EXPERIMENTATION IN THE HYPORHEIC ZONE - CHALLENGES AND PROSPECTUS

Increased experimentation is essential if we are to understand the biotically rich hyporheic zone and how it influences processes in other parts of lotic systems. Unique challenges face experimenters because the hyporheic zone is both extremely complex hydrologically and relatively inaccessible and difficult to manipulate. I discuss five major obstacles that impede experimental progress in hyporheic research and I suggest corollary experiments or technical developments that are critical to our future research agenda. The first obstacle is that a conceptualization of the hyporheic zone, in which there are clearly definable boundaries that apply across all streams, is unlikely because of significant variations in geology and hydrology between drainage basins. How this zone is delineated may depend on the experimental question and we should ''exploit'' cross-system differences to motivate experiments. Second, developing methods of obtaining deep streambed samples in an undisturbed fashion, from defined positions within the streambed, and evaluating the effect of our experimental intervention on the process under study requires serious effort. Third, evaluating the impact of bed movement on hyporheic processes and quantifying or controlling for this movement in experiments will require new or modified techniques. Fourth, developing methods for quantifying and experimentally manipulating subsurface flows should be an essential part of research to determine how these flows influence system and community-level processes. This will require adaptation of existing techniques for measuring subsurface flows, so that they are useable at a variety of spatial scales, and simulation of subsurface flows in artificial streams and in-stream chambers. Fifth, the nature and extent to which a hyporheic component or ecological process is influenced by surface vs. groundwater inputs must be quantified. This will require the ability to separate surface from groundwater effects by means of experimental manipulation or design.