Role of the Hyporheic Zone in Increasing the Resilience of Mountain Streams Facing Intermittency

Maria Cristina Bruno,Luca Ridolfi,Stefano Fenoglio,Fulvio Boano,Alberto Doretto

doi:10.3390/w12072034

Abstract

We investigated the impact of intermittence in previously-perennial Alpine stream reaches, targeting the role of the hyporheic zone in increasing the resilience of these aquatic systems. We selected a perennial and an intermittent site in a reach of the Po River (North-Western Italy). We installed piezometers reaching −1 m (permanent and intermittent site), and −3 m (intermittent site) and monitored three supraseasonal droughts over a period of three years. We classified the hyporheic fauna into three categories of increasing affinity to life in the hyporheic (stygoxene, stygophile, stygobite), and used communities composition, abundance, beta-diversity and functional groups: (1) to compare assemblages at the same depth but with different hydrological characteristics, as well as assemblages from two depths at the intermittent site, and (2) to assess how the connection with surface water and the direction of the vertical aquifer flow determined the faunistic assemblages. Different taxonomic groups responded differently to intermittence, the hyporheic zone acted as a refuge increasing the resilience of the system, but resilience decreased with increasing degree of affinity to hyporheic life. Disentangling the effects of intermittence on the different faunistic component in the hyporheic zone can help guiding effective protection and restoration measures of river systems with temporary reaches.

Highlights

The climate of Earth is changing rapidly [1], posing challenges for species and habitat conservation.Temperature increases and changes in precipitation amounts, patterns and seasonality are leading to habitat loss and fragmentation, changes in species phenology and enhanced rates of biodiversity loss [2,3]
We examined the use of the hyporheic by benthic and hyporheic taxa in an intermittent reach affected by supraseasonal droughts in previously-perennial stream reaches
We targeted different faunistic groups collected only in the hyporheic zone, and their responses to disturbances differed based on their affinity with the hyporheic habitat, i.e., if they were already present in the interstitial space before the disturbances occurred [30], or if they infiltrated into the HZ during disturbance

Summary

Introduction

Temperature increases and changes in precipitation amounts, patterns and seasonality are leading to habitat loss and fragmentation, changes in species phenology and enhanced rates of biodiversity loss [2,3]. The main effects of climate change on lotic ecosystems are the increased frequency and magnitude of hydrological extremes, with more frequent and extended droughts predicted for the mid-latitudes [4,5]. The Alpine area is strongly impacted by climate change, and it is under the increasing pressure of water abstraction; as a result, Alpine and perialpine streams are extremely sensitive to the effects of droughts [6]. Drought is a ‘ramp’ disturbance that disrupts lateral, longitudinal and vertical hydrological connectivity [8], representing a major threat for stream invertebrates [9,10,11,12]

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Discussion

Conclusion