**2. Investigation and analysis**

Surveying and analyzing are basic to study the physical and chemical properties of soil in reclamation regions. This chapter is based on the field surveys that were carried out along the coast line of the Bohai Sea, China. The surveys were taken on typical sea reclamation projects with similar climatic conditions.

#### **2.1. Study area**

resources. Along with the population growth, the utilization and development of coastal regions have increased in recent years and the changes in socioeconomic and environmental conditions are continuing. To cope with the expansion of urbanization, land reclamation was

Overloaded population and the needs for more agricultural land and for flood protection are the main reasons for the reclaiming. Land reclamation has expanded rapidly to adjust to economic development in coastal regions. It brings about more space, which alleviates the contradiction between supply and demand of land resources. Many coastal countries, includ‐ ing the developed ones such as the USA, Japan and Netherlands, have long histories of coastal

lakes since the 1300s, which covers up to 21% of the total land surface of the country [1].

However, reclamation disturbs the hydro‐environment near the coast. It disrupts the water‐ salt movement and causes engineering, environmental and ecological problems. The quality of groundwater was affected by saline intrusion in the Netherlands [1]. Mangrove forest in China has been reported to be reduced by 53% than that in 1950s [3]. These degradations of marine habitats indicate that coastal ecosystem and hydrodynamic conditions are disturbed. The high density of salt in reclaimed regions exerts pressure on the local plants. If the salt pressure is weak, the injury to the plant could be recovered. The salinity in reclamation soil is

(0.3%). The mineralization ability in groundwater is more than 50 g/L. Only plant with shallow roots and high salt tolerance could survive in reclamation areas. Once the salt pressure exceeds the salt resistance of the plant, the life cycle of it will be destroyed and hence disturbs the whole ecosystem. Apart from this, social underground infrastructures are other victims of soil salinization. Seawater accelerates the corrosion rates of reinforced concretes and underground pipe networks which would threaten the security of coastal structures. Therefore, the under‐ standing and mitigation of soil salinization in reclamation regions are important for coastal

Soil salinization is a tough problem for coastal environment and has drawn attention on a worldwide scale. Efforts have been made to study the mechanism and mitigation measures of it. Armstrong et al. [4] studied the seasonal variation in water and salt distribution in fields with both grassland and arable saline‐sodic clay soils under temperate rain‐fed conditions. Chen and Jiao [5] analyzed the groundwater chemistry in coastal aquifer and found that groundwater pumping was the reason for seawater intrusion. Iost et al. [6] found that reclamation influenced the local pH and carbonate content by decreasing calcium, magnesium and potassium while studying the initial pedogenesis of reclaimed saline marsh soils.

The objective of this chapter is to explore the mechanism of soil salinization in reclaimed coastal regions, especially that under semi‐humid climate where evaporation is more than precipita‐ tion. In this chapter, the Bohai Rim, China, is selected as an example to study the water and salt migration in reclaimed soil. Physical model and numerical model are built for under‐

which is much larger than the largest salinity that the most plants could bare

from the sea and inland

in the worldwide scale, and still

reclamation. Netherlands, as an example, reclaimed about 7000 km2

Currently, these new formed lands have exceeded 140,000 km2

increasing rapidly in some countries such as China [2].

160 Soil Contamination - Current Consequences and Further Solutions

carried out.

1–4% in 1 m3

environmental protection.

The study area is located in the Bohai Rim, China (**Figure 1**), which has a semi‐humid temperate monsoon climate with the average annual temperatures of 8.3–12.4°C. The annual sunshine duration is 2500–2900 h, and the annual total radiation is 5000–5800 MJ/m2 . The annual precipitation is 612–640 mm, which is concentrated in summer (60–75%), and the annual evapotranspiration is 1300–1900 mm. The ratio of precipitation and evaporation maintains 0.33, which makes the water balance in the soils negative. The land reclamation projects were started during the 1980s. From 1996 to 2007, 551 km2 new lands were reclaimed and the annual reclamation area covers 80% of the country.

**Figure 1.** Location of the Bohai Rim.

The samplings of the research were carried out along the Bohai Rim. Samples of soil were collected from five main coastal cities where the reclamation projects were completed and the level of salt was stable. The reclaimed soil samples were collected using soil auger to a depth of 20 cm, and control samples were collected in the natural coast nearby. Samples were then dried at 40 °C and sieved with 1 mm plastic sieve based on the standard for classification of soils (GBJ145‐90). The physical and chemical properties of the soil were then analyzed in the laboratory.

