journal of Hebei Academy of Sciences 1(1), 18±25. CONCLUSIONS Xu, Qinghai, Chen, Shuyin, Kong, Zhaochen, and Du, Naiqiu (1988). Pre- liminary discussion of vegetation succession and climate change since Pollen analysis of alluvium is suitable for interpreting the the Holocene in the Baiyangdian Lake . Acta Phytoecologica et ancient vegetation and past climate, but it is important to Geobotanica Sinica 12(2), 143±151. make allowances for variations within different sedimentary Xu, Qinghai, Wu, Chen, Wang, Zihui, Tong, Guobang, Wu, Shaojie, Zhang, facies and geomorphic settings. High percentages of pollen Junpai, Du, Naiqiu, and Kong, Zhaochen (1993). Approach to palaeoenvi- and spores of Pinus and Selaginella in alluvium can be used ronment in the west coast of Bohai Bay since 25000 a B.P. Acta Phytoeco- as an indicator of ¯ood conditions. Total pollen concentra- logica et Geobotanica Sinica 17(1), 20±32. tion in alluvium also varies with geomorphic setting. Xu, Qinghai, Wu, Chen, Meng, Lingyao, Wang, Zihui, Yang, Xiaolan, and Yao, Zuju (1994a). ``Study on pollen assemblages of different deposi- ACKNOWLEDGMENT tional Facies on the North China Plain.'' Xian Cartography Press, pp. 1±132. This study was supported by the Nation's Natural Sciences Foundation Xu, Qinghai, Wu, Chen, Meng, Lingyao, Wang, Zihui, and Yang, Xiaolan of China. (1994b) Alluvial pollen assemblages at different geomorphological zones on the North China Plain. Chinese Science Bulletin 39(19), 1792±1795. REFERENCES Yu, Fenglan, Qian, Jinping, and Li, Enqing (1994). ``Water resource and Brush, G. S., and Brush, L. M., Jr. (1972). Transport of pollen in a sediment- its utilization of the Luan River,'' pp. 1±214 Science Press. laden channel: A laboratory study. American Journal of Science 272, Zhou, Kunshu (1965). Investigation and pollen analysis on two burried 359±381. peats near Beijing. Quaternary Sciences of Sinica 4(1), 188±142.

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