Changes of shallow groundwater resources in Laizhou Bay area of Shandong Province

(1. Geological Survey Institute of Shandong Province, Jinan 250013,2. Shandong Geological Engineering Survey Institute, Jinan 2500 14)

Fund Project: Land and Resources Survey Project: Investigation and Evaluation of Groundwater Resources and Environmental Geology in Bohai Rim Region (2001kloc-0/2400005).

Author introduction: Xu Jianguo (1965—), senior engineer, bachelor degree, mainly engaged in hydrogeology and environmental geology investigation.

Laizhou Bay is an area with serious environmental geological problems such as groundwater overexploitation, seawater intrusion and groundwater pollution. The change of shallow groundwater resources is an important reason for these problems. The change of shallow groundwater resources is manifested in two aspects: quantity and quality. In terms of water quantity, with the change of climate and hydrogeological conditions, shallow groundwater resources have changed, and the natural resources in wet season and dry season are 19.73× 108m3/a and 12.70× 108m3/a respectively. In terms of water quality, the water quality in some areas has deteriorated, and the contents of conventional ions such as total hardness, chloride ion, sulfate ion and nitrate ion have increased. The drinking water quality of shallow groundwater exceeded the standard from 5 142km2 in 1980 to 5853km2 in 2000-2002.

Keywords: Laizhou Bay; Shallow groundwater; Salt pollution; Resource change

Introduction to 0

Laizhou Bay is adjacent to Laizhou Bay in Bohai Sea in the north, the piedmont plain at the northern foot of Mount Tai in the south, Jiaodong Peninsula in the east and the hinterland of central Shandong in the west. It is semicircular along the coast of Laizhou Bay. The whole area includes 7 cities (counties, districts) including Longkou, Zhaoyuan, Laizhou, Changyi, Hanting, Shouguang and Guangrao, and a small part of Pingdu, with a total area of about 10 1658.

This region is a region with a high level of economic development in eastern Shandong Province. In 2002, the population was 4.639 million, and the gross national product was 55.92 billion yuan, accounting for 6.8% of the province. With the rapid development of regional economic construction, especially in the early 1980s, Han Wei, Changyi, Shouguang, Longkou and other centralized water supply sources were put into operation one after another, which made the amount of groundwater exploitation in this area increase year by year, and the mining intensity increased continuously. The exploitable amount of shallow groundwater in the whole region is 7.52× 108m3/a, and the current exploitation amount is 8. 13× 108m3. Overexploitation of 0.62× 108m3/a has caused environmental geological problems such as continuous decline of groundwater level and seawater (salty) water intrusion, which has caused great harm to local ecological environment quality, industrial and agricultural production and people's life. The reason is that the increase of water demand is one of the important factors, but the gradual decrease of water resources is another important reason. The study on the change of shallow groundwater, an important water supply source in Laizhou Bay area, will help to formulate a reasonable water resources development and utilization plan, and is of great significance to alleviate the contradiction between supply and demand of water resources and improve the ecological environment.

Geological environment of 1

The topography of Laizhou Bay area is complex. Generally speaking, the semicircle study is divided into two parts: the east and the west, and the west is the piedmont alluvial plain and the coastal marine plain, in which the piedmont alluvial plain is composed of multiple alluvial fan groups with crossed fan edges, and its leading edge is buried by marine sediments or Yellow River alluvium, with thick aquifer and multi-layer structure. In the vertical direction, the aquifer particles tend to be thinner from bottom to top, while in the horizontal direction, they have the hydrogeological characteristics of alluvial-diluvial fans. The water inflow of a single well is generally 1000 ~ 5000 m3/d, which is rich in water. The eastern part belongs to eastern Shandong hilly region and coastal plain. The groundwater in this area mainly occurs in the Quaternary aquifer of coastal plain and the Quaternary aquifer of intermountain valley plain, and the fractured groundwater mainly occurs in the weathered cracks of bedrock. The water inflow of a single well in Quaternary distribution area is generally 500 ~ 1500m3/d, and the water yield is relatively weak. Water inflow of single well on both sides of the valley 1000m3/d, and water inflow of single well is 3000m3/d.

