Challenges of Data Integration in the Study of a Complex System: A Case Study of Lake Atitlán in Guatemala Edwin J. Castellanos a, Maricruz de Mejía a,b, Beatriz López b, Nancy Girón, a and Willy Knedel a a Universidad del Valle de Guatemala b Medical Entomology Research and Training Unit/Guatemala-CDC The watershed of Lake Atitlán in the Highlands of Guatemala is presented as an example of the high level of complexity found in a system that involves natural, social, and economic forces interacting in a small but extremely diverse geographical area. This poster describes our efforts to use a multidisciplinary approach to study the two main forces of natural and social change in the area: coffee production and tourism; as well as to understand how these interact with a highly intertwined system of institutions. We used Landsat TM images to study the large changes in land use brought about by the increase in coffee production in the last decades. This crop has meant mixed blessings in terms of vegetation cover for the area. Our analysis shows that coffee has been the single most important cause of forest cover loss in the area: 14% of the land was changed from forest to coffee between 1986 and On the other hand, for the same period, shaded coffee plantations substituted 6,000 ha. of corn fields, replacing an annual crop of little ecological value with an agroforestry system that provides habitat for wildlife and better soil conservation, among other environmental benefits. Tourism has been another important force of change in the area. Due to its natural beauty and rich cultural heritage, the Atitlán area has developed in the last decades as the third most important tourist destination in the country. The number of hotels, resorts, and chalets around the lake has increased by a factor of five in the last forty years. Again, the boom in this industry has been a mixed blessing for the locals: indigenous groups who have lived there for hundreds of years, and who are now struggling to adapt to living with outsiders from other parts of the country as well as from other parts of the world. These natural and social changes are occurring with the backdrop of an increasingly complex system of institutions interacting in the area. We have identified seven governmental institutions having jurisdiction in the region and various national and international non- governmental organizations working mainly with the indigenous groups who, themselves, zealously keep their own system of institutions. In spite of the large number of institutions present, little is achieved in terms of planning and managing the region in a sustainable way and the degradation of the environmental conditions is now evident in both the land and in the water. We have recently started an effort to link an additional set of data to this analysis integrating land use, social elements, and institutional aspects. We are examining the use of biophysical parameters of lake water quality: nutrient levels, presence of fecal bacteria, pesticide residue levels, and the like, as integrative indicators of changes in the different factors that affect the resources and the people in the watershed. The simultaneous analysis of sets of data from various scientific disciplines is a challenging task for the scientific team, but can provide the decision-makers with an invaluable tool. ABSTRACT SITE DESCRIPTION SITE LOCATION GENERAL RESEARCH QUESTION How can we use physical and chemical water quality parameters as integrative indicators of the effects of human-induced changes on the resources of a lake watershed? METHODS  Lake Atitlán is a very deep lake (340 m) of volcanic origin located in the highlands of Guatemala at 1,562 m above sea level.  The lake has no surface outlets; underground fissures and seep holes allow water to filter to two rivers draining to the Pacific.  Lake sides are steep, due to its geological origins. The lake lies in a heavy seismic zone.  Hundreds of thousands of Mayan inhabitants belonging to two linguistic groups have lived there for centuries. More recently, the crystal blue lake has attracted thousands of tourists from around the world.  The lake and its watershed were declared a National Park in To date, no conservation laws are enforced in the area.  The region is considered one of the poorest in the country with high rates of illiteracy and public health problems.  Landsat TM images from 1986 and 1996 were used to examine patterns of land use and land-cover change for the region.  Special emphasis was placed on differentiating coffee plantations from natural forests given the importance of that crop on the land-use dynamics for the region. Band 6 (thermal) of the images proved to be crucial in achieving this goal.  A complete GIS system was developed for the area that included physical and social features.  Water quality parameters were measured in situ at 28 sites around the lake during the dry (April) and rainy (September) seasons. Each site was located using a GPS. Samples were brought back to the lab for more sophisticated microbiology and chemical analyses.  Relevant socio-economic indicators for the 11 municipalities that surround the lake were compiled from various sources. Town of Sololá Town of San Lucas Pumping water to analyze for Giardia Onion plantations near San Pablo