Eğirdir Gölü su kalite modellemesi

Abstract

Initially use of complicated EPA models such as WASP ( Water Analysis Simulation Program) was tried but such programs require detailed and extensive data. In order to calibrate the eutrophication model (GMODEL) the data collected during the period of 1983 -1984 within the TÜBİTAK Turkish Technical Research Council) research projects (ÇA?-45, ÇA?-47 and ÇA?-46/G) were used. Verification of the model was achieved using Eğirdir Aquatic Products Department measurements in 1991, and MİMKO A.Ş. measurements in 1992. The models constants were chosen to minimize the difference between the measured and calculated values of the water quality parameters such as nitrogen, phosphorus and chlorophyl-a concentrations. The range of the values reported in the literature was also kept in mind before deciding on the value of a constant in the model. Apparently great differences between the calculated and the measured values in the graphs are due to the large scale used in the drawings. Different scenarious included changing the loads on the lake. When the nitrogen load was increased from 87.32 tons / month to 187.32 tons / month in the second year, a sharp increase of the algae concentration was also observed in the second year. In the same way, by running the GMODEL program for five years, when the third year daylight is dropped to 1 hour from 10-13 hour, a sharp decrease in algae concentration is observed. And this drop causes a concentration increase in nitrogen and phosphorus concentrations especially in the third year. In forth and fifth years, increase of algal concentration results in small flactuation ranges of total nitrogen and phosphorus concentrations. Smaller fluctuations indicate that the steady-state conditions are being approached. Another scenario included changes on the lake volume and changes of the water withdrawals for the followings five years. XXll

