Eutrophication assessment of Lake Manzala, Egypt using geographical information systems (GIS) techniques Mahmoud H. Ahmed, Noha Donia and Mamdouh A. Fahmy ABSTRACT Mahmoud H. Ahmed National Authority for Remote Sensing and Space Sciences (NARSS), Cairo, Egypt Noha Donia (corresponding author) Engineering Department, Institute of Environmental Studies and Researches, Ain Shams University, Cairo, Egypt Mamdouh A. Fahmy National Institute of Oceanography & Fisheries, Alexandria, Egypt Lake Manzala is in grave danger of suffering pollution from the drainage of industries, agriculture and urban sewage that affects the physio-chemical and biological parameters in the lake. A geographical information system (GIS)-based method of lake trophic status assessment was undertaken to study the spatial distribution of eutrophic conditions of Lake Manzala. In the present study, tabular data supported by field checks have been analyzed by GIS functions and operations to assess, monitor and model the environmental conditions of the lake. A representation of the spatial distribution was developed using the inverse distance weighted (IDW) interpolation method. The eutrophic state index was calculated to describe the state of the lake’s environment. A GIS overlay technique was applied to synthesize the information into a final map illustrating the spatial distribution of eutrophication conditions within the study area. The different levels associated with trophic status classification using GIS were then discussed in relation to environmental change and external loading from tributary inflows. The study revealed that the lake changed to eutrophic freshwater. This change is due to the increase of freshwater inputs and nutrient loading associated with agricultural land reclamation and urban waste disposal. Key words | GIS, ILWIS, lake eutrophication, Lake Manzala, nutrient loading, TSI INTRODUCTION There are two universal systems of lake classification. These are the physical or thermal classification and the classifi- cation by trophic level (Chapman 1992). For Lake Manzala, as eutrophication is the principal water quality problem, the classification was based upon the trophic level. The concept of trophic status as a system of classification was introduced by early limnologists such as Naumann (1919) and Vollen- weider (1968), and has been subject to continuous develop- ment up to the present time (Pouriot & Meybeck 1995). The process of eutrophication underlying this scheme is one of the most significant processes affecting lake management and is therefore described in more detail. Eutrophication is the process by which lakes are enriched with nutrients, increas- ing the production of rooted aquatic plants and algae to levels that are considered to be an interference with desirable water uses such as recreation, fish maintenance and water supply. Eutrophication can also result in detrimental effects on the biological stability of lake and reservoir ecosystems, affecting virtually all the biological populations and their interactions in the water body. Consequently, eutrophication of lakes and reservoirs can have significant negative ecological, health, social and economic impacts on human use of a primary and finite resource. It is also well known that the growth and proliferation of aquatic plants is a result of the utilization and assimilation of organic materials through photosynthesis. Thus the plant biomass increases by the uptake of available phosphorus and nitrogen from the water. It was found that the nutrient that will control the maximum amount of plant biomass is the nutrient that “runs off” or reaches a minimum before other nutrients. Therefore, under certain condition, nitrogen may reach a minimum value before phosphorus and, as a result, doi: 10.2166/hydro.2006.014 101 Q IWA Publishing 2006 Journal of Hydroinformatics | 8.2 | 2006 Downloaded from http://iwaponline.com/jh/article-pdf/8/2/101/392791/101.pdf by guest on 22 February 2023