http://www.paper.edu.cn

Catena 60 (2005) 267–277

Environmental change and its impacts on human settlement in the Delta, P.R.

Q. Zhanga,*, C. Zhub, C.L. Liub, T. Jianga

aNanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing, 210008, P.R. China bDepartment of Urban and Resources Sciences, Nanjing University, Nanjing, 210008, P.R. China Received 18 August 2003; received in revised form 6 December 2004; accepted 16 December 2004

Abstract

Archaeological excavations and environment–archaeology studies over many years in the Yangtze Delta region have provided exceptional information about climatic variations, growth and demise of human civilization and human–environment interactions. The archaeological excavations show that the cultural layers of the Neolithic sites are interrupted by barren layers without any cultural relics (so-called cultural interruptions), which may be the result of harsh environmental conditions (arid, flooding, extreme cold or warmth). Temporal and spatial analyses of 14C-dates for buried trees, peat, shell ridges, and Neolithic sites show that environmental changes are responsible for the rise and fall of human civilization. The progress of human civilization was interrupted at least 5 times in the Yangtze Delta, matching 5 periods of high sea level, peat accumulation, and burial of trees. The collapse of the Liangzhu culture about 4000 BP was followed by the less- developed Maqiao culture and resulted from extreme environmental and hydrological conditions such as floods. D 2004 Elsevier B.V. All rights reserved.

Keywords: Holocene epoch; Environmental conditions; Human–environment correlation; Yangtze Delta

* Corresponding author. Tel.: +86 25 3221034 12; fax: +86 25 7714759. E-mail address: [email protected] (Q. Zhang).

0341-8162/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2004.12.001

转载 中国科技论文在线 http://www.paper.edu.cn 268 Q. Zhang et al. / Catena 60 (2005) 267–277

1. Introduction

Archaeological excavations over many years in the Yangtze Delta have indicated that the cultural layers in many of the Neolithic sites are discontinuous, being divided by cultural interruptions, which correspond to periods of peat formation and burial of trees. This suggests that they reflected short-term extreme climatic variations (Yu et al., 1998, 1999). Chinese scientists hold different viewpoints concerning climatic variation and its role in the rise and fall of human civilization in the Delta region. Daniel and Chen (1996) and Chen and Daniel (1998) suggested that sea level changes and expansion of the Taihu Lake greatly affected human settlements. Historical flood records documented in Chinese annals provide useful information for understanding past climatic changes and their role in the human occupation history of the region (Chen, 1987). Zhou and Zheng (2000), however, suggested that social factors played the main role in the rise and fall of civilization, notably that wars between tribes caused the collapse of the Liangzhu Culture. They suggested that people usually lived on higher places to escape floods, but Ding and He (1997) proposed that ancient religious activities and human social position rather than environmental changes decided the altitude of human settlement. In this paper, numerous 14C-dates for peat, shell ridges, buried trees, and Neolithic cultural sites are used to evaluate possible connections between human settlements and climatic change. The dates are all taken from published papers or excavation reports (e.g. LIACASS, 1996), and were calibrated to calendar years according to the methods of Stuiver and Reimer (1986, 1993) for comparison with international climatic research results.

2. Study region

Climatically the Yangtze Delta (308N–338N, 1198E–1228E; Fig. 1) is of the subtropical monsoon type. Natural vegetation in the study region is dominated by deciduous and evergreen forests. The mean annual precipitation is 1235 mm. Rainfall in summer months accounts for 40% of the total and only 11% falls during the winter months. The region is climatologically sensitive because it lies along the demarcation line between subtropical and temperate climate that separates disparate air masses. Thus it always experiences floods that mostly result from excess rainfall during summer especially June and July (the so-called Plum Rainy Season), when slowly drifting cold fronts meet the moist and stable subtropical air mass (Xiang and Bao, 1981). Geomorphologically, a nearly level plain with an elevation of 2–7 m above sea level covers 95% of the region, making this region prone to flooding and sea level changes.

