Impact assessment of land-use changes on groundwater quality in Dahram watershed of Fars province

Introduction
Groundwater is the sole source of water for drinking, irrigation, and industrial uses in many arid and semi-arid regions of the world. Groundwater can be contaminated by natural as well as anthropogenic influences. Residential, municipal, commercial, industrial, and agricultural activities can all affect groundwater quality. Groundwater contamination results in poor drinking water quality, loss of water supply, high cleanup costs, high costs for alternative water supplies, and/or potential health problems. In Iran, dependence on groundwater has increased tremendously in recent years. Groundwaters can be contaminated by natural as well as human influences. Land use changes, residential and agricultural activities can affect the quality of groundwater. Groundwater contamination can lead to poor drinking water quality, loss of water resources, high cleanup costs, high costs for alternative water sources, and problems for watershed health. In Iran, dependence on underground water in most watersheds has increased greatly in recent years. Therefore, the evaluation, protection and proper management of underground water resources is very necessary for optimal and sustainable use of water resources. Water quality assessment includes the assessment of the physical, chemical and biological nature of water in relation to its natural quality, human effects and intended uses, especially uses that may affect human health and the health of the water system itself. The use of geographic information system technology has greatly simplified the assessment of natural resources and environmental concerns, including groundwater. In groundwater studies, GIS is commonly used to analyze site suitability, manage watershed assessment data, estimate groundwater vulnerability to contamination, model groundwater flow, model solute transport and leaching, and integrate groundwater quality assessment models with spatial data to create Spatial decision support systems are used. This study attempts to assess the influence of changing land-use patterns on the groundwater quality in the Dehram, Fars province. The study area is an agricultural developing region with land development progressing at a fast pace. The objective of this article is to demonstrate the influence of land-use transformations, land-use transition, on the quality of groundwater using geographical information systems. The study also aims at evaluating the significance and applicability of a groundwater quality index (GQI) generated using geographical information system (GIS) approach for the assessment of groundwater quality in a medium sized catchment. Moreover, a simple methodology for the preparation of a groundwater quality sustainability map, for use in planning and management decisions by local government authorities, is developed in this work.
 
Materials and Methods
The water samples were collected from 6 wells in the study area in 2021, which are added to the urban water system for drinking purposes. For 2014, the available data were used to observe the general changes in the quality of underground water during this period. Sampling in the summer season, due to the lack of water in this season, by taking water from wells in the area and injecting it into the drinking water system, in three repetitions for the year 1400 according to the standard method of the American Public Health Association (APHA) with field sampling and the available data of year 2013 were used to show seasonal changes in different water quality parameters during both years. Therefore, samples were taken from each well of the available data three times in 2013 and three times in summer (July to August) 1400. The geographic coordinates of the sampling wells were recorded manually using a Garmin e-Trex GPS receiver. The hydrochemical data obtained from the laboratory analysis of the water samples were linked to the spatial database of the sampling points. Spatial data shapefiles were prepared in vector format showing the locations of sample wells along with associated hydrochemical data. To evaluate the location of the sampling wells according to the potential sources of groundwater pollution, these shapefiles were placed on the land use map. Then, point shape files were used to prepare variable concentration maps by applying Kriging interpolation method. The GQI proposed was used for quality assessment. To generate the index, seven parameters listed in World Health Organization guidelines for drinking water quality were selected from the main dataset. Six parameters (Cl^-, Na⁺, Ca⁺², Mg⁺², SO₄^-2, and TDS) can be categorized as chemically derived contaminants that could alter the water taste, odor, or appearance and affect its ‘‘acceptability’’ by consumers. NO^-3 was categorized under chemicals that might inflict ‘‘potential health risk’’ and a guideline value of 50 mg/l was assigned. The GQI integrates the different water quality parameters to give a quantitative index value that can be used for spatio-temporal provides in groundwater quality. In the present study, the land use/cover map for two different periods (2013 and 2014) was prepared to evaluate land use and land cover transition patterns using Landsat satellite images from ETM⁺ sensors (2013) and OLI (2014).
 
Results and Discussion
The land-use pattern has changed drastically with the increased agricultural and built-up area at the expense of other land uses. The analysis reveals a rapid deterioration of groundwater quality related mainly to the increase in built-up land, drought and land-use change in agricultural lands and uncontrolled withdrawal of water by farmers from wells in the region. Mean GQI decreased from 86.42 to 57.36 over a period of 7 years from 2014 to 2021, which indicates a decrease in water quality. The quality of groundwater in the region in 2014 has a desirable quality and is in a very suitable range. But in 2021 the water quality changed from very good and good to poor and bad.
 
Conclusion
GQI and land use were integrated into GIS to yield groundwater quality, in terms of water quality. Zones of sustainable and unsustainable groundwater use were demarcated for better decision making related to land use allotment in this rapidly changing region. The GQI index provides the possibility of mapping the spatial changes of groundwater quality in the study area, which shows that the water quality of the area is generally good, but the deterioration has started with the onset of urbanization. The main sources of pollution identified in this study are agricultural and residential activities. Although agricultural activities and the application of fertilizers related to it have been the main factor in reducing the quality of groundwater, in addition, this study showed that the increase in urbanization has a dominant contribution to pollution in the region. Agricultural activities must comply with methods that ensure minimal impact on groundwater. This study also shows the effectiveness of GIS in groundwater quality assessment. Similarly, GIS-based assessment techniques can be used to characterize groundwater contamination preferably in large watersheds. Of course, the selection of parameters and weights may be different in each location depending on the prevailing land use conditions.