Assessment of geodiversity sensitivity in Babolrod Catchment, Mazandaran province

Introduction

Geodiversity is the heterogeneity of the non-living environment of the earth, which is the basis of most human activities and ecosystem life. The expansion of human activities and the destruction of this lifeless environment are the most important factors threatening the geosystem and ecosystem. The spread of kinds of human activities on the surface of the earth is considered as a threat to geodiversity and biodiversity. Most of the researches conducted for geodiversity assessment and human treats and destruction impacts have not been taken into consideration. Among the researches, only Betard and Paulvast (2019) evaluate geodiversity indices with indicators of human threats (desertification and land use) in an integrated manner in Brazil. In this study, areas with high geodiversity that are threatened by human activities have been introduced as geodiversity hotspots. The northern slopes of the Alborz mountains (Iran) are among the areas with high land diversity and extensive human activities in various economic and tourism sectors have caused many land use changes. Therefore, this research was conducted with the aim of quantitatively evaluating geodiversity and combining it with the index of human activities, in order to determine the sensitivity of geodiversity in the Babolrod catchment (Mazandaran province).

Methodology

For the quantitative assessment of geodiversity, four main indexes of geology (lithology and faults), geomorphology, soil and hydrography (rivers and springs) were used and the number of elements were counted in square grids of 1.5 x 1.5 km. Then, the total values of six layers were calculated and the grid layer was converted into a point layer. These points were interpolated using the ordinary kriging method and the geodiversity map of the basin was obtained. To evaluate the level of human intervention and destruction in the landscape, the land use map of the basin was used. This map became the Hemerobi index. Based on this index, the amount of human intervention in land use is classified into seven classes. Classes one to seven represent completely natural state to very intense human impact, respectively (Walz and Stein, 2014). After performing steps one and two, the two geodiversity layers and the hemerobic index layer were multiplied together and the geodiversity sensitivity map of the region was obtained and classified into five sensitivity classes.

Results and discussion

The geodiversity map of the catchment was classified into 5 groups based on the natural break method. The very low (4-11) and low (11-16) classes include a total of 53% of the area of the catchment and are mainly located in the northern parts of the region. High (18-23) and very high (23-31) classes include 22.3 and 1% of the catchment area, respectively, which are mostly observed in the central and southeastern parts. Among the indices in the geodiversity map, the geomorphology index with an average value of 44.5% has the highest proportion of values compared to other indices. The weighted values of the hemeroby index ranged from 1.6 (weak human impacts) to 5.36 (severe human impacts). The plain area in the north of the basin, which are affected by many human activities, have the highest score, and the central areas of the basin, which are dominated by dense forests, have the lowest score. The southern parts of the basin, which are covered by pastures, are in an medium condition. According to the geodiversity sensitivity map, 11.32% and 12.25% of the basin area were classified as very high (69-92) and high (55-69), respectively. Most of these areas were located in the south and east of the basin. Very high sensitivity class is located in the southern parts of the basin with pasture use and the eastern parts of the basin in the location of the Alborz Dam lake and its downstream, which is used for agriculture. The forest areas where there has been a lot of human intervention and clearing and destruction have been placed in the medium and high sensitivity class. The low sensitivity class (32-44) with 41.5% of the area of the basin has the highest distribution in the basin. This class is mainly located in the plain parts of the north of the basin and forest areas with high density and minimal human intervention. In order to further analyze the geodiversity sensitivity map, the correlation coefficient of this map was calculated with the type of soil erosion map. This coefficient was calculated pixel by pixel in ARC GIS software and the value of 0.81 was obtained, which indicates a good relationship between these two factors.

Conclusion

In the geodiversity sensitivity map at the regional scale, areas with high geodiversity and high threat index are identified as sensitive areas. This approach to geodiversity (preparation of geodiversity sensitivity map) can be used to create geoconservation plans and land use management at the basin scale by geoscientists, planners and decision makers in environmental management and developing effective strategies.