Appendix S1: Rice cultivation, wetlands and lakes in China
1. Rice cultivation in China
Recent evidence reveals that rice cultivation in China can be dated back 7700 years
(Zong et al., 2007). Today, China is the principal rice producer in the world,
cultivating approximately 29.2 million ha of rice paddies accounting for
approximately 18.8% of the global total (IRRI, 2009). In China, rice cultivation is
primarily in warm humid subtropical zones with plentiful summer rainfall (Fig.1).
The two agriculture ecosystem zones (AEZs) are AEZ 6 and AEZ 7 in southeastern
China (IRRI, 1997). High temperatures and water availability in this area (AEZ 7 is a
warm/cool humid subtropical climate with plentiful summer rainfall) makes an ideal
environment for rice cultivation favorable to long growth periods. As a result, double
crops of rice are planted in most parts of this region. In central and southwestern
China (AEZ 6is warm sub-humid subtropical climates with plentiful summer rainfall),
cultivated land is used on a rotational rice-wheat or rice-rape farming principle. This
region is divided into AEZ 6A and AEZ 6B due to consistently higher CH4 flux from
fields in the western part of AEZ 6 than that in eastern AEZ 6 (Yan et al. 2003). In
northern and northeastern China (AEZ 5 is a warm arid and semiarid subtropical
climate with summer rainfall, and part of AEZ 8 is a cool subtropical climate with
summer rainfall), low temperature and water availability limit rice cultivation area.
Rice cultivation in this area is mainly located in Northeastern part of AEZ 8 (AEZ
8A). Certain fields made into rice paddies can also sporadically crop up in arid and
semiarid regions of northwestern China (AEZ 8B). There is almost no rice cultivation
on Qinghai-Tibetan Plateau and the northeast part of china (AEZ 8C). Ever since the
Reform and Opening-up policy was put in place in China in 1978, rice cultivation in
terms of area in China has decreased from its peak (36.2 million ha in 1976) and has
moved northwards (Hijmans, 2007 , IRRI, 2009). Economic development has
contributed greatly to the decrease in rice cultivation in southern China. For example,
the southern province of Guangdong lost more than half of its rice cultivation area to
urbanization. Due to an increasing demand for japonica varieties of rice that are better
adapted to temperate climates, rice cultivation in the north of China increased
considerably as did the irrigation infrastructure and the consequent contribution of
rice cultivation to global warming. The northern province of Heilongjiang, for
example, increased its rice area by ten times from 0.206 million ha in 1979 to 2.553
million ha in 2007 (IRRI, 2009).
Fig.1Rice cultivation regions within China according to the Agricultural Ecosystem
Zoning (AEZ) of FAO
2. Natural wetlands in China
The total area of natural wetlands in China excluding lake and floodplain systems is
approximately 94, 000 km2(Zhao, 1999). Natural wetlands are distributed unevenly
and primarily occur in the Qinghai-Tibetan Plateau (50%) and in northeastern China
(30%) (Ding et al., 2004). They account for 10% of all wetlands found throughout the
world (Lu & Jiang, 2004). Moreover, all 26 natural wetland types delineated by the
Ramsar Convention are found in China (An et al., 2007). Four primary wetland types
prevail: peatland, freshwater marsh, salt marsh, and swamp. Peatland is the largest
wetland type found in China. It is mostly found in the northeastern region of the
country (dominated by Carex, Juncus, and Scirpus species) and on the
Qinghai-Tibetan Plateau (dominated by Carex, Pedicularis, and Scirpus species). The
freshwater marsh is also an important wetland type found primarily in northeastern
China (Phragmites, Cyperus, Blymus,and Deyeuxia). The salt marsh is primarily
found in the Qinghai-Tibetan Plateau (Phragmites,Salicornia, and Suaeda),
northwestern China (Phragmites,Salicornia, and Suaeda) and coastal regions of China
(Phragmites,Spartina, and Scirpus). Swampland is only found in northeastern China
(dominated by Alnus and Larix) and in the coastal regions of China (mangrove,
dominated by Avicennia, Rhizophora, and Bruguiera). Expansive tracts of natural
wetlands have been lost during the last 50 years in China due to reclamation, water
diversion, global warming, etc. (An et al., 2007). In the early 1990s, China began
restoring degraded wetlands and is working to restore and recreate an additional
14,000 km2 of natural wetlands through the funding of 53 large programs by the year
2030(An et al., 2007).
3. Lakes (including ponds, reservoirs) in China
China is a country with numerous lakes and reservoirs. There are 2,759 lakes
(larger than 1 km2) (Wang & Dou, 1998) and 83,387 reservoirs in China that cover an
area of 83,516 km2 and 22,850 km2, respectively. In addition, many small ponds also
exist, comprising a total area of 19,220 km2 (National Bureau of Statistics of
China ,2008). All the lakes and ponds in China make up 2.7% of all inland water (4.6
million km2 in area) throughout the world (Downing et al., 2006). Lakes can be found
in five major regions in China: the plains of eastern China, the Qinghai-Tibetan
Plateau, the Yunnan-Guizhou Plateau, the Mongolia-Xinjiang Plateau, and the
Northeast China Plain (Wang & Dou, 1998). Most lake systems are distributed
throughout the Qinghai-Tibetan Plateau and the plains of eastern China,
approximately 79.3% of the total area of all lakes in China
(NationalBureauofStatisticsofChina, 2008). Reservoirs and ponds are primarily
distributed in the southern and eastern regions of China where water resources are
plentiful. Many lakes in China, however, are degrading at rapid rates due to
anthropogenic activity (An et al., 2007, Chen, 1995, Zhao et al., 2004).
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