Effects of riffle-step restoration on hyporheic zone chemistry in N-rich lowland streams

Tamao Kasahara, Alan R. Hill, Tamao Kasahara, Alan R. Hill

Research output: Contribution to journalArticlepeer-review

100 Citations (Scopus)


Stream restoration projects that aim to rehabilitate ecosystem health have not considered surface-subsurface linkages, although stream water and groundwater interaction has an important role in sustaining stream ecosystem functions. The present study examined the effect of constructed riffles and a step on hyporheic exchange flow and chemistry in restored reaches of several N-rich agricultural and urban streams in southern Ontario. Hydrometric data collected from a network of piezometers and conservative tracer releases indicated that the constructed riffles and steps were effective in inducing hyporheic exchange. However, despite the use of cobbles and boulders in the riffle construction, high stream dissolved oxygen (DO) concentrations were depleted rapidly with depth into the hyporheic zones. Differences between observed and predicted nitrate concentrations based on conservative ion concentration patterns indicated that these hyporheic zones were also nitrate sinks. Zones of low hydraulic conductivity and the occurrence of interstitial fines in the restored cobble-boulder layers suggest that siltation and clogging of the streambed may reduce the downwelling of oxygen- and nitrate-rich stream water. Increases in streambed DO levels and enhancement of habitat for hyporheic fauna that result from riffle-step construction projects may only be temporary in streams that receive increased sediment and nutrient inputs from urban areas and croplands.

Original languageEnglish
Pages (from-to)120-133
Number of pages14
JournalCanadian Journal of Fisheries and Aquatic Sciences
Issue number1
Publication statusPublished - Jan 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science


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