(Hainan Geological Survey Institute, Haikou 570206)

This paper discusses the evaluation system of eco-geological environment quality in the northeast of Hainan Island, studies the evaluation system of ecological suitability, determines the evaluation principles and methods, and discusses how to evaluate technical standards and methods.

Key words: quality of eco-geological environment; Evaluation index; evaluation methodology

Qionghai County, Hainan Province1:250,000 Eco-environmental Geological Survey Project is a large-scale land resources survey project of the Ministry of Land and Resources in 2000, which was undertaken by Hainan Geological Survey Institute and completed in 2003. Based on the investigation of eco-geological environment, this paper analyzes and evaluates the quality of eco-geological environment in the eastern part of Hainan Island from environmental factors such as geological environment conditions, geological disasters, geological resources and human activities, which provides scientific basis for the construction of "ecological province" in Hainan.

1 Eco-geological environment quality evaluation system

According to the characteristics of geological environment in Qionghai research area, the main environmental factors are seven environmental factors in four subsystems: geological environmental conditions, geological disasters, geological resources and human activities. According to their priority and correlation, the evaluation system network as shown in figure 1 is established.

Figure 1 Network Diagram of Comprehensive Evaluation System for Eco-geological Environment Quality

2 Eco-geological environment quality evaluation procedures

Evaluate according to the following procedure (Figure 2).

(1) Divide the evaluation units according to the geological environment conditions of the evaluation area.

(2) Specify the corresponding evaluation standard value and its weight for each evaluation factor to show the relative importance of each environmental factor in the environmental system.

(3) According to the geological environment quality evaluation standard, calculate the quality index of each evaluation unit.

Fig. 2 Block diagram of comprehensive evaluation program for eco-geological environment quality

(4) Comprehensive evaluation is carried out in each district according to the quality grade.

3 Eco-geological environment quality evaluation unit division

According to the geotechnical types and geomorphological factors, considering the influence of geological structure, geological disasters and groundwater factors, the evaluation units are divided according to the coordinate network.

4. Determine the principle of selecting ecological suitability evaluation factors.

First, the selected ecological factors have a significant impact on the ecosystem, and second, the distribution of the selected ecological factors in each grid unit is significantly different.

After screening, the main evaluation factors are terrain slope, overburden thickness, stratum or rock, population density, groundwater depth, geological disasters and soil beneficial elements.

5. Establish the evaluation standard and assignment principle of eco-geological environment quality evaluation factors.

According to the positive and negative impact of each evaluation factor on ecology, the evaluation standard is established. The principles are as follows: first, the role of evaluation factors on ecological impact; Secondly, according to the spatial and temporal distribution of evaluation factors in the region. Operation background, ecological suitability and operation scope are 1, 3, 5, 7 and 9***. 1 is divided into ecological suitability, 3 into ecological suitability, 5 into ecological basic suitability, 7 into ecological extremely unsuitable, and 9 into ecological extremely unsuitable.

5. 1 Geological environment conditions

5. 1. 1 terrain slope evaluation coefficient (X 1)

According to the influence degree of terrain slope on ecological suitability, grading assignment is carried out. 1 < x 1 ≤ 5, and the score is assigned as1; 5 < x 1 ≤ 15, with a score of 3; 15 < x 1 ≤ 25, with a score of 5; 25 < x 1 ≤ 35, score 7; X 1 > 35, and the score is 9.

5. 1.2 Covering layer thickness (X2)

According to the influence degree of covering thickness on ecological suitability, grading assignment is carried out. X2 > 5m, and the score is assigned as1; 3m < x2 ≤ 5m, with a score of 3; The score of 1m < x2 ≤ 3m is assigned to 5; 0.5m < x2 ≤ 1m, score 7; X2≤0.5m, with a score of 9.

5. 1.3 stratum or rock (X3)

According to the influence degree of strata or rocks on ecological suitability, grading assignment is made. The scores of granite and metamorphic rocks are 3; Volcanic rock score is 5; The score of sedimentary rocks is 7; The score of loose layer (sand) is 9.

5. 1.4 Groundwater depth (X4)

According to the influence degree of groundwater depth on ecological suitability, grading assignment is carried out. 1.5m < x4 ≤ 2.5m, and the score is assigned as1; 1m < x4 ≤ 1.5m or 2.5m < x4 ≤ 3m, with a score of 3; 0.5 < x4 ≤ 1.0m or 3.0 < x4 ≤ 5.0m, with a score of 5; 0m < x4 ≤ 0.5m or 5m < x4 ≤ 10m, with a score of 7; X4≤0m or x4 > 10m, with a score of 9.

5.2 Geological disasters (disaster point or disaster area X5)

Geological disasters in the study area mainly include soil erosion, land desertification, landslide, collapse, coastal erosion, river bank erosion and siltation, groundwater siltation and so on. According to its distribution characteristics and ecological environment conditions in the region, it is assigned according to the following criteria: X5≤0 or X5≤0km2, and the score is1; 0 < X6 ≤ 2 or 0km2 < X6 ≤ 2.5km2, with a score of 3; 2 < X6 ≤ 4 or 2.5km2 < X6 ≤ 5.0km2, and the score is given as 5 points; 4 < X6 ≤ 6 or 5.0km2 < X6 ≤ 9km2, with a score of 7; X5 > 6 or X5 > 9km2, with a score of 9.

