Assessing the groundwater pollution potential of Köyceğiz-Dalyan watershed using DRASTIC method

Groundwater pollution as a contributor to the degredation of quality of surface waters has been recognized all over the world. The main parameter among all the parameters causing groundwater pollution is nitrate. Nitrogen is a main nutrient for plants. It is associated with healty growth of leaves and the green colour of the leaves. Plants can use nitrogen as nitrate (NO3-) or ammonium (NH4+). As a nitrogen source plants can use soil media, atmosphere and fertilizers. Because of uncontrolled and over use of fertilizers, nitrate pollution is strongly associated with agricultural activities. Nitrate pollution in groundwater causes many health problems of which of some is fatal like blue baby syndrome. Besides human and animal health, pollution of groundwater affects environmental ecology and environmental sustainability. In Chapter 1, groundwater pollution and national and non-national regulations are explained. In this study a groundwater vulnerability map is obtained for Köyceğiz-Dalyan Watershed. There are two vulnerability concepts, specific vulnerability and intrinsic vulnerability. Specific vulnerability methods takes into consideration of both of the natural protection of an area and pollutant characteristics. In intrinsic vulnerability methods pollutant characteristics are not assessed. In these methods groundwater vulnerability means the concept of the natural protection of a geological setting to pollution without taking consideration of the pollutant characteristics. There are many methods for estimating groundwater vulnerability; Statistical methods, index methods and process methods. For this study DRASTIC method developed by Unites States Environmental Protection Agency (USEPA) was chosen to be used. DRASTIC is one of the index methods. In Chapter 2, other main index methods are explained besides DRASTIC. DRASTIC Method has been developed to be used in the hydrogeological setting of the United States. It is a very easy to understand and implement method. Besides, it allows the user to integrate his/her experience and estimations. DRASTIC is a flexible method that some modifications can be made by the user. Because of these reasons, there are many cases that DRASTIC had been used for assessing the groundwater pollution potential all over the world. DRASTIC Method evaluates seven different parametes of a groundwater environment. There parameters are depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone and hydraulic conductivity. First letters of these parametes make up the name DRASTIC. All of these parameters have weights according to their effect on pollution. These weights are explained in the manual and can not be changed by the user. Besides these weights there are ratings to all parameters. While giving the rating values the user can add his/her experience. Rating values differ for every case study. By multiplying each weight and rating for each of these seven parameters and then adding these products, DRASTIC Index is obtained. A lagoon is a shallow water body that is separated from the sea by a barrier, connected to sea by one or more inlets. Depending on the situation of sea and of rivers ending in the lagoon, the lagoons exhibit sometimes fresh, and sometimes brackish or saline water character. Unpolluted coastal lagoons have long been known as perfect environments for various aquatic products, expecially for fishes. In this study, Köyceğiz-Dalyan Lagoon and its watershed was selected as the case study area. Some part of the study area is under environmental special protection. The area is a host for many endemic plant species. Besides İztuzu Beach is a nesting area of a turtle species called Caretta caretta that is endangered. In Köyceğiz-Dalyan Watershed the lagoon ecosystem is considered to be dependent on the groundwater sources. There is no doubt that any pollution to happen in the groundwater is going to affect the water quality of the lagoon. Besides, the water of Köyceğiz Lake is brackish. Because of this reason groundwater is used as a source for drinking water and irrigation in the watershed. These facts make the main motivation for the study. In the study area pollution of grondwater means health problems in people, environmental pollution and losing the environemental sustainability. There are many previous studies made in Köyceğiz-Dalyan Watershed. Some data for applying the method was derived from these past studies. In Chapter 3, detailed information about the study area can be found. Data needed for the parametes are obtained from a variety of sources. Some data was received from the past studies made in Köyceğiz-Dalyan Watershed. Data about soil and hydrogeology was obtained from the internet. Digitization and calculations were made using ArcGIS software. ArcGIS is a geographical information system for working with maps and geographic information. The main component of ArcGIS suite, ArcMap was used for this purpose. ArcMap is used for viewing, editing, creating and analyzing geospatial data. Seven different layers of each parameter were prepared in ArcMap, and than added together in order to obtain the DRASTIC Index Map and DRASTIC Vulnerability Map. All the steps are explained in Chapter 4 in detail. The output of applying the DRASTIC Method to Köyceğiz-Dalyan Lagoon watershed is first DRASTIC rating maps of each of the DRASTIC factors. After having these maps, each map is weighed according to the methods constant weight values. Lastly, by adding all the weighed DRASTIC rating values, the DRASTIC Index Map is obtained. According to a commonly used DRASTIC Index Classification there are five classes classes indicating vulnerability; Very Low (<79), Low (80-119), Moderate (120-159), High (160-199) and Very High (200<). Based on these classification ranges, calculated DRASTIC Indexes are mapped as the DRASTIC Vulnerability Map for Köyceğiz-Dalyan Watershed. According to the DRASTIC Vulnerability Map of Köyceğiz-Dalyan Watershed, a major part has high and moderate vulnerability to groundwater pollution. It has been estimated that there are no areas that have very low vulnerability. It can be said that a considerable percentage of the study area has moderate vulnerability. High vulnerability does not mean that there is going to be pollution in groundwater whereas no pollution is guaranteed in low vulnerable areas. If there is not a pollutant source in highly vulnerable areas, it is very hard for the pollution to occur. In addition to this in a case where a pollution is defined in low vulnerable areas, a pollution in groundwater is expected. Because of this reason, land use map and vulnerability map is evaluated together. When land use map and vulnerability map is evaluated together, it can be said that the areas where agricultural activities take place are very vulnerable to pollution. High vulnerability near Köyceğiz and intense agricultural activity is remarkable. These evaluations made with DRASTIC Vulnerability Map and land use map of Köyceğiz-Dalyan Watershed can be a guide for decision makers. The results of the study is explained in Chapter 5 in detail. Finally, recommendations for future studies are stated in Section 6. For the sustainable ecosystem management of Köyceğiz-Dalyan Watershed, groundwater quality is a very important issue. It is not a feasible and easy action to remediate after a pollution has happened. In this study, it is aimed that the vulnerability map of Köyceğiz-Dalyan Watershed can be a guide for taking steps for avoiding groundwater pollution.