There are more than 20 rivers in the whole region, such as Xiaoqing River, Huaihe River, Mihe River, Jiaolai River, Bailang River, Wanghe River and Huangshui River, which belong to the coastal water system of Huaihe River Basin. Most of these rivers originate from the hills and mountains in the south and flow into the sea alone in the north. The annual average precipitation in the whole region is 594.7mm, and the annual average surface runoff is 12.94× 108 m3 (including tourists from upstream). Runoff in flood season accounts for 70% ~ 85% of the whole year, and flood surges and falls, making it difficult to regulate and store, while runoff in dry season is very small, even cut off for a long time, and there is no water available.

2 changes in precipitation and surface water resources

2. 1 precipitation change

As the main recharge source of shallow groundwater in Laizhou Bay area, atmospheric precipitation has the characteristics of periodic change, and its change is a rather complicated random process. The precipitation process is the result of the interaction between atmospheric circulation and thermal conditions of the underlying surface. The formation and precipitation of a precipitation are disturbed by many random factors, which leads to the fluctuation of precipitation process and precipitation.

In order to suppress or eliminate the interference of random factors, and thus extract useful information for the analysis of precipitation periodic change, firstly, the digital filtering algorithm is used to filter the original meteorological observation data, and the filtered data is used as the observation data for the next step of calculating differential product, and then the differential product curve is made according to the calculated differential product value to analyze the precipitation period. The analysis process is as follows.

2. 1. 1 Precipitation observation data of weather station are filtered by moving average method.

Moving average method is one of the algorithms of one-dimensional trend analysis and a simple digital filtering method. Its function is to smooth the curve composed of data, suppress or eliminate short-period components and random interference, and keep long-period trends, so as to determine the trend values in different periods. The calculation formula is as follows:

Shandong environmental geology collection

Where: Δ xi is the sliding trend value of precipitation observation data of weather station; Xi is a series of original meteorological observation data; Is the filter operator, where m is the number of sliding points (the greater the value of m, the cleaner the short-period components removed and the smoother the curve).

2. 1.2 Analyze the sliding trend value of precipitation observation data by differential product.

Differential product analysis is a method commonly used to determine the periodic change of time series. The so-called difference product is the sum of the point-by-point difference between the observation sequence value and the average value of each point, that is, after determining the deviation of each observation point, it is accumulated point by point to determine the periodic change of this accumulated sequence. The curve drawn by the calculation results is called differential product curve, the descending arc represents the low water section and the ascending arc represents the high water section, so the precipitation curve composed of low water period and high water period represents a precipitation cycle. Calculation formula:

Shandong environmental geology collection

Where Yj is the difference product value of each observation point; Xi is the original observation value of each point in the sequence; Is the average of the original observation values of the sequence; N is the number of observation points in the sequence.

Laizhou Bay meteorological station lacks a long series of precipitation monitoring data, but the precipitation monitoring data in the nearby area can be used to analyze the precipitation change law in this area. There is a long list of meteorological monitoring data at Yantai, Qingdao and Jinan meteorological stations near Laizhou Bay. By using the above method, the precipitation period and precipitation change trend are analyzed by using the precipitation observation data of three cities in 80 ~ 1 10, which can basically reflect the precipitation characteristics in Laizhou Bay area. Figure 1 Based on Yantai Meteorological Station 1887 ~ 200 1, Qingdao Meteorological Station 1889 ~ 200 1, Jinan Meteorological Station1916 ~ 200.

Figure 1 Annual Precipitation of Meteorological Station 10 Annual Sliding Differential Product Curve

From the differential product curve, it can be seen that the precipitation changes in the three cities are almost synchronous, and they have all experienced a dry-abundant-dry cycle. Since 19 15, the study area has experienced a complete precipitation cycle with a period of 86 years, in which 19 15 ~ 1948 is the dry season. The system precipitation data in the study area starts from 1956, in which 1956 ~ 65438+675mm/a in wet season and 1980 ~ 200 1 in dry season is 578mm/a, with a difference of 97mm/a (table

Table 1 List of changes in precipitation and surface water resources

2.2 Changes in surface water volume

The surface water resources in Laizhou Bay area change with the periodic change of precipitation. According to the statistical analysis, the surface water resources in the whole region decreased from 15.22× 108 m3/a in the wet season to 9.89× 108 m3/a in the dry season, a decrease of 35% (table 1). The available surface water supply is 6.60× 1960 ~ 1980 in the high water season and only 3.3×108m3 in the low water season.

