Song Shuhong

Institute of Hydrogeology and Environmental Geology, CAGS,Shijiazhuang, P.R.China e-mail: ssh5228@163.com

 

Abstract:Various problems are concerned with groundwater and induced by exploration and utilization of the groundwater in the Yellow River Delta, such as wetland degradation, soil saline and alkaline soil, seawater intrusion etc. The geological environment is fragile. Based on the groundwater table and the hydro-geological conditions, combining with the characteristics of micro-topography, a model depicts the response of the wetland protected and the extracted groundwater was built to solve the problems, the feasible data were provided for the utilization of groundwater in the Yellow River Delta.

Key words Yellow River Delta (YRD); wetland; groundwater; water resource; water environmental.

        The Yellow River Delta in this paper is the modern delta, an alluvial fan that is made up with great amount of Quaternary fluvial deposit of the Yellow River since 1855. It lies along the seacoast of the Bohai Gulfand the Laizhou Gulf. The average elevation is lower than 15m, with total area about 5450km². According to Chinese administrative region partition, Dongying city of Shandong Province is the main part of the Yellow River Delta. Because of the fluvial deposition of the Yellow River, new land has been formed on the estuary delta gradually. According to Hu Chunhong et al. (1996), average rate of the estuary extruding into the sea is about 2.6km/a, and a relatively lower rate has been observed recently, which is about 1.1 km/a (Ding Dong et al., 2001). Accordingly, the wetland has been expanded and extruded into the sea gradually, and about 21.3 km² sea area is replaced by new formed land every year (Xu Jianmin, 2001). The Yellow River Delta is a typical estuary wetland, which has not only the most complete but also the youngest wetland ecosystem types over warm temperate zone in China. Therefore, it is an ideal area to study the formation, evolution and development of the newly formed wetland over estuary area.

1 The Wetland Ecosystem of the Yellow River Delta is Fragile and Affected by the Yellow River Water Evidently

1.1 The wetland ecosystem of the Yellow River Delta is fragile

Due to the low and flat topography, the river flows very slowly and lots of wetlands have been formed in Yellow River Delta. The total area of the wetland is about 333,427km².From the view of hydrology, the perennial wetland is main part that accounts for 63% of the total wetland area and the seasonal wetland area occupies 37 %( Xu Jianmin, 2001).  Since the wetland has been formed or developed with the relatively short time and main land cover is still the grass vegetation, the ecosystem is very fragile to the outer environmental change, especially for some species, such as red-crowned crane, whose is easy to be hurt due to the lower ability of propagation.

According to the effect of human activity, the wetland in the Yellow River Delta can be classified into two categories, natural wetland and man-made wetland. Natural wetland is the wetland that is not or rarely disturbed by human activities for the moment, such as shallow sea or beach wetland, river wetland, swamp, meadow wetland and natural freshwater area etc. Man-made wetland is the wetland that is fiercely affected or developed by human activities, such as reservoir, ditch, paddy field, breed aquatics pool and saltern etc (Chen Weifeng et al., 2003). In recent years, the total area of wetland has been increased, of which the natural wetland area has been decreases and that the man-made wetland area has been increased (Table 1). At present, the man-made wetland occupies 1/3 of total wetland area and the natural wetland is inclined to decrease and degenerate, and that the total area of wetland is more or less keep the same. Since 1998, the zero-flow season of Yellow River hasn’t happened any more, so the development wetland ecosystem is stable.

Table 1 The area of different types of wetland in the Yellow River Delta (Dongying) during 1981-1998

 (after Xu Jianmin, 2001)

1.2 The wetland area is affected by income amount of the Yellow River

Water is essential for wetland and the natural condition of wetland is affected by the quantity and quality of available water sources (Yang Zhifeng, et al., 2003). Yellow River is the main water source of the study area, which formed and maintained the wetland ecosystem, and the wetland area is affected by total incoming water resources of Yellow River. During 1985 to 1997, when the Yellow River drainage area is continually dried up, the incoming water went on reducing. As a result, converse succession took place in the seral community, some halophilic enduring vegetation has been developed, and the area of reed wetland decreased while the area of reservoir, pool and saltern increased, the overlay rate of vegetation reduces obviously. Some animals and plants surviving by wetland decrease obviously, and the original ecosystem of the estuary have been degenerated (Chen Weifeng, et al., 2003).

