Conceptual Challenges and Practical Issues in Building The Global Lake Ecological Observatory Network Sameer Tilak, Peter Arzberger, David Balsiger, Barbara Benson, Rohit Bhalerao, Kenneth Chiu, Tony Fountain, David Hamilton, Paul Hanson, Tim Kratz, Fang-Pang Lin, Tim Meinke, Luke Winslow sameer@sdsc.edu, arzberg@sdsc.edu, dbalsiger@wisc.edu, bjbenson@wisc.edu, rohit.bhalerao@gmail.com, kchiu@cs.binghamton.edu, fountain@sdsc.edu, d.hamilton@waikato.ac.nz, pchanson@wisc.edu, tkkratz@wisc.edu, c00fpl00@nchc.org.tw, twmeinke@facstaff.wisc.edu, lawinslow@wisc.edu Abstract Freshwater lakes provide a number of important ecosystem services such as supply of drinking water, support of biotic diversity, transportation of commer- cial goods, and opportunity for recreation. Wireless sensor networks allow continuous, fine-grained, in situ measurements of key variables such as water temperature, dissolved gases, pH, conductivity, and chlorophyll. Instrumenting lakes with sensors capa- ble of sampling environmental variables is becoming a standard practice. Furthermore, many limnologists around the world are interested in getting access to and performing research on data collected from lakes around the globe to provide local, regional and even global understanding of lake ecosystems. To that end, a number of limnologists, information technology ex- perts, and engineers have joined forces to create a new, grassroots, international network, the Global Lake Ecological Observatory Network. One of our goals is to build a global scalable, persistent network of lake ecology observatories. However, implementing and de- signing technology that meets requirements of a large- scale distributed observing systems such as GLEON has, thus far, been challenging and instructive. In this paper, we describe several key conceptual challenges in building GLEON network. We also describe several practical issues and lessons learned during operation of a typical GLEON site. 1. I NTRODUCTION Freshwater lakes provide a number of important ecosystem services such as supply of drinking water, support of biotic diversity, transportation of com- mercial goods, and opportunity for recreation. Un- fortunately, statistics indicate that these services are increasingly coming under stress. For example, the Millennium Ecosystem Assessment project concluded that current use of freshwater for drinking, industry, and irrigation is unsustainable. Approximately 1.1 billion people lack access to clean drinking water and inadequate water, sanitation, and hygiene con- ditions result in deaths of about 1.7 million people per year. This is further exacerbated due to the fact that the global demand for freshwater is expected to continue increasing into the future (e.g., it has doubled from 1960 to 2000) [1]. These statistics motivate the importance of understanding how changes in land- use, human population, and climate interact with lake dynamics at local, regional, continental, and global scales. Developing this understanding at such scales is a daunting challenge, in part because ecological systems are characterized by high spatial and temporal variability [2], non-linear dynamics [3], [4], and cou- pled physical/biological processes [5]. For example, ecologists are interested in getting deeper understand- ing of causes of sudden and short-lived algal blooms, changes in frequency and response to disturbances such as mixing events caused by typhoons, sudden changes in rates of biogeochemical processes, and the wax and wane of fish stocks [6]. Researchers around the globe are using multiple ap- proaches to understand this complexity and variability. Their effort primarily includes modeling, comparative analyses, and long-term observations. Central to all these approaches is high quality, spatially and tem- porally dense, comprehensive, well-documented, and easily accessible data [7], [8]. To that end, advance- ments in sensors and wireless network technology is revolutionizing science by giving access to data at unprecedented spatial and temporal granularities. For example, wireless sensor networks allow continuous fine-grained in situ measurements of key variables such as water temperature, dissolved gases, pH, con- ductivity, and chlorophyll. Instrumenting lakes with sensors capable of sampling environmental variables is becoming a standard practice. Furthermore, many limnologists around the world are interested in getting access to and performing research on data collected from lakes around the globe to provide local, regional and even global understanding of lake ecosystems [9]. A. The Global Lake Ecological Observatory Network To respond to these challenges and to explore opportu- nities, a number of limnologists, information technol- ogy experts, and engineers have created a new, grass- roots, international network, the Global Lake Ecolog- ical Observatory Network (GLEON, www.gleon.org).