Monitoring Biotic And Abiotic Processes Across The Hyporheic/Groundwater Interface

Abstract

A new in situ sampling technique, use of a colonization corer, was used to collect subsurface chemical, biological, and hydrogeological data and thereby monitor processes at the hyporheic/groundwater interface. Evaluation of sample quality indicated that: 1) the colonization corer did not compromise the integrity of interstitial water samples; 2) the device did not display a capture bias for taxon type or particular size classes within the interstitial community; and 3) no difference occurred between repeated water-level measurements taken using the colonization corer and more conventional mini-piezometers. The colonization corer proved especially useful for measuring subtle biotic and abiotic changes over small (meters to tens of meters) spatial scales in the near-stream zone. For example: 1) the chemical signatures of two separate water masses were identified (hyporheic water and groundwater); 2) the interstitial macroinvertebrate community was divisible into two main components whose distribution was related to the location of the boundary between the water masses; and 3) zones of upwelling (areas of groundwater discharged into the channel) were distinguished from zones of downwelling (areas of surface water recharged into the interstices). Use of the colonization corer permits the scale upon which groundwater flow and contaminant transport models have traditionally been based to be refined to include hyporheic processes.