Figure 1 Time-series runoff of the Yellow River at the hydrology station in Lijing during 1985—2005

2 Groundwater System

2.1 The dynamics of groundwater system in rainy season and dry season

The dynamics of groundwater is mainly affected by precipitation, evapotranspiration (including evaporation and transpiration),irrigation and drainage (Guan Yuanxiu, 2000). Under the certain circumstance, for example, climate conditions, topography and geological background, the more water comes from outside, the more highly of the local groundwater table rises. Hence, the groundwater table is higher in rainy seasons while lower in dry seasons.

14 points in the Yellow Delta(Dongying) and 43 points that lie in Dongming、Yuncheng、Liangshan、Dongping、Jiyang、Ji’nan、Qihe、Dong’e、Yanggu etc in the low reach of the Yellow River has been investigated and groundwater levels measured in different seasons are shown as Fig.2 and Fig.3 respectively. As it is shown, annual amplitude of groundwater table is lower with the maximum less than 1m in Yellow River Delta, while the maximum can reach 4m in other area.

 

Figure 2 Comparison between groundwater table in rainy season and dry season in the Yellow River Delta

 

Figure 3 Comparison between groundwater table in rainy season and dry season in the Yellow River low reach plain

2.2 Due to the modulation of wetland, the dynamic of groundwater table is less in rainy season and dry season

The flood season of the Yellow River includes July, August and September, which is also the rainy season of the Yellow River, and due to the time-lag, the effect of the incoming Yellow River water on groundwater system will be obvious soon later. Hence, the time for groundwater levels measuring is selected in the last ten-day of September when these wells had accepted water supply from rainfall and seepage of the Yellow River. The data observed in the Yellow River Delta indicates that the dynamics of groundwater table is less in rainy season and dry season due to the regulation function of the Yellow River Delta wetland. In addition, the great environmental regulation function and ecological benefit of wetland is reflected not only by the groundwater systems, but also for water supply, climate adjustment, water resources protection, flood control, silt promote, new land formation, contamination degradation, and biological diversity maintaining.

3 Reasonable Utilization of Wetland to Ensure its Function

While natural wetland area in the Yellow River Delta decreased and manual wetland area increased, the regulation ability of wetland decreased. The construction of manual wetland is for the sake of raising the groundwater table to supply wetland by using the Yellow River for irrigation. Since 1999, a project to recover the ecosystem of the wetland has been implemented, and by the end of 2004, the area of wetland with fresh water had been enlarged obviously and more than 1.3´10⁴ha salted land had been reclaimed to wetland. Because maintain of manual wetland depends on the directly supply of the Yellow River water, the effect on the man-made wetland by Yellow River is stronger compared with natural wetland. However, due to the bare land presented, man-made wetland has less ecological functions.

Because water quantity of the Yellow River is not stable and the available water resource is limited, reasonable exploitation and utilization is a guarantee to ensure the well development of the environment. In the case of manual irrigation, the water resources needed by wetland ecosystem should be fully taken into account. According to Cui Baoshan et al(2003), the water resources requirements for the wetland in Yellow River Delta area should be with in the range of 9.8~12.6´10⁸m³ to 36.7~42.7´10⁸m³ to maintain the healthily development of the wetland， and the optimal water resources required is 23.4~28.2´10⁸m³.

4 Conclusions and Discussions

The Yellow River has an affect on the regional environment through the groundwater system, and vice versa.

The wetland ecosystem in the Yellow River Delta is dominated by climate and incoming water resources of the Yellow River. The environmental factors such as geologic condition, climate etc. can be regarded as connatural, but the groundwater table and the means of land utilization can be changed, so the effect of human activities can not be ignored. In the process of human activities to change the nature, the order of nature should be fully considered to promote the relation between humanity and nature. In order to realize the sustainable development of the Yellow River Delta area, the relations between incoming water resources fromYellow River, regional groundwater levels changes and water requirement of wetland should be know clearly.

Based on previous discussion, a model that reflects the response among wetland area, shallow layer groundwater table and the incoming water resources from Yellow River were constructed as following:

where, Ls is wetland area, t-1 forecast time, t original time, EI income water resources, GWd groundwater table, St climate, Lt tiny physiognomy type, Lu means of land utilization, Cl water resources of the Yellow River (runoff observed in Lijing station), “Cl”corresponds to “GWd” and “Ls” in the model.

Taken the wetland in Yellow River Delta area as a pilot, a model that depicts the response between total areas of wetland, shallow groundwater leves as well as incoming water resources from Yellow River were constructed, which is believed to be meaningful to guide the reasonable utilization or local water resources. 

References

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