3. Materials and methods

3.1. Neolithic sites

Archaeological excavations over many years indicate the following cultural succession: Majiabang Culture (6800~7800 cal. BP), Songze Culture (5700~6800 cal. BP), Liangzhu 中国科技论文在线 http://www.paper.edu.cn Q. Zhang et al. / Catena 60 (2005) 267–277 269

Fig. 1. Location of the study region.

Culture (4100~5700 cal. BP), and Maqiao Culture (3300~4100 cal. BP). If a place is suitable for human settlement, more people will live there and more sites will be left. These clusters of dates suggest periods when Neolithic activities flourished and the intervening gaps suggest the demise of human culture (Yu et al., 2000a). The spatial distribution of sites demonstrates the response of human settlements to changes in coastline and the shrinkage and expansion of water bodies.

3.2. Shell ridges

Shell ridges result from storm waves (Liu et al., 1985), depositing near high tide level (Zhang et al., 1982). Micropaleontological studies have shown that the altitude of the shell ridge bottom matches the high tide level. Therefore, they can serve as proxy indicators showing coastline changes (Mason, 1990; Federico et al., 1999).

3.3. Buried trees

The buried trees in the study region are mainly distributed around the lakes in the Taihu Plain and the mountainous valley in the Ning (Nanjing)–Zhen (Zhenjiang) and Yi 中国科技论文在线 http://www.paper.edu.cn 270 Q. Zhang et al. / Catena 60 (2005) 267–277

(Yixing)–Li (Liyang) regions. Most buried trees were found at À2toÀ8 m depth mixed with boulders, coarse sand and gravel. Scanning electron microscope studies of quartz sand grain surfaces indicate that the trees were buried in a high-energy mountain torrent environment (Zhu et al., 1997), and therefore act as proxy indicators of excessive precipitation.

3.4. Peat accumulation

Peat usually accumulates in wetland areas where plant production exceeds organic losses, because cold or anaerobic conditions hinder soil respiration (Lynn, 1990; Zoltai and Vitt, 1990). In the study region, peats occur near alluvial fans, billabongs, marshes, and shallow lakes in the Taihu Lake plain, and serve as an indicator of periods with increased water surface water (Miller and Futyma, 1987; Oertel et al., 1992; Jordan and Mason, 1999). Increased surface water leading to formation of peat could have resulted from excessive precipitation or high sea level, both of which would not favor human settlements.

4. Results

4.1. Distribution of Neolithic sites

Figs. 2–5 demonstrate that the Neolithic sites of different periods occur mainly around the Taihu Lake region, mainly in the eastern part, with some tendency to extend

119E 120E 121E 122 E 33 N N

Gaoyou Lake Huanghai Sea

Yangtze River 32 N

Majiabang culture (6800-7800 cal. BP) 31 N Coastline Taihu Lake Gehu Lake

Majiabang cultural sites 200 0 200 km Hangzhou Bay Shell ridge sample points Peat sample points 30 N

Fig. 2. Distribution of Majiabang culture sites (6800–7800 cal. BP) and the inferred coastlines reconstructed from the shell ridges in the Yangtze Delta. 中国科技论文在线 http://www.paper.edu.cn Q. Zhang et al. / Catena 60 (2005) 267–277 271

northwards from the Taihu Lake plain. This suggests that coastline changes played an important role in the expansion of human civilization in the region. Fig. 2 indicates that the Neolithic sites occur on the western side of the coastlines, demonstrating the considerable impact of sea level change on human settlements. People lived near the lakes and coastline for the convenience of obtaining living materials. Peat points distribute mostly around the lakes and along the coastlines, showing that formation of the peat was the result of expansion of water bodies induced by excessive precipitation and sea level changes. Pollen studies at the Songze cultural site (Wang et al., 1980) and Weidun cultural site (Wang, 1983) indicate that the vegetation was dominated by plants suited to wet conditions like Carpinus, Castanea, Liquidambar, and Cyperaceae. Herbs such as Artemisia and Chenopodiaceae, which were typical of dry conditions, are less abundant. The buildings of the Majiabang cultural period were supported on long poles, and some Neolithic sites were located on higher ground around the lakes to escape the rising water level (Zou, 2000). Fig. 3 demonstrates greater peat accumulation in the Songze than in the Liangzhu culture period (Fig. 4), probably because of a colder and wetter climate. Many peat points occur along the coastline, indicating the role of sea level changes in the formation of the peat. Higher sea level hinders the discharge of the ground and surface waters, leading to the formation of shallow lakes, which provide areas suitable for the peat formation. Many peat points around the lakes further corroborate this viewpoint. Pollen analysis (Wang,