SUMMARY THE VVATER OUALITY MODELLING OF E?İRDİR LAKE The aim of this study is to predict the water quality of Eğirdir Lake by applying a relatively simple model. in this study, informations as regard to morphological, geological characteristics, pollutant resources and water quality data of Eğirdir Lake, were collected and evaluated on the basis of a project, that has been initiated for the Ministery of Environment of Turkey. The project aimed water quality modelling studies of nine lakes located in ` Lake' s Region ` of Turkey, in Mid-West Anatolia. Eğirdir Lake vvas selected out of total nine lakes studied because Eğirdir Lake is öne of the unpolluted lakes of the region and is used for recreation, aquatic products, irrigation and also for drinking purposes. There are plans to supply the drinking water demand of İsparta city located about 25 km from Eğirdir Lake. The future vvater withdrawal is estimated to be about 86.400 m3/day. Local authorithies want to inquire whether an additional water withdrawal will upset the ecological balance and wi!l reduce the water potential and recreational value of the lake. General informations and background about the region were presented. Also by calculating the water inputs and outputs of the lake basin, rainy and drought periods were determined. Then geological and hydrological characteristics of the lake area vvas investigated and amount of vvater taken from lake vvas determined, depth of vvater - area - volume curves were dravvn by using input (precipitation, surface runoff, ete.), and output flovvrates (evaporation, artificial discharge, ete.) of the lake. Also an input - output equation of the lake vvas developed. The variation range of the lake volume and surface area within the period of 1958-1991 are as follovvs: xixElevation of vvater surface, m : 915.33 - 919.11 Surface area, m2: 453 x106 - 481.5 x106 Volume, m3: 2740 x106 - 4440 x106 Mean depth, m: 5.7 - 9.8 Eğirdir Lake has an alongated shape divided into two parts with a throat section of 3 km wide. The length of the lake in the North-South direction is about 50 km. The maximum vvater depth is 15 m. Temperature and precipitation values measured at Eğirdir station are given in Table -1. Table -1 : Range and Mean Values of the Monthy Average Temperature and Precipitation Readings at Eğirdir Station (Period: 1930-1988) ParameterRangeMeanTemperature, °C2.8- 24.013.1Precipitation, mm/month 7.4-131.862.8 Annual precipitation is 753.6 mm. The total drainage area of the Eğirdir lake is 3321 km2. Eğirdir lake receives the surface runoff from agricultural fields and municipal wastewater discharge. The total pollution loads including the nutrient loads of direct precipitation are estimated (Table - 2). Table - 2 : Pollution Loads of Eğirdir Lake PollutantPeriod(ton/year)1983 -1984 l 1991 -1992 BOD5258.931.2 SS317.534.7 TN1047.9751.0 TPl 51.3 46.2 Approximately 90 percent of the town of Eğirdir is served with a new sanitary sewer system. Therefore pollutant loads have been reduced in the years of 1991-1992. XXConsiderable data has also been collected for Eğirdir Lake by different research groups. Water quality measurements required to run the quality model were conducted in the field. A mathematical model that can simulate the nitrogen, phosphorus and algae concentrations using the available data was improved. Pollutant resources andpollutant loads were investigated, pollution levels were determined,agricultural areas and loads caused by agricultural areas werepresented. Annual pollution loads due to pollutant resources weredetermined. in order to evaluate the strategies and altematives of vvater quality management of the lake and to help to the manager ör responsible persons on their decisions, a water quality model of the lake was developed. Using this model its possible to make the future estimates ör scenarios that predict the effect of pollutant loads on vvater quality of the lake. The trophic level that indicates the nutrient level of the lake was investigated. Present vvater guality of Eğirdir Lake can be classified as oligotrophic. The lake water can be used for drinking, irrigation, fishing vvater products and recreation purposes. While deciding on the trophic level of Eğirdir Lake, many parameters including nitrogen and phosphorus loads, chlorophyl-a concentrations, Secchi dişe depths, and dissolved oxygen prof i leş were considered. A dBASE III Plus program was written to organise & classify the collected data. The dBASE III Plus program can be used to organise past and future data. Scenarios were made to illustrate the implication of the model and results were discussed by using the computer outputs, profiles graphics, ete. The purpose of developing a new model was to be able to obtain predictions using the available data. The data on lake vvater quality and the loads is very restricted and does not go beyond few years. xxiInitially use of complicated EPA models such as WASP ( Water Analysis Simulation Program) was tried but such programs require detailed and extensive data. In order to calibrate the eutrophication model (GMODEL) the data collected during the period of 1983 -1984 within the TÜBİTAK Turkish Technical Research Council) research projects (ÇA?-45, ÇA?-47 and ÇA?-46/G) were used. Verification of the model was achieved using Eğirdir Aquatic Products Department measurements in 1991, and MİMKO A.Ş. measurements in 1992. The models constants were chosen to minimize the difference between the measured and calculated values of the water quality parameters such as nitrogen, phosphorus and chlorophyl-a concentrations. The range of the values reported in the literature was also kept in mind before deciding on the value of a constant in the model. Apparently great differences between the calculated and the measured values in the graphs are due to the large scale used in the drawings. Different scenarious included changing the loads on the lake. When the nitrogen load was increased from 87.32 tons / month to 187.32 tons / month in the second year, a sharp increase of the algae concentration was also observed in the second year. In the same way, by running the GMODEL program for five years, when the third year daylight is dropped to 1 hour from 10-13 hour, a sharp decrease in algae concentration is observed. And this drop causes a concentration increase in nitrogen and phosphorus concentrations especially in the third year. In forth and fifth years, increase of algal concentration results in small flactuation ranges of total nitrogen and phosphorus concentrations. Smaller fluctuations indicate that the steady-state conditions are being approached. Another scenario included changes on the lake volume and changes of the water withdrawals for the followings five years. XXllFour times decrease of lake volume in second year was assumed and the water withdrawal was increased to 500 x 106 m3/ month from 20 - 50 x106 m3/tnonth. Such volume and flowrate withdrawals the algae production. And this caused sharp decrease in total organic nitrogen and phosphorus concentrations in second year, tendency to the steady - state condition has started in fourth year. A similar study using different volume and water withdrawals for seven years was done. A tendency towards to the steady - state condition was observed similar to the simulations done for a period of five years. XX1U1