Ecology of the hyporheic zone: origins, current knowledge and future directions

Traian Orghidan's seminal paper on the hyporheic zone was published in German in Archiv fur Hydrobiologie 50 years ago. To celebrate this anniversary, it has now been translated into English and republished in Fundamental and Applied Limnology, the successor to Archiv fur Hydrobiologie, as part of this special issue on hyporheic zone ecology. Here we examine the development and current state of knowledge of four aspects of hyporheic zone ecology first articulated by Orghidan. First, we consider the ecotonal nature of the hyporheic zone (HZ) and its relationship to the wider stream ecosystem; second, surface water and groundwater habitat interconnectivity within the hyporheic zone; third, the spatial and temporal heterogeneity of the HZ and how this may influence its function as a refugium for taxa during disturbances; and lastly interactions between hyporheic invertebrates and pore water volume, bacterial densities and particulate organic carbon. We outline the characteristics of the hyporheic zone that may determine how effective it will be as a refugium for benthic taxa during disturbances and consider the biological traits of benthic species most able to utilise the HZ as a refugium. Finally, we examine an important avenue of research that has developed since Orghidans paper reflecting significant scientific and technological advances; the role of the hyporheic zone in stream nutrient dynamics. We conclude by considering some areas where further research is likely to advance our understanding of the hyporheic zone and its interaction with the wider stream ecosystem