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close this bookLand Resources of the People's Republic of China (UNU, 1983, 84 pages)
close this folderI. Land-use evaluation and classification
View the document1. Major land-type categories of China
View the document2. Land classification and mapping in China
View the document3. Classification scheme for the 1:1,000,000 map of China's land resources
View the document4. Supplement to the preliminary standard classification system for land evaluation in China
View the document5. Land use on the Lake Taihu Plain
View the document6. Salt-marsh resources of China

6. Salt-marsh resources of China

Song Daquan
Institute of Forestry and Soil Sciences, Chinese Academy of Sciences, Shenyang, Liaoning Province

Abstract

In China salt-marsh resources have been used for more than 4,000 years. Coastal marshlands offer a variety of ecological niches where crops. aquatic products, salt and grasses are produced. Detailed studies have been conducted along the coasts of the northern Yellow Sea and southern Zhejian Province, using LANDSAT images and aerial photographs to analyse soil and water conditions as well as land-use patterns. An interdisciplinary study should be conducted in each coastal province to understand better the resource endowment and the problems of its utilization.

Introduction

China has about 18,000 km of coastline and some 6,000 coastal islands. The coastal zone of China is ecologically complex and economically highly productive, and includes extensive marsh areas. Based on coastal geomorphology, three major categories of coast can be recognized in China: plain (deltaic), rocky, and biological.

The plain coast comprises mostly the deltas of large rivers, such as the Huanghe, Yangzi, and the Zhu. This type of coast is subdivisible into a depositional type and corrosional type. The former occurs where large quantities of silt have been deposited in estuaries, largely as a consequence of the misuse of upstream resources. In the estuaries of these three rivers, nearly 2,000 million t/yr of silt and sand are deposited, causing continuous seaward progradation. Only a few areas are corrosional-type coastal plains, the best example being the estuary of the old Yellow River, in north-eastern Jiangsu Province.

A rocky coast occurs mainly along the Liaodong and Shandong peninsulas on the Yellow Sea and the Gulf of Bohai. In south China, rocky coast predominates from Hangzhou Bay to Guangdong and Guangxi, and on the southern coast of Hainan Island, except for some estuarine and deltaic areas.

Biological seacoasts occur in northern Fujian Province, on Hainan Island, and on some islands in the South China Sea. That in Fujian Province consists mainly of mangrove and tobira (Pittosporaceae) forests, the dominant species of the latter being Aegiceras comiculatum and Scaevola hainanensis. Those in the South China Sea consist mostly of mangrove forests and coral reefs.

Salt-marsh Resources in China and Problems of their Utilization

Salt-marsh resources in the coastal plains of north and east China have been used by farmers and fishermen for more than 4,000 years. The large coastal plains formed by the major rivers of China have, over the millennia, gradually been developed into fertile agricultural lands where rice, wheat, corn, soybean, and cotton are highly productive. Abundant aquatic products are produced in the many ponds, lakes, and waterways of these plains. The population density of the long-urbanized and highly developed lower Yangzi and Zhu valleys is 100-200 persons/kmĀ²

In the lower Liao delta of north-east China, where irrigation and drainage systems have been constructed and salinized soils reclaimed, the application of green manures and commercial fertilizers has greatly increased productivity, and the rice yields are now 6-7.5 Vha. In South China, sugar-cane, citrus, and rice thrive in reclaimed areas of former salt marsh. Double and triple cropping is practiced there, and average rice and wheat yields may reach 10-20 t/ha/yr 2

For centuries Chinese farmers have made tidal flats by enclosing salt marshes. Coastal marshlands offer a variety of ecological niches suitable for cropping, aquaculture, salt-making, and the cultivation of Phragmites sp. and other useful grasses (fig. 6.1). The inter-tidal zone of the higher beach, beyond 3 m in elevation, is suitable for the cultivation of rice, other crops, or for pasture. Aquaculture of prawns, clams, mussels. oysters, and razor clams can be practiced 2-3 m below sea level, where mud or silt deposits are abundant in nutrients and biological products. This middle tidal zone is also suitable for cultivating Spartina anglica, which may grow in tidal water with up to 3 per cent salt content. Because of its rapid propagation this valuable grass hastens the deposition of salt marsh and increases its depth at the rate of between 0.120.40 m/yr. This grass also protects dikes along shores, and its leaves and stems can be fed to livestock, used for green manure or for making paper.



Fig. 6.1. Schematic Diagram of Resource Potentials of Tidal Flats in South Zhejiang Province

It can also increase the fertility of the tidal salt marsh, in which the total organic matter can be increased from 1.2 to 1.3 per cent while the salt content of the surface horizons decreases 0.45-0.20 per cent. In estuaries where the salt content of the water is less than 0.5 per cent, phragmites may form reed beds.

