Study On Response Process Of Karst Groundwater To Urban Land Use And Landscape Pattern Evolution

Karst groundwater,as the basic supporting resources for national economic and social development,is inevitably affected by urbanization.Under the influence of human activities,the land use and landscape pattern in urban areas have changed dramatically,and the spatial and temporal distribution of karst groundwater level and hydrochemistry have been affected.Therefore,in view of the characteristics of urbanization development in Guiyang City,a thorough understanding of the response characteristics of karst groundwater evolution to land use and pattern in the process of urbanization is conducive to providing a scientific basis for environmental protection and land development and utilization of karst groundwater in urban areas.This paper is based on the26-year-span Landsat satellite images of 1990,1995,2000,2005,2010 and 2016 and the long-term groundwater observation data of 1990-2017 in Guiyang City.By using GIS technology and RDA analysis and related analysis methods,the land use pattern,the evolution characteristics of groundwater quality and water level,and the relationship between groundwater quality and water level and the evolution of land use and pattern in Guiyang City were systematically analyzed.The Major achievements are as follows.?1?In the process of urbanization,the area of construction land in Guiyang City is affected by the construction of new urban areas in stages,from the mutual transfer of agricultural land to the flow of agricultural land to construction land.Landscape pattern changes under the influence of land use change,in which the number of landscape patches,patch edge density and landscape diversity show an increasing trend over a long period of time.Because of the rapid expansion of the city,the maximum patch index is increasing constantly,and the patch combination degree of forest land is increasing in a long time series.This shows that Guiyang city has always adhered to the concept of ecological development in urban development,making the change of forest land area stable in many years.?2?The groundwater table in the study area is between 0.00 m and 15.90 m,which shows an overall upward trend.TDS concentration showed an upward trend in general,and the range of concentration>500 mg/L after 2010 was characterized by diffusion from the central part of the study area to the surrounding area.There are obvious differences between TH units.The change of TDS concentration in underground river monitoring points is consistent with the construction period of Guanshan Lake area.COD concentration ranged from 0.00 mg/L to 10.4 mg/L,showing a general downward trend.?3?The spatial variations of HCO₃^-are quite different,and the high concentration areas of Mg²⁺and Ca²⁺tend to expand to the north and northwest.SO4^2-,K⁺,Na⁺,Cl^-,NO₃^-and F^-show an overall upward trend in the long-term sequence and the spatial distribution was different due to the influence of human activities.The hydrochemical types of urban underground rivers evolved from single HCO₃·SO₄-Ca·Mg type in dry season and HCO₃-Ca·Mg type in flood season to HCO₃·Cl-Ca type,HCO₃·SO₄-Ca type,HCO₃-Ca type and HCO₃·SO₄-Ca·Mg type.?4?Increasing ground hardening in urban construction has changed groundwater recharge path and quantity.Groundwater with better water conservation,such as woodland,can be used as potential water supply to keep groundwater level stable to a certain extent.Urban construction land promotes the increase of water quality indicators such as TDS,K⁺,Na⁺,Cl^-,NO₃^-and SO₄^2-in groundwater.Rapid urban expansion will become one of the main threats to groundwater pollution.Forest land and grass/irrigation have important functions of water and soil conservation and pollution interception,which act as"sink"for pollutants.?5?Groundwater recharge is blocked by the increase of the maximum patch index in the hydrogeological unit of the construction land owner,but it is possible to recharge groundwater when the aggregation index and connectivity index of the forest land with water conservation function increase.Groundwater chemical indicators show obvious response to landscape fragmentation,patch combination,aggregation and maximum patch changes due to the difference of dominant landscape and landscape evolution within the unit.?6?Influenced by the stages of regional urbanization,the hydrochemical response of underground rivers shows rapid response and high consistency.The correlation analysis shows that construction land promotes the growth of hydrochemical indexes of most underground rivers,while forest land and grass/shrub inhibit the growth of some hydrochemical indexes.The karst underground river system is closely related to the outside world and is vulnerable to external influences.In the process of urbanization,the underground river system contains abundant hydrochemical records.