5.3 Human activities (X6)

Considering human activities mainly from population density, X6 ≤ < 300 people /km2, and the score is assigned as1; 300 persons /km2 < X6 ≤ 400 persons /km2, with a value of 3; 400 people/km2 < X6 ≤ 500 people/km2, with a value of 5; 500 people /km2 < X6 ≤ 1000 people /km2, with a value of 7; X6 > 1000 people /km2, with a value of 9.

5.4 Geological Resources (X7)

Geological resources mainly consider soil element factors, among which total potassium, total phosphorus and total nitrogen are the main ecological factors, so they are assigned according to sampling and testing concentrations.

Total potassium concentration (y 1): y 1 > 2.50%, score1; 1.2% < Y 1 ≤ 2.5%, score 3; 0.4% < y 1 ≤ 1.2%, score 5; 0.2% < y 1 ≤ 0.4%, with a score of 7; Y 1 ≤ 0.2%, score 9.

Total phosphorus concentration (Y2): Y2 > 0.04%, assigned as1; 0.03% < y2 ≤ 0.04%, score 3; 0.02% < y2 ≤ 0.03%, score 5 points; 0.0 1% < y2 ≤ 0.02%, score 7; Y2 ≤ 0.0 1%, score 9.

Total nitrogen concentration (Y3): Y3 > 0. 15%, assigned as1; 0. 10 < Y3 ≤ 0. 15%, score 3; 0.05 < Y3 ≤ 0. 10%, and the assignment score is 5; 0.03% < Y3 ≤ 0.05%, score 7 points; Y3≤0.03%%, score 9.

See table 1 for the grading and assignment standard of single factor ecological suitability.

Table 1 single factor suitability grading standard

6 evaluation unit (within the grid) evaluation factor assignment and calculation

(1) If each evaluation unit has an evaluation factor, it is directly assigned according to the evaluation factor assignment standard, and its representative point is in the center of the evaluation unit.

(2) If each evaluation unit has multiple evaluation factors, the area is weighted and averaged according to the evaluation factor assignment standard, and the mathematical expression is as follows:

Compilation of geological survey results in East China: 1999~2005

Where: x is the calculated value of an evaluation unit (grid);

Xi-the score of a factor;

AI- the area occupied by a certain factor.

7 Determination of weight

Weight can indicate the relative importance of each environmental evaluation factor in the subsystem and in the whole evaluation system, which can be divided into primary subsystem evaluation factor and secondary subsystem evaluation factor. The evaluation factors of the first-level subsystem include terrain slope, overburden thickness, stratum or rock, population density, groundwater depth, geological disasters and soil elements.

The evaluation factors of the secondary subsystem (under soil elements) are total potassium, total phosphorus and total nitrogen.

The weight is determined according to the influence degree of various factors on ecological suitability. Geological disasters are the main factors that destroy and cause the deterioration of eco-geological environment, and the weight value is large, taking X5 as 0.4; Human activities have a great influence on the ecological environment, so the value of X6 is 0.2; The influence of stratum or rock (X3) and soil beneficial elements (X7) is not obvious, so the values are relatively small, that is, the values of X3 and X7 are 0.05, and other weights of X 1, and the values of X2 and X4 are 0. 1. The weighted sum of each factor is equal to 1. See Table 2 for the weight of ecological suitability influenced by single factor.

Table 2 Weight table of ecological suitability under the influence of single factor

8 Mathematical model of eco-geological environment quality evaluation

The evaluation of eco-geological environment quality adopts the weighted average method, and its mathematical model is:

Compilation of geological survey results in East China: 1999~2005

Where: b is the comprehensive evaluation value of the I-th grid;

Ws-the weight of a single factor affecting ecological suitability;

Xi—— the evaluation value of the ith grid and single factor X.

9 Zoning Standard for Eco-geological Environment Quality Assessment

The basis of determining the zoning standard of eco-geological environment quality evaluation is the single factor ecological suitability evaluation standard and the comprehensive evaluation value of ecological suitability in the study area.

Each level of comprehensive evaluation of eco-geological environment quality corresponds to an evaluation value interval, and finding the endpoint or upper and lower bounds of each interval becomes the key to judge the comprehensive grading standard of eco-geological environment quality. Combined with the ecological conditions in the region, the classification boundary of eco-geological environment quality is drawn up (see Table 3).

Table 3 Classification results of eco-geological environment quality classification limit table:

Compilation of geological survey results in East China: 1999~2005

According to the classification limit and comprehensive evaluation value (n), the eco-geological environment quality in the study area is divided into five grade intervals: 1 < n ≤ 2, which is the excellent area; 2 < n ≤ 4, which is a good area; 4 < n ≤ 6, which is a medium area; 6 < n ≤ 8 is the difference area; 8 < n ≤ 9 is the limit range (see Table 4).