At depths of 1-15 m below the middle tidal zone, fertile muds are suitable for the cultivation of kelp, laver (Porphyra spp.) and sea cucumber, all rich in protein. The area lying below the tidal zone, at depths of -5 to -15 m, may be several times as wide as the intertidal zone, and can be used to cultivate kelp and other edible seaweeds.



Fig. 6.2. Land Use near Yingkou City, Liaoning Province

The salt-marsh water in the upper part of the middle tidal zone has a salt content of about 3 per cent. Here salt pans may be constructed. Coastal salt production in China amounts to about 10 million t/yr. The country has more than 2 million ha of salt pans, mostly in north China, especially along Bohai and Liaodong Bays. About 20 per cent of China's salt is produced along the East China and South China Seas.

The development of salt marshes must be based on detailed studies to assist in the better understanding of the alternative uses of coastal resources; thus Chinese teams have conducted comprehensive research on the natural resources and economic conditions of the coastal zone, and have examined coastal geology, geomorphology, hydrology, meteorology, sedimentation, biology, soils, and land use. Maps of coastal resources have been prepared, based on field data, aerial photography and LANDSAT images. Researchers have studied the chemical, physical, biological, and mineralogical characteristics of the marshes. evaluated the quality of different kinds of coastal natural resources, and conducted research on the protection of the ecological systems of the coastal environment. In the final report, suggestions are made for the comprehensive development and use of salt-marsh resources in different parts of China.

Coastal Resources along the Northern Yellow Sea

Black-and-white 1:30,000 aerial photographs, 1:50,000 topographic maps and marine charts and colour LANDSAT images were used to compile soil and land-use maps along the Yellow Sea coast.3 Figures 6.2 and 6.3 show parts of land-use maps of two study areas along the coast of Liaoning Province.



Fig. 6.3. Land Use between Donggou and Zhuanghe, Northern Yellow Sea Coast

TABLE. 6.1. Salt Content of Salt Marsh Soils. Northern Yellow Sea Coast. North-east China

Type of Salt Marsh Depth (cm) Total
Salt
pH Ion Content (m.e./100g)
        HCO3-
(%)
Cl-
(%)
SO4-
(%)
Ca++
(%)
Mg++
(%)
Na++K+
(%)
Salt-marsh soil (sample from Tongkou) 0-15 1.40 7.0 0.14 20.88 2.62 0.42 2.33 20.75
15-30 1.38 7.0 0.12 20.53 2.71 0.49 2.71 20.17
30-50 1.55 7.6 0.12 22.79 3.20 0.58 2.80 22.74
50-70 1.45 7.8 0.14 21.23 0.06 0.49 2.44 21.50
Groundwater 70 49.17a 7.6 5.8a 830.9a 31.8a 39.6a 221.6a 607.2a
Salt-marsh soil with salt (Sample from Xingging) 0-15 5.86 8.3 0.33 63.42 30.20 2.091 0.39 81.47
15-30 2.65 8.2 0.38 40.31 4.03 1.23 4.92 38.23
30-50 2.82 8.1 0.28 43.65 4.03 1.23 5.47 41.26
50-70 3.07 8.2 0.38 47.50 4.29 1.35 5.90 44.92
70-100 2.60 8.2 0.40 39.80 3.94 1.17 4.49 38.48
Groundwater 135 77.70a 7.8 6.8a 1071.2a 24.8a 50.8a 224.9a 829.3a
Desalinized salt-marsh soil

(Sample from Tongkou)

0-15 0.86 6.8 0.47 11.81 1.96 0.37 1.44 12.44
15-30 0.48 6.9 0.47 6.42 1.26 0.21 0.69 7.26
30-50 0.43 6.7 0.28 6.29 0.58 0.18 0.25 6.72
50-70 0.49 6.8 0.28 6.93 0.92 0.21 0.53 7.40
70-100 0.63 6.7 0.28 8.78 1.41 0.34 0.70 9.43
Groundwater 120 31.90a - 1.4a 484.7a 23.9a 18.3a 63.8a 427.0a

a. The unit of total salt content in the Groundwater is Img/l), as is the unit of anion and cation

TABLE 6.2 Nutrient Content of Paddy Soils and Salt Marsh Soils, Northern Yellow Sea Coast, North-east China