119 E 120E 121 EE12 2 33 N N

Gaoyou Lake Huanghai Sea

Yangtze River 32 N

Shijiu Lake

Songze culture (5700-6800 cal. BP) 31 N Coastline Taihu Lake Gehu Lake

Songze cultural sites 200 0 200 km Shell ridge sample points Hangzhou Bay

Peat sample points 30 N

Fig. 3. Distribution of Songze culture sites (5700–6800 cal. BP) and the inferred coastline reconstructed from the shell ridges in the Yangtze Delta. 中国科技论文在线 http://www.paper.edu.cn 272 Q. Zhang et al. / Catena 60 (2005) 267–277

119E 120E 121E 122 E 33 N N Gaoyou Lake

Huanghai Sea

Yangtze River 32 N Shijiu Lake

Liangzhu culture (4100-5700 cal. BP) 31 N Coastline Taihu Lake Gehu Lake Liangzhu cultural sites

Shell ridge sample points Hangzhou Bay 200 0 200 km Peat sampling points

Buried trees 30 N

Fig. 4. Distribution of Liangzhu culture sites (4100–5700 cal. BP) and the inferred coastline reconstructed from the shell ridges in the Yangtze Delta.

1983) indicated that the vegetation is dominated by plants of wet areas, such as Polypodiaceae, Cyclobalanopsis, Castanopsis, and Quercus (Yu et al., 1999). The herbaceous pollen is dominated by halophytes (e.g. Chenopodiaceae), suggesting that the sea extended to near the peat sample points. The close spatial connections between peat and shell ridge samples support this suggestion. Fig. 4 indicates fewer peat sample points in the Liangzhu than the Songze cultural period. Cultural sites are distributed widely around the lakes and along the coastline. Pollen analysis of the Liangzhu cultural layers showed that wetland plants decreased greatly, and xerophilic plants (e.g. Artemisia) increased, suggesting a drier and warmer climate with shrinking lake areas (Ni and Ji, 1997). Excavation of about 50 paleo-wells at the Xinglong site, Changshu, province (Wu, 1994), indicated that the people dug wells to increase water resources and adapt to the arid climatic condition. Some of the Liangzhu cultural sites are also found at the bottom of Taihu, Dianshan, and Chengshan Lakes (Huo, 1985), indicating that the lake floors were partly dry and suitable for human settlement. Warm and dry climatic conditions led to increased land area, offering more space for agricultural activities, which allowed the Liangzhu culture to flourish. Archaeological excavations indicate that the Liangzhu cultural period disappeared mysteriously (Wu, 1988; Ni and Ji, 1997). As the cultural layers are usually interrupted by muddy or sandy and gravelly layers with buried trees (Zhu et al., 1996), the collapse of the Liangzhu culture could have resulted from increasing frequency of floods. 中国科技论文在线 http://www.paper.edu.cn Q. Zhang et al. / Catena 60 (2005) 267–277 273

Soon after the collapse of the Liangzhu culture, the less-developed Maqiao culture emerged. Fig. 5 indicates that most of the Maqiao sites occur near the coastline as indicated by shell ridges. The higher sea level led to collapse of the earlier human settlements. Settlement of the region resumed during the Tang Dynasty (AD 618–907) when climatic conditions again became more favorable for agriculture (Yu et al., 2000b).

4.2. Climatic variations, sea level changes, and human settlements

Fig. 6 shows the temporal relationships between the climatic variations and the human settlements. During at least five periods, a decline in human settlements (the shaded zones marked by a, b, c, d, and e) is indicated by fewer Neolithic cultural sites. These five periods match five periods of high sea level and five periods with more peat and buried trees samples. For example, from 5700 to 7800 cal. BP, burial of numerous trees and formation of peat indicate lake expansion and frequent floods; at the same time, there were fewer places suitable for human settlement (shaded zone e). At 7800 to 6800 cal. BP (Majiabang cultural period) the climate was warm and humid, and high sea level resulted in high ground water level suitable for peat accumulation. Floods and ground-surface water expansion left fewer places suitable for human settlement and this led to the collapse of the Majiabang culture (shaded zone d).

119EEEE 120 121 122 33 N Gaoyou Lake N

Huanghai Sea

Yangtze River 32 N Shijiu Lake

Maqiao culture (3300-4100 cal. BP) 31 N Taihu Lake Gehu Lake Coastline

Maqiao Neolithic sites Peat sample points 2000 200 km Hangzhou Bay Shell ridge sample points

30 N

Fig. 5. Distribution of Maqiao culture sites (3300–4100 cal. BP) and the inferred coastline reconstructed from the shell ridges in the Yangtze Delta. 中国科技论文在线 http://www.paper.edu.cn 274 Q. Zhang et al. / Catena 60 (2005) 267–277

Fig. 6. Temporal relationships between sea level, frequency of dates of the buried trees, peats, and number of Neolithic sites in the Yangtze Delta. (A) Frequency of dates for buried trees; (B) frequency of dates for peat; (C) frequency of dates for Neolithic cultural sites; and (D) sea level changes (m) reconstructed from shell ridges and peat. Shaded zones marked a–e indicate the periods of cultural decline. Dashed lines separate the different cultural periods.

The Songze period (5700~6800 cal. BP) was in the hypsithermal, with a climate that allowed the Songze culture to flourish. Fig. 6 suggests that this culture declined because of frequently fluctuating sea level and harsh climatic conditions (shaded zone c), with many trees buried by gravels, coarse sand, and mud, indicating flood environments (Zhu et al., 中国科技论文在线 http://www.paper.edu.cn Q. Zhang et al. / Catena 60 (2005) 267–277 275

1997). Fig. 6 also indicates that frequent floods occurred to the early Songze culture and this may have led to the collapse of the Majiabang culture. The Liangzhu culture (4100~5700 cal. BP) was a flourishing period of human civilization. Pollen analysis indicates an absence of wetland plants (e.g. Cyclobalanopsis), whereas Pinus and Artemisia suited to a dry environment increase in quantity (Jing, 1989). The area of also shrank at this time (Ni and Ji, 1997). Warm and dry climatic conditions exposed large area of land, providing enough space for human activities so that the Liangzhu culture flourished. It collapsed about 4100 cal. BP (Fig. 6), when the sea level rose, leading to a rise in ground water level and expansion of the Taihu lakes. In addition, many buried trees were found in layers above the late Liangzhu culture layer (Yang et al., 1987), suggesting the occurrence of floods, which could have contributed to the fall of the Liangzhu culture. Expansion of water bodies due to cold and wet climatic conditions, together with higher sea level, resulted in the fall of the Maqiao culture (3300–4100 cal. BP; shaded zone a in Fig. 6).

5. Conclusions

The Holocene climate in the Yangtze Delta was unstable and fluctuated strongly (Beck et al., 1997; Bender et al., 1994; Obrien et al., 1995). The timing and duration of the Holocene climatic events were also quite variable (Meese et al., 1994). At the boundary between the subtropical and temperate climates, the fluctuating climate led to frequent floods, fluctuating lake levels and peat formation. On the low-lying plain, settlements were susceptible to floods, sea level changes, and lake water expansion. Spatial and temporal analysis of the numerous 14C dates for shell ridges, peat, buried trees, and Neolithic sites indicates that human settlements in the Yangtze Delta were seriously influenced by these environmental variations. Periods with adverse environ- mental conditions resulted in the decline of human civilization. The collapse of the Maya civilization provides perhaps the clearest example (Curtis et al., 1996; Hodell et al., 1995). In the Yangtze Delta, there were 5 declines in human civilization during the Holocene (the shaded zones a–e in the Fig. 6), which match the 5 periods of high sea level, increased development of peat and burial of trees by floods. This indicates that the environmental variations exerted tremendous impacts on human settlement and the development of human civilization. Climatic conditions, to some degree, can hinder the human civilization progress.

Acknowledgements

The research reported in this paper was supported financially by the Key Project of the Chinese Academy of Sciences (KZCX3-SW-331), the National Natural Science Foundation of China (Grant No. 40271112), the National Postdoctoral Foundation of China, and the K. C. Wong Education Foundation, Hong Kong. Thanks should also be extended to Dr. Martin Metzler for fruitful discussion. We cordially thank the 中国科技论文在线 http://www.paper.edu.cn 276 Q. Zhang et al. / Catena 60 (2005) 267–277

anonymous reviewers for critically perusing the manuscript and rectifying the language.

References

Beck, J.W., Recy, J., Taylor, F., Edwards, R.L., Cabioch, G., 1997. Abrupt changes in early Holocene tropical sea surface temperature derived from coral records. Nature 385, 705–707. Bender, M., Sowers, T., Dicksonn, M., Orchardo, J., Grootes, P., Mayewski, P.A., Meese, D.A., 1994. Climate correlations between Greenland and Antarctica during the past 100,000 years. Nature 372, 663–666. Chen, J.Q., 1987. An approach to the data processing of historical climate materials on the basis of floods and droughts of Taihu Basin. Acta Geographica Sinica 42, 231–242 (in Chinese). Chen, Z.Y., Daniel, J.S., 1998. Sea level rise on Eastern China, the Yangtze Delta. Journal of Coastal Research 1, 360–366. Curtis, J.H., Hodell, D.A., Brenner, M., 1996. Climate variability on the Yucatan Peninsula (Mexico) during the past 3500 years, and implication for Maya cultural evolution. Quaternary Research 46, 37–47. Daniel, J.S., Chen, Z.Y., 1996. Neolithic settlement distribution as a function of sea level controlled topography in the Yangtze delta, China. Geology 12, 1083–1086. Ding, J.L., He, F.Y., 1997. Preliminary analysis on the high earth-built sites of the Liangzhu culture. South East Culture 3, 54–56 (in Chinese). Federico, V., Alfredo, A., Marcelo, F., Federico, I., 1999. Subantarctic macrotidal flats, cheniers and beaches in San Sebastian Bay, Tierra Del Fuego, Argentina. Marine Geology 160, 301–326. Hodell, D.A., Curtis, J.H., Brenner, M., 1995. Possible role of climate in the collapse of Classic Maya civilization. Nature 375, 391–394. Huo, Y.X., 1985. Investigation on the prehistorical human settlement in the Yangtze delta. Collections of Nanjing Museum 6, 41–47 (in Chinese). Jing, C.Y., 1989. Development of Neolithic and middle Neolithic human culture and environment in the Taihu Plain. Journal of Nanjing Normal University 3, 81–87 (in Chinese). Jordan, J.W., Mason, O.K., 1999. A 5000 year record of intertidal peat stratigraphy and sea level change from northwest Alaska. Quaternary International 60, 37–47. LIACASS (Laboratory of Institute for Archaeology, Chinese Academy of Social Sciences), 1996. Report of radiocarbon dates. Archaeology 7 (23), 642–645 (in Chinese). Liu, C., Wu, L., Cao, M., 1985. Sedimentary characteristics, formation and chronology of shell ridges on the Yangtze Delta. Acta Oceanologica Sinica 7, 55–66 (in Chinese). Lynn, O., 1990. Peat accumulation in northern wetlands. Quaternary Research 33, 377–386. Mason, O.K., 1990. Beach Ridge Geomorphology of Kotzebue Sound: Implications for Paleoclimatology and Archeology. University of Alaska (PhD thesis). Meese, D.A., Gow, A.J., Grootes, P., Mayewski, P.A., Ram, M., Stuiver, M., Taylor, K.C., Waddington, E.D., Zielinski, G.A., 1994. The accumulation record from the GISP2 core as an indicator of climate change throughout the Holocene. Science 266, 1680–1682. Miller, N.G., Futyma, R.P., 1987. Paleohydrological implication of Holocene peatland development in Northern Michigan. Quaternary Research 27, 297–311. Ni, H., Ji, L., 1997. Environment changes and the formation of the lake systems in the Yangchenghu lake region from the Neolithic sites. Lake Science 1, 35–40 (in Chinese). Obrien, S.R., Mayewski, P.A., Meeker, L.D., Meese, D.A., Twickler, M.S., Whitlow, S.I., 1995. Complexity of Holocene climate as reconstructed from a Greenland ice core. Science 270, 1962–1964. Oertel, G.F., Kraft, J.C., Kearney, M.S., Woo, H.J., 1992. A rational theory for barrier-lagoon development. Quaternary Coasts of the United States: Marine and Lacustrine Systems, Special Publication-Society of Economic Paleontologists and Mineralogists, vol. 48, pp. 77–87. Stuiver, M., Reimer, P.J., 1986. A computer program for radiocarbon age calibration. Radiocarbon 28, 1022–1030. Stuiver, M., Reimer, P.J., 1993. Extended 14C data base and revised Calib 3.0 14C age calibration program. Radiocarbon 35 (1), 215–230. 中国科技论文在线 http://www.paper.edu.cn Q. Zhang et al. / Catena 60 (2005) 267–277 277

Wang, K.F., 1983. Pollen diagram and its environmental meaning in the Weidun site, Changzhou, Jiangsu Province. Historical Geography 1, 13–125 (in Chinese). Wang, K.F., Zhang, Y.L., Ye, Z.H., 1980. Pollen analysis performed on the Songze site. Acta Archaeologia Sinica 1, 59–66 (in Chinese). Wu, J., 1988. Distribution of the prehistoric sites and environment changes on the Yangtze Delta. Southeastern Cultures 6, 16–35 (in Chinese). Wu, G.T., 1994. Relics study in the Changshu region. Guwuxuan Publishing House, Suzhou (in Chinese). Xiang, Y., Bao, C., 1981. The Weather in the Middle and Lower Reaches of Yangtze River. Meteorological Press, Beijing, pp. 27–136 (in Chinese). Yang, H.R., Xie, Z.R., Yang, D.Y., 1987. Formation and evolution of the Taihu lake and the Holocene sea level. In: Yang, H.R. (Ed.), Collection of the Quaternary Glaciation and Quaternary Geology. Publishing House of Geology, Beijing, pp. 49–64 (in Chinese). Yu, S., Zhu, C., Shi, W., 1998. Middle and late Holocene of Maqiao, Shanghai. Acta Oceanologica Sinica 20, 58–64 (in Chinese). Yu, S.Y., Zhu, C., Qu, W.Z., 1999. Climate transition in the Holocene and the Neolithic cultural interruptions in the eastern part of the Taihu lake plain. Geographical Sciences 6, 549–554 (in Chinese). Yu, S.Y., Zhu, C., Wang, F.B., Li, H., 2000a. Abrupt shifts in Holocene climate and sea level on the Taihu Basin and culture implication. Scientia Geographica Sinica 4, 331–336 (in Chinese). Yu, S., Zhu, C., Song, J., Qu, W., 2000b. Role of climate in the rise and fall of Neolithic cultures on the Yangtze Delta. Boreas 29, 157–165. Zhang, S., Yan, Q., Guo, X., 1982. Shell ridges on the coastal plain of Shanghai. Journal of East China Normal University 3, 81–93 (in Chinese). Zhou, H., Zheng, X.M., 2000. Role of environment changes on prehistorical human civilization-taking the collapse of Liangzhu culture in the north part of the Changjiang delta plain as an example. Journal of East Normal University 4, 71–77 (in Chinese). Zhu, C., Song, J., You, K.Y., 1996. Formation of the cultural interruption in the Maqiao site, Shanghai. Chinese Science Bulletin 4, 148–152 (in Chinese). Zhu, C., Yu, S., Shi, W., Zhang, B., 1997. Holocene deposition and paleofloods on the north bank of Yangtze River, Nanjing. Geographical Research 16, 23–30 (in Chinese). Zoltai, S.C., Vitt, D.H., 1990. Holocene climatic change and the distribution of peatlands in western interior Canada. Quaternary Research 33, 231–240. Zou, H.B., 2000. 50-year archaeology of the Jiangsu Province. Nanjing Relics Publishing House, Nanjing (in Chinese).