Table 4 Zoning Criteria for Comprehensive Evaluation of Eco-geological Environment Quality

10 evaluation steps

According to the evaluation system, the first step is to divide the evaluation units according to the coordinate network on the map of the study area1:250,000, with an area of 5×5km2. * * * 669 evaluation units (grids) are divided and numbered, and the evaluation units are represented by grid center coordinates; The second step is to assign values to the nine evaluation factors of each evaluation unit. The data sources are X1:50,000 topographic map, X2 from Quaternary geological landform map, X3 from geological map, X4 from Hainan Atlas, X4 from phreatic hydrogeology map, X5 from eco-geological environment map, Y 1 from soil element isoline map (all k), and Y2 from soil element isoline map (all k). Step 3, calculate the comprehensive value of the secondary evaluation factor as the factor value, and then calculate the comprehensive evaluation value of the primary evaluation factor; The fourth step is to partition and draw on the computer through the comprehensive evaluation value.

1 1 Evaluation results of eco-geological environment quality

The evaluation results show that the comprehensive evaluation value of 669 evaluation units in the whole region is between 1 ~ 6, and the comprehensive evaluation value of > 6 is lacking. Therefore, the study area lacks poor and extremely poor eco-geological environment quality areas, and there are only three eco-geological environment quality areas, namely, excellent eco-geological environment quality area, good eco-geological environment quality area and medium eco-geological environment quality area.

The quality of eco-geological environment in the study area is generally good, and the first-level area (the area with excellent eco-geological environment quality) is scattered, with an area of 1358.5km2, accounting for 8.9% of the study area. Grade II areas (areas with good eco-geological environment quality) are distributed in the whole region, with an area of 12442.8km2, accounting for the vast majority, accounting for 8 1.6%. Grade III area (the area with moderate eco-geological environment quality) mainly includes densely populated areas and geological disaster areas, with an area of 1442.5km2, accounting for only 9.5%, and the evaluation results are in line with the actual situation.

12 control factors of eco-geological environment quality

The main factors affecting the quality of eco-geological environment are geological disasters and human activities. Hainan is located in the tropics, with abundant light, heat and water resources, extremely developed soil and rich minerals decomposed by weathering of rocks and soil, which is beneficial to the growth and development of plants.

The quality of eco-geological environment in the study area is mostly above a good level. However, due to the influence of human activities (reclamation, mining and ground construction), the development of geological disasters such as land desertification will inevitably lead to the decline of eco-geological environment quality. For example, if the northeast coastal zone is affected by mining, the eco-geological environment quality will continue to decline, and natural disasters such as coastal erosion and collapse will also lead to the decline of the eco-geological environment quality in the coastal zone, mainly distributed in the eastern suburbs of Wenchang City and Chengmai.

Controlling the occurrence and development of geological disasters plays a key role in the quality of eco-geological environment. Limiting man-made damage to the geological environment, reducing water and soil pollution and controlling geological disasters such as soil erosion, land desertification, coastal erosion and landslides will be conducive to the development of eco-geological environment quality in a good direction.

13 conclusion

(1) Ecological suitability refers to the influence of environmental factors on ecology in a certain area, and the evaluation of eco-geological environment quality is based on ecological suitability.

(2) The evaluation of eco-geological environment quality is divided into four steps: one is to determine the evaluation system; The second is to determine the ecological factors and select the evaluation factors; Thirdly, according to the influence degree of each evaluation factor on the eco-geological environment, the assignment and weight of evaluation factors are determined; Fourth, comprehensive calculation of evaluation unit and zoning evaluation of geological environment quality.

(3) Most of the eco-geological environment quality in the study area is above a good level, and the eco-geological environment quality in the whole area is divided into three areas, namely, excellent area, good area and central area.

refer to

[1] Zhou, Cai. Theory and application of geological environment quality assessment. Wuhan: China Geo University Press, 1998.

Liao, Zhang Benren, et al. Study on soil environmental geochemistry in northeastern Qionghai. Geology and Exploration, 2004, 39 (6): 68 ~ 70.

Liao, Wu Dan, et al. Geochemical characteristics of soil trace elements in northeastern Qionghai. Bulletin of China Agriculture (Geochemical Edition), 2004, 20: 64 ~ 67.

Liao, Feng Yasheng, et al. Evaluation of geological environment in northeastern Qionghai. Journal of Jilin University, 2005,35 (5): 646 ~ 652.

[5], Liao, Feng Yasheng, et al. Investigation Report on Eco-geological Environment of Qionghai County1:250,000 .2003

[6], Liao, Feng Yasheng, et al. Technical methods of eco-geological environment quality assessment in tropical areas of Hainan Island.2003.

Discussion on technical methods of eco-geological environment quality evaluation in Qionghai, Hainan

Xue Guicheng, Xu Zhongsheng, Xia Changjian

(Hainan Geological Survey Institute, Haikou 570206)

Abstract: The quality evaluation system and suitability evaluation system of eco-geological environment in the northeast of Hainan Island are discussed, and the evaluation theory and method are determined.

Key words: quality of eco-geological environment; Evaluation index; appraisal procedure