Locality and
Soil No.
Soil
Type
Depth (cm) Organic matter (%) pH Total N (%) Total P2O5 (%) Water soluble N (mg/1009) (%) AvailableP2O5 (%) (mg/100g) (%) Available K(mg/100g) (%)
Tongkou
80-100
Paddy
soil
0-20 1.3 6.39 0.21 0.08 6.97 2.60 29.9
  20-40 1.0 6.72 0.23 0.08 5.96 2.54 47.2
  40 60 0.6 6.74 0.14 0.115 4.47 3.60 50.0
Zhuanghe
80-66
Paddy
soil
0-20 1.2 6.58 0.15 0.07 7.18 2.08 10.6
  20-50 1.0 6.69 0.15 0.05 3.87 1.22 14.2
  50-70 0.8 6.73 0.12 0.07 2.06 1.20 19.2
Tongkou
80-96
Salt
marsh
0-18 1.5 6.94 0.07 0.15 3.38 7.40 146.0
  18-45 1.3 6.52 0.05 0.11 1.98 4.38 104.5
  45 0.7 6.40 0.06 0.09 1.48 4.12 121.0
80-5 Salt
marsh
0 32 0.5 7.74 0.14 0.01 3.02 1.54 30.0
  32-62 0.2 7.72 0.09 0.02 2.15 1.32 35.6
  62-80 0.1 7.34 0.14 0.02 1.46 1.56 62.7
80-12 Salt
marsh
0-10 1.6 7.74 0.16 0.03 4.94 0.94 12.4
  10 16 1.3 8.60 0.10 0.02 3.00 0.92 12.0
  16-55 0.9 7.38 0.11 0.02 3.90 0.78 15.6

The land-use patterns of the salt-marsh region near Yingkou are shown in figure 6.2. Desalinized former salt marsh soils along the Liaohe delta are used for rice-fields. Phragmites beds and ponds are located near the estuary, the latter being used for raising prawns and fin fish. South of Yingkou City is a salt pan of approximately 20,000 ha. East of the city are extensive areas of dry farmland developed on former salt-marsh deposits and used to grow maize, sorghum, and millet, usually with high yields. Low hills with meadow brown forest soil are scattered over the plain, and support apple orchards. Larger hills with moderate slope are covered mostly by secondary forest, with Ouercus liaotungensis and Pinus tabulaeformis as the dominant species.4 Land use around the Dayanghe estuary, on the Yellow Sea coast, is shown in figure 6.3. Along the coast are salt marshes of 5-10 km in width. Some salt pans and fish ponds are distributed along the coast. The slightly elevated land is used mostly for dry farming, whereas stony hills are under broad-leaf forests, and the few small hills are planted with apple trees. Phragmites beds are located along the estuary, and rice fields are widespread in the flat lowland that has been developed from the former salt marshes. Many reservoirs for irrigation and raising freshwater fishes lie in the northern part of the area.

To evaluate land resources we analysed the salt content of different kinds of salt-marsh soils (table 6.1 ) and investigated the nutrient content of the salt marsh and paddy soils (table 6.2). The coastal paddy soils have a medium organic matter content, high N content, and modest P content. The productivity of rice is either moderately high or high. The organic matter as well as the N content of the salt marsh soils are medium to high, and the pH ranges between 6.4 and 7.7, mostly neutral in reaction. The texture of the paddy soils and salt-marsh soils ranges from silty clay loam to silty clay.



Fig. 6.4. Coastal Soils and Land Use near Wenzhou, Zheliang Province

Land Use in the Wenzhou Area, Southern Zheiiang Province

A soil and land-use map along the coast around Wenzbou, a city in southern Zheiiang Province, is given in figure 6.4. This map was prepared in connection with a 1979 comprehensive survey of the salt-marsh resources of the area, and was based on blackand-white LANDSAT images, aerial photographs, and two months of fieldwork.6,7 7 The red-earth soil sub-group (1 a) is derived

from red clay, sandstone, shales, and acidic crystaline rocks, and the Young red-earth sub-group (1 b) is derived from coarse granitic rocks. These two soils are surrounded by paddy soils, some of which have been formed from former salt-marsh deposits dating back to the Tang, Song, and Ming dynasties (about A.D. 600-1600), but for the most part the soils and the coastal plain along the East China Sea have developed only in the last 200300 years.

Paddy soils developed on clay deposits are usually old rice soils, whereas those developed on silty clay or silty clay loam deposits are usually new rice soils which are distributed behind the sea dikes. These soils are highly productive and can yield rice at about 15 t/ha/yr. On the other hand, the fertility of the desalinized paddy soils near the sea dikes is only modest, and they produce rice at a rate of about 7-8 t/ha/yr.