The reason for the decrease of surface water resources is the decrease of precipitation and the construction of a large number of surface water storage projects in the middle and upper reaches of major rivers, which makes the runoff in the middle and lower reaches of rivers continue to decrease and some rivers are cut off all the year round.

3 changes in hydrogeological conditions

Since 1980, the dynamic field of shallow groundwater in Laizhou Bay has changed greatly. From 1980 to the western section of Laizhou Bay, the area with buried depth less than 4m decreased from 23297km2 to 65438+4637km2, a decrease of 28%, while the area with buried depth greater than 10m increased from 0km2 of 1980 to 2,000km2. The negative funnel area of shallow groundwater level is 1470km2, accounting for 14.5% of the total area of the whole region. Shallow groundwater subsidence funnel began to appear in the coastal plain in the east of Laizhou Bay in the late 1970s. By 1990, the total area of groundwater negative funnel reached 49 1km2, accounting for 42.3% of the total area of coastal plain. The height of the water level in the center of the funnel is generally lower than-10 meter, and the groundwater level will remain at a relatively low level in the next 10 year.

The research results of hydrogeological parameters show that when the groundwater level exceeds 4 ~ 6m, the recharge of shallow groundwater will decrease with the increase of groundwater level. Table 2 shows that the precipitation infiltration coefficient in Laizhou Bay has obviously decreased in recent 20 years.

Table 2 Variation Table of Regional Area of Precipitation Infiltration Supplement Coefficient

4 changes in shallow groundwater resources

Shallow groundwater resources are random variables closely related to precipitation, farmland irrigation, groundwater flow field and other factors. In recent 20 years, with the changes of the above factors, shallow groundwater resources will inevitably change. According to the analysis of the changes of precipitation, surface water and hydrogeological conditions, the natural resources are calculated. The shallow groundwater depth 1980 and 200 1 year represent the groundwater depth 1956 ~ 1980 and1980 ~ 200/kloc respectively. The calculation results show that the natural resources decreased from19.73x108m3/a in the wet season to12.7x108m3/a in the dry season, with a decrease of 35.6% (Table 3). The main influencing factor is the decrease of precipitation infiltration recharge which accounts for the whole resource change.

Table 3 Changes of Natural Resources of Shallow Groundwater (unit: 108m3/a)

5 changes in the quality of shallow groundwater

Laizhou Bay area is an area with developed economy and strong human engineering activities, which is mainly manifested in high population density, dense industrial and mining enterprises and high intensity of groundwater exploitation. In addition, the vadose zone and aquifer have coarse lithology and poor groundwater pollution resistance, which is a serious groundwater pollution area. The comparative data of chemical conventional components of groundwater quality monitoring points show that the shallow groundwater pollution in this area is mainly salt pollution, that is, the conventional components such as salinity and total hardness in most monitoring points are obviously increased. Salt pollution has strong spatial and temporal distribution characteristics, generally planar or banded, and its discriminant indexes are generally total hardness, chloride ion, sulfate ion and nitrate ion.

5. 1 total hardness increased.

The increase of total hardness is an important manifestation of the change of shallow groundwater quality in Laizhou Bay area. There must be a large number of sources of calcium and magnesium to increase the hardness of groundwater. The soil and weathering crust in this area are rich in carbonate, and some calcareous nodules have high carbonate content. The rich Ca2 ++ and Mg2 ++ in soil are the main sources to increase the hardness of groundwater. With the rapid development of industry and the increase of population in this area, domestic waste, industrial waste, especially sewage containing a lot of organic matter and soluble salts, seeps into groundwater in the form of solution, and reacts chemically with carbonate in soil to generate soluble calcium and magnesium salts, which increases the hardness of shallow groundwater.

