Aquatic systems play a salient role in the complex processes of energy and matter exchange between the geosphere and the atmosphere. For example, reactions taking place in cloud water droplets can substantially alter the atmospheric budget and chemistry of trace gases; pollution induced weathering reactions at water/soil interfaces can affect the availability of nutrients and increase the concentration of potentially toxic metals in groundwaters. Moreover, the inextricable links between the water cycle, the geosphere and the atmosphere ensure that apparently localized environmental problems have increasingly impacts in other parts of the world. To identify local-to-global scale variables associated with environmental changes, a focus must be placed on the recognition of processes, rather than a continued reliance on monitoring state variables. However, in heterogeneous aquatic systems, small scale aspects of a process under observation may not be summed directly to obtain regional estimates because of process nonlinearities with change in scale. To understand this, the integrated use of measurements across a range of scales is required.