TABLE 6.3 Nutrient and Physical Properties of Salt March Wenzhoru Zhejiang Province

Soil type Locality and field No. Depth (cm) pH Nutrient content (%) humus Total N (%) Total P (%) Physical sand >0.01 mm (%) Physical clay <0.01 mm (%) Soil texture Clay minerals
Meadow
Saline soil
Salt marsh of Lingguan Island
  79-W-16 0-20 8.28 1.66 0.11 0.11 29.6 70 4 Light clay -
Salt marsh
Soil
Salt marsh of Wugisa 0-20 8.24 1.01 0.08 0.10 43.2 56.8 Heavy clay loam Hydrated mica
  79-W - 4 20-40 8.18 - - - 41.6 58.4 Light clay loam Vermiculite Kaolinite
Salt-marsh
Soil
Pazou salt-marsh soil 0-20 8.41 1.22 0.09 0.09 45.2 54.8 Light clay loam  
    20-40 8.16 - - - 49.0 51.0 Light clay loam  
  79-W-48  

 

TABLE 6.4 Salt content of Salt Marsh Soils, Wenzbou, Zheiiana Province

Soil type Locality and field No. Depth (cm) Total salt (%) Ion content (m.e./100g)
        CO3-
(%)
HCO3-
(%)
Cl-
(%)
SO4-
(%)
Ca++
(%)
Mg++
(%)
Na+ + K+
(%)
Meadow saline soil Lingguan Island 0-20 0.91 - 0.47 12.56 1.97 0.47 1.09 13.44
79-W-16 40-60 0.87 - 0.39 13.80 2.09 0.66 1.71 9.74
Salt-marsh soil Wugisa 0.20 1.00 - 0.37 14.06 2.32 0.82 1.74 14.20
79-W-4 20-40 1.00 - 0.32 12.95 3.31 0.89 1.76 13.93
Salt-marsh soil Pazou 0-20 0.85 - 0.33 11.94 1.93 0.62 1.50 12.09
79-W-48 40-60 1.03 - 0.43 11.62 3.03 0.76 1.80 14.52

Immediately behind the sea dikes are salinized meadow soils with a pH value of 8.28. They are calcareous in reaction. Their humus content is 1.66 per cent, and the total N and total P both 0.1 1 per cent. The texture is mostly light clay. The clay mineral composition of the saltmarsh deposits are hydrated mica, vermiculite and kaolinite, ail detected by X-ray defection and by using an electron microscope. These clay minerals are quite similar to those found in deposits near the Yangzi delta. The nutrient content and the physical properties of the salt marshes near Wenzhou are listed in table 6.3, and the salt content of the meadow saline soils and sea marsh soils is shown in table 6.4.

Conclusion

Preliminary estimates show that China has some 2 million ha of tidal flats. Research on coastal and saltmarsh resources and their proper use is still going on. It is recommended that an interdisciplinary investigation be conducted in each coastal province better to understand its coastal resources and the problems of their utilization. Such knowledge is basic to the better planning, use and management of resources.

References

1. Chen Jiyu, " Comments on the Comprehensive Survey and Rational Utilization of Tidal Flat Resources, " Ziran Ziyuan [Natural resources] 1(1979): 53-57 (in Chinese).

2. Song Daquan, "The Significance of Strengthening the Investigation and Research on China's Tidal Flat Resources and the Prospect for the Study of Coastal Ecosystems," Ziran Ziyuan [Natural resources] (1978): 48-52 (in Chinese).

3. Institute of Forestry and Soil Sciences. Chinese Academy of Sciences, Shenyang, " Using LANDSAT Images for the Study of Salt Marsh Resources in Liaoning Province." Unpublished research paper, 1973 (in Chinese).

4. Pei Yong, " Land Types along the Coast of Southern Liaoning Province, North east China." Unpublished research paper, Institute of Forestry and Soil Sciences, Chinese Academy of Sciences, Shenyang, 1980 (in Chinese.)

5. Luo Xuan, "Characteristics of Tidal Flats in Liaoning Province, and Their Improvement and Utilization," Turang Tongbao [Soils bulletin] 1(1980): 17-21 (in Chinese).

6. Cai Ouinquan et al., "Land Use in the Wenzhou Area, Zhejiang Province." Unpublished research paper, Institute of Geography, Chinese Academy of Sciences, Shenyang, 1980 (in Chinese).

7. Song Daquan et al., "Soils and Land Resources in the Wenzhou Area, Zhejiang Province, East China." Unpublished research paper, Institute of Forestry and Soil Sciences. Chinese Academy of Sciences, Shenyang, 1980 (in Chinese).