In Laizhou Bay area, except the coastal area on the south bank, the shallow groundwater hardness exceeding the standard is just a densely populated area where industrial pollution sources are relatively concentrated, and it is also a shallow groundwater funnel area. Especially in recent 20 years, with the rapid development of industry and agriculture in the work area, especially the increase of township enterprises, the sewage discharge is increasing, and the problem of surface water sewage irrigation is becoming more and more serious, which makes the scope and degree of groundwater hardness exceeding the standard increase year by year. 1980 or so, the total hardness exceeding the standard area is located in the coastal brine distribution area on the south bank of Laizhou Bay and the estuary area of some rivers in Jiaodong Peninsula, mainly belonging to the original hardness exceeding the standard area. The secondary total hardness exceeding the standard caused by human pollution is small, and it is distributed in blocks on both sides of several major sewage rivers in this area, with a total area of 4965.8km2 By 2002, the total hardness exceeding the standard along the coast of Laizhou Bay was 5704.9km2, with an increase rate of 33.6km2/a (Figure 2).

Variation diagram of total hardness of shallow groundwater exceeding the standard.

5.2 chloride ion content increased

Before 1980, the degree of groundwater exploitation in this area was low, and the Cl- exceeding standard area was mainly the first-class exceeding standard area, mainly distributed in the coastal area on the south bank of Laizhou Bay (Figure 3). During the 22 years from 1980 to 2002, the content of Cl- in some areas increased greatly, and the distribution area exceeding the drinking water standard of 250mg/L increased from 3598.5km2 around 1980 to 4767.7km2 around 2002, with a growth rate of 53.1km2/a/.

Fig. 3 Variation diagram of chloride ion exceeding standard area in shallow groundwater

5.3 sulfate ion content increased

1980 or so, the total area of the over-standard area in Laizhou Bay is 2709.5km2 Except for the original over-standard area along the coast of Laizhou Bay, the content of Xiaoqing River and some areas in gaomi city exceeds the sanitary standard for drinking water by 250mg/L, which is caused by surface water and sewage irrigation. During the 22 years from 1980 to 2002, the groundwater content in some areas increased greatly. By 2002, the over-standard area reached 3 164.0km2, with an average annual increase of 20.7km2 The over-standard growth areas were mainly located in Xiaoqing River, Jiehe River Basin, Zouping, Zibo and Gaomi (Figure 4).

Comprehensive analysis of several common pollution indicators of shallow groundwater shows that the drinking water exceeding the standard increased from 65438+5 142km2 in 1980 to 5853km2 in 2002, with an increase of 13.8%, accounting for 57.7% of the total area of Laizhou Bay (Figure 5).

6 conclusion

Laizhou Bay area is one of the areas with the greatest changes in groundwater environment in Shandong Province. Shallow groundwater is the main water supply source in this area, and its change is reflected in two aspects: quantity and quality. The change of water quantity is manifested as the change of recharge conditions. First of all, precipitation and surface runoff, which are the main recharge sources, are obviously reduced. From the analysis of the characteristics of atmospheric precipitation, it is found that 1980 has been in the dry season and will remain in the dry season in the next 20 ~ 30 years. The decrease of precipitation and the construction of a large number of surface storage projects in the upper reaches of major rivers have reduced the recharge of shallow groundwater in the alluvial-diluvial plain and coastal marine plain of Laizhou Bay by 35.6%. The change of shallow groundwater quality is mainly manifested in salt pollution, that is, the increase of conventional components, which has the characteristics of areal distribution. At present, the distribution area of shallow groundwater suitable for drinking only accounts for 42% of the total area of the study area, and the area exceeding the standard has increased by 13.8% compared with 20 years ago. The contradiction between supply and demand of water resources is the main problem in Laizhou Bay. The main ways to solve this problem are to attract tourists to replenish water and strengthen environmental protection and governance.

Fig. 4 Variation Diagram of Superstandard Area of Sulfate Ion in Shallow Groundwater

Variation map of drinking water exceeding the standard area in shallow groundwater.

refer to

Deng Huiping, Zhao Minghua.2001. Impact of climate change on the vulnerability of water resources in Laizhou Bay. Journal of Natural Resources,16 (1): 9 ~11.

Xu, Kang Fengxin. 200 1. Study on sustainable development and utilization of groundwater resources in Shandong Province. Beijing: Ocean Press.