Stream ecology and surface-hyporheic hydrologic exchange: Implications, techniques and limitations

Abstract

In many streams with coarse substrata, there is continuous exchange between surface water and interstitial (hyporheic) water. Upwelling hyporheic water usually contains less dissolved oxygen and may provide nutrients that are limiting in the surface water. Downwelling stream water carries oxygen, surface detritus and other material to the hyporheic zone where microbes and invertebrates reside. The magnitude and direction of this hydrologic exchange can be measured using relatively simple techniques (such as dye injections and mini-piezometers) although there are some important limitations to consider. As hydrologic exchange has been shown to affect the distribution of benthic algae and invertebrates in some streams, this variable has implications for a variety of lotic studies including those of drift, leaf breakdown, benthic invertebrate colonization, sedimentation, and nutrient limitation. Experiments in flumes and artificial stream channels usually remove the influence of hydrologic exchange although it would be possible to incorporate this into their design. Stream ecologists should consider assessing the significance of the hyporheic zone to surface processes by quantifying the vectors of hydrologic exchange to ascertain how these may affect results of work conducted on the benthos at a variety of scales.