#### **2.2. Salinization in land reclamation area**

Land formation in coastal area includes natural sedimentation and artificial landfills. Every year, the Yellow River brings about 1.5 billion tons of sediment to the estuary, two‐thirds of which deposit in the delta. This area has the fastest land formation speed, where the shoreline is extended with an average distance of 1.8 km and formed 21.3 km2 tidelands each year. Artificial reclamation is often carried out on natural beaches using sea sand, mountain soils, minerals and construction waste, depending on the geological condition of the coast. Regions with hills and low mountains would use riprap filling method. While in river deltas, the method used is dredger filling (hydraulic filling). Although the soil structures are similar, there are differences in physical and chemical characteristics (**Table 1**).


**Table 1.** Location of the Bohai Rim.

Our research shows that Tianjin, Caofeidian and Laizhou are dredger filling reclamation regions, and Dalian and Yingkou are riprap filling land reclamation regions. The physical properties are analyzed and are listed in **Table 1**. The grain size of dredger filling soil is smaller than that of riprap filling soil. Seventy percent of the riprap filling soil is sand, which is also more than that of the soil from the hills where the riprap filling soil comes from. The density of riprap filling soil is smaller, while the porosity and the permeability coefficients are larger, which indicate the variation in salt water migration characteristics. The soil texture of dredger

filling is heavier, and the original salinity is higher, which may cause salinization. Riprap fill, on the contrary, with greater thickness and larger bottom, has better connectivity to prevent salinization. The differences between riprap land reclamation and dredger fill reclamation are listed in **Table 2**. Large areas of these projects were built directly on former salt pans, which are the extreme examples of deposited salt density in sediment. This fact aggravates the surface salinization in the backfill area. The results show that the salt contents of the reclamation soil are consistent with the surface soil of salt pans nearby, which indicate the process of salt releasing from the sediment. This consistency tends to be clearer over time. The migration of water and salt in the backfill soil is controlled by the grain composition, which reflects the aquifer permeability and adsorbing capability of the soil particle. The salt in backfilling soil is accumulated in the surface layer. The groundwater was shallow buried (1.5–2.5 m) in the sampling sites which were all within the limit depth of phreatic evaporation. Therefore, the phreatic evaporation may be the main driving force of the salt accumulation in surface layer in reclamation regions. The main types of salt are NaCl and CaCl2 for dredger filling soil and CaSO4 for riprap filling soil.


**Table 2.** Differences between dredger filling and riprap filling land reclamation.

#### **2.3. The movement of water and salt**

Rainfall, evaporation and runoff carry dissolved minerals and salts in continuous movement and form a uniform material flow. Different characteristics of salt migration occur in the different conditions of climate, soil and irrigation management, etc. In general, this process could be classified as salt leaching, salt accumulation and the release process of salts from sediment in the land reclamation regions.

#### *2.3.1. Salt leaching process*

level of salt was stable. The reclaimed soil samples were collected using soil auger to a depth of 20 cm, and control samples were collected in the natural coast nearby. Samples were then dried at 40 °C and sieved with 1 mm plastic sieve based on the standard for classification of soils (GBJ145‐90). The physical and chemical properties of the soil were then analyzed in the

Land formation in coastal area includes natural sedimentation and artificial landfills. Every year, the Yellow River brings about 1.5 billion tons of sediment to the estuary, two‐thirds of which deposit in the delta. This area has the fastest land formation speed, where the shoreline

Artificial reclamation is often carried out on natural beaches using sea sand, mountain soils, minerals and construction waste, depending on the geological condition of the coast. Regions with hills and low mountains would use riprap filling method. While in river deltas, the method used is dredger filling (hydraulic filling). Although the soil structures are similar, there

> **Specific gravity**

Reclamation 22.9 18.2 2.63 36 39.7 5.83 × 10−6

Reclamation 2.9 14.6 2.35 38.1 14.3 1.11 × 10−5

Reclamation 26.1 16.9 2.43 44.2 26.8 7.19 × 10−4

Our research shows that Tianjin, Caofeidian and Laizhou are dredger filling reclamation regions, and Dalian and Yingkou are riprap filling land reclamation regions. The physical properties are analyzed and are listed in **Table 1**. The grain size of dredger filling soil is smaller than that of riprap filling soil. Seventy percent of the riprap filling soil is sand, which is also more than that of the soil from the hills where the riprap filling soil comes from. The density of riprap filling soil is smaller, while the porosity and the permeability coefficients are larger, which indicate the variation in salt water migration characteristics. The soil texture of dredger

**Porosity (%)**

**Water‐ holding capacity (%)**

**Volumetric weight (kN/m3 )**

Tianjin Reclamation 20.2 18.8 2.38 32.8 51.1 8.33 × 10−7

Caofeidian Reclamation 3.4 13.9 2.61 45.8 22.9 2.75 × 10−5

Yingkou Reclamation 10.9 13.2 2.49 51.3 29.6 3.23 × 10−5

Reclamation 19.2 17.3 2.45 35.4 21.1

tidelands each year.

**Permeability coefficient (%)**

is extended with an average distance of 1.8 km and formed 21.3 km2

are differences in physical and chemical characteristics (**Table 1**).

**content (%)**

Laizhou Planting 4.5 10.8 2.45 51.1

Planting 3.9 14.2 2.22 41.1

Hill 26.7 16.7 2.41 44 Dalian Reclamation 27.2 16.6 2.39 43.8 23.6

laboratory.

**2.2. Salinization in land reclamation area**

162 Soil Contamination - Current Consequences and Further Solutions

**City Soil type Water**

**Table 1.** Location of the Bohai Rim.

Affected by the soil texture and structure, the impact depth of rainwater is limited, and the leaching effect in surface soil is stronger than that of the deep soil. The salinity peak declines with infiltration process until it disappears. The distribution of soil moisture in the 0–80 cm depth consists of a logarithmic curve in the absence of crops, and little effect was shown below 1.0 m. A critical mutation in salinity variety exists around 40 cm depth, and a transition region appears from 50 to 70 cm. Drizzle is not stronger enough to wash salt away, but it carries salt to the surface after rain stops. In agricultural area, large‐scale irrigation contaminates fresh‐ water, and washes minerals and nitrate away, which may cause low soil permeability and nutrient content.

#### *2.3.2. Salt accumulation*

There has been a history of salt and water movement under evapotranspiration conditions. Fritton et al. [7] examined the differences of water‐salt distributions under various evaporation intensities, and much research was subsequently focused on salt and water transport in soil [8]. A variety of formulas are widely used to calculate evaporation. However, studies on salt transport fell behind, relatively. Groundwater has significant effects on salt accumulation, although the drainage system is blocking it with flattening landform. The higher the salinity of groundwater, the more serious the salt accumulation. In the capillary rise zone, evaporation maintains a constant generally, but it decreases rapidly at the bottom of this zone and tends to zero, while the groundwater exceeds the impact depth. Throughout this process, the cumula‐ tive evaporation has a power function in relation to the diving depth [9]. It is easier to prevent salt upward and improve the leaching efficiency with a higher hydraulic gradient when the water table is deep. However, plants cannot grow up when the root zone lacks water. Zhang and Zhang [10] considered that the groundwater should be controlled at 0.7–0.8 m during the growth period, and fell to 1.2–1.4 m without crops.

In the high salinity environment, plants play an important role in salt regulation [11]. Plants may exacerbate salinization in sea reclamation areas during evapotranspiration, and the impact depth should be the sum of root depth and capillary rise height. The movements of salt and water become stable only when the groundwater is below the limited depth of phreatic evaporation.

#### *2.3.3. Salt releasing from sediment*

Sediment deposited on the seabed for years has high salinity of more than 10%. When the environment changes to reclamation, salt in sediment will be gradually released. Environ‐ mental factors have obvious effects on the release of salt. For example, wind and temperature can promote this process, while the initial mineralization of groundwater will hinder it. In an acidic environment, the chemical properties maintain relative balances. Once these ions are in alkaline conditions, Mg2+ and Ca2+ would flocculate to deposition, which also accelerate the dispersion of magnesium and calcium.

Moreover, the environment of land reclamation areas is more complex than that of the natural coast. Groundwater replaces part of the saline water with the movement of fresh‐salt water interface. Due to the restriction of upper soil, groundwater exchange is slow, and the accom‐ panying removal of salt is too low. Cl− is a conservative ion excluded by soil colloids, which can migrate within groundwater freely, and of which the concentration is determined by the salinity of groundwater. In an open system, Na+ is released from the sediment in exchanges for a continuous supply of H+ . Meanwhile, CO2 released by plant roots generates excess HCO3 − and CO3 2 −, which may cause hydrolysis and acid erosion on rock and generate more dissolved salts. But in a closed system as reclamation region, the absence of CO2 decreases HCO3 − and CO3 2 − concentration. The bicarbonate‐type groundwater transforms to chloride‐type ground‐ water. Thus, the salinization will be intensified in land reclamation regions.
