Sensor networks that provide high resolution spatial and temporal measurements will soon support real-time environmental modeling and forecasting. But the reliability of the resulting datasets (including both original measurements and derivative models and forecasts) will depend on the ability to reproduce the processes used to create them and to verify that these processes are scientifically sound. We are developing cyberinfrastructure tools that support precise description and execution of processes, based on a formal process definition called an "analytic web." This approach guarantees dataset reproducibility by providing (1) detailed process metadata that precisely describes all sub-processes, (2) a complete audit trail of all artifacts (e.g., datasets, code, models) used or created in a particular execution of a process, and (3) annotation of these artifacts with the appropriate process metadata. It also supports rigorous evaluation of processes for errors, including logical, statistical, and propagation of measurement errors. These tools are being incorporated into a sensor network that will integrate meteorological, hydrological, eddy flux, and tree physiological measurements to study the movement of water through a forest ecosystem. The system is designed to provide optimal real-time data and process metadata for modeling and forecasting. Features will include: (1) real-time quality control, modeling, and gap filling; (2) scheduled post-processing to update models with subsequent measurements; and (3) facilities for substituting corrected or alternate measurements as needed. The analytic web tools are specifically designed to handle the complex process features of such a system, including concurrency, real-time data streaming, and exception handling. These are features that we believe will be commonplace in sensor networks of the future.