Environmental Change and Its Impacts on Human Settlement in the Yangtze Delta, P.R

http://www.paper.edu.cn Catena 60 (2005) 267–277 Environmental change and its impacts on human settlement in the Yangtze Delta, P.R. China 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 Shijiu